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bewitched · 02-01-2011, 16:31

Quote:

Originally Posted by Marksman

My apologies Bewitched

No need to apologise - I misread post all the time and go off in completely the wrong direction.

Greggegner · 03-01-2011, 06:06

You may never have any issue but some of the statements are not correct. The force on the boom is the same no matter where the mainsheet is. Deciding how to distribute the load and how the point load (like during an accidental jibe) is your problem. Momentum counts, when the boom comes over fast and the main sheet at the end on the boom come up tight the middle of the boom wants to continue moving. This put a tremendous stress of the boom. The amount of stress is proportional to the distance from the center of the boom to the closest attachment point. I would suggest adding a permanent preventer (the friction type) and call it a day.

ozskipper · 03-01-2011, 07:07

Quote:

Originally Posted by Greggegner

You may never have any issue but some of the statements are not correct. The force on the boom is the same no matter where the mainsheet is. Deciding how to distribute the load and how the point load (like during an accidental jibe) is your problem. Momentum counts, when the boom comes over fast and the main sheet at the end on the boom come up tight the middle of the boom wants to continue moving. This put a tremendous stress of the boom. The amount of stress is proportional to the distance from the center of the boom to the closest attachment point. I would suggest adding a permanent preventer (the friction type) and call it a day.

The forces on the gallows are larger as you move sheeting forward. Try and push the boom into the wind from, say, where the vang attatches. Now do the same from the back of the boom- you will find there is less load aft. Therefore less load on the gallows and less strain on the boom via the mainsheet.

Of course the pressure at the goosneck will still be the same.

Cheers
Oz

cal40john · 03-01-2011, 15:15

Quote:

Originally Posted by Greggegner

You may never have any issue but some of the statements are not correct. The force on the boom is the same no matter where the mainsheet is. Deciding how to distribute the load and how the point load (like during an accidental jibe) is your problem. Momentum counts, when the boom comes over fast and the main sheet at the end on the boom come up tight the middle of the boom wants to continue moving. This put a tremendous stress of the boom. The amount of stress is proportional to the distance from the center of the boom to the closest attachment point. I would suggest adding a permanent preventer (the friction type) and call it a day.

Yes the mass of the boom itself wants to keep going, but this is minor compared to the sail pulling on the boom. Most of the sail's load is at the end of the boom, with loose footed it's all at the end. Where's the best place to put a preventer, at the end of the boom.

Get a metal pipe, put a weight on the end. Swing it like a bat and hit something at the end of the pipe. Now do it again hitting something somewhere in the middle of the pipe. Which time did the pipe fold up?

John

Laidback · 03-01-2011, 16:00

Quote:

Originally Posted by Greggegner

I would suggest adding a permanent preventer (the friction type) and call it a day.

A 'permanent' preventer - maybe NOT a good idea - a Boom brake, far far better - the simple stainless one picture above works very well.

Greggegner · 03-01-2011, 16:44

Yes, I Misspoke boom brake not preventer...thanks

WeeHope · 05-01-2011, 17:32

Here's a similar idea I installed on a Cal 20 a few years ago. It does present a bit of a problem with hardware moving quickly while tacking in a bit of a breeze, solution was to whip line around the tiller handle. My goal with the main sheet was to reduce the amount of line that would be needed in the previous racing photo.

Chris

mbrault · 12-01-2011, 15:58

Thank you all this is an eye opener / confirmation for many isssues... I realy like the ideas... It will go on with the arch which will be composed of 4 x sch 80 6061 Aluminium 2.5" tubing. The tubes will be rolled into shape then covered with 1/8" 6061 Aluminium sheet to create the tapered shape and 2 vertical sections of 1/4" will be integrated inside to prevent any distortion that might be created by the lateral force applied to the top section... If that makes any sense to you.

What is a boom brake? Anyone has any pictures?