Gunwhale problems...

[Maximus]

I'm in the middle of building Radoslaw Werszko's 4.5m dinghy and have had troubles with making and fitting the gunwhales. I tried making them out of two pieces of oak with a scarf joint about a thrid of the way down the sheer but while fitting it into place the joint snapped.

I'm wondering since I have to start over if there's a better wood available in the midwest (minneapolis) for my use or where I might find a 16ft long piece of red or white oak that I can rip without too much runout in the grain.

http://www.facebook.com/home.php#/pages/Brents-Boat/104119274923?ref=mf

Thx,
Maximus

[DGentry]

Sounds like a bad scarf joint, rather than bad wood . . . that's easy to mess up.
I don't know anything about your boat, but I respectfully suggest that a longer joint with a better fit and better glue up will usually solve a weak scarf joint problem.

Good luck!
Dave
http://www.clcboats.com/shoptips/stitch_glue/boatbuilding_wood.html

[Lewisboats]

You could also go with half the thickness and laminate them in place...bends a lot easier that way.

When you get done you should look into coming to the Midwest (Lake Pepin) Messabout...1st weekend in June at Lake Pepin...about 70 miles SE of Minneapolis. Bill Paxton hosts it (he has an open Weekender). There are usually a dozen or so boats there. This year was a bust though...rainy and about 47 deg at night. Most I have gone to have been VERY nice though. I make the drive as part of my yearly duo of Messabouts...the second is the next weekend at Rend Lake in southern Illinois (Jim Michalak's). Hope to see you at Pepin

[Bruce Hooke]

I agree with the take that it sounds like there may be an issue with the strength of the scarf joints. However, there are a few things to check in terms of procedure:

1. Did you put the scarf joint near the transom or near the bow? The easiest route is going to be to put the scarf joint in a place where the bend is less severe. From the pictures of your boat it is a little hard to tell where this is but it looks like there may be less bend near the bow.

2. When bending on the gunwale, did you start from the bow or the stern? When trying to bend a piece of wood around a curve it is always easiest to start with the end that needs more of a bend in it so that you have the long end of the board to lever against. However, this will put extra stress on the scarf joint so it may be better to try to avoid levering too much against the board beyond the scarf joint if you can, at least until you get to where you have to in order to get the last section of the gunwale into place. Unfortunately, #1 and #2 work a bit against each other...

3. How long was your scarf joint? A scarf joint with a slope of at least 8 to 1 would be a good idea. For a 3/4" thick gunwale that means a 6" long scarf joint. Going even longer would increase the strength. A 12:1 scarf is common if you need a really sturdy joint.

4. Did you use white oak and if so did you glue it with epoxy? Epoxy and white oak sometimes do not work well together. This is a difficult problem because the usual alternative glue (Resorcinol) requires a very tight-fitting joint and leaves an ugly purple glue line. Red oak is not a good alternative in most cases because it has no rot resistance. Ditto for ash.

[Candyfloss]

How dry is your timber? Kiln dried wood tends to be brittle. Wet it with water from a spray bottle & bend it on slowly. Start from the middle & use lots of clamps, working in both directions. Every clamp you put on stops the stress at that point. Otherwise all the stress builds up in the middle of the bend & it breaks. Do you have to screw it on? Screw holes cause weakness. Avoid them if you can. Good luck.

[ishmael]

It's impossible to tell from what you've said. Some of the above comments... a longer scarf might help. But, I'll bet you are gluing with epoxy. Unlike resorcinal, epoxy wants light clamping pressure. Get the joint lined up, get the pieces together, and that's it. Too much pressure and you squidge the stuff out. Mr. Epoxy likes some company.

Nice boat, BTW.

[davebrown]

i encountered ishmael's point earlier this year. i think i overtighted my scarfs on my gunwales, and they popped when i turned the boat. i reglued and kept the clamps light. that worked.

[S B]

Bending a dry piece? You might try draping a wet rag over it and taking the heat gun/blow torch to the rag, sort of steaming it in place.