The Offshore Voyaging Reference Site

Do We Need Watertight Bulkheads?


Should our boats have watertight bullheads? It’s a question that comes up often and the obvious answer is “yes”. But not so fast:

My thinking is that, while I agree that a forward watertight bulkhead is a desirable feature in a voyaging boat, it is far from essential and that trying to incorporate multiple watertight bulkheads can cause more problems than it’s worth.

I’m going to write at some length (what else is new) on this subject because I think it represents an interesting exercise in risk evaluation, a process all of us who wish to sail offshore must become adept at, because if we treat all risks as equal, and try to guard against each of them equally, we will quite simply never leave the wharf.

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paul shard

All good points John! Especially about “not leaving the wharf” if we tried to do everything possible. And I like your idea that floating containers are often blamed when the more common scenario is a faulty hose clamp…

Our 49-foot boat does have a collision bulkhead about 7 feet from the bow and it is sealed right up to the deck level, but our previous boats did not have this feature.

Perhaps some multihull enthusiasts will also wade in with comments about how easily their boats can be made “unsinkable” since they don’t carry ballast??

Keep up the good work!

Paul Shard
SV Distant Shores II – Southerly 49 with collision bulkhead 🙂

Marc Dacey

Our steel pilothouse cutter has a keel to deck steel bulkhead that is NOT watertight…unless a couple of limber holes are plugged. So that’s high on the “check and complete” list before pushing off.

We are the third owners, and it’s a custom boat, so I can only surmise that the logic was as follows: plug the holes and, if the bow is pierced or breached, you can repair it and then drain the last foot or so into the main bilges. I’ve half a mind to seal them up, frankly. and just rig a decent Patay manual pump. All conduits are under the deck…if they are awash, we have bigger problems.

Such a bulkhead enormously stiffens the bow, I’ve found, and creates a triangular-shaped, seven foot long “workshop” accessed from the deck above. I have been toying with the idea of cutting an access hatch so I can wiggle from the saloon into the forepeak workshop. I can keep the bulkhead strong with cross-members, and can keep the “watertight” aspect with the hatch high on the bulkhead and opening outward.

While it is true that this setup does lose living space, I personally find the usual sort of V-berth next to useless in any kind of a seaway, and this keeps the “industrial” side of the boat out of the remaining interior living space of saloon, galley, pilothouse and aft cabin. Adding a hatch high in the saloon would allow interesting projects like repairing the boom, inside, during bad weather! Not to mention keeping the heavy gasketed steel deck hatch of the forepeak firmly closed if green water is coming over the bow.

A last point: The leading edge of our box-keel (a sort of modified long keel) extends *forward* of this deck to keel bulkhead.

I am reasonably confident that we could stay afloat in most collision scenarios that didn’t involve considerably larger vessels or very pointy rocks upon which we were dropped. I also think that the bulkhead would buy us precious time in an out-and-out sinking.

That said, if I didn’t have one, I doubt I would create one in a production boat being fitted out for voyaging. I would “add more pumps”!

I would, however, consider strengthening the bow and would be quite attentive to the way the keel tied into the hull. These are not aspects of modern production boat design I find reassuring, frankly.

Very interesting discussion, by the way. I had our boat for a couple of years before I even thought of why the designer chose to draw collision bulkheads (and half and full bulkheads aft) on a not-overlarge steel boat.


Great post. Thank you.

Based on insurance claims, a plurality (30%) of underway sinkings are caused by heavy weather and taking water though topside enclosures—which in turn causes stability issues and thus sinking.

Next is though-hull leaks (18%). Then,
Raw water cooling systems (12%)
Missing drain plugs (12%)
Groundings (10%)
Poor construction (6%)
Leaks at outdrives (4%) NA for this audience
Struck floating debris (4%)
Other (4%)

So, as an engineer, and professionally trained mariner (although not practicing), I agree with your analysis in principal. However, as a cautious mariner, I would also say that many of these causes can be prevented by good maintenance and solid seamanship (no excuse to lose your boat to a loose thru-hull fitting). When I start to get down to the truly random events (or eventual mistakes—weather, grounding, debris—given enough time on the water) the idea of watertight bulkheads starts to look more appealing.

However, based on this set of data there is no doubt that the order of importance is:
1. Maintain your boat regularly (46% of singings)
2. Buy a seaworthy and well-constructed boat (36% of singings)
3. Don’t hit stuff (14%)

Fair winds,


Erik de Jong

Hi John,

Nicely written again. In general, I totally agree with your opinion on WT bulkheads in cruising yachts (and that while I’m a Naval Architect!). All your points are correct if we are looking at yachts in the range up to approx. 45 feet.
But as soon as one starts looking at bigger boats, and I’m thinking about approximately 50′-55′ and over, the picture is starting to change in favour of the water tight comparted vessels.
I managed to implement 4 WT bulkheads, a double bottom in the main compartment and a watertight engine room in our own boat (50′). If it wasn’t for the hefty doors with big dogs and hinges, you wouldn’t even know it’s there.
At a boat of such a size, and the larger they are, the easier it gets, the bulkheads are not so much of an interior layout obstruction anymore. Also, when spaced correctly, the boat remains stable and sailable without having to pump out the flooded compartment.
As for the cost, on our boat, I think it was less than 1% of the construction costs of the boat for the 4 bulkheads and the engine room together (labour hours included). Depending on the construction of the boat, and the layout of the interior, the bulkheads replace wooden partial bulkheads in the interior which would require their own amount of work.

As you correctly pointed out, most yachts that sink, have a failure other than a collision. Be it a prop shaft that gets disconnected from the drive and slips out of the stern tube, or a broken rudder stock that let’s water in, or a ruptured hose or broken sea valve. I know even some occasions where yachts sunk because the forgot to close a window in the hull. I do not know the statistics, but I wouldn’t be surprised if these kind of water ingress sources account for more than 95% of al sinkings. And these are all single compartment floodings.
Agreed, most of those are preventable with proper maintenance.

Another advantage I found while living aboard in cold climates, is that it is much easier to divide the boat in smaller parts to save on diesel for the heater. The bulkheads in our boat are made of steel and insulated the same way as the hull itself, including the WT doors. It is simply a matter of closing one or more doors to save hugely on heating costs.
In addition to this, the insulation on the bulkheads and doors is also a fire insulation. Theoretically, a fire could be contained to just a single compartment. Which could even be flooded to extinguish the fire if needed.

And last but not least, bulkheads do make a vessel stronger and stiffer at relatively low weight increase. Something that never hurts on a cruising boat. But again, not really useful on smaller boats.

To summarize it all, I do agree with both Matt and yourself, but only if we separate the cruising fleet into 50 feet and over, and 50 feet and under. For the smaller boats, it is impractical and not adding that much to the safety, on the larger boats, pretty much none of the disadvantages remain valid.

Best Regards,
Erik de Jong

Erik de Jong

Hi John,

You are correct about LWL vs LOA, the location of the collision bulkhead is always a certain distance from the fwd end of the waterline. The aft peak bulkhead is normally 1 or 2 frame spaces ahead of the rudder stock. These two bulkheads determine the positioning of the other bulkheads.

As for tolerating the bulkheads? I guess so?!
The boat looks small from the inside compared to other boats of the same length, but I always blamed the slender lines to make her a good upwind and light air sailer rather than a motorboat, but you might be right.

Victor Raymond

John and Matt,
I am not a betting man however I made the gamble to go with a used boat without watertight bulkheads. Having said that we do have a crash bulkhead in the bow below the forepeak locker. We also have integrated fuel, water tanks and waste tanks which translates to double hulls except where the coffer dams are. We also have probably the thickest hull plating in the AAC fleet. We also have only one hole below the waterline that does not have a standpipe above the waterline. (Actually that it is not exactly true but virtually so.)
Nevertheless I can’t help but wonder can I do more to protect our floating home. You and Matt have done well to explain the pluses and minuses. My hope is that I never have to put all the theory to the test as I develop my seamanship and nautical experience.

Marc Dacey

Very good points, Victor, especially about the “virtual double hulls” of proper keel tankage and the oft-neglected standpipe above WL. I think these things, like doggable companionway doors, lockage cabin sole panels, and sealable ventilators/Dorades/heater flues go a long way to keeping a bad turn of events (a capsize or complete rollover) from becoming a “cascade failure” of water ingress and flying provisions.

Even basic stuff, like doubled opposing SS hose clamps and tapered plugs tied to seacocks, seems to be missing on a lot of boats these days. I could take being sunk in the Perfect Storm, I suppose, but because I cheaped out on a hose clamp? I’d have trouble living with the shame in the liferaft!

Matt Marsh

You know what, John? I can’t refute any of your points. I can’t say “no, John, you’re wrong” because everything you’ve said is valid and reasonable.

It is only on the cost figure that I may have a quibble; I have a hard time believing that we could save 10% of total cost by stripping out watertight bulkheads. Open ring frames that can do the same structural stiffening role as full bulkheads are not easy or cheap to build.

I do, however, come from a powerboat and multihull perspective here, where speeds are much higher than in the keelboat fleet and layouts are often more amenable to compartmentalization. The trimaran I’m building now has 13 (!) watertight or semi-watertight divisions between her three hulls, and there are collision scenarios where we might expect three or four of them to be breached.

Would I try to retrofit watertight bulkheads to a boat that didn’t have them? No. You could upgrade all the through-hulls to big-flange bronze, replace the entire raw water system, and replace all the hatches and portholes with offshore-grade ones with that money. Those upgrades would have a much larger effect on the probability of sinking.

Would I design or commission a new boat that didn’t, at the very least, have a forepeak collision bulkhead? No. If you’re starting from scratch, it makes sense to hedge against as many risks as you can, within reason.

Robert Sapp

I think you can gain quite a bit of additional safety with minimal cost by ensuring that whatever type of partial bulkhead supports the forward berth is glassed and sealed to form a water tight dam. Remember, if you hit something and punch a hole in the bow, the boat isn’t going to fill up and sink if you can contain the inflow, it will only settle by the head until the water level has risen to the height of the new draft. Take your average layout with a forward V-berth. If the partition that forms the aft part of the berth is glassed in place to make it act as a dam, if you punched a hole under the berth, it would flood the space, but the partition would contain the inflow if it were high enough and the boat would stop flooding once the bow settled to where the water level in the flooded space equaled that of the vessel’s waterline. How high would this partition have to be? It depends on each particular vessel’s draft and the volume of the area under the berth. The advantage though is that most existing production boats could probably be upgraded by the owner for a reasonable expense.

Rob Lythgoe

Something I have never seen on a cruising yacht is buoyancy on demand. Would very strong inflatable bladders strategically located with canisters attached that could be inflated on demand/automatically not be an option? I went on a sea survival course recently and the main lesson learned was that I don’t ever want to be in a life raft! You may have guessed by now that I’m no engineer, but the fire-brigade routinely lift lorries with similar arrangements. Perhaps they could be concealed in cabin head linings like an airbag in a steering wheel.

Svein Lamark

Hey, John, I agree with you, a small boat can sail in the Arctic rather safely without bulkheads. I have pumped my way south two times without problems. In my motor boat I have a pump 12 kbm pr hour always running. This is maybe an overkill, but it keeps the boat dry. And I feel safe when looking at the empty pump every day. In my sailboat I have tree big pumps ready. They have never been used. But I do support Matts way of thinking very much. Matt has a good point that can be very relevant some day. This day I hope is fare away.

Alex Penninckx

The Etap Yachting sailboats are foam filled double skin constructions making her unsinkable.
Years of building this type of boats resulted in strong (double skin constructions) sailboats (20 till 46 ft) which, even with seacocks open, stay afloat and are able to continue the voyage. It is a question of knowing where to put the foam. Watertight bulkhead keeps in general the boat only afloat.
Nothing is perfect. A fire could destroy them. But this doesn’t dismiss us to build boats who are as unsinkable as possible. Many sailors forget this and prefer to appeal on rescue services and put these (volunteers) crews in danger.

Colin Speedie

Hi Alan

Etap were always one of those excellent builders who marched to a different drum. I liked the 39 a lot – it’s a pity they are no longer in production.

They weren’t alone in producing double skinned/foam filled yachts, as Sadler Yachts (UK) also did the same with some of their later models such as the 34. This allowed them to make the claim that they were unsinkable, which was true, but at the same time they were probably untenable as a ‘life raft’ in anything other than a flat sea. If my memory serves me correctly one was even put to the test after a collision with a freighter in the English Channel, and it worked – but it was a good job that conditions were mild, or the crew might simply have been swept away.

In my view all of the approaches (WT bulkheads/crash bulkheads/foam filled etc) have their place, and for an ocean voyaging boat should be considered seriously. But will they make a truly viable ‘get you home’ option? I doubt it – but they may buy you time to get a mayday out, satphone message, keep the pumps working and prepare to abandon (if that becomes necessary) in good shape. And there’s much to recommend that.

Best wishes


Erik de Jong

Hi Colin,

I had the change to have quite a few long discussions with the designer of the early Etaps (Jac. de Ridder). When he came up with one of the first Etaps, I believe the good old 22, he put one of these boats to the test himself.
If my memory serves me well, he and two of his buddies sailed across the northsea to proof functionallity of a flooded Etap. They opened the seacocks in a harbour somewhere in the Netherlands, let the boat settle at its new draft, and head out for the UK in a stiff breeze. The boat became extremely slow, maximum two knots or so, but it sailed, remained steerable, remained acceptably stable, and could even sail upwind. In any possible way much better and more comfortable compared to a life raft.
I think he did this in the late 70’s, well before I was born, but his stories are always interesting.

The big disadvantage is that you lose a lot of interior space, especially below the waterline.

Best Regards,
Erik de Jong

paul Mills

Hi Erik,

Your last para made me laugh out loud, in the nicest way…. . I guess with the boat flooded – below the water line- that does have the effect of reducing living space :0 ….. mind you it would be novel to be able to say in a 22′ foot yacht ‘I’m just going below for a swim,!

More seriously, I recall the Wayfarer sailing dinghy Mark V. The builders decided to make it unsinkable, and self draining on a mooring. They did this by raising the floor and filling the void with foam: result, after a capsize all the water trapped inside was above the waterline – and as a result the boat was completely unstable, and even bailing out without it capsizing again was a real challenge.

I am a big fan of Etap and also like a lot of the design thoughts that went into them, truly boats ahead of their time.



Horatio Marteleira

Watertight bulkheads are like seat belts – chances are you’ll never need seat belts, but you wear them anyway. My boat came with them – don’t think I would build them otherwise, but I like them anyway.
As for a flooded bulkhead affecting the capacity to sail or motor, I have this to say: I once motored into heavy weather in my Corbin 39 for many hours (please don’t ask me why] with green water constantly flowing over the deck. When I reached port, I noticed that the forward cabin’s mattress was soaked. Investigation revealed that the undersized drain plug in the sail locker hatch had clogged, along with the drain at the locker’s bottom that would have drained the water into to the forward bilge where it would be pumped out. The sail locker isn’t 100% sealed from the front cabin, so it actually overflowed into the cabin.
Moral of the story: that sail locker is very large and likely holds much more water than any of my watertight bulkhead compartments, except one, and I didn’t notice anything and made it port just fine lugging a huge water tank at the bow.
Other than that, I agree with most of what was said – it’s a matter of perspective.


Am someone preparing to become LD cruiser who has only done a little thus far, so with that caveat:

was watching a couple of vids of Roger Taylor (‘Simple Sailor’) re-fitting his new (mini) cruiser for long distance voyaging. His approach is to make things as simple and safe as possible for single-handing.

One can debate whether or not his approaches work etc., but in terms of this topic, if memory serves well he sacrificed one area in the bow and two compartments where the cockpit usually is to foam, the idea presumably being to achieve positive buoyancy no matter what happens to the hull structure.

Assuming his alterations work as intended, I think they have merit, for ideally every vessel should be as unsinkable as is reasonably possible.

Further, I find it hard to believe that it would add considerably to cost, and the marine architect above mentioned as much, albeit of course it might prove a design challenge in terms fitting everything into less vessel space.

In any case, there is an important distinction to be considered here: positive buoyancy compartments vs. watertight compartments/bulkheads. These are related design elements but with key differences. Personally, I think the buoyancy element is one worth serious consideration unless the size vessel you are contemplating is simply far too heavy for such features to be practically attainable.


An excellent discussion and glad you’re raising it. While sinking due to collision with objects isn’t that high a risk % – the location where it happens can be more inconvenient that sinking at the dock! Also, w.t. bulkheads can be closed even if a hose fails and limit flooding; maybe keeping the boat afloat.

As others have pointed out 10% extra cost isn’t likely. A few % at most. You already have to have bulkheads throughout the boat so you’re really only making them more robust for the pressure head and adding w.t. doors.

Sealing cables is done all the time with cable glands. Sealing steering cables? Run them in a conduit that is sealed and exits at cockpit sole level.

Distribution of w.t. bhds: you need smaller compartments at bow/stern so the boat doesn’t trim down as much. Bigger compartments can be in the middle where a flooded compartment sinks the boat more level. So that disrupts the arrangements less.

I think a flooded boat can make a better liferaft if it’s afloat. You have food, probably water, and a much bigger target for rescuers. Look at the abandoned yachts found still floating after the 79 Fastnet. Look at the numbers of people who died in liferafts.

Inflatable bags – we had a 30′ monohull with 4 bags. Cost same as a cheaper liferaft. No significant service cost because we could inspect ourselves and they were out in the open. However with a bigger boat the cost quickly exceeds the cost of a good liferaft. They also had to be bolted to structural members that could take the buoyancy force (~1.5 T from memory) and where the inflated bag would fit. Not easy.

A cheap compromise is to seal off under the V berth on smaller boats where you are most likely to strike debris. On larger boats have a big sail locker forward.

We have a cat with 7 w.t. compartments; 3 in one hull, 4 in another. Lots of peace of mind. We also have a false foam bow that has hit several big logs at 6 knots or so. Just crushes the foam/glass skin and we repair at next haulout. Acts like a car bumper with low speed collisions.

We also had a leaking shaft seal that started to fill the engine compartment. Transom of one hull was 1′ below normal when we noticed. Having a w.t. bulkhead aft of the engine room reduced the volume that came in. We stopped the leak, pumped out most of the water before the CG arrived. And continued on our way. Knowing your boat can’t sink under you provides a lot of peace of mind. We weren’t thinking “abandon ship” – we were thinking “better get this leak stopped before it soaks the interior”.

Eric Klem

Having worked on the commercial end of things, I have run into the USCG requirements for watertight bulkheads a few times. They require that any single compartment be able to be completely filled with no portion of the deck going underwater. This means that you end up with a few small compartments in the ends of the vessel and a few large ones in the middle. For example, a 92′ schooner had 5 compartments with all of the living accommodations in the middle 3 which were quite large. I also have first hand experience with seeing how much a poorly sealed bulkhead can leak (cracked seacock).

Personally, I really like to have a collision bulkhead up forward which is fully watertight on a boat that is small enough to be handled by a couple. This does create an interesting space issue because you can only store stuff up there that you don’t want to get to in rough weather assuming that you only have deck access. Most people carry enough stuff like bikes, spinnakers, etc that it can be filled with stuff that is not too dense allowing more accommodation space to be opened up aft if it is designed in from the start.


Bill Gardyne

Interesting discussion. One of the questions that has not been asked here is ‘What is the intent of watertight bulkheads?” Determining ‘intent’ is crucial to most issues but rarely teased out to focus the argument/s. In this case is it to:

A. Keep the boat afloat so that it can be sailed or motored to port?
B. Stay afloat in a form that can be salvaged (towed) to port?
C. Float long enough for safe egress?
D. Stay afloat long enough for the crew to be rescued?

These have very different requirements and levels of sophistication.

A monohull with its large hunk of lead stuck to the bottom really makes the issue of flotation when flooded problematic. Once lost, the boat is lost, however it may then allow it to float and make rescue more likely (e.g. Tony Bullimore in the Southern Ocean).

For smaller boats where watertight bulkheads are impractical, the provision of the needed 30 or 40 tonnes of airtight positive flotation is largely impractical so consequently keeping the boat afloat is not really an option if the source of the leak cannot be stemmed. Larger boats offer more options as long as the doors are actually used at all times, as John notes above).

Multihulls, on the other hand, normally float as they are not constrained by the aforementioned large hunk of lead. Their foam or timber lined or cored hulls and decks provide significant positive displacement, even upside down or after suffering catastrophic failure. There have been some extraordinary survival stories of sailors living for long periods in upturned multis (e.g. 118 days in the upturned trimaran Rose-Noelle). There are many respected multihull sailors who don’t bother with life rafts as they are safer to stay with the boat.

My father was a Master Mariner who did his apprenticeship aboard the last of the commercial sailing vessels that ran from Dunedin, NZ to London, i.e. via the Southern Ocean and Cape Horn in the late 1940s. He spent time sitting on the hull of the first of the Liberty ships that did not completely flip due to the previously unknown issue of sudden and catastrophic movement of the ballast due to bellying of the lightweight lower deck that allowed the fore-aft timber beams securing the load to become unrestrained.

I am based on th east coast of Australia, and experienced my first cyclone onboard a sailing trimaran with him when I was 9 years old and never felt afraid for my life. Apprehensive, yes. But not afraid. I have, however been beyond concerned on a heavy mono in big seas when we were launching off the top of huge steep seas that were breaking top to bottom and causing the boat to flex such that the windows were popping and leaking heavily.

As a consequence my attitude to safety is rather biased. My father’s advice was always to buy the best safety gear that you can afford and hope that you never have to use it. Today, I interpret that as the boat itself.

Regardless of one’s preference for the number of hulls taking us for a ride (I like sailor’s versions of all three forms – monos, cats, and tris, but particularly like aluminium cats), one cannot really argue that survival is probably better with a multi as one is less likely to have to step up into the life raft than with a mono.

However, as noted in your earlier post, most sinkings are due to poor seamanship rather than a poor ship.


William Koppe

Hi John,
I have put in watertight doors and only needed 2 in the accommodation as well as 2 into the engine room and 1 between the watertight sail locker and the anchor locker. The total cost of the 5 doors was A $20k . They were made in Italy.
All hull penetrations were made in the engine room except for speed and depth and sonar.
I moved the aft bulkhead a foot forward so that the rudder post was in the lazarette.
So losing a prop shaft or rudder is accounted for.
Then in the case of a serious leak I only need to inspect the the 3 items above.
In addressing the floating calculations, we need to also address the volume of the cockpit that becomes flooded. In our case we float 100mm deck above water.
This is still much preferable to a life raft and the comments in the 98 Sydney Hobart books illustrate the problems of a raft in big seas.

William Koppe

Hi John,
24M see for accommodation plan.
Watertight doors to forward cabin and galley to crew cabin.
The cockpit holds 8t of water
A US door supplier quoted $A20k for a single door.