laminated keels woods and glues

what would be the pros and cons of laminating a keel for a 30 ft motor cruiser, carvel built ,with approx 60hp engine 7tons rough displacement out of 1) oak -european
2) iroko
Laminations to be from inch timber
glues thoughts on 1) polyurethane
2) cascamite
3) other

 

I'm wondering the same -- re: adhesives. I'd much rather avoid using expoy where I am laminating things that will be fully encapuslated... There is a polyurethane adhesive called 'Gorrilla Glue' that I am seriously considering....

 

I've understood that 'resorcinol' is a good alternative when you don't want to use epoxy.

 

Just been involved with some masts that were laminated with 'resorcinol', not a good scene, laminates coming off, mind you might have been how they were laid up.

Gorilla glue, had a mate that decided to try it out, glued two pieces together, allowed it to set then dumped it in a swamp for a few months. Pulled it out and tested it to destruction, glue held, wood split. Not sure of the type of wood used.

 

Iroko is an oily wood, so gluing it may present difficulties.
Oak is a very acid wood and not very suitable for laminating.

Polyurethane glues are not the best for structural purposes, and the resorcinols (and similar old glues) need a perfect surface state, a very, very thin joint and very high pression while the glue is curing. Resorcinol asks for about 5 kg/ cm2 (about 71 PSI) during 24 hours...you'll need for a keel hundreds of heavy duty C clamps...

In fact the epoxies are gap filling, structurally very strong and do not need hard clamping. But they do not like to be wetted and dried, so the glue lines must be protected by a full encapsulation.

For a boat like yours and using iroko (oak destroys all steel even stainless) there is an alternative: nailed, and screwed laminate with no glues or just a waterproof cheap glue to seal the joints.

 

Martin, what year and construction method is used to build your boat? What about the design/construction of this craft do you feel needs a different approach then the one the designer took?

The reason I ask is some advise here hasn't been quite accurate.
> BJL SAILOR doesn't want to use epoxy when encapsulating . . .
Ilan pointed out that this is WHEN you DO want to use epoxy and is correct. Though oak is difficult to laminate, it can be done with special prep.

Large timbers, which may be the case in your yacht's keel, don't lend themselves to glue lamination well, though mechanical lamination works quite well.

If the size of the timbers require lamination, then mechanical lamination with an edge caulk line may be a better way to go. This caulk can be traditional or a poly smeared into the groove along the edge of the joined pieces.

This is the reason for the questions I opened this post with. It's difficult to provide accurate replies without an understanding of what's trying to be done. If this is traditional construction technique used in this vessel, then you'll be best served sticking with what's done or a slight modification to same. Hardening of the joints with the use of epoxy or other firm adhesive may defeat the properties designed into the structure of the keel and related assemblies, which can lead to a host of other issues cropping up, that haven't been a problem thus far.

 

You're perfectly right PAR.

I shall add that mechanical lamination is an old proven method: almost all 19th century clippers had laminated keels. Some used plumb minium paint to seal the joints (not very ecologic, very toxic but effective) and protect all the steel hardware.

Elm was the traditionnal wood for keels in France. When the Dutch disease killed almost all european elms, a new wood had to be found.

It became also very hard to find long good pieces of lumber. So many switched to Iroko, a wood from West Africa which has qualities close to the teak (it's used as substitute for teak): it's a good wood, medium hard to work and laminated it makes good resilient keels, very convenient for planked boats.

European Oak is acid (more than american oak): it's almost impossible to glue it and "eats" any piece of metal when it gets humid.

For an amateur, if the boat has a design compatible with the method, mechanically laminated keels may a good choice; it does not need special skills or formation, nor special tooling and lends by itself to good average results.

The US Forest Products Laboratory (http://www.fpl.fs.fed.us/) has published a paper about the four layers nail laminated posts (ref FPL-RP-528) which can be downloaded under the name fplrp528.pdf

Althought the methods of lamination used by the searchers of the FPL are rather crude, the conclusions may be extended to the 6 to 20 layers or more found in boat keels.