Sliding Mainsheet to Servo Arm ?

In reading one of Lester Gilbert’s pages, I was looking specifically for any discussion on a method for attaching a sliding mainsheet attachment to a winch arm. I couldn’t find anything specific, but did find a bit of discussion about a sliding “Boom” attachment.

Using Lester’s provided graphic drawing (below) - but assuming it is a winch arm, not a boom … what would be the possibility of doing similar on a winch arm?

Forgetting the relationship of the arm and sheeting to the best arm location relative to the direction of pull - here are my thoughts…

  1. With a wire attached to the swing arm and the mainsheet attached via a sliding metal clip…

  2. When the arm is in position to let the main all the way out, the clip and mainsheet would slide out to the end of the winch arm letting boom travel all the way out for running.

  3. As the winch arm moves to pull the mainsheet in for beating, the clip would slide inward on the arm. This might provide …a) a shorter arm lever for more precise sail adjustments and …b) the shorter winch arm location might increase the leverage of the arm to assist in holding it’s position if gusty/windy conditions exist.

For the majority of time for the main in/out, speed is a greater need than strength or fine adjustments. Once the main (and boom) begin to reach maximum in-haul, the more precise and minute are the adjustment needs.

I haven’t stopped to consider an angled wire on the winch arm to encourage the mainsheet clip to slide one way or the other easier, nor have I thought about shallow “indents” on the wire to capture/hold the sliding clip in place a bit longer as it slides along the wire.

If there are any comments or opinions, please post - and if you know a more detailed posting on a website somewhere, relative to these thoughts, I’d appreciate your posting of the URL.


Dick, when I try to visualize what you are proposing, I don’t see the movement as being progressive. I think that the sheet would rest against one endstop and as the angle changes, it would pass through a balance point where it would immediately slide to the other extreem end.

Reversing the pull, the same would happen. It would stay at the stop until the critical point is passed and slip all the way to the other end.

So you would get a smooth sheet adjustment with a jump in the middle going either way.

It sounds like you are trying to increase the end movement sort of exponentially, with very fine adjustment at close hauled and coarse adjustment at full out. If so, why not get a good digital servo and program it that way. (remember KISS)

Hi John -

yes - looking for some exponential in servo power/adjustment.

Idea was for the RG-65 and trying to keep it inexpensive for new sailors. I keep hearing via the various forums about how many new sailors hate to spend the money ( thus they buy import “crap” ) and then get disappointed in the modifications required to make the boat able to sail - let alone competitive.

We promoted a decent but inexpensive AM radio with servo, winch, battery holder, switch, received and transmitter all for less than $90 (thank you American-RC Hobby) - so I suppose you could say I continued to foster the “cheap” theory. :rolleyes: For those who are serious, digital and DX radios probably will find their way on the water. I was trying to see if possible to give the beginning (or more casual) sailor an option if they stay with the small servos mostly being used by the RG builders. I guess - in an indirect way - as the servo arm begins to parallel the sheeting angle (or line up with it), it’s arm movement is making a much smaller adjustment than when it is at right angles to the sheeting direction.

You are probably correct in the “jump” from one end to the other of the arm wire.

I think the progressive change effect of the properly installed arm winch is the simplest. But arm winches reqiuire a lot of power and are constantly ‘at work’ as the sail is always trying to pull back and pull the servo out of the selected position.

To allow the use of an inexpensive servo, look at Lester’s torque constant cam tensioner

The idea is that as the winch lets the sail out, it tensions a spring. As the servo works harder to bring in the sail, the spring provides a ‘power assist’. This is the exact opposite of an elastic tensioner, that causes the winch to work harder pulling both the sail and the elastic as it tries to come to close hauled.

It does work, and was done back in the 70’s when servos were notoriously short of throw (travel) and power. However, this was not without problems or we would see more of it today. I used the system which was just referred to as a traveller way back when and installed by wire exactly as you describe. Granted, they were more crude… normally they worked… but they did tend to hang up from time to time which caused the sails to be cycled to kick it loose which normally would happen. Of course then there were problems in light air… as there always are… and then winches became more friendly and powerful and the need for them went away.

I have the original drawings from Reynolds Mfg for the Heritage and the EC-12meter showing the installation on the mainboom exactly as you describe it.


Roger Stollery used the exact method Dick mentions…he calls it a power lever and it appears to work well on his footy design “Bug”
You can see it here if you look closely,

Hi Dick:

Try this!!!

Maximo, can you explain to me what advantage this rigging has?

This may be common knowledge but if you have end point adjustments you can get progressive sheeting. My knowlegde is limited to Futaba pistol grip but I’ll explain. If you turn the end points it only controls the travel on that side of center. The center point stays in the same spot. So if you have the closehauled end point set to minimum travel and the running end point set to maximum the sail only moves a little for the first half stick movement and a lot for the last half. I hope you can understand my explanation.