Building a 16 Foot Trimaran

Major update

2011-05-23T21:00:00.000-07:00

It's been about year since I update this blog. Sorry to any followers of this blog for the prolonged absence. The boat is complete now except for rigging, which I hope to finish some time in June. Large life experiences have happened within the last year including a one month trip to Europe I made with my son Max. I'm moving future updates on this boat to my own website due to the clunkiness of the blogspot format. Please see this page for updates in the future.

Random Yet Significant Progress

2010-05-28T17:35:00.000-07:00

I ordered some parts from JMS Online (www.jmsonline.net). Two 6" deck hatches, one 8" deck hatch and three 5/16" bow eyes. JMS had good prices. Delivery time was typical. I'd buy from them again, and probably will. One 6" hatch goes at the bow, as will one of the bow eyes to anchor the base of the jib. The hatch there will allow me to access the nuts to the bow eye below the deck, and to inspect the nose compartment and pump out any water that may get in there. One 6" hatch will go at the rear of the cockpit floor to allow pumping out any accumulated water. The 8" hatch will go on the top surface of the far rear compartment by the rudder. The other two bow eyes will be used to anchor the bases of the water stays that will strengthen the akas (ladders).

I really wanted to install the forward bow eye and deck hatch when they arrived, but in a typical case of "one thing leads to another" I realized I needed to install and finish the nose deck surface first. I couldn't do that until the lips to the big deck hatches were installed. So I bit the bullet and installed them. They were much more complicated than I thought they'd be. After ripping 3" wide strips of luan wood and cutting sections for the side-to-side pieces of the correct length with 90 degree end cuts, I realized the end cuts needed to be angled due to the sidewalls and chine logs being in a "V" shape. And, the angle varied for each piece of wood since the sidewalls were closer to a "V" at the middle, yet vertical at the bow. After re-cutting new strips, I installed the far forward one first, then the rear one, and then stretched strings from the top of one to the top of the other. That way I could line up the two middle ones so both the front and back deck hatches would be in the same plane. After installing the side-to-side lips, I installed the side ones. Lots of epoxy, screws to hold them together while the epoxy cured, and thickened epoxy fillets at corners and around the edges where they meet the deck surface. Will make the hatches "real soon now".

The bow. I epoxied the luan wood top on and weighted it down with various high density items. Sanded, then laminated on the glass. Two layers at the tip of the nose, and an extra patch where the bow eye will go. Have since painted with another layer of resin for the first filler coat. Will be fun to cut the hole for the deck hatch, drill the holes for the bow eye and install it.

Here's the mast base. An earlier post showed the framework below with fiberglass reinforcing. This is one layer of luan, then a patch of fiberglass, then a piece of 1/2" beveled plywood, another layer of fiberglass and then one more piece of beveled 1/2" plywood. The idea is to have a strong surface where I can screw in whatever I want for any mast that I choose. The screws shown in the picture are only to hold things tight together while the epoxy cures. They'll come out tomorrow.

The daggerboard box again. I added a wedge of 2x4" lumber with some fiberglass on top to help brace it. I keep envisioning a catastrophic crash into a log at 20 knots. I know the daggerboard won't break, and now I don't think the daggerboard box and hull bottom will break. I wonder what will? I mean might?

A close up of the reinforcing wedge.

A view into the cockpit. If you look carefully, you can see what I call the "crash bone", which is the beveled piece of cedar laminated to the bottom of the hull that goes from the back of the daggerboard box to the bulkhead at the back of the cockpit. This picture also shows the two luan bulkheads I'm laminating in to help support the cockpit floor. I'm using 3/8" douglas fir plywood laminated with fiberglass cloth on both sides for the cockpit floor. I tested 1/4" fir plywood at the lumber store for this, but it was pretty obvious after stomping on a piece held up by a couple of blocks of wood that it wouldn't be strong enough for the floor.

A view of the cockpit floor panel with freshly laminated fiberglass cloth, tented and curing with a heater.

Here's the top of the daggerboard with the 1 1/4" wood dowel epoxied in. The dowel is stabilized with rubber bands while the epoxy cures. Note the curvaceous handle.

A close up of the wood dowel stop set up for curing.

Back to Work

2010-05-21T14:48:00.001-07:00

I've been slacking on posting lately even though I've been working on the boat. Finally finished sanding the hull exterior. Also finished sanding the daggerboard, then moved on to what you see below.

Finished shaping the rudder and glassed it. Had to do a poor man's vacuum bag job on the bottom when laying the glass around the curvy bottom edge. That means applying the epoxy and glass, then wrapping with Saran Wrap and shoving the end down into a box of moist sand. It does a pretty darn good job of keeping the air out of the glass layup, but doesn't get rid of excess resin like real vacuum bagging does. Seems like a nice shape though.

I drilled bigger than needed holes for the the pivot bolt and holes where the shock cord will be routed through for keeping the rudder down. Filled the extra large holes with resin, and will drill the right sized (smaller) holes through the resin. That way no wood will be exposed and the pivot bolt will have a good durable surface to pivot against.

Starting to cut panels for the top of the hull now. Here's the one for the bow. I have 3 "bow eyes" on order. They're basically U-bolts. One for the bow to catch the base of the jib. Two for the water stays that'll brace the ladder aka.

Here's the framework that goes below the mast. It's nice and strong. One inch thick cedar epoxied to bulkheads reinforced with multiple layers of glass. Multiple layers of plywood will go on top of that. On another note, I bought a new/used mast from Igor, a nice guy who owns a Tremolino. The mast is made by Proctor from England. It's made for a Flying Dutchman, is aluminum and has a tapered top. Super lightweight too. Turns out the Hobie 14 mast I'd planned to use was cracked at the bottom. It was too short too, so the new mast is a good thing.

A view of the cockpit with the cedar rails epoxied in to support the plywood floor, which is about 15" from the top surface of the hull and about 14" from the bottom.

A close up of the rails from underneath. They're beveled and reinforced with fiberglass.

A prototype of the daggerboard slot, made with luan plywood and two ripped pieces of cedar.

Here's where the daggerboard slot will go.

Here are the actual pieces of luan that'll make up the slot sides, laminated with epoxy and fiberglass.

Time to finish the centerboard. I decided it'll be approximately five feet long. When fully inserted, there'll be about 3'-9" of board protruding from the bottom of the hull. That ought to do it. Now time to make the handle and the stop that'll keep it from sliding down into the slot.

A close up showing the partially drilled holes for the handle and stop.

Holes drilled out and lines drawn to finish cutting the hole for the handle.

Shaping the handle now.

Now with the stop inserted for a test fit.

And glassed.

Shaping the Daggerboard

2010-04-07T22:37:00.001-07:00

I had to take a break from sanding the hull, so I thought I'd shape the daggerboard. This, after deciding to make a daggerboard rather than a swinging centerboard. I had considered this design because it eliminated the below-waterline pivot bolt, but decided to make things simpler with a daggerboard.

Here's a printout of a NACA 0009 profile that seems to be common for daggerboard profiles.

And here's a little template I made from plywood that roughly matches that profile for the 13.5" wide laminated cedar plank I made.

I drew lines at the half-thick mark on both sides of the plank, and also drew lines 1/3 of the way back from the leading edge where the thickest part of the foil would be.

Tools used for shaping; first the planer, then the belt sander with a 60 grit belt, then a block of wood with 60 grit paper, then the foam backed sanding block with 60 grit paper. Here's the plank with the trailing edge of one side planed.

It's planed down to the half-thick mark (blue Sharpie line) on the trailing edge.

A view from the end, lying on my strong back.

Now the leading edge side is planed.

Another end view with one half of the plank roughly shaped.

Now finished. Rough shaping to final sanding. It's ready to be laminated with fiberglass. The leading edge is made with a piece of oak for better impact resistance.

A view from the end. Before shaping the plank, I worried a bit about how much this weighed. Well, a ton of wood was removed in this shaping. So much in fact that my shop vac filled up with cedar shavings while planing. It's very light now.

Glassing the Hull

2010-04-07T22:22:00.001-07:00

I was a bit worried that I didn't have enough fiberglass for the hull, but after measuring out a piece of my 60" wide roll as long as the entire hull I realized I had way more than enough. The tallest part of the hull side was 30", so I cut the piece down the middle and laminated those pieces to the sides using a foam roller from the nearby Lowes home improvement store.

I thought I'd need a helper to do this, but rolling on epoxy at the top of the strip of cloth worked well to hold it in place.

Then it was just a matter of rolling out the rest of the cloth. I mixed up about 4 16 ounce cups of epoxy to do both sides. Seemed like a lot. Now that I've sanded the sides I realized a lot of that epoxy got sanded off.

After doing the sides I did the bottom. Here's the rough cut cloth laid on the bottom.

Then trimmed to size.

And laminated on. I added a second layer of glass on the front half of the bottom for better abrasion resistance when beaching it.

Here's the hull after sanding the bottom, the transom and one side. What a major pain in the butt it is to sand this, even with a good random orbital sander. I ended up using 60 grit paper on a foam backed sanding block (a re-purposed grout spreader with a nice handle) prior to using the random orbital sander. It's a lot of work to get rid of all those shiny low spots. Seriously tedious work. With the hand sanding it makes for an awesome upper body workout though.

One more entire side to go still. SIGH.

I bought another 3 gallon kit of Raka epoxy with the no blush hardener. Read about this trick of draining the remains of the old bottles into the new. Was SUPER careful about not mixing up the bottles!

Ready for Glassing

2010-03-27T11:11:00.000-07:00

After patching voids, sanding, and reading this great article on How to Make a Transparent Glass Lay-up, I coated the hull exterior with epoxy using a roller to get ready for laminating on fiberglass. The article (from Laughing Loon) recommends heating your shop up before applying the resin, then letting it gradually cool while the resin cures. Allegedly this reverses the off-gassing that occurs when you heat up wood, and draws the resin down into the wood's pores. I got my shop heated up to 71 degrees, applied the resin, then opened doors. Last I checked it was 69 degrees. We'll see what happens. Here's the hull coated with resin:

I spent quite a bit of time sanding the now-filled screw head voids, and the outer corners. First I used my good old Makita finish palm sander, but then I bought a DeWalt variable speed random orbital sander. Hand sanded with a block of wood with 100 grit sandpaper on the outer corners, then with a foam sanding pad for the final radiusing of the corners. It looks pretty good to me.

The plywood seams are very smooth. If you run you hand over them with your eyes closed you can't tell where they are.

My new random orbital sander. It seems highly useful. As recommended in the article above, I attached my shop vac to it. Very little dust that way.

The rubber pad on the bottom of my Makita sander was toast, and I didn't have a vacuum attachment for it. I priced both on the internet (about $25 total with shipping), then decided to make a new pad from some medium density closed cell foam I had lying around, and made a vacuum attachment from an extra shop vac part. Whenever I'm in a thrift store I usually search for vacuum attachments.

The Big Flip

2010-03-25T09:23:00.001-07:00

The plywood skin is complete here, with all the screw holes patched with thickened epoxy.

Tried to make the bow fine...

Then it came time to flip the hull. I unscrewed all the blocks and braces that held it to the strong back and hoisted the stern with a rope and a screw hook from above.

After pulling the strongback out of the way it was pretty simple to just rotate the hull...

And then lower it to the floor.

Two skateboards screwed to some blocks made a decent dolly to roll it outside for sanding and planing.

A view of the dolly.

Some pics of the bow after planing the top chine logs.

Bulkheads where the ladders will attach.

The sanded and planed hull back in the garage. I was pleased with the hull's weight. I think it's pretty similar to my canoe at this point (I can lift it by myself), so it probably won't be too much heavier than the original 320 pound canoe trimaran.

Some interior pics...

Skin

2010-03-18T23:21:00.000-07:00

Here's the plywood on the starboard side all clamped up with the epoxy curing. I bought a long piece of 4" ABS pipe and went nuts with the pipe clamps.

Also used screws to hold the plywood really tight to the chine logs and cedar strips on the bulkheads.

I got these spiffy screws from Lowes that have a nice flat head and a self tapping tip.

Clamps removed after the epoxy cured.

A view from the bow.

Here's a plywood splice being butt jointed. I'm epoxying a 4" strip of plywood on the backside, with a layer of glass between the plywood strip and the hull skin. I sandwiched the joint with plastic sheeting and boards on each side, and screwed the boards together to act as a clamp. Seems to be working well.

The forward seam curing, viewed from the inside.

The rear seam curing.

Cutting Plywood

2010-03-17T17:52:00.000-07:00

I've been looking forward to but also dreading this moment. In retrospect, cutting the plywood was really easy, but I'd thought it would be difficult and complicated for some reason. Just clamp the plywood in place, draw a line...

and cut! I made some of those cheezy but spiffy econo-clamps out of ABS plastic pipe. Pennies per clamp. Pretty cool.

A view of the bow. This ought to slice through swells pretty well.

Looking down from above.

Working towards the stern...

All panels on. It took one small extra panel near the stern besides the two, 8' panels to complete the entire length.

Looking down inside the hull at the splice between the two forward panels. I'm not scarf jointing my plywood. Will instead butt joint it with a scabbed on additional layer of plywood. Jim Michalak's article on JOINING PLYWOOD SHEETS helped me decide on this type of joint.

My butt plate:

Plywood sheets layed out ready to coat with resin before installing. I didn't have table space for this.

First coat of expoxy resin applied.

Small stern plywood sections, and butt plates epoxied.

Other butt plates epoxied.

Preparing for plywood

2010-03-16T17:36:00.000-07:00

Here's a view of the hull structure ready for installing plywood. Note that a few bulkheads have been cut out more in an effort to lighten things up.

I changed the wood at the bow to form a more knife-like leading edge, and to be strong. Did this by laminating two cedar 1x2s on the front and cutting out some of the base wood on the back of the vertical beam.

Here's the reinforcement for where the base of the jib attaches. It's plywood with two layers of 3/4" cedar, with the thick 10 oz. fiberglass cloth laminated in between.

I cut some slots on the bottom chine logs to allow them to bend with the right amount of nose rocker. Previously I'd attached a rope to pull the bow down to form the rocker, but I realized that tension wouldn't be good. Some thickened epoxy in the cut slots restored some strength to the chine logs.

After looking at construction photos of the Cross 18 trimaran I decided to add some cedar to my bulkhead edges. My original plan for the bulkhead-plywood skin junction was to make fillets and then laminate with fiberglass. But some additional wood their seems like a good idea.

The lightened bulkheads.

Rather than use rectangular pieces of cedar at the bulkhead edges, I ripped some cedar into triangle profiles. That way fiberglass can be more easily from the bulkheads to the plywood skin.

Also laminated some glass to reinforce wood that will contain the rear aka.

Chine logs complete

2010-03-11T14:29:00.001-08:00

Got the two, lower chine logs epoxied on today, along with the vertical wood beam at the bow. This picture shows a view from the rear. The gray colored OSB bulkhead is only there to keep the chine logs in alignment, and will be removed after the plywood skin is added.

A view from the bow. I spent quite a bit of time this morning making sure the deck will be flat and that the rocker on the bottom is right. After putting a string along my strongback, I realized it sagged in the middle. So I propped it up and screwed on some legs. Nice and level now. Then had to adjust the height of a couple of bulkheads. The rocker is a nice, smooth curve now. A little more curve than I had intended, but I'm thinking now that it'll be a good thing. I think this hull will plane towards 20 knots of wind. As a long time windsurfer (since 1981), I know that designers spend a lot of time designing rockered vs. flat board bottoms to tailor boards for slalom sailing (speed) vs. wave/swell sailing. This hull is my best guess for a hull with a good compromise between wave piercing and planing. We'll see.

For the sharpest rocker near the bow, I had to pull the front end of the chine logs down. Did this with rope fed through scrap plywood, then nailed to the strong back.

A view of the deck chine logs at the bow, with the rope pulling the lower chine logs down. You can see how the vertical bow board meets the chine logs here.

Where the lower chine logs meet the transom.

The slot where the rear aka will fit, all epoxied now. It's super strong and rigid.

The forward aka made from the full-width ladder will fit between these bulkheads.

A view from the bow. Chine logs all epoxied. Heater and fan on. Plywood skin is next.

Bulkheads and chine logs

2010-03-11T13:58:00.000-08:00

My 15 year old son Max was amused when I told him I "scarf jointed me chine logs" and was "thinking 'bout pintels an gudgeons". Reminded him of Dave Barry imitating the English. I'll have to bone up on boat terms.

Speaking of scarf jointed chine logs, mine came out nicely, and I moved right on to epoxying them to the bulkheads. Setting up my bulkheads on the strongback was a bit tricky, because the main bulkheads that secure the aluminum ladder akas are 3 inches taller than the others. The boat will have a flat deck, so all bulkheads but the main ones have to be elevated about 3" off the surface of the strong back.

This picture shows the chine logs notched into the main bulkheads, secured with a strap.

Originally I had two full-size bulkheads to secure the rear aka, but realized I only needed a partial bulkhead for one. So I cut it down and put a cedar spacer between the two of them where the aka will fit.

Here's a closeup of where the chine log meets the transom. A piece of cedar is epoxied on to it, and catches the tail ends of the chine logs.

A view of the bow, showing the rocker.

A view from the stern. The big space between two of the bulkheads is the footwell for the seating area. A retractable centerboard will go there too.

A closer view of the footwell/seating area.

I epoxied then filleted each joint between the chine logs and bulkheads.

Another closeup of fillets.

Scarf Joints and Bulkhead Cutouts

2010-03-04T16:34:00.001-08:00

While the reinforcement laminating on my main bulkheads are curing, I spliced my 10' long clear cedar 1"x2" chine log lumber together with scarf joints. I read that the joint should be at least 5 times longer than the width of the wood, and cut the angle quite nicely with my spiffy new japanese style pull-saw. Why didn't I buy one of these things decades ago? What a cool tool. Anyway, here are the spliced together pieces of cedar:

Close up of the scarf joints clamped together. 3 clamps per joint with bits of plywood on each side, all surrounded with plastic.

Another closeup. I painted the exposed ends with straight epoxy, let sit and soak into the grain, painted again, let sit, then applied some epoxy thickened a bit with micro balloons.

A couple of bulkheads I hadn't gotten around to cutting before. These are cut out for lighter weight. The perimeter rings are at least 4" wide.

Here's a view of the notched in the corners of the bulkheads where the chine logs will fit:

Bulkheads

2010-03-04T00:52:00.000-08:00

I cut the transom and four main bulkheads out of the 3/8" plywood yesterday. This drawing shows where the ladder will nestle in between the two front main bulkheads. Two rear main bulkheads will secure the rear aka (aluminum box beam made from a ladder section). Short lengths of 1" aluminum tubes will pin the ladder in place by fitting through holes at the top corners of the bulkheads, and through two ladder rungs.

To reinforce the top corners of the bulkheads where the aluminum tubing will fit, I cut out two extra pieces of plywood per bulkhead:

These pictures show how the additional layers of plywood will fit:

I decided to laminate in layers of fiberglass cloth between the plywood to give it greater strength. This show shows the cut out pieces of glass and plywood, and how they're sandwiched together:

Here's a closeup of the cloth. I lucked into a large quantity of multi layer glass (probably 10 oz), sold most of it but kept some. It soaks up a LOT of resin and is pretty difficult to wet out:

The full sandwich of plywood and glass before applying epoxy:

Two bulkheads clamped after epoxying:

The other two:

Here's the center board all epoxied together with cedar strips. Will fair into a NACA profile eventually:

Just bought this today, to fair the center board and rudder:

And bought some 10' clear cedar 1x2" boards today for my chine logs:

Lumber and Ladders

2010-03-02T06:31:00.001-08:00

I bought plywood for the hull skin and bulkheads yesterday. Door skins from Lowes and 3/8" exterior fir from Ace Hardware. There's a lot of forum discussion on plywood for boatbuilding, and for every person who insists on using Okoume there's someone who says luan door skins worked fine. It depends on the boat, the builder and the quality of the non-marine plywood. I shopped around, and the luan at Lowes was pretty amazing. Virtually no voids, 5 layers, and no surface cracks or "footballs". It looks more like 4 mm to me than 5. It'll be epoxied, glassed and painted anyway, and this boat is only a day sailer. Hell, I have no idea really how it'll sail anyway, so maybe it's a prototype. Here's a view of the surface of the door skins:

An edge view of the luan, no voids:

Lowe's 3/8" plywwod was awful. Ace Hardware's exterior stuff looked great on the other hand. Again, virtually no voids, and only a few splits on the surface that I can work around when cutting bulkheads:

An edge view of the 3/8" stuff:

I spent some time on the ladder sections yesterday in order to understand the spacing of the bulkheads that secure them. Dismantled the 28" extension ladder, cut both sections to length (they're about 13' long). The rear cross beam (aka)gets collapsed down to the width of the side pieces. It doesn't need the lateral strength since front aka will be the full, intact ladder. I cut the rungs out, initially with a hacksaw (slow, difficult), but then with a reciprocating saw (much faster):

After filing the sharp edges off of the cuts, I spliced the sides back together with some rung sections. Will use 2" x 1/8" plate aluminum pop riveted to the tops and bottoms to permanently attach the halves:

The rear aka spliced together, forming a box beam:

I also epoxied the centerboard pieces together. Here are the cedar strips prior to applying the epoxy:

The centerboard epoxied, weighted down for flatness, and clamped:

Also epoxied a piece of oak on the bottom edge of the rudder:

Final Design

2010-02-25T21:27:00.001-08:00

Had enough time today to do the basic final design on the center hull (vaka). Here's a few week old sketch of what it should like:

You can see a few things pretty clearly here. The fabric seats are supported on the outside by what will be an aluminum tube routed through a sleeve in fabric, and then inserted into ladder rung holes. I actually think I'll make struts to hole the outer tube up higher to make a proper backrest, like a sling chair. This will use a 28 foot extension ladder. One section of the ladder will be used up front, and form a gang plank out to the amas, where beach chairs will be mounted as on my prior trimaran. For the rear cross beam (aka), I'll cut the rungs out of the other section of the ladder, and splice it back together so it'll be more of a small box beam. By doing so, I can make a slotted track in the middle where a traveler will be installed for the main sheet. The ladder and rear aka will attach to the deck via 1" aluminum tubes used as pins to fit through bulkhead extensions that protrude up through the deck. It should be quick to assemble that way; lay the ladder down, shove two pins in, done. I plan to stay the ladder with synthetic rigging line anchored to the hull side down near the water line, and then out to the a ladder rung by the ama. This'll put the ladder under compression instead of shear. Much stronger. There will be a raised floor about one foot down from the deck.

Here's the actual plan. Approx. 10 degree slant to the side walls, more so at the transom. Very slight rocker to the bottom of the hull.

Looks like I'll need two sheets of thicker plywood for the bulkheads. Was hoping to do it in one based on the price, but oh well.

Rudder

2010-02-24T08:56:00.000-08:00

I lucked into a good source for western red cedar nearby and ripped clear pieces into 1" wide strips in order to epoxy them together. This pictures shows test setup for clamping prior to applying epoxy:

Here's a closeup showing the leading edge, corner and bottom, where I'm using oak instead of cedar for impact durability:

I'm using Raka epoxy with a non-blush hardener. I've used West Systems and MAS epoxy before, but this stuff was cheaper and seems great. There's insulation in my garage ceiling, and sometimes I heat the garage, but mostly it's cool. Despite this the epoxy cures just fine.

That's 3 mil plastic sheeting (visqueen) above and below the rudder. The concrete blocks are used to keep things flat, along with plenty of tapping with a hammer and block of wood.

Strongback

2010-02-23T19:01:00.000-08:00

Here's my strongback:

It's made from stuff I had lying around, some thick OSB, some 1/2" plywood, 2x4s, and other plywood. I was able to level it on my garage floor by screwing the feet (2x4s at very bottom) onto the legs (plywood/OSB) after getting the top surface level. It's rock solid and totally flat. I outlined the corners of the feet on the concrete floor with a Sharpie pen in case it moves.

I had considered balsa composite construction for the hull because I bought this pile of 7/8" thick end-grain balsa panels from a guy a few months ago:

Interesting stuff. Everyone says to not use it below the waterline, I'll probably use it for decking in some areas, and maybe as decking for the top of the ladder.

Out with the old, in with the new

2010-02-22T18:00:00.000-08:00

Here we go. More shameless nattering about boatbuilding. I'm only doing this because somewhere out there, there are people who will want to build a boat like the one I'm building. I know this because I receive email every few days about my first small trimaran, which was a Grumman aluminum canoe converted into a trimaran that used an extension ladder to connect the canoe (the vaka) to the floats (the amas). I loved this boat. It carried a ton of stuff and was really fast. Planing fast. It died a few months ago in 20-25 knot winds on Liberty Bay here in Poulsbo, WA, when the steel tube supporting the mast bent under heavy load, causing the wire stays to go slack.

Sailor Paul sititng on the windward ama and holding the mast up while we limp in.

The (black) bent steel tube that held the mast up. It was 2" x .065" chrome-moly steel.

As fun as this boat was, it had problems. When I resigned myself to building a "real" trimaran, I wanted the new boat to:

Not take on lots of water due to low gunwales (it was a lake canoe, not a whitewater canoe)
Be faster, even though the canoe would plane
Be quicker to set up
Have a traveler to keep the boom end lower when not sheeted in. Maybe a vang too.
Maybe be lighter, even though the old boat weighed only 320 pounds total. That included a Hobie 16' mainsail and jib.

No "serious" boat builder is going to take me seriously, but I firmly believe that an extension ladder is GREAT way to connect the hulls in a trimaran. It's cheap, readily available, allows you to get out the amas without need of a trampoline in a precarious yet very fun manner, is lightweight and strong, and easy to work with. I'm sticking with it.

Here's an early sketch of what I'm planning for my new vaka, showing seats constructed of plywood:

I've since abandoned such elaborate seating designs after thinking about canvas beach chairs, and have come up with this simpler, lighter designs for seats (shaded sections are fabric, slung seating):

You can get design paralysis by reading too much stuff on the internet about plywood, vs. cedar strip, vs. balsa or foam composite construction. "V" vs. multi-chined vs. hemi-cylindrical hull shapes, Then there's planing vs. wave piercing hulls. Optimal aspect ratios for hull width/length. NACA profiles for centerboard and ruder designs. After reading too much about cedar strip construction, I ruled that out as too labor intensive for three matching hulls. Edensaw Woods in Port Townsend is near enough to me to make Okoume plywood construction a possiblity, and that's what I've decided to do. I debated about these two designs:

which boil down to a "v" bottom (upper) vs. a flat bottom (lower). Most of the objection to flat bottom hulls I've read about are the tendancy to pound in swells, and their instability when built as a monohull. Given that this is a multihull, and given that I'm going for wave piercing hulls, I'm going with a flat bottom hull with sidewalls slanted at 10 degrees, and little if any rocker in the vaka. This is modeled somewhat after an Internation Moth which has a flat bottom and vertical sidewalls. I'll make my amas with some rocker for planing ability though.

Well, enough with design pontification. Will post final design sketch soon.