Spreaders

[slowpoke]

Chad, What is the advantage you are looking for with the diamond arrangement for the top shrouds? And are they really adjustable?

[Chad]

By bringing the bottoms together I can adjust them both with one string, is all. I'm using a lever down below to adjust them, but may abandon that in favor of a simple purchase. Not sure the lever will have enough throw...

[slowpoke]

Seems like you're going to need a 6 to 1 purchase at least, if not more. Didn't you say you are looking at 400# stressed?

[Chad]

A bit less for the caps, I think.
I have the 4-ish to 1 lever, with a 2:1 line currently, so that's about 8:1 and it's easy to pull.
There's plenty of room for whatever purchase I end up needing, along the compression post.

[Warren Nethercote]

I am pulling this topic back from page 5 .......

My mast-builder (Fast Composites) is talking about spreaders with me. Their designer had earlier suggested 27 inch long lowers and 15 inch long uppers, both raked at 20 degrees. Looking at the Watershed deck plan it would seem that the chain plates lie something like 22 degrees abaft the mast step centre, so 20 degrees appears reasonable, particularly after mast rake.

Earlier in this string Chad spoke of 1100mm/600mm (43 inches/23.6 inches) from C-Tech and Phil appeared to have made his spreaders 42 and 30 inches. Both of these are much longer than the recommendation I have received. My concern with shorter spreaders is that they will not deflect the V1s and V2s as much as longer spreaders would and thereby would be less capable of inducing pre-bend.

In another string, identity forgotten, I recall someone (Chad?) talking of 30 degrees spreader rake, which seems big (but if Chad, it is a rotating mast so may be a red herring).

So, from the boats actually sailing out there with non-rotating masts: what spreader lengths and what spreader rake are you using (If it is 'stock' C-Tech, what are the numbers?) Are you happy with the result or would you recommend something different?

[Chad]

I kept the stock Ctech lengths with my floppy-spreadered, rotating mast.

With wide chain plates, longish spreaders, and 30-ish degree rake, your boat needs less/sees less tension. For a boat with no main bulkhead at the mast/chain plate station, it's just a good idea to choose a lower tension setup. There's no reason I can imagine to use narrow shrouds.

So lowers are (cut length) 46" long, swept 30, and have 10degree of up dihedral.
The uppers are 26", swept 30, and up 15.

[Warren Nethercote]

So Chad, if I interpret this correctly, by going with spreader rake greater than chainplate rake (ie, 30 deg vs 22 deg) and long spreaders you get pre-bend with lower static rigging tensions (which seems logical)? Conversely, with shorter spreaders I will need more static rig tension .... which seems undesirable. The longer, higher rake set up should also be more amenable to mast-bend control through a forestay tackle.

[jray]

Warren, just measured my spreaders. C-tech mast, originally set up for single spreaders. I added the uppers for insurance. My uppers measure 406 mm out from the mast out and the lowers are 889 mm measured the same way. They were pre assembled from C-Tech to fit the mast. I can look for the angle information but think what Chad provided you is the same numbers.

With the uppers it is easy to tune prebend. I run around 5" of bend. Wouldn't change anything on how it is set up.

[Chad]

From early days, we've all put our chain plates at 30, not at the place suggested by the plan.

[Warren Nethercote]

Thank you all!

[ryderp]

Warren,

I ended up shortening my upper spreaders a bit - they just look better. I think that the lowers need to be about as long as the diagonal from the mast to a vertical line drawn up from the chain plates, plus a little bit of sweep angle and length to bend the mast forward. Unless you are moving your chainplates inward, the lengths recommended by Fast Composites seems too short.

Phil

[Warren Nethercote]

Phil, I am inclined to think so too. With class rules not allowing outboard sheeting of the jib on a beat there is no benefit to a narrow shroud base, and if you go wide, why not go long with spreaders to reduce mast compressive loads (I think this was the point that Chad made earlier - easier induction of pre-bend is just a side effect).

[Mist]

I'm building Mist's spreaders. Thought I'd show the jig I made to align them.