Outrigger shear scarf goes bang!

[brian.cunningham]

Pictures can be found here (http://temp.corvetteforum.net/c4/bcunningham//swiftwood/torture2.htm).

I cleared space down in the basement and put the bulkheads are put back in. That's were the trouble starts.... The aft bulkhead goes in no problem. I used zip ties to help pull the sides together. The forces proved to be so great, that I needed to clamp pieces of wood to the bulkheads to keep them from buckling.

The forces on the forward bulkhead proved to be great for a shear scarf. It failed, ripping up the inner layer off the ply. I need to undo all I just did to repair both the scarf and the ply.

Seems that the forces involved in getting this rather thick plywood to bend are greater than I anticipated. Since the outriggers are 20ft long, I didn’t want to use a thinner ply. While I'm taking it apart to repair the failed scarf, I may redesign it:
1) Too much lose of depth of the keel at the stern. Take a look at the “comparison” photos.
2) The aft bulk is too wide.
3) The keel angle it too wide.
4) Torturing the wood puts a lot of stress in the hulls.

I may go back to a simple stitched Vee bottom design. Keep in mind that the outrigger will be mounted bow up, to help them go over waves. So the shear was never intended to be level.

[David Greenup]

hey brian
saw the pictures and cant realy help you but,
how do you keep the glue off the clean laundry?

dave

[ 12-21-2002, 10:55 PM: Message edited by: David Greenup ]

[NormMessinger]

It looks as if you glued the inwales to the sides prior to bending. If so, that really stiffens thing up.

--Norm

[Leon m]

Brian
I think your design looks fine.I think your
depth of keel looks good.Everything I've learned
about tri's tells me the more rocker the
better you will turn through a tack.some
things that came to mind while looking at your thread: Do you realy need thick ply for
outriggers? why not thin ply reinforced with more bulkheads and f-glass ? do your shear clamps
have nice straight grain with no runout?
are your bulkheads pefectly simetrical on
both sides so they are not creating any
extra twist in the already tortured wood?
Thats all I could come up with smile.gif

Good Luck Leon

[mmd]

I agree with Norm - you'll be able to torture the plywood into shape easier if you install the inwales after the bulkheads are installed. Leon is also right on the money about rocker, too.

[videoguy]

Brian I can't tell to well from the photos but it looks like the bilge is somewhat rounded.Ifso it can be very difficult to make a compond bend in the panel.Or you might be able to use 2 layers of thinner ply . .....phil

[brian.cunningham]

Well I fixed up that scarf last night. I had to undo everthing and lay them flat again. :rolleyes: This gave me the opportunity to recheck the panels to make sure that they match, they did.

I been told with my long outrggers that SWIFTWOOD will "track like it's on rails", but at the same time it may get "locked in irons". So putting some rocker in may be a good thing. But if you look at the photos all the rocker was added to the shearclamps, and not the keel. I put in that extremme amount of beam so the shears would straighten out. Originally it was more knife edged. Before I took it apart I put the front bulkhead at the rear's location. I liked the shape I was getting. I'll have to either put in a bresthook or some kind of form to get the bow to the shape that I want.

This might have been easier with thinner wood ( like the original plans ), or putting the shears on later ( the original plans did put the shears on first ). Unless I want to start again, sort of a mute point.