(Re)moving bulkhead CMP boat

[SvenH]

The front bulkhead in our cold molded plywood boat makes the bed a few cm too short.

The boat was designed for single sheet plywood multi-chine (is it called that?) but was just built in CMP from the original plans, so I could be stronger than needed.

But I read (on the internets, how reliable can you get) that removing a bulkhead can have a big impact on the hulls strength.

The bulkhead is about 50 cm from the decks front tip and goes down to the point where the bow ends and the keel begins.

Do any of you guys know more about this stuff?

( I have asked the boats designer to look in to this but so far he is not responding)

 

[pvb]

If it's only a few cm, could you cut out a "trotter box" which would let you stretch your feet out but wouldn't totally destroy the strength of the bulkhead?

 

[lw395]

I think you'd have to go through the design process to calculate the scantlings needed. I can understand the designer not wanting to get involved.
You could probably cut away large amounts of the old bulkhead and add a new bulkhead forward of it, but nobody is going to take responsibility over the internet.
Maybe have a look at a few yacht design books like Gerr's 'boat strength' and Larson and Eliasson (sp?).

 

[Boathook]

Does the bulkhead support the mast. I suspect though, that the bulkhead is structural and removal will cause problems. I can understand why the designer has failed to respond and the build is different from the plans.

 

[SvenH]

Quite a long time since I posted this...

Designer (or rather his son who took over) has responded, was actually taking part in a dualhanded race.

He advised me I can remove the current bulkhead above the bed floor if I put a new one forward of it.
Then connect the new one with the old one, horizontally at the bed floor but extent it aft of where the old one will be removed.

I have made the first two crude new bulkhead templates and am about to fit the first well fitting template in mdf.
When that fits, I'll start removing the old bulkhead and preparing to make and fit the new one.

I may leave part of the old bulkhead because it is much thicker than I expected, removing it neatly would probably turn out to be little hell.

 

[SvenH]

The new bulkhead is ready for precise fitting.
As I hope that will not be too much work because of several previous fittings I am thinking of starting removing the old one.

But slightly worried...

Do any of you have experience in removing a bulkhead?
Does that make the hul relax a bit, changing the shape of the hull where the new bulkhead will go?

I plan to bond the new bulkhead in place when the temperatures are up again but removing the old can be done now.

 

[oldharry]

If the boat is ashore and properly supported at the bow and stern as well as on the keels, and the mast is down there should be little stress on the bulkhead. But if you remove the bulkhead completely the hull will almost certainly relax a bit. You can build in temporary bracing to prevent this. Extra support deck to keel should prevent it relaxing outwards enough to be able to keep it's shape.

Remember the bulkhead is there to give rigidity to the hull when it is working hard, being thrown round in a seaway, and with the mast pumping and applying hefty loads as she comes off each wave!

 

[SvenH]

Good point, about the mast!
I was only thinking about residual stress in the hull.

I guess I'd better wait for the higher temperatures, or maybe get cold epoxy/heat the boat/put halogen light at the curing bulkhead.

And I can also start prepping the bonding area, that'l take some time too.