PDRacer Sailboat

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Unstayed Masts
An unstayed mast is the simplest of all, it is basically a stick that is held upright from the base. The mast is standing on a "step" shown here on the bottom of the hull, and is held upright by a "partner", which in this example is the deck with a hole in it.

With this type of mast, all of the stress is focused at the partner, so it is very important to have a strong partner, and have it high enough away from the step. The closer the partner is to the step, the stronger the lever arm is between them.

Partner to Step Distance
A typical pdracer will probably need a step-to-partner seperation distance of atleast 12". The smaller it gets, the stronger the partner and step has to be.

Mast Size
If you are using a wooden mast, then something around the 2.25" diameter should be fine. You should also taper the mast to make it lighter. With a triangle sail, all of the stress is focused at the base of the mast, the top of the mast doesn't have that much stress on it, and is mostly just there to hold up the top portion of your sail, so it can be tapered down to about 1". A lug type sail (something with a yard on it), will have similar light loads on the top of the mast when the sail is pressed against the mast, but when the boat is on the other tack and the sail is pulling from the halyard at the top, more more of the stress is transmitted to the mast head so it should not be tapered so small.

Rotating Mast
A nice feature of unstayed masts is that if you make your mast round, it will be able to rotate. This is nice for a number of reasons, such as if you are using a sprit boom with a snotter, the pressure on the snotter stays the same giving you a constant sail shape. Also if you get into trouble, you can release the main sheet and the sail can rotate all the way around forward depowering the sail. This feature has saved my bacon a number of times.

Types Of Mast Steps And Partners

Overhaning Deck With Bolt On Step
The simplest of all, just put a hole in your deck and bolt a step to your bulkhead. Not really a step, more like a tube. Best to attach the step to the bulkhead before 3D assembly. Works good, easy to do. The only drawback is that as the mast rotates, it tends to wear a spot on the bottom, so you might want to put a buffer underneath the mast like a piece of 1/4" plywood or some fiberglass.

Overhaning Deck
Similar to above, only you mount a block of wood to the bottom of the hull that has a hole to receive the mast.

Bolt On Blocks
A couple of blocks are bolted onto the bulkhead, and the mast is supported between the blocks. The aft edge of the mast partner does not have much stress on it, so it only needs a small strap to hold the mast up.

Some people even use rope on the aft edge of their partner.

Mast Tube
A tube can be made, here is one that is very simple to make. It uses 2x4 as the sides (well, they are more like 2 x 2.25"), and 3/4" plywood on the forward and aft edge. The bottom of the tube has a slot for the water to leave, if trapped in there the water could rot out your tube.

An extra brace is put on the forward edge of this tube because the bulkhead is so short. This bulkhead is only about 6" high, if the bulkhead was around 12" high it would not need the extra brace. Also a cap should be installed on the tube, something as simple as a piece of plywood with a hole in it. The cap will even out the load to the whole tube instead of just one side.

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