Sailing Kayak Project

Sailing Kayak Concept

I plan to resume my 2004/5 kayak sailing experiments and I am looking for any advice you have to offer.

Back then I was using a single square flat Bruce foil about 10% of the sail area, canted at 45 degrees with a low aspect triangular sail with the mast offset from the hull center line and canted in the opposite direction to the hydrofoil so as to produce positive or negative lift to aid cancelling heeling force. Foil offset from the center line was adjusted for 100% cancellation of heeling force on a broad reach. Results with up to 15 sq ft sail area were very successful, hull speed being easily reached on a run or reach, with the bow wave at times up to my elbows. However tacking was pathetic due to more than 10 degrees of leeway. With such a small sail it never dumped me overboard although there was an exciting moment when I realized the foil outrigger was gradually dismantling itself in choppy water; the ability to raise or furl the sail in 30 seconds was of great value then!

My general plan for the next design is as follows:

The sail will again be a low aspect lifting design about 25 sq ft. I plan to use a single loose-footed lateen sail, but with an unstayed aluminum yard mounted directly to the hull at the forward end rather than using a mast to avoid having to shunt the sail around the mast. I may mount the yard on a bowsprit to get more sail area. The sheet will be controlled from the cockpit by hand using a hand-held telescopic pole to optimize sail trim and perhaps allow the sail to be twisted.

The sail will be a waterproof material such as tarp because it is impossible to keep the sail dry in a kayak. I am hoping to incorporate roller reefing and furling.

I plan to have twin Bruce foils about 1.5 sq ft with perhaps 4:1 aspect ratio, asymmetrical ogive section flat on the leeward side about 4 to 6% thickness, with about 3 degree attack angle to provide lift and toe-in to (hopefully) eliminate leeway. Because I am using wood it is difficult to have a sophisticated foil shape so they will be straight viewed from ahead, although I can shape their profile.

The previous rig’s windward performance was severely limited by the boat’s lack of agility, so I may experiment with an off-axis rudder so I can put it closer to the foil to reduce the turning radius.

It’s hard to hike from a kayak so I will design the rig for 100% cancellation of heeling forces. When reaching I will heel the boat using body weight to lift the weather foil as far out of the water as possible, because of the toe-in.

In such a small boat my body area contributes greatly to leeway limiting windward performance, but I would like to achieve useful tacking capability with this rig. However, it will probably always be faster to paddle upwind.

The parts of the rig that will take the most work will be the foils, so I am particularly looking for input in this area, but any ideas at all will be much appreciated.

 

Have you got any photos of the original set up to save me the effort of working out what you mean from all those words.

My preference is an outrigger set up so I am not relying on dynamic stability but I suppose you can get some clever foil systems with automatic activation.

Rick W

 

The attached jpg sketch shows the general idea; conceptual only, not to scale. I haven't generated much detail yet as I am still researching. Hull length is 10 ft on my most stable kayak. Total weight about 250 lb.

For sail area 25 sq ft, COE about 3.5 ft high, I am considering 2.5 x 0.6 ft foils (immersed area 1.5 sq ft) with NACA5315 or 6315 profile toed in at the zero lift angle (about 2 deg?) for 4 deg alpha on the leeward foil on 4 ft outriggers. Hopefully that will provide enough lift to eliminate most of the leeway, and that hull has little drag at a few degrees of leeway. My other most suitable boat tracks like a railcar and would interfere with foil operation.

I have abandoned the use of body weight heeling to lift the weather foil out of the water, it is not practical or safe in my boat. I am hoping the drag of the leeward foil will be negligible at zero lift.

Foils will be on outriggers about 3 ft out, I may use small lifting floats where the foils attach to the outriggers, about 0.5 ft above the surface, for a measure of static stability but in a sudden gust I find that quick reflexes and the damping action of the foil are my best friends.

"clever foil systems with automatic activation" - no clever mechanisms allowed; the whole thing must be light and able to be dismantled and stored on deck while I am sitting in the cockpit. Thanks for your help!

 

AK, have you considered a small fixed(retractable?) skeg on the back end of the boat so you could pivot the entire assembly in lieu of a normal "rudder"? That would allow the foils to be at zero angle of incidence when in line(cross arm at 90 degrees to the cl) and you could "steer"(rotate) the entire assembly. That would allow you to maximize both vertical lift and lateral resistance from both foils-and they could be symetrical foils....Good luck-sounds like fun!

 

I know of a current boat that has several of the ideas on which you are working. There are a couple of photos of the boat below. You can see that the owner, Mark Balogh, has incorporated an ama, as well as a retractable Bruce foil on his boat. The foil is controllable from the cockpit.

Mark produces the well-known Balogh sailing system for canoes and kayaks and is an experienced multihull sailor, to include a wild sailing journey with Russell Brown (son of legendary multihull designer, Jim Brown) aboard a proa when they were mere lads. http://www.wingo.com/proa/brown/jzerrophotos.html

You can reach Mark through his website: http://www.baloghsaildesigns.com/

Chris Ostlind
Lunada Design
www.lunadadesign.com

 

AK
It looks good. A few comments.

If you are using asymmetric foils then they will provide lift at zero angle of attack. You need to be careful not to set them too aggressively because they will have detached flow and just ventilate.

Javafoil has the ability to generate foil sections and to give you all the data. You can even set the aspect ratio.
http://www.mh-aerotools.de/airfoils/jf_applet.htm
You need to set options to water parameters. I have attached a screen dump from a 16-series NACA that JavaFoil generated. This is the sort of shape I think you should aim for. I have attached the data at Re#200000 for an aspect of 4. You can see it gets good results at in-line condition.

You could pivot the foil beam along the axis of the boat with stops so it can set on either tack without causing the hull to roll. Would require the sail loads to be taken into the beam. The whole thing could be set up so all sail loads are carried independently of the hull other than at the axial pivots.

I would make the outrigger floats if any long and slender so they wave pierce if required. With a rig pivot there is less risk of roll though.

Rick W.

 

When I shape a foil I put the section shape on paper and then enclose it with a rectangle. Then make four tangental lines to the surface that intersect the rectangle. These form sanding lines in the third dimension so you sand to 4 angled facets meeting two flat facets. Round the facets to get smooth transitions. The 16-series section provided will not take a huge amount of sanding.

Rick W

 

Doug: I am not sure I understand the difference between your idea and a regular rudder. I used a regular rudder previously but this time I thought a pivoting blade offset to one side will enable it to be closer to the foils for faster turns. I am also considering a bow rudder.

The twin foils with toe-in and asymmetrical NACA profile will outperform the single flat foil used previously and I think it will provide less leeway and drag than two symmetrical profile foils parallel to the centerline. It also keeps most of the lift on the lee side; the single foil worked better on the lee side. The foils will be hollow and sealed for extra bouyancy.

Chris: that's a nice boat; I will need retracting foils as well. In my previous effort the single foil was mounted on a pair of hinged outrigger booms and retracted against the side of the bow. I haven't yet decided how to retract the twin foils.

I know of the Balogh system and there are several others that work well. Most of the ones I know of have amas for stability, some inflatable and some hardshell. They all have one or two leeboards instead of Bruce foils. Hobie has a sailing kayak which I believe has a centerboard.

I haven't seen one with a lateen sail so there is a lot of novelty (and no doubt some risk) in this concept. On the plus side it should be very light and compact when folded up; I have some nice nesting aluminum tubing so the elements can telescope. The earlier (all-wood) version was about 7 lb all-up: when folded I could wrap the fingers of one hand around it, but it was not telescopic. Of course the foil stuck out at one end but it could be knocked down and stowed on the foredeck and did not interfere with paddling. Not all the sail systems out there can do that (the Balogh does).

 

Cool concept!

Much more of an amateur than some of the above gentlemen, but have a thought or two, mostly critical in fact:

Steering and dynamic stability:

Rudder to CLR distance= leverage.
I would not move the rudder forward.
If you are stalling it @high AOA low speed (tacks etc) it is probably because it is too small. A bigger one will make more force @ lower AOA. Small drag penalty.

If separated main foils are both immersed, might they not increase dynamic stability to the point steering is much harder? Not really my area, but I also wonder if the foils sound too big, on an instinctive level. There is a pic above of a yak with a big foil and cracks in the akas....

Rig balance, handling and structure:

With the rig in the sketch (cat-lateen?) I would be concerned over the rig CG being far forward, causing pitching trouble.
The CE could potentially shift forward, giving lee helm and more problems to weather.


It would probably be easier to get the design "right" if the rig is kept in the middle. Also easier to adjust it, strike it in a squall, or for lunch...

Finally the geometry could make a lot of boat twisting torque between the midships foils and the forward mast/yard step. All this might require the weight of reinforcement in places it would not be ideal.

Sorry for being critical, those are the problems I see.
But you can find solutions, maybe better than what someone else would. Best luck!

 

Thanks Rick. I was thinking of about 2 deg toe-in per foil since most thin profiles have near-zero lift at -2 deg, but I will allow for adjustment. At 2 deg they should not stall. Is that the same thing as detached flow? I am far from home technology-wise; I used to develop robotic control systems ...

That's an interesting looking foil, is it super-critical? Would it have significantly better performance than a NACAnnnn profile? Those are encouraging drag numbers, foil drag should be much less than hull drag. I was going to make the foil by bending two thin ply planks around ribs like a model airplane wing using a dowel leading edge. The TE would be somewhat blunt, about 2.5%, not a knife edge, for durability.

The pivot idea is great. I will achieve that by making the mast, outrigger, mast and floats into a single rigid assembly attached with 2 athwart straps to the hull, maybe with a quick release. Then all wind and water forces will cancel within the assembly except thrust and bouyancy.

I am not yet sure that I need outrigger floats but the long skinny wave piercing design sounds like a plan. I may be able to make the foils and floats into a single monocoque structure.

 

BWD: experience is a good teacher but heavy-handed; I prefer constructive criticism any day. On the rudder to CLR distance, the rudder on the previous design was initially about 12% of foil area; I increased it to about 20% which helped but the improvement was not great. Windward the boat was slow, maybe 2k, and the tacking angle was more than 90 deg so changing tack took a long time and I often ended boxing and wearing was more reliable. The new rig should have better speed and less tacking angle so I will try the regular rudder location first.

I don’t see why twin immersed main foils would make steering harder. Foil size is only 50% larger than the previous design. At the low speeds involved when tacking the turning rate of the kayak using the rudder was similar when sailing or paddling.

I am not too nervous about pitch-poling, but the old rig sometimes could not be brought into the wind; the forward mounting is an unavoidable consequence of using a kayak as the hull because of the cockpit, but the sail is on a longer yard than shown (not to scale) which will move the CoE more astern. I plan to release the sheet in a squall and in an emergency dump the entire rig over the side. That has worked for me in the past.

The torque between the foils and the forward mast/yard step is a design issue. Thanks for pointing it out. I will use a torque tube or spine to tie everything together, about double the mast diameter which should be about 4 times as stiff. Main problem will be the joints as I am not able to weld aluminum. My idea for joining tubing at right angles using a ring bolt is shown in the attached sketch.

 

After all the structural and technical things are sorted, there is really only a few really important things to get settled.

Will the advantages of the foils outweigh the added drag?

Will the planned sail area be able to produce enough power to overcome the added drag? As in, something significant beyond the existing potential of a kayak under sail?

Will the added fiddle factor be worth the rigging time, compared to a more conventionally rigged sailing kayak?

I just love that you are willing to put all of your discoveries and planning out in front of a group like this and simply ask for input. If there is anything in the development of the design in which I may be of help, just let me know.

Below is a photo of one of my sailing kayak designs. Yeah, it's a real picture without any Photoshop gimmickry. It was taken off the coast of Catalina Island, some 26 miles off the SoCal shore when the boat was a part of a group of three small boats that circumnavigated the Island.

I hope that your adventure with this boat leads to similar types of sailing trips.

Chris Ostlind
www.lunadadesign.com

 

I have attached the data for a NACA 4-series with 8% thickness and 2% camber. Its performance is not much different. The things to note is that the L/D is just a little lower and its range of operation is narrower. The reason I like the 16-series is that you keep more volume so you you get a stronger section and it is less sanding. You can make it slightly thinner and have the same strength.

It is certainly worth the effort to feather the trailing edge. It is a matter of tapering both pieces of ply before gluing them down the trailing edge seam. A bit of fibreglass tape around the leading and trailing edges will improve strength tremendously. I use plastic sheet to stretch over the tape while it sets to get a smooth finish and ensure the tape bonds well.

Neither foil have flow separation near the leading edge in their normal range. The 16-series has a flatter negative pressure distribution so it will have very marginally less tendency to partial aerating down the leading edge.

Rick W

 

Chris: The main advantage of using foils and a lifting sail is the ability to carry significant sail area; using a leeboard and vertical mast I found about 8 sq ft was all the kayak could safely handle. I am already at double that looking to go to triple, perhaps more. The planned sail area is 50% more than before, when I had a good performance at all points except windward, and I am hoping for less drag despite extra foil area due to better profiles. The main problem with a sailing kayak is the paddler sticking up into the breeze when try to progess upwind, 50% more sail and foil area should improve performance significantly.

I may not beat out a regular sailing kayak with hefty floats, vertical foil and more sail area but if I can equal it with a more compact, lower cost rig it's worth while. I expect the assembly and rigging time to be no more than the previous design, which was about 3 minutes at the waterside and about 30 sec to either set sail or resume paddling with no added drag.

I think it’s a blast that I can rope in serious and experienced sail folk in an area where I have very little knowledge, and you have already been of considerable help, thank you. Love the sailing kayak and especially the background! I rarely see cruise ships on my local pond.

Rick: You give good reasons for using the 16-series profile and there seems no reason not to, so I will. I detest using fibreglass but the 16-series has a less tapered TE so it should be stronger than the NACA even if not taped. I will soak the wood in epoxy however and may include a hardwood TE. As before, my thanks for the suggestions.

 

As an afterthought, I decided the amount of bouyancy I can get with floats that are small enough to stow on a kayak's tiny foredeck is not worth the trouble so I will start off at least with plain, flat foils.

I was looking at concepts for folding boats some time back, there was one that folded flat with longitudinal cloth hinges, it might be worth a try at a later date. Or there's those neat inflatable floats in the Balogh system ...