traveller

[imabinder]

The traveller on my 32' steel sloop is currently in front of the companionway. I want to move it forward of my dodger. According to formula for vertical load this would create a vertical load of 1766lbs or so (20 knot V). If I were to attach my mainsheet to the cockpit sole beneath the end of boom then run it 7 feet along the boom and down to the traveller (then it runs forward to mast and then back to cockpit) does this change the E-X from 13-7 to 13 -1?
E=13
P=40
X=7
Pros and cons of this rig? ( My idea was actually to weld a 3-4 foot "pedestal" in front of the wheel for the attachment point so when sheeted out it would clear coamings and lifelines.)
Thanks, in advance, for any feedback.

[Brion Toss]

Hi there,
The good news is that you would reduce the load on the sheet by anchoring part of it further aft. The bad news is that you would drastically reduce the efficiency of the traveler, because a sizable component of the sheet's force would always be pulling to centreline, when you frequently (usually) want to be pulling higher or lower than that.
Instead of a pedestal, you might consider boom gallows, with traveler built-in, at the aft location. Requires some engineering, but it is an elegant way to do it, and efficient.
If you take everything forward of the dodger, there are ways to minimize strain on the boom and reduce effort.
Fair leads,
Brion Toss

[imabinder]

I like the idea of a boom gallows but engineering seems a bear. If the traveler was moved forward of dodger with a run aft to a block at end of boom then forward and down to traveller
again does this improve the load on the mid-boom purchase?

[allene]

Originally Posted by imabinder

I like the idea of a boom gallows but engineering seems a bear. If the traveler was moved forward of dodger with a run aft to a block at end of boom then forward and down to traveller
again does this improve the load on the mid-boom purchase?

The way to think of this is that the line will have constant force so every part exerts the same force on the boom. The effectiveness is then related to where the attachment point is. In your example, can I assume you have one part at the end of the boom and one part down to the traveler (I wasn't clear on that)? To make the story easy, I will assume the mid boom attachment is mid boom (half way). In this case, the force at boom end and at mid boom are the same. The force at mid boom is 1/2 as effective as the end boom line. That means that you are getting effectively 1.5x the line force on the boom end compared to 2x if both lines went to the end of the boom. If both lines went to the traveler, you would get only .5x force. So if you need 1 unit of force on the boom end, you would need 2 units of force if all lines were mid boom but only .66 units if one of the lines is end boom.

But the same math implies that the traveler is only supplying 1/3 of the load so you have basically cut the length of your traveler in third. Now if you put two or three parts to the traveler, it gains both efficiency and load.

If you move your traveler to the end of the boom, it has full efficiency but then again is is probably much shorter so that hurts. Your mid boom traveler is 2x as long effectively if it is actually the same length as an aft boom mounted traveler. This means that the mid boom traveler with one line going to it would be .6 as effective as the end boom traveler the same length.

Perhaps putting two parts to the mid boom traveler would be a good compromise. You will have to work the numbers with your actual proposed setup.

In case this helps, I put together a page with a variety of mainsheet systems including the unique one I use on Papoose (double ended).http://L-36.com/mainsheet_systems.php