SC20 diamond wire tension

Technical discussion of ARC products
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efinley
Professional
Posts: 69
Joined: March 10th, 2004, 3:23 pm
Location: Ione. CA

SC20 diamond wire tension

Post by efinley »

So I have an SC20 that is old enough I assume it does not have a prebend mast (Hull #113). I tried searching but couldn't find the answer to this...

What is the proper way to tension the diamond wires? Or can someone send me the link to the right thread? I have a vague memory that they should be loose but I can't find it with search.

Funny story (ok kind of funny). This past weekend after my Monterey race we went back out for some more sailing. Just outside the harbor entrance we had steep triangular waves, I call it a washing machine. A couple minutes later I noticed my windward diamond wire slapping the sail and I quickly realized that the turnbuckle had loosened enough that the plastic insert had come out of the end of the spreader bars It was windy enough that this caused a fair amount of "pucker" factor because I was worried about the mast buckling. After thinking about it for a couple minutes I tacked, traveled and sheeted way out and slowly sailed back into the harbor w/o incident. I assume I did not properly tension the locking nuts against the center part of the turnbuckle which allowed it to come loose.

Thanks,
Eric
phoeve
Novice
Posts: 8
Joined: September 12th, 2012, 10:00 pm
Boat Make/Model: ARC22

Re: SC20 diamond wire tension

Post by phoeve »

Glad you realized this ! I had a 1982 SC20 years ago with triple spreaders. One of the spreader caps popped out, however I think it was due to UV deterioration. In maybe 8 kts of breeze we broke the mast. Had to be towed home. Replaced it with the newer mast and never had another issue. Please tune your diamond wires. Call Tom Haberman @ Aquarius sail for details.

I now sail an ARC22 and always watch them closely. With the spin you have to be careful not to dump the main as it supports the mast - it acts as a backstay for the mast.
havliii
Professional
Posts: 272
Joined: March 27th, 2011, 8:12 pm
Boat Make/Model: SuperCat 19, Modded SC20
Location: Fredericksburg Virginia

Re: SC20 diamond wire tension

Post by havliii »

Efinley,

Tom tells me there is no 'number spec' on the diamond tension. (I called with this very question) Measure above the turnbuckle 15 inches (I think) and see if you can press the wires until they contact the mast, then experiment from there. I run mine way tighter than this.

Do not trust the marks on the turnbuckle to be equal tension side to side, one wire is always longer than the other, thus the marks will not yield equal tension. (I made a rig to measure the tension on each side.)

Likely you have the original spreader bar as do I. No pre-bend is possible since the tips of the spreader do not extend past the centerline of the mast, you are only able to pull the mast into a nice straight column.

I find with a dacron sail I can adjust the draft adequately with proper selection of which hole on the clew plate that I use. Hope this helps.
efinley
Professional
Posts: 69
Joined: March 10th, 2004, 3:23 pm
Location: Ione. CA

Re: SC20 diamond wire tension

Post by efinley »

I'm pretty sure that if I ran them this slack the nylon inserts would still be able to pop out again. Sounds like I'll just make them just tight enough to be not loose and call it good enough. :)
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