Custom 19' all weather, minimalist, strip plank composite 'go fast'

Got the strongback almost ready for planking. I had work stuff to do and then went very slow on certain bulkheads and the transom since they needed to be almost final and in the form prior to planking, plus a little R&D on one of the forward maintenance hatches that needs to be 100% water tight, then a lot of hand shaping on the keel to get that right since the deadrise angle changes over the length of the boat. Ended up redoing the stem, which is laminated white oak since after redesigning and bulking up fore sections the first iteration of the stem wouldn't fit properly. On the upside, I now have plenty of WRC--my neighbor was moving and cleaning out his garage and had a couple hundred square feet of nicely milled prepackaged 1/4" cedar for interior planking.

 

I haven't posted an update in a while...

Got the bow pretty much finished up, including most of the fairing. It's two layers of 1/4" WRC with white oak chines and of course the white oak stem and keel. Ended up doing more steam bending for the bow chines. The rear airboxes are also about done and today I started laying the white oak chines along the hull. I also did a layer of 6oz S2 glass with a layer of 6oz CF on the inside of the rear airboxes just to practice... The inner sides of the airboxes is only 1/4" thick WRC so it was cool to see how adding the layers of fiber stiffened this up. Also makes me realize that this boat hull at 1/2" WRC is going to be really, really solid. Ran a string line yesterday to mark the deck line; some of the transverse under deck structural supports will go in tomorrow then I'll be ready to start planking the hull.

Design and build-wise I have a really clear picture of the direction it needs to go and so now I'm starting to think about the console and order the gauges and electronics around which the console will be built. Some of the structural console support will also go in tomorrow and be truly built into the hull and stringers as well since the console is little pedestal type thing. I'm also realizing that the console will be quite a feat of engineering and woodworking to be as small as I want, shaped the way I want, and sturdy as I want but I think by the time I get there I'll be ready to handle it; I learned a lot while building the bow because it's structurally so complex.

I had bought a small pile of the expensive siliconized brass screws but have only had to use about 10 of them in a few places, to make some of the curves on the bow chines and for the rear airboxes--mostly just using temporary screws, pulling them out when the glue is dry, the injecting epoxy into the hole and burying a bamboo toothpick. The inside fairing of the bow is going to be a lot but luckily it is a small boat and I bought a cheap power planer, which I realize would have made the exterior bow go alot faster. The hull planks will be cove and bead so I will be able to keep them a little neater, and also get in as I'm building to wipe out the inside as I go. This wasn't possible with the bow.

Starting the first layer of the bow (slow to start, I didn't realize how many clamps I'd ultimately be using!):


More the first layer of 1/4" built up:


One of the rear airboxes in progress:


Finishing up the bow, this was the second layer of 1/4" WRC:


Here it is yesterday, bow is pretty much finished; I will do one more light fairing pass but am saving that until the rest of the hull is built up to the same stage:

 

She is certainly coming along well.
It looks like you will have a scarph joint with maybe a 6" overlap (?) where the bow section will be joined to the rest of the hull?
I know that epoxy is strong, but I don't think I would be too keen on doing what is effectively a butt joint right around the hull with just a small overlap / scarph.

 

Yes, I did give this a lot of thought. The bow/hull scarf joint there will have a 5" overlap, and it'll be a half lap joint in 1/2" wood with a 5" overlap, not a tapered scarf or butt joint, and since it is a straight half lap it is pretty freaking strong. The hull plank will have a corresponding half lap cut into the underside where it joins to this bow section. The epoxy is a good deal stronger than the WRC fibers so the wood around would fail before the joint, making it very, very different than a butt joint. One pretty cool I thing I am also discovering about the WRC is that it really, really wicks epoxy so even butt joints have the potential to be stronger than expected. That aside, this joint will be encased in two layers of 6oz fiber on either side. Also bridging it though is the solid white oak keel @ 2"x2", white oak chines 3"x0.5", and (not there yet) longitudinal white oak stringers @ 0.75" x 3.5", bow locker decking @ 0.5" thick hardwood laminate, and WRC/white oak laminated outwales @ 0.75". So, an awful lot of stronger pieces would have to give way before that joint even feels stress...

 

Why not plank the whole hull all at once? Also, I noticed you did 0/90 for the two layers. Typically, I see 0 (strip-planked) or +/-45 (cold-molded) or 0 and +/-45. What was the reason for 0/90?

The tapered scarf is definitely stronger than a half-lap, but I'm not sure it is necessary here. Mark Bowdidge uses a method of strip planking with all butt joints, but they are staggered throughout the hull, you have a straight line connecting the bow section to the rest of the hull. He also uses a heavy skin on both sides like you are doing.

 

The butt joints would only be possible when the boat is wrapped in fibers, they prevent the joint from moving. I'm not worried about the half lap here since there is so much solid white oak and structure at that joint (besides the bow locker decking there is also a vertical divider there that will run top to bottom), and the bow section also will not take that much stress... It's not a straight line cut because there are the steam bent and laminated white oak chines, the white oak keel/stem, and laminated outwale (WRC and WO), plus interior deck and divider, and top cowling... All those parts have significantly more strength and stiffness than the 1/2" WRC sides.

I am going to do half lap for all my scarfs (but in the straight hull they will be staggered) since it's easy to do with a trim router and jig, even if the boards are already on the hull.

Originally I was going to plank the whole hull at once but there was no way kiln dried 1/2" WRC would make the bow bends. Even 1/4" was kind of tight. 0/90 was mostly based on the bends that I could make. If I was finishing the outer hull bright I think 45 would look better but this section will be covered and painted.. It shouldn't matter that much whether it's +/- 45 or 0/90, both provide the same cross grain stack for stiffness and strength. On a larger boat (more surface area) it might start to matter? When you start to factor hydrostatic forces and directions but in this tiny bow (there is also a bulkhead in there) it won't matter. It's been cool to work with the wood this way--you can really feel how the laminations stiffen the structure; two layers of 1/4" WRC laminated are about as stiff or stiffer than 1/2" hardwood ply at a fraction of the weight. I probably could have gone with 3/8", oh well. I am going off mostly the Gougeon book, they mostly cite 1/2" to 1" for power boats and big sailboats and 1/4" for canoes. My slip neighbor is running one of the original Radon's. It's older than me and still going strong in commercial use (lobster boat), been sitting in the water for decades... He said the wood in the its hull is 3/4" thick. The Gougeon book mentions some race sailing builds that were 3/8" thick but my vessel would be running on a regular basis at a higher speed so I thought 1/2" would be safer. An extra 1/8" of thickness is going to add only maybe 10-15 lbs...

 

Personally, I think three layers of 3-4mm veneers would be ideal. The problem being where to find them. In an ideal world, these would be cheaper than resawn wood because there is no waste and probably wider strips for faster planking. No need to bead and cove with the strips that thin, and if there was ever any moisture change in the hull the odd number of strips would help prevent warping.

 

The wood looks pretty dry. If you are glassing that with light woven; you might want to neat coat it with epoxy at 2 oz per yard first.

on the half lap, the best thing to do is add a fiberglass patch on the inside like a butt block

and

the idea/notion that epoxy is stronger fails here to some degree, I have bonded two boards together no lap and allowed it to cure for days and come back and the bond fails (using in a stack). The reason for the bond failure is the end grains simply suck a lot of resins out of a thickened mix, no different than old or resawn, so you can liberally wet the joint with raw epoxy an hour prior to the thickened stuff for a better result

 

Thanks, the wood is very dry. It's all kiln dried furniture quality but being built outdoors a mile from the water in a covered area so it's probably come up to near equilibrium which is what I want. I am going to do multiple coats of epoxy on the outside with the West Systems barrier coat before fiber since this boat is intended to sit in the water and no portion of the exterior is meant to be finished bright. I also intend to glass the entire inside surface for water and abrasion/impact resistance--the WRC is really, really soft. A lot of interior and topside surfaces will get or have a white oak veneer for impact resistance and the look, I may not glass this, I need to test if it's actually necessary although it might be best as a moisture barrier. I found this Softsand paint additive that I also need to test for the deck, gunwales and railing. I may not glass a few interior bulkhead surfaces that are marine ply but even most of my bulkheads I ended up doing composite layers of WRC, or 1/4" marine ply with layers of WRC, it's just came out so much stronger and lighter than marine ply. WRC needs glass.

Thanks, per the Gougeon recommendations and past experience ANYWHERE there is glue on an end grain piece I have been brushing unthickened epoxy over the end, let it wick until dry (5 mins), do it again, then actually use thickened epoxy plus screws or (mostly) dowels or temp screw then dowel+more injected epoxy. Besides fairing/filler type stuff, even the fillets and side grain bonds are done this way--brush on unthickened epoxy, let it soak while I mix in the filler, then apply the thickened epoxy. Since I am mixing white oak and WRC, the white oak gets hit with a heat gun, then brushed with gflex instead of the 105. Only wet gflex touches white oak. The gflex is okay on WRC but WRC wicks the 105 up nicely, and wet gflex and wet 105 are fine together.

I'm doing a stupid amount of fine detail and mixing, adding wooden filets, etc, mostly since I can... my engine is still backordered with no shipping date and my city is a Covid apocalypse.

 

Did you declare a laminate?

I'd want something better than woven on the outside. I really like 12 oz biax, but it does leave stitching lines to deal with.

A little surprised you didn't 45 the top layer a bit more.

I'd try to go monocoque om the hull. Glass the outside, build full height cradles for the flip that don't move. Flip it, glass the inside all the way. Install the guts. Hull is safe from all your intended ingress.

Otherwise, rot city too soon.

 

Some of the build logistics are subject to where I'm working and what I have available... I want to move the boat around depending on the construction step I'm doing. Currently the strongback and forms are significantly heavier than the hull will be at this stage, so after planking I will want to partially dissassemble the strongback. Once the hull is planked, I'll apply fairing compound, then move it out from under the porch to the yard for final sanding... our back porch is not a full indoor space but it's not exactly a boat shed either and there's all kinds of stuff there that I'd rather not have coated in loads of epoxy dust. After final sanding the plan is to carry it inside the house through the back French doors and do all the exterior epoxy and fiber in one fell swoop, wet on wet/green epoxy where I can control temperature. If I screw anything up and it needs sanding between coats then it'll need to be carried back into the yard. After that I'll flip it and start the inside and bow deck/cowling under the porch. Final painting I will also do in the living room where I can again control temp and dust.. This works pretty well, when we refinished our cabinets with two part marine urethane last year we did it this way--can create falling temps with cross breezes, open doors, and central heat/AC. I'm not vacuum bagging anything so I'll want the hull really hot when I start the first actual layer of epoxy. (My wife is one in a million.)

I will post of a picture in a day or two when I finish this step which will make more sense but the boat should flip just fine without flexing because I am going to be planking around some transverse below deck supports. I'll make a cradle to hold it but again, I think the structure will be very, very rigid. It's not much bigger than a very large canoe but got a 1/2" hull plus all the white oak. There's two permanent bulkheads in the forward section then there'll be 3 below deck transverse supports along the hull that will be glued and doweled into the hull. I'm doing something of a monocoque design but certain guts are being built right in, which is slow but if done right awfully solid since it's wood on wood bonds. Most backyard one-off's wouldn't be done this way but I am working off pretty detailed plans that I have a fair bit of faith in since it's been modeled in the computer and real world with a 1/13th scale wood model; both of those lined up and empirically looking at the scale boat it makes sense.

Plan for the outside is a few layers of epoxy, then 6oz CF twill along the bottom to just a little ways above the chines. Where the CF ends I'll do 6oz S2 up to the sheerline. Then over that first layer for abrasion protection I'll do another layer of 6oz S2 (I know for strength this should be under the CF since the CF is stiffer than glass but the hull is so solid it doesn't need it--I just want to protect the CF from abrasion). The seam where the CF and glass meet on the base layer will be under the red paint, which ends a little above the chines leaving some CF bright on the bottom (on the renders of the boat this the black bottom). Clear urethane over all that and then clear urethane/teflon bottom paint. I think a lot of builders might go with even more fiber on the bottom but I don't think it is necessary since the keel and chines are solid white oak--very stiff, very well protected against impact. The interior bilge will have some portions of 12oz glass tape along some stringer and bulkhead edges, maybe some scrap 6oz glass in a few more spots etc, and then be topped with 6oz CF. Visible portions of the interior hull (above the deck) will get two layers of 6oz S2, finished bright. The S2 is plain weave so I'll lay it diagonal and straight to create crossing fibers.

 

Not a fan of the laminate plan. The reason is simple. Half of the woven fibers will be going the same direction as your outer layer, rendering half of them fairly useless.

I know how stubborn you are and you'll say the glass is not needed, but I'd still layup that hull with 12oz biax on the outside, sand off the stitching and lay on 6 oz woven. If there is a way to get fiber orientations so they cross the timber more; that'd be the goal. Of course laying the woven on at an angle achieves it, but the overlaps are a cosmetic problem.

 

I will think on this. I know many ultralight sailing racers are done that way, a single layer of unidirectional carbon fiber running perpendicular to the hull, crossing the wood. But those are so many magnitudes larger than my design (displacementwise), with thinner wood for the hull and only a single layer of fiber. Unidirectional fiber when I was pricing it just costs a fortune even compared to regular carbon fiber and S-2 glass. If needed for strength unidirectional fiber can be the first layer on the exterior... I also will probably make that judgement once the hull is put together and I see how stiff it is (or isn't). The 1/2" bow section on the strongback, even at the unsupported edge where the sheer line is, is so stiff it takes a lot of strength with my weight behind it to make it deflect and it's only going to get a lot stiffer once the outwales and any fiber is added. I'm also basing this on way the rear airboxes changed as I started to composite them on so far only one side, the inside--there's a protected inner panel facing the outboard that is only 1/4" thick WRC that has a span of about 24" x 18". With no fiber it felt very strong but still not very hard to deflect if I pressed in the center of that panel. After one layer of 6oz plane weave s-2 it stiffened noticeably, then with a layer of 6oz CF twill on top it got almost as stiff as my 1/2" bow section... And that is with just fiber on one side.

As far as cosmetic overlaps, that portion isn't finished bright it won't much matter. I'm also not bagging it so I can possibly pull up overlapping edges when the epoxy is barely even green and cut them with a straight edge. Dunno, seems really messy but the Gougeon book says to do it that way for a clean edge. I have an aerospace friend who has a lot of glass and carbon experience that is going to take a look and maybe pitch in when I am to that point.

 

Actually, looking at it now on the strong back I am less concerned... once the hull is finished though I will assess... but the unorthodox design makes the way this boat will be stressed very atypical of 20' boats. Since it is long and narrow I am giving it an awful lot of longitudinal structure and support, but the sides are going to have a very hard time flexing because the freeboard edge is so so very short (bear in mind my deck is also very much structural). On most 20' boats a 30" freeboard would be considered pretty minimal.. mine is never more than 10". It's mostly a very sturdy, long skinny wooden box/surfboard with plenty of internal trusses, not a cup.

 

Tillikum was really narrow and handled the Pacific ocean nicely.
tilikum canoe - Google Search https://www.google.com/search?q=tilikum+canoe&rlz=1C1CAFA_enUS800US800&sxsrf=AOaemvINE8AC7p74EHiQfKUzXwsrgzvSvA:1642118033607&tbm=isch&source=iu&ictx=1&vet=1&fir=0U7aJryUQen3FM%252C_-stDcPp6tT62M%252C_%253BRORTozIfMaAV-M%252CIODf0PUzWFNTUM%252C_%253BYC15vvSkoYJNtM%252C5ArFDrP8qJY7bM%252C_%253BEJ0-8fllsedn7M%252CXdReXDC0zkv8dM%252C_%253BC_iqUmbiExPVWM%252C5ArFDrP8qJY7bM%252C_&usg=AI4_-kQ5ggMY0AhOimns3DnxR_s-TfVv2Q&sa=X&ved=2ahUKEwi4ysmw9q_1AhWsHjQIHcVlDAYQ_h16BAgqEAE#imgrc=YC15vvSkoYJNtM