Friday, February24, 2017

Jibsheet Fairleads

Improve your sheeting angle

Do you find that you get wraps on your jib winches or just want give a better lead angle to the winch? In the last race we did, a crew member got a wrap so tight that the only way to release it was to cut the sheet with a knife. We strung the lazy sheet to the secondary winch and took the pressure
off but that was not enough to free the wrap, that is when the knife came out. It cost us only one place in the race but got me to investigate the issue of providing some kind of better lead angle into the winch. The winch manufacturer recommends between 3 and 8 degrees as the ideal sheeting angle. In my case, after careful measurements I found I had a 2 inch drop in 36 inches which is just a tad over 3 degrees, which is at the low end of the recommendation. Given that it did wrap, something like 6 degrees might help the situation. It is often good to start with just two wraps and then add more if needed after the jib is most of the way in. In my case, with Andersen winches, two wraps is sufficient against my 1/2 inch jib sheets. But before making the measurement of the actual lead angle I used the sketch to the left which is part of a 3-d CAD model I have for my boat. It showed 0 degrees lead angle so apparently it is not all that accurate. Thus started my look at alternatives.

The most obvious change would be to add a block on the deck. This has the advantage of being low friction and would clearly do the job. It has the disadvantage of the cost of the block plus the added deck clutter, the block banging into things and how to mount it. Do I put down a track to give some adjustment or a fixed stand up block? These questions led me to investigate using a non block fairlead and that will be the thrust of this article.

inches degrees
1 1.5
2 3
3 5
4 6
5 8
6 9 1/2
7 11
The recommended lead angle for my winch (Andersen) is 3 to 8 degrees. To measure the lead angle take a yard stick and align it parallel to the winch mounting plate. Hold it out and measure down from the height where the sheet contacts the winch to the point at the far end of the yard stick. In this case, the measurement is 4 inches. Here is a table of the degrees of lead angle. For a 6 degree lead angle, use 4 inches per yard or 10.5 cm per meter. Antal recommend between 2 and 10 degrees. Harken recommends 5 to 8 degrees. Lewmar says 5 to 10 degrees. Barient said 3 to 8 degrees.

I measured the friction in a 1/2 inch StaSet sheet at several deflection angles. What I found was a linear increase in friction up to about 30 degrees and a sharp increase in friction above that. For the 10 degree deflection I would need to take a sheet from 0 degrees to 5 degrees the added friction was negligible, about 3 percent.

From this there appears to be little advantage of a block over a friction fairlead. Cover wear is an unknown and one I don't know how to predict. I suspect it would follow a similar curve with small angles giving less cover wear but I really don't know and I assume it will depend some on the material and weave of the cover.

UPDATE: Better data on the friction can be found HERE. It looks like 10 degrees would cause 7-10% added friction, still negligable.

At one end of the scale in complexity would be a simple padeye with the sheet let through the eye. The concern here was not so much the added friction on the sheet but the friction on the line causing premature failure of the line itself. I don't know if this is an issue but it is something to consider. It would be nice to have a larger radius to help minimize this issue. It will also cut the friction some unmeasurable amount.

The next step up is a fairly standard control line fairlead. The question here was one of strength. It was reported that this has been successfully used on a T-10 in this application. This is a strong candidate although the fact that it is plastic is a concern. Whenever considering something that might break you have to ask what the consequences would be of failure. If someone could get hurt, don't try it. In this case, there might be some inconvenience in having to remove the broken part from the line and continue on without the fairlead. Not a large risk. But not really built for sheets, more for control lines.

I really liked the look of this particular fairlead with the exception that the hole was 1/2 inch, too small for 1/2 inch line. I also don't think the radius is smooth enough to actually reduce the friction. This fairlead will act more like two sharp bends rather than one gradual one.

The Suncor Bullseye Fairlead at $15 to $20 will hold 5/8" line and is a good candidate. Again, not a very smooth rounding in the opening which I don't like.

A bit of a high tech or hybrid approach is to put the standard padeye on the deck and tie a ring to a low friction or for that matter any ring. The REI rings discussed in other articles are low friction and would probably work as well although not as classy looking.

This looks like the best one and the one I am purchasing. It is under $25, has a 3/4" opening with a smooth rounded opening. Mauri Pro Sailing had them in stock and the order has been placed.

Here is what the finished product should look like.
Maybe not quite the setup of a TP-52 shown here but close.

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