Question about sail servo

Since I’m still totally new and totally blank :confused: on most everything, let me ask about how a servo controls the sail. Let’s just go with a single main sail, no jib. If using an arm type servo, am I correct that the servo does not actually pull the boom from, let’s say, port to starboard, but instead it just either pulls the boom to center, or lets slack out and the wind is actually causing the sail to move to port or starboard. Is that correct?

You got it!

The wind pushes the sail out and the string (called the sheet) pulls it back in.

Usually, there is a sheet to the jib boom and a sheet to the main boom.

Those sheets are tied to a common line that goes to the sail servo or winch.

When the servo or winch pulls in, both sails move together.

A simple set up is to set the distance from the jib pivot to its sheet attachment to be about the same length as the distance from the main boom swivel (the gooseneck) to its sheet attachment point. That way both sails move in and out ‘in parallel’ and so are correctly trimmed at all ‘points of sail’.

Thank you…

Now a thought about that. Wouldn’t it be better to have a servo set-up where the the booms were controlled (taught sheet) at all times (looped circuit) and would you be able to use a servo where you might be able to control either direction only as far as you wanted? The booms would always have tension on them as they moved. Would that give more control or is it a waste of time and just more problems having too many adjustments?


One thing about this hobby, if you have an idea, go try it. On a boat like a Footy, it would be an easy and inexpensive experiment.

Now my opinion is that it would not work well. On a conventionally rigged boat, you can luff the sails (the sail acts like a flag). That can be very important as it allow you to spill the wind. This may be necessary to control the boat in a strong gust for example.

However ask yourself how a rigidly attached sail would behave. If the sail is not free to rotate, the wind could push against the back side of the sail and suddenly cause the boat to heel to weather and rock violently from side to side as the wind alternates on either side of the sail.

If there was a range of slack sheet, you could luff by just being close to the right trim, yet you could backwind the main to back up if you need to…


On a Footy, I’ve seen the mast ‘plugged in’ to the servo shaft…the mast rotated with the main boom mounted solidly to the mast.