bulkheads

[blaze]

how many for a 20' boat, as some would be aware I busted mine across the cabain bulkhead basicly because of insuffent stringers. Survey require a bulkhead every meter but also require the glass thickness to be greater especialy along chines and keel line, with modern boats that is basicly the bottom of the boat. This time I will be putting 230mm full lenth stringers in and laying up mat,woven, mat (600g mat) up the chines. after the stringers go in I will layup mat,woven,mat up along the keel line and up the stringers. My First bulkhead will be about 500mm from the transom, then next 600 further (this will end up the fishbox). The fuel tank will then go in 1450mm long (under the tank there will only be tank supports at spacing of about 300mm and at the highest point will only be 50mm high) now another bulkhead. (this will be a full height bulkhead and cabin doorway). from there foward there will be a series of hatches and storage compartments.
How many bulkheads is enough
cheers
blaze

[familyman]

Dont know about enough bulkheads but too many is when you need a bigger donk to get it up on the plane ;D ;)
Seriously look at the hull as a whole and try to imagine that the bulkheads hold the stringers and hull in shape,stringers provide longitudinal stiffness and panel stength.Imagine the hull supported only by points at the bow and stern,will it be stiff enough to not buckle?
When you seat a bulkhead onto the hull make sure there is a foam section between b'head and the hull skin and cut holes in the b'head around the joint section to allow the resin proper purchase on the b'head.
The foam is to prevent hard spots on the hull.
Sorry about the fibreglassing 101 course,forgot who I was responding to ;)
cheers jon

[blaze]

cheers,
never to old to learn.
one of the reason for the question I suppose is that every thing I rebuilt before held together fine(bloody hard to remove to i might add), the failure occurred where I stopped (all look perfect). I you have also hit on my concern - HP, looks like I will be adding around 300kg when loaded with fuel, so I am trying to minimise weight without affecting the strucual integrety. Wanta build it so I can come of the top of a 6m wave and not a little 3m one
cheers
blaze

[familyman]

Get some carbon fibre ;) ;D
Its a balance between hull stregth and weight,the lighter the skin,the heavier the frame and vice versa.
Also with sandwich panels you will increase strength with minimal increase in weight
cheers jon

[blaze]

dont know about carbon fibre, only a fishin boat.
so far to lighten it I have gone for hollow glass stringers (no timber) and will also be using definacell (close cell form to replace ply) for some of the construction. This is not cheap so I dont Know If I will do the complete floor with it.
May have to go a bigger HP outboard, just wait and see I suppose
cheers
blaze

[FNQCairns]

Hope you get it sorted Blaze, just don't beat me to the finish line OK! ;D

Don't know about how many bulkheads will suit your boat but the last 1/4 to 1/3 possibly doesn't need any if the rest of the construction is good enough.

With regard to weight because of where you live consider 2 identical boats one heavy and one light. As the waves start building the heavy one will be the most comfortable with the lighter one being tossed around more then as the waves get bigger the time will come where the heavy boat can no longer lift and go over the waves and will try and go through, the lighter one will still be able to bridge those waves and will be the one that gets you home if the shit really hits the fan.

Good luck with it, I wouldn't go back to that stage for all the tea in china.

cheers fnq

[blaze]

3 months

[FNQCairns]

Bugger!! 8-) 8-)