Time to Join The Hull

[CatBuilder]

It's time to join the hull halves together now and put in bulkheads. I have a few questions to try and save myself some time. I wanted to see how you guys usually did the following:

Bulkheads

My bulkheads are solid Okoume instead of composite. I chose this option to save myself time, a little money and to add weight.

When installing these bulkheads, they are put in place with a cove joint. Sometimes, people pre-coat bulkheads with epoxy, then install them. Seems to me this would take longer than "painting" them with epoxy once they are in place.

What are the pros and cons to pre-coating bulkheads before installation?

I'm imagining I can just cut them out, fit them in, cove them, then "paint" them with epoxy. Will that make some part of them less than waterproof?

Will the edges under the cove joint be able to find bilge water and absorb it?

What is the right way to do this so the boat comes out most seaworthy? Maybe I should just precoat the edges, let the cove take care of the outer border, and "paint" the faces with epoxy?

What would you do?

Installing Bow Crash Bulkheads and Stem

My hulls are on their sides in a mold. I have two halves of a hull coming together in a single mold. The bows will come together at the same time as the rest of the hull. Somehow, I have to cove a forward crash bulkhead that has, literally, 10" of hull beam. How do I reach the side of this bulkhead that forms the inside of the crash-bow? I can't reach in because the bow will be closed as the hulls come together. I also can't reach through this solid bulkhead to cove the far side in the crash-bow. It's not accessible.

What do people usually do about this?

Also, while we're at it: My plans call for a lot of coving forward of this bulkhead in the above paragraph. They coving is to keep the stem in place. How do people usually do this coving inside the hull when you can't reach?

Catbuilder, anytime your laminating anything with epoxy it's a good idea to prime your surfaces with neat epoxy. Thickened stuff doesn't get into the surface like neat does and when laminating glass you don't want the surface and the glass competing for resin in the bond line. Think of it as a tree with roots or a tree with no roots. Better yet, do a bit of testing. Take a piece of Okume and laminate a 6 inch layer of tri-ax to it. Then prime a piece of Okume and laminate to it. Pull 'em apart the next day and see what happens. As always, mind the blush.

[CatBuilder]

Good save, fg1inc. Thanks.

I suppose I can wet out just the edge and the border where the cove will go while I'm installing the bulkhead. I can do this just before I do the cove, so I don't have to sand anything. Then, I can "paint" the rest of the bulkhead afterward at any time.

Thanks for that input.

[TeddyDiver]

"Maybe I should just precoat the edges, let the cove take care of the outer border, and "paint" the faces with epoxy? "
And gf strip overlap the cove

"Installing Bow Crash Bulkheads and Stem
How do I reach the side of this bulkhead that forms the inside of the crash-bow?"
Make a prefit, make bow side coves ready (triangular strips) leave it of now and install after the inside and bow is ready..

[Dean Smith]

Originally Posted by fg1inc

Catbuilder, anytime your laminating anything with epoxy it's a good idea to prime your surfaces with neat epoxy. Thickened stuff doesn't get into the surface like neat does and when laminating glass you don't want the surface and the glass competing for resin in the bond line. Think of it as a tree with roots or a tree with no roots. Better yet, do a bit of testing. Take a piece of Okume and laminate a 6 inch layer of tri-ax to it. Then prime a piece of Okume and laminate to it. Pull 'em apart the next day and see what happens. As always, mind the blush.

what zackkly do you mean by NEAT?
First coat on surfaces we are just coating with epoxy instead of paint we use heavily thinned with Universal thinners, which is cheap and gets the timber/ply soaked Nice post by the way.
of course many try sell you epoxy thinners, blind you with science, but when you are using 100,s of litres, it is a big saving

[Lurvio]

For the crash bulkhead, make a glass flange first, join the hull halfs and the stick the bulkhead in place with some goo, make sure the hidden surface is well coated.

Fram's building blog
This is a pic that first came to my mind. Difference being, you'd make the flange in the middle of the hull side, not the end.

[AndrewK]

Originally Posted by CatBuilder

I

When installing these bulkheads, they are put in place with a cove joint. Sometimes, people pre-coat bulkheads with epoxy, then install them. Seems to me this would take longer than "painting" them with epoxy once they are in place.

What are the pros and cons to pre-coating bulkheads before installation?

I'm imagining I can just cut them out, fit them in, cove them, then "paint" them with epoxy. Will that make some part of them less than waterproof?

Will the edges under the cove joint be able to find bilge water and absorb it?

What is the right way to do this so the boat comes out most seaworthy? Maybe I should just precoat the edges, let the cove take care of the outer border, and "paint" the faces with epoxy?

What would you do?
If it was all ply boat then I would install b/h's and seal after. But in your case I would seal the b/h's first. Advantage of sealing first is that you dont get runs as you are working on horizontal surface. Two horizontal heavy coats would be equal to 3 - 4 thin vertical coats.

Installing Bow Crash Bulkheads and Stem

My hulls are on their sides in a mold. I have two halves of a hull coming together in a single mold. The bows will come together at the same time as the rest of the hull. Somehow, I have to cove a forward crash bulkhead that has, literally, 10" of hull beam. How do I reach the side of this bulkhead that forms the inside of the crash-bow? I can't reach in because the bow will be closed as the hulls come together. I also can't reach through this solid bulkhead to cove the far side in the crash-bow. It's not accessible.

What do people usually do about this?
The only way to do this on any sealed compartment is to make bonding flanges first.

Also, while we're at it: My plans call for a lot of coving forward of this bulkhead in the above paragraph. They coving is to keep the stem in place. How do people usually do this coving inside the hull when you can't reach?
What do you mean by a lot of coving? a large diameter fillet" or lots of reinforcement on top of the fillet?

A common way of dealing with this is to finish the hull at the crash bulkead, glassed both sides. Then the bow is formed by gluing, shaping and glassing over solid foam. Low density pvc, corcell or extruded styrofoam.

The only other way is to make a boding flange in each half hull before you bring them together for the crash b/h. Join the hulls, cove and glass the stem first. Then glue in the crash b/h then cove and glass the back of it.

When you have very fine bows the solid foam is the easier option.

[CatBuilder]

Ah!! So that's how it's done!

Thanks, everyone. I had no clue.

Andrew: answering your question... By "a lot of coving", I mean a rove and cove inside the hull to keep the stem in place. Here is the concept...



So given this is the schematic of how the stem is done, would you still have the same thoughts on putting the stem in?

It is the "Rove and Cove" that I anticipate having a lot of problems with.

I guess I should build in the flange inside the hull, just aft of the stem to be ready for the crash bulkhead. Then, I can bring the hull halves together and stick the bow piece into place, like seen in the diagram. Next, I can "rove and cove" inside the hull by squeezing up there *before* the crash bulkhead is in place. Lastly, I can press that crash bulkhead up into the already-built flange, sealing off the compartment.

Thanks for the help. I'm thinking this should work now.

[rwatson]

Originally Posted by Dean Smith

what zackkly do you mean by NEAT?
First coat on surfaces we are just coating with epoxy instead of paint we use heavily thinned with Universal thinners, which is cheap and gets the timber/ply soaked Nice post by the way.
of course many try sell you epoxy thinners, blind you with science, but when you are using 100,s of litres, it is a big saving

"Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected"

http://www.seqair.com/skunkworks/Glu.../Thinning.html

[rasorinc]

All plywood needs to be carefully sealed. Edges and face need 3 coats of epoxy to fully encapsulate the ply. Any less and the ply will act like a sponge and give you fits in the future. Par posted awhile back the negatives of thinning your epoxy, please read his posting on this. Glen-L sells an epoxy for encapsulating only--2 part, 50/50 I belive called poxy shield.

[AndrewK]

OK you do have a solid foam bow.
I'm just not clear on how many b/h's you have there;
a. b/h where the forebeam connects to, then a small cavity space between this and the crash b/h shown above, then the solid foam cap?
b. crash b/h shown is where the forebeam attaches and there is no cavity space?

If its a. then you need two sets of bonding flanges, one for the back side of the crash b/h and another for the front side of the forebeam b/h.

If its b. then even though the crash b/h is only 10" at max width you will not require a bonding flange as you should still be able to cove and glass the back of this while the hull is on its side.

[bntii]

Looking at the line dwg, it looks to be a bulkhead at the beam, then a space to the stem detail as shown above.

Cat- do you have a scale reference on the stem detail dwg shown above?
I am guessing that the foam fill at stem is ~3 or 4" long?

[Herman]

On coating before or after installation.

Personally I like to coat plywood before installation. Nice and easy on perfect working height. Also sanding is easy, dust extraction is not in the way, etc. Many panels can be done like that in a matter of days.

But if you like to coat and sand in an awkward position, with a vacuum cleaner on your lap, cramped in the bow of the boat, I will not stop you....

Think of your boat as a car. I am sure you have seen some video footage of car assembly lines. Most parts come to the car as large subassemblies, to minimise work on the car (your boat) itself. This way things can be done more easily, faster and cheaper. Go for it!

[viking north]

Guys-on my boatbuilding thread "Building the Nancy G"--------- I describe my non traditional use of a dust collector in extracting toxic vapours from epoxy and polyester resins especially working in confined spaces. A basic portable dust collector will cost you around $100. money well spent to reduce toxics and an additional plus of cooling the work area---Geo
P.S. I also use it for extracting welding fumes-- your dust collector becomes a multiuse machine--vacuum, fume extractor and a little air conditioning to boot.