How do you retro fit a f'wrd collision bulkhead?

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anubis

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How do you retro fit a f\'wrd collision bulkhead?

Hi,
I am interested in fitting a forward collision bulkhead. Has anyone experience of doing this themselves? Any advice would be really welcome~ how to measure, materials, must watch out for or do stuff etc?
Many thanks
A
 
Re: How do you retro fit a f\'wrd collision bulkhead?

why?
what are you thinking of hitting?

if less than 60' long, its more a case of why bother?

Exactly how to do it is very specific to each boat, the method of construction and the energy that you anticipate needs to be dissipated in a collsion. Find a decent yacht designer & do it properly as any quick forum response is unlikely to be adequate.
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Presumably by collision bulhead you mean a seal near the front of the hull which may just as easily be described as a floatation tank.
Presumably you have a GRP AWB (average white boat)
Depending on the size of the area you wish to seal you will probably need an access hatch so the area can be used for storage or just for access to the inside of the hull. A far better job can be done if you can glass in the bulhead form both sides.

My best suggestion would be to make a dummy panel of cardboard.
This will enable you to fairly easily get the shape right and also confirm you can get it into place.

I would suggest you use plywood for the panel and cover it with fibreglass and resin. Epoxy is always better on wood and for glueing to existing f/g although polyester may be ok. (that is the original f/g material.
The plywood can be quite thick with a faiirly thin f/g cover and glued into place but far better is thin plywood with a thick f/g layer over both sides.
You will need to be a little experienced on f/g work so do some practice first.
You can lay up the fibreglass layers of woven rovings, chop strand mat or glass cloth onto the plywood bedore fitting.
One very strong attachment method is to have an overhang of 2 inches of (preferably) cloth which can bend across the join to be resined flat onto the skin. On both sides would be best.
The trick is to keep the resin out of the flap of glass until it is in place when you saturate it with resin. (any resin in the flap that goes hard will stop it bending) You can also add f/g tap around the join later. But it will be difficult to get it to sit flat. A bead of filler in the corner will help. You want no airbubbles.
The strength and thickness of the whole bulhead will be whatever makes you happy and is comensurate with the rest of the boat.

The final finish can be in a resin with pigment and filler like microballoons which can be sanded and made reasonably smooth. You will find it difficult to get a really smooth finish like your outer hull.
The access hatch can be screw on panel or hinged but sealing door with latch.

So it sounds like your own brain wave so it can be done to suit your own wishes. Most boats don't bother. My 21ft T/S now I understand comes from the facory with a bulkhead sealing off the stern area for floatation and which also provides support for the cockpit floor. But there is no way I would try to fit one. It does have a section in the bow under the bunks which is sealed horozontally and vertically to form what you maight can a collision bulkhead.
I think however that smaller boats tend to be much stronger especially for the weight such that puncturing the hull is unlikely however capsize and filling with water is more a concern.

So there is olewill waffling again. tell us more about your ideas olewill
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Thank you Ole Will for an excellent dissertation on collision bulkheads! I am amazed that generally most cruising yachts (both power and sail) have very little or no water-tight subdivision whatsoever, unlike many commercial vessels, where the regulations (eg the MCA codes of conduct for passenger vessels) are much more strict.

Here is an excellent account by James Baldwin re how he effectively made his 28' Pearson Triton 'Atom' as unsinkable as possible by installation of watertight bulkheads - http://atomvoyages.com/projects/UnsinkableBoat.htm

This is a truly brilliant website, with just so much useful information for all cruising sailors!
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Thanks for the link an interesting story. I made the staement that small boats are possibly too strong to be holed. Of course a very sharp object will penetrate but I suspect that boats less than about 22 ft a light weight would not carry enough enertia to be badly damaged by collision. (I wonder if I am right) Abuse of my poor boat over many years makes me think this. (slightly less than 1 ton but fairly thick skin.
On it s first outing I dropped it off the trailer and it skidded about 1 boat length across the concrete ramp to end up floating in the water with barely more than cosmetic scratches.
The keel a lifting foil is susceptible to damage but tend s to just crumple with superficial damage. After hitting reefs at over 6 knots.

But as a boat gets heavier there is more inertia so more energy to dissipate with probably similar thickness hull but with larger flat areas.

The comments about needing bouyancy up high to improve stability is important but on the other hand bouyancy or rather sealed compartments under floor may stop water coming in or at least slow it down. I suppose it depends on whether the water is coming in via the hole low in the hull or via the main entrannce hatch. I think the subkject might warrant some comments. olewill
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Very many thanks for taking the time for this clear explanation...I'll contact the boat builders and discuss further before I go ahead.
VB
A
 
Re: How do you retro fit a f\'wrd collision bulkhead?

I agree an EXCELLENT source of info....much appreciated
 
Re: How do you retro fit a f\'wrd collision bulkhead?

An easier way than cardboard mentioned above to create a more accurate template for the bulkhead - is to use thin wood battens cross hatched across the space.
If you understand what I mean - align the first from 10 o'clock to 4 o'clock, the next 8 o'clock to 2 o'clock etc. Just keep overlaying new ones and pinning each to the others using a staple gun. Eventually you'll have an exact shape you can remove and copy onto the GRP or ply sheet you plan to use for your bulkhead.
Have fun
JOHN
 
Re: How do you retro fit a f\'wrd collision bulkhead?

On top of the other replys PBO did an article a while back about building a barge type boat. On the subject of bulkheads the recommendation was to cut to size and then remove 10mm, replacing with locker sealing foam and then glassing in place. This reduced the likihood of stress cracking on the hull outside, by the bulkhead.
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Nothing personnal Artic, its a great idea, honest, there is an easy way. But I will keep it too myself, the cynics will only take the pi$$s.

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Following on from Galadriel post, think Airbags /forums/images/graemlins/smile.gif

I successfully used these in a small yatch some years ago. My idea was to give bouyancy in case of collision and subsequent sinking?

I used the type of inflatable bags which are used by firemen to 'jack-up' car crashes to remove the victim /forums/images/graemlins/confused.gif

All you need for a scaled up version is a method of inflating quickly or automatically, sub-aqua air tanks?? /forums/images/graemlins/smirk.gif
 
Re: How do you retro fit a f\'wrd collision bulkhead?

Another reason to buy a cruising cat - most of them have them in both ends to make the boat completely unsinkable. But lets not restart the mono/multi thing!
 
Re: How do you retro fit a f\'wrd collision bulkhead?

[ QUOTE ]
But lets not restart the mono/multi thing!

[/ QUOTE ]

Doesnt have to be a multi Simon, but we are thinking alike. Why go to all that trouble when you can buy a ready built solution?!

But dont mention unsinkable boats on here, the Cynics who dont understand, dont want to believe!

Sorry I've said to much already. /forums/images/graemlins/wink.gif
 
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