Joining sheets of ply into one long 25 x 10 ft panel?

All that is true, which is why I would want to make the panels above the final location, not beside or below. And having a few female moulds or nest to support the panels in place is essential.

I thought seriously about the problem after a builder of a 27ft houseboat from Bateau
http://www.bateau.com/proddetail.php?prod=GT27

hurt his back badly just manhandling the 26 foot central keel stringers, not even the sides.

having big panels might make the assembly a bit more 'simple', but the manipulation of the panels is fraught.

 

This is my thought as well. A few 2x4's in key locations will make inserting them into the jig possible, though you will not know about issues, 2x4 locations, etc. until you try it. This is something I'd want to do only once, so it would need to be well thought out or you have a big panel to remove, just to try again.

Maybe make slightly smaller panels, preforming all the prep for scarfs or Payson butt joints, but lower the more easily handled panels in first, then joining the panel sections.

I like the idea, though I'm not fond of female jigs.

 

Good diagram rwatson. Im looking at that assuming the panels you are talking about are the topsides panels? the 25 x 10 i mentioned was an arbitrary figure...just to something like that could be achieved...i doubt id ever use that size of sheet but wanted to see how it could be approached.
Par is right there would be a lot of floppiness to the panel. this helps in decking where there is curvature to the deck. or bending the topsides to shape-which i thought was another advantage of long wide panels. I cant see how your idea wouldnt work. how heavy are they?..this is a consideration in sliding them into the mold...id have standby crew to help.
or maybe use a come along or a winch just in case...
looks like your are building something ive seen called pre-lam. that is laminating up long sheets for planking instead of molding the fiberglass onm a mold...then its simple sheet material and easily built--ive heard of this method but never seen it...

 

just to clarify on the panels--i chose 25 x10 as an arbitrary figure - because i dont know how wide a panel ill need. maybe it would only even need to be 4 ft, but ive wondered if i ever built a ply boat that has a wide deck- how this could be accomplished?...i understand about butt blocks and -now i get the idea of a payson joint--but because you have to join end to end and side to side i thought this might start to get complicated over anything that requires a 4 ft wide panel??

..but also wondered if this was a good idea because you could use the inherent floppiness to advantage in throwing it on a deck or topside? or planking the bottom because the floppiness-when built upside down using one single sheet would make an easier more relaxed way to curve the wood on a single plane?

plus what the limits were for length and width if any...

 

Yes, certainly the topside panel, but once they were in, remove the temporary braces and drop the bottom panels in as well, or vice versa. I cant think of a reason why either order wouldnt work

Sure - a ten foot wide panel is a bit unusual, but the one I am planning on building is a single chine, 28footer, and the panels are about 7.25 feet wide. I tried to talk the NA into splitting the side panels in two for ease of building, but no success yet. ( are you reading this Mr G ?? )It would make sense to have the joins horizontal rather than vertical to avoid nasty hard spots, to produce an unfair hull line.

Floppiness is not a problem in a female mould. Gravity will force the panel into the right shape against the frames. You could simply kick the whole panel in with little guidance, and it would crash heavily onto the retaining moulds, and assume the correct shape. I found floppiness on a simple 16ft kayak on male moulds was a real pain, which is why I am going to try the female moulds.

The idea is that by using gravity, you should be able to do the whole thing yourself with a few blocks and tackle. I have a large overhead gantry as well. I went through the reverse process recently, getting some very heavy 18 foot x 4ft, particle board sheets up to a mezzanine floor in the shed. I managed it solo with clever balancing and leverage. With patience, lots of rope and wise placing of temporary beams in a retaining female frame, I think its quite do-able for a boat.

Its the process that Derek Kelsall used on his plywood boats (cats) , before he switched to the foam and glass layups he uses now. He even put some of the stringers on, to help with the lining up on the frames and assure reliable self fairing. Laying the exterior glass horizontally saves a truckload of glass finishing using nothing but low-tech PeelPly. Its the exterior finishing that is the killer. True, Derek used male mould's, so I hope Pars dislike for female moulds doesnt mean I will discover some nasty 'gotchas'

 

The female mould/frame system apparently works well for some of the Van De Stadt multi-chine steel boat designs so I can't see why it won't work for plywood. Both steel & ply are flat sheets that don't like to be bent in compound curves, and both are floppy.

I used a spreader bar to pick up long floppy steel sheets so it's not a single point lift. This is easy with steel but I can't see any real problems doing it with ply, just need to think on how the attachment points are going to work rather than using plate clamps.

PDW

 

The Payson joint ....
http://www.instantboats.com/gbj/index.html

has one problem - it creates a hard spot on the panel, with potential for an unfair hull if you have to bend ply around or over moulds.

Its also rather unnecessary, as it is 200% stronger than the panel it joins. If the plywood is going to have fiberglass on both sides, its redundant from a strength and weight perspective.

I am a big fan of cnc cut "joiners" and "puzzle joints". These provide the required strength with the added advantage of ensuring mm precise panel alignment, which is always a problem with scarf joints.

I am wanting to try my "Compound Scarfe" concept also. Its a form of scarfe that wont slip along its axis, is easy to create, and is self aligning.

 

I would use wood magnets.

(bits of timber screwed onto the ply )

 

Yes. that'd work fine. For some reason I was thinking about holes through the ply & shackles. I think I've been playing with steel for too long.

PDW

 

I like that compound scarf idea. I think I will try it. Henceforth I shall call it the "Watson Scarf".

 

The butt joints are incredibly strong.



The size of sheet your considering is possible but you'll need special lifting equipment to flip it over. This is one of my side panels. 32' x 5' and three joints. I had to brace the lifting edge with 2x3's and plenty of clamps. I used my electric winch rigged to the shed peak to lift the sheet. It flopped around like a flag in the wind. I was able to do it single handedly though but I wouldn't recommend it.



Below is the cabin roof getting glued up. It's 16' x 8' but only 1/4" ply. We glassed one side (underside) entirely while we had gravity working on our side. This panel was about the same to flip as the side panels. It took 4 people to move it outside though. It was extremely flimsy.



So I guess in answer to your query, yes it can be done.

 

That'll do until we find its real name. I am sure it has been done before, but I haven't located it yet.

 

Agreed.

 

I have been meaning to update this post for years.
Its a Scissor Joint.
I can now rest easy