Foam vs. Air

I've been thinking of sailing my 23' wooden cutter in the Jester Challenge, 2018. She's already a substantial sea boat, but I've been thinking of things I could do to make her even more seaworthy, such as adding lifelines and bulwarks, perhaps adding roller reefing for the jib (currently set flying on the end of a 8' long bowsprit), and making her unsinkable.

(I don't see a way to post pictures. Here's a link to one, and there are lots more on my blog. https://dl.dropboxusercontent.com/u/15652299/blog/IMG_4775.jpg)

She was designed to have an inboard engine, but the builder was a real spartan and sailed her all over the Caribbean without an engine. So the whole under-cockpit area is empty space.

The area between the mast and the bow is also empty space, free of any built-in furniture. (I said he was a spartan!)

It's a wooden boat with substantial laminated frames and deck beams.

So, what I've been thinking is that I could easily add a waterproof bulkhead under the bridge deck, and also just forward of the mast. I could install a water proof hatch in the aft bulkhead, to give me access to the space under the cockpit for stowage. The forward area already has a deck hatch over it, but I could also build a water-tight door into the forward space, again giving me access to the space for stowage.

Since it's a wooden boat, I would also want to leave the hatches open in good weather, to allow circulation through the boat. I'd only dog them down in really bad weather.

Adding foam to a wooden boat isn't really a good idea because of moisture build up, so it's not something I'm considering. But I was wondering if there are complications I'm not considering with having these two floatation compartments filled with air, only?

For example, I've been imagining what would happen if I hit a log or something, and the forward compartment sprang a leak. It seems to me the forward compartment would only fill with water to the boat's waterline, which wouldn't be that much water, really.

This seems like such a good idea that I'm wondering why all boats aren't built this way. Am I missing something obvious?

Any thoughts or comments, much appreciated.

-- John

 

If the boat takes on water, the waterline will go up considerably. It may be enough to compromise the stability(water sloshing) or the reserve flotation enough to completely swamp the boat. Watertight bulkheads in a small boat leave very little room. However, if you sail alone, that may not be much of a problem. Have you considered flotation bags?

 

Maybe this isn't the right forum for this question.

 

No, it's the right one.

Have you considered ping pong balls in your voids?

They don't seem like they would want to trap moisture and can be easily removed for inspection and repairs.

 

Watertight "collision" bulkheads which separate the bow from the rest of the boat are common and required on many boats in commercial use. If the bow is holed below the waterline the volume ahead of the bulkhead it will no longer contribute to floatation (assuming the air above the hole leaks out) and the boat will trim down by the bow as a result. The boat will probably be less stable. Calculating what happens when a compartment is holed and flooded is a standard part of naval architecture.

 

Since I'm going to Europe, maybe soccer balls would be a better choice.

 

Actually, I proposed ping pong balls because, being plastic and waterproof, they have been used to raise boats.

 

I agree with gonzo. Flotation bags custom made to fit the space. Can be pvc or tpu, glued or welded, can be self made. In port or for coastal cruising deflate and ventilate or use the space for storage. For really cheap you can just use plastic bottles or jars in a net.
Or you can put some slats on (like a ceiling) and put foam blocks inside. That way there is a space between the foam and the wood for ventilation.
If this is just for the jester challenge I would install the whole bulkhead to be removable. Glue a flange to one of the frames and cut a rubber gasket (plus some polysulfide for aded security) and then install the (glassed) plywood (or other material like lexan or aluminium) bulkhead with machine screws all around. Use a watertight inspection port for ventilation. This way is you can reuse the space after the race. The flange can be formed in situ from a heavy laminate, plywood, etc. The nuts (or bolts) can be epoxied into the flange. After removal of the bulkhead you are left with a thicker frame with holes in it.

 

Jalmberg. I saw your blog. I wish you well. I hope to do a Jest challenge myself someday. I like your cutter. I too have been following folks like Roger Taylor and his Mingming 1 and 2. I agree with his idea of making the boat unsinkable. With your cutter that means a lot more buoyancy is required. Custom inflatable bags can be very expensive. Maybe 2 litre pop bottles. You would need a few thousand, but you can probably get them from a recycle centre at the recycling cost, and then return them when you are done with them. Another approach might be garbage bags filled with expandable foam, but that is a less environmentally friendly option for when you are done. For survivability I would also have a watertight cabin-within-a-cabin where you can go to to get warm and dry and get some rest. You have to stay afloat even if you spring a leak. You have to be able to make repairs if you spring a leak. You have to be able to pump the water out. But you also need to be able to get some rest, and maybe be able to pump from there also. You would also keep your electronics dry in such a place. So I would look at some of the micro-challengers, like Yrvind and others, for ideas on how to keep all you need in one very small place, and then use the rest of the boat for work space and buoyancy and storage for the less essential items. Best regards.

 

So is this the current layout?
http://sailboatdata.com/viewrecord.asp?class_id=5907