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Old 08-03-2008, 10:54   #1
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Watertight doors on cats.

Ok...possible dumb question. I keep reading about catamarans having watertight compartments divided by of course, watertight bulkheads. The forward collision bulkhead being one and an aft bulkhead between the living area and the engine space being another. But I keep reading about multiple watertight compartments throughout the hull. In all the pictures I have seen of the interiors of catamarans, I have never seen anything that resembles a watertight door..and I mean a door that can be dogged down and made 100% watertight. Do true watertight doors exist on catamarans?
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Old 08-03-2008, 11:06   #2
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The water-tight compartments are typically not accessed by a door, but rather are areas that are sealed off to provide floatation. Very few production cats have real watertight doors, even at the companionway.

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Old 08-03-2008, 11:07   #3
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Old 08-03-2008, 23:38   #4
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I haven't seen any on production boats but not too difficult to do on your own. My boat has elliptical doors that are dogged down. Watertight but I can squeeze through when open.

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Old 09-03-2008, 09:50   #5
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Prout 45 has dedicated compartments forward and aft with watertight doors secured by acorn nuts. Very rugged construction that I've heard broadblue continues. I've also seen pictures of Atlantic 42 using the escape type hatches often found in the hulls of catamarans on the inside forward bulkhead providing access in case of inversion. Our particular boat has around 100 cu ft forward bow compartments with access hatches which I will make watertight similar to the Prout 45. By simply creating a flange around the inside of the door, putting in a gasket and then securing with anchored bolts and acorn nuts. Very straight forward easy solution. I imagine creating water tight doors to the cabins could be done if you also provided dedicated bilge pumps and put the conduits for water and electrical up high so the limber holes don't destroy the integrity of the compartment. A friend just got a birthing pool which is a portable hot tub which consists of simply foam walls held together by plastic fittings into which a plastic liner snaps. I was amazed that it actually worked, about two feet deep which is tremendous pressure. You could also make half height doors which would serve as koffer dams.
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Old 09-03-2008, 11:56   #6
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On the FastCat 435 and 455 we have 3 forward water tight compartments and the third one is accesable with w 500 x 500 mm watertight lexan hatch.
The rear transom of the boat has 2 water tight compartments aft of the rudder stock and one 1.8 cubic meter compartment under the king sized beed on each side .
There are more spaces that contain air and are water tight and we have well over 6 cubic meters of closed cell foam installed in the boat.
Our compression beam and the connecting beams are also foamed up so in case of a capsize or pitchpole these will also help in keeping the cat afloat.
I have looked at water tight doors and there is a Dutch company called rondal that produces these for Superyachts but the weight and the price are prohibitive for the type of Cat I want to produce.
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Old 09-03-2008, 14:34   #7
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The Leopard 40 (Moorrings 40) has sealed off bow compartments, plus 2 underbed sealed off compartments in both hulls under the bunks which can be used as storage, but it is actually kofferdams to above the waterline.
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Old 09-03-2008, 16:40   #8
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The question about watertight doors makes unnecessary assumptions-

You don't have to have watertight doors to have watertight compartments, if your access to compartments is via the bridgedeck, as in Wharram designs, for example. In your typical mid-side cruising catamaran, which is what you seem to be assuming, this assumption is valid. However, you don't have to do the usual, and use your deck house and hulls as companionways. Designers who think that they are saving weight by using the cabin as a connector instead of a beam for the forward half of the catamaran (exclusive of any relatively light connector right forward,) have not reckoned with the weight effect of making a larger house than necessary, and losing accommodation space by using the hulls as companionways. IMHO, the typical design comes from the effort to make the most of a given length, probably in order to keep marina fees down. ***** ***** ***** ***** ***** ***** ***** ***** If this is not a design goal, you can make a much lighter and more efficient catamaran with a higher speed potential by making the boat longer, and stuffing less into the design by making a much smaller deck house and omitting berth shelves. If you stretch the typical 45' design into a stripped down 65' design, you gain waterline length, keep the same weight and accommodations, and go faster for the same $$$. Such a vessel can easily have 10 watertight compartments, 4 complete heads with showers, 2 single compartments with no showers, and spacious engine rooms. The only downside here is a higher fee if you are going to keep it in a marina, and higher hauling fees. ***** ***** ***** ***** ***** ***** ***** IMHO, catamarans don't need to be hauled except for fairly serious hull work, as they dry out so nicely, or at least, can if designed to do so. Also, as they don't roll much in a swell, and are (can be) relatively shoal draft, they have more anchoring/ or lying to mooring options and so are less likely to need a marina than, say, a mono.
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Old 09-03-2008, 19:29   #9
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In our eleven year circumnavigation, we always sailed with our salon doors wide open when offshore. We had a bimini top with a large cockpit, and it was extremely rare that we would ever need close the doors. There were three days in the south Pacific, two days in the Red Sea, and three days in the Atlantic on the way to the Canary Islands when we closed our salon doors. The rest of the time they were wide open.

We need to close the doors only when there is rain and twenty-five to fifty knots of wind coming up the stern. The doors are closed because of the driving rain coming from aft.

In 33,000 miles of offshore sailing, we have never taken water over the stern - not even close. Occasionally a beam sea will splash up on deck and slowly run down into the cockpit, but I am talking about quarts of water rather than gallons.

Our catamaran tends to be quite dry in the cockpit, and there is a deep drainage well along the front edge of the cockpit, so the need for water tight doors is negligible.

I have never run downwind in over fifty knots of wind, but in winds to fifty knots, the extreme boyancy in the stern of Exit Only lifts the stern with the following seas and any breaking waves have passed under the bridge deck rather than climbing on board.

If I was in winds over fifty knots, I wouldn't be running down wind. I would be lying to a parachute sea anchor, and my salon doors would still be wide open.
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Old 10-03-2008, 07:40   #10
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EXIT ONLY,

You have been there, and done it. I find it encouraging that in less than 50knots of wind Exit Only would still raise her sterns I am still a rookie at cats in heavy weather. I have not seen over 40 knots, but I am truly pleased with the handling charactaristics of my boat so far. Your insight is always appreciated...........
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Old 10-03-2008, 10:41   #11
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True watertight doors and collision bulkheads, like you will see on steel merchantmen and warships, are just too damned heavy, bulky, and expensive to be found on mass market production boats.

The doors you are hearing about are probably the custom construction on world-class ocean racers, where the racing rules for those events require them.
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Old 10-03-2008, 11:41   #12
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Thanks everyone for the good information.

Having watertight bulkheads towards the forward and rear sections of the boat makes sense from both a safety and practical standpoint. Having a watertight bulkhead more toward amidships with a W/T door seems like it would be a real pain to have to go though frequently, even if it was a lightweight aluminum door bolted onto a fiberglass transverse bulkhead. I have permanent dents in my shins having gone through not quite right, enough watertight doors in the past. I was just wondering if they exist...and they don't seem to on medium to smaller sailboats. Thanks!
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Old 10-03-2008, 15:59   #13
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Freeman Marine Equipment, Inc. provides the finest marine and specialty closures available. Custom fabricated doors, hatches, portlights and windows.
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Old 10-03-2008, 17:24   #14
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doesn't the real problem occur when it comes time to dog down the hatches? I mean cats and dogs ...

sorry, couldn't resist!
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Old 10-03-2008, 18:12   #15
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Bigcat, that's a nice resource but "Call for price" tells me that I, for one, won't be able to buy any of them. A first class seat to a breakers' yard in India and a return trip home with two slightly used bulkhead doors probably will be half the price and twice the fun. "Yesyes".
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