Lee wants a new trimaran design...

[Lee.007]

You've not been to Lowes lately, have you?

Oops, I stand corrected. I was looking at the 2 foot x 4 foot sheets of luan on their website without realizing it was not 4 x 8 sheets.

Well, for that price, I could buy two cedar 2 x 4 's at $19.48 each and make 3/16 strips out them. Subtracting the blade kerf, one board gives me 14 strips, multiplied by 2 inches wide (rough sawn is actually 2 inches wide) and laid side by side will make a 96" x 28" panel. Do that twice and I have more than a 4'x8' panel for less than same price of a nice sheet of 1/4" maple plywood.

[Lee.007]

I am still contemplating prices here. Lowes has SPF 2x4's pretty close to pre-covid prices now. Has anybody ever built a boat out of just straight Spruce / Pine / Fir wood? I am curious about the weight comparisons. From what I can see just poking around on google, some sites say pine is the same as cedar, some say more. From my experience I know cedar is much easier to bend and work with the pine. Just curious if anyone else had an opinion?

[Tomcat]

Normally the SPF we get is black spruce, which in old books was said to be similar to sitka, which in 2x form it is not. When you find nice stuff it is pretty good. Often strips cut from wider boards have better grade and yield. Normally it would weigh a lot more than cedar. But you never want to bank on weight, you have to do some tests.

[Lee.007]

Yeah I agree on not banking on weight, especially for wood bought at the big boxes. But every cedar piece I have bought has been pretty lightweight. The others can be heavy as lead, especially the ones that still have a lot of moisture. I have bought 2x4's that are downright wet from the big boxes. I have a whole lot of "western red" cedar from a stack that my father-in-law gave me. I think I will just have to mill it up into strips and see how much I can get out of it before I start buying lumber.

I purchased the Slingshot 19 plans and downloaded the pdf's from Duckworks today. They did a good job drawing it up. Lots of full view drawings. Only complaint I have is that they are all on 8 1/2 x 11 pages, but I guess I can blow them up at office max if I want. Can't wait to start sawing boards and slinging epoxy!! My son still has his jeep in the garage, so I am going to just mill up strips, make some framing parts, then when he finally gets the jeep done I will be ready to put it all together and lay down some glass and epoxy.

[Tomcat]

Sounds like fun. I made my trimaran out of doorskins. 30 years later it is still fine. May not have been the waterproof glue kind. Doesn't seem to have mattered.

[Tomcat]

Stressform/plywood, is a simple method of making a P and S panel, and stitching them together along the keel line, then folding them up until they pop into a perfect looking multihull. Ideal for floats, main hulls can be made the same way, but for racy boats, or simply lengthened a little for less racy boats. Fastest, cheapest, highest performing multihull hull, you can make. I made my 24 footer for 3500 Canadian about 30 years ago, and I think one could come close to the same money today. Mainly because the cost of epoxy and glass have up till now, fallen a lot. I have more sources for wood, so I am probably not that far off there either. But even at the doubled price for plywood, tripled at times over the last few years, It only contributes so much to the overall cost of the boat.

[Lee.007]

May not have been the waterproof glue kind. Doesn't seem to have mattered.

I think that is true as long as it is well covered with epoxy. On my current little kayak trimaran, I really laid the epoxy on thick on the plywood case for the kick up rudder, and it is definitely not waterproof or even pressure treated. Not a bit of delamination after a year and a half now. The partner however, I didn't lay it on as thick and it is starting to de-laminate.

The only think I think I would worry about with the luan doorskins is voids. I don't know what the specs are for luan, but I don't think it is "cabinet grade". It would be just my luck to catch a sharp rock or stick at just the right angle on that one spot on my hull that had a void.

[Lee.007]

After reading the construction manual and carefully going over the drawings, I have realized there are a lot of things missing in the Slingshot 19 package. If anybody has built one of these before, please chime in and answer these questions:

1. What are the dimensions of the shear clamps? I cant find a thickness or width anywhere in the drawings. Looks like 1" x .5", but I am not sure.
2. Frank talks about using bondo to fair the hull. Uh, no. Since I am going to do a strip build and bright finish, that's not happening. Has anybody ever built a wooden boat and used bondo?
3. Frank also says he used PL Premium construction adhesive. Has anybody done this before and how did it last compared to thickened epoxy?
4. Frank only fiberglassed & epoxied the floor of the inside of the boat, not the sides. I think I should glass and epoxy all exposed wood, within reason. Am I crazy for thinking that is the way to go?
5. What are the length dimensions of the cross pieces? There are NO drawings of the cross pieces themselves, only a mention that they are 1"thick x 2"wide in photo 53. I may have to SWAG these i guess.
6. Frank used two layers of 6oz cloth on the hull exterior. Does anyone think it really needs 2 layers of 6oz? I was thinking one layer of 6oz, or 2 layers of 4oz at the most.
7. What is the width and thickness of the frame pieces attached to the stern face of the ama bulkheads? There is no length dimension either, but I can figure that from the bulkhead dimensions.
8. Do I need to follow Frank's rudder / leeboard profiles or can I pick my favorite NACA foil profile and use it? I don't think it really matters, I have seen some rudders that just cut a 45deg bevel on the leading and trailing edges and call it good. But I want the boat to be as fast and as efficient as possible.
9. Are the rudder control lines terminated at the pedals, or do they go through the bulkhead, pass through a pulley, and then return back out??

Call me picky, but I spent 12 years as an electro-mechanical design engineer and if the machinists had to shut down a mill and waste time to come to my office and ask for a missing dimension on my drawings, my boss would lose his mind. I really expected more from a set of drawings that cost $119. Matter of fact, the free Drifter 16 drawings were more detailed than these. I am still going to build it though, because I like the hull design already being big enough for two people and camping gear. We will see how it goes!

[mattglynn]

Most of your questions should really be put to the designer, most of the time paying for plans includes the ability to email the designer questions. It looks like his email is on the duckworks page.

2. On plywood/fiberglass/epoxy boats a lot of people use fairing compound aka bondo to fair in the fiberglass cloth edges before painting. For example when the deck cloth is wrapped down onto the hull.

3. My faher-in-law has experimented with PL premium extensively for the past ten years or so on boats that live in the water in the south Florida sun. It works surprisingly well as long as you have good clamping pressure, however it doesn't seem to work on treated lumber.

8. You can use whatever profile you like, however I'm not sure if there is any difference in optimum profile between a daggerboard and leeboard, thats a question for a more knowledgeable person.

[upchurchmr]

Per my understanding, Bondo and fairing compound should not be considered the same thing.
And I wouldn't use Bondo on a boat.
Bondo is a trade name for a specific product used on cars.
IMHO - well, not so humble.

[mattglynn]

Yeah I should have been more clear, the concept is the same between an automotive fairing compound and a marine fairing fairing compound but their composition is different. I have heard about people using Bondo brand filler on small boats but have no idea how successful it was

[Lee.007]

Most of your questions should really be put to the designer, most of the time paying for plans includes the ability to email the designer questions. It looks like his email is on the duckworks page.

Yup, I did that. No response. So then I emailed Duckworks. They sent him an email and said that he should respond, since he still recieves their payments. So 3 days later he responded to them. He was extremely rude, and all of his answers were mostly, "Anybody that reads the drawings and the construction manual should know the answers to those questions." So, I re-read the manuals 2 more times thinking I had missed something. No, I had not missed anything, and in fact I found more missing dimensions.

Even though I bought the plans, I think I am going to do a kit-bash of the Drifter 16 and the Slingshot 19. Combine what I like most about each design, and then build it using the construction method of the Drifter. I think the Drifter drawings, even though they are hand drawn, are far superior and easier to understand than the Slingshot drawings.

As I go along, I am going to make drawing adjustments. And heck, I just might create a nice cad package with complete detail drawings like I used to do when I was a design engineer and sell it on Duckworks.

[Michael K.]

There is a Slingshot on eBay. Think of all the time and effort you'd save, even if it required a trip to Michigan.

[Lee.007]

Hi Michael,

I looked that one up. It is a 16 footer. I am looking for an 18 to 20 footer, and I have plenty of cedar now to build one. I really do want to build one out of cedar and do a bright finish. Many of my Army friends have shown pictures of my boat to some colonels and generals and there is apparently an interest in hand made "craftsmanship" type boats. I figured I would build another one for me, and then start building some to sell as a retirement income when I retire in a few years.

Thanks for the suggestion though. The current bid is only $102, and even with the $300 boat angel document fee the trailer is easily worth that. If it was down here in the CSRA in Georgia, I would drive over and offer the guy 200(+the boat angel fee) right now. That trailer looks nice. The only thing I would be worried about is a mast and sails. I didn't see any in the photos and there was no mention of them that I could find in the description.

[Lee.007]

Alright everybody,

Yesterday I ripped up all the cedar from the last batch my father in-law gave me into 1" x 1/4" strips, and according to my board feet calculations, I should have enough to do another trimaran, either the Slingshot or the Drifter. I still have almost the same amount on my racks in my garage that I didn't use from last time. So I am sitting on much more cedar than I originally thought. So the kit bash begins. I think I am going to call this new boat a "DRIFT SHOT". Catchy, eh?

I think I am going to build the Slingshot 19, but make bulkhead forms and stringers like the Drifter has. I want to have a skeleton under the skin. With 1/4" strips, and a solid frame underneath, this baby ought to be rock solid and last me a good while. It will make it slightly heavier, but since I am using cedar for 90% of the construction I'm not worried about that. I think I will make panels from strips, cut the hull pieces out of the panels, fiberglass / epoxy the insides of the panels, lay them up on the skeleton, and then fiberglass the outside. I like the hull profile design with the 3 planes (sides, bilges, bottoms) of the Slingshot better than the flat bottom Drifter, but I like the construction method of the Drifter better.

I also like the laminated akas on the Drifter better than the aluminum pipe akas on the Slingshot. I think they give a wooden boat a better "craftsman" feel. I may have mentioned once before doing birdsmouth akas, which Duckworks said would work just fine, but I am maybe thinking about laminated wood akas now. Much easier to make, and I can build the housing for the folding system like the Slingshot has whether they are laminated or birdsmouth beams.

The Leeboards and rudder I am boing to make the same way I did last time, laminating 1" or 3/4" thick pieces together opposing each other's grain to avoid cupping, and use a NACA foil like I did last time.

The mast is going to be tricky. Slingshot plans call for a 23 foot mast. Pulling this behind my truck on the trailer I currently have will be impossible. Anybody got any good designs you can point me to for a sturdy folding birdsmouth mast system?

So here we go. I am drawing up some form / bulkheads based off inferred dimensions from the Slingshot plans, and will soon be building the frame. I plan to be finished by summer, so I can get on the water with it within 8 to 12 months. Wish me luck!!

[Todd Bradshaw]

Yup, I did that. No response. So then I emailed Duckworks. They sent him an email and said that he should respond, since he still recieves their payments. So 3 days later he responded to them. He was extremely rude, and all of his answers were mostly, "Anybody that reads the drawings and the construction manual should know the answers to those questions."

At that point, I'd return them to Duckworks for a refund and tell them why. There is no reason for somebody in our business to behave like that, and I doubt they would be too happy knowing that one of their suppliers acts like that to their customers. There are plenty of good boat designs out there. No reason to deal with jerks.

[upchurchmr]

Lee,

A 23' mast should be simple to trailer.
you need a support at the front of the trailer which is fairly tall, that puts the mast over the top of the truck.
Hobies did this with a 26' mast, and my Tornado did it with a 31' mast.
You build a support at the rear of the main hull and extend the mast just a small amount past the stern.
As a matter of fact, comment #87 shows exactly this setup.

This should be one of your smallest issues.

Please don't ever make a folding mast!!!!! Please.

PS: Seriously consider finding a Hobie 16 mast and sails, it will do everything you want. Good used sails will be hard to find, you might have to buy new. Do yourself a huge favor.

[Lee.007]

Yeah Todd, I did think about that. I keep finding more errors the more I study the drawings. I figured since I am using the drawings as a base to design something different, I would keep them. But I certainly won't be looking at any of the other slingshots.

Upchurchmr, thanks for the advice. I will see what I can rig up on my trailer. Since I bought my new truck I realized there is not a roof rack to tie my mast to like there was on the jeep. So I gotta make something for my current boat anyway.

[Lee.007]

I have made up my mind now. I am going to use the Drifter hull as a base design for the vaka. I might use some of the multi panel and bilges idea from the slingshot, but for the most part the hull design is coming from the Drifter. I scaled it up to 19 feet using my autocad, and rounded all the dimensions to the nearest 1/16". There may be some small errors induced with doing this, but I think overall it will be okay since I am going to strip it with cedar and I am not trying to fit a plywood cutout to a perfect fit dimension. That's another reason I like the strip build. I can be less literal with the dimensions.

I plan to use the mast step / partner design, the seat and steering pedals assembly, the rudder lower and raising system, and the folding aka system from the slingshot. I like the akas folding in a plane parallel to the water instead of folding them up over the vaka. This allows me to stow the sails, fold the akas, and slide up to the dock or pier so I don't have to get wet taking the boat out of the water. I also plan to install more frames than just the 3 plus the transom. I want the hull to have a frame/bulkhead at least every 24~25 inches to give me something to hold the shape when I apply the strips.

As soon as I can get the dimensions for the frames drawn out from my scaled drawing, I can start building the skeleton! I'll try to post some pictures when I get that far.

[Lee.007]

I think I may have asked this before. But who knows where the plans are to be had for this : https://www.youtube.com/watch?v=ZgLdHjNcLjU

[Lee.007]

I should probably shut up and let y'all respond to my questions above, but I could resist posting this. I am really liking the way this is scaling up. The water line length to waterline beam ratio comes out to 9.5. According to a Northrop Grumman hull design video I watched, that is smack dab in the middle of their "Fast Hull" classification of 9 to 10. The dimensions I have on here are the overall length and beam. You can see some of the bulkheads I have started to add to the existing ones.

EDIT: I just realized after posting that there is an optical illusion in this picture that makes the starboard ama look bigger than the port ama. They are the same, just in case you were wondering. Oh, and dimensions are in inches.


DriftShot 20.jpg

[mattglynn]

Upchurchmr is right, a used Hobie or similar beachcat rig would be the easiest way to go. You should have the sailplan sorted before you get to far along in the building process so you can balance everything and figure out where your mast is placed and work through any complications. Hopefully someone more knowledgeable chimes in, but if you are scaling the drifter up roughly 19% and the plans call for a 68sqft sail does the sailplan scale linearly? If it does then it would be around 81 sqft of sail, and most beachcat rigs would be overpowered. Now that I've contradicted myself hopefully someone like Todd will clear things up. We put together the rig for our trimaran piecemeal from a Hobie Tiger mast and Hobie 18 sail, and a combination of new and used blocks and lines. I thought I was being clever, but it was frustrating and took a year of sailing to sort out, it also ended up being much more expensive than just buying a complete used rig. Oh well, hope you can learn something from my mistake.

[Lee.007]

Good advice Matt. When I built my "kayak trimaran", I read some books and there was some calculation that I used to figure where the mast needed to go based of of the center of effort of the sail plan and some other variables. I forget now exactly how I did it, but I still have the books. And I do remember after figuring up where the mast needed to go, it was going to be right in the center of one of my kayak hatches. Obviously I had to move it from the optimum location. Because I built the kayak and then decided to make it a sail boat. So, I am definitely going to do the figuring for the mast location before I decide where everything else is going to go.

As far as the sail area, I am also basing that somewhat off of the Slingshot design as well. Some of Frank Smoots comments in the plans manuals say the single bermuda rig was faster than the sloop rig. But, in light airs a jib certainly makes a difference. I am all about simplicity, but when I added the jib to my kayak trimaran it made a HUGE difference in everything. Probably because it moved the center of effort so the mast location was more optimal. I could sail almost twice as fast in little to no wind than before, I could tack on a dime, I could point higher, but it didn't seem like the top speed increased that much. My max is still about 9.5 mph with about a 15 mph wind. That's mostly because I have to start dumping air to keep from putting my mast on the bottom of the lake. But, I could get 2 mph out of a 1.5 to 2 mph wind. Both speeds were measured going up wind. Adding the jib gave me right at 100sqft. And my little kayak only has the little CLC Sailrig amas with about 100 lbs of buoyancy in each. I do have to hike out a bit when the winds are 15mph+, but its exhilarating going upwind. According to the volume calculations in my AutoCAD, both the Slingshot and the Drifter have about 500lbs+ of buoyancy in each, so I am planning on carrying a little more sail. I am thinking around 130 to 150 sqft max. If I can get that out of one sail, I might just stick with a single sail. The Slingshot manual has the plans for a 128 sqft vertical batten sail, so I think I should be pretty safe with 150 sqft. The sling shot also has two locations built in for the mast, one for single sail, one for sloop rig because adding a jib changes the location of the center of effort. I will definitely add that into the scaled up Drifter design to give me more flexibility. I am still debating whether or not to add a jib.....

Decisions... Decisions... Everything is a compromise.

[mattglynn]

I would add a jib. Trimarans can be hard to tack, and being able to back the jib to help bring the bow around is useful. You can kind of stall out or heave to by backing the jib and pushing the tiller all the way upwind, useful if you need a minute to sort something out. The trimarans I've sailed all seem to point higher with a jib, and it seems like there is better airflow over the main with a jib. I don't really know how to explain it but my telltales are happier, and it feels more powerful. Also, with your foot pedal steering you're going to need something to do with your hands

[kleppar]

What about the W17 trimaran? There is also a larger W19 with more carrying capacity.
https://smalltridesign.com/W17/greyb...-Trimaran.html
https://www.klepsvik.info/w17
https://www.klepsvik.info/w17-cruising
https://www.klepsvik.info/float-design
https://www.klepsvik.info/on-board-W17


My W17 was built with folding beams, similar to Dragonfly; completed about one month ago.

[luckystrike118]

I think I may have asked this before. But who knows where the plans are to be had for this : https://www.youtube.com/watch?v=ZgLdHjNcLjU

Hello Lee, the Drifter 17 is designed by Mark Gumprecht back in 2011. You can read at SmallTrimarans.com that Mark had provided Plans for it ready to be built. I dont know if Mark is still in buisiness, his building blog is not uptated and stripped since 2012. But you can send him an E-Mail and have a look.mwgumprecht@comcast.net. (e-mail information is also from 10 years ago).

If you cannot get a contact and a construction plan, send me a pm. I can send you plans for a similar boat, 18' long.

Have fun, Michel

[Lee.007]

So the more I draw this new boat, the more I realize scaling and using other features from these two boats just aint gonna match up right. So, I am just going to roll my own, and build me a complete new design. I will modify the current hull a bit, and about the only thing I am doing really is measuring the rocker to get an idea of how much would be needed. I'll post some pictures once I get the whole thing done. But I think it is going to be just as good, if not better, than the Drifter or the Slingshot.

I like the roomy look of the w17, but it looks a bit heavier than what I am wanting to do.

Michel, that 18' design sounds interesting.

[kleppar]

Weight of W17 is about 200 kg.

[upchurchmr]

What's that in real terms?

[kleppar]

200 kg boat without crew and gear, but on such a boat you do not bring a lot of gear........

[Lee.007]

Hey guys, I have finished drawing most of the big parts that matter. I kind of had to scrap scaling the drifter, because the amas were too close to the vaka, pivot points on my folding akas were not in the same plane, and other issues, but I think I have her worked out now. Using AutoCAD to calculate my volume, center of lateral resistance, etc., I am coming up with 734 pounds of displacement at the waterline. It will hold more, but that is where the design waterline is. So that is enough for 2 people and some camping gear. I haven't made up my mind on a sail rig. I really would like to add a jib. I just haven't figured up the location of the mast for a sloop rig yet. They way I have it in this picture, the mast is leading the CLR by 15% (I dug out my books). As you can see, it is actually pretty roomy for two people. I plan to add some planks or trampoline between the amas for more space if necessary. What do you guys think?

Skipper and 1st mate.jpg

[kleppar]

When I chose my W17 design, I quickly ruled out the canoe/kayak type trimaran, where you sit facing forward, simply from my experience with a Hobie Adventure Island. Such a position, when the trimaran heels (and yes, it does heel), simply gives an uncomfortable ride. It is OK for very short trips, for longer journeys you will certainly feel the discomfort. Anyway, good luck with you build.

[mattglynn]

I agree with Kleppar, it is an uncomfortable position to stay in for long periods of time, and with your low buoyancy amas you might want to hike out sometimes for more spirited sailing. Definitely keep the option to sit kayak style and reach all the necessary things, its more protected from the wind and spray on chilly days, but it probably won't be where you end up spending most of your time if you have other options.

You could simply glue one of your stripped panels to the underside of your aka housing outside of the gunwales, you only need 12" or so of width, and it won't interfere with your folding mechanism.

Is it just me or does it seem like your forward aka is VERY far forward?

[Woxbox]

Looks like a good start. Most trimarans carry the forward akas as far back as is practical. If not, they will catch the wavetops more often and throw spray while slowing the boat. And what happens next, especially if the skipper and crew are seated low in the boat, is they get facefuls of water.

We'd need more numbers to comment any further. What is the full displacement of the amas? Will they bury when hard pressed? And where is the center of buoyancy of the amas in relation to that of the main hull? As the boat heels, will it take on a bow up or bow down attitude? These are key elements that will determine whether or not you'll be able to push the boat as the wind picks up.

As I've pointed out before, when pushed hard, a trimaran is sailing on the lee hull -- the other two are pretty much just being carried along for the ride. To get good performance potential, the amas have to be designed just as carefully as the main hull.

[kleppar]

This article might be relevant:
https://www.klepsvik.info/float-design