Keel deflection in canting or standard systems

Does anyone worry about keel (fin) deflection in the canting systems?
i have been close to tears after trying various combinations in materials,resins, etc. to build a stiff foil but to no avail i’m up to mk5 now and i’m still not happy with it’s deflection. Correct me if i’m wrong but in a canting system with the keel at full tilt the extra forces that come into play will make a normal fin deflect ALOT more than in a standard setup. My only thaught is to bite the bullet and increase the thickness (and weight) to make up for it.
I’ve been a boat builder for about 7 years now and sail in offshore races in “larger” boats and i understand that all keels deflect a little but too much deflection in a canting system seems to defeat the purpose.

Anyone have any ideas or experience in constuction of stiff foils i’d love some ideas and maybie thickness’ used and materials

cheers in advance, Sean.

Deflection is not good in either keel type. In a canting keel it means you are not achieving the cant angle you want and in a standard system it means the boat is heeling more than it should.
Make sure you’re using the best resin you can find and that you use matched molds bonded under high pressure. You need a combination of una directional and 45/45 woven carbon-no glass-no kevlar. You can experiment with the woven because its contribution is mainly to prevent twist. I’m about to start doing some experimental work on fins shortly but just got thru building a 16" fin using standard carbon. It has a 4" chord and supports 17 pounds with 1/4" deflection when set up horizontally-well within what I needed for this particular boat.
I’ll post more on this subject down the line.
Two others I’ve heard build stiff fins are Mike Eldred(no contact info) and Graham Bantock- Sails Etc.
PS- Sean, a couple other thoughts: on a 55 degree canting keel system at max cant on a boat with a 20 degree angle of heel the deflection of the canting keel would hurt very little EXCEPT in so far as the deflection is a sign of flexibility: if the keel is flexible and almost horizontal it will shake the rig(and the whole boat) in waves…
Are you working on a canting keel project?

Doug Lord
–High Technology Sailing/Racing

Thanks alot Doug, are you making theese fins solid carbon? and what thinkness do they come out? for mk6 i was going to have a balsa core with a single stainless rod running the full length tapped one end and welded to canting system the other encased in two layers of medium weight uni directonal carbon tape… but you’ve got me thinking again. My hat is off to you i’ve read many of your posts and you’ve raised my eyebrows on many occasions! Are you in the industry or full time into rc?

I am working on a canting keel rc around marble size. Live in Melbourne AUS and often have 4 foot rollers come in the back door of my workplace (along with 30+kn). I’ve built a cat (lots of fun till they hit the trough then it’s time to strip and go for a swim before the servo’s fry) a little smaller than a IOM (great fun but needed alot of “run up” to start to surf and it struggled to point through the swell) and a 1.2 that was great but wasn’t happy with the hull shape. So here i am in production stages again. Have the hull built, rudder(s), a rig and have worked out a way of having a “automatic” canting system without the need for an extra servo, but I’m stuck on the fin. There is also a protected floating marina a short walk out the pier when i feel like a flat water cruise. The apprentice at work is also building the same boat with his own input and a engeneer who owns a (big)boat at the club has finished building his (standard keel) first boat and we’re also getting intrest from others aswell. I just started out wanting to see if it could be done!
thanks for your input, Sean.

Sean, I do some full size prototyping and the model business-been in the full size end to one degree or another 40 plus years.
My fin is 7% t/c ratio which comes out to .28"(7mm) for the fin I just built. You need to use AT LEAST 6 layers 5.7oz.(189 g/meter) ,45/45 cut woven material plus at least 8 layers of 54,000psi tensile, .033lb./sq.ft.(161 g/meter) UNA EACH SIDE(!) to achieve stiffness.Note: you lay each side of the mold up first- squeegee each layer- and then clamp using a bonding resin gel; do all at the same time; use at least ten clamps on an extremely well reinforced mold(.375"–9.5mm aluminum minimum)-matched CNC cut aluminum molds are best; this is next best and produces close to perfect results. My recent fin used no core but you can experiment with a core- 6-12lb cu. ft. foam would be best I think.
I’ll be talking with one of the best carbon experts in the industry shortly-Vince Kelly- to get help to improve my laminations. I’ll pass on what I can…
Automatic canting keel? Sounds cool! Can you divulge its secrets? I’ve sailed canting keel boats a lot and have found that it is huge fun and from a racing standpoint -necessary- to control the cant angle manually(via radio). So I’m interested what you’re thinking is. Also read “Sailing a Canting Keel Boat” UNDER NEW CLASSES SECTION if you haven’t already-you have to wade thru some “Edit” BS but both Grunta and I posted descriptions of the system we use to control a canting keel-each totally different!
Anyway ,good luck and keep me -and the forum- informed.Happy Holidays!

Doug Lord
–High Technology Sailing/Racing

After checking with a few experts they politely suggested that their are alternate layer and laminate schedules for carbon fiber keels significantly different than those put forth by Mr. Lord that will lead to a lighter, thinner and stiffer fin. In Australia, Jeff Byerly, Brad Gibson, and Craig Smith all have produced hundreds of r/c boats and you might try to seek out their advice and help (or even consider buying a fin from one of them). Also keep in mind that twist is at least as important as deflection in designing a fin.

Roy; whats the point of a lighter fin? It kinda defetes the object if it can float!
Doug; For canting keel boats where the keel fin is not meant to provide lateral resistance, what foil sections are used?

If its not blowing it sucks!

It would be interesting to see facts posted by Mr. Langbord rather than unsupported speculation.
I posted a specific layup schedule that works well; I’m sure there are improved ways of accomplishing the same thing but rather than make loosely supported statements it would be nice to see an alternate layup with details as opposed to the same old baseless inuendo.

Doug Lord
–High Technology Sailing/Racing

The lighter you make the fin (just like any other part of the boat), the more wieght you can put into the lead bulb, and the more righting moment you will have. or, if you leave the lead constant, the less wieght in the keel, the lighter the boat. . . the faster the acceleration etc. All in all, any wieght you can take out of the boat, is a net gain on speed and or performance.

As for the layup schedule, I compliment doug for sharing what he has found to be optimal for his process, yet at the same time agree with Roy’s comments that there are many other layup schedules that may (or may not) be superior. It is important to note though, that doug was working on a fin to support 17 lbs, where as the IOM builders (and some marblehead I believe) are normally supporting 6-9 lbs.
Quite a difference.

Matthew, in full size boats using CBTF the chord of the canting keel strut can be made shorter and the fin thicker since the boat is not making leeway; other canting keel systems won’t benefit from this unless they are a single gybing daggerboard(not fixed) or twin asymetrical daggerboards. And even then the angle of incidence is not correct for all cases as it can be with a CBTF arrangement. That means that these other forms of lateral resistance don’t prevent the keel strut 100% from developing lift and that the section must be different on them as opposed to a CBTF strut.
On models this same “trick” will not work because the thinner(6-7% t/c ratio) is best even for a foil NOT developing lateral resistance. So on a model the canting keel strut on a CBTF boat is governed by one thing: the chord it takes to provide a strong enough fin with the above t/c ratio.
Grunta’s Ultimate Warrior is an example of a canting keel system where both the strut and fixed daggerboard develop lift-lift(= induced drag) that changes as the keel cants. On a CBTF model the twin foils are turned collectively a few degrees and that zero’s out leeway so even though the models’ strut chord is proportionately greater than a full size CBTF strut it still develops no induced drag.
Matthew, I can’t tell you a specific section for the CBTF boat since they were designed by David Hollom and have no specific designation and they remain his property.
Check out the sections used on Bantocks boats and /or familiarize yourself with X-foil and design your own…
Keep in mind the thinnest t/c ratio is best…
Doug Lord
–High Technology Sailing/Racing

tb;I understand that, but if the fin is light enough to FLOAT, then surely as soon as the boat heels the fin’s buoyancy will work against the righting moment from the keel, or am i totally wrong here?

If its not blowing it sucks!

Matthew, the key thing is the bulb/fin CG: it’s obvious that you want it as low as possible. So if you could build the fin with zero to little deflection out of balsa or foam that would be ideal. Definitely impractical but ideal. So anything else is a compromise with the ideal section and aspect ratio as the constraints and the deflection the least possible within those constraints.
Another way to look at it: if you recognize that the t/c ratio is important and your aspect ratio is suitable for that t/c ratio AND minimum deflection then you can see that no matter what you build the fin out of it is going to have the same buoyancy-what changes is the density of material needed to achieve minimum deflection within the constraints of aspect ratio and t/c ratio.
As I pointed out earlier I have contacted one of the top experts in the field of the application of carbon fiber to structural reinforcement to improve my fin lamination. My fins are getting better all the time and the last one was superb; I will relate more details as I know more. If others could share details and facts as well everybody would be better off…
Happy Holidays to everone on this board!
Doug Lord
–High Technology Sailing/Racing

Ok ok, hands up, I was wrong! Brain kinda swiches off around this time of year…
Thanks for the clear explanation Doug.

If its not blowing it sucks!

Whoops! I mentioned in an earlier post that “Sailing a Canting Keel Boat” was in this section. It is under “New Classes” and contains interesting information on how I set up and sail a canting keel boat and on how Grunta McKinnon sets up and sails his Ultimate Warrior-the first production canting keel boat. You have to wade thru some completely off topic “Edit” discussion but the good stuff is there.

Doug Lord
–High Technology Sailing/Racing

Thanks alot Doug for your fin secrets it’s great to see good help is still out there rather than people keeping their technology to themselves to keep their edge. I dont work alot in carbon so i’m not at all suprised i’m totally on the wrong track. Will try out some of you methods as soon as suppliers open in the new year. Aluminium moulds are a great idea but i have a slight lack of a cnc machine or freindship with someone who has, have you ever buildt some out of plain old GRP using a plug?
anyone toyed with using Titanium?

Doug - thanks alot i just read the posts… yes i have come up with yet another pendulum system all apologies and i understand all points you made in that thread but for those that don’t want to play with their keels or dont want a 4 channel i’m going to post a new subject covering what i have come up with only because i have not found any info on such systems. hope i dont offend.

Merry Christmas and happy holidays to all.
ishing ideal conditions on everyone.

In my college days, I was involved in some huan powered vehicle stuff (aircraft and hydrofoils). Weight was a critical issue (Daedalus had a 112 foot wingspan and weight only 68 lbs) so we made our own carbon tubes for structural members. We had a spreadsheet where we could enter in the critical parameters (length, diameter) and loads (bending moment and torque) of the tube and it would spit out the layup schedule. most of our tubes were generally either a torque tube or a bending tube. The layup schedule for each type of tube was very different and the resulting tubes were very different. you could bend by hand a 1 inch diameter torque tube without much effort. You could twist a bending tube without much effort. But try to bend a bending tube or twist a torque tube and it was rock solid. We did have a few torque/bending tubes (main wing spar was a prime example). We had to decide where in the tradeoff space we wanted to design our spar.

Now an airfoil shape is fundamentally different from a tube. The Ixx is much different from the Iyy. However, the priciples that wnet into that spreadsheet are the same. The critical thing is to dcide where in the tradeoff space you want to be. If bending is much more important than torque, you would go with a lot of unis down the tube and only a scrim off axis. But of course torque is important too so you need more off axis fibers. 0 +30 -30 might be a good comprimise.

But of course everyone knows you can buy cloth with orthoganal weave. So the +/- 45 that doug proposes is something you can buy off the shelf to give you good torsional strength without spending a lot of time with custom unidirectional layups. And a cloth can give you better surface finish with minimal delamination concerns than unis (especially in a closed clamshell mold). So I would say that Doug’s original design is not too bad. The 5% extra that you will get from a fully optimized layup schedule may not be worth the extra cost and headaches associated with building it.

  • Will

Will Gorgen


I was not clear when talking about the +45/-45 cloth. This is basically 0/90 cloth turned 45 degrees. Stuff you can find at your local hobby shop.

BTW, if you want something other than +45/-45 you can stretch the cloth along the bias and get anything from about +30/-30 to +60/-60 without stressing the fibers too badly.

Will: To try to be more specific from my prior post (without disclosing other people’s methods), designers who are regularly building carbon fiber fins are using two to three layers of material per side and a core (either foam or balsa). This is not a difference of 5% from the layup schedule proposed by Doug Lord, its closer to a 75% weight savings. They are using either pre-preg or carbon fiber cloth available from suppliers to the aircraft and boat industry, not the local hobby shop. In the United States, those interested in building fins might try to contact Mike Eldred, Jon Elmaleh or Bob Sterne (Canada) to name just a few.

These other designer’s layup schedules will produce a 16" fin that will deflect less than 1/4" when supporting 17 pounds? I bet all these CBTF guys would benefit from this knowledge - anyone gonna check with the guys mentioned?

I think it is a shame that Mr. Langbord can’t provide more specific information on the fins he is talking about. A close reading of Mr. Langbords posts shows some possible confusion between the fin I described(7% section 4" chord 16" fin supporting 17lbs. with a 1" “head” inserted in the boat) and a IOM or Marblehead fin. Or else if he is comparing my fin to another lamination on a similar boat it would be helpfull to know the boat, the layup schedule, the t/c ratio, the chord, the length ,the “head” length(part inserted into boat) and the amount of weight being supported; forget the layup schedule if you want just provide the other information.
Can’t you please clear up the confusion and add some detail to your comments?

Doug Lord
–High Technology Sailing/Racing

The layup and fiber schedule provided by Mr. Lord in this thread was in response to a generic question about fins and a follow-up post that described the proposed fin as being for a boat of “marble[head]” size. Nowhere did Mr. Lord directly advise that his method is only for fins designed to support 17 lbs of lead. If Mr. Lord has other different systems for the lower bulb weights that are more commonly used in model boats, he should be able to clear up the confusion and provide his layup/laminate schedules for other fins.

As to specifics on fin layups and laminations, as I said earlier I am not at liberty to give out other people’s working methods, but for those building fins, feel free to contact any of the many names I have provided and ask them for their thoughts. As I mentioned earlier, I can say with some certainty that the methods and layup schedules described by Mr. Lord are not used by any of the many people I am aware of who regularly build fins for r/c racing boats of any type or class. I am also certain that other methods will yield stronger and lighter fins.

FYI, to the best of my knowledge no one also uses a 1" head on keels for an attachment system.

Hmmmmm, I guess I’m confused. I thought that the answer provided directly responded to the question posted:

“Does anyone worry about keel (fin) deflection in the canting systems?”

Anyway - how does the home builder without access to CNC address the challenges?