How Strong Does Your Mast Need To Be?
The strength that your mast needs to be, is based on the width of your hull, not the size of your sail.
At first this doesn't seem right, you would intuitively think that the larger the sail, the stronger the mast you need.
But think about it, the mast is a lever arm that is trying to knock your boat over.
It exherts force right up to the point where your hull goes over, at which time is the maximum force that will be required of that mast.
So the smaller the boat, the smaller the mast you can use.
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.
For sprit sails, most people seem to be using wooden masts that are 2-1/4" in diameter at the base, then tapered to 1.25" at the head.
For lug sails, the base of the masts are about the same at 2-1/4", but only tapered to around 1-3/4" at the head.
When on the good tack, a lug sail will pull half it's weight from the top, that is why they are thicker up top.
I have also seen a couple of people using 10' long x 1.5" diameter galvanized electrical conduit for an unstayed lug mast.
Stayed Mast
A stayed mast is one that has wires or ropes to hold it up, these are called stays.
It behaves very differently from an unstayed mast, what happens is that when the wind blows agasint the sail, stay holds on and keeps the mast from bending sideways, so the force is converted into compression and pushes the mast down.
So with all that force pushing down, it is very important to have a strong step.
Some of the other neat characteristics is that you don't need a partner at all, the stays take all the side pushing stress.
Also the step can be a very simple one such as a socket or knob, it's only purpose is to keep the base of the mast in one location.
A simple stayed mast you could make is using the top rail from chain link fence.
They are 1.25" diameter galvanized, and have one tapered end to join them in series.
Combination Stayed / Unstayed
A third basic type of mast is to have a combination.
This would be a typical unstayed mast that has both the step and partner, and has a set of side stays, but no forestay.
The side stays allow the mast to take greater loads, but since there is not stay on the bow, it is really easy to hoist and manage additional sails up there like a spinnaker.
Unstayed Masts
Stayed Mast