Any tricks for bulkhead templates?

larby · 13-02-2010, 06:47 PM

Hi all,

I'm gonna have to cut out 3 or 4 templates for bulkheads, 2 of which are full height quite complicated ones, the engine firewall and the one between the cockpit and cabin.

Are there any tricks for taking a template for these? My current best plan is to get as close as possible with a 2x1 wooden frame, then add bits of cardboard to get the tricky bits. I can't help but feel there must be an easier way though.

My only other concern is that the top half may have lost shape a bit. The widest point of the boat is currently about level with the screen, she's a bit 'oval' if you know what I mean. Trouble is, I didn't actually check this bit before I ripped out.
I'm planning to check the shape against the brochure pic someone posted for me the other day, but I could've sworn she was parallel sided.

Would revenger be likely to be able to print me out what shape the bulkheads should be, in the same way Cookee had his structures laser cut? That way I'd be able to get the bulkhead shapes easily, and I'd know they'd be the right shape! I'm worried that I may end up glassing her in the wrong shape!

Cheers, James

Jon Fuller · 13-02-2010, 07:09 PM

Cardboard templates.

Outboard packing cases are ideal, large expanse of thick, firm card. I get a rough undersize shape, then use double sided adhesive tape and smaller bits of card to fill in the gaps.

You want your bulkhead to finish about 20mm short of touching the skin, and use some 'method' when glassing in, or you'll get terrible 'pull' in the topsides, deck and running surface when it cures, leaving a very unsightly crease, that you can't get rid of.

motorvator · 13-02-2010, 07:13 PM

Forget about making the bulkheads until you have it back in shape first James. You'll have to draw it up before you glass anyway so do it now before she relaxes further.

Simplist method of getting the actual bulkheads is to treat each plane seperately with an individual piece of ply and scribe that to the shape then pin them all together with a 2x1 frame (cramp in place and screw together when happy)

larby · 13-02-2010, 07:35 PM

Oh I'm not worrying about making them yet, just wanting to make sure how I'm gonna do it. I plan to take the templates for the bulkheads after the initial glassing, but before I put any stringers in. Less to get around that way! I can mark in the stringers by measuring that way.

2x1 frame with bits of board, wood or whatever sounds like the way forward

Jon, you mention this 'pull'... I plan to put some form of a pad between th bulkhead and skin to widen the surface area, how do i glass it in order to stop the 'pull'?

James

Jon Fuller · 13-02-2010, 07:41 PM

I'll need to do some sketches, can't explain quickly in words. will try to do some later.

larby · 13-02-2010, 08:20 PM

Sweet. Do i need to have the pad I'm planning to make if the bulkhead doesn't touch the sides? I was gonna do it from small sections of ply or something?
I'm guessing that the glass bit between the bulkhead and side has to have a curve to it rather that be straight? Bit like this... )(

James

Big Dutch · 13-02-2010, 08:34 PM

I would use some MDF full size template
Start on the largest one first so you can use it on the smaller ones when you screw up !
Remember Larby MDF not MILF !

larby · 13-02-2010, 08:52 PM

Trouble is Simon, how would I get the sheet of MDF into the boat, then how would I find the shape??

Maybe I could just cut the whole boat in 3, then trace around the edge?

James

Big Dutch · 13-02-2010, 10:16 PM

Ah I forgot the deck was still on.

Well its still easy-scribe the edges and transpose it onto full size template
use 3mm MDF-

You are presumably going to build the Bulkhead in one piece of Plywood

I wouldnt make it dead tight to the side of the hull either

Matt · 14-02-2010, 09:56 AM

For me, this worked.
1st, 2"x1" batten frames, tight into all the corners to get the basic shape.

Then copied onto 10mm mdf to produce a tight template. I used these to produce a mock up of the boat layout.

Then, as per Jon's post, draw lines on the template following the hull lines with at least 20mm gap to the edge.
Trim the template, check the fit and transfer to the real stuff.

I would stongly agree with "at least 20mm" to avoid the topside pulling.
I've got 1 that has pulled very slightly, and it was the full 20mm - nothing I can do about it now.

With hindsight, I should have done it Tony's way, but too late now.

biffer · 14-02-2010, 10:36 AM

you can use 2/3mm ply, you can cut it with stanley knife fairly easy, cut it into bits of useable size, scribe in one bit and leave it in place, over lap and scribe in another bit and mark the overlap, the trick is use the first one as a datum for the next one, you can build up the whole beam in bits, lay all the bits on the floor and you should have a shape good enough to draw round, true the boat up first and if your'e not going to take the deck off you will have to glass them in almost the same way as making the template, good luck and i hope my drivel make sense

Jon Fuller · 14-02-2010, 10:39 AM

Quote:

Originally Posted by Matt

I would stongly agree with "at least 20mm" to avoid the topside pulling.
I've got 1 that has pulled very slightly, and it was the full 20mm - nothing I can do about it now.

20mm alone will not stop pull. hence my comment about tech-neek, or 'method' as I called it.

The foam pad way seems to work ok, in fact, you can buy pre formed foam that fits the edge of the ply, and gives a nice radius onto the skin. can't remember where I saw that.

All one needs to remember is, a tight right angle in curing glass will pull into a tighter bend (<90 degree), so if the glass leaves the bulkhead, and attaches to the skin in close proximity, it will bend the skin around the edge of the ply. so some distance and a gentle rad prevents this. The pre-formed foam is a dummies fix for where skill and understanding of the cause are missing. Actually, maybe that's a bit harsh, the foam would make it quicker and easier in most situations to fit the bulkheads.

larby · 14-02-2010, 11:38 AM

With what i took out (apart from the dash bulkhead which seemed to be an after-thought), there was a balsa pad glassed to the boat, then the bulkhead glassed on top of that. no uniform gaps or anything fancy, some touched, some didn't.

from what I've read then, it should look like the below picture?
What is the reason for the gap, rather than seating the bulkhead to the pad/skin with krestomer or sommit?

James

larby · 14-02-2010, 11:39 AM

Ahh, you created a nice pic too then jon while I was doing mine!

Your version looks much easier!

James

Matt · 14-02-2010, 11:56 AM

Nice pic.
With a 20mm gap, I put a 20mm radius on the glass, which I found to be marginal.

So between me not having any technique, and TD being a dummy, what's Lozza?

Quote:

Originally Posted by Jon Fuller

20mm alone will not stop pull. hence my comment about tech-neek, or 'method' as I called it.

The foam pad way seems to work ok, in fact, you can buy pre formed foam that fits the edge of the ply, and gives a nice radius onto the skin. can't remember where I saw that.

All one needs to remember is, a tight right angle in curing glass will pull into a tighter bend (<90 degree), so if the glass leaves the bulkhead, and attaches to the skin in close proximity, it will bend the skin around the edge of the ply. so some distance and a gentle rad prevents this. The pre-formed foam is a dummies fix for where skill and understanding of the cause are missing. Actually, maybe that's a bit harsh, the foam would make it quicker and easier in most situations to fit the bulkheads.

Jon Fuller · 14-02-2010, 01:05 PM

Chaos is just 'unique'.

Captain Chaos · 15-02-2010, 12:54 AM

Quote:

Originally Posted by Jon Fuller

Chaos is just 'unique'.

ta very much

Hydrostream · 19-02-2010, 11:26 PM

I make rough templates with ply or mdf, hold them in place, cut and staple cardboard to to fill in the edges.

Our bulkhead pads are shaped from 18mm HD foam core.

Bulkheads are made from 3/4" honecomb, all the bulkheads and knees in our cat weigh just 20kg.

larby · 20-02-2010, 07:51 AM

What it is to be able to get all the supplies you need eh!

I'm a bit restricted on what I can get, so I'll be making bulkheads from ply i think. It's impossible to get thin enough foam core locally, and far too costly to ship it here, not to mention time.

Can't wait to get started (and finished!) with the glassing, I'm off up to put the final touches to the prep work today.

Cheers, James