How do I convert sail area to Kg force?

[grpanes]

I have a jib of 128sq.feet and am considering fitting a furling drum which is rated with a S.W.L of 554 Kg. How can I calculate if this is adequate? I assume there is a formula which needs estimated maximum windspeed to be input. I sail a gaff cutter, total sail area approx 600 sq ft and weight about 5/6 tonnes.

 

[FWB]

Try this

 

[alec]

Nice find Dylan !

Thanks

Regards,

Alec

 

[grpanes]

Dylan, thanks for this. I am now looking at it. Graham

 

[Roberto]

Graham,

if I read correctly the indicated spreadsheet, it only gives an indication of the total force produced by the sail

the force applied to the tack angle (and the furming drum) can be of a very different magnitude, it basically depends upon the amount of catenary you are ready to accept in the forward stay, especially if you use the sail for windward work, bringing the catenary to an acceptable limit may mean having to multiply the total force on the sail by X times to have an idea of the force applied to the tack angle

maybe the best option is to ask your sailmaker for what kind of forward stay shape he built the sail, then ask the drum manufacturer "I need 1-2-3% (or whatever) catenary, what will be the tension on the stay/drum?"

with a really "straight" stay, the tension can be as much as 5/10 times the force produced by the sail..

 

[grpanes]

Roberto, Thanks for your comments. There are two headsails. The "inner" (staysail) is hanked to a forestay that supports the mast and is under high tension. The sail I am concerned with is the "outer" jib which flies from a long bowsprit and has a sewn in luff wire - fixed only at head and tack. It is difficult to get high tension in this so there is a considerable catenary to windward. I think you are right in suggesting that I contact the drum manufacturer.