RE: Steady sail......
This is a popular topic on the Grand Banks owners forum. To answer your first question, when we inquired about having a steady sail made for our boat not long after buying it the sailmakers we talked to all said the only way they'd do it was to come to the boat and take their own measurements. Every mast and boom is different, and they didn't want to rely on builder's specs or owner measurements. The cost at the time for a sail the size we would most likely need was about $700. This was in 1999. Plus we would have had to install the track and the running rigging.
Whether or not it helps in a beam sea is debatable. A few GB owners who have them say it does, most of them say it doesn't. And even most of the ones who say it has an effect admit the effect is minimal. The ones who say it's worthwhile all tend to be people who run in the open ocean with large swells and wind waves on top of them. So a lot of boat motion.
But everyone, even the folks who say their steady sails work, says that compared to real stabilizers, either passive birds or active fins, a steady sail does not even come close.
The one value that is spoken of, which is why we were interested in a steady sail, is that it can reduce a boat's tendency to hunt or yaw on a mooring or at anchor. This can be uncomfortable because as the boat swings into an angle to the oncoming waves an element of roll is added to the pitching. The steady sail helps reduce the yawing because the sail is in essence like adding another feather to the back of an arrow. It tends to keep the thing pointed into the wind.
While there is no denying the principle invovled, how effective a steady sail will be to prevent yawing is dependent on your boat's structure. On a GB, much of the lower body of the sail will be in the "wind shadow' of the superstructure. So the only part truly exposed to the wind is the small top part. Is this enough to help reduce yaw? Some people say yes, some say not enough to make the sail worth messing with.
On a working lobsterboat with no flying bridge and a long open cockpit a steady sail can be very effective--- we saw a number of lobsterboats at moorings in Maine with a steady sail stepped on a braced, removeable mast attached to the transom.
A steady sail is probably more effective on a full-displacement boat, which tends to roll farther over in a beam sea. So there will be much more movement of the sail sideways through the air. But with the semi-planing hull on a GB with its fast "snap-back' roll, I tend to side with the GB owners who say a steady sail does nothing significant to reduce rolling.
There is something to the argument that the wind pressure on one side of the sail in a crosswind will reduce rolling, but apparently given the size of the sail that can be carried on the typical tralwer, it's still not much of a reduction. And you have to make damn sure your mast and stays are capable of withstanding the stress.
So based on the "not so effective in damping beam sea roll" testimony by GB owners and the minimal effect it might have on reducing yawing on a buoy or anchor because of our boat's superstructure configuration, we decided to forget about it. If yawing on a moorage is a problem, we put out a stern anchor.
But... if you want a steady sail because it looks cool, then go for it. As long as your mast and rigging can take the stress in a strong crosswind coupled with the inertia from the rolling, it certainly won't hurt anything and it might help a little. You won't know until you try it.