Access to Catamaran's Water-Tight Compartments when Capsized

[mikereed100]

I've long been an admirer of Oram's designs. I like the way he takes a certain accomodation and puts as long a hull on it as possible rather than taking a certain hull size and packing as much accomodation in it as possible. If I were to build from scratch it would probably be an Oram 44 (with the front cockpit, just to piss people off ).

[maxingout]

Our Privilege 39 catamaran has the "escape hatch" in the bridgedeck in the salon area. I have often wondered whether the hatch would be submerged if the cat turned over. I really don't know. I suspect that I might need a snorkle to get in and out of the yacht through the escape hatch.

When we were cruising in New Zealand, I saw an Atlantic 48 that had survival compartments built into the forward bow compartments. There was a large interior hatch going through the forward bulkhead inside the yacht into the bow compartments. The accomodations inside the bow compartments were arranged upside down in such a manner that the compartment would be habitable (right side up) when the catamaran was in the inverted position. Interesting concept. You live in the normal section of the yacht in normal conditions, and if she ever goes over, you live in the bows.

It was an interesting solution. At least if your yacht goes over, you might have a semi habitable space to insure your survival until help comes.

Cheers,

Dave
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[Moby Dick]

while you can go 'overboard' (sorry) in thinking about inversion scenarios (which are so unlikely in a cruising cat) has anybody looked at would happen in a Lagoon 420, when you have gawd knows how many KwH of batteries getting very wet in sea water?

[Intentional Drifter]

I happen to be reading "Fatal Storm" at the moment, about the Syndey-Hobart race disaster. Although they were mono's in that storm, the crew stories about the conditions in their rolled/capsized boats are truly horrific. I really don't know that the difference between having the contents of 4 or 6 lead acid batteries vs that of 12 would really make all that much difference. Whether you're in the 6th circle of hell or the 7th, you're still in hell. Keeping yourself from being in those conditions in the first place seems (to me) to be the better strategy to take.

ID

[ess105]

Inverted lead acids may not be so much fun but you don't have to go with these. Also, in the medium term future I'm pretty convinced there will be no lead acids on these boats.

In the end they may turn out to be an extremely useful resource. As they are under the bed, they'll actually be at the high point in an inverted boat. That means they stand a good chance or remaining dry and therefore being a source of energy if one is sufficiently prepared to utilise them. Being able to flip over to an emergency 72V emergency lighting / heating solution would improve survival prospects - particularly if this could be used to attract attention at night.

Plenty to think about ....

Steve

[Moby Dick]

I was meaning less the possibility of acid spillage, and more the possibility of electrolysis. Some cats have the batteries outside the living compartments, but I beleive the Lagoon 420 batteries are in the cabins. So even if they are above water, I presume (maybe not, if it has been thought about) at some point you will have bare terminals under water at 72V driving electrlolysis of seawater = chlorine production

[adamskiinasia]

What about closed cell foam sealed in places of no use like the roof of the deck ? I've seen barges float literally tons on just them. Surely a 10 foot X 10 foot X 1 foot slab on the deck roof (yes the deck roof would have to be raised) but that would surely float a 5 metric ton boat and not hinder its comfort OR performance. Or for that matter, why not the underside of the deck. For example as said a huge slab under there. If it capsizes then the deck "foam pontoons" could conceivably keep both hulls out of the water ?

Or what about a high pressure gas (like car air bags) system again, under the deck. Whereas the boat capsizes the inversion causes the bag to deploy. Yes the air bag system would cost 5 grand but it would save the boat and its occupants I would think. Perhaps get a better price on insurance ? Just thinking out of the box.

Possible ?

[GordMay]

Foam materials are usually available in different densities and different forms. The density refers to the weight of the foam per cubic foot of material. In order to determine the net value for flotation purposes, the weight of the foam per cubic foot must be deducted from the weight of the water per cubic foot. For example, salt water weighs about 64 lbs. per cubic foot, and fresh water about 62 1/2 lbs. per cubic foot.

If the foam being used weighs 2 lbs. per cubic foot, this will leave a net flotation value of 62 lbs. per cubic foot if the boat is used in salt water, and a net flotation value of 60 1/2 lbs. per cubic foot when the boat is used in fresh water. It can readily be seen that the lighter the density of foam used, the higher the flotation value per cubic foot of volume.

So, your 10 x 10 x 1 foot foam slab (100 Cubic Feet) would only support about 6,050 pounds of boat (100 x 60.5) or about half your 5 ton assumption (11,000#).

[Dockhead]

Originally Posted by GordMay

Foam materials are usually available in different densities and different forms. The density refers to the weight of the foam per cubic foot of material. In order to determine the net value for flotation purposes, the weight of the foam per cubic foot must be deducted from the weight of the water per cubic foot. For example, salt water weighs about 64 lbs. per cubic foot, and fresh water about 62 1/2 lbs. per cubic foot.

If the foam being used weighs 2 lbs. per cubic foot, this will leave a net flotation value of 62 lbs. per cubic foot if the boat is used in salt water, and a net flotation value of 60 1/2 lbs. per cubic foot when the boat is used in fresh water. It can readily be seen that the lighter the density of foam used, the higher the flotation value per cubic foot of volume.

So, your 10 x 10 x 1 foot foam slab (100 Cubic Feet) would only support about 6,050 pounds of boat (100 x 60.5) or about half your 5 ton assumption (11,000#).

The calculation is not quite that simple since a boat which weighs 6,050 pounds in the atmosphere will weigh somewhat less when immersed in water. The weight would only be the same if the density of the boat were infinite.

[GordMay]

Originally Posted by Dockhead

The calculation is not quite that simple since a boat which weighs 6,050 pounds in the atmosphere will weigh somewhat less when immersed in water. The weight would only be the same if the density of the boat were infinite.

Indeed.

Should specific gravity = 1.0 be substituted for infinite density of boat?

For a more detailed look at the calculations, see ABYC H-8
“Buoyancy in the Event of Swamping”
Here ➥ http://newboatbuilders.com/docs/H-08.pdf

[adamskiinasia]

Wow, and here I was thinking all you 5 star members were salty dogs and now I have to go reference physics formulas ! Excellent.

Well, my point wasnt exactly that my slab would support the boat but whether or not A slab could support the boat. I've watched curiously the construction of some decks and noticed them using what looked like 2 inch sheet styrofoam fit into the underside. I thought to myself. Is that supposed to be for buoyancy ?? In the event of ....?

So do you think that foam foam foam is just not feasible ? Rather than a water tight compartment at both ends why not a foam compartment at both ends of each hull, then you wouldnt have to be cramped up atleast. Again, I dont know much about how foam in either end of the hull would affect the boat's handling.

Am I wrong to assume the Atlantic 57 had air tight compartments ? When I saw it on youtube it looked mostly submerged. Wasnt sitting very high. Is that the best 500,000$ can do in terms of design ?? I must be missing something about design cause it seems that an excellent quality boat such as the Atlantic 57 would have contingency ?

O.K what about , lets call it an "Inversion air bag" or IAB for short. For all I know they have them already. How much does a very good quality survival covered liferaft cost ? I think they are very expensive. O.K granted the ones I am thinking of are designed for oil rigs in the north sea and can hold up to 20 men but ... That a cat won't sink and has area for an IAB might make it MORE feasible than a life raft and at the same time, almost as importantly, save the boat ! ...?

[David M]

Much of the decision comes down to water temperature and how soon hypothermia would set in within colder waters. Even if you get into raft because of cold water temperatures, stay with the inverted cat because the combination of them both make for a larger radar and visual contact with which to be seen.

Even if the air inside was not contaminated, it would not be long before the oxygen drops to unacceptable levels.

[adamskiinasia]

I see. But even in the raft , there's exposure is there not ? My point was that I read everywhere about "water-tight compartments" built into these expensive boats and other than keeping this boat from sinking is that the only purpose or is it to provide a haven ?

I'm interested in building a kit cat and want to understand the logic of these designs and if designers still give you that option. I had no idea boats as stable and heavy as cats still capsize !! A 500,000 boat is nearly trashed because the sheets wouldnt release quick enough as the blow came in ? I must be missing something or perhaps people dont think of contingency cause they know they are insured ?? I'm not a salty but I know it would cross MY mind.

[sandy daugherty]

After a career investigating fatal accidents, I tend to focus on survivability in the initial event that causes the capsize. These are horrific circumstances, and they will continue for hours before any action beyond holding on for dear life can be considered. No one is going to cut holes, round up resources and cook dinner until the storm abates.

With water rushing into what had been a safe dry place that is now too dark to see, filled with roaring, screaming and tearing noises, frightening smells and painful injuries; rational thought and super human heroics are just not happening. If you think you would react differently, you have never been really scared. This scenario is really, really scary. Some people do incredibly stupid things, most can do nothing at all.

The vessel must provide all the security and protection for the duration. It must not rely on complicated systems, auto-inflating airbags, or foam dispersion. And a boat with a boat-sized life preserver on is not a pretty picture.

So: It has to have water-tight compartments. They must be high enough in a right-side-up vessel to float it with survivable space inside. They don't have to be inaccessible, just airtight for several hours.

for long term survival, say 48 hours or longer, one sufficiently large space must offer a way to get out of the water, get fresh air, have enough light, and contain emergency supplies. It must allow ingress and egress, and preferably be where Epirbs, flares and such are stored.

The idea of swimming around under an inverted sailboat with broken spars, rigging and sails ready to snare the foolish diver is not to be entertained.

A life raft is the last option; only a fire would justify leaving a floating multi. Any space you can get in and out of is preferable, and something as large as a cruising catamaran is infinitely more desirable, neh?

So be a bit more realistic about what you need, and a lot more careful about how far you push the envelope. And remember the lesson from Chris White; all it takes is a 64 knot gust when you can't reach the traveler.

[neelie]

I have often wondered just how watertight those compartments really are. What with deck fittings, stanchions, rub rails etc etc screwed in - 101 pathways for water ingress. I think they may not be the panacea which we are planning on.

Is there a case to made for filling up the voids with polystyrene foam blocks or similar?