Shetland - no life raft, no EPIRB/PLBs, no survival suits - would you?

[pmagowan]

You talk as if the idea of making the main bulkhead watertight is somehow a new and as yet untried concept. It isn't. Twenty five or thirty years ago when 'high latitude' or adventure sailing (call it what you will) was gaining momentum, making the front bulkhead watertight appeared to be one of those 'no-brainers'. After all, ice class ships, navy vessels and such like all had them, so 'obviously' it was the thing to do. As you say; "for the blue water cruiser with a plan to visit Greenland and the Northwest passage they seem like very reasonable and basic precautions".

However your other assertion that "It takes very little extra effort in both the design stage and in construction" proved to be very wide of the mark. There were some incidents amongst the Open class boats or Whitbread boats where these early implementations were found to be woefully inadequate to achieve anything like the imagined effectiveness. Further analysis , especially of the behaviour of part flooded small yachts in big waves showed the loads imposed on these 'water tight' bulkheads to be enormous and the engineering of effective structures both expensive and complex.

But this wasn't the reason they fell from favour. The real reason was that as more people gained experience of cruising in high latitudes, it became increasingly obvious that these watertight bulkheads were a solution looking for a problem. Yachts are not 'ice class ships' in either their capabilities or the way they are handled. Your analogy that they are comparable to seat belts in cars is inaccurate. They are more akin to having the drivers and passengers wear lifejackets in cars: it's conceivable that there may be situations where they might save a life of someone driving into a river or off the quayside, but are they worth it? Even for people who drive near the water regularly?

Any safety 'designed' into a boat should mitigate the 'risks' it will face in some hierarchical order. There is a litany of significant risks that could be addressed at the design long before a watertight bulkhead will show any benefit. Trips, falls, head injuries from the boom, rigging failure, badly stowed objects flying around the cabin . . etc, etc. And in the boat structure itself, some foam filled compartments at and about the waterline at the bow have proved to be both effective and easily implemented. Then at the aft end, research by the ISAF shows that hull structure damaged caused by issues with the rudder and drive gear to also be significant. Aft watertight bulkheads with access similar to lazarette openings are again well proven.

As for watertight compartments used to store things - well, all I can say is go look at a RNLI lifeboat and see what it takes to make a storage compartment truly watertight. Then imagine having to turn six heavy dog latches and swing a large metal door open, every time you want to get to the tea bags.

Thats rubbish, I'm sorry, but to compare a simple watertight compartment to the massive high impact watertight hatches of a specially designed all weather lifeboat is ludicrous. If you can build a boat which is just one large watertight compartment then I don't see it being beyond you to build an effective watertight bulkhead in one let alone non-structural compartments. Comparing it to a virtually nonexistent risk and ineffective solution for cars crashing into rivers does you no justice.

Boats sink and they do so in numbers every year. Most boats are not used in situations where the risk is even marginal yet still some sink. It is not beyond the wit of man to reduce the risk and since we are not building an all weather lifeboat required to slam into heavy seas at 30 knots then the engineering should be designed for the actual use envisaged. Front and back crash bulkheads are watertight bulkheads. They happen to be in the highest risk positions and therefore are the most important. However, it is quite possible to have additional watertight bulkheads with 'minimal' problems. If commercial builders are as incapable as you suggest I am glad I am not going for a commercial build.

Water is one of the basic things for which many constants are based in physics and engineering. It is not hard even without computers to calculate the effects of water on boats with various degrees of flooding. In my research I have seen multiple in depth analyses of such things ranging from ferries to dinghies. Many boats successfully include watertight bulkheads and watertight compartments without having the rather hyperbolic problems you envisage.

On a boat there are many risks. Some are unavoidable and simply inherent to the activity. I will continue to mitigate the ones I feel are reasonable to do so, lifelines, life jackets, fire safety, and protection from sinking. With modern composite construction a virtually monocoque construction can be achieved especially with the addition of structural bulkheads and the cost savings of such construction (particularly on custom boats) will easily justify the minor extra effort in designing the boat for the risks of the environment for which it is intended.

 

[TimBennet]

You sound like everyone else 25 years ago.
Then we built some examples.
Then we saw the results of things in practice.
Then we did the research.
Then we realised it wasn't so simple.

But hey, you know best.

 

[Tranona]

Thats rubbish, I'm sorry, but to compare a simple watertight compartment to the massive high impact watertight hatches of a specially designed all weather lifeboat is ludicrous. If you can build a boat which is just one large watertight compartment then I don't see it being beyond you to build an effective watertight bulkhead in one let alone non-structural compartments. Comparing it to a virtually nonexistent risk and ineffective solution for cars crashing into rivers does you no justice.

Boats sink and they do so in numbers every year. Most boats are not used in situations where the risk is even marginal yet still some sink. It is not beyond the wit of man to reduce the risk and since we are not building an all weather lifeboat required to slam into heavy seas at 30 knots then the engineering should be designed for the actual use envisaged. Front and back crash bulkheads are watertight bulkheads. They happen to be in the highest risk positions and therefore are the most important. However, it is quite possible to have additional watertight bulkheads with 'minimal' problems. If commercial builders are as incapable as you suggest I am glad I am not going for a commercial build.

Water is one of the basic things for which many constants are based in physics and engineering. It is not hard even without computers to calculate the effects of water on boats with various degrees of flooding. In my research I have seen multiple in depth analyses of such things ranging from ferries to dinghies. Many boats successfully include watertight bulkheads and watertight compartments without having the rather hyperbolic problems you envisage.

On a boat there are many risks. Some are unavoidable and simply inherent to the activity. I will continue to mitigate the ones I feel are reasonable to do so, lifelines, life jackets, fire safety, and protection from sinking. With modern composite construction a virtually monocoque construction can be achieved especially with the addition of structural bulkheads and the cost savings of such construction (particularly on custom boats) will easily justify the minor extra effort in designing the boat for the risks of the environment for which it is intended.

You seem in danger of re-inventing the wheel. As Tim says all these things have been tried - and not pursued - because in trying them it is often found that the perceived benefits do not pan out, and the losses are too great. Very few boats sink - suggest you read the YM series on trying to wreck a boat then you will realise how difficult it is to sink a yacht, even a simple cheap production boat.

You would perhaps do better by looking at what things have been tried in the past and learn from them by understanding why they have not become established, rather than trying to prove all the past experience is wrong.

You might also care to look at what seasoned voyagers wish they had more of to improve their boats and cruising life. Think you will find KISS principle rules together with things like more stowage, good light airs performance, easy handling, lack of chafe etc. You may well see that few of the things you ask about in relation to designing your perfect boat actually appear on the must have list!

 

[pmagowan]

You sound like everyone else 25 years ago.
Then we built some examples.
Then we saw the results of things in practice.
Then we did the research.
Then we realised it wasn't so simple.

But hey, you know best.

Ok, so what is the catastrophic consequence of sealing a structural bulkhead in a composite cold moulded monocoque hull so that it is watertight. There is no significant strengthening of the bulkhead required since it is structurally strong. The only thing required is attention to detail of the glass fibre filleting and bonding to the hull. Then there is the requirement to strengthen the door and give it a sealable gasket. No requirement for massive steel dogs or anything else.

 

[TimBennet]

Ok, so what is the catastrophic consequence of sealing a structural bulkhead in a composite cold moulded monocoque hull so that it is watertight. There is no significant strengthening of the bulkhead required since it is structurally strong. The only thing required is attention to detail of the glass fibre filleting and bonding to the hull. Then there is the requirement to strengthen the door and give it a sealable gasket. No requirement for massive steel dogs or anything else.

Are you certain your bulkhead won't need to be 'significantly strengthened? Have you taken the design of the boat, punctured the forepeak area, allowed it to free flood and then trim. What is the calm water hydrostatic head your bulkhead and door will have to resist?

Now add a reasonable 'average' sea state. What is the maximum head your structure will have to stand in such a sea state?

Now add in the dynamic loadings caused by all that water in the forepeak 'sloshing about'.

Finally predict the failure mode of the forward structure of your vessel that might occur after an impact great enough to cause this loss of hull integrity. Does such an impact compromise the structure of your bulkhead?

I presume you have answers to these questions in order to be certain that "there is no significant strengthening of the bulkhead required since it is structurally strong and no requirement for massive steel dogs or anything else".

 

[Concerto]

Ok, so what is the catastrophic consequence of sealing a structural bulkhead in a composite cold moulded monocoque hull so that it is watertight. There is no significant strengthening of the bulkhead required since it is structurally strong. The only thing required is attention to detail of the glass fibre filleting and bonding to the hull. Then there is the requirement to strengthen the door and give it a sealable gasket. No requirement for massive steel dogs or anything else.

Not forgetting to seal every cable, pipe etc through the bulkhead. Even then you will still get some leakage due to movement, no boat is totally rigid. Sorry pmagowan your idea is totally impracticable and too expensive to do. If you want to do it to your boat best of luck. Everyone else sails without and does not deem it to be a necessary essential to fit.

 

[PlankWalker]

More people drown in their car than drown at sea.
Should I start carrying a life raft in my car?

 

[pmagowan]

Are you certain your bulkhead won't need to be 'significantly strengthened? Have you taken the design of the boat, punctured the forepeak area, allowed it to free flood and then trim. What is the calm water hydrostatic head your bulkhead and door will have to resist?

Now add a reasonable 'average' sea state. What is the maximum head your structure will have to stand in such a sea state?

Now add in the dynamic loadings caused by all that water in the forepeak 'sloshing about'.

Finally predict the failure mode of the forward structure of your vessel that might occur after an impact great enough to cause this loss of hull integrity. Does such an impact compromise the structure of your bulkhead?

I presume you have answers to these questions in order to be certain that "there is no significant strengthening of the bulkhead required since it is structurally strong and no requirement for massive steel dogs or anything else".

I don't currently have the full scantlings for my boat as it is not at that stage yet. I am basing it on similar builds. For one thing the idea that significant 'sloshing' forces cause problems has been shown to be false in such cases. The effect of partial flooding (which a failure if a single bulkhead causes) is mitigated by the buoyancy of the remaining intact craft and also the inertia of a partially flooded structure reduces significant 'sloshing'. The forces to be resisted are significantly less than for, say, the transom, which also forms a similar watertight 'bulkhead'. When the structure does not require normal frames due to the composite cold moulded on strip plank design it is useful to have a structural bulkhead to help stabilise against flex and twisting forces. Since this has to be structural anyway and bonded to the hull then it requires only minor modification to make it watertight. It has been done in a number of custom cold moulded yachts and the construction techniques are described in detail in a number of books on this construction method. In standard GRP it would require much more extensive modification as internal bulkheads tend to be far less structural and many boats have a framed construction where ribs provide much of the structural strength.

i am still interested in why it would be a bad idea to take care of making a good bond with the hull or with making a two ply door to match the bulkhead.

 

[pmagowan]

Not forgetting to seal every cable, pipe etc through the bulkhead. Even then you will still get some leakage due to movement, no boat is totally rigid. Sorry pmagowan your idea is totally impracticable and too expensive to do. If you want to do it to your boat best of luck. Everyone else sails without and does not deem it to be a necessary essential to fit.

Cables do not need to be sealed, you simply run them above the flooded waterline. The idea is to keep the boat afloat so these bulkheads will only ever have to deal with partial flooding, the whole rest of the boat still acting as buoyancy. They also do not have to be totally watertight. They only need to keep enough flow rate down so that pumps can keep up. There would be relatively little pressure as there is still buoyancy. The only place where it could leak is from the door seal as the rest of the bulkhead would be integral to the structure of the boat.

This is not a new design feature for blue water cruisers.

 

[pmagowan]

More people drown in their car than drown at sea.
Should I start carrying a life raft in my car?

Only if you really don't understand statistics

 

[GHA]

Or, in other words, safety gear is the stuff you use to avoid using the life saving gear.

Using that definition I would suggest that life saving gear should only be addressed after you've done everything you can think of not to need it.

 

[basic]

Having sailed all my life without a raft a friend who thought I should have one swapped his with me for a Walker log. It is a good quality Avon ocean 4 man and I have serviced it myself twice in the last 10 years so I know it is in good condition. I still despise it for the space it takes on the boat and its weight but can't bring myself to dump it.
I think its best not to get this stuff in the first place. What you never had you never miss.

 

[GrahamM376]

so what journey is too short to not need a life raft?

should every yacht, no matter how small, have a life raft?

D

I think it's more a matter of where you sail, how many other boats are around and water temperatures. Sailing off the Algarve in winter I can survive in 17 degrees water for quite a long time and there are many other boats around whereas, in cold remoter UK waters, I would most likely have died with hypothermia by the time help arrived.

Most boats are in coastal waters where there are far more things to bump into so, yes, in an ideal world, boats would be safer if all had some type of flotation raft, not necessarily a full blown life raft.

UK boaters have life easy as safety equipment is down to personal choice which I agree with. Here we have no choice, life raft (and lots more) + life jackets carried (not worn) in the tender or, potential big fines. Recent legislation now dictates all fisherman in small boats have to wear life jackets.

 

[JumbleDuck]

Ok, so what is the catastrophic consequence of sealing a structural bulkhead in a composite cold moulded monocoque hull so that it is watertight. There is no significant strengthening of the bulkhead required since it is structurally strong. The only thing required is attention to detail of the glass fibre filleting and bonding to the hull. Then there is the requirement to strengthen the door and give it a sealable gasket. No requirement for massive steel dogs or anything else.

A 50cm square hatch with 2m of water above it (smashed bow hitting a medium wave) will have a force on it of 1000 x 2 x (0..5)^2 = 500 kgf. I'm pretty sure that the catch on my chain locker door won't take half a ton.

 

[JumbleDuck]

Using that definition I would suggest that life saving gear should only be addressed after you've done everything you can think of not to need it.

Yup. Spot-on.

 

[pmagowan]

Why would an internal hatch have 2m of water pressure on it even with a massive breach in the hull?

 

[JumbleDuck]

Why would an internal hatch have 2m of water pressure on it even with a massive breach in the hull?

Which bit of "smashed bow hitting a medium wave" was unclear? What do you think the maximum pressure difference across the bulkhead might be when the compartment is flooded?

 

[pmagowan]

Which bit of "smashed bow hitting a medium wave" was unclear? What do you think the maximum pressure difference across the bulkhead might be when the compartment is flooded?

I am not sure I am understanding your question. You said 2m 'above it', so I presume you are refering to a hatch in a watertight compartment, not a main bulkhead. I don't see how a hatch in a compartment would have 2m above it since there is not room unless the whole front is ripped off, in which case the compartment is not watertight anyway. A wave, casing a pressure surge equal in effect to it's height could potentially be problematic in this unusual situation but since a hatch would be top opening there would really be little problem making it almost completely watertight.

If you actually mean the whole front of the boat has been ripped off and the forward watertight bulkhead is now open to the sea than it also will not have a 2m head above it as it is verticle, not horizontal. The force from water pressure would be relative to the height of the flooding and different in different parts of the bulkhead. A wave, smashing in to the bulkhead would exert considerably greater force than simply the head of water, as you calculate, in this extreme example. Even so, the door or 'hatch' would be forward opening so the force would be to close it and thus spread reasonably evenly. It is possible that extreme conditions could breach this but it is not beyond the ability of engineering to design it for most reasonable scenarios.

The actual bulkhead would be fully bonded to the hull, and thus integral. It would be double skined and cored. It would be braced from deck to floors. All this would simply be a requirment of the design without it being watertight. If you take a can opener and take the bow off what you would expose is similar to a transom and it would have to stand similar forces. The door would be the weak point but as I said it would be strongest in the most likely scenario of hull breach.

In my research I have found that the extreme example you have made is very unlikely to occur. Much more likely is a failure of a through-hull or a problem with keel/hull join or evn, rarely, a hull breach from a collision. In all these scenarios the past examples suggest that the conditions internally are much less severe than you alude to.

 

[doug748]

pmagawan could have a point. 1min 50 in:

 

[JumbleDuck]

I am not sure I am understanding your question. You said 2m 'above it', so I presume you are refering to a hatch in a watertight compartment, not a main bulkhead. I don't see how a hatch in a compartment would have 2m above it since there is not room unless the whole front is ripped off, in which case the compartment is not watertight anyway. A wave, casing a pressure surge equal in effect to it's height could potentially be problematic in this unusual situation but since a hatch would be top opening there would really be little problem making it almost completely watertight.

OK, now I am completely confused. I thought you wanted a waterproof compartment at the front in case of a collision seriously damaging the bow - in which case I reckon the ability to withstand a 2m head would be the absolute minimum. And, of course, depends on having a collision hard enough to bust open the bow but not hard enough to damage your bulkhead.

Now I think you're saying that the compartment is more like a buoyancy tank for a dinghy, keeping the boat up if the hull fills. The cruising weight of my 26' boat is four tons, so allowing for a bit of buoyancy in the materials I would need three cubic metres of watertight compartment to keep me afloat. How much are you planning for your world-girdler, and what's yourr projected displacement?