Newbie needs help with small DIY sail plan, trimaran setup.

[Lee.007]

Dusty, laminated aka, freaking good idea. I wish I could claim credit for that. This why I came to this forum. I am not too prideful to admit when I don't know something. Especially when I am building something that could possibly endanger my life (in the extreme situation).

Than you so much. I was really hating the way my original design had uprights coming out of the ama's to attach them to the aka's. It just didn't look natural, and also created a moment arm against the upright-aka joint that could be easily ripped off if I smack a rock or something with the aka. Assuming I was going really fast of course. That may never happen, but we will see how fast I can get this thing. So I am definitely going to rip some strips and build a laminated curved aka setup. There is about a 8 to 12 inch drop from the top of the deck to the top of the ama's. A curved aka will blend that out very nicely. I think I will alternate cedar/pine/cedar/pine to reduce the weight some, and make sure I have pine on the outer layers. I say pine, but it is whatever lowes calls spruce/pine/fir. So what would you think a good cross sectional dimension be to ensure the right strength? 2 x 3 inches or so? Being a laminate I think I should get away with less cross sectional area than if I was using just a plain board.

And yes, I plan to use lashings. I was already planning on create a laminate base plate nest on the deck with through holes and cleats to lash the aka's. And I agree 100% about distributing the load. If you bolt something, all of the stress is concentrated on that single point, the bolt. I could spread out the load with more bolts, but then my kayak looks like swiss cheese.

I will have to do some research and learn about the step and mast partner. That is a new thing to me.

I am going to try to get some work done this week, hopefully have some pics by next week of some sweet aka's!!

[upchurchmr]

Lee,

If you want to laminate the aka, use higher density/ strength wood on the top and bottom only.
All the interior wood can be cedar for weight reduction.
The highest stresses are in the very top and bottom fibers of the beam.

Once you build them, see if you can test them to be sure they are safe.
Holding one down in the middle with weight, then standing on the end can be an effective test and will give you a feel for how much they will bend in use. You might decide to use more than one body for test weight. Be creative.

[Lee.007]

I got a lot of sawing done yesterday, and laid up and dry fitted the aka's and ama's. I am going to use two 1.5" x 1/4" thick strips of the SPF for outer layers, and then put maybe 4 to 6 strips of cedar in the middle. Total cross section should end up some where around 1.5 x 2 inches or 1.5 x 2.5 inches. Do you guys think that will be enough?

Here are some pics of my dry fit. I really like the way the laminates are going to just gently curve down. I only have the SPF strips in these pictures. I have not cut the cedar yet. I haven't built any nests yet for the aka's to sit on. That is my next objective.
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[Lee.007]

Ignore that "attached thumbnails". Somehow that got attached when I was uploaded the pictures. I tried to edit the post and delete it off, but could not figure it out. That is the skeleton forms from when I originally built the kayak.

[Lee.007]

So I have been doing some reading about mast step and partner. Does the mast just sit in the holes?? Is there nothing actually holding it in the boat except for its own weight and friction between the step and partner? Seems kind of sketchy to me. What if a sudden updraft pulls it out and now you have a kyte instead of a sail? I think surely the bigger boats gotta be bolted down. But "cartopper" and "trailerable" boats with removable masts don't have any fixing mechanisms? If that is how it works, then that is easy to rig up. Let me know if I am understanding this right. I don't want to see my hard work go flying away into the wild blue yonder, or into the ocean deep for the matter.

[Dusty Yevsky]

Dusty, laminated aka, freaking good idea. I wish I could claim credit for that.

So do I but laminated akas are the established standard for kayak tris.

Total cross section should end up some where around 1.5 x 2 inches or 1.5 x 2.5 inches. Do you guys think that will be enough?

2 1/2" H x 1 1/2" W should be plenty. I would play around the location of the akas via straps, clamps, etc. What you have there is not the norm. Generally the akas surround the cockpit or are aft of the cockpit. If you place the bow aka near the front of the cockpit you can add the partner to it and drill a hole through the hull to accommodate the mast. That said, you really want to have the location of the akas dialed in before you do this. You will also need to beef up the hull where the akas are placed because the local forces will be considerably more than what's exerted by a paddle. Maybe a ring frame for the front aka and a bulkhead for the rear if you place them around the cockpit.

Does the mast just sit in the holes?? Is there nothing actually holding it in the boat except for its own weight and friction between the step and partner? Seems kind of sketchy to me. What if a sudden updraft pulls it out and now you have a kyte instead of a sail?

Yes, the mast can just sit in the hole but some sort of retention is desirable. The sail won't generate any kind of lift that will pull it out of the hull but in the unlikely event that you capsize or turtle you want the mast to stay put lest it move out of the step. If that happens the mast can exert tremendous leverage on the partner and rip it right out and probably tear up the hull.

For inspiration, think of the hood clips on a 60's American muscle car.

[Chris249]

I've sailed a few small tris (Tri Fly, Supernova, Outrigger, the very fun Windrider, the awesome HSP which is one of the world's fastest singlehanders, etc) and would just like to say that you're getting good advice from Tom, Upchurch, Woxie, Dusty and others.

It's also good to see the spirit in which you're working. I'd be worried that your amas are too small and your rig is too big, but you sound like you're a cool guy and the best of luck with your project.

[Lee.007]

Today I took my ama's out to the pool to test their buoyancy. Yeah, not going to work. They will hold about 20 pounds before they start to sink. If i space them out 5 feet from the centerline, that works out to 100 foot pounds of torque, but I think I need more than that if I am going to use a 60 square foot sail. I kept thinking in my head that if my kayak holds 350 pounds just fine (me plus several dumbells), if I scale it down by 1/3 it should scale the buoyancy by 1/3. I guess it is not a linear relationship.

I am glad you guys kept hinting that they were too small. I am a pretty stubborn dog-face Soldier, but I aint crazy either. When there is a preponderance of evidence countering my theory, I will certainly double check myself. That's why I took them out to the pool before I went any further.

So I decided to order the kayak trimaran conversion plans from Chesapeake Light Craft. Its only 62$ and they are running a 10% discount on plans this weekend for Labor Day holiday. All the reviews look good. I don't want to get the kit since I have a lot of lumber and stuff laying around the house that is pretty close to the materials list, and it is $1600 for the kit.

Any reason anybody would want to talk me out of building the CLC conversion rig?

[Woxbox]

Today I took my ama's out to the pool to test their buoyancy. Yeah, not going to work. They will hold about 20 pounds before they start to sink. If i space them out 5 feet from the centerline, that works out to 100 foot pounds of torque, but I think I need more than that if I am going to use a 60 square foot sail. I kept thinking in my head that if my kayak holds 350 pounds just fine (me plus several dumbells), if I scale it down by 1/3 it should scale the buoyancy by 1/3. I guess it is not a linear relationship.

I am glad you guys kept hinting that they were too small. I am a pretty stubborn dog-face Soldier, but I aint crazy either. When there is a preponderance of evidence countering my theory, I will certainly double check myself. That's why I took them out to the pool before I went any further.

So I decided to order the kayak trimaran conversion plans from Chesapeake Light Craft. Its only 62$ and they are running a 10% discount on plans this weekend for Labor Day holiday. All the reviews look good. I don't want to get the kit since I have a lot of lumber and stuff laying around the house that is pretty close to the materials list, and it is $1600 for the kit.

Any reason anybody would want to talk me out of building the CLC conversion rig?

A very smart move and the kit should be a very good match for your kayak.

BTW, I estimated more like 60 pounds of buoyancy in those amas. Only 20, really? Also, hull volume increases/decreases at a cubed rate if all the dimensions are changed. This is why the kayak that is optimized for a 250 pound paddler is hardly any bigger than one designed for 150 pounds. Just a few inches here and there does it.

[Lee.007]

Dave, I put a 20 pound dumbbell in the hull section, and it nearly sank it. I know if I put the deck on and sealed it up, it would increase enclosed volume and thereby increase buoyancy, but probably only by another 20 pounds since the deck is about half the volume of the hull. I realized that it is no where near the 100 pounds I was banking on. So, I am going to build some much bigger amas. I told my son he can have the smaller amas for a RC catamaran battleship. He was stoked.

I haven't read up too much on the CLC kit. I plan to doing some research while I wait on delivery of the plans. I assume it is a stitch and glue. Would there be any reason why I could not make the amas a cedar strip to match my kayak?

[upchurchmr]

The Chesapeake plans will give you 100# displacement to the deckline.
I asked once before.
Probably pretty good.

Volume= length x depth x width x a reduction for it not being a rectangular box (60% is a guess I've used before and it worked OK).
So if length =1/3, depth = 1/3, width = 1/3
Then 1/3 x 1/3 x 1/3 = 1/27 the original volume

$1600 is a lot for that kit. Let us know what you think you spend (used up) for what you use.

[bluedog225]

Not disagreeing but curious how the Angus and others get away with those tiny little amas.

[Woxbox]

They reef early and often. Good tris are exciting because you can push them hard, and this requires the very high stability numbers that come with high volume amas.

[Lee.007]

$1600 is a lot for that kit. Let us know what you think you spend (used up) for what you use.

I know, right?? I have plenty of stuff laying around the house, and I can get most of the hardware at Lowes or Home Depot for cheaper, and I don't pay shipping, and I also get 10% military discount at both. I have access to probably hundreds of board feet of cedar cause my father in-law has a stack that is about 10 feet long, 3 feet wide, and 2 feet tall of various thickness and lengths of boards, so lumber won't be much of an issue if I do a cedar stripped ama. I have a table saw and plenty of different blades to rip it into the thickness and widths I need. Which I am probably going to do. Its kind of a pain scarfing out the knots, but cedar just looks so freaking cool. Much better I think than plain old plywood, and marine plywood is not cheap either. Most places around here don't even carry it. I guess if you are planning on painting it then plywood is faster, but I really would like the amas to match the kayak.

I can't guarantee I will keep track of the lumber, but I can definitely keep track of the hardware and specialized lumber pieces(if any) that I can't create myself. I expect more epoxy and fiberglass is probably going to run me another $150 or so. Just as a point of note, I only have about $500 so far in materials for my kayak. Not too bad for a 17 foot cedar stripped kayak I guess. Especially given that I have seen 10 year old cedar Guillemot kayaks go for $1500 on ebay and craigs list.

[Jfitzger]

Not disagreeing but curious how the Angus and others get away with those tiny little amas.

I think Angus and others, including most traditional Polynesian craft get away with it because they have a SA/D ratio that’s lower than a modern trimaran. The Farrier F-26 has a SA/D of 38 while the Angus rowcruiser is 22 with a single person aboard and 13 loaded to capacity. This is inline with most commercial kayak tris like the Hobie Islander which is 20 with a single person. 20 is typical for a fast monohull such as the Beneteau First 210. I find it helpful to think of the amas as a substitute for ballast. The more sail area the more ballast/ ama volume.

Big floats would make it really difficult for them to be clear of the water when paddling. Based on my small tri experience I also think they would be a problem in big waves in a little boat. When the windward ama is struck by a beam or quartering wave the dynamic force is transferred to the kayak. Small amas present less resistance.

I have the CLC sailrig plans and I’m impressed by how thorough and well thought out they appear to be.

[Jfitzger]

The CLC plans call for laminated spruce akas. I’ve had good luck picking through the 2x6x16 spf stud pile at Home Depot. I found two perfectly clear spruce boards to make oars from. In my parts anything over a 2x6 is Douglas Fir so by concentrating on the 2x6x16 your looking through the biggest and oldest of the spf.

[Lee.007]

I picked up some 2 x 6 x 12's for my original plan. I ripped them into 1/4 inch thick strips. I haven't got the plans yet, do the akas need to made of 12 foot long or 16 foot long strips? I can get some more if need be.

Oh, just got my shipping notification, plans should be here in 3 days. Cant wait!!

[upchurchmr]

Those ama plans are for plywood.
Not strip planked.

[Lee.007]

I find it helpful to think of the amas as a substitute for ballast. The more sail area the more ballast/ ama volume.

So I keep wondering, do you count the ama's displacement toward the total displacement when figuring the SA/D ratio? If so, I need more sail than 60 square feet to get above a ratio of 15. I also keep wondering if I am running those numbers right. Assuming max loading, if I count 100 pounds x 2 amas plus 300 pounds for my kayak and 60 square feet of sail, I get 14.98 for SA/D ratio. If I just count the kayak, I get 21.06. I guess the real number will be somewhere in between? Or is my math wrong?

[Lee.007]

Those ama plans are for plywood.
Not strip planked.

Any reason why they can't be stripped?

[Jfitzger]

You don’t count the amas in figuring SA/D so 21.06 is your number. I’m not an expert by any means but I wouldn’t go above 60 ft/2 for the sail.

The plans call for 18) 1/4”x1 1/2” x 12’ spruce strips for the akas. I only mentioned 16’ because I’ve had better luck finding clear wood in the longer lengths.

You might have a tough go converting the CLC plans to cedar strip. They only have panel layout not mold shape. You might be able to draft them in CAD using the provided panel offsets. They call for 3mm okoume and there’s a fair amount of twist near the bow. Maybe make the ama hulls plywood and strip the deck?

[upchurchmr]

Lee,

You can strip them if you can figure out the shape of them as built as plywood.
Unfortunately, you are going to get plywood cutout shapes which you have to stitch together at the keel, spread apart at the gunwale, and possibly pull together after the keel line is epoxied.
This makes a shape which is not easily understood until you have built the amas.
Then you could take the shapes of the cross-sections every 1' mount them on something, then strip the shape.

You can include the ama volume in the Sa/D ratio if the amas are immersed when at rest. But you can only include the amount immersed.
Normally, the amas will be at or above the waterline. when the wind blows the ama will support that wind force. But that amount of support will be subtracted from the main hull displacement. The main hull wil rise the same amount (volume) as the ama depresses.

[Lee.007]

Aha! So I was right in assuming it will be somewhere between 15 and 21 depending on how the wind blows, how much weight I carry, etc. And yes, I plan on putting the amas just kissing the waterline of the kayak. So if I go downwind, I would think very little of the ama should be immersed.

For stripping, if the internal bulkheads/forms stay in the ama when constructed, and I can make a keel and bow and stern stems that match the final shape, I just might try stripping. Maybe I will email CLC and ask them if anyone has tried it before. If it turns into a dragon, I will just do plywood for the hull sides and strip the deck with cedar. I think that might look cool. Can I use "door skin" luan plywood, or does it absolutely have to be marine plywood?

[upchurchmr]

Luan has been used for quite a few builds. Check out diy-tris.com, the designer/ builder uses luan for most of his boats.

You might be able to make a strip planked flat panel to use for the deck. You would need to glass the inside of the panel before cutting it to the plywood shape provided.

You could also try making the sides of the boat from strip planked flat panels, again glassing the inside of the panel before cutting to shape, and then assembling as the plans show.
I'm pretty sure it will work, but it's a bit of an experiment. I have done something similar, just to a simple curvature.

[Chris249]

Not disagreeing but curious how the Angus and others get away with those tiny little amas.

I love the Angus in some ways, but do we have any real objective evidence as to how it "gets away" with them, and whether it would be a much superior boat in many ways with bigger amas?

[Jfitzger]

I love the Angus in some ways, but do we have any real objective evidence as to how it "gets away" with them, and whether it would be a much superior boat in many ways with bigger amas?

I think the fact that it won the fastest boat under 20’ in the R2AK is pretty good evidence. It might be a better boat for some people with bigger amas but it would need a bigger and more expensive rig to take advantage. You would also probably need to give up sliding seat rowing and the ability to store the amas in the boat. Given the limitations of what is essentially a rowboat hull it’s hard to imagine it would get much faster than the 11 knots it’s capable of in stock form. In other words it would be a different boat for a different purpose.

I hope I’m not derailing the conversation but I hope it’s helpful to point out that what works for a pure sailing boat doesn’t mean it works for a paddle and sail boat. I’ve beach cruised a Hobie Islander a fair amount in Lake Superior and would absolutely not want amas sized as if they were for a pure sailing trimaran. In addition to the drawbacks of handling in waves the extra outboard weight and windage would make paddling worse.

Its not a perfect model but I find it helpful to compare the psf of the wind on the sail as if it were a wall broadside to the wind with the volume of the amas. Given the CLCs ama displacement of 200# and a 60ft2 sail it would take a wind of 36 mph to put them under. Given that a sailing kayak can go at most 10 knots in perfect conditions bigger amas or sail doesn’t make a lot of sense.

[upchurchmr]

Jiziger,

The ama's on the CLC rig are 100#/ side. Only one side matters when you are sailing. Not 200# like you used.

Who says you can only go 10 kts? Probably true on a poorly designed kayak sailor (graded on speed, and what direction are you talking about?)

Different designs for different people. And for different uses.

[Jfitzger]

Good to know it’s 100# per side. I read the 200# and assumed it was per side since total displacement for the amas isn’t a terribly useful number. That would change the wind speed needed to submerge the ama to 26 mph in my hypothetical model.

This article does a good job explaining the hydrodynamic and structural issues that limit kayak based trimarans to around 10 kts.

https://www.clcboats.com/life-of-boa...iling-rig.html

[upchurchmr]

The Harris article on limitations of a kayak sailor is by far the best overall look at the type I've seen.
However, there are some assumptions that lead to the 10 kt limit theory.

One limit of the article is that he does not relate each limit to the direction of sailing.
What he says about submarining a narrow beamed boat applies primarily to sailing directly downwind.
One handicap not discussed, is that in typical beach cats, the fore and aft position of the crew weight matters a great deal. In a typical kayak you cannot shift your weight backwards to prevent nose diving.
But also typical is that modern cats do not sail directly downwind. They tack downwind at around +/- 45 degrees. This puts the weight on the ama, not the main hull. In this case, the ama needs to be big with stiff akas (crossbeams). As he does a good job of describing, this starts another "design cycle" which increases the size, cost, and required strength of the parts - which is difficult to control.
Another method for controlling nose diving is to move the mast, akas, and cockpit back in the boat. Difficult to do in a stock boat, especially with a double ended hull shape.

Sailing on a reach is the fastest direction of sail. If you are willing to sail with the main hull out of the water, the speed potential depends upon the size of the ama, its beam from the main hull, the ability of the crossbeams to control the twist between the main hull and the ama, the ability to control the sail (and the rig strength), and the courage of the sailor. Again, moving crew weight backward while sailing would help, but is not typically possible. Something like the CLC rig which has 100# flotation will be driven under the water before the main hull lifts off (which would reduce drag).

Sailing into the wind doesn't cause nosediving typically, but does press the ama to go underwater, the most. It might be possible to press the ama bow underwater, but typically the whole thing will submerge at once. Not a very helpful distinction because you are still limited in how much sail force you can apply before you quit sailing and start swimming. Again you can do a "design spiral" to upsize the ama, upsize the crossbeams, widen the beam, and upsize the sail.

The whole design spiral can get better than 10 kts in specific directions and specific wind strength, but will slow the boat in lesser wind speed. FYI, the pursuit of speed will mean better/ bigger sails, leeboard (or other), and rudder.

So I agree with Harris and his experience within the limits of the boats he has designed for.

It is a pity that the 16' tri he says he is designing has never shown up. That article is at least 5 years old (might be 10).
Mr. Harris has a habit of previewing boats I would build, for them to never show up.

[Lee.007]

Wow, what a great debate. For me, I want this thing to go fast, but not so fast that I break my boat and lose my gear.

I think what I really want this thing to do is go comfortably fast, pulling a lot of weight. So if I decide to string some cargo nets between the akas, have my wife hang out there, and throw enough gear in the yak for a weekend on a barrier island, I would still want to move fast enough to carry all that weight in moderate seas. And also have enough time to explore the island before dark. So maybe I am looking for more horse power out of my sail than I am actual speed.

With that said, are there sail designs out there that are meant to pull a load at an efficient speed as opposed to going fast just for the sake of going fast? Or are they one in the same and the sail design needs to be super fast at light weight, so you get the speed you want when carrying a load?

[Woxbox]

I think what I really want this thing to do is go comfortably fast, pulling a lot of weight. So if I decide to string some cargo nets between the akas, have my wife hang out there, and throw enough gear in the yak for a weekend on a barrier island, I would still want to move fast enough to carry all that weight in moderate seas. And also have enough time to explore the island before dark. So maybe I am looking for more horse power out of my sail than I am actual speed.

And more boat. The standard kayak just can't take a second person on board and be expected to move anywhere near the performance attained with one person. Multihulls in general are extremely sensitive to weight. I used to race one, and the guys who won would strip every unnecessary item from the boat before a race. Even cushions. So my buddy and I would have a cooler packed with beer and everything needed for a few days cruise after the race. We had good fun, but only rarely won a trophy.

A small tri-kayak will be even more sensitive to any additional load. You can't really fix that with a different shaped sail.

[Jfitzger]

I think your asking a bit much for two people plus gear on a single kayak. You, your wife and gear plus the weight of the sail rig would have to be under the 300# displacement of your kayak. Preferably well under for decent performance. The weight would be too far forward and the nets would make paddling impossible. The nice part about CLCs sail rig is that it’s pretty versatile so you could transfer it to a double kayak down the line.

I love blasting along on my friends Nacra catamaran at ridiculous speeds on inland lakes but for a kayak trimaran on big water closer to 6 kts is perfect. With your butt in the water it feels plenty fast and allows you cover some territory. Last month I was able to do a 14 mile passage in under 2.5 hours in the Apostle Islands with a heading varying between a beam reach and close hauled. Winds 20+ with waves around 2’. You can’t steer a straight course because you’ll plow into quartering waves. I steer into the wave slightly and fall off as I hit the peak. This reduces the chance for capsize and keeps the boat closer to level so I don’t lose sail power. The faster you go the harder this gets to do safely. In these conditions your consistently getting doused by water.

The main difference in sails meant to go fast is they can be trimmed very flat. The faster you go the greater the Apparent wind which means you near flatter sails.

[upchurchmr]

Your kayak is too small as said above for 2 people.
If you were to make a microBootlegger tandem kayak it has payload for more than 500#. Plans available from CLC or the designer.
It would be even better as a sailboat if the stern was modified to be wide.
I made one for my daughter and ex-husband and kept thinking about making a second one for a sailboat. Probably better off to build one designed as a sailboat instead.

Woxbox knows what he is talking about. Todd Bradshaw built small boat sails professionally for a long time. You might solicit an opinion for what would word to pull a larger load via PM.

[Lee.007]

So what you're saying is, ...I need another tri-yak! "look what I bought for you honey!"

I guess I will have to finish mine, get the bugs worked out, and then build a duplicate for the wife. Assuming she is willing to learn to sail. She is very competitive, so I think if I challenged her to a race that would get her going. Or maybe a tandem/double.

Still no more shipping updates from CLC. How long did it take for y'all to get plans last time y'all ordered them?

[upchurchmr]

Before you jump in and build another kayak-tri, go to diy-tris.com.
Those boats might be easier to build, cheaper, quicker and get you more speed.