when designing a boat for plywood sheeting?

[Pericles]

Raggi,

Yes, I have them bookmarked.

Thanks,

Perry

[alan white]

"I'd take them to a sheet steel rolling press and bung them through a few times."

Just joking, right?

Alan

[Pericles]

It's like putting them through an old fashioned mangle. Panel beaters use steel rolls to produce a curve in plate steel. Ship building?

Heated steel rollers are used to produce parer, card and plywood. If you've deep sixed your ply, then putting it through a mangle would squeeze out the surplus moisture : ?:

Pericles

[alan white]

Yes, I guess it would. After sinking your plywood, it makes sense to carry on with rolling and squeezing. As seldom mentioned side benefits, sinking it keeps it from getting stolen, and squeezing it makes it easier to carry.
You can't say that about epoxying two thinner sheets together!

A.

actaully there are no limits at all,
you can use the cold moulded, double diagonal or triple diag to build any round bilge yacht,
This is how it was done in days before GRP and still is actually done a lot in NZ
makes very strong shell and is easier than carvel, , take a look at it, these days with that glue they use( will find out cos I forgot name) you have about 5 mins to work with it, and bang it goes off Like Sherman tank
usually the strips are about 6 inches or less wide, and as the method suggests they are laid diagonally over the frames
Many werer made in mahogany not ply and varnished, you see those squillion dollar picnic boat replicas? well many are done like this

googel up double diagonal boats, and sorry I did not reply directly to "sheeting)
Another thing we do for moulding ply, stick the sheet in a hot shower and bend it around a wooden mould, good for interior curved thing, not compound of coarse
nice test for the glue too)

[alan white]

Yeah, compound-curving ply as a sheet is totally relegated to miniscule limits.
The method of diagonal planking mentioned is very strong and the compounding of such a narrow strip is very miniscule, just pinning down the edges or the center. Wonder if this has been done with external molds, which for the most part would allow a single fastener per frame (later cut off).
Granted this method would introduce new challenges in other areas.

A.

[Pericles]

Back in 196I we did a bit of water skiing off Broadstairs in Kent behind a hot moulded ,mahogany ply, 16 foot, round bilge speed boat with a 60 hp Mercury IIRC.
In one season we damn near wrecked the boat, because it was just not tough enough. You could see the hull bottom oil canning all over the place.

I am convinced that I can do a much better job when I start my build in June this year, because adhesives and boat design have moved on. However, there's many a slip, 'twixt cup and lip.

Pericles

well thats an inditement(or is that how it's spelt) ON HER POOR ENGINEERING DESIGN, nothing to do with the method at all is it You still have to have the right framing, skin , panel size Nope if I were building in timber, I would never consider any other way

[Pericles]

LJ

In answer to your post, yes! Her engineering design was probably due to the builder using the shape of a plank on frame speedboat from which the frames were then omitted. The hull was hand laid and the whole caboodle placed in an heated closed mould until cooked.

You seem to say that if you were still building in wood, you would hot mould. Why? GRP boats are production line products, as would be any hot moulded boat, if it were still made today, because of the enormous cost of the moulds. Changes cannot be implemented without great expense for either type of craft construction. In addition. hand laid diagonal ply or strip is skilled work costing far more than laminating GRP in female moulds.

The high prices achieved for epoxy composite cold moulded boats like Jarrett Bay and Scully are because they are custom hand built to the owners exact requirements Hot moulding is as restrictive as GRP and so, the custom boat business serves those owners who want that extra special ooomph.

My thoughts are that of building the hull shape using shaped and developed BS 1088 marine ply panels, stitched and glued, over a number of moulds, mounted on a strong back. Nothing new there.

The basic shape is overlaid with more marine ply until the designed scantlings are achieved. This results in an incredibly strong and stiff monocoque shell. Laminated sheer clamp are added and after temporary cross bracing is attached, up and over she goes. Nothing new there either, really, except no stringers, no frames, no bulkheads. As mentioned earlier---.

"I just cannot see any reason to continue to include frames, ribs, stringers etc. in a epoxy ply composite boat. They do not contribute strength, only unnecessary weight. Laminated ply sheer clamps, however, do have some structural purpose in retaining initial hull shape and a strong base to which the decks are secured. Longitudinal bulkheads (berth flats and lockers) supply both stiffness and some of the interior furniture fittings."

What I am not going to reveal here is why my design of hull has much greater longitudinal stiffness than would be expected from reading my brief description here. Suffice it to say, it will become obvious when I start posting progress photos some time in June this year.

One clue, my personal feeling is that if the weight of the frames, fastenings and ribs etc. were incorporated into the hull in the form of marine ply laminations, instead of being frames, fastenings and ribs etc. the resulting hull would only be destructible by fire or a drop from 500 feet.

Pericles