Modifying a Kayak for Sail

Hello all, thanks for a great forum! I have a Feelfree Moken 10 V2 Kayak, here's the website for it:

Moken 10 V2 https://www.feelfreeus.com/products/moken-10-standard-v2?variant=31999390908555

It’s a great kayak for fishing. Since I’m a tinkerer though, I decided to get the Falcon Sails kit to convert it into a sail kayak. Here’s what it looks like after the kit was installed:





I’m delighted with how it turned out, and when I’m running with the wind, the sail works great. I’ve found that its performance towards the wind isn’t great though (Close hauled). The sail will fill at about 50 degrees either side, and it will sail upwind, but very slowly, and it’s hard to get any kind of momentum to tack.

So my plan is to make a proper keel for it. On this model, there is a console type storage space (seen above) which is where the pedal drive is mounted on the pedal model. On mine, it just functions as a box. I have some nice thick and heavy cypress that I plan to make into a removable keel/centre board, and I have some cedar for the frame. I’ll lock it in with some steel pins. For the installation, I’m planning on cutting into the plastic, and using a heat gun to melt the edges, then sand/epoxy/rivet the wooden frame in so it doesn’t leak, and coat all the wooden parts with epoxy to keep them in good shape for as long as possible.

My question is whether or not the spot where the pedal drive would be located would be a good place for the centreboard, or if it should be further back? I think it’s behind what looks like the centre of the sail (it’s a 1.4 metre sail), but I’m wondering where would the optimal place to put it be before I start cutting it up. I'm worried it might actually be better to put it back more towards the seat. The console is a convenient place to put it, but I don’t mind making more modifications if it will be more functional! The plan is for the keel to extend about 1.5 feet (46 cm) below the bottom of the boat when inserted because that is a convenient size, but I also don’t mind making it longer! Too long and I'll struggle to get it in while at sea (lake) though.

The second question is whether this will improve upwind performance much! If you think there’s another strategy that will work better, or if for instance it would be better to make a longer centreboard, I’m all ears! I communicated with Patrick Forrester, my contact at Falcon sails, but I haven’t heard back from him yet. I've read some of the other relevant posts, but I'm not sure I understand the engineering perfectly yet. Thanks for your attention.

 

Hello Carlos, from behind my computer it's easy to make a suggestion! If you cut a slot in the floor of a rotomoulded hull you will have to seal the two "ungluable" faces together, or possibly use gaskets. How about trying out a lashup with leeboards to see if your idea works? It looks like you have accessory attachment points just behind the box, maybe you could fit a plank across there to support temporary leeboards. Or lash something to those substantial looking hand holds although they might be too far aft.

 

+1 re Alan's excellent suggestion above re leeboards - or even just one to start off with.
Can anything be attached to those black plastic tracks on the side deck port and starboard, outboard of where the box is?
A plank lashed across the boat would allow you to move the leeboard(s) forward or aft relatively easily, to determine where their optimum position would be.
Have you got a rudder kit as well?
Rudders & Skegs https://www.feelfreeus.com/collections/rudders-skegs

 

Carlos, look at the bottom of the hull. If there's no sign of a pedal-drive well there, then leave that notion and go to a detachable leeboard setup. I'd recommend leeboards anyway, because their size and shape won't be limited by the dimensions of the pedal-drive well, and you can experiment with that, as well as being able to find their optimal fore-aft location. Also, if done right, the leeboards can be trimmed on the fly by rotation.

Also, try to contact the manufacturer and simply ask if the hull can be modified to accept a pedal-drive, but I strongly suspect the answer is no. It's typical for there to be two completely different hulls made for pedal and non-pedal use.

 

Thanks all for the advice! From your greater experience, it sounds like it's going to be hard to modify the hull, so I'll nix that plan! It's not really made to be modified, and the pedal drive model is a whole separate model, as suggested. I do have a rudder, but I'm still in the process of mounting it. The mounting pin is smaller diameter than the hole provided to mount to, so I need to make some kind of bracket. Otherwise, on to making lee boards it is!

The black rails on each side are actually some kind of metal, so they are quite rugged and durable. They are meant for attaching reels and fishing equipment, so they should work well for lee board mounts! I've got some bolts suitable for T bolts, just have to buy the right washers. I'll go ahead and make the lee board according to the design I was planning for the centreboard, and I'll make a cedar frame for each side to hold it in. I'll take it on the water and report back on how it does!

 

Leeboards will give you a satisfactory result I feel. As Far as upwind performance, that existing hull and rig wont contribute a lot.
There may be some benefit to making the Leeboards quite long and well shaped, and just plan on having one of them down at a time, for beating.
One long well shaped board will provide better windward assistance than two stumpy boards.
If you build your flip up leeboard holders right, you can have a selection of test boards to try out to see which provides the best solutions.

 

Thanks RWatson. Now I've been researching lee board design. I see a lot of different lee board designs out there, and this article on this forum:

Leeboard Orientation https://www.boatdesign.net/threads/leeboard-orientation.54667/

So from my research, I should have a convex face on the lee board pointing in, flat face on the outside, and that it should slightly taper in width as it goes down, with the outward face perfectly parallel, and the inward face tapering towards the outward edge, and yet have a square tip. Some have the posterior edge longer than the leading edge, but I don't think I should do this if I plan it to be usable on both sides! And the board should go straight down relative to the plane of the boat, and not angle laterally to the side. Am I right on this, or have I misunderstood something along the way? It will be made of wood and I have plenty of resources to shape wood into the shape I desire, so I'm not limited in that way.

Also, I'm sure that the wider the board is the better, but there is probably a point in which it is too wide. What length and width of the board would be recommendable in my case? I'm thinking of a 2 foot width at the top, tapering to ~1.5 feet at the tip, maybe 3 feet deep into the water when installed. The whole boat is 10 feet long.

 

Well, I got to reading more here:

Leeboards https://www.duckworksmagazine.com/01/articles/leeboards/

Looks like they do recommend that the lee board stick out at an angle (literally 9.5 degrees). I'm not sure if that matters for a small boat, but I will make it that angle unless I hear from you guys, just in case.

I also set out the wood, and it will be more economical to use wood I already have. So I'm making the lee board out of whitewood, and I'll make it ~5 feet long. I have enough wood to make a 2 foot wide board, but I think it will be a little too wide to maneuver! so I'm making it a maximum 13 inches wide in the slot, tapering to 9 inches, with a rib that starts at 9 inches, and tapers to 5 inches. Looks like the "wing" gradient needs a fairly gentle, round shape, so I won't sand the edges down too much. The frame will be made of cedar. I filed some washers I had already to be the T bolts.

The article suggests the lee board be able to be rotated in and out, but that would be challenging for me to be able to arrange, and probably too much strain on the mounts. As it is, I'm probably going to reinforce them with rivets to make sure the board doesn't pull out the screws! If I find the rails aren't strong enough for the job, I'll retrofit a cross bar later. If I find the lee board is working too well, I can always cut it down later, or maybe make it so it sits a bit higher in the slot. At the moment it will be just under 4 feet in the water.

 

Off the top of my head, and based purely on gut feel from small dinghy boards, I would say y0u can go down significantly in size. 2 foot wide is more for small cabin cruisers than SOT. 12" to 15" is plenty. I think 3 feet under the water is also all you need. The angle can be just straight up and down to make rotation out of the water easiest.

Also, optimum shape is not nearly as critical in such a low performance boat You are basically just fighting sideways drift, and at the speeds you can attain, shape is not critical as the boat hull is so inefficient, any "lift" from the aerofoil shape will be negligible.

Save yourself some effort, and just make the leeboard out of two faces of thin marine ply, with a wood spar forced down the middle to provide a bit of curve. The spar can be joined to a larger bit of wood that will provide a solid backing plate for attaching to the boat.

I would also make my life easier, and put a removable cross member in now, to support the boards. Trying to cope with inadvertent loads ( like grounding) on those side rails, will be a nightmare.

This video has a Leeboard seems about the right size for you.

 

A possible solution would be to attach two boards to a horizontel beam (such as a 1 x 4). The boards could project below the water by just slightly more than 1 ft deep, if they are about 1 ft long. the boards would have a triangular top, which would project above the beam by about six inches or more. This would be for a gusset to keep the boards down without help of them leaning against the hull. This way, they can be spaced apart at a distance greater than the beam of the kayak. There would be two advantages of having them this way. 1.) would be so they can be put at just about any point along the length of the kayak, except where you sit. and 2.) they would enhance the initial stability of the boat.
This beam could be held down by a single elastic strap. If the boards were to hit an underwater obstruction, the beam could rotate, letting the boards kick up. You could also rotate the beam yourself to get the boards out of the water for easier paddling.

the depth of the boards would be as follows: about 6 inches (for the top gussetts) + the thickness of the beam (while on flat) + the height the beam is above the waterline + about 1 foot for their underwater depth.

 

Thanks RWatson and Sharpii2, that's helpful. I should have waited for more input before I started doing things, but I had some time so I spent it working!

RWatson: I made the width about 13 inches for most of it, I got it glued up, the epoxy just has to set! I'll epoxy the whole surface once the seam cures and I've done the shaping to make it more aerodynamic! That's good that the angle can be straight up and down, I was not relishing figuring out how to mount it at an angle! It's a bit too late to make the shape out of marine ply, but I'm sure the shape I ended up with will work in any case! I'll put in a cross member for support, since that's easy enough to do, and I agree with you I don't want to have to worry about grounding it and so on! I like the video you linked a lot, that looks like a fun boat! Also, now I see the advantages of it being able to rotate back.

Sharpii2: It seems like what you're talking about are sort of like outriggers with lee boards built in, with a triangular support to hold them onto the boat. That would work too, and I would be less afraid of flipping it again! I'll have to think on that. Another option is to make outriggers with a slot for the huge lee board I already made!


Here's the lee board I came up with. It's about 5 feet long, so about 4 feet in the water. I was worried the board by itself would not be strong enough to take a hit, so I reinforced it with the rib! I glued them with epoxy, and this is everything I could think of that was heavy to help them bond! I was thinking of cutting it down, but I left it the length of the spare board I had because I can always cut it down if it turns out to be too long.


Here are the planks of cedar with the holes drilled in them for mounting. With your advice, the plan is to connect these with a cross member (probably also cedar or whitewood as above) epoxied and bolted on to give them strength. The washer and T bolt go in the rail, and then they are bolted on the top here with another washer and a nut. The rail will be riveted and screwed into the boat.


I had some cedar posts that I cut up for another project, and my thought was to glue them together into two posts like the one above, glue them to the cedar planks above, and carve the slot for the board into them. However, what I think I will do instead is glue some other cedar blocks I have to the planks above, carve the slot into these, and mount these to the other cedar blocks with a large machine screw, so they can rotate, and rig up some bungie cord and rigging like in the video so the lee board, when slotted in, will bounce back if it hits anything. That seems to me to be the best of both worlds! The outrigger idea is tempting though, I'll have to think if I have anything that would work for that.

 

Hello all,

I've been thinking about this project, and I think the best will actually be to make two outriggers like Sharpii2 advised, and put 2 small lee boards that only project 1 foot into the water on each of these outriggers. The 2 posts I'm gluing up above will be carved into the outriggers, and I'll have a triangular frame on each side to hold it to the boat, and a sturdy frame to hold them to the mounting planks. The reason for this is if I put too much beside me, it will interfere with paddling! The outriggers will go pretty far back, since they'll mount to the back rails instead of the front, but I still think it will be more stable! I'll use the other lee board I made for another project.

 

Make a custom combo double ended paddle that breaks apart to become 2 lee boards. IMO having something that serves two purposes and thus stays out of the way becomes even more important the smaller the boat is. Maybe a modified fishing pole holder for the shafts of "store bought" double end paddles, so you just need to replace the paddle blades that aren't in good lee-board shape to something that will be great lee-boards and acceptable as paddles. Figure this rig will be mostly for sailing.

For a SOT kayak with scupper holes maybe make keel skegs with shafts with some padded collars that fit into the holes. But I've been told those holes tend to be a weak spot. Maybe keel skegs with shafts and panels that form fit to the hull and secure with webbing straps around the hull.

 

It is not considered a structural glue joint to butt end grain pieces together as you have done with your sections of fence post. A scarf joint joint is what is normally used, although your pieces are too short for that.
It would be interesting to see how your glued end grain holds to up immersion in water though.

 

Thanks Squidly-Diddly and Waterwitch,

Squidly-Diddly: Thanks for your suggestions. For the custom paddle, my concern is how I'm going to attach it to the boat? At the moment, I'm thinking of making the two lee boards attached to the sides of the outriggers permanently, since they will only go a foot down, and will have rounded ends. It will be too far out for me to reach, so trying to fiddle with them there will be difficult. My boat does have fishing pole holders, but I hope to eventually also use those to fish (or more specifically, troll).

I thought about the scupper holes, but I'm also concerned about the structural integrity! I think the rear rails, once reinforced, and provided the structure of the frame that holds on the outriggers is solid, will be enough to hold it together. If not, I'll make a structural brace that form fits under the boat as you suggest.

Waterwitch: You're probably right it's not a perfect joint! I only did that because I had the scrap wood. Those joints are epoxied, so I would consider them pretty strong on land, but I agree with you I don't know how they will fare on the water! The plan is to shape them into outrigger shapes, sand, then epoxy them on the outside, so at least I don't think that water will get into the joint. Usually epoxied surfaces are pretty reliable with water. If they fall apart, I'll buy another cedar post! At least the outriggers aren't an essential structural ingredient. They're just to help stabilize the boat, and mount the lee boards to give it better performance upwind!