Wishbone rig questions

[Bruce46]

Seeing the work some designers have done with unstayed masts and wishbone/spirt rigs has stirred my interest.  However, I am finding it difficult to find information about what is the proper relationship (angle) between the mast and the wishbone boom. Equally elusive is how the running rigging is laid out.

Is there a book or technical paper that would provide answers? One person suggested going around to marinas and looking at boats, however, I not very good at climbing over gates or running from rent-a-cops.

Thanks for any guidance.

Bruce 

[PAR]

Is there a specific question(s) you had in mind as the subject could get pretty involved. I don't know of books or technical papers, though a few owner's manuals might be helpful.

[Bruce46]

Par thanks for your reply.

I know that the angle of the boom can alleviate the need for a boom vang, how is that determined? I would imagine that there is no perfect angle for all boats, and experimentation would be necessary for the perfect set up for a specific boat. 

[PAR]

The boom angle can be fairly arbitrary, but it eliminates the need for a vang because it can't rise up like a conventional boom. This is the very reason we use a boom vang, to control boom rise (and of course sail shape on Bermudian sails). So, to answer you question, yes there is a perfect angle, though one or two degrees either way wouldn't likely hurt things much. For example, if you replace your sail with one from a different design, though other wise of the same dimensions, you'll likely have to make adjustments to the snotter and hence the angle of the boom. Also depending on how much difference the boom angle is from the previous sail, the boom length may not accommodate the new sail. Most boats will have a narrow window of adjustment and learning how to incorporate this as well as the other sail shape controls, will determine how effective you can be with the sprit rig.

[Ray Frechette Jr]

Add to the mix that the perfect angle will change according to conditions.

The sprit or wishboom controlls both leech tension and outhaul tension.

A steeper angle provides more leech tension and less foot tension.

Shallower angle reverses that.

On the CoreSounds as designed by graham you have more hoist on the mast than you have sail for given track length.

So in light airs you hoist to top of mast.  This gets sail higher in clearer air and reduces leech tension relative to foot tension and allows sail to twist off in upper reaches more.  And as a happy happenstance you want more twist in light airs as difference between true windspeed and relative windspeed vectors is greater as you raise up wind column.

As windspeed increases, the vectors narrow.  You want less twist.

You also want to lower center of effort on sails so you lower sail to bottom of track.

This steepens the sprit angle which induces more leech tension flattening the sail twist angle.

So practically speaking you alter your sprit angle by adjusting sail height rather than snotter attachment position.