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Software Digital Certificate / WINDOWS 11 Compatibility

While we have reliably sold software worldwide since the mid 1980’s and have always been sure to maintain a secure website for secure financial transactions we had not previously taken the extra step of Digitally Signing our distributed software. This had not been a problem for WINDOWS OS through version 8 but starting with WIN 10 and especially WIN 11 it has become apparent that proving software is not supplied by a dubious source is of paramount importance. We witnessed the distressing warning messages shown to WIN 11 users in particular when software is not digitally signed and have decided the time has come to apply for a Global digital certificate and install full Digital Code Signing for all of our DEMO and Full operational software to assure all users worldwide that the products we deliver and sell are trustworthy and from a reliable source.

All Vacanti Software Digitally Signed by July 4, 2022

We have therefore applied for a full EXTENDED VERSION, Global Digital Certificate of Authenticity from GlobalSign (World Wide Provider of Digital Software Certificates). We will receive our hardware validated and Encrypted Digital Software Certificate in a few days and will completely revise and replace all of our Software Installers for all Software by July 4, 2022.

We invite anyone who has had any issues with installing our software, especially any Demonstration Software to re-apply for free demo versions of the software with the new installer after July 4, 2022. We are certain that none of our previously distributed products is harmful in any way but Microsoft and other entities have substantially raised the bar for software security for any software installed on a PC. This is a very good thing in general and protects all of us from as many harmful and potentially dangerous applications.

We want to always assure our customers and any one interested in our software that our code is safe, is developed by us alone and has not been sourced from any other entity. We use a state of the art Delphi Compiler provided and supported worldwide by Embarcadero. All of the code used in our software is vetted and is not intended to be dangerous in any way. It is critical however that any computer user employ proper software security steps to prevent malware and rogue software from infecting ANY of their computer software. This is normal and standard practice for any Computer user (PC, MAC etc).

The addition of our new Digital Certificate will also make it more difficult for “bad actor” viruses or other software to specifically infect our software once it is posted on our website. We have already installed protection systems on our professional WordPress website to prevent infection and attack by outside bad actors. We will always be diligent in maintaining a safe and helpful website for all to use.

We ask that anyone who has had distressing messages displayed by the WINDOWS OS when installing our software to please contact us and arrange for a new copy of our Digitally Signed software that has the highest possible “automatic green light” from WINDOWS 8 / 10 / 11.

OLDER WINDOWS (Previous to WINDOWS 8) Compatibility

It is also very important to understand that we do not support WIN 7 or earlier WINDOWS versions due to a number of compatibility issues and a number of copy protection issues. We stated in 2020 that our older software designed before WIN 10 could not be supported any longer on WINDOWS 8 and higher because our old copy protection system was no longer compatible with WINDOWS 8. We therefore adopted a new State if the Art copy protection system provided by a major software supplier that will continue to be compatible for many years to come. We also strive to provide the best possible products that operate at high resolution with great detail to make the task of computer aided drafting more rewarding. We know that our professional users appreciate this capability and it provides a high quality experience for students and hobbyists.

Therefore versions of our software previous to PROLINES 8, LOFT 11, FOIL 10 and WINGS 10 are no longer supported for new “unlock” or “License Key” code requests for re-installation on computers. We have no means to digitally sign this older software and no means to provide copy protection “unlock codes” or “license keys”. We have created all new versions of our programs that provide many new features and capabilities, higher speed and higher screen resolution capability and compatibility with new WINDOWS 11 and future operating systems. We encourage any user of older software versions to purchase SOFTWARE UPGRADES to any of our programs for a fraction of the cost of a new copy of any program.

Please contact us with any questions!

Vacanti Yacht Design LLC, June 2022

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Our Sicilian Ancestry – A tour of Valledolmo Sicily

Many of the visitors to Vacanti Yacht Design LLC website may well wonder about our Vacanti name being at least Italian in origin. In fact it is actually Sicilian as both sides of my family emigrated from the small town of Valledolmo Sicily along with about 3000 other people from the same town to the US about 1895. Nearly all of these immigrants to the USA settled in the farming country of Western New York State between Rochester, NY and Erie PA.


The blog is a personal one and is intended primarily for the use of our extended family so that they may see what we saw and possibly consider a trip to Valledolmo as well. This posting is covered by Copyright Vacanti Yacht Design LLC and is not intended for use by any commercial entity.

Valledolmo – South East of Palermo, Sicily

There have been a number of American families, who are descendants of the original 19th Century immigrants who have made the trek back to Valledolmo Sicily, Italy to see if they can find connections to their past or at least see where their families began. This Blog post will detail a recent trip we took to Valledolmo in Early June 2022.

We were privileged to visit this lovely farming town in June of 2022. We re-discovered the warmth and charm we have always known among our US family members among the people we met in Valledolmo. We also discovered that the town is well known for a special type of tomato, wine (White, sparkling and red), excellent Pasta, Lentils and other produce.

Approach to Valledolmo!

The view below is what a visitor first sees when approaching Valledolmo from Palermo. The newly paved road made it a very easy drive and was especially wonderful to see the town from the road just outside of town. This very lovely hillside town is surrounded by pastoral scenes and state of the art Wind Farm and Solar arrays on the surrounding hills. It was a great thrill to see this place that my grandfather had described to me well over 50 years ago.

On the way to Valledolmo
Windmills On the Hills Around Valledolmo
On the way to Valledolmo!
Valledolmo Comes into View from the Road

Upon arrival in town at the Municipal Building (Town Hall) you are greeted with the scene below.

Town Hall

And the main square of the town

Main Square in Valledolmo

Our visit began as our local Sicilian Guide Silvia was joined by town representatives (Mr Orazio Pizzolanti and Rosella Battaglia). We admired the town hall and its furnishings as we were encouraged to go upstairs to the Town Hall Conference room.

On the way upstairs we tried to absorb photos of town celebrations and functions that had been captured in large photos and displayed on a square tower located in the stairwell so that it can be viewed as you ascend or descend on the stairs.

When we arrived in the council conference room we were surprised with a large spread of traditional Sicilian food that I easily recognized as being identical to what I grew up with when visiting my Grandmothers’ home. We had a chance to talk to many towns people, some of who had relatives that matched my paternal and maternal family names. It was sometimes startling to see someone who closely resembled Aunts and Uncles of my own family. Because so many people emigrated to the same area of Western NY (Dunkirk, Fredonia, Buffalo, Rochester and others) I found that the family surnames of those we met were the same as children I went to school with in Fredonia NY.

An Amazing Collection of Traditional Sicilian Family Foods were assembled as a huge surprising Welcome for us!

We had a delightful time meeting town folk and members of the town council , especially the Mayor (sitting with Italian flag colored banner) and the Council President (far left). Shirley and I are center in the photo below. I am looking closely at the plaque that was made for our visit and placed in a special velvet case.

Greeted by the Town Council with a Ceramic Plaque in memory of our visit and a very lovely flower bouquet for Shirley
Our memorial plaque,samples of Chick Peas, Lentils and Pasta from Valledolmo and the fabulous bouquet given to Shirley

We were asked to be photographed with the Mayor(center), council members. Mr Pizzolanti and Silvia (our tour guide) are shown back left. They combined with Rossella Battaglia (third from back left) to provide a very memorable experience in Valledolmo. This little town was filled with friendly, warm and welcoming people that were a great pleasure to meet.

As we sampled the great food prepared by town families, we had a chance to visit with towns people who had relatives who moved to the US in the 19th century and who had relatives with names that matched my maternal and paternal family names. It was a great thrill to wonder if I was meeting relatives of my family. As of this writing the towns records department was looking into the names and birth dates of my family grandparents and a couple great grand parents. I hope we someday have great news about finding family connections.

Possible Relatives? We are working to find out! We could see what seemed to be “familiar faces” in the people we met

Be aware that most town folks only speak Italian / Sicilian and that we were blessed to have Rosella, our guide Silvia (Sicilian born) and our local professional driver Ludovica who all spoke Italian and Sicilian to help us a great deal. I encourage US families to try to learn a little conversational Italian to help with your visit.

After our traditional foods and chats with town members we headed out to the records keeping area and saw the very old registers of recorded births in the city. The records seem to date from about 1820.

I’m looking at possible Vacanti Relatives with one of the towns record keepers
Chiesa Nuova (New Church)

The Catholic church shown above after restoration from being bombed by the Allies near the end of World War II. We were told that the new church was rebuilt with some donations made by US descendants of Valledolmo Families who had emigrated to the US about 50-60 years earlier.

Beautifully Decorated Steps to Chiesa Nuova. The tiles were made by a local Artisan and show the produce grown around Valledolmo. You can see Tomatoes, Grapes, Wheat Olives and more

On this typical inclined street in Valledolmo, we were surprised to learn that this home on the corner had been abandoned since the late 1890’s when the family emigrated to the US. It is available for purchase and restoration by Americans who would be willing to participate in an Italian Renovation program that allows the homes to be purchased for a few thousand Euro so long as the building was then renovated and brought up to modern standards. We understand that renovation expenses would then be rebated to some extent by the Italian government.

The views down the streets in Valledolmo are just beautiful. At its highest point Valledolmo sits at an altitude of about 3000 ft (~1 Km) and is the equivalent of a Western Washington (USA) person living at the same altitude as Snoqualmie Pass in the Cascade Mountains near our present home in Anacortes, WA and about 1000ft higher than the Allegheny State Park Mountains East of Fredonia and Dunkirk NY.

My grandfather told me stories about being a boy in Valledolmo whose chore was to walk a donkey up the local mountain sides to pick fruit and place it in saddle bags or baskets carried by the donkey. I can only imagine which of the hills surrounding town were the scene of my Grandfathers chores!

A different view of the surrounding hill sides greets you as you look down any street. The hills nearby grow grapes, fruit, chick peas, lentils, wheat and much more. There are at least two wineries associated with Valledolmo. We were happy to sample a delicious sparkling white wine from the Castellucci Miano Winery. An excellent description of the heritage of the Catarratto and Perricone grapes from Valledolmo can be found on a page in the Castelluci Miano Winery Website:

After our short walking tour of the city area near the town center we drove a short distance to a wonderful family restaurant where we had a fantastic dinner meal of local produce and meats.

Our prepared table above was soon covered with several fabulous dishes made with local materials and prepared just before our getting to the restaurant.

A sampling of the first courses is seen below and was followed by delicious lamb chops and local sausage.

A wonderful Pasta Dish that used Fava Beans (similar to large Lima Beans) to form the green sauce seen above. It was fantastic!
Lamb/sausage with local orange

Our trip to Valledolmo was made very special by the great warmth and welcoming that was expressed to us by the towns people. We strongly encourage any Valledolmo Descendant American Family to visit the town if you have the means to make the trip. We would advise hiring a professional driver to assure the easiest and the shortest possible trip from Palermo or Cefalu. Expect at least an hour drive through mountains and valleys from either of the two larger cities.

The people of Valledolmo encourage American descendants to visit and to contact the town to make arrangements for a visit with plenty of advance notice to the town before you arrive. Our travel agent contacted the town well before we visited and worked with the town council to arrange for the surprise meeting with the council and the towns people. We were very much surprised and very touched by the generosity of the town in greeting us.

Valledolmo does not have a hotel but they do have a few local Bed and Breakfast houses that might be able to allow you to stay a bit longer than the long afternoon we were able to experience. Be sure to provide as much detailed information about family members – such as full original names (not anglicized in the US) dates of birth or marriage if you wish to learn more about your relatives. The records are organized by date of birth so that information is of the greatest value. If you have the year of birth of your family member that can be sufficient if there are not too many similar names of family members born in the same year.

Travel Arrangements to Valledolmo / Sicily

Our travel arrangements were handled for us by Rem Malloy at Italy4Real (, Rem has team members who are natives of Sicily and who made a special effort to travel to Valledolmo to meet the town Mayor and other town members before they arranged our visit. They now have the detailed knowledge of who to contact and the best means of making your visit as rewarding as possible. The newly re-elected Mayor Dott. Angelo Conti and his staff are very welcoming and encourage your visit and your on going support of Valledolmo. They know Rem’s team (Mattia and others) so the visit will be made much easier. We have known Rem and Italy4Real for over 18 years now and have had two exceptional trips with his travel service.

Contacting the Town of Valledolmo

As of this writing in June of 2022 you are encouraged to contact either Mr Orazio Pizzolanti (Segreteria Commune di Valledolmo) at or Ms Rossella Battaglia at Rossella speaks excellent English and Mr Pizzolanti is very good as well. The town website (in Italian / Sicilian) is here:

Even if you are not able to physically visit Valledolmo, I would encourage you to write to either Mr Pizzolanti or Ms Battaglia to let them know you are interested in the town.

Web Resources About Valledolmo

An excellent website with Genealogy information about the town of Valledolmo can be found here:

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Benefits of Using Combined Marine Radar and Automatic Identification System (AIS)

Benefits and Shortfalls of AIS for Recreational Boaters

Boaters tend to regard AIS as a source of absolutely correct and valid information that they can rely on to provide them with data regarding approaching and overtaking vessels. But the fact is that AIS data can be erroneous and it can lack critical details about vessels that may pose a hazard to them.

Lets give at least two specific examples about AIS data that may be surprising. The first example is AIS data from a tug with a tow. The AIS reported position is at the location of the tug and does not depict the fact that a tow is following several hundred feet behind and that the length of the towed barge is not presented on the MFD. Thus if a boater were in bad weather or cruising at night with a tug and tow crossing perpendicular to the path of the cruising boat. If that boater follows a path that is immediately aft of the tug and does not see the trailing barge the mistake could be fatal when the cruiser hits the huge tow hawser just underwater.

The second example is when AIS data for direction, speed or location are erroneous. This author has witnessed several vessels that were traveling in directions nearly 180 degrees from the true course / heading of the vessel. The error arises when the AIS transponder uses a Heading or Course data source that has not been calibrated or validated at the time of the AIS transponder installation. This can occur because you cannot see your own AIS ICON on your own chart plotter or MFD. It requires a separate boat that has AIS receive capability to verify that the reported heading /course over ground is correct. This author has witnessed even County Sheriff Patrol boats transmitting wildly inaccurate heading or course data as shown in the image below.

Erroneous AIS Data Showing the vessel ahead approaching our Port Bow – In fact it was headed away from us at 15 – 20 Kts. Note that the AIS Target would have gone aground had it been following the plotted direction! Magenta color spots are radar returns from Raymarine Cyclone PRO Radar.

In the first example the AIS broadcast is valid and is not misleading in terms of the tug itself. But your MFD / chart plotter will not show an extended target that properly indicates the full nature of the threat. In the case of large ferries and other ships, the chart plotter or MFD usually reports a special AIS vessel icon that implies a ship or other large vessel is present. But there is no display of a hybrid vessel that consists of two vessels – one powered and the other towed. The only way to know that you are crossing paths with both a tug and tow is to either physically see the vessels or to observe them via radar.

In the second case one must be lucky to visually observe that the transmitted heading / course over ground data vector (usually a line with an arrow that is 3-6 minutes long at the vessel reported speed) does not fall anywhere along the actual periodic GNSS position updates that are reported by the vessel transponder. This is very hard to detect happening when there is a busy waterway involved. A skipper assumes the plotted direction vector data is correct and plans his course accordingly. The only way to detect the AIS course data is in error is to observe the vessel on radar and being using “trails” or MARPA / ARPA target vector data that is independently measured by the radar itself.

It is an interesting thing to observe that if an ownship course or heading data is in error then radar observations of other vessels will also show incorrect course data of EVERY other vessel that is being reported by the radar. Now one would hope that an error this large would be easily detected and corrected by the vessel owner.

Using only AIS Receive

Vessels equipped with no radar and AIS receive only are certainly ahead of the game when compared with a vessel with neither capability. AIS receive equipped vessels have the benefit of seeing other threats around them and certainly this dramatically improves their chances of safe travel at night or in poor visibility conditions.

These vessels can receive emergency man over board or other vessel emergencies in order to render assistance or to steer clear of a critical situation. They can also observe special Aids to Navigation (ATN), buoys or markers that physically are not present as anchored buoys or day marks but exist only as a mark that is present only on an AIS equipped vessel.

Thus the vessel equipped with AIS receive only has gained several advantages but it is not broadcasting its own presence to other vessels. Therefore this vessel must assume other vessels may not be observing them visually or on radar and must choose to navigation to avoid collision without interaction with other vessels or by contacting other vessels on VHF radio on 16 or other Vessel Traffic System channel to avoid a hazardous crossing.

The great value of AIS is in poor visibility conditions. So the AIS receive only vessel is burdened with making sure they have been observed when crossing with other vessels. Certainly they are far better off than a vessel with no AIS and no Radar but they do have some handicap.

In the image below one can see radar returns painted in magenta (purple) for the nearby islands and a nearby AIS icon for a vessel passing well to starboard aft of the Own Ship Icon. The image shows that the actual position of the AIS target is in front of the current location. This reflects the delay in transmitting position for high speed vessels. Just to the right and below of the AIS target is another Radar target on a second vessel that is not carrying AIS. While this radar target for the second vessel shows it poses no problems for the Own Ship vessel it does point out that AIS does not report everything on the water.

By only carrying AIS receive and not using Radar a vessel still cannot detect other recreational vessels that are not equipped with an AIS transponder. This suggests that a vessel without radar and only AIS receive will be at risk in poor visibility conditions and should avoid being underway in such conditions. Certainly this is not too great a limitation in fine summer boating weather on salt water or small inland lakes where pontoon boats do not carry AIS transponders!

Low Cost AIS Protection

AIS is a great asset for safety and general situational awareness on board most recreational vessels. Given that there are now VHF communications radios that provide built in GPS receiver, AIS receive and even an AIS target display and target list even small boats can easily afford to have AIS monitoring capability even if they do not have a Chart Plotter or MFD installed. For vessels that do have a chart plotter or MFD installed these same VHF radios with built in AIS receive can provide AIS data to the Chart plotter or MFD via NMEA 2000 or NMEA 0183 High Speed data.

AIS receive capability is a tremendous help to displacement or semi-displacement vessels like sailboats and trawlers that travel at relatively slow speeds and therefore have limited ability to make meaningful course changes in the event of a close encounter with a high speed vessel like a ferry (330+ ft and 17+Kts in Pacific NW of USA) or standard shipping that can be 1000ft and traveling close to 20+kts.

If a small slow vessel does not carry Radar, the least expensive alternative to provide the most cost effective collision avoidance is a modest VHF Communications radio with AIS receive and display built in. These systems typically sell for under $500 and offer emergency distress calling when registered with an MMSI number in addition to providing AIS information. Examples are the Standard Horizon GX2400 and GX6000 that both retail for under $500 (The GPS Store prices May, 2022).

In congested waterways like the beautiful San Juan Islands of Washington State and The Gulf Islands of Canadian British Columbia AIS is a huge help in detecting the many ferries, ships and tugs that ply these waters. Being able to know that there is a high speed ferry approaching from behind an island is a great asset indeed! Being caught in summer time fog in these channels not only poses a navigation hazard but is a real threat when commercial ferries traveling close to 20Kts can be expected at any time.

Adding Marine Radar to Compliment AIS at Sea

In the image below we highlight a busy water way in the San Juan Islands of Washington State in the US. In this image the tow tug Island Mist AIS Icon can be seen with a radar detection that follows the AIS Icon. This is a direct indication that there is a TOW barge present that does not have a corresponding AIS Icon. While it appears that the Radar return (red blob) is very close to the reported AIS Icon, note that the image scale shows 1 Nmi is about 1/2″ on the display! So the red radar image is actually a long way aft of the reported AIS Icon for Island Mist at this scale. Zooming on the chart plotter would readily show the actual separation distance.

You can also notice that the “Own Ship” Vessel Icon in the center of the image is being followed close behind by an AIS Icon from another trawler and intends to pass to Starboard. At this range the radar return for the very close vessel may have been suppressed but would appear when zoomed in to shorter range for tactical information.

Radar Limitations

In the image above we notice that there is a large AIS target (designated as shipping by the AIS Icon type) just to the right of Island Mist. There is no radar detection of this vessel because it is just behind the high point of Cypress Island. The island is blocking the direct illumination of the vessel by the radar. This shows that while AIS signals can leapfrog over most nearby land masses radar cannot “see around corners”.

If you look closely at this image you will note that there appears to be a number areas that are missing radar detections, such as the left side of Guemes Island and no detections of Sinclair Island. In all of these cases the issue is “radar shadowing”. If the radar does not have a direct line of sight to the object because of a large object in the foreground the radar cannot see that target.

AIS can receive signals that are behind many (not all) other land masses because it does not depend on illuminating the target with a transmitted signal. But it can receive a signal that is either refracted (bent) or bounced from other land masses to the AIS receiver. These bounced or bent signals may flicker or come and go as the own ship changes position but they are at least observable part of the time.

Another significant problem for radar is angular resolution of multiple closely spaced targets. When it comes to radar systems, size does matter. A small radome radar that encloses a hidden rotating antenna that is barely 18″ across will produce a very wide beamwidth that can be as much as 6.5 degrees wide. Consider that at 3000ft (1/2 Nmi) a 6.5 degree radar beam will be 331ft wide! Clearly a couple of 100ft long boats could be within 100ft of each other and so far as the small radar is concerned there is just ONE vessel present because it cannot measure less than 331ft.

A 6ft long open array on the other hand will have a 1.2 degree beamwidth and can resolve 61ft of separation between targets. It will clearly show the two 100ft vessels placed 100ft apart and report them as both being present.

Finally the most challenging conditions for a radar system are very heavy seas or very heavy rain conditions. In these conditions waves themselves generate radar reflections that directly compete with the reflections from small vessels. Attempting to attenuate “sea clutter” or reflections from wave tops can also eliminate detection of small vessels in the same wave structure.

Rain can pose a similar problem when it is very heavy (1 – 2″ inches per hour – a very heavy storm by any measure) by generating large areas of “volume detections” – meaning that rain can fill the entire 22Degrees of vertical extent and say 1.2 degrees of azimuth extent with rain that is readily detected. This competing “rain clutter” can be attenuated but it will also cause small targets in the same area as the rain to be eliminated as well. Heavy rain (>1″ an hour) will also directly attenuate the radar signals themselves on both the transmit and receive paths.

While attenuation of typical X Band Marine Radar signals is virtually hill in heavy fog conditions, heavy rain poses a threat of total loss of visibility and attenuation of radar detections as well. When combined with heavy seas and wind, heavy rain conditions pose the most threatening conditions on the water so far as collision avoidance is concerned. Commercial shipping carry C Band radars that employ very large antennas of 6 -12 feet so that under heavy rain and wind conditions they can still maintain radar visibility. C Band radar incurs much lower attenuation of radar signals and can penetrate rain with less rain reflectivity. But C Band radars operate at 3 GHz and will require antennas that are on the order of 2- 3 times larger than a standard X band antenna to achieve the same angular resolution. Carrying a 12f – 18ft open array antenna on recreational vessels is totally impractical and is reserved only for large ships for that reason.

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Rudder Design for C&C 35 – Success!! Updated with Race Results

WINGS 10 Designed C&C 35 Rudder

Many older sailboats are still being actively raced and cruised by families that love their vessels but wish they had some performance improvements that would possibly make the sailing experience a bit more exciting, safer or perhaps more competitive. I have had many requests for changes to vessels over the years and each one is a unique case.

Design Result Update

We are really pleased to report that the C&C 35 was raced in the 2021 Trans Superior Yacht Race and took 1st Place in Class and placed 10th Overall on corrected time. The owner supplied an excellent presentation that shows the manufacturing methods he used and the results of the race, including crew comments on how the boat behaved with the new rudder. There was significant experience with this boat on similar races with the old rudder so the crew were able to comment with good knowledge of past and present performance.

So far as Vacanti Yacht Design LLC is concerned the most telling comments relate to what the crew described as the elimination of “weather helm” and not needing to “chase the sail” downwind. The specific “Fish Tail” foil shape we designed was specifically created to provide exceptionally large “stall angles”, that angle where lift coefficient suddenly drops to an intermediate value from near max lift and cuts overall lift (steering force) in half or more. The “fishtail” design does not stall until well beyond 20 degrees. This means the rudder will continue to provide control authority even at extreme angles of attack without adding a large step in drag as would otherwise commonly occur.

The planform shape was also designed to reduce the apparent sweep back angle of the mid chord line, especially near the lower 1/3 of the rudder span. The very highly swept and rounded leading edge of the original rudder design caused some serious problems with performance. The highly swept tip of the original led to the weather helm and loss of speed (drag increase as the rudder acted as a brake not a lifting surface. What really happens in a planform like the original is that the very short chord lengths result in very low Reynolds numbers for that region of the rudder. It is also likely that the very short chord lengths in that area are not true foil shapes but are simply cut off sections of the main foil shape so that there is no proper leading edge and transition shape present. This leads to a lot of problems with high drag flow over the planform.

The high sweep back angle of the leading edge makes it worse because it induces span-wise flow down the rudder from the root to tip. Transport Aircraft use sweep back to reduce apparent airflow speed via span-wise flow to avoid developing super sonic shock waves and exceptionally high drag. Sweep in keel and rudder design is useless really and is only used in moderation to achieve a desired taper from root to chord. Rarely is more than10 – 15 degrees of leading edge sweep back ever justified in keel or rudder design.

Vacanti Yacht Design LLC was prevented from completely changing the leading edge sweep back angle because it would have required massive structural hull design changes to implement a vertical rudder stock. So the design was done in a manner to reduce the impact of the sweep back to the largest extent possible. The near vertical trailing edge at the bottom of the rudder causes the location of the mid chord line to become more nearly vertical in this region.

The owner, Dan Larson commented on the addition of 6″ near the root chord – he is referring to the region between the hull and the top of the rudder aft of the rudder post. The water flow this far aft on the hull is not laminar and will be turbulent especially at hull speed (1.34*Sqrt(LWL in feet)). For the section of the rudder above the rudder post and up to the hull there is no leading edge section of the foil shape. Thus it is not clear how the turbulent flow along the hull and the rudder will interact. Apparently this resulted in cavitation (vibration reported by the crew) – which is the formation of air bubbles as flow separates from the hull or the rudder. The crew comments suggest the bubbles formed just against the hull. This problem has occurred because the huge leading edge sweep back angle created the gap in the first place. Modern hull designs with more nearly flat aft sections and nearly vertical rudder stocks will not have this issue.

Here now continues the original design methodology narrative….

It is very important however to understand that making structural changes to the keel or rudder is not a low cost project and it can be time consuming to complete. Making small changes such as accurately fairing a keel or rudder so that the foil shapes (running chordwise along the length of the keel or rudder) accurately reflect a well known NACA shape or at least so that the foil shape is symmetric on both sides can have some benefit and be a much lower cost project. Making small changes like fairing can be very valuable if the basic planform (outline shape of the keel or rudder) is fairly efficient design as built. Many times, rudders or keels that are very heavily swept back, have very odd tapers (root chord versus tip chord lengths), heavily curved edges and other deformations cannot be sufficiently improved by just making the foil shapes more accurate or symmetric. These keels and rudders can’t be improved without replacement.

Recently I was asked to redesign a rudder for a well loved C&C 35 that was still being raced on the Great Lakes. Because the owner had access to CNC machinery (Computer Numerically Controlled milling machines) an all new planform and foil shape was possible. The existing C&C 35 rudder was a heavily stylized 70’s design that had some serious defects such that no amount of fairing changes would be useful. Given these two factors a new design was deemed reasonable.

The owner required that the existing swept back rudder stock be re-used for the new rudder. This posed a serious challenge for trying to improve the Lift / Drag performance by more than just changing out the foil shapes.

Original Design

The original rudder design shown above was also installed at a 25 degree sweep back angle built into the rudder stock. It would require major structural changes to the boat to revise that aspect of the rudder design, so it was necessary to look for an alternative that would potentially reduce the impact of the sweep back angle.

The design above actually only has a very small central region where the the leading or trailing edges are not massively swept or tapered. The upper end of the rudder also has a very large aperture that made a large gap between the hull and the rudder top, causing loss of efficiency. The sweep back of the rudder stock that parallels the leading edge of the rudder caused the sweep of the leading edge in the lower third of the rudder to take an even more severe sweep angle relative to the water flow. Heavy sweep back angles result in loss in “Lift Curve Slope” (LCS) and increase in induced vortex drag. It can also result in the rudder stalling (loss of lift) at just modest angles of attack. This can be a serious safety concern when sailing off the wind, especially reaching under spinnaker or large Genoa headsail. “Round Ups” caused by heavy wind gusts can result in a broach if the rudder does not have sufficient control authority to keep the keel under the vessel.

Reduction in LCS means the rudder has to be steered to larger angles of attack to achieve the same lift or steering force that could have been achieved by a more efficient planform. This can mean the rudder stalls or generates high levels of drag under normal steering conditions.

After some consideration I arrived at the rudder design shown above. The drawing shows a heavy red line that represents the “Quarter Chord” of the planform. The sweep back angle of the Quarter Chord determines the LCS (Lift Curve Slope) of the planform. You can see that despite the required 25 degree sweep back angle of the leading edge, I was able to cause the sweep of the lower third of the rudder quarter chord to be reduced by at least 5 degrees by tapering the trailing edge of the rudder in this area.

The trailing edge taper has the effect of increasing the aspect ratio (ratio of rudder Span to Average Chord Length), reduce wetted surface, reduce lifting forces at the tip of the rudder and as a result reduce vortex drag.

New Rudder Design Rendered Using WINGS 10 STL file

The new planform design shown above will be created by CNC machining a new female mold and laying up glass mat and high density, closed cell foam. An interesting video that shows this process can be seen here:

Actual Rudder During Build Phase

In addition to the planform changes, it was very important to choose a foil shape. Let me rant for a moment regarding the tendency in sailing circles to misuse the the term “foil”. “Foil” does not refer to the outline shape despite the new AC 75 boats being called “Foilers” or when they sail to be called “Foiling” or being “on foil” etc!! An airplane does not “foil”, it flies on a WING. Not a foil! A FOIL shape is the specific NACA or Custom design shape the rudder or keel in the chord (fore and aft) direction. This shape is critical to lift, drag and stall characteristics of the overall planform – the outline shape of the wing or rudder or keel.

Simple examples of popular rudder FOIL shapes are NACA -0010 or 0012 as are cataloged in various books and online. Normally this is a good conservative foil shape to choose when compared with the more typical “low drag” laminar flow sections known as 63-010 or the higher 64, 65 or even 66 series foil shapes. These “60” series foil shapes have a definite place in keel design but are rarely good choices for rudders. Please look at my other papers to see explanations for why this is the case.

Lift Coefficient Vs Angle of Attack (Rudder Angle) for NACA 0010
NACA 0010 Foil Shape

The plot above shows the lift characteristics of the standard NACA 0010 rudder foil shape as a function of rudder angle. It is very clear that at angles above 9 degrees that the foil shape suffers a huge 60% reduction in lift that never recovered, even at angles as high as 20 degrees. Drag is also very high under these high steering angles so that the rudder becomes a brake rather than a steering function.

Custom Foil shape
Custom Foil Design

The new customized foil shape shown above takes its concept from a class of rudder foils known as “Fishtail” shapes. This type of foil and rudders that use “fishtail” foil shapes can be found in internet searches.

This particular variant of the “fishtail shape” was chosen for strength of the rudder and ease of manufacture. It was also chosen for its very graceful degradation of lift as can be seen in the plot above. Now it can be seen that at rudder angles above 10 degrees the rudder will continue to develop lift and will not have the dramatic loss of lift experienced with the NACA 0010 series at angles above 10 degrees. This will provide the owner with a substantial margin of safety when sailing on the Great Lakes in heavy conditions.

True “fishtail” foil shapes have been shown to achieve exceptionally high levels of lift coefficient without stalling and exhibit a very high foil shape “Lift Curve Slope”. But these shapes can have some serious mechanical structure issues at the trailing edge and are challenging to actually implement. Never the less they are used extensively on ships, tug boats and work vessels that require exceptional maneuvering capabilities with very large steering angles and must have very responsive helms at even low steering angles.

Despite these high lift features the new custom foil shape shown above has an exceptionally wide Drag bucket” or region of low drag coefficients that do not change rapidly with steering angle.


Despite all appearances, the new rudder design has virtually identical surface area to the original design. The more consistent chord lengths of the new design will keep the vast majority of the rudder in the same Reynolds number range (operating conditions) versus the original design with a very large variation in chord lengths that resulted in a huge range of Reynolds numbers. Small chords operate at low Reynolds numbers and result in highly degraded performance relative to the longer chords. Also the very short chords are typically never properly implemented and are achieved by simplistic fairing and smoothing “by eye”. This rarely results in good behaviors.

We expect that the CNC machined mold for the new rudder will result in high accuracy implementation of the foil shape and the new rudder planform will dramatically improve steering response and offer better “feel” in heavy round up conditions that are far less likely to result in a broach caused by loss of control (lift) at the rudder due to the old planform shape and the new foil shape. Drag will be reduced because the rudder will deliver the needed turning forces at small rudder angles. Smaller and less frequent movements of the rudder will result with an overall reduction in drag due to dynamic conditions.

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WINGS 10 New Features and Development

February 2021 Update

WINGS 10 is the NEW version of WINGS for Keel and Rudder Design NOW BEING released. It will replace all previous versions of WINGS including the current WINGS 32. The new version will include major improvements in display quality by supporting high resolution screens up to 4K. An all new Parametric Design Dialog will include a highly revised dialog screen with new input capabilities and includes an image of the keel or rudder type that is being designed via the parametric design process. The next few images show the sorts of parametric design methods we are discussing that are specific to rudder design. Keel design parametric data will also include keel bolt locations, size and material strength. All calculations are per American Bureau of Shipping for Offshore Racing Yachts. We may add CE / IMO calculations as well for stock materials and dimensions for various classes of ocean applications.

Keel or Rudder design via “parameters” (parametric design) requires the entry of a few defining overall characteristics of the keel and rudder so that WINGS 10 can automatically create a preliminary design and draw it for the user instantly. This allows for the very rapid creation of a design without the tedious entry of individual curves, lines, corners etc that many CAD tools are based on. All of our Vacanti Yacht Design LLC software tools are based on the parametric design concept. Programs like WINGS then offer detailed editing tools that permit the detailed refinement of the original Parametric design to meet specific needs. This allows infinite design variation and optimization.

WINGS 10 now includes Keel Bolt Design Capability and provides required minimum bolt diameter per 2021 ABS Rules for Offshore Sailing Yachts. The image below shows a standard fin keel with bolts drawn per diameter and per location in the bolt table. Depth of the bolt is shown in the PROFILE view below left.

WINGS 10 computes the required minimum bolt diameter based on keel weight, center of gravity, bolt locations and choice of steel for the bolts. A list of 24 Steel bolt choices is provided that ranges from Aqualoy to Stainless 304 and beyond. User can enter Mass of the vessel for use in computing grounding stress per ABS rules, Pressing Calculate button updates all bolt locations in the drawings and computes new stresses and min bolt diameter at base of thread depth. A Text Data file for all bolt and material information is recorded for use in implementation of the keel.

Flanged Keel Design Bolt Placement

WINGS retains the same NURB (Non-Uniform Rational B-Spline) surface design that we made popular in PROLINES. The only imitation to the NURB surface is that we enforce the aerodynamic shape of the foils (NACA 00, 63, 64, 65, 66 Series and custom foils designed in FOIL 10). Other than that the overall shape and thickness distribution is entirely editable by the user.

WINGS 10 Keel Rendered with WIN 10 Built in Tools

WINGS 10 retains the ability to use any combination of foil shapes to achieve a desired volume distribution along the span of keels in particular. While it is not likely that a rudder might use more than one foil type a user many also modify the placement of any number of foil shapes as a function of span.

WINGS 10 will include the new STL (Stereo Lithography) file format that is now available in the PRO version of PROLINES 8. This STL file will permit 3D printing of scale models of keels and rudders, export to hull drag analysis packages such as HydroComp NavCad and permit 3D CNC machining of molds or finish milling for Keel and rudder manufacturing. STL files can also be used for photo realistic rendering of any keel or rudder design.

WINGS 10 Now Directly Calls WIN 10 Rendering Tools

We are also working on new Rudder Design features such as rudder stock thickness distribution and rudder torque and bending calculations to permit safe design of steering gear and rudder stock material selection.

We invite comments and suggestions for desired WINGS 10 features and reports of existing bugs or fixes that may be needed in WINGS 32 so that we can address those issues before WINGS 10 release.

Cheers and all the best in Keel and Rudder design!

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PROLINES 8 Improvements Under Development

We have received some requests for changes and improvements to PROLINES 8 (all versions) that include use of the mouse wheel for zoom control in any view (once a view is active) and ability to rotate the perspective view by holding the Left Mouse button down and dragging. Both of these concepts are under review for incorporation in a future release of PROLINES 8.

We are also currently working on changes to the initial Parametric Design for a new Hull Design. We have added a new Catamaran Hull type that allows for the instant creation of a dual hull catamaran for power or sail. This new hull type will require changes to Hydrostatics and Stability calculations before it can be released. This is a significant change and will require considerable work to validate all calculations before the new version is released.

We are also considering the addition of a body view image of the selected hull type during the parametric hull design (File, New…) design dialog. This will better indicate the basic shape of the hull type that is being designed.

We plan other changes to PROLINES existing fairing tools to offer easier to use and understand data plots of curvature or slope of hull shape in various planes. We have already heavily improved the Edit, Visual Vertex feature in PROLINES and may add capability there as well.

Please write and send us your concepts for PROLINES features or comment on any issue you have found so that we can correct any errors.

Cheers and all the best for great boat/ yacht / ship designs with PROLINES.

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PROLINES 98, PROLINES 7, LOFT 2011 and FOIL 5 Versions are Now Obsolete

As of October 31, 2020 Vacanti Yacht Design LLC will no longer honor requests for License Keys or technical support for any version of PROLINES, LOFT 2011, FOIL 5 or older other than PROLINES 8, WINGS 10 and FOIL 10. All previous versions of PROLINES 5 (DOS), PROLINES 6 (Windows 3 Thru Windows XP) and PROLINES 98 or PROLINES 7, FOIL 5 and older will be obsolete. Due to changes in Windows operating systems 7,8 and 10 we can no longer offer support for these older versions of PROLINES, LOFT and FOIL.

We do offer low cost upgrades for each version of PROLINES, LOFT and FOIL that have been designed for Windows 7, 8 10 and beyond. We know that there are thousands of users of the older versions of PROLINES, WINGS and FOIL so we make an unlimited offer for an upgrade to the new version of PROLINES , WINGS or FOIL that will not expire with time.

In addition to adopting new Windows 10 technology features, PROLINES 8 now includes many new features for editing, new 3D CAD file export, direct integration with HydroComp NavCad that is an excellent Propulsion analysis tool for all PROLINES hull designs. Many more features will continue to be added to PROLINES 8 at no cost to existing owners of PROLINES 8. We encourage you to consider upgrading soon. WINGS 10 will also include STL file export as well as many other new features.

November 2020 Update on WINGS 32 / WINGS 10.

WINGS 10 is currently still in development with many major new features being installed and tested. New features include ABS calculations for Rudder Stock and Keel Bolts, Improved Parametric design tools, Improved display and tools and support for very high resolution 4K screens. WINGS 10 will offer separate parametric design entries for rudders and keels and separate hydrostatics calculations.

We will support WINGS 32 owners until WINGS 10 is released. No further unlock codes or other technical support will be provided for WINGS 32 once WINGS 10 is released.

New PROLINES, WINGS, FOIL Features Solicited

We encourage you to contact us and send requests for new features that could potentially be added to our software. Please us a Contact Us form to send your suggestions.

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Cruising in San Juan Islands of Pacific Northwest

August in the San Juan Islands brings warm weather, light winds and opportunity for enjoying the best of boat types. Our style is a North Pacific 39 pilot house trawler. Speeds to 9.5 knots but cruise at 8 allows needing just an hour or two to reach most destinations and up to 4 hours for longer trips. Many enjoy high speed cruisers that run in the teens and near 20kts. But they can leave huge wakes and cause problems for shorelines and other boaters.

Anchorages are protected and beautiful in the San Juan’s. Plenty of room for lots of boats of every description. The beautiful area compliments some lovely boats as well.

In these COVID19 days people are friendly and mutually respectful wearing masks when gathered on trails or small stores for supplies.

Shaw Island General Store has a long history and is the center of traffic on and off the island with a Washington state ferry terminal adjacent to the store.

Local Dungeness crab is a delicacy alone or added to any meal. Crab is readily caught with traps and requires little cleaning before being prepared for dining.

Choosing the right anchorage is critical to a good night’s rest when winds in the nearby Strait of Juan de Fuca can reach 30 knots overnight usually WSW but can become southerly and spread among the islands. Steep chop spaced close together can challenge any boat design at rest or underway.

Having boated in the Pacific Northwest for over 30 years on 4 boats we owned and others we chartered has lead to an appreciation for many boat types and concerns about others.

Early mornings frequently are accompanied by ribbons of fog. As the sun rises it burns off and is replaced by warm sun and modest breezes.

Anchored in Parks Bay a research preserve on SW Shaw Island

The forecast is for rain and wind late tonight. So boats have gathered in Parks Bay to gain protection from expected strong Southerly and South westerly winds. The bay is open to the North but tall trees and rising hillside provide protection.

UW Research Dock

The south end of the bay shallows slowly after much of the bay is 45 feet deep. At the head of the bay a UW Research dock is graced by an older trawler that likely transports staff to and from nearby Friday Harbor where a large research facility is installed.

The head of the bay shallows to a more useful 20 to 25ft for anchoring.

High thin clouds and a steeply dropping barometer portends change is coming. In 72 hours the calm should return.

Sunset at Parks Bay

Sunset with gathering clouds was followed by a wonderful peaceful night with no wind in the bay despite a strong WSW wind blowing in the Strait of Juan de Fuca just a few miles south.

Early morning brought steady cool rain that ended just before departure at 9 AM for Island Marine Center in Fishermen’s Bay just 7 Nmi to the SE.

Our trip to Fisherman’s Bay on Lopez Island with a squall arriving was complicated by shoal draft of barely 5 ft at low tide in the serpentine entrance channel to the bay. Clearly we needed to plan for tide and wind conditions when choosing a departure time. We consulted our subscription to PredictWind weather service to note that winds would be lighter before 10 AM and that tides provided by Navionics charts confirmed a 10 AM arrival would be safest to navigate the entrance channel.

Entrance Channel

Planning was important because those 7 miles cross San Juan channel and are open to the wind from the adjacent Strait of Juan de Fuca.

Our planning proved accurate as winds were modest and depth in the approach channel was excellent. Shortly after our arrival winds increased dramatically and have been blowing well over 20 and gusting 28.

Wind in the harbor

Mostly clear blue skies accompanied the wind all day

Lopez Island looking West

Friday promises calm winds and a chance to explore nearby anchorages.

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February 2021 News Updates

Watch our Blog Section for information on Boating in the Pacific Northwest, Marine Radar and AIS and Progress on any of our software products

WINGS 10 Released this week!

WINGS 10 now includes Rudder Stock Design and Analysis per ABS Rules and Keel Bolt Design and Analysis Per 2021 ABS Rules as well. Full graphical display of the chosen rudder stock and rudder or keel bolt pattern and bolt locations is provided in both cases. Now designers can not only create CAD files and compute LIFT / Drag and hydrostatics analysis for Keels and Rudders they can also generate required installation hardware information for both Keels and Rudders. This makes WINGS 10 substantially more useful than any previous version and serves the needs of Professionals and Home Builders alike. WINGS 10 now also includes full 3D Realistic Rendering using WIN 10 tools directly within WINGS 10. With this release any user who has purchased WINGS 32 after November 11, 2020 is entitled to a free upgrade to WINGS 10.

We are also working on B-PLATES and ABS Construct versions for release and use with the new PROLINES 8 Rx.x editions (Basic, PRO and Student)

PROLINES 6, 98, 7, LOFT 2011 and older, FOIL 5 and older are now obsolete and are no longer supported. We encourage users of these programs that have been around for 10 to 20 years to consider upgrading to PROLINES 8, LOFT 2018 and FOIL 10 that offer many new features and will operate on WIN 10 and later.