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Thistle 1040 - Bow tank bulkhead


By Thistle1040 - Posted on 17 March 2012

bow tank bulkheadI installed the bulkhead for the forward bow tank today. All fiberglass Thistles have an air tank in the bow to help with floatation. Most wooden Thistles have giant foam blocks that are not as effective. To be self-rescuing, Thistles need as much floatation as possible. My #1 reason for installing the bow tank is to give the boat as much floatation as allowed by class rules to make the boat safer.

Below I'll post a photo of the tank I installed in Thistle 1014. This one will be similar. The class rules say that all parts of the tank must be 14" below the height of the sheer. The tank must also be forward of the stanchions. These limits determine the maximum size of the tank.

My tank is made out of 1/8" door skin and is attached to the hull with a large fillet and fiberglass tape. The fillet is made from epoxy and microspheres so it's lightweight. When it's faired and sanded, it will look great, just like the photo below. The vertical bulkhead is curved when installed. I do that because a curved panel is stronger than a flat panel. I also curve the top of the tank so that water will not collect, but instead, will run off into the bottom of the boat. The top of the tank will be made of two layers of door skin with a 3/8" layer of foam sandwiched in between. The rules do not allow for any kind of interior bracing inside the tank but the curved top and sandwich construction make a top that is strong enough to stand on and yet still light in weight. The whole tank will weigh less than 10 pounds.

You'll see that I've cut holes for inspection ports. These also have plywood backing plates glued into place so the ports can be firmly installed in the bulkhead. There are also wooden blocks glued in place where fittings will be attached.

The downside to having a tank is that it creates a dark place on the boat where water may collect. Bad things happen to wooden boats when they sit around with water in them, or even water vapor. That's why we have the inspection ports. With these open, the tank can dry out. The inside is coated with epoxy and there will be small battens glued into place that will keep the required foam floatation blocks from sitting on the hull surface but will instead be 1/2" off the deck so air can circulate.

Thistle floatation tanks are required to be filled with foam blocks as a safety measure. There was a tragic accident where a Thistle crew was not able to self-rescue from a capsize because their air tanks were leaky. Partially filled with water, the boat was too low to recover and sail dry. All three sailors died. This accident led to several safety requirements for all Thistles, one being foam blocks inside air tanks.

See image below for photo of a finished bow tank. This tank is also crowned and sloped back to promote drainage and prevent standing water. Note the plugs to drain the tank in the bottom center part of the bulkhead.

finished bow tank

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