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Thread: Water Tight bulkheads?

  1. #1
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    Default Water Tight bulkheads?

    Forgive my ignorance on this subject but should all bulkheads in a cat be water tight? I had seen a few on cats when were were looking that had an area at the bottom left open ( like a 3/4" gap so any water could make its way back? Wouldnt haveing it sealed and then maybe a drain plug hole at the botom be better? safer?

  2. #2

    Default Re: Water Tight bulkheads?

    Quote Originally Posted by HappyEnding View Post
    Forgive my ignorance on this subject but should all bulkheads in a cat be water tight? I had seen a few on cats when were were looking that had an area at the bottom left open ( like a 3/4" gap so any water could make its way back? Wouldnt haveing it sealed and then maybe a drain plug hole at the botom be better? safer?
    It would be nice, but it's not always practical.

    For instance, if you have a bulkhead between your main hull area and a forward stateroom, it will have a door. Making that watertight is difficult, but can be done.

    If you are talking just about the end bulkhead (fore and aft), if you want to float when holed, they better well be watertight.

  3. #3
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    Default Re: Water Tight bulkheads?

    Quote Originally Posted by Sully View Post
    It would be nice, but it's not always practical.


    If you are talking just about the end bulkhead (fore and aft), if you want to float when holed, they better well be watertight.

    They were below floor bulkheads fore and aft. The aft ones looked sealed, the fore ones had the space. I wondered why, as the broker was saying it had crash compartments but looked like water could still traverse to the middle section below floor and then upinto the boat.
    Shouldnt that have been sealed?

  4. #4
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    Default Re: Water Tight bulkheads?

    Old wooden vessels of years ago all had "limber holes" in their beams so that the small amount of water that came through the planking, and kept it tight, would flow down to the deepest point at the stern where it could be pumped out.

    With the advent of modern "dry" fibreglass boats the limber holes become irrelevant. However they are useful if you have leaky windows or something as it again allows the water to settle in one place for pumping out.

    These same limber holes conflict with the need for watertight compartments. You can't have it both ways!

    Mike
    Nothing works on an old boat, except the skipper.

  5. #5

    Default Re: Water Tight bulkheads?

    Quote Originally Posted by HappyEnding View Post
    They were below floor bulkheads fore and aft. The aft ones looked sealed, the fore ones had the space. I wondered why, as the broker was saying it had crash compartments but looked like water could still traverse to the middle section below floor and then upinto the boat.
    Shouldnt that have been sealed?
    Personally, I'm not a big fan. Dmmbruce is correct. They are useful if you want any water to make its way to the main bilge.

    Personally, I would rather have every bulkhead watertight below the cabin sole. That way, you can more quickly identify any window leak by what compartment it is in.

    However, every bulkhead that is touted as a watertight/crash/flotation bulkhead must, by definition, be 100% watertight. No holes. Your gut instinct was correct.

    The good news is it's pretty easy to fill the hole in and slap a little fiberglass over the top of it if you are looking at this boat seriously.

  6. #6
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    Default Re: Water Tight bulkheads?

    If a boat has watertight compartments that are required to be closed for buoyancy then under the RCD there should be a placard saying "keep closed at sea". But then I know of two boats that were holed when at anchor and dried out onto rocks....

    I also know of a Strider owner who cut a hole in his inner tray moulding to fit an echosounder transducer. Later he hit something and sank that hull

    Having said that I like limber holes with bungs so I can check there is no water in sealed compartments. Also its good to leave them open when stored ashore to avoid condensation problems

    There are a LOT of production catamarans that do not float if holed

    Richard Woods of Woods Designs

    www.sailingcatamarans.com

  7. #7

    Default Re: Water Tight bulkheads?

    If a compartment is sealed there should be no condensation problems. Only the moisture from the original air in the compartment should be there. If it's sealed, no more can get in.

    Ideally you'd seal compartments on a very cold very dry day, but even if you didn't, there should only be a tiny amount of moisture inside.

    On my boat there are more than 50 sealed compartments. But even without them it couldn't sink. The material to build just the shell took 3 double pallets, stacked 1 metre tall. So 3 x 1.2 x 2.4 = 8.64 m3.

    That means to sink, it would need to displace over 8 1/2 tonnes of water, not including all the internal furniture, fitout etc. The boat launched at 4.8 tonnes, without it's rig. We're currently cruising at a bit less than 6 tonnes.

  8. #8
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    Default Re: Water Tight bulkheads?

    It's easy enough to design a catamaran with all major compartments being watertight. I think the problem is that safety at sea is usually much less of a priority than making a catamaran feel spacious. It's also cheaper to build a catamaran with no watertight bulkheads. The best way to do this is to just make it so that each cabin has its own entrance from the hull or bridgedeck. Even a "sleeps 6 to 8" catamaran 42 feet long can be built this way, with a total of 4 compartments per hull.
    Currently concentrating on http://earthnurture.com .

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