First-time post and first-time boat builder. I am currently running a 15’ aluminum high school shop class special, apparently shaped from a Willy’s high side. While I can appreciate the ruggedness of metal, I am pumped to build a wood boat. I am working on the Rogue River Special from Fletcher’s book. I ended up making a 40% scale model with $50 of materials from HD to see if I even had the chops to attempt the full size. Good enough for me to proceed.
On the full size, I have made it to dry fitting the chine logs at this point and wowzers…I am using ash, cut to spec. Man there was a lot of tension, at one point I put on my bike helmet out of fear of getting whipped. With some doing, straps and a couple of beers, I was able to at least get it part way in the slot, but not flush as you can see from the pictures. There was a very strong resistance to the twist that was needed to happen to get it to come into alignment with the slot.
There was a lot of pressure on everything, the plywood was bowed out at the chine with the way the wood was pushing.
I was able to eventually overcome this resistance to the twist with a bunch of clamps, but as I was tightening them, I blew out the scarf joint and some of the plywood attached to the transom.
The funky notch in the chine log at the transom was as a result of me giving up after 3 iterations of trying to figure out what that space needed to be ahead of time. It was a 9” scarf with plenty of T-88. The joint surfaces were just the result of the table saw scarf cut. I’m not terribly worried about the plywood on the transom. I think with the eventual addition of screws and glue, it should be good.
I am thinking of taking 1/16” off the width as a result of this experience. As well as making shallow crosshatch with a hand saw on the surfaces of the scarf joint to increase the surface area and using Gelmagic. Other ideas on making this happen without blowing anything else up?
Thanks so much - this forum is fantastic!
What thickness is your chine log? 7/8 of an inch is common if I remember correctly. I will later check out a chunk I have left from my chine log that came as part of a Tatmen kit many years ago.
3/4 x 2 1/2 with a bevel taken out.
Here are a couple of suggestions - I'd roughen up your scarf surfaces with some 80 grit paper and redo the epoxy, this time with a bit of cabosil to enhance the space filling characteristics of the epoxy. I'd say it's pretty unusual to see a scarf joint like that fail. When I built my boat I steam bent the chines and chine logs that worked well. Your dimensions for the chine log are fine.
T-88 is an epoxy adhesive with gap filling capability. It probably would not be improved by adding a modifier. Some woods, like white oak (I can't recall about ash) have oils that inhibit a good bond using conventional epoxy adhesives. West sells an epoxy adhesive specifically for these types of woods.
I have used T-88 to scarf ash. I wiped down the scarf with ethyl alcohol, then applied a coat of laminating epoxy, and once that started to set, applied the T-88. No failures yet.
Also, the joint may have been too tightly clamped and too much glue squeezed out, leaving a starved joint.
I don't get over here much anymore. Here is my .02 after building close to 40 boats.
Use West Gflex on that scarf. I had a few failures with t-88. Wipe it down with rubbing alcohol several times first.
Steam that chine!. Clamp it on the outside at the scarf and use 4" PVC. Make a set up so you can remove the tube easily, steam it for 45 min. remove the tube and clamp it to the side. You will have to do the front half then the rear half.
Leave it for a day or two. When you remove the clamps it will spring back some but will have enough curve built in to make installing it a LOT easier.
Others have done the plastic bag trick and may chine in here (pun intended :).
B.T.W. that is one of the most brutal boats to build due to the flair angle and flat spot.
Is the chine log fastened to the ply side at the chine? If not, consider resawing the chine log into (2) x 3/8" thick planks, and laminate them together. The laminate will be slippery enough before it cures that you can get it to conform to the curve of the chine. When it cures, it will be locked in place.
I wouldn't steam a scarfed joint--it will likely fail when you heat it.
Is your ash green or kiln-dried? When I did my gunnels, I clamped them in place for a month while I worked on other parts of the boat. As they dried, they held shape. This could work for you, but would also cost a delay in the building process.
Yet another option would be to clamp on an outer board (could be 1x4 pine) to get the chine log to curve without twisting or deforming your ply until the chine settles.
Usually I'd advocate you "listen to the wood", but your chine log is screaming at you, and you need to give it some persuasion! And if it makes you feel better, I'll point out the flaws in Great Falls. We all have things we'd do differently and few others will ever notice!
Thanks all for the advice all. One down and one to go!
I use 5/8" thick chine logs. never a failure. But what I find most important is that flat sawn material be used. looking at your grain lines, you are trying to bend it the hard way against the grain. rotating your stock to be flat sawn, bending in the way it wants to (or resists less) is key.
I have moved away from 3/4" stock on all my boats, to 5/8" I don't notice any difference and don't baby any boat I have or will ever own.