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Old 17-03-2006, 21:03   #1
Kai Nui
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Watertight Bulkheads

In the next year, I will be doing a major interior refit on my Challenger. This will include completely rebuilding the head and forward cabin to include the forward bulkhead. The boat currently has no watertight bulkheads, and I would like to add at least one. Possibly a second one in the form of a chain locker below the forward berth. These will be marine ply glassed to the hull. Any suggestions about appropriate thickness? Also any design tips would be appreciated. I am not worried about weight, as I am removing quite a bit in the new design. I also want to build a watertight door for the main forward bulkhead. Any suggestions about the design of this door would also be appreciated.
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Old 17-03-2006, 21:16   #2
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You might want to contact me by email. Too much precission stuff to detail here.

I even have a couple of catalogs that could inspire you, and give you some ideas. Ideas that could point you in the right direction.

That's about as good as I can discribe this subject to you, on this thread?

Sorry!!
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Old 17-03-2006, 21:57   #3
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K, did I mention that I do not want to use metal doors?
Seriously though, enlighten me. Throw some of that info out here. I have always thought watertight bulkheads were far too few in production boats, yet a very important safety item.
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Old 17-03-2006, 23:23   #4
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Not a problem then.

I'll just send you some photos. And when I come out to California. I'll give you some more detailed drawings that could help you out!!
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Old 17-03-2006, 23:26   #5
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Thanks K
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Old 18-03-2006, 00:32   #6
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I sent a bunch of detailed sketches via email to ya Kai. Including a few photos!!

A few didn't want to upload. So I'll have to send them by regular mail to you?

This'll give you some good ideas on what to follow on. I hope this is to your expectations?
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Old 18-03-2006, 16:22   #7
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Got them K. Thanks. I am thinking more along the lines of a wood door. I saw a set up on a Spray that I like. It has a solid door through the bulkhead, but also has hatch boards that drop in front of the door to reinforce it. (on the saloon side) I am planning to laminate 2-1" pieces of marine ply together giving me a 2" bulkhead. A 1" plywood door with 1" hatch boards to fit. The wheel and dogs set up is not going to work for me. I intend to use traditional hardware to latch and hinge the door. I realize this is not nearly as strong as the traditional steel or aluminum dogged hatch, but I think it will be sufficient, and will still maintain the apearance I want.
Opinions?
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Old 18-03-2006, 16:40   #8
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You could use a "one handle" type of dogging hatch.

Basically this one handle operates the six "dogs". And when you go open the hatch. You raise up on the handle. And all six dogs move to allow the user to open the hatch. And the same in reverse while closing the hatch!!

You could try that approach, Kai?

The method of building material is fine. As long as it's straight "flat", and flushed. It has to mated up against the wall. Or the a blade that makes the connect for a watertight hatch to connect to a watertight bulkhead.
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Old 19-03-2006, 12:57   #9
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Hi Kai, this needs a little more thinking. Firstly, you need to work out just how much water you are wanting to hold back. and then, what possible situations you maybe in when wanting to hold it back. Example: 1 cubic metre of water weighs 1000kg. Thats some weight and your door maybe fine as long as it is all sitting still. Now factor in boat motion. Your 1000kg can increase dramaticly if it is sloshing around down their. Force equalls Mass x Accleration. So even something as small as slosh could double the force of that cubic metre against a bulkhead. So what do you need to consider.
Well it's one thing to have a door that can take that force, but you also have to have a bulhead that can support the door. And then the bulhead has to be fixed the structure of the vessel so it can take the weight as well. Not all impossible, but you see, it is a little more than JUST the door.
Personaly, I would build in Aluminium. Timber is going to take some doing. But what ever, you need to calculate the following.

If flooded, what level will water be behind that area. Factor in that the boat will also have a new waterline with loss of that floatation.
How many cubic metres(cubic ft) of water will then need to be held back.
Times that by two for momentum. Chances are, if you have a leak forward, it will be in a ruff sea condition.
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Old 19-03-2006, 15:45   #10
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Possible rule of thumb...

Gerr in "Boat Strenght for Builders, Designers and Owners" (Formula 9-26 - Watertight Collision Bulkheads) states (in part) that "As a general guide this bulkhead should be neither less than ) 0.10 nor more than 0.25 times the LOA aft of the bow" and that
"Where collision bulkheads are required by government agencies or classification societies their requirements must be followed" and that "Watertight-Bulkhead thickness = standard topside plank thickness" and that "Watertight -Bulkhead Stiffener Siding = standard frame siding for hull topsides"
I may have made a transscription error with the above, and it does need to be read in the context of the entire book so I would strongly recomend buying the book.
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Old 21-03-2006, 17:56   #11
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I dont believe that its practical to retrofit Watertight Bulkheads into most cruising sailboats. Some of the difficulties of retrofitting effective Watertight Bulkheads are addressed in the two following articles.

The Truth About Unsinkable Boats ~ By Michael Carr
Blue Water Sailing (8/1998)
A professional mariner tells how you might avoid sinking
http://www.boats.com/boat-articles/S...oats/1251.html

Fibreglass Boats and Damage Control ~ by Hugo du Plessis
http://www.caribbeancompass.com/damagecont.htm
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Old 21-03-2006, 23:23   #12
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THanks guys, that is what I was looking for. Aluminum is not really an option as much due to asthetics as anything. Calculating the strength of the bulkhead, and it's ability to handle the pressure is no problem, but the real weak spot is the connection to the hull. I am not really expecting the bulkhead to completely seal the forward section until I can get to safety, but I am hoping it will buy some time. More importantly, since I am building the boat to sell, I am interested in increasing value. As for the formula that Chris31415 posted, the bulkhead will be approx 2x the deck thickness, however the bulkhead will be wood, and the deck is glass. Hard to compare strengths here. Allot of boats advertise watertight bulkheads, but I suppose that does not mean they will work. Still, if I can go with a design that is accepted as conventional, it should suit my needs.
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Old 20-12-2013, 18:12   #13
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Re: Watertight bulkheads

Oh my, did you say two inches of plywood. A bulkhead built out of two inch thick plywood would be very, very heavy and not at all very practical. Go to home depot and try to pick up a 4' X 8' sheet just 3/4" thick, you may change your mind. I think this would be way overkill. You also have to be careful not to create hard spots where loads are concentrated at the hull to bulkhead interface.

If I were you, I'd go with 3/4" balsa core and three layers of 1708 glass on each side. Use epoxy as it bonds better in secondary bonds, and is stronger anyway. It is very easy to work with these materials, much more so than ply when trying to fit a new bulkhead into an existing hull. You can build the bulkhead in sections, and glass it in with some overlaps on each layer as you put it all together. This would be more than enough to handle the loads and pressures involved. You can build the door the same way, just make it open into the compartment so water pressure would force the door closed onto the seal. You would make a door frame out of hardwood set in epoxy for the door to seat on. This is all pretty easy once you get the hang of working with these materials. See West System Epoxy website for some help. This would be a lot lighter, stronger, and bond better to the old glass than ply. You may spend a bit more than you would with just ply, but it would be much easier to get it installed. I think you'd need around 6 gallons of epoxy, plus the core and glass. On eBay, Great Lakes Skipper sells glass and core. Jamestown Distributors is another good source. You don't want core that is scored to conform to hull shape. So you need to be clear on that. 1708 is a combination glass and mat that lays up very nice. Three layers, hand laid up, would get you almost 3/8" skins. You could go with 2408, but I don't think you need it. The way I would do it, is to install the balsa, gluing it into place and to the hull. Make some epoxy fillets along the balsa and hull side interface, then lay up your glass in sections, maybe three on each side, overlapping them. You can make a pattern out of clear plastic sheeting to use to cut your fiberglass to the correct shape. It is easier to work with smaller sections, this is why I'd make three sections on each side. Wet out the balsa with epoxy, then lay out one section of fiberglass, mat side up, on a plastic sheet, and wet it out with epoxy. Make sure it is saturated but not dripping with epoxy. Now roll it up and take onto the boat and roll it onto the balsa bulkhead, mat side onto the balsa. Roll on a bit more epoxy with a foam roller and use a bubble buster to roll out the bubbles. You can, if you organize well, put all three layers on, one after the other. After it sets up, but is still a little tacky, mix some epoxy with some thinking filler (Cabosil silica epoxy thickener) to a catsup consistency and use a plastic trowel to fill in the surface so you'll have less sanding to do later. You don't want to be sanding into the fibers to get a smooth surface anyway. You can sand and paint the bulkhead, or you could cover it with veneer, or even door skin material put on with, and sealed with, epoxy. Then paint or varnish to your taste.

Good luck,
Tim
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Old 20-12-2013, 18:52   #14
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Re: Watertight bulkheads

G'DAy Tim...

While I think that your advice is excellent, you might not have noticed that you were replying to posts made nearly eight years ago! Those chaps have long since finished or abandoned their bulkhead projects.

Anyway, welcome to CF, and please continue to contribute in the same thoughtful and knowledgeable manner.

Cheers,

Jim
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Old 20-12-2013, 19:42   #15
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Re: Watertight Bulkheads

Maybe not, some things take longer than you think :-) and...maybe someone else might find it useful.
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