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Guests & Members Post & Read => Building, Maintaining and Repairing => Topic started by: Breizhglace on October 14, 2021, 08:24:41 AM



Title: Plank Build -PPU glue
Post by: Breizhglace on October 14, 2021, 08:24:41 AM
Hi,
Quick question to the group of building experts!
Has anyone ever used PPU glue to build a plank?
It is a polyurethane glue i used to build sailboat nasts in the past.
I believe it is known for being flexible and not crack when flexing
Thanks,
Nic
KC5508


Title: Re: Plank Build -PPU glue
Post by: Bob Gray on October 16, 2021, 07:41:51 AM
Most everyone now is building planks with an epoxy system like West System. Back before these systems glue was used. Iím not sure which type though. The only problem I can see is getting enough gluing pressure, that is proper clamping, while itís in prebend ( the over bending necessary to get the desired crown after the glue dries).
Bob


Title: Re: Plank Build -PPU glue
Post by: Breizhglace on October 16, 2021, 05:03:58 PM
Thanks Bob,
I think I will go with the epoxy and make things simple!
If you have any information on how much crown to put in the gluing process so I get the right one post cure, I am interested

Take care!!
Nic


Title: Re: Plank Build -PPU glue
Post by: wnethercote on October 16, 2021, 05:42:29 PM
Hi Nic,

Spring back of a curved lamination after removal from the mould is proportional to the thickness of the individual laminations and inversely proportional to the square of the number of laminations, if all the laminations have the same young's modulus.  The proviso isn't true if you are using different woods for the skins and the core (but Young's Molulus doesn't vary all that much between species), and the 'rule' also assumes equal thickness laminations, but it's probably close enough to say springback is something like 1/n squared.

So a two layer plank will spring back about a quarter (1/2 squared) of the crown of the mould and a three lamination plank will spring back about a ninth (1/3 squared) of the crown of the mould.  My experience is that the 1/9th estimate is pretty good.

Warren Nethercote
KC 3786


Title: Re: Plank Build -PPU glue
Post by: Breizhglace on October 25, 2021, 07:50:22 AM
Hi Warren,
It is exactly what I was looking for, thanks a lot!!!!

I am almost done with the spare hull, so this is going to be next!
Cheers,
Nic