Cunningham new installation

[andre]

Hi everybody. I am in the snow for a couple of months and for the next saison i want to install a cunningham for my main sail. Do you have an idea for do that.

[Ron Hill]

Andre : From your post I assume that you do not have "In the mast mainsail furling" ?

[andre]

Hi Ron what do you mean about. I don't understand

[Ken Juul]

This is how mine is set up.  Pretend the 2x4 is the mast.  With a strap attach one end of the line with a bowline so it can be removed if needed.  First turning block is attached with a carabiner to the lower vang attachment.  Line goes up through the block with the cunningham hook and then back down to a cleat.  If I remember my engineering correctly the lower block halves the force put on the strap so you don't pull it out of the mast.

[andre]

Thank you very much Ken for the good explication and photo

[Craig Illman]

When I added my solid vang, I just bought a cunningham hook and added it to the fiddle block that used to attach to the boom bail on the old vang. I think you'd want at least 5:1 purchase for a cunningham on our large mainsails. That being said, I don't remember if I ever actually used it for anything other than maybe a preventer once or twice. Obviously as a preventor, the foot end was attached somewhere other than the mast base. I don't intend to have this thread morph into a preventor discussion. It's well covered elsewhere. 

Craig

[Ken Juul]

I used this set up a quite a few times on my old blown out main.  With the sail luffing it had plenty of pull, didn't try it with a load on.  With the newer sail I can get plenty of tension with the halyard.  I agree if you have a spare vang it makes sense to use it as either a cunningham or preventer.

[Stu Jackson]

Our 3:1 cunningham blocks died late last year.  We use Ken's idea of running a line through the cunningham hole in the luff of the mainsail, 'cuz the S hook I used kept falling out, even after I learned that a cunningham hook fell out even more.  Before I went and invested in yet more blocks for the cunningham, I tried it with just the straight line, 1:1 purchase.  It works just fine (although we do have Batt cars on our main).  You might want to try the 1:1 before you spend $ on blocks.

[andre]

Thank you everebody. I read your explication with my dictionnary but it's very interresting.

[Tom Soko]

Ken,
I've been pondering your comment about halving the force on the strap for a few days.  I THINK that the downward force on the cunningham and the downward force on the strap are a factor of one (and equal, ignoring friction), and the upward force on the block is a factor of two. So in other words, I don't think the block is accomplishing anything.  I could be completely wrong, but that's what my feeble brain is telling me.

[waterdog]

Wouldn't it be a full load on the luff and lower block attachment; half load on the strap and the cleat?  If you imagine pulling at the strap or cleat locations you would have to pull two feet of line for every foot of movement on the luff giving you a 2:1 advantage...

[Ken Juul]

Made me go back to the books.  As set up there is no mechanical advantage, to give a 2:1 one of the blocks would need to have a becket for the bitter end of the line to attach to.  In my case the bottom block could be eliminated and the line attach there instead of using the strap.  I think the reason the PO did it this way was to eliminate clutter at the base of the mast.  Also I think it is good to have the downward pull as parallel to the mast as you can make it.

[waterdog]

Ken, you are right as set up the lower block doesn't do much, but there is still very definitely a 2:1 advantage in the system.    A becket would give you 3:1.

[Stu Jackson]

I had the 3:1 as sketched by Steve before my blocks died (Lewmar Synchro Blocks) - less expensive, but the cheeks didn't take the sun here at all (second pair, guess I'd go Garhauer if I did it again).