Watertight Bulkheads

[pmagowan]

Shouldn't make too much difference - the average forepeak doesn't have tons of electrical gear in it to run wiring to. A well fitted out boat would have all the wiring high up anyway - either above the headlining or in the corner between deck and topsides - so even if you made no attempt to seal them you're fine until full submersion. But a couple of glands for the windlass cables plus one of those drill-your-own-holes multi-glands for other wiring should cover even that.

Pete

Yes, nothing insurmountable, it just takes some thought at the planning stage.

 

[Deleted member 36384]

Yes, nothing insurmountable, it just takes some thought at the planning stage.

You can purchase IP68 cable glands which are certified water tight to 10 bar pressure. Loads on the market in plastic, stainless, brass materials. There are also cable transit systems such as Roxtec which are adjustable and thus allow future cable or pipe transits e.g. from a single cable to multiple cables just by changing the inserts. The Roxtec ones could also give you decent ideas for home fabrication, the principle is not that hard to replicate.

 

[Bajansailor]

The Joint Services (JSTC) used to have a fleet of Victoria 34's outfitted for sail training - I went on board one some years ago, and noticed that she had a water tight bulkhead between the saloon and the forecabin, complete with a 'proper' water tight door that had 'dogs' around the perimeter and all connected on a linkage allowing the seal to be compressed all around when the door is shut.

Watertight bulkheads are a good idea for sure, but the problem is implementing them practically...... it is a requirement for pretty much all commercial working boats to conform to at least a one compartment standard of subdivision, and I think that it is a two compartment standard for passenger vessels.

It is feasible on yachts - here is an excellent account of how one sailor made his 28' yacht 'unsinkable' (well, almost) by adding various water tight compartments inside.

http://atomvoyages.com/articles/improvement-projects/258-unsinkableboat-1.html

 

[pmagowan]

Thanks that is a great site. He has done exactly what I am planning to do only he had to retrofit and I can design it in from the start. It is nice to know that I am not alone in having this idea. I am confident I can make my boat positively buoyant and thus have an 'unsinkable' boat. I think this must be a very advantageous thing to have for blue water sailing. It certainly gives peace of mind. I have an idea to do the Northwest passage some day and icebergs would be less scary in a positively buoyant boat.

 

[KellysEye]

As said there are structural issues with watertight bulkheads but do you think you would ever need them?

We bought a steel boat because we were going long distance sailing and our view was it's only a matter of time before you hit something or something hits you. We sailed just over 10,000 miles and we got hit twice both times while at anchor and both times a GRP boat would have been holed above the waterline. Hitting something or being hit is rare.

 

[GAJ]

I am not sure why it would be a problem. Water pressure is easy to calculate as are the scantings for bulkheads. If you think about it the transom is just a watertight bulkhead at the end of the boat. Using plyboard and glass fibre it should be relatively straight forward. The main problems I envisage is the changes to wiring layout that would be required. The doors and frames would need to be a bit bulkier as per Northcave but this is not designed to be holding back water permanently. I would have thought a forward opening door with a rubber seal would seal itself quite well from water pressure alone.

My current plan is to have all the berths and saloon seats as watertight compartments with simple watertight hatches for access to storage. I recon I can get at least 8 tonnes of bouyancy from these alone. Then a watertight crash bulkhead fore and aft and the forward cabin being seperated by a watertight bulkhead. With built in water and fuel tanks this scenario would give me a second hull in most areas, massive bouyancy and great defense against all but the most severe breach of the hull. It would also do so with minimal disruption to the 'flow' of the boat layout. It would require additional flood sensors and additional bilge pumping complexity, but nothing overly complicated. It would also make storage in these spaces a minor inconvenience but then it already is.

I think since most boats do not get used for blue water cruising most people do not consider these things high on their priorities. There will be extra work and complexity in the design but for a home build I think that is justified. Obviously commercial operations have different priorities.

I am in agreement that most boats are not designed for blue water cruising, nor do they need to be as not that many venture offshore for extended periods in comparison to the number built. Including watertight bulkheads and compartments has a cost and may be uncompetitive in the market place. Your ideas sound to be just the job to me but I am a conservative old geezer these days.

It may be worth you having a look at the way Amel do it, as is usual for them their ideas are simple and, hopefully, effective. I am biased being an Amel owner though

The anchor locker/crash bulkhead is watertight and has its own drain that can be closed in emergency. The fwd part of the hull fwd of the crash bulkhead below waterline is solid grp and massively strong.

The forward facing main bulkhead door is of 22mm ply, it seals on a forward facing half round neoprene gasket let into the framework. The door is closed isolating the forecabin and heads and temporarily secured by a bolt and then two strong-backs are fitted and dogged down. The fwd compartment drain (no limber holes leading aft through main bulkhead) is then closed by operating a valve located under the main cabin sole. Most wiring is at deck level and sealed although there are two large cables that run under the sole and through the bulkhead through watertight glands. The pipework for the fwd heads also runs through watertight glands at sole level.
In addition the larger Amels have watertight compartments aft but our tiddler doesn't have them.

As far a bilge pumping goes we have a deep central sump at the aft end of the keel that collects any water ingress. It has two independent water level sensors. There are both manual and electric pumps fitted and we also have a roving manual pump and a high capacity 12v pump that can be operated in any part of the boat, as long as we have battery power that is!

I should have a photo or two of the door etc. should you be interested.

 

[Ric]

Amel yachts have forward and rear watertight bulkheads with elegantly built watertight doors.

 

[Tim Good]

If you could post any pictures I would be very interested. Particularly in the structure of the door. There is no point in reinventing the wheel if someone has already done the work. Thanks

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See here for technical draws of boat where you can see waterline below bunk height and bulkhead where door is.

http://seastream.co.uk/wp-content/uploads/2014/06/Seastream-43-Plans.pdf

 

[nigelmercier]

Would it be fair to say that in general removable panels are not meant to be watertight? I ask because I'd quite like to fit a few vents in the panel at the foot of the bunks.

 

[pmagowan]

Thanks Northcave. Those pictures are very useful. It is nice to see that the door still looks like an ordinary door and not a submarine hatch. Looks like it should be easy enough to create a good seal.

I am not sure what you mean Nigel, I would think that any panel could be designed to be either watertight or not, as required. The thing is that you don't necessarily need things to be watertight all the time. It can be similar to storm windows in that you only fit them if you feel the need. So, watertight bulkheads could be sealed on long passages or in bad conditions but left open at other times. It may even be possible to fit them only in the event of a leak that you can't stop.

 

[Tim Good]

Thanks Northcave. Those pictures are very useful. It is nice to see that the door still looks like an ordinary door and not a submarine hatch. Looks like it should be easy enough to create a good seal.

I think having the sealed V bunk above the waterline is most important. If a holing did occur by a partially submerged object then likely it will happen at the bow or 6ft from it. The V berth in mine will therefore fill and that is all. In the absolute worst case scenario the whole forecabin would fill to waterline level and can only assume the designeds have done the calculations of force to allow the door to be strong enough for that. It is not as simple as to say there is, for example, 8 cubic meters of space in the cabin and therefore 8T of force on the door.

Anyway based on the size of the hinges on the inside, then I'd say it also performs the job of being a dry compartment also, should the deck saloon be flooded, god forbid.

 

[cliff]

It doesn't need to be deckhead height. If you are flooded that high, it's time to leave.

That was one of the problems with the Titanic - the WTB did not come up far enough - stopped a couple of deck too low

 

[pmagowan]

That was one of the problems with the Titanic - the WTB did not come up far enough - stopped a couple of deck too low

I think the breach was too great over multiple compartments anyway. The difficulty is that you have to recalculate the stability figures with each compartment flooded and see if the boat can still sit in a reasonable position. Most of the calculations would be for a boat to be able to stay afloat and provide life support with only one major compartment flooded. Any more and the trim would be such that it would only delay the inevitable.

I have a number of options up my sleeve which I think will make things work well in an 'unsinkable' way. For a start, having enough buoyancy in compartments such as beneath berths and saloon seats so that the boat would have a positive buoyancy even in the event of complete flooding. Secondly, these buoyancy compartments also act like a second skin so that a breach in most parts of the hull could only flood one small compartment. Third, having watertight bulkheads in the main cabins plus a crash bulkhead fore and aft means that any breach can be isolated to one section of the boat. Then, significantly greater bilge pump capacity than an AWB would give much more potential to recovering from a significant hull breach.

So, a head on collision would likely only damage the forward crash bulkhead and thus not risk the boat, same for a collision in the stern. In the event of a move major crash that breached all the way through the bulkhead into the main cabins then the watertight bulkhead could isoate this. In the event of an underwater breach from an iceberg or shipping container the damage should be limited, in all likelihood, to a single compartment. The only way the boat could sink would be if a catastrophic collision occured that was significant enough to rupture multiple bulkheads and compartments. With a cold moulded composite construction this would have to be so large a collision that I would suggest the breach in the hull would be the least of your concerns. Essentially, I think the boat could be made unsinkable with minmal disruption to normal use.