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Rudder Design for C&C 35

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.

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: https://www.youtube.com/watch?v=HqBXDuI5NzY

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.

Summary

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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The Next Marine Radar Technology

Back in 2007/8 I was employed by Honeywell Aerospace in Redmond Washington and was working on solid state pulse compression weather radars for aviation. The newly developed RDR 4000 (and now the RDR 7000) had just hit the market. It was the first replacement of the original simple pulse modulated solid state radars (replacing Magnetron tube transmitters with transistor based transmitters) with a pulse compression waveform (FM Chirp on top of a pulse waveform). This technology pre-dated the first of the commercially available solid state marine radars by several years. In 2008 we installed the Transmit Receive module of the RDR 4000 in the base unit of a 6 foot open array antenna and installed it on a 43Ft North Pacific Yachts Trawler. We took that radar out on the waters near Anacortes, WA (USA) and collected images of marine targets and in various wind conditions. This was the first time a solid state pulse compression radar had been demonstrated as a Recreational or Commercial Marine Radar.

Notice of those test results and some images were presented publicly in Seattle at a Maritime Navigation conference and published on the Panbo Marine Electronics blog – https://mt.panbo.com/2008/11/honeywell_pc_ss_radar_wow_again.html. That was the beginning of what is now accepted as common place Marine Radar technology for both Recreational and Commercial applications. Major manufacturers Raymarine, Garmin, Furuno and Navico all sell very good Solid State Pulse Compression radar systems. At the time of this writing Garmin had just announced its new 250W peak Solid State Marine radar with performance rivaling 4KW and 12Kw Magnetron based radars of old.

An example of the 40 Watt Honeywell Marine Radar images compared with Magnetron systems in 2008: Honeywell data on Left in the combined image taken in Guemes Channel just North of Fidalgo Island in Washington State.

Now that solid state pulse compression systems have been perfected and are being introduced in ever high power and more capable systems by competitors, where is the next form of Marine Radar Technology going to come from?

I propose that the next generation of Marine Radar will be a low cost Phased Array Radar with electronic beam steering in AZ only and multiple beams generated in the EL dimension. Traditionally Marine Radars have a fixed elevation beamwidth of 22 degrees that is designed to keep the sea surface in view as a function of boat motion. It is also useful to provide long range detection of rain squalls to provide some level of protection from thunderstorms and microbursts that can create exceptionally dangerous conditions in relatively small areas that are to be avoided. This 22 degrees of elevation could be broken into multiple contiguous beams to provide detailed elevation information. I further propose that while a single panel phased array system would normally be limited to about 90 to 100 degree field of regard in AZ, this array could be rotated 360 degrees as current traditional systems are done. While this 360 degree mechanical rotation of an AZ scanning radar may seem redundant note that the AZ scan is exceptionally fast electronic steering that permits revisiting of tracked targets during a single scan and for multiple AZ scans of the same area during a single mechanical rotation. The potential for vastly improved target detection probabilities is obvious.

So where will this low cost phased array radar technology come from? I propose that it can be found both in at least two of my patents (9,897,695 and 10,775,498) and others in my name and assigned to Honeywell. A current radar being flight tested and ground tested at Honeywell is known as the IntuVue RDR 84K. A brief video of the radar can be found here: https://youtu.be/MT0zWKzNV14

US Patent 9.897,695

US Patent 10,775,498

Where previous Phased Array Radar technology has been exceptionally expensive ( think millions of dollars) the small solid state systems that are possible today at K band (24GHz) and X Band (8 – 10 GHz) using digital beam steering rather than microwave phase shifters is on the order of thousands of dollars and rivals the cost of the most recent Garmin 250W mechanically scanned marine radars.

The potential of electronic beam steering in AZ when combined with multiple elevation beams would be unrivaled for marine radar applications. Consider an 8″ wide array (RDR 84K is 8″ x 4″) that can produce an 8 degree beamwidth in AZ and EL planes with the potential to subresolve that down to 0.8 degrees or better. A small system like this would be of tremendous value to the Washington State Ferry System that daily has to thread the needle among small pleasure boats that do not carry AIS transponders and that cannot be seen by standard radar systems at short (<1Nmi) when mounted some 50 – 75ft above the waterline. One or two small phased array systems similar to the RDR 84K could be mounted near the car deck level and provide exceptional images at ranges of 1Nmi with no mechanical scanning. The radars could also supplement visual systems for approaches to terminals in poor visibility conditions.

Similarly small recreational vessels like sailboats that cannot use anything larger than a 24″ radome base radar on the mast would see tremendous benefit in the imaging capabilities of a mechanically scanned phased array radar.

The technically savvy person may also immediately wonder about the applicability of the new Automotive Collision avoidance radars. But these systems operate at 80GHz and are intended to provide no more than about 300 meters of detection range. Hardly enough to provide sufficient warning about an approaching threat that is 1Nmi or more away and traveling at 20 Kts without AIS transmissions. Automotive radars are highly specialized to their application and would require considerable modification to provide any value in a marine environment.

There are other possible adaptations of the patented technology that is presented here that can be considered for a very low cost multiple beam mechanically scanned array with imaging capabilities but lacking multiple revisit features during a single mechanical rotation. None the less this could afford excellent radar performance for the tens of thousands of small fishing boats in the range below 30ft that currently blast along at 30 kts come fog or not without any collision avoidance capability beyond a chart plotter with AIS. Given the large number of non-AIS targets that can be present in littoral regions all over the world, it would seem this could be a large untapped market for Radar technology that currently is not served.

While I am the inventor of record, these patents are the property of Honeywell. The patents are available in the public domain and are presented here as such. Vacanti Yacht Design LLC does not represent that it has any ability to field these systems in the proposed applications but as the inventor I find the potential for their use to be obvious and are news worthy in that regard. I suggest any interested party contact Honeywell directly using the contact information provided with the Video and Website for the RDR84K. VYD LLC has not been paid for this article in any way and the article is the creation of the inventor of record solely for the interest of patrons of my website. I am available for consultation on matters of radar design and development as Vacanti Consulting Services LLC.

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Vacanti “Active Fence” Keel Design

Well known Yacht Designer / Naval Architect Dave Gerr approached me some time back as he was writing a keel and rudder design methods article for a well known Yacht Design School. He had noticed the article I had published for Sailing World that described a keel design that was used on a winning J36 on the Newport – Bermuda race.

I provided some details of how the design was intended to work and why I believed that it was an improvement over many keel designs of that era. Dave included the description of the keel in course work he was writing and also published a short article that compared several keel design types. At the time the keel I used on the J36 was radical because it defied the then current concept that the keel / hull joint was the source of a great deal of drag. The conclusion by many designers at the time was to dramatically reduce the root chord length (keel to hull location) as much as physically possible in order to reduce this keel to hull drag.

My design, seen in the downloadable article listed below, flew in the face of that concept by using an even longer hull to keel joint but done using a method perfected on aircraft wing to fuselage joints going back 80 years (1940’s). The most typical design could be seen on the exceptionally fast P51 Mustang fighters of WWI and still seen on modern Piper low wing aircraft today. The concept is to use a highly swept back (~45 degrees) short span segment that sharply breaks into a far lower sweep back angle on the order of 10 degrees. The highly swept portion of the root section of the keel or wing causes span wise flow to be induced away from the fuselage / hull joint until the sharp leading edge change is encountered. The sharp break in the leading edge induces a local vortex to form that effectively seals the upper portion of the keel and enhances steady flow on the remainder of the keel / wing span. The very slight leading edge sweep angle of the remaining leading edge resists span wise flow and reduces tip vortex drag and reduces keel drag overall. Leading edge sweep or at least quarter chord sweep angle of near zero degrees is required for maximum keel lift and reduced keel drag.

Here is the article showing the various keel types that includes the Vacanti Keel concept.

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Keel and Rudder Design Methodology

WINGS 32

I published a number of keel and rudder design articles over the course of about 3 decades in magazines ranging from SAIL, Sailing World, 48 North (Seattle Sailing Local Magazine) and most recently in Professional Boat Builder. I have provided a link below to the article that I last published in Professional Boat Builder because it is the most comprehensive article of all of those that I published. I have not seen any similar set of details provided by any other author to my knowledge. While there are excellent hydrodynamic articles by well known author C J Marchaj (Aero-Hydrodynamics of Sailing – Dodd-Mead) specific details of specific foil shapes and definition of the true value and function of the once popular Winged Keels are not provided in most books.

Our WINGS and FOIL programs are designed to allow the optimization of Keels and Rudders for low speed power ( Speed to Length Ratios under 2) and sail applications. True state of the art performance analysis of Keels and rudders would require the use of 3D Computational Fluid Dynamics software and a detailed knowledge of the modeling methods needed to use the this advanced analysis software. We have endeavored to offer programs and design methods (described in the download article) that are within the grasp and financial resources of the great majority of designers and hobby builders. We recommend the more advanced software in our companion blog article on “How to Make a Good Boat Faster”.

Please consider the following article as a technical introduction to Keel and Rudder design based on well known Aero-Hydrodynamic principles. Many keels and rudders have been designed with our software that have contributed to winning major offshore Sailing races, including the Newport- Bermuda race in which a Vacanti Keel modification to a J36 resulted in an overall victory over Farr and other well known boat designs.

Once last critical thing that must be understood in Keel and Rudder design is implementation accuracy. Any keel or rudder design can be rendered useless if the actual implementation or build of the design is not done with sufficient accuracy. A good example was a keel design I created for a Six Meter Sailing yacht named Steverino. The builder of the keel did a great job but at the last minute decided that the “look” of the keel was not agreeable to him. The builder then heavily modified the intended leading edge nose of the keel by grinding the off the forward 6 inches of the leading edge into a more visually appealing (to him) rounded shape. This modification destroyed the entire foil shape structure of the keel tip design and resulted in poor performance. Similarly if good CNC or other high accuracy mold methods are not used the expected performance of the keel or rudder may be destroyed.

Boat Stability and Keel Design

While most designers worry about athwartship stability normally provided by a keel, one client and user of our software reported that he was working on a boat that had the terrible tendency to bury its bow while running downwind. We looked carefully at the choice of foil shape used on the keel and determined that it had exceptionally poor stall characteristics that could result in very high drag. While most consider the keel to operate near zero angle of attack when running downwind, the boat is constantly being steered to keep the apparent wind at the required location relative to the spinnaker and mainsail. This particular boat required that all crew remain aft in the cockpit to keep the bow up and prevent submerging in waves.

After the keel was redesigned with an appropriate foil shape, specifically designed for the Reynolds number range of that boat, the boat downwind characteristics changed dramatically. Literally the boat was “tripping” over its own keel and was being forced nose down by the large moment arm of the keel drag located well below the waterline. Many have not accepted this hypothesis but none the less, accuracy of build and proper foil shape selection (use of FOIL and WINGS) resulted in a boat that won and was sailed safely off the wind.

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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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Marine Radar Technology

I have worked in radar technology for over 44 years in application to military missiles, radar altimeters, aviation weather radar and small phased array systems for drone collision avoidance, mapping radar Altimeters and brown out landing aids for helicopters.

I’ve watched as recreational and commercial marine radars transitioned from very high power systems ( up to 25,000 watts peak) based on nearly 80 year old magnetron transmitter technology to low power solid state radars that might transmit a mere fraction of a watt.

Solid state systems offer Doppler speed measurement to detect relative motion between the radar and other vessels. Older magnetron systems are not sufficiently stable in operating frequency to permit Doppler detection. Older magnetron tube systems transmit exceptionally short pulses at very high power. But a receiver designed to collect those very short pulses must have a very wide bandwidth that includes competing noise. Solid state systems transmit far longer pulses that are typically encoded with linear frequency modulation called “chirp”. The combination of a long pulse that allows a narrow bandwidth receiver with far less noise results in greater detection range per watt of transmit power. The encoded frequency chirp achieves fine range resolution. Low power solid state systems can also use very short pulses for very fine resolution short range detection to a fraction of a mile.

Therefore newer solid state systems from Raymarine, Navico, Garmin and Furuno offer excellent performance in open array scanner systems and fine performance in small dome packages. These systems have virtually standardized on Ethernet digital data and simple 12 to 24vdc power.

With the advent of low power transmitters radiating less than 0.1% of the power of some older radars, the danger of suffering physical damage to eyes due to microwave heating has all but been eliminated.

Only the Navico Broadband Radar employs FMCW modulation and radiates less than a watt of power. This system enjoys favor with small boats where use is confined to 5 Nmi or less. In places like the San Juan Islands of Washington and the Gulf Islands of Canadian British Columbia that is more than sufficient for collision avoidance.

FMCW or Frequency Modulation Continuous Wave is a very powerful radar scheme when properly implemented. I have several patents related to this technology that includes new products currently in production as radar Altimeters and Millimeterwave Phased Array Radar.

A PDF presentation on recreational marine Radar will be added to this blog in the near future. The file includes more on radar modulation technology, installation advice, complimentary functionality with AIS and much more.

Contact us for consulting on marine Radar selection, site selection for optimal performance and comments on radar technology in general related to marine applications.

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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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PROLINES First Design Project

Learn how to use PROLINES for fast and easy development of a boat, yacht, ship, SUP, Canoe or Kayak! PROLINES uses powerful NURB mathematics to instantly create a full 3D Hull shape from a few basic values for Length, Width (Beam) and depth (Draft) of the boat you want to design.