Mast Eye Strap for Spinnaker block - what size?

[jeremyshaw]

My spinnaker halyard is at the mast head so I get chafe problems. The solution would be to fix a shackled block to the mast a foot or two down so that it can move about and lead the halyard down through that - pretty standard I believe.

But I'm having trouble finding a good fixing. The best I can find is a forged s/s eye strap with two 6mm fixing holes 40mm apart, which I could fix with monel rivets, Duralac etc.

Not sure the exact size of the spinnaker but I think it must be about 750sq ft, so I calculate (though I'm no expert in this) that the load on the block could be several hundred lbs at 20kts.

I'm worried that eye strap may not be strong enough, or the mast material may not take the load. Not had any joy from Z Spars so does anyone have any advice on whether this will be OK or there's a better way to do it? Thanks.

 

[fluffc]

What is causing the chafe?

 

[jeremyshaw]

Q: What is causing the chafe?

A: As the spinnaker yaws the halyard is chafing on the sheaves of the block - or possibly the mast itself (not managed to get up there to see while flying it!). I've tried getting the peak right up tight and various strategems to reduce the yaw, but I'm told the only real solution will be to use this block arrangement, and I can see the logic of that. BTW it's a catamaran, though not sure that makes a difference here.

 

[Guest]

[ QUOTE ]
Q: What is causing the chafe?

A: As the spinnaker yaws the halyard is chafing on the sheaves of the block - or possibly the mast itself (not managed to get up there to see while flying it!). I've tried getting the peak right up tight and various strategems to reduce the yaw, but I'm told the only real solution will be to use this block arrangement, and I can see the logic of that. BTW it's a catamaran, though not sure that makes a difference here.

[/ QUOTE ]

From waht you say ... I asume the present set-up is spinny halyard runs up inside mast and exits via a block set in mast head ? Then if that's case - the halyard is chafing on the mast head edges past the sheave faces.
If the sheave is "axled" by a pin and split pins as a lot are ... can you replace pin with longer and mount a second swivelling block from that pin by a bridle ? then halyard will pass out of existing block to the new added one ... as spinnaker yaws / flies etc. the new block will swivel / follow it. The halyard will stay straight from original.

The strap you mention in original post is nowhere near man enough in fixing to stay for years - which is what you would want. You would have to have a longer strap to pass halfway round mast ... as a part collar ... with maybe 2 or 3 fastenings each side to take the load. That spinny has a lot of force in it ....

 

[jeremyshaw]

SBC, the set up is as you suppose, yes. The sheave is fairly close to the edge of the mast so I think the chafe could be coming from there. As is often the case nowadays there is a whole assembly up there with 4 sheaves on and two pins. Not much room for manoeuvre, but your idea of a bridle would otherwise work. A wrap-round strap would certainly do the job and I could get a local fabricator to make one up. However I 've seen a couple of sister boats with a fixing that's not wrap round; unfortunately the people on them didn't seem to know what the arrangement was, and even with the bins I could not get a good look. Some kinid of custom fixture may well be the best bet - thanks for your thoughts.

 

[William_H]

I am a bit confused by the description of the sheave.
However I have had similar problems. My spin halyard exits through a pulley box set into the front of the mast. ie the sheave is more inside than out. I found the sides of the sheave box were wearing badly partly because I haul the spin out of the main hatch under the boom so initial drag is very much sideways as it is pulled up and simillarly coming down. ( 21fter)
The fix was that I used a plastic dead eye with SS insert which I mounted to SS sheet this was bent up so that one end attached under the sheave box attach rivets the other by 2 more rivets a little lower.
So the halyard exits the sheave straight ahead and down at about 45degrees where it goes through the dead eye then away sideways to the main hatch or whatever...
A diagram would be better but imagine a dead eye attached to the mast uner the sheave box then imagine that mounted out fromm the mast by 30mm or so and at an angle so the hole points toward the bow. At least now the departure from the sheave is always square.
good luck olewill

PS had a wild spin ride Friday night in the dark in a race poor little boat was surfing at times. Crew were gung ho skipper was a bit nervous.( to say the least) I would have rather a smaller spin as the wind was rising. anyway all safe.......back at it again this afternoon..
I had a bad experiencee a few weeks ago in a spin gybe. Lost a man overboard and managed to lose the wind pointer on mast top by dunking under the waves. its a treacherous little boat (yes got the crew back he was happy [warm water]).

 

[jeremyshaw]

Olewill - that seems like a good solution, thanks. Will have to think about the friction etc on a bigger sail, but it would be a lot simpler.

Thanks again

 

[Guest]

[ QUOTE ]
SBC, the set up is as you suppose, yes. The sheave is fairly close to the edge of the mast so I think the chafe could be coming from there. As is often the case nowadays there is a whole assembly up there with 4 sheaves on and two pins. Not much room for manoeuvre, but your idea of a bridle would otherwise work. A wrap-round strap would certainly do the job and I could get a local fabricator to make one up. However I 've seen a couple of sister boats with a fixing that's not wrap round; unfortunately the people on them didn't seem to know what the arrangement was, and even with the bins I could not get a good look. Some kinid of custom fixture may well be the best bet - thanks for your thoughts.

[/ QUOTE ]

On my race boat ... we wanted to have more control over mast bend ... and to stop mast vibration when we were beating ... So we fabricated a "stirrup" to fix to the mast and a second forestay ... the stirrup passed round the mast and stopped a few cms from the mainsail channel. Each side had 2 rivets to fix (might have been 3 ... while ago now !!). OK this was set-up at just above cross trees height and stay was like a cutter or fore-baby stay. But it certainly worked.

I think whatever you do will be difficult as the spinny halyard should exit above forestay or at least as near to above as possible ... so even if you cure the masthead chafe - you could induce a problem of chafe on the stay ...