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.

[CaptainK]

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!!

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.

[CaptainK]

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!!

Thanks K

[CaptainK]

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?

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?

[CaptainK]

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.

[Alan Wheeler]

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.

[Boracay]

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.

[GordMay]

I don’t believe that it’s 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

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.