Plywood beams

[Lakesailor]

[ QUOTE ]
Someone else told me to laminate boards together then saw the desired shape.

[/ QUOTE ] Do you talk to the village idiot a lot then? That would sacrifice any structural integrity in the timber and leave you relying entirely on the bonding quality of your adhesive. Open-ended grain on wood may split. Make use of the natural strength of the wood and add to that the multiplier effect of bonding layers of wood together, following the curve of your beam.

 

[Woodlouse]

If you put a bend into a piece of fir, and the mast pushes down, against the curve then it will not budge however springy the wood. It'll be an arch see. Very strong.

 

[themoose]

I'll throw a curve ball here. I did a bit of research into glues - it is a lot easier to get answers off the internet with glue. For glueing wood, if you don't mind the purple stain, resorcinal is apparently the best glue to use. There is mounting evidence of expoxy failing. Resorcinal is sold in this country as Aerodux 500.
Now having said that, I can get expoxy very easily, even here on the Isle of Man (where a lot else is nigh impossible to get or is twice as much after the Steam Racket Co. has had its cut for bringing it over). Aerodux 500 I can only get from B&K Resins, Bromley , Kent as far as I can tell. As the glue is for the beams in the main, and the evidence of failure of expoxy is still quite a small % I may go for it just so I can move this project on a bit. Another factor is that I have a touch of de-lamination around the two outer of the three keels so have to get epoxy to deal with that.

 

[themoose]

[ QUOTE ]
Do you talk to the village idiot a lot then?

[/ QUOTE ]

It makes you wonder doesn't it? The bloke in question has a joinery shop at the entrance to the boatyard so you would THINK he would know what he is about. Mind you I guess joiners don't have much to do with laminating.

 

[themoose]

[ QUOTE ]
If you put a bend into a piece of fir, and the mast pushes down, against the curve then it will not budge however springy the wood. It'll be an arch see. Very strong.

[/ QUOTE ]

Yes I can see that, and this method of construction keeps coming up. I am just baffled as to the why's and wherefore's of the original construction. The on top method is certainly something I feel I can tackle easily enough.

 

[dur]

Definitely horizontal laminations for beams! Here in douglas fir...

laminated beams

 

[cliffordpope]

An arch is only strong if it is adequately braced at the sides.

I would say the choice depends on the degree of curvature required. Conventional deck beams curve I think at 1 1/2" per 6', or something like that, so are best sawn out of solid wood. The grain direction effect is minimal, and in any case the wood can be selected so that the cut follows any natural curve tendency in the wood.
Laminating sounds a good strong alternative, and probably a lot cheaper than solid wood, and easily achieved without access to an accurate bandsaw and cutting jig. Also it can be used just as easily to produce a greater curve, the greater curve requiring thinner strips in order to avoid steaming.
Laminating and then cutting sounds like a technique more appropriate for making cheap furniture or theatrical sets.
I can't see any benefit from laminating plywood strips rather than real wood, and it looks horrible when varnished unless you are deliberately going for a zebra effect.

 

[themoose]

No, one thing this thread has convinced me of is that ply wood for beams is out.
I reckon it will be laminated, as to what - who knows! I have checked the two major timber merchants on the Isle of Man and neither stock fir, spruce or anything apart from 'European redwood - maybe pine" in the softwood dept. Had a quote for solid timber (mahogany) enough to make the two bridgedeck beams - £120!! Still a half dozen beams to go! I don't think so. I don't mind spending a few bob on the old girl, especially if it's really needed but I think that is a bit much! Anyone got any views on that? That was for 4.2 m of 150X75 mahogany carcass with 20 minutes of cutting.

 

[Captain Coochie]

So around £30 per m ? Ive paid tripple that for some timbers /forums/images/graemlins/mad.gif Speak to the joiner at the end of your yard , he may be able or willing to buy in what you want or may well have it in stock .

 

[Lakesailor]

But he's the bloke who wants to cut a laminated block to shape!!

Timber has become very expensive. I've paid lots for silly little mahogany stringers and rubbing strakes.

 

[ccscott49]

Are you sure he doesnt mean laminate bigger/wider planks, not thicker, to the beam shape and then cut all the beams or a lot out of the bent/laminated/glued planks? I've seen this done, lots.
If you understand me!

 

[themoose]

Yes, that's basically what he is saying. These beams appear to be made from 5 X 2m planks 1 cm thick and 18cm wide. So there are 5 laminates. Its a long shallow arch with a 2 cm rise over the two metres. However he was talking about cutting the shape from the laminated planks - no bending or steaming.
/forums/images/graemlins/confused.gif

 

[pyrojames]

I woudln't turn your nose up at European redwood. It is the main structural timber for housing, and as long as you use good layers of epoxy in the laminate, and then epoxy coat the outside, and ensure that you run a small dribble of epoxy into any holes you use for fixings, it should be perfectly OK for the boat.

 

[Lakesailor]

Ahh, 2 cm rise should leave 16cm intact, or 14cm if the bottom is taken out as well. However that leaves the load-bearing to a straight board which will flex downwards as easily as upward. A bent beam will not easily flex downward as loads will compress the fibres.

I think that makes sense, even if the terminology is a bit wierd.

 

[themoose]

Now that's very interesting as there seems to be plenty of it about. Also its not half as costly as douglas fir or hardwood AND I can get it in strips which are suitable for laminating.
If folk reckon this will do the job I can get a load on saturday and get cracking!
/forums/images/graemlins/ooo.gif

 

[themoose]

I am sorry Lakesailor but I haven't a clue what you are on about!! I will put that down to my ignorance. Would you care to explain further?

One thing I would like to say. I registered on ybw.com back in 2003. I had a Seawych down in Portsmouth harbour back then. Never really used the forum much - just looked for anything interesting to purchase (always too late though!).
When I became baffled with all the advice I was given locally I thought I would give this a shot. I have to say I am delighted with the response and sound advice I have received. Thank you one and all.
/forums/images/graemlins/smirk.gif

 

[Lakesailor]

A quick drawing may explain it better.

See how the pressure would cause the sawn one to bend downwards.The same pressure would make the moulded beam more resistant to deflection because of the way the grain is running.

 

[themoose]

Got it! Nice one. It was the 14cm vs. 16cm that baffled me - still not sure what that was about.
/forums/images/graemlins/laugh.gif

 

[Captain Coochie]

It would also be better if you can get quater sawn rather than plain sawn . I.E the growth rings of the timber run top to bottom on quater sawn and they curve from side to side on plain sawn .

 

[themoose]

Ahh, something else to consider - I am running out of notebook! At least I understand what you are talking about! Cheers.