plywood on frames versus S&G

[fabrice]

Hi there,
I'm sure it's been asked before but can't find the answer :
what will be heavier ?
plywood on frame with stringers, or plywood S&G ?

I read a lot of reports on S&G building : It seems from time to time that the weight bill comes awfully over expectations, so I'm trying to figure out if it's worth building carefully and skillfully on frame, instead of gluing insanely thick plywood like a mad monkey

[hoytedow]

You don't have to use a thicker plywood with stitch and glue than you do with frames. Frames would be heavier and less "comfortable" than the streamlined interior of a stitch and glue creation.

[jehardiman]

Actually, it will depend on the size of the boat/panels and the amount of curvature. For narrow panels with lots of bulkheads like a small kayak, Hoyt is correct, you don't necessarily need thicker panels or stringers. The larger the boat/panel becomes, and the distance between frames/bulkheads, there comes a break point where you can start putting in stringers and reducing skin thickness.

[fabrice]

Yes, this makes sense to me.
plywood is a great asset, if only you understand well how it bends, and why.

Fortunately building small canoes and kayaks one only needs small widths.

So, asking again while being a bit more accurate in my terms :
Doing the same small boat, assuming we choose the panels right thickness in both construction (shouldn't be the same I guess), which "program" will be lighter ?
which one will be easier to keep in boundaries of a weight bill without drifting too much ?

[lewisboats]

Generally S&G will be lighter depending on how thick you make your fillets, the weight of the cloth, what type of cloth used (dynell will suck up much more resin and so be heavier in combination). Generally a fillet thickness (from corner of joint to closest surface on the inside of the fillet should run about the same thickness as the thicker plywood used. So using 5mm bottom and 3mm sides the fillet depth should be 5 mm and taper around double the depth (10-12 mm) to nothing on each panel. Best way is to boarder tape the fillet area with painter's tape and do your fillets then pull the tape...like so:



To give you a fillet that looks like this:

[fcfc]

English reply

Technically, the plating is the same thickness for the same panel size. There is absolutely no reason to have it different.


I fear the biggest problem is the designer/builder self confidence.

For a framed construction, the plating is often bonded AND fastened. Kind of belt and braces, because the bonding only should be enough. If the plating is debonding, and need the fastening, there is something catastrophically wrong in the design or building.

In a stich and glue, there is ONLY the bonding. So, there is a human tendancy to do a overkill bonding and filleting, just in case.

There is also a severe lack of data for stitch and glue design for fillet size / epoxy charge to use and reinforcing tape with/weigth to use for S&G. In fact, I have not found engineering and design information on epoxy filleted T-joints for plywood.

microfiber charge only, glass bubble charge + woven tape, phenolic bubble charge + biaxial tape, radius, tape width and weight

[lewisboats]

OK...so I will go with Empirical data...I ain't never broken anything yet with the fillet I describe! I have used it in 8+ boats without a problem...no cracks, leaks or other structural failures. One fillet, one layer of cloth inside and one outside for anything under around 12 ft/ 700 lbs displacement (canoe/kayak style excepted...up to around 18 ft length for those). Over that add layers of cloth.

[gonzo]

It can be either way depending on design.

[fabrice]

lewis, I'll stick to that (what an accurate word in the context )

I wander on forum looking esentially for this kind of answer :
Experience, helping me to figure out what I really need or want.

BTW, your pics show a really clean job, congrats !

FCFC : j'ai rien compris !

[hoytedow]

Fabrice,

Vous comprenez plus que vous dire.