Rigging mod - for riggers?

[oldbilbo]

I've been puzzling for some time over this. P'rhaps someone with more joined-up grey cells will spread a little wisdom.....

Consider a modest BMU-masthead sailboat of about 28' oal/30' mast/3 tons displacement. Modest....

Now consider the implications on the backstay arrangements of adding an inner forestay via a suitable mastwall fitting <1 metre below the main forestay attachment - which is what's recommended by Selden and others.

It seems to me that, with this 'new' stay tensioned, plus the existing tension wound into the main forestay, the total load imparted to the backstay will be increased considerably. That has me wondering if the backstay needs to be 'beefed up'.....

....or is it of little consequence when only one of the forestays will carry the load of a filled sail at any one time?

 

[Blueboatman]

Ooer. You need some vectors!
Simple answer . Leave well alone on the backstay or if you are heading off to the sun, consider turning a perceived worry into a useful safely feature ( for all that tradewind running and rig pumping) and convert to two backstays from the transom corners ... Which will give you a nice attachment for a sun awning !
But add weight and windage too.
I have a temp inner that will never achieve the pretension of the outer forestay . In fact a barber hauler arrangement is useful for getting a really flat, windward sail shape on the jib.

One could argue that a double reefed mainsail sheeted in will assist support in line with the working, inner forestay..

Once upon a time I could vector the real loads and mast compression, prob the deflection too.
So, perhaps of little help Bilbo for yer peace of mind!

 

[lustyd]

Surely if it's below the main forestay then the backstay tension will reduce and the main forestay tension may increase?

 

[srp]

It seems to me that, with this 'new' stay tensioned, plus the existing tension wound into the main forestay, the total load imparted to the backstay will be increased considerably. That has me wondering if the backstay needs to be 'beefed up'.....

Only if you are increasing the compressive load at the mast step - if you keep this load the same then the backstay load will remain the same, and the original forestay load will reduce as it is now shared by the new inner forestay. If you're planning on increasing the (main) forestay tension, and adding some more on an inner forestay, then you will increase the backstay tension, so you might have to either add a second backstay, or go up a wire size or two. But, at the same time, you will need to increase the strength of the mast step and the attachment arrangements for the forestay and backstay, to make sure they can carry this extra load.
Having seen what over- enthusiastic rig tensions do to a small sailing boat, and carried out the repairs as a result, I would definitely look further than the backstay if you want to beef things up.

 

[BabaYaga]

Now consider the implications on the backstay arrangements of adding an inner forestay via a suitable mastwall fitting <1 metre below the main forestay attachment - which is what's recommended by Selden and others.

The recommendation from Seldén is that an unsupported IF fitting should be positioned at a point 3 to 6 percent of the mast length (or rather fore triangle height) below the main forestay fitting. So for a 30' mast considerably less than 1 metre at most.

 

[oldbilbo]

The recommendation from Seldén is that an unsupported IF fitting should be positioned at a point 3 to 6 percent of the mast length (or rather fore triangle height) below the main forestay fitting. So for a 30' mast considerably less than 1 metre at most.

Yes, thanks, I have the paper catalogue too - the one that shows an IF with a 'storm jib' set and a full-hoist mainsail..... and the info you post. Then again, I've actually spoken with several of the guys who do the work, at Selden and elsewhere, and I'll follow their deeply-experienced and hands-on guidance.

The thots from them on 'beefing up the backstay' tended to focus on rather larger racing boats with hydraulic rams or multi-part cascading purchases with skinny, bendy masts.... which is why I thought to ask here.

 

[Avocet]

I could be way off the mark here, but when you tension the inner forestay, won't that reduce the tension on the outer forestay (thereby keeping the tension on the backstay more or less the same? Is it common to take up the tension on the other one after tensioning the inner one?

 

[William_H]

Oldbilbo I think your guess last line of firsdt post is correct. Indeed with the inmner forestay lower than the outer forestay the tension on backs tay will be slightly less but with more tension on the lower aft mounted shrouds. Certainly when you load up the temporary inner forestay witha sail full of wind the outer forestay will go slack or at least have little tension without a sial full of wind. Either way no concern about the backstay. Indeed as said I believe much of the load of a backstay is taken by the mainsail mainsheet when close hauled. IMHO the rigging load when static no sails will always be a lot less than loads when pressed under sail. So in practice it is one forestay or the other unless you fit 2 jibs. Even then only in a true cutter hard on the wind will back stay get a lot of tension. good luck olewill