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Old 05-03-2007, 09:17   #1
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Access to Catamaran's Water-Tight Compartments when Capsized

Very long title, sorry, but it is a question that's being brought up over and over again. If you have a catamaran with escape hatches and you flip and then open these escape hatches, your boat will sink further on that side because you've just compromised the air pocket in that hull. The boat will eventually sink till that hatch is underwater. My particular boat has escape hatches located just aft of the forward bulkhead for the anchor locker, in the inside of the forward heads around 10 ft aft of the bow and about a foot above the waterline. I would imagine in the event of a capsize, I would not open these hatches at all if I could swim under and out or under and in. Anyone thought this through with a good plan?
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Old 05-03-2007, 12:36   #2
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I've wondered the same thing. Also, many designers and multihull boosters make a fuss about how you can camp out comfortably in your overturned condo but when I picture my own cat upside down I see in my mind's eye waves sloshing back and forth and myself being tossed about like a dookie in a toilet bowl. I just don't see going back into the boat as anything but a very temporary visit to retrieve essentials.

So what to do? How to stay with the boat and avoid exposure until rescue? I think that if I were in a situation where I was truly worried about capsize I would see that I had a suitably sized parachute anchor out with adequate rode. I would then put on my wetsuit. Uncomfortable but warm. Then, what about trailing the inflatable off the stern. It will capsize but that's OK, I am at anchor. Then, if the boat were to flip I would (hopefully) make my way to the bridgedeck, retrieve the inflatable and secure it to the boat, maybe using a network of lines to the corners. If the dingy were equipped with some sort of shelter, even a small spray dodger, it would help quite a bit to avoid exposure. I would then curl up in the fetal position around my epirb.

Don't know how practical this would be but the best I can come up with.
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Old 05-03-2007, 13:46   #3
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Don't rely on a dinghy or liferaft tethered to the boat, the attachment points on neither will be up to the job. Start thinking long and hard about surviving inside the upturned boat, read John Glennie's book of the Rose Noelle. Anywhere outside the tropics you will die of exposure unless you are inside, in any sort of seaway you will be washed off the boat if you are outside. If you think your boat will be too low in the water add some buoyancy up high.
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Old 05-03-2007, 15:34   #4
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All cat's that I have owned or had anything to do with have had strong ropes with figure of 8 knot loop's every couple of metres , attached from the front beam back to a pad eye or some other attachment point aft.

This is a permanent thing, not done after a flip, and we have of these on the B/D panel.

You know have somwhere to attach your harness too and sonething to hold onto.

I also only sail on light composite cat's so expect them to be floating high in the water when rolled.

Hopfully i'll never put this to the test.





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Old 05-03-2007, 20:34   #5
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Quote:
Originally Posted by mikereed100
I would then curl up in the fetal position around my epirb.
From the March 2007 issue of BoatU.S. magazine:
Quote:
Second, many people instinctively want to clutch the beacon to them. EPIRBs work best floating freely. Both PLBs and EPIRBs need a clear view of the sky to function properly. Never obstruct the view of the antenna or hold the antenna. Holding the antenna causes the signal to radiate into you instead of into the sky.
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Old 05-03-2007, 20:57   #6
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I forgot to add "with the antenna protruding conspicuously from beneath my armpit"
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Old 06-03-2007, 06:44   #7
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Ah - the misnamed escape hatches. Should really be called reentry hatches as thats all they are good for.
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Old 06-03-2007, 11:37   #8
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[
Quote:
QUOTEDon't rely on a dinghy or liferaft tethered to the boat, the attachment points on neither will be up to the job. Start thinking long and hard about surviving inside the upturned boat, read John Glennie's book of the Rose Noelle. Anywhere outside the tropics you will die of exposure unless you are inside, in any sort of seaway you will be washed off the boat if you are outside. If you think your boat will be too low in the water add some buoyancy up high.
][/quote]
All excellent points and well taken. I agree it would be far preferable to spend ones leisure hours awaiting rescue inside the hulls rather than bobbing in a dinghy/liferaft.
My question is, is this really practical in most catamarans. I don't think it would be in just about any production boat where watertight compartments are of secondary importance to usable accomodation. It may well be possible, as Cat Man Do proposes, in a lightweight, composite boat with adequate flotation. The cat in the photo above seems to be floating pretty high. On the other hand I recall a few months ago an Atlantic 42 capsized in the great lakes. The crew were able to stay inside the boat but it looks from the photo that even this boat could have benefitted from a bit more flotation aft.

My own boat is very lightweight with dedicated flotation compartments forward, aft and in the crossbeams. Maybe the main hull would be habitable, but if rescue is a long time coming the hull will have to be breached either with a rusty axe or by opening a hatch. Once done this will cause the boat to settle further due to the loss of flotation from the main hull compartment. I wonder how long one can live waist deep in cold water. I am thinking hard about a dedicated compartment, sealed off from the rest of the boat, that could be accessed from the outside. Maybe a forward compartment that could be entered through a deck hatch. The hatch could then be closed behind. Inside the compartment would be an augur and keyhole saw to make an opening in the hull for air and bailing. Stashed within would be hammocks, wool clothing and perhaps a wee dram. Just thinking out loud.

The Rose Noelle is an excellent case in point but as I recall it was a trimaran which will be well supported by the flotation in the amas even if a hole is punched in the hull. If I ever capsize let it be in a tri.

Again, the above might be difficult to accomplish in a production boat like Cat Shot which is what got me to thinking about taking refuge in the dinghy. I still think it might be tried in a RIB with solid, 4 point attachments to the dinghy and boat but I hope I'm never that desperate.

Mike
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Old 06-03-2007, 12:15   #9
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My own boat is very lightweight with dedicated flotation compartments forward, aft and in the crossbeams. Maybe the main hull would be habitable, but if rescue is a long time coming the hull will have to be breached either with a rusty axe or by opening a hatch. Once done this will cause the boat to settle further due to the loss of flotation from the main hull compartment. I wonder how long one can live waist deep in cold water. I am thinking hard about a dedicated compartment, sealed off from the rest of the boat, that could be accessed from the outside. Maybe a forward compartment that could be entered through a deck hatch. The hatch could then be closed behind. Inside the compartment would be an augur and keyhole saw to make an opening in the hull for air and bailing. Stashed within would be hammocks, wool clothing and perhaps a wee dram. Just thinking out loud.

Mike

Chris White writes that some of the floatation can be built into structures like the bridgedeck. Perhaps even the cabin top could have an extra thick foam core. Maybe a call to the manufacturer to ask where they think the waterline is upside down, and whether they are relying on the area where the hatch to be sealed for floatation. My guess is that they did not calculate in that space as being sealed.


Read Lost. It's a novelization about a real story of a trimaran that capsized off of the PNW. They definitely weren't happy or comfortable, but they fashioned berths out of the water, so they could spend a lot of time out of the water, any moving around was in knee deep water. Never done it, but it seems to me a liferaft is going to be just as wet unless there are very calm conditions. Does your liferaft have the inflatable floor? If not you are basically sitting on the water as far as thermal protection goes. Any leaks and you're sitting in a puddle all the time.

I guess my opinion boiled down is that I believe life rafts suck, anything else is a step up.

John
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Old 06-03-2007, 12:37   #10
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That's a great idea regarding the hammock Mike. Taking it one step further, put provisions and supplies forward such as a VHF for hailing and GPS for stating coordinates and water and then putting these items under a net which would be anchored to the floor of the foreward anchor locker. In the event of a capsize, these provisions would be suspended, stay dry and wouldn't bang around too much, and the net then would become a hammock.
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Old 09-03-2007, 04:18   #11
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Quote:
Originally Posted by schoonerdog
Very long title, sorry, but it is a question that's being brought up over and over again. If you have a catamaran with escape hatches and you flip and then open these escape hatches, your boat will sink further on that side because you've just compromised the air pocket in that hull. The boat will eventually sink till that hatch is underwater. My particular boat has escape hatches located just aft of the forward bulkhead for the anchor locker, in the inside of the forward heads around 10 ft aft of the bow and about a foot above the waterline. I would imagine in the event of a capsize, I would not open these hatches at all if I could swim under and out or under and in. Anyone thought this through with a good plan?
Is your boat of cored construction? If so, it's not just the air trapped in the hull that keeps it afloat. The actual material it's made of is also very bouyant. Maybe a lot more bouyant than you would imagine. For instance, the materials for my boat weighed 2.5 tonnes, including all the packaging, a 200 litre steel drum, (of epoxy) a 200 litre plastic drum, 10x 20 litre plastic drums,(also epoxy) several large cardboard boxes, and 4 pallets, as well as the Duflex and fibreglass. It all occupied 4.5 cubic metres. Even without assembling it all into a boat (which has about 50 sealed bouyancy chambers) it would float high in the water. OK so that doesn't include the heavy bits like engines and rig, but even unassembled it has 4.5 tonnes of bouyancy, and it is only going to displace 5.2 tonnes fully loaded, and shaped like a boat.

A Duflex boat I know of that was flipped actually floated so high in the water it's inboard diesel engines hardly got wet. In fact only one of them needed a replacement alternator. Neither needed a rebuild. It was upside down for several days, and washed up onto a beach.

I would think it would be preferable to use the hatches rather than risk swimming under the boat, with all the ropes and other possible snags that would be present.
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Old 09-03-2007, 08:46   #12
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I think cored deck bouyancy gets a little over estimated in the difference it makes. My cored decks and hulls (above the water line) are only 1 inch thick, so that doesn't provide as much bouyancy as you would think. My boat weighs around 15000 lbs, 17000 when loaded with everything. My starboard hulls cored composite (40x5x2/12) translates into only 33 cu ft and provide just a little over 2000 lbs of lift if submerged, my cored decks are around 3000 lbs of lift, so cored construction still leaves me way shy of positive floatation. My only point would be that there's no substitute for large water tight compartments. My foreward sail lockers are 5.5 ft high by 3 ft wide by 8 ft long and behind an air tight door. Its an odd shape, but around 88 cu ft altogether. Were my boat to have a birth up forward with a small crash compartment below it and not be the existing water tight compartments, I would sacrifice over 5000 lbs of lift. It would go much more easily to the bottom should I be breached. All of which isn't particularly relavent to a capsize though because as long as your hulls aren't breached, hundreds of cu ft of the air in it is trapped and you have a LOTs of bouyancy. The problem is the moment you open that escape hatch, you breach your hull, the trapped air is forced out and you begin to sink much lower. I think that's the reason some catamarans put escape hatches in the bottom of the bridgedeck. Due to the salon door, it's probably going to be close to awash anyway and when you open it, you're not sacrificing the large captive air pocket in the hulls. You are also not tempted to open it under way for ventillation.
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Old 09-03-2007, 10:04   #13
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A Duflex boat I know of that was flipped actually floated so high in the water it's inboard diesel engines hardly got wet. In fact only one of them needed a replacement alternator. Neither needed a rebuild. It was upside down for several days, and washed up onto a beach.
That is very encouraging. On the other hand, as Schoonerdog points out, if the hulls were not breached they would be providing the greater part of the bouyancy. Cored construction can provide bouyancy but I wonder how much in practical terms. A couple years ago a Wildcat 36 got tangled up with a sandbar in El Salvador. The crew abandoned ship on surfboards and were picked up by pangas shortly thereafter. The boat was eventually towed into harbor. There were some pictures in Latitude 38 which showed the foredeck and cabin top barely poking above water (the boat was upright). Presumably the hulls were breached or filled with water due to wave action. I don't know how many watertight compartments the boat had but, while it didn't sink, there was no portion of the boat that would have been habitable.
I quess my point is that while cored construction may provide some bouyancy it's no substitute for watertight compartments, but of course you don't need to hear that from me as you already have 50 of them!
By the way, your boat sounds very interesting, is it your own design?

Mike
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Old 09-03-2007, 10:25   #14
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I looked, the wild cat has very little reserve bouyancy in it's bows, probably less than 10 cu ft, same is true aft. A well designed catamaran, made for survivability for a hull breach, should have sacrificial keels and large water tight compartments forward and aft. There have been boats like the PDQ 44 for instance which have been against a reef in a storm, in identical situations to the lost wildcat, and it simply lost her keels and then just glided over the reef with a no keel draft of less than a foot. No water intrusion whatsoever into any compartment of the boat. Puncture that type of boat forward, amidship, or aft and it will still be fully functional. But you have to give up interior room for safety, a trade off that many boat designers don't want to do because their boats are designed to maximize accomodations instead. I second the question to 44 cruising cat, whatcha building?
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Old 09-03-2007, 16:20   #15
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I'm building an Oram 44C. With a few modifications because of my height (6 foot 8) - the sheerline has been raised by 180mm, and the beam increased by 300mm. There are some photo's here: http://www.cruisersforum.com/gallery...00&userid=3477

Bob Oram is one designer who is happy enough to consider changes to his boats - (he might kill me for saying it though - it does create more work for him) he looks at what you want to do, runs the numbers through his computer, and tells you if it can be done or not, and what other modifications will need to be done as a result. (For instance, because I wanted to increase the beam of the boat, the uni flanges on the mast beam and back beam had to be increased, the composite chainplates were specced up slightly, and the shrouds will be of bigger wire.
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