Should we have Collision Bulkheads ?

[Guest]

Apart from all that wood now floating around and the threat of half sunk containers.

I have also just read about a yacht sinking a few years back due to the forestay fitting ripping half the deck up in a blow due to poor backing plates and filling the boat up very quickly . It was a new boat cruising boat, and it sank ,but the crew were fortunately saved by a ship.

Is it feasible in a GRP boat and how would one go about it ?

 

[kidnapped]

I'm sure it is possible. I was on a HR49 which claimed to have such a thing. On smaller HRs,Najads etc. the 'V' berths are quite high, the reason I've been given is that the forward part of the hull can be punctured and the boat will continue to float as the water is retained behind the 'half' bulkhead supporting the 'V' berth.

 

[Guest]

The bulkheads the easy bit it a water tight door that couldbe a problem? You also need to think about pumps, if its waer tight and the door is shut are you going to finish up throwing buckets out of the forehatch?

Roly, Voya Con Dios, Glasson, Lancaster

 

[Lynette]

A forward collision bulkhead is normal on steel yachts. Maybe they go in for head-butts!

Seriously though, I can't ever recall seeing serious damage to a GRP hull that would have been contained by a forward collision bulkhead. GRP boats that have been in collisions seem to end up with long splits in their hull.

 

[Guest]

Racers have them ... ORC 0

The ORC Special Regulations for all multihulls and for ORC Category 0 boats must have...

"a watertight 'crash' bulkhead within 15% LOA from the bow ... or permanently installed closed cell foam bouyancy effectively filling the forward 30% LOA of the hull"

Of course Cat 0 is the highest rating - I belive intended for boats sailing in the roaring 40's. Of course it can be done in GRP - but steel boats have a distinct advantage.

 

[PaulJ]

I have been fitting out my steel hull for the last four and a bit years and when I was at that stage, considered making the bulkhead at the aft end of the forward cabin as a water-tight bulkhead. I contacted the designer (Alan Pape) whose comment was that if the whole forward compartment was flooded, the boat would float so much bows down that the boat would become unstable and could even capsize.

In the end I decided on the scheme outlined by "kidnapped" and built a series of mini water-tight compartments under the forward double berth the top of which is about 18" above the water-line. These compartments will be used to stow bikes and other stuff that will never be needed at sea. All boat design is a compromise but this scheme gives some peace of mind if nothing else!

 

[HaraldS]

Re: Racers have them ... ORC 0

Interesting, haven't heard about that rule. Just calculated my watertight bulkhead and it's 17% of LOA from the bow. Still always felt is was quite far forward, but some folks told me that a hit further aft would bounce along the hull without puncturing it. This far forward it was possible to make it solid with no door and all access to the forward lockers is from the deck only. I have a small fitting and "seacock" in the bulkhead with a hose leading to the deep bilge, because otherwise I would have to pump out separately.

Also I went with two Twaron layers for the whole bow section reaching back to 25% of waterline. Not sure how much it helps, but it feels better.

There are several GRP production yachts, like the Amel, that have several collision bulkheads and watertight doors.

 

[Guest]

I quoted from ORC

The ORC Special Rgulations for 2001 etc. It would rule out a lot of boats, but then if you can afford to enter the Cat 0 races that's probably less of a threat!

 

[Guest]

My last boat had an ingenious solution to the probelm. The previous owner had glassed in a holding tank in the bow of the boat which then also served as a collision bulkhead. I never had to test it in a collision, but the holding tank worked fine.

 

[HaraldS]

Gee, this might make the collision worse if it doesn't "hold".

 

[Guest]

If it didn't hold I would not have been on board very long anyway!

 

[PaulJ]

An integral tank of which the hull forms the outside may not be such a wonderful idea. My first boat, a Hurley24, had a glassfibre water tank though it was not integral with the hull. When I took the top off the tank in order to clean inside I found the finest example of osmosis you could ever wish to see. An integral holding tank would mean that the hull is being attacked from both sides. I understand that "Fresh" water is even worse for osmosis than salt water - 'not sure where effluent comes in the scheme of things but I don't think I would want to try it!

 

[Guest]

I appreciate your observations, however, although I did not inspect it myself, I was assured that there was a seperate holding tank within the glassed in crash bulkhead. The boat was custom fitted out to the highest quality by an engineer, and I never had to worry about the integrity of any of the fittings.

Never had the boat long enough to test the crash bulkhead though!

 

[PeterGibbs]

This is really a complex question. Here are some further thoughts!

The stem of most boats will by definition take a pretty heavy clout before deforming or giving way. The crash situations we see in the press rarely show damage to the stem itself. This is defence one in case of a head on collision.

It is also likely that an object at the water level will deflect the bow of a family sailing vessel upwards if approaching at upto 6 knots or so - or it should! Most of us have "shallow feet" just behind the bow and this should deflect the bow upwards. In the case of big boats this will not be true - laws of momentum etc.

But as some contributions above have pointed out, it is more likely the real risk is from an impact off centre that smashes in the large panel between the anchor locker and the first bulkhead - a typical stetup on many GRP boats. There is no practical way of fitting a water tight door to this bulkhead.

If the space under the forward bunks was sealed to the waterline level with no openings to the boat below this level, water from a split in the forward hull should be contained in this section - provided through motion etc it did not slop over into the rest of the boat and overwhelm the pumps. On this proviso alone this sounds to be a poor defence strategy. Having a forward water tank would hardly improve this since bonding the tank to the hull sufficient to prevent water ingress is most difficult!
More boats are built today with some extra strengthening in this forward area - Kevlar (Bavaria) comes to mind. This must reduce the chance of a catastrophic breach in the forward hull.

My old Westerly had a delightful chink in its armour. The chain locker had an inspection panel that opened into the forward cabin. So any protection from a sealed anchor locker was immediately lost. Nice one! This could be sealed for greater security.

However, in the run of things it seems that compared with the NM's done by the fleet, the collisions we suffer are remarcably few. Having reviewed the above, I think that, assuming a good watch is kept, there is a relatively small chance of catastrophic damage at sea from striking a foreign object: one is more likely to be T-boned in the marina - just when you're least expecting a sinking!

PWG