Unsinkable

[uranus]

Please excuse my ignorance (and I'm new to this forum), but . .

With the obvious exception of RIBs, I never see any reference to safety buoyancy on larger power craft. In dinghies and workboats it's a given that there'll be a reserve of buoyancy in the hull, but as soon as one moves into the world of larger and more luxurious craft, all mention of the subject disappears.

Collisions with rocks, flotsam and other craft are still possible in expensive boats!

What happens to a shiny new Windy, Sunseeker, Princess etc. if the hull is holed?

Does it just go to the bottom?

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[BrendanS]

There was a Princess tied up at Sheppards pontoon in Cowes last Saturday doing it's very best to go to the bottom. Don't think it was a hole though, more likely a seal or skin fitting. The amount of water they were pumping overboard was amazing. If they hadn't got a pump going, it would surely have sunk. It came up about a foot once they got the ingress under control despite the fact that must have been pumping near on a gallon a secon

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[Happy1]

What's up uranus? Are you worried about the one you have, or are you afraid of being shafted by a salesman who is not telling you all? Are you sure you are ready to go larger yet if you have these concerns? Big is not always safer, especially if you are concerned about a hole, the bigger it is the longer it may take to go down. I am taking my time before I try anything bigger, although it is tempting to just go for it sometimes.

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[jfm]

Yes, if holed badly they sink. Plenty have. Difference is these boats are big enuf to carry liferafts etc and also they're v unlikely to capsize (remember, the main reason for buoyancy tanks in a sailing dinghy is not risk of getting holed, it's risk of capsize. If a dinghy is holed, it's likely to be inside a buoyancy tank). And of course the market doesn't want buoyancy tanks the size of a bedroom, which is what a big mobo would need.

There are exceptions, eg boston whalers, but they cheat slightly by putting buoyancy into a space that was no good for anything else anyway.

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[hlb]

Bigger ones are made with bulk heads. The idea being that the front or back might go down but the other end dont.. Whether this works in practice will depend how many holes the electician or others have drilled through the bulk heads!

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Haydn

 

[jfm]

dont rely on bulkheads in MoBos

But the bulkheads are not exactly full bulkheads. They reach to the cabin sole, no higher. So about 1 meter up from the keel! Above that, bulkheads have (non watertight) flippin doors cut into them!

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[uranus]

>> Difference is these boats are big enuf to carry liferafts etc

Liferafts are not always an attractive option . . never mind the pain of seeing your pride and joy go down.

>>There are exceptions, eg boston whalers, but they cheat slightly by putting buoyancy into a space that was no good for anything else anyway.

Is that cheating? Sounds like good design to me! Shame that Whaler only make fishing boats. I see that they claim that their "350 Defiance [is] the only boat of its size that can stay afloat if it's holed or swamped. "


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[tcm]

Re: sinking time

agreed, they sink. But only with big whamming hole in the hull, quite few example last year between the islands off Cannes. But if you hit a pot marker or somthing harder at 30 knot,s the water wooshes in nice and fast. If you whack it by crucnhing gently into the side iof the rocks you get long enough to pack your stuff. Otherwise you might have time to put in a vhf call, or not, cos it is quite quick. Another great way to hit the bottom is to have a sterndriove and rip one of them off on a rock, leaving a big hole, then zoom back to the marina and wave arms to lift you quick, then sink inside a minute, at least you are handier to get back in the car and drive home.

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[jfm]

No, you need a more balanced approach to risk. Big MoBos getting holed and sinking is very rare. It's so unlikely people wd rather not spoil the boat by having massive buoyancy tanks. If it holes, it sinks, sod it. All insured. Very very unlikely. Whereas big buoyancy tanks are very very likely to spoil pleasure of using boat. Liferafts are indeed unattractive, so is a plane crash yet we get onnem every week without even a parachute. Point is, both very unlikely

Re Bostons, I was saying cheating lightheartedly. Of course they are fab design. But they do only put buoyancy where it is out of the way, so as not to spoil boatshow/showroom appeal. They dont only make fishing boats though, they have very nice outrages and some cabin-adorned 30 odd footers now.

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[hlb]

Re: dont rely on bulkheads in MoBos

Arr. But. So had the Titanic. It had doors too and bulk heads only came part way up. So the idea being that if you get a hole in the front.. The other two tanks wont let you go down, well only a bit anyway. But similar to Titanic. I have two big exhaust pipes go straight though my back bulk head. So thats a fat lot of good. But in the African Queen. That did not sink, just turned upside down, cos of the steam engine, now acting as the keel. So it blew up the nasty German thingy, just before Audry Hepburn and that bloke got hung and saved there lives.
Hope this helps!

<hr width=100% size=1> <font color=blue>No one can force me to come here.<font color=red> I'm a volunteer!!.<font color=blue>

Haydn

 

[LeytonC]

Welcome to the forum!!!

I carry different sized rubber bungs just incase of skin fitting problems
(and its happened to me when i first had the boat, had 2 inch hole with
large amount of water coming thru it)

if is a big hole (and you can get to it), stuff anything u can in to it to slow the flow down so the pumps can cope with it eg. sleeping bags, quilts, pillows etc etc.

otherwise its a case of mayday and overboard!

IMHO

Also, fill your profile!



<hr width=100% size=1>Thanks

Leyton
(EXTAR Solutions - Software that works for you)

 

[uranus]

>Re Bostons, I was saying cheating lightheartedly.

I guessed you were . . . .

> Of course they are fab design. But they do only put buoyancy where it is out of the way, so as not to spoil boatshow/showroom appeal.

What in my naivety I find odd is that they are the only people so to do. No doubt there are some cost and performance drawbacks, but if one is buying a Sunseeker one is past the stage of counting pennies, and do the Whalers perform so badly? Perhaps Whaler have patents, but I doubt it.

>They dont only make fishing boats though, they have very nice outrages and some cabin-adorned 30 odd footers now.

They do. But they have no sense of style, sadly.


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[hlb]

Sinking is mostly about navigation. So mostly if you do not want to sink. You navigate around the rocks and things that are liable to sink you. Having a bigger boat is much help with this and also keeps you keep dry whilst doing it. Boats are a bit like cars. Cars dont like it when they meet water. Boats like wise, dont like it when they meet land. Other wise both are ok.

<hr width=100% size=1> <font color=blue>No one can force me to come here.<font color=red> I'm a volunteer!!.<font color=blue>

Haydn

 

[qsiv]

Re: sinking time

..and its also a function of space. My current boat displaces 28 tonnes - that would imply a bouyancy volume of 28 cubic metres. Okay - it's a sailing boat so it's heavier. My last boat ( a Nelson 40) displaced around 12 tonnes, so I have to find room for 12 cubic metres of bouyancy. The engineroom is full of hot machinery, and the space is needed for maintenance. So it has to take space out of the accomodation. If 4 inches of foam went around the entire hull, except the engineroom, then that might be close - but you've still reduced the internal volume by 12 cubic metres - and there were only about 40 cubic metres to start with...

All that and I cant EVER remember an instance of a similar boat sinking (I know of one or two that got up close and personal with 'coastal features'), so the risk reward ratio seems imbalanced. Added to this foam bouyancy is prone to breaking down, and damage from either water or sovents, and makes repairs extraordinarily difficult. Oh - and you've added weight and cost (you'll need a liner now as well). I know Etap do it - but the fact ther'es only one builder (of yachts) shows how highly the customers as a whole value the technology

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[jfm]

Uranus:

The space that Boston fill with foam is not really available on big MoBos. Take a look, down there is lots of piping, aircon/heat ducts, pumps, shower sumps and such like, plus engines. Well, it is available, but no-one wants to give it up to foam filling gunge

The whaler has a double skin hill. No large MoBo has ever been built that way, too difficult to tool up I guess - the production runs are often just 100 or so boats. JCL half did it in the 70s, they had a two part mould so there was gelcoat both sides but that wasn't a double skin with a gap to stuff foam in.

But seriously there is no demand for it. No one wants a MoBo with a dozen cubic metres of buoyancy space. The risk of holing/sinking is just too remote.

I'm outraged by your whaler comments. No style! How can you say that! They are beautiful boats!



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[Chris_d]

My Cruisers 224 has positive buoyancy, its 25ft with a 4 berth cabin and definately not a fishing boat. All the areas under the vee berths, toilet, galley, floor and
engine compartment are full of foam. I wouldn't like to put it to the test and with extra weight added it might only delay a sinking, but its nice to know its there and it certainly reassures SWMBO. It would be harder to find areas for enough foam on a larger boat, but not impossible. It will be the usual excuse, if the market doesn't
want it why spend money on it, "safety doen't sell you know".

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[Dave_Snelson]

Triumph make a range of boats from Roplene (like thick hard polythene), which is tougher than GRP and lighter than water. They just cannot sink. If reports are true, they can take a full whack from a sledge-hammer without damage. They only make up to sports cuddy size though, cos apparently making one huge plastic mould is technically difficult.

I do see your point though....

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[tcm]

Re: Unsinkabilty - useless on a big crusier

Note that the unsinkability of a crusing boat would be a lifesaver, not a boat-saver. Fill a 30+ foot boat with seawater and the thing is fit for scrap. You lose the boat either with or without in being unsinkable. So the unsinkability would at least eliminate the need for a liferaft? Nope - if there's a fire you need to get off immediately. Forget "unsinakbility" in a biggish crusiing boat.

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[tcm]

Can they take a 1 ton punch with a sharp pickaxe? Or a run up the rocks at 25 knots? Or a nice petrol fire in the bilge? - even if the boat can take these things, the occupants can't. You still need a liferaft, tho tough materials are useful for whamming around in shallow water/rivers. imho

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[jimi]

Re: Unsinkabilty - useless on a big crusier

probably fire is about the only situation you're liable to need to deploy a liferaft fast (other than a catatrophic collision) .. so in this context unsinkability is irrelevant to the decision to carry a life raft. Also where a liferaft is carried then becomes critical ... you're not going to be able to fight through a fire to get 40kg (or whatever it is) of liferaft extracted froma locker and then deployed. It needs to be in a postion where it can be deployed from its storage location. All IMHO of course

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