Watertight Bulkheads

[pmagowan]

With all this talk about sinking going on I got to thinking about watertight bulkheads in any new construction. I am interested to know what you all think.

It is simple enough to make a crash bulkhead at the extreme end of the bow where the anchor locker is and most new boats seem to have this. When I did research into more rigorous examples they talk about dividing the boat up into sections and, in general, having no less than 3 equal watertight compartments. Now this would be difficult to achieve and would be cumbersome to use, IMO.

I presume that the most likely area to have a hull breach is in the forward quarters and thus a single additional watertight bulkhead to the forward cabin would be of benefit in the vast majority of cases. I presume that the two requirements for this would be a strong bulkhead with minimal sealed conduit runs and a strong, multipoint fixed door.

I wonder could such a thing be achieved where the door would not be arduous to use for the 99.999% of the time when you are not sinking and yet still work when you need it?

My other thought is that it would be a good idea to have the engine in its own watertight container, boxed in with 'snorkle' vents etc so that throughout an emergency you could rely on it to keep producing power for lights and pumps. You can get some powerful engine driven bilge pumps which could be used in an emergency but obviously useless once the engine is awash.

What are your thoughts?

 

[sailorman]

On AWBs it would req MR grade MDF

 

[Robert Wilson]

Sounds good to me, but improvement on the "Unsinkable Titanic's" watertight bulkheads!
As to the easy watertight fore-cabin door, p'raps four (or six) latches as per grey-funnel line craft for perfect tightness, but just use one for non-emergency traffic?

 

[pmagowan]

I was thinking of a wood/glass epoxy composite door, as light as possible to be as normal to use as possible. There must be some kind of latch system, i.e. just an ordinary door handle for normal use but if conditions are rough a central handle that activates 4 or more point locking. I see plenty of metal bulkhead doors of this nature but harder to find an aesthetic wooden one. If the forward cabin was sealed completely then you would expect all the functions of the boat to be intact in a major collision even with the forward compartment flooded. You could then activate emergency pumps and attempt a repair or ride out the storm until it was safe to do so.

Making the door strong would be easy, as would making the bulkhead strong as it only needs to replicate the hull strength. A couple of boards of ply with a core material and some glass should be sufficient. It is making the door opening watertight and strong that would be tricky but I think it could be done without much fuss.

 

[Graham_Wright]

I was thinking of a wood/glass epoxy composite door, as light as possible to be as normal to use as possible. There must be some kind of latch system, i.e. just an ordinary door handle for normal use but if conditions are rough a central handle that activates 4 or more point locking. I see plenty of metal bulkhead doors of this nature but harder to find an aesthetic wooden one. If the forward cabin was sealed completely then you would expect all the functions of the boat to be intact in a major collision even with the forward compartment flooded. You could then activate emergency pumps and attempt a repair or ride out the storm until it was safe to do so.

Making the door strong would be easy, as would making the bulkhead strong as it only needs to replicate the hull strength. A couple of boards of ply with a core material and some glass should be sufficient. It is making the door opening watertight and strong that would be tricky but I think it could be done without much fuss.

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

 

[prv]

A while ago I did a sketch design (ie no proper naval architecture, calculations, etc) for a steel blue-water cruising vessel. When I started it, I had just finished a passage from the Azores to Southampton on Stavros ( http://en.wikipedia.org/wiki/Stavros_S_Niarchos ), and while you obviously can't miniaturise a 600-tonne ship into a 45-foot boat, some of the ideas stuck. In this case, the idea of a focsle store and workshop, with a watertight bulkhead aft of it and entered via a hatch on the foredeck.

The ubiquitous V-berth is a good way for a builder to fit lots of bunks into a hull, and potentially it helps keep weight out of the ends, but otherwise it doesn't have much to recommend it. My design originally started out as a larger version of Tom Macnaughton's Crown Jewel ( http://www.macnaughtongroup.com/crown.htm ) and retained the full and flush-decked stern, so there's plenty of room for the "master cabin" back there. Living in the bow is no fun in a seaway, so I pulled the forward bunks back to alongside the mast - although bear in mind I have a substantial bowsprit and a mizzen, so my mainmast is a little further forward than some. I also only have four bunks (plus convertible sofa for occasional guests) whereas most production designs would want to cram more in.

Anyway, all this means I have the bow space for the compact workshop and "garden shed" that a true cruising boat needs. The bulkhead between it and the accommodation provides crash protection (though probably not full unsinkability) and means that dirt and fumes from sawing or painting don't invade the cabin. The hatch direct from the deck (with coaming and side-screens, and a proper ladder, not like clambering through a modern Lewmar forehatch) again avoids jobs traipsing through the saloon. In port, the idea would be to set up a workbench under an awning on the foredeck for major jobs. The one downside is that it's not near the engine, but for routine engine jobs there's a fairly limited set of tools needed and I've designed a tool drawer into the engine box, together with an access panel that lowers to provide a work area to avoid getting oil all over the sole.

As I've said, the main entry to the focsle is the deck hatch, but I have also included a small oval hatch below decks. This would be in one of the sleeping cabins, so definitely not a routine thoroughfare. It opens into the focsle, partly to better resist water pressure in the event of flooding, and partly to avoid needing to dedicate space in the tiny sleeping cabin for it to swing into. Instead it opens into the space at the foot of the ladder, which ought to remain clear anyway.

The boat has wiring runs arranged in the deckhead, so they could pass through the top of the bulkhead without too much in the way of specialist fittings. By the time there's any significant water pressure at that point, the boat would have already sunk! Probably just a short welded-in piece of tube with some kind of putty packed around the wires. I don't think there'd be much in the way of plumbing needing to pass through - bilge pumping would be independent for the two compartments.

Anyway, those are my ideas - probably for a very different boat to what you have in mind, but maybe the odd bit will be useful.

Pete

 

[prv]

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

If you have a strong enough bulkhead to deckhead height, perhaps it needn't be time to leave?

Pete

 

[pmagowan]

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

I think the point is that you could be flooded that high, or close in one section and the bulkhead would make it so that you didn't need to leave. Partially flooded boats are supposed to be better than liferafts.

Imagine a stormy sea miles from anywhere and a log drifting over from Canada punctures the bow quarter under the waterline, making a 4 inch gash. There is no way that you could save a boat from the massive influx of water without a watertight bulkhead. With it the forward compartment would fill up, probably not fully but quite a lot. The water would be sloshing around but apart from the change in trim of the boat you would have over 2 thirds of the boat still operational. You could steer and move, albeit with considerable discomfort but you would have enough of the boat to protect you until the storm subsided. At this stage it would be possible to find the gash, make some repairs and pump the forward cabin dry.

There is probably no good reason not to continue the bulkhead to deck height as is traditional anyhow and it would assist with the bracing required. You could take the wires etc through at this height so as to reduce the pressure on any glands etc. I imagine a seperate bilge pump tube going into this area also, connected to an engine driven bilge pump.

All this would make the boat a lot safer for long passages where you can not rely on help.

 

[lw395]

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

When you take into account hitting something while heeled, it may need to be deckhead height at the sides. Add a few waves....

I wonder how many yachts that get holed have the damage very near the bow though, some of the worst damage I've seen has been to the underside of a yacht between the mast foot and the keel.
Of course water tight compartments in the bow and stern will help if the centre of the yacht floods.

 

[Graham_Wright]

If you have a strong enough bulkhead to deckhead height, perhaps it needn't be time to leave?

Pete

The boat will only flood to water line level. Even with a flooded bow, the reduction in freeboard won't alter that by more than a foot or so.

For the water to rise to deckhead level, the deck will be almost submerged.

 

[bigman1]

What about Turtle pac.com the Australian company that supply floatation bags as survival kits,they have been around for a long time so must be doing something right. A sea collision can't be foretold the damage could be a neat puncture hole or a hull length tear,so i would if going deep sea go down the Turtle Pac road. I have no connection whatever with them but that's what i would do. Thanks. Ronnie.

 

[DownWest]

In the classic layout of heads near the mainmast with a bulkhead to the forecabin, seems an ideal place to seal off. The pressure would not be from shock from wave action, but just from the inflow and depth. So not difficult to make strong enough. Also, slight leaks from the door seals can be coped with. With your planned wooden hull, I suspect any really bad impact from a big log might cause problems beyond the bulkhead. Personally, I would be thinking of steel for a long distance boat at 40ft plus. But then I make stuff in it and the paint systems are so much better now. Friend who has a ferro/cement boat that he built in the 80s, would now go for steel. Mostly because it would be stronger and quicker to build.

 

[pmagowan]

In the classic layout of heads near the mainmast with a bulkhead to the forecabin, seems an ideal place to seal off. The pressure would not be from shock from wave action, but just from the inflow and depth. So not difficult to make strong enough. Also, slight leaks from the door seals can be coped with. With your planned wooden hull, I suspect any really bad impact from a big log might cause problems beyond the bulkhead. Personally, I would be thinking of steel for a long distance boat at 40ft plus. But then I make stuff in it and the paint systems are so much better now. Friend who has a ferro/cement boat that he built in the 80s, would now go for steel. Mostly because it would be stronger and quicker to build.

I suspect that wood composite can be made stronger than steel for less weight. In fact when you look at the Gougeon brothers data is is significant;y stronger with much better fatigue resistance.

 

[prv]

I suspect that wood composite can be made stronger than steel for less weight.

Ah - you're thinking of strip plank or similar, rather than traditional carvel? Certainly a lot to be said for that.

Pete

 

[pmagowan]

Ah - you're thinking of strip plank or similar, rather than traditional carvel? Certainly a lot to be said for that.

Pete

Strip plank with 3 layers of multidirectional veneer bedded in epoxy and sheaved in glass fibre inside and out with the potential for more exotic fibres in areas of higher abrasion risk.

 

[prv]

Strip plank with 3 layers of multidirectional veneer bedded in epoxy and sheaved in glass fibre inside and out with the potential for more exotic fibres in areas of higher abrasion risk.

It's wood, Jim, but not as we know it

Pete

 

[Lizzie_B]

The boat will only flood to water line level. Even with a flooded bow, the reduction in freeboard won't alter that by more than a foot or so.

For the water to rise to deckhead level, the deck will be almost submerged.

without a full height bulkhead every time the boat rolled or rose and fell to a sea water would come sloppong over the top. It's just as straightforward, if not easier to build full height anyway, so it would just be potentially spoiling the ship for a hap'worth of tar (or in this case resin).

 

[GH29]

Sealing the engine sounds sensible and I'd do the batteries as well to protect my electrics. Then I can use the VHF to call the lifeboat!

 

[alanch]

The ideas mentioned on here are venturing into the realms of commercial ship/boat design, where full height water tight bulkheads are the norm, with the appropriate bilge pumping and cable/pipe runs. The only small boats I can think of with that sort of protection are lifeboats and pilot cutters. If you get the chance to have a close look inside a proper pilot cutter you will realise how flimsy the average leisure craft are!

 

[Graham_Wright]

without a full height bulkhead every time the boat rolled or rose and fell to a sea water would come sloppong over the top. It's just as straightforward, if not easier to build full height anyway, so it would just be potentially spoiling the ship for a hap'worth of tar (or in this case resin).

My deckhead is a good six feet above the normal waterline!

If you instal a deckhead bulkhead, how do you access the damaged area with a view to repairing the damage?
I would prefer to try to seal any hole and start pumping to improve my chances.

I have a three foot high panel to section off the area between the heads and the forecabin. The sail locker in the forecabin is sealed up to berth level. The bulkhead forward of that to the chain locker is sealed.

Sod's law dictates that I will be thumped from astern by a high speed container!

Main cabin and aft is much more difficult to provide for.