Monofilament Mayhem

This article is about the monofilament line that runs from the sail servo drum up and around the bow roller (or mast step on earlier boats).

You are probably reading this article because you experienced the misfortune of having this line come off the drum. There are two ways that can happen – one is that you had the line jump off the drum while in service because it was too loose, or misadjusted – or two, you had the drum off greasing the servo post, and it got away from you.

It looks simple

One track (groove) of the servo drum takes in the line while the other track lets it out. The line runs up and around the bow roller (or mast step), slick as a whistle. The moving knot where your mainsheet attaches runs the full length from drum to pulley. How nice. What a slick job of engineering to make this look and work so easily.

Ah, but alas!

It is the monofilament line itself that makes reloading the system a challenge. We have tried other lines, by the way, but none really work quite as well as the 100# test monofilament. It is hard to set up, but it is the best material for the job.What follows are the steps for rewinding the line and making adjustments to it.

If you are installing a brand new line, then see Replacing the Monofilament line below for information on installing the new line, tying the end knots, and adjusting the length of the line. Then return here to wind it and adjust it.

Mayhem untangled

To understand the following steps, we must all start at the same place. So no matter how you got in this mess, the first thing to do is straighten out the lines.

  1. To do this, remove the drum from the servo post. Take the screw out of the center of the drum, and then pull up on the drum and it will slide off the top of the splined servo post. You do not need to remove the bridge over the drum to do this.
  2. Now, untangle the lines – but do not untie the end knots that are in the center of the drum. When you have the lines straighten out, and all loops on the drum removed, orient the drum so that your holding the line taught and the drum is right side up. You can tell the bottom of the drum because of the splined seat for the servo post. You should now be holding the drum right side up with one line leading forward on each side all the way to the bow roller and no wraps on the drum.
  3. Wind two wraps of the port line clockwise around the bottom track of the drum. Then wrap two turns of the starboard line counterclockwise around the top track of the drum. Hold the drum so the line stays tight as you are doing this part.
  4. Being careful to hold the drum with one finger on each side to keep the line on the drum, hold the drum over the servo post like you were going to install it. If both sides of the line are taught, you are ready to reinstall the drum. If not, take another wrap on one line, or the other, until you position the drum over the servo post.
  5. Now you need to get the knot in the monofilament line (that you attach the mainsheet to) in the right place. Turn on the transmitter and then your boat. Put the left control lever on your transmitter in the full trim position – usually down. Slide the trim tab for that control all the way in the same direction you have just moved the stick (usually down). The winch will turn until it stops at that trim point (full sail trim). Carefully turn the drum in your hand (being careful not to let that pesky monofilament get loose again) until the monofilament knot is just about touching the bow roller housing (1/2″ at the most).
  6. If you you run out of monofilament on the top drum track before the knot gets to the bow roller housing, simply add a wrap of monofilament counterclockwise on the top track, and unwind one wrap on the bottom track.
  7. Install the drum on the servo post. Note – put a good amount of Vaseline in the deck hole around the servo post where it comes through the deck, and a little in the flat space on the deck where the drum will sit before installing drum). The line should be taught when the drum is in place.
  8. Test the travel of the monofilament knot. Using the radio controls, the knot should go from just about touching the bow roller, to just about touching the drum itself. If not, lift drum carefully and turn one way or the other slightly and reinstall until you get the knot travel correct. It is very important that the knot has no way to reach either the bow roller housing or the drum.
  9. When you put the drum on, the lines should be very tight at first. After you run the servo lock to lock a couple of times, the line adjusts itself better on the drum. The line should end up being quite taught, like a base guitar string. Better tight than loose. If it is loose, see instructions below.
  10. Replace the screw in the drum, and you are ready to go.

Replacing the Monofilament line

If you need to replace the monofilament line, or need to tighten it, there are a couple more steps.

  1. Install the monofilament line through the bow roller. If you are installing a new line, tie the knot in the right place (marked if you get a piece of line from me or measure from your old line. Then stick one end of the line through the bow roller so that the knot is on the right (starboard) side of the roller. Run the two ends aft to the drum.
  2. With the drum off the servo post, stick the right line into the hole in the top track (from the outside in), and loosely tie a knot in the end. Put the left line through the hole in the bottom track and tie a knot.
  3. Follow the steps in Mayhem Untangled above. In step 4, if you adjust the wraps to get the drum close to where it will fit on the servo, but the line is too tight (can’t reach the servo post) – you need to adjust the end knots closer to the end of each line. If the line is too loose, and taking another wrap around the drum is too much, then you need to pull the line through the hole more and tie the end knot to shorten the line.
  4. Old Version?

    If you have an RC Laser where the monofilament line goes around the mast step instead of through a bow roller, you may upgrade your boat. You can buy the new bow roller assembly, and a new piece of monofilament and then follow these instructions to upgrade your boat. Both systems work equally well, so there is no need to upgrade if your system is working well.

    This article was written by Steve Lang of