Within the last year I have purchased an ‘PASSIVE DESIGN’ “A” Class RC Yacht which I have aptly named SPACE INVADER II.

The hull has masses of room inside for a working spinnaker, so I have set about constructing the spinnaker chute (very similar to those life size dinghies) I have installed an RMG380HD sail winch for the hoist. It works absolutley fine up to a force 4 breeze. Any more than that, the spinnaker head starts to pull against the winch and subsequently against the motor. I suppose one will say, “Well keep the motor to hoist then.” OK, I’ve done that and the Lithium Jelly rechargeable batteries tend to get very warm and the motor is under strain!!

I would appreciate any (sensible) suggestion as to hjow I should lock the drum from unwinding.


perhaps put a lock on the gears and only use it when the boat is coming back to you unless a second servo is used to disengage the lock. Or, perhaps a brake on the shaft operated by a second servo. Thats just my 2cents worth

[:D] One suggestion you may like to investigate is to fit your spinnaker halyard with a locking device. Once hoisted the halyard locks into a keyhole like devise and releases all the tension off the winch drive. The next trick is to disengage the lock to allow the lowering of the spinnaker. Sorry mate that is where I come unstuck. I know enough to be dangerous. I am sure there are others here who are far more clever than myself who will come to your aid. [:-angel]
Can we have a photo please?[:-jump2]

Do it NOW before it`s too late.<font color=“red”>Edited for crap spelling</font id=“red”>

Give me a few days to look. Somewhere I have info on creating a “locking” mainsheet that was used on the old “PeaPod” class. Basically a small servo controls the sheet, and a stretched rubber band pulls on the sheet and is under tension until the “locking” arm is released. Will see if I can find it and post a sketch.

[:-angel] See, cleverdick to the rescue.[:-batman]
Sorry, That should read, clever DICK to the rescue! [:-clown]

Do it NOW before it`s too late.

The winches we have available today all suffer from high current use when stopped, but holding a steady load, such as sheets being held in one position.
This is because the winch drive motor is simply geared down to drive the output drum or arm.
The same applies to all servos, twist the output arm and the drive motor will turn.

A simple gear train is capable of being driven either way, gearing up, or gearing down, like changing down a gear in the car, slows the car down, a braking effect.

The engineering solution to this, is to incorporate a Worm and Pinion reduction gear into the drive gearing.
A Worm and Pinion can NOT be driven in Reverse,it is widely used in things like Lifts, or Cranes, where stopping the Motor for any period, does not incur a Power loss.

The simple gear train used in our servos and winches MUST use power when stopped, the only way to cut down the power used is to increase the gear ratio from the drive motor, to the output drum or arm.
This would slow the speed of operation very much, too much to be viable.

The same gear reduction we now suffer, could be achieved with ONE Worm/Pinion assembly,the output would run at the same speed as the original, but it could STOP and stay stopped, but NOT use ANY Power at all!.
This would mean a complete redesign of present servos and winches, but just look how different a RMG winch is compared to all the others!
I have seen ultra light servos used in Indoor planes which use Worm/Pinions, but only to cut down on weight, never heard or seen any commercial ones though.

I have often wondered wht they didn’t use worm gears in servos. It sure seems like the answer. Must be expensive. When you produce 1,000,000 servos the price probably goes up 10 cents a servo. Reason enough to charge us another $50. Sorry, my cynicism is showing.

Don Case
 Vancouver Island

I think a mechanical stop off is the answer. I’ve seen this implemented for arm winches (on adjustable backstays in the US1M fleet).

There is a picture of it here: http://photos.groups.yahoo.com/group/us1mrcsailing/vwp?.dir=/Talon+II&.src=gr&.dnm=Backstay+Lock.jpg

It might take a bit of trickery to get it to pop out of the locking cup. You might be able to use an idler pulley and spring on the return line so that if the return line is tensioned it pops the ball out of the cup…

Will Gorgen

Edit: I should give credit to Steve Andre for this design. The picture is of his boat also. I have not tried to implement this, but I saw it in Model Yachting and thought it was just brilliant. Well done, Steve!

[:-banghead] Sorry Will but I keep getting an error message with your link.?[:-banghead]

Do it NOW before it`s too late.

I get a sign-in msg…sorry for the troubles


_/ if it isn’t broken, don’t fix it! _


Why don’t you common togher the two wires of the motor to give an Electrical BRAKE. Have done this on far larger motor works well.

Don’t overlook the guys at ServoCity !

They seem to be interested in working with sailors - and here is just one new offering:

Over 2,000 in-oz. of torque and 180 degrees of rotation when used with the new HSR-5995TG.
Only $79.90 for 665 in-oz. of power
This combination still gives you a full 90 degrees of rotation due to the new external potentiometer.
HS-645MG + 5:1 ServoPower Gearbox = $79.90)

It looks like the photo page is for members only. Sorry about that.


I was looking at those mega gearbox winches a while back, but I couldn’t get anyone there to tell be about the rotation issue. Obviously when you up the torque you decrease the speed, so speed might be an issue. but maybe for a spin halyard you would be alright. The next issue is going to be getting the arm long enough for the halyard travel. But with a 2:1, 3:1 or even a 4:1 pulley system, you should be able to get enough travel. THe nice part about an arm winch is you can get it to lock off so that your holding torque is 0 and the servo does not drain the battery just to hold the halyard.

  • Will

Will Gorgen

Correct Wil -

if one were to swap gear sizes, the thing would “rip” the spinnaker to the top of the mast but not sure it would have holding power. I do note that they (Servo City) has a servo with an output shaft to which a worm gear add-on might be possible. CHeck out the “Footy” discussion topic, as I posted name and email of a fellow who responded to my question about 360 servo modifications. At least it is a name to start with.


Since I possed the question, I have made several experiments.

I acquired a ‘ratchet and pawl’

I attached the ratchet to the outside of the winch drum and a short travel servo close to the drum. The pawl attached to the ratchet works fine.

The only problem is that any plastic or nylon ratchet has insufficient strength on the teeth to hold the pawl from slipping out and the system fails.

Therefore, the ratchet and pawl has to be made of metal.

Metal is heavy.

I took the ratchet & pawl to a metal turner and they dramatically reduced their overall weight by skimming and drilling.


use titanium, might be a bit more expensive, but it will be light & strong.

I see said the blind man to the crippled nudist who put his hands in his pockets & promptly walked away.


I could be wrong, but I’m guessing that you are leading your spinnaker halyard directly to the SW380’s drum spool. I’m guessing, also, that you are using a drum of large diameter so as to haul in a lot of string in a hurry when you hoist or retract the spinnaker.

One thing I’m sure of is that you are one brave and adventurous sort of guy to be sailing an A-Class boat under spinnaker in Force 4 winds! How do you keep the mast in the boat? How do you keep the boat in the lake?

Two suggestions regarding the problem of having pull on the halyard causing the drum to fight unwinding…

Forget using a ratchet and pawl. Sure, the RMG winch is wonderfully accurate in going to the assigned start/stop position, but if there is an unintentional change to the transmitter’s control lever while the winch is in mechanically locked position you really run risk of harming it. The winch fighting slowly to reel the halyard back in seems to me to be a lot less brutal than the winch fighting against being locked solidly in position by a mechanical device.

Consider using a smaller drum on the winch along with using a two-to-one block and tackle for the halyard. There is much more “leverage” force to resist unwinding with a smaller drum. The block and tackle will provide the means to haul in a bunch of string in a hurry. I do not know the technical why and how of it, but it works for me. Actually, the one and only problem with spinnakers I haven’t yet dealt with is that of a halyard unwinding.

I’m forwarding to Dick Lemke by separate email a photo showing the spinnaker drive I have installed on an AMYA AC Class boat. Dick is an authority on what it takes to get a photo posted on this forum. I haven’t a clue as to how to do the photo here and now. Him, being
the nice guy he is, will hopefully do me the favor of posting the photo in the manner of a follow-up message.

The photo shows a SW380 mounted on starboard and being fitted with the 26mm-Wide drum available from RMG. A line from the drum is led aft to a turning block and a line from the other sheave on the drum is led forward to a turning block. These two lines from the winch pull a trolley back and forth on the deck. On the trolley is a double block. One end of the halyard line is cleated aft. The other end of the halyard is led forward through a sheave on this “traveling” block, then aft, and from there it is led up the mast. In five seconds the trolley goes forty inches while hauling in eighty inches of halyard. The spinnaker retractor line is led (and works) in opposite fashion to the halyard. A single elastic cord passing through a sleeve that is epoxied to the trolley handles the spinnaker sheet, afterguy, foreguy and pole topping lift.

Rich Matt

The following photo is being posted for Rich Matt to better illustrate his above response regarding the issues involved in using any kind of locking device which could damage a servo/winch. Please direct questions regarding the photo directly to Rich.


Here is an idea that I finally found, that controls a line as a servo operated jamb cleat. This was originally designed as a Pea Pod mainsheet adjustment. One end of the line is under rubberband tension… pulling mainsheet in. When this cleat is released by the servo, the rubber band either pulls the sials in - or if wind is blowing, the sials will move out. At desired location, servo turns the fitting and the line is cleated in place until the in/out holes line up and once again the rubber band handles the sheeting location.

Not sophisticated, but it worked until strong arm winches came along. Perhaps the “concept” could be adapted to a one-way sheeting (or halyard) idea for spinnakers… or other needs on board where line adjustments might be needed.

What is nice, is that the servo doesn’t need to be large to hold line tension - and the winch (unlike arm type) isn’t using battery power during use except when cleating/uncleating line. You can see the dotted lines representing the clevis attachment to servo in the drawing.

Download Attachment: [ Jamb Cleat1.jpg](http://www.rcsailing.net/forum1/data/Dick Lemke/200533105450_Jamb Cleat1.jpg)