plywood for ribs y/n

[JLM]

I was talking to a guy who owens a small wooden boat(lapstrake) that he built in his shed.he was telling me he used marine ply to make his ribs(one piece of 3/4x3"wide)my ? is has anyone ever done this on a bigger boat.the reason i ask is mine are 1"x 2 1/2 oak. i started steaming some but it takes alot of time.what i'm thinking of doing is 2 pieces 3/4 x 3"glued with epoxy.so the piece will be 1 1/2x 3 when finished.

(BIQ)1970 34'pembroke mahog lapstrake on oak

[Hugh Paterson]

Hmmmmmm not a good idea, acceptable on small(ish) pulling boats with glued lapstrake/clinker hulls maybe but thats about it. Steam or laminate...the latter is better for strength and will reduce the possibility of frames splitting or cracking, takes
longer to do though ;)

Shug.

[On Vacation]

My fellow hardwood users, we use a great alternative for heavy and complicated round and cross grain cuttings of ribs and frames. Of course many will say cedar and laugh, but if you have read my post in the past on this wood , you will understand the type we are using. This is only one type of lightweight wood that can be used.

Cut your framing undersized out of whatever, cross cut or just pieces and then use 1/4 plywood to sandwich with good glue and you eliminate the weight factor and avaliable woods problem for many applications in new construction. Even the crown cabin tops are done with laminated flat strips and then sandwich material.

We make I-beams for decks that way to allow for more span for cabin soles over the engine room compartments in salons.

[stef]

Oyster, are you talking about making a I-beam with the web following the frame's curve perpendicular to the hull surface and the flanges following the surface of the hull parallel(sp) and separated by the frame thickness?

As I see it this would give you and equivalent moment of inertia in the frame ( effectively a box beam) and save weight. This would be difficult to do without adhesive technology.

Sorry for the non marine terms in the above post.

Best regards

Stefan

[Bob Cleek]

Y/N? ..... N.

[kpenokie]

Y What is plywood but pre-laminated wood?

[G. Schollmeier]

N... With plywood the plys are laminated in the wrong direction. Oyster's suggestion has some merit.
Gary

[Bruce Hooke]

The problem is that half the grain in plywood is running in the 'wrong' direction, perpendicular to the length of the frame. You might be able to get away with it given the increase in frame dimensions that you are proposing but I don't think it would be wise. Aside from the strength issue there is also all the extra weight you will be adding by using this method. In addition I think you would have trouble bending 3/4" plywood into place without the wood in the plywood starting to fail. Also, frames laminated from plywood would have a huge amount of end grain exposed along the sides just waiting for water to get in and rot to start it's nasty work.

If steaming is a problem I would laminate the frames the 'right' way, using strips of solid wood, so that the grain is all running the length of the frame. When you say steaming takes a lot of time, are you trying to put one frame in the steambox, pull it out and put it on the boat and then put the next frame in the steambox? If so you could probably speed things up quite a bit by putting one frame in the box, adding another 10 minutes later and so on. If this is not viable (steambox too small, old frames are removed one at a time..) then I would laminate the new frames from solid wood.

[WWheeler]

The Shellback and Pooduck skiff call for strips of mahogany epoxied to form the stem and a main rib. Is this a form of homemade plywood? (except that the grain runs with the bend)

The technique's probably intended to form a strong curved piece without steambending, which is what you're after.

[Bruce Hooke]

Originally posted by WWheeler:
The Shellback and Pooduck skiff call for strips of mahogany epoxied to form the stem and a main rib. Is this a form of homemade plywood? (except that the grain runs with the bend)

The technique's probably intended to form a strong curved piece without steambending, which is what you're after.This is 'traditional' (standard) laminating, and this is what I and others have recommended above -- strips of solid wood glued together in a curve. The key phrase is "except that the grain runs with the bend" -- this is what distinguished a standard laminated beam from something glued up from strips of plywood...

[brian.cunningham]

The frames that came with my kayak kit were made from laminated ply. Cheaper for the manufacturer, uses up the scrap plywood. I made sure I put extra coats of epoxy on the them. All that endgrain scare me. :eek:

When I laminated my additional frames I use 1x1/4 strips of solid wood.

[JLM]

its not that i want to use plywood.i was just wondering if anyone ever tryed it before in a bigger boat.the guy i talked about built a small ply boat that he used in a pond for fishing and epoxed the whole thing.nothing great just cheap.
as for laminated ribs (frames)from what i've been reading white oak does not glue well with epoxy.
steaming is what im doing now have 5 done 27 to go
i can steam 2 maybe 3 pieces at a time and when there ready i clamp them in a form i made and let them cool for 10 to 15 min then install while the other ribs are cooking.not to bad once you get things started.thanks to all who replyed. :D

JLM

(BIQ)1970 34'pembrooke hundoras mahog on wht oak

[On Vacation]

Just got in and have gotten to this thread. No plywood is bent on the edge of the ribs or frame. The solid wood is cut as regular but the thickness is not as great as regular ribs and frames. The plywood is then glue to the side of the cut solid wood.

Even if part of it winds up a little cross cut, the plywood holds it all together. The advantage of solid wood is the screwing aspect of it instead of the regular plywood. The I beams for decks are straight and the curved cabin tops and the crown deck beams are bent on a jig with a master curve and glued and then plywood reinforces the beam on the side glued on. Then they are cut to length using a center line through all of them.

There is a major weight savings with using cedar or fir for the solid wood instead of oak or mahogany an the cost is less. Labor time is a little longer.

[ 07-08-2002, 11:15 PM: Message edited by: oyster ]

[On Vacation]

If you notice in the bottom left corner, you will see a white piece of plywood sticking out past the solid rib. This shows how you can have a cross grain piece and the plywood scabed and glued to the side and will keep any pieces from splitting and any weaking of wood in a drastic grain weakness.
http://www.imagestation.com/picture/sraid15/p340e9a928ab11a5d2c100d2bcac0ca94/fde604c7.jpg

[TomRobb]

N :rolleyes:
Steaming goes quickly. What took so long that it turned you off?

[JLM]

TOM its not that i got turned of by steaming i think its kind of neat.this is my first time steaming wood and the first couple broke. then i steamed one alittle longer(about 1 1/2 hrs) and it went in ok .Know im going to steam 2 boards and put them in a simple form i made and let them cool while the others are steaming should speed things up a bit.? for you if i steam even longer will the wood bend easyer i have a few tight bends and i dont want to break any.thanks JLM

[TomRobb]

Bending them into the boat might be more efficient than the intermediate step w/ the forms.
And of course nobody wants to break wood but it happens - you just prepare extra stock as a contingency. The oak prefers to be green and have little or no grain run-out. Rounding over the edges may help a bit. Have fun - amaze your friends. :D