Loosening our jumper wires

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Loosening our jumper wires

Postby rs vernon » Fri Aug 28, 2015 12:06 pm

Here is a solution to a problem you probably never knew you had, and more than likely you do not have it. "Jumpers" is always a popular subject for discussion. And that is a good thing.

The book Optimizing tells us to put a bit of “starting tension” in the jumper wires when we build a rig. Before we add tension by sliding the swage/tube down the wires, supposedly there should enough tension to start bowing the mast forward. I have made some rigs where the wires are too tight for light air. The mast cannot be made to be straight (or bend aft) up high with the standard light air minimal backstay tension. The draft in my upper main will be too far forward and the upper part of the sail will luff early, with no solution on the water.

So I want looser wires. A lot of the time I have to rewire the jumpers, but there are a few other possible solutions that can give me the looser starting tension I am looking for. (I am a fan of putting 2 sliding swages on the jumper wires, one above the jumpers and one below. Can't hurt.)

Let me emphasize that a small change will cause a lot of slackening of the jumpers, so do not overdo it.

The easiest solution might be to take out the screw on the mast at the bottom of the jumper wires and tie the jumper wires to the screw instead of having them run through the screw. Tie 2 knots, one around the screw and one around the jumper bottom loop(s). That will allow the jumper wires to twist off rather than to sit sideways like they will if you just tie a loop. Too loose? Move the screw down, then tie the jumper wires to it. I find that relocating the screw slightly higher on the mast always gives me too little starting tension in the wires. Some of us have the jumper wires coming out of a hole in the front of the mast, so this is not a possible solution.

Or shorten the jumper struts or cut/file the slots in the jumper struts a little deeper.

Disclaimer: I am talking about aluminum boat parts rather than carbon fiber. Do not breath carbon fiber dust. Big health hazard.

If there is no screw on the mast cut at a downward angle from the top of the aluminum crane to the hole that the wires run through making a hook instead of a hole in the crane. Be careful not to cut into the jumper wire. (You might want to aim at the forward edge of the hole with your cut to keep from sawing into the jumper wires.) Then unhook the jumper wires and see if tying them below the crane solves the problem. Tie a line over the hook and thru the jumpers. 2 knots like above on the mast screw to let it twist off. Often this gives too slack jumpers.

If so, try further cutting downward on your new crane hook. Re-hook the wires and see if you are happy with how much looser they are. My experience is that an aluminum crane can be pretty thin at the bottom of the hook and still be strong enough for tight jumpers to not break it. Proper judgment is required.

If you worry that you might do more harm than good, do not attempt cutting into the crane.

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rs vernon
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