Lee wants a new trimaran design...

[Woxbox]

Two batteries will run my 1 ton boat for hours. A light multi should be fine with a 12 volt motor and a single deep cycle. Of course, lithium is much better if you want to pay for it.

[Lee.007]

Hey Dave, I know we aren't supposed to promote products on here, but can you recommend a name brand or three that are good, and which ones I should stay away from? When you say a light multi, do you mean a trolling motor, or an actual electric outboard motor? A lot of the electric outboards I have seen on amazon are 48 Volts, and the batteries are like 300~400 bucks. I would rather stick with 12 volts so I can pick up a marine battery locally when I need to. Oh yeah, I went sailing again today. I am going to post some videos when I get a chance on my other thread. I won't hijack my own thread with the details. But yeah, let me know what you think the best bang for the buck is with electric motors. If two batteries will run a 1 ton boat for hours, I am sure 150 pound boat should get up and go pretty good on electric power.

[Woxbox]

No problems with naming brands here as long as it's not a salesman talking. I use a 24V Minn Kota trolling motor on my pocket cruiser powered by a pair of MTech or Miller Tech lithium batteries. But that's a ton of boat to be pushed. I would expect a 45-pound thrust 12V motor to be plenty to drive a 20' trimaran. Paired with a lead-acid deep cycle marine battery you'd be set for $500 or less. Go to a lithium battery and the cost would go up by several hundred dollars, but you'd save a lot of weight and you can actually get more miles out of a lithium battery with the same amp-hour rating as a lead acid battery. So the calculations can get confusing. (The lithium battery delivers good voltage until it's nearly dead. The lead battery voltage drops off as the cells discharge.)

Even the smallest outboard will set you back close to a grand, and they're noisy and require keeping gas in the boat and all that mess.

You could get more efficiency in a smaller package with a Torqueedo, but the cost gets crazy for what I see as a small advantage in a motor that won't be used most of the time.

[Lee.007]

Greetings trimaran fans! Long time no posting. Sorry, I have been busy with work, Soldier, training, master's degree, all kinds of worthless things that take away from my boat time. So update on this new trimaran project, I emailed Duckworks to see if they had any contact with Mark Gumprecht. No joy. But, their design guy said there is a 20% rule of thumb on changing dimensions. As long as you don't change dimensions by more than 20%, you don't need a complete re-design. Not sure if I am real comfortable with that, but I ain't no naval architect. I am going to stretch the drifter 16 out to 18 feet, and see how it goes. Only bad thing is, I have to wait for my 21 year old son to finish restoring a 1982 Jeep CJ7 so I can have room to build a new boat in the garage. Maybe by then lumber prices will come back down. Anybody know where I can get some cheaper than dirt Cedar?

Anyway, I got out on the water Friday evening. Gorgeous sunset on Strom Thurmond Lake. Finally got time to get another video in while the water and the wind was sort of calm. Water calmed down after all the crazy power boaters ran like chickens from the storm and stopped churning up the lake. I stayed out, furled the jib, left the main up, and held on for dear life. Once the storm passed, I was treated to this AMAZING sunset. The 3 foot waves calmed to a ripple so I let the jib back out. There was still some big wind that kept me moving at 4 to 7 mph. That feels like 60 on a small kayak Trimaran. According to the history on my Garmin GPS, I hit 10 mph (8.7 kts) in the storm. New speed record for me!! I was hiked out as far as I could go and was still burying the leeward ama. Almost went over several times but I was able to let the sheet out to dump some air, turn into the eye of the wind, and slow her down before I flipped. I probably shouldn't have been out there, but I always say if you are not living on the edge you are taking up too much space!! Enjoy the sunset:



The video didn't show up as well as I thought. Here is a pic I snapped with my phone:
IMG_20220617_210414739_MP.jpg

[luckystrike118]

Hello, sorry, Iam late to this thread.

Motor: If you are interested: a Torqueedo or a E-Propulsion E-Outboard motor with 1100Watt are a 3HP petrol outboard (thrust) equivalent. With a included Lithium battery it wheighs in at 17kg. More than enough for a light trimaran.

Boat: If you have decided for the Seaclipper or Drifter trimaran design, give the W17 Trimaran Design a chance. Mike Waters has got all the design details right, that are so important to give the three panel Vaka with a flat bottom a good performance and -balance. An excellent boat!!! A much better design than the Drifters.

Have Fun, Michel

[Lee.007]

Thanks, I was just doing the Drifters to have something for right now, and to do it on the cheap. The Seaclipper 20 is the ultimate goal. It will be the flagship in my family armada.

[Lee.007]

Motor: If you are interested: a Torqueedo or a E-Propulsion E-Outboard motor with 1100Watt are a 3HP petrol outboard (thrust) equivalent. With a included Lithium battery it wheighs in at 17kg. More than enough for a light trimaran.

Whooaaa... That torqeedo or the e-propulsion is going to cost more than I planned to spend on the boat hull and half the sail. Sorry, I'm a cheapskate cause my status in life forces me to be. Especially in today's world. That's why I am going to build a small boat with free wood I picked up from my father-in-law. Thanks for the tips though. I will certainly keep them on my wish list.

[Tomcat]

If you are building a trimaran, in wood, it's crazy not to do a stressform boat. I built an ama for my 24 footer, it was 20 foot long, in 20 hours. 5 evenings 2 hours ish, and 10 hours over a weekend. Compare that to the Devlin I am building at 13 foot where just tabing the hull is taking like 30 hours, and it is a step that really doesn't do anything that is essential in the final boat. I am sure I am doing it wrong, but I am closing on 300 feet of stitch and glue, and am normally ahead of the pack. Hey, Jim Brown said so.

It is the cheapest way to build a multihull, and the fastest, and the lightest. My boat is 24 foot. I was looking at a sailing mag where there was an ad for a "24 foot" (turned out to be 22 foot) trimaran, that was carbon fiber foam, and the weight was higher than my boat. No doubt it was great, but plywood in stessform will regularly beat carbon fiber super yachts, in some conditions. And, as I said, light and high performance also translate to cheap and fast to build in this one case.

You need to get some mastery of numbers if you haven't already. So what is a reasonable displacement for 20 foot trimaran main hull. Well KHSD has one and it is 900 pounds, and the boat weighs 500 pounds. Now yours might weigh less if it is not designed to carry heavy sailing loads and is basically a canoe. But I would guess that you will not get a hull that weighs 200 pounds and carries 800. Say a 16 foot stripper is 60 pounds, a 20 footer, all else equal would be exactly twice as heavy.

You don't need to design it yourself, but one does need to get some numbers under the belt. Nothing is more common than a mountain of BS, and fake promises where multihull designs are concerned, particularly for the small ones. That double berth turns out to 16" wide. And here is the kicker I was on one of these designer geniuses's boats once, and his double was the same width as on my 24 footer.

Gougeons built a trimaran in this class, the Victor T. and you can find their plans and their boatbuilding book online, or probably in libraries. They also had a plan for a 20 foot proa canoe. They used that hull over and over in a variety of projects.

1/4" ply, which is the most likely material for a flat panel boat this size, is about 30-40 pounds a sheet, and would add 100 pounds just for the wood. the Weight will add up.

Nothing is more common than a boat features list that has a lot of interesting and reasonable sounding parts, and for which no boat actually exists that will fit it. But there are usually a lot of boats out there that claim that they do. Nowhere is this worse than in small multis. They are not just large multis scaled down. I have said it twice...

If I was building a boat that was sorta what you want to build, and would actually work, it would be a Farrier 18. But I wouldn't built that today. I would be tempted to build a Scarab 18. Plans are 100 bucks and the end result would be something you could sell, so over time it would cheaper than building something less well thought out.

I have had consistently bad luck trying to nail a boat to a social obligation. And I have tried. Ends up the kids aren't interested, the girfriend wants a horse, etc... I have learned to be entirely selfish. What boat do I want for the next while.

[upchurchmr]

Lee,

I know of a Farrier 18 which has never been completed. The current owner just died, his widow needs to sell it.
Amas are complete, the Main hull is framed but not planked.
Both were done in West system. Planking is a part of the package.
Cross arms are not built, but the folding mechanism is complete but not assembled.
A trailer is available - it was used to bring all the components from Oregon. It used to be mine for a Tornado catamaran 20+ years ago. New tires.

If you have any interest, I can contact the lady.

Marc

[Edward Pearson]

During Covid, Dudley Dix beavered away turning his Paperjet into a trimaran...






More pictures on his facebook stream...

https://www.facebook.com/DudleyDixYachtDesign/

[Lee.007]

Thanks so much again guys for all the advice. I wish I could just take off and start building right now. The itch hasn't been scratched in almost a year. But, I gotta finish my masters degree, and my son needs to get his jeep out of my boat building garage.

upchurchmr - I really appreciate the offer to help broker a deal on the Farrier, but I can't swing a trip to Texas right now.

Tomcat - Sound advice. Duly noted about being selfish on my next boat. Now you have me wondering if I want to be selfish about a boat right now, or wait until the next one. I don't know what the stressfoam method is. I will have to read up on it. You have a link to some good instruction?

Edward - Now you have me thinking also. I saw a video on Dudley's facebook about a race to Alaska. The sailboat had four oarsmen. I am pretty sure they knew what they were doing cause I noticed they feathered their oar blades with each back stroke. Maybe setting some oarlocks on some amas and stowing oars aboard would be a lot better when becalmed than a single paddle, hmmmmmmm...

I was going to go sailing this weekend, but the honey-do list wouldn't let go of me. Maybe next week!

[luckystrike118]

For a detailed Information you can download the famous Gougeon Brothers Book for free: "The Gougeon Brothers On Boat Construction". Beside all (and I mean "all") information on how to use Epoxy and modern wood construction techniques you will find a detailed discription about compounded plywood construction and design (Sressform, tortured plywood).

https://www.westsystem.com/wp-content/uploads/GougeonBook-061205-1.pdf

Have fun, Michel

[luckystrike118]

And a PDF from Russel Brown with his experiments

http://www.ptwatercraft.com/Begining%20Tortured%20Plywood%201-6.pdf

Have fun, Michel

[Lee.007]

Thank the Lord I have finally finished my masters degree. SO, I have been thinking again on which boat to build, which method / technique to use, etc. I am still rolling the idea of stretching the drifter 16 out to 20 foot just by dropping a four foot section of hull in the middle and adding another station, but I am also going to look and see if any new plans have shown up in the last year or so. I still want most of my original design requirements. We'll see how this goes!

[John Perry]

It is not at all unusual for it to take an entire season of sailing to learn to reliably tack a trimaran, but that is one place that a jib helps. You leave it cleated on what will soon be the "wrong" side and let the backwinding jib help to push the bow over onto the new tack. As mentioned before though, a jib really needs shrouds or backstays (or both) to maintain decent shape and keep the luff tight.

Todd - Re. tacking with a trimaran, our Farrier F32R trimaran tacks beautifully, you can do slow tacks or quick tacks just as you choose. If you actually wanted to miss stays and go into irons you would have to try quite hard to do that, then if you want to start moving again you can just let it go astern, flick the rudder the other way and off it goes again. Absolutely no need to back the jib when tacking! As for maintaining jib luff tension the mainsheet actually plays a big part. Our mainsheet has a 12:1 purchase which can be increased to 36:1 by a 3:1 'fine tuning' tackle within the boom. When you haul down hard on that 36:1 purchase you can really get some tension in the jib luff. We are still learning about the boat, its both our first yacht and our first trimaran but we are already getting 9 to 12 knots close hauled. Interesting that when I was considering whether to buy the boat someone at our club said "don't buy a trimaran - the problem is that they can only sail down wind, you will never make any ground to windward" We actually find that the weakpoint with our trimaran is if you need to sail dead downwind - in that situation it just hardly seems to move, but perhaps that is because we are leaving the big asymetric spinaker on shore until we gain more experience.

[Lee.007]

John, my current boat is nowhere near as big at that, about 1/3 the size actually, but going dead downwind seems the same for me, unless I have a 10 to 12 knot wind. Less wind that that, and I use my jib and main sail wing and wing and she does pretty good. But for tacking, its a beast without the jib. I leave it as Todd suggested and it really does help a lot on my small boat. Have a look here if you want: http://forum.woodenboat.com/showthre...t=#post6646589 .

[John Perry]

Lee - I have a bad habit of doodling with CAD, this is my latest doodle - proposed trimaran about 20foot LOA. Primary aim is a test bed to try out some ideas for hydrofoils but it also does also feature overnight camping style accomodation for two person. Not intended as a replacement for our luxurious F32 though. Next stage is to do some tests with the proposed hydrofoil systems over the coming winter.

trimarn 04.jpgtrimarn 05.jpgtrimarn 06.jpg

[Woxbox]

Todd - Re. tacking with a trimaran, our Farrier F32R trimaran tacks beautifully, you can do slow tacks or quick tacks just as you choose. If you actually wanted to miss stays and go into irons you would have to try quite hard to do that, then if you want to start moving again you can just let it go astern, flick the rudder the other way and off it goes again. Absolutely no need to back the jib when tacking! As for maintaining jib luff tension the mainsheet actually plays a big part. Our mainsheet has a 12:1 purchase which can be increased to 36:1 by a 3:1 'fine tuning' tackle within the boom. When you haul down hard on that 36:1 purchase you can really get some tension in the jib luff. We are still learning about the boat, its both our first yacht and our first trimaran but we are already getting 9 to 12 knots close hauled. Interesting that when I was considering whether to buy the boat someone at our club said "don't buy a trimaran - the problem is that they can only sail down wind, you will never make any ground to windward" We actually find that the weakpoint with our trimaran is if you need to sail dead downwind - in that situation it just hardly seems to move, but perhaps that is because we are leaving the big asymetric spinaker on shore until we gain more experience.

All true, I had an F27 that sailed the same. But the Farrier Tris were/are well evolved designs that should have put to rest all the bad tri performance stories. But somehow the tales are still out there. You don't even need the jib up to tack a Farrier trimaran. Under main alone, they'll go wherever you point them in pretty much all wind conditions.

[Lee.007]

John,
I am recovering CAD addict myself. I spent 12 years as an electro-mechanical design engineer building robots before I came back in the Army. I still diddle a bit to keep my skills fresh. I am trying to teach myself DELFTShip, but being an AutoCAD guy it is a pretty steep learning curve to convert to a new software. I am fluent with AutoCAD, but I have been looking for a software package designed for naval architecture (but im no naval architect) so it will give me easier access to the hydrostatics. Your boat looks interesting, which software package do you use? What do you think of my idea to stretch the Drifter 16 out to 20 feet, keeping the beam mostly the same, maybe increasing it a few inches?

Dave,
Some day my designs will be evolved! LOL!! Nah, I think maybe I should just stick to someone else's tried and true designs that already got the bugs worked out. But still... my hard headedness wants to roll my own sometimes. Or at least modify something like stretching the Drifter 16 out to 20 feet. I have definitely learned a lot from you and the rest of the crew on here, and I very much appreciate that!

Edit to add: And my dang kayak does not have that nice swept up stern keel like the Farrier's do. I think that is 90% the reason my boat turns like an 18 wheeler on a mountain trail. It is hard to even push it by hand while I am standing in the water when I don't get it lined up on the trailer just right.

[John Perry]

Lee - I use SolidWorks CAD which I find excellent. Years ago I used 2D Autocad and I would say that any decent 3D system is a huge advance on that. I dont know about DELFShip, I am guessing that this is orientated towards just drawing hulls and doing hydrostatic calculations so not really comparable to Solidworks which can be used to draw anything you can imagine - not just a boat. I believe there is an add on for Solidworks to do hydrostatic calculations but I have not found that necessary. To work out how the boat will float I just start with the hull as a solid block, guess a waterline, chop off everything above that and Solidworks tells then shows me where the centre of bouyancy is, then I adjust the guessed waterline till the position of the CoB matches the CoG. This sounds complicated but it only takes a few minutes once you are used to it. For a monohull you probably need to do this proceedure for several different angles of heel, each time allowing for the change of pitch as the boat heels over, but you dont really need to do that for a multihull since a simple calculation gives you a good indication of the maximum righting moment which is the main piece of information you need to design the rig and the structure of the boat. SolidWorks is parametric, without going into details, I can say that I think this is a big advantage over non-parametric software (such as Rhino, as far as I am aware). I understand that there are now some free, or at least cheap, alternatives to Solidworks, (maybe FreeCad?) but I have no experience of using these so cannot comment on how good they are.

I took a quick look at the Drifter 16 and I agree that it looks OK for a really simple easy to build trimaran. I expect it would be OK to lengthen it to 20 feet if you really dont mind the extra length for road trailing and on-shore storage. Probably good to increase the beam a bit if you do that.

I would say that I much prefer to design and build my own boats and all the ones I have done so far have been successful. Buying the Farrier F32 secondhand was a bit of an aberation for me but I had been wondering what it would be like to sail a yacht sized boat and I worked out that I probably would not live long enough to ever finish building a boat that size and I don't have a big enough shed to do it anyway.

[Lee.007]

Thanks for the advice and info on solidworks. I dunno, I just never could wrap my head around grabbing and pulling on solid surfaces in cad to make it look like something I meant to draw. I messed around with fusion for a bit, but everything I drew looked like wadded up paper balls. Maybe I should take a class. I use the solid modeling functions in autocad 2013. Basically draw cubes and cylinders or such and carve off the mass I don't need. Sometimes I will extrude 2d surfaces to make a solid. Works ok, but its not near as powerful as solid modelling.

I was planning on increasing the beam a few inches, but not much on the drifter 16. I was going to copy station 2 and offset its perimeter by an inch or inch and a half, position it 2 feet behind station 2, make another station 2 and position it 2 feet behind my created station piece, and the rest is original design. That will add 4 feet to the length and 2 to 3 inches to the beam. Do you think I should widen the beam more?

[Woxbox]

Do you think I should widen the beam more?

Probably not, but the best approach is to determine final displacement and work the model to hit that target.

[JimConlin]

Probably not, but the best approach is to determine final displacement and work the model to hit that target.

Also consider heeling and righting moments.
What heeling moment will the rig impose? What moment does it take to tip the whole works over or submerge the leeward float?

[Lee.007]

Jim is going to make me get my physics book back out..I am assuming healing moment means the force required to push the boat over far enough to capsize, correct? How do I calculate that?

Dave, that's sort of the way I started. Finding the displacement I want to be able to carry the people and gear I want to carry. Trying to find a cad package I can afford to give me that easily with a user friendly interface is my challenge.

[JimConlin]

Jim is going to make me get my physics book back out..I am assuming healing moment means the force required to push the boat over far enough to capsize, correct? How do I calculate that?

Dave, that's sort of the way I started. Finding the displacement I want to be able to carry the people and gear I want to carry. Trying to find a cad package I can afford to give me that easily with a user friendly interface is my challenge.

My other name for heeling moment is the torque that’s trying to tip the boat over.
It’s something like Sail_area * Height of sailplan’s_center_of_effort * (wind_speed)^2 * some_constant.

My other name for righting moment in a trimaran is the torque that the boat’s hulls and mass exert to resist the heeling moment.
It’s roughly (distance from CL of float to CL of boat) * the lesser of:
(Weight of the boat in lbs.) and (Displacement of leeward float in pounds).

If there’s too much heeling moment, either the main hull lifts out of the water and something bad happens or the leeward float submerges and something bad happens.

[upchurchmr]

Lee, have you asked the designer what he thinks about your proposed changes?
Are you going to increase the sail area due to the increased displacement, or are you going to just let the boat have a slower top speed?

[Lee.007]

I will definitely increase the sail area. once I use the advice above and do some digging to figure out what the heeling moment is, I think I will design the sail plan to be just under enough to capsize in a 20mph wind. And definitely plan in reefing points.

[Lee.007]

Hey all, it's been been a minute since I have been looking at boat designs. So, even though I think it would be fun to try my own hand at stretching the drifter to 18 or 20 feet, I think I am going to go with a slingshot 19. It checks most of the boxes of what I want, and I have seen several recent videos on YouTube that shows some pretty nice sailing. And I really like the way the mast stepping works. I think it is better for me to build a design that is tried and true, instead of rolling my own until I get a better understanding of naval architecture and more experience with knowing what happens when I change certain dimensions and how they affect the performance of the boat.
I am 30 days out from my spinal fusion surgery and I am finally getting back on my feet and able to move like I want to, so it's time to start building. Does anyone know of a "cheaper than dirt" source for cedar wood? I have quite a bit of cedar from the pile my father-in-law gave me, but it's not very clear and mostly only 3/4 inch thick 8 foot boards. I just can't make myself pay $19 for a rough sawn 8 foot 2x4 from Lowes.

[Lee.007]

Oh, by the way, I have tried to contact both Mark Gumprect and Frank Smooth via the last known emails, but the guy that runs the small tri guy website told me they have pretty much shuttered themselves from the internet, so I certainly don't want to change someone's designs without at least a short conversation with them.

[upchurchmr]

How are you planning to make the hulls?
I thought Smooth's boats were plywood designed.

Are you going to strip plank to the same hull shape?

[Lee.007]

I do plan to strip plank it. I haven't decided if I want to make panels and then install them like plywood, or just lay the strips on like a traditional kayak. If I do panels, it would be harder to make a cool design with the strips. But I want to use cedar to make it as light as I can, without paying a fortune for plywood with waterproof glue between the layers.

[upchurchmr]

If you do use a kayak like method, remember the cost of the forms. It might make the two methods similar in cost. I've never tried to make a cost comparison.

I think I've said this, but I will not do another kayak bright. I've replaced glass coatings too many times. And that costs a lot. I have one waiting for me to work up the commitment to redo the glass.
From now on I'll use paint on top of the glass/ epoxy.
Much more durable.
But not as pretty.

[Lee.007]

Well, for the kayak method I already have a lot of cedar, I just don't want to use it unless I have to since it is not very straight or clear. I can scarf a lot of it together, which is no problem it just takes longer and makes it harder to create a nice pattern.

As far as the forms go, I won't need to do a clamshell deal. The forms are pretty much part of the boat when you finish from what I can see of the pictures and similar designs. I think most of the forms will be made of 3/8" plywood for the Slingshot. I am wondering if I can just fabricate some out of SPF boards or even cedar boards. After I cover cedar or SPF with fiber glass, is plywood that much stronger?

Oh, and I called Duckworks and asked if I could replace the aluminum mast and akas with a birdsmouth mast and birdsmouth beam akas. They said that would be just fine, and I think it might perform better than a bendy aluminum mast, if I have the right sail design. I was thinking of doing a custom designed sloop rig with the help of the guys at Sailrite. I am looking for the max sail area to be about 140~150 Square feet.

And as far as painting goes, I am still debating. I think doing the cedar in bright is what gives it that traditional allure and draws people to my current boat since it is all cedar and clear finish. If I was going to paint it, I might just buy some simple luan plywood to build it. But I would have be real careful about sealing it good with the epoxy to prevent the water from getting to the plywood glue. Oh well, decisions, decisions...

[Lee.007]

Uh-oh, I just had an idea (dangerous, right?) - what about using the luan plywood, now at lowes and home depot for around 10 bucks a sheet, for the gunwales and keel sections below the water line, and cedar for the deck and parts of the gunwales that are above the water line?? That way the luan could be covered heavily with fiberglass and epoxy and painted for durability against the rocky, sandy, beaches and boat ramps, but yet I keep the beauty and craftsmanship appeal of the cedar, without having to scarf so much of it together.

Or... why not just make it all out of cedar, paying no mind to how the pattern lays out under the water line, epoxy/fiberglass it really thick from the waterline down for durability, then paint it? Kind of like the old wooden Chris Craft boats is what I am thinking. Maybe even add strips of polished stainless or polished brass down the bows and keels and trim the transoms with it too. I bet that would make a right handsome and classy trimaran sailboat. This way I keep the lightest weight building material (cedar) and still make a durable and traditional "American Craftsmanship" style boat. Only draw back I see to this method is the sole will look like crap if I don't care what the cedar pattern works out to be. What do you guys think???

[ulav8r]

You've not been to Lowes lately, have you? Their website does not even have 4x8 sheets of luan. They have a 2x2 sheet for $7.28 , a 4x8 sheet of poplar underlayment for $30.95, or a 4x8 sheet of sanded pine for $37.42! Menards has a 1/4 nominal, 4x8 sanded utility plywood, species not specified for $22.46. It stated not for use as underlayment. It looks similar to luan but not sure how it might be for voids which can be a problem for use in boats. I have bought some of that to use as panels in painted cabinets but have not cut it yet to know how many voids it might have. The Lowes poplar underlayment should have few voids but it would probably rot as fast or faster than luan.

The closest thing Home Depot shows is 5.2mm Sandeply, a South American hardwood panle, for $32.88. Actual thickness is listed as .205 inches.