Diamond Wire Tension

george · Post by **george** » October 26th, 2007, 9:44 am

Hi all, just bought Dave Farmer's SuperCat 20 (#55) and after a white knuckled adventure trailering her across country (WA to MD), I am in the final stages of getting her rigged and in the water.

So, I have a question about the diamond wire tension. I found a previous post about wire tension on a SC19, should this be the same for the SC20? I know in theory it should change with wind conditions, but are there some general guidelines I could follow for setting these to a good overall tension for most conditions? Anything specific to the boat?

One other question, Dave had replaced on the transoms on the boat and mentioned that this was probably the only real problem with the older SuperCats; the integrity of the transoms. Has anyone found some suitable ways to upgrade and reinforce these? What do you think about mounting some 3/4 or 1/2 plywood, epoxied into place inside the hull that the fiberglass transom can mount to? Just some thoughts.

thanks for any input. Seems like a great small group of supercat/arc enthusiasts here.

george

Kevin Keller · Post by **Kevin Keller** » October 26th, 2007, 8:55 pm

I think I am going to put an access port on each transom between the rudder gudgeons.

This will allow access to the inside to lay a little more fiberglass in there. Since the fiberglass is so thin where it would be installed I don't think it would cause a loss of strength.

It would also be good for drying out the hulls.

I saw a picture of someones SC20 on the internet that looked like it had been done.

Any thoughts on doing this?

Kevin

Post by **Matt Haberman** » October 27th, 2007, 5:11 pm

I would recomend against putting the access port in the transom. The access ports are not very structurally sound and will only help to weaken the transom. I would also suggest that you avoid wood. No matter what wood you use it will rot over time.
In the past we have always cut an opening in the deck of the hull about 3-4" in front of the transom. We have used this area to access the inside of the hull and repair the transom. We then replace the piece we cut out, glass over it and replace the non-skid in this area. If you cut the access opening like a pumpkin it will make it quite easy to replace.

Eric2101 · Post by **Eric2101** » October 27th, 2007, 7:07 pm

What about an access port on the vertical surface of the hull on the inside above the water line? From thee you could access the rudder stuff and rear beam?

Post by **Matt Haberman** » October 28th, 2007, 1:25 pm

Eric,
I would highly recomend NOT putting a port in the side of the hull as you suggest. There are structural bulkheads and reinforecements under the beam that extend fore and aft from it. By putting an opening in this location you would be destroying the integrity of those reinforcements which could lead to structural problems with the rear beam saddle. In short, putting a $10 port in the hull could cause $1000's in damage.
Not to mention the fact that there is really nothing in there that you could or would want access to.

Eric2101 · Post by **Eric2101** » October 29th, 2007, 6:30 pm

Is the force from the rudders behind the rear beam that great? If so, thank you for pointing that out, I would have put a port there if the situation arose.

efinley · Post by **efinley** » October 30th, 2007, 2:00 pm

I have actually done this exact repair. I had a moderate leak where the rear transom meets the main part of the hull. I had planned to cut 1 hole on the top of the hull a couple inches in front of the back of the hull. While cutting I noticed it got much harder at one point. At the very top of the hull on the inside there is a lip where the 2 halves of the hulls join (at least that is my guess). So once I hit that I turn and ran lengthwise down it. It the end I actually made 2 small rectangular holes on either side of that lip. I repaired the transom and then expoxied the 2 pieces back in. It was my first epoxy job so it isn't too pretty but I could take pictures if people are interested.

-Eric

george · Post by **george** » October 30th, 2007, 5:19 pm

Hi thanks for all the feedback, and if it isn't too difficult to post pictures, that would be great.

So, back to my original question, diamond wires, any input beyond what I found in terms of the supercat 19 in this forum? What is too tight or too loose?

I appreciate the input, hope to get out this weekend. Cooling off here, but nothing a wetsuit can't help.

george

Kevin Keller · Post by **Kevin Keller** » October 30th, 2007, 5:23 pm

I asked either Matt or Tom one time about the tightness. They told me something about using a bungy cord wrapped around the wires to check them. I can't remember exaclty what they said. Maybe one of them can write something up about it.

Post by **Matt Haberman** » October 30th, 2007, 6:34 pm

Diamond Wires:
I will refer you to this thread viewtopic.php?t=97&highlight=diamond

Transom / Port Holes:
Eric the loads on the transom can be significant, in fact these guys are talking about some cracking which means the loads must have been high enough to exceed the strength of the material, cutting a hole in it and putting a wimpy plastic port in will just make things worse. That being said, the reinforcements that I am refering to are actually there to anchor the rear beam into the hull.

Kevin Keller · Post by **Kevin Keller** » October 31st, 2007, 5:33 am

Matt,

I read the Diamond Wire post you referenced. I am not sure if it make sense to me.

With a good wind my SC-20 33' mast tends to bend concave to the wind. In other words, the middle of the mast bends to the leeward side. The leeward side diamond wire is the side that is tight and the windward side is loose in this situation.

With the mast bending concave to the windward side(diamond wires loose) would seem to me to be catching more wind and powering up the sail, not depowering it.

When I tightened both sides it seemed to straighten the mast more. This to me would seem to depower the sail more than a concave sail.

Am I screwed up? I hope I explained this well enough.

Thanks,

Kevin

Post by **Matt Haberman** » November 1st, 2007, 12:16 pm

Kevin,

The mast should always be bending in the middle to the leeward side, if it is bending to windward your going to have problems.

By letting the mast bend more it will effectivly "absorb" the luff round and flatten the mainsail. By keeping the rig taunt in light air the mast cannot bend and thus the sail stays fuller.

Again as mentioned in the previous post, this applies to NON-Prebent rigs found on the SC19 and SC20 (33' mast). Diamond wire tension on the SC-20 tall rig with the triple spreaders is a different animal.

Kevin Keller · Post by **Kevin Keller** » November 2nd, 2007, 10:32 am

Thanks Matt,

Come to think about it if the mast does bend like that and it is rotated it will flatten the sail.

In one of your previous posts you said, " the SuperCat 19, 20 & 20TR do not utilize a pre-bent mast and were designed to be adjusted / tuned as I previously described".

Is the TR treated differently or not?

Since I do plan on installing the TR when I am finished when you get a chance can you tell us how it is tuned?

Thanks,

Kevin

Post by **Matt Haberman** » November 2nd, 2007, 5:56 pm

Kevin,

The 20 Tall Rig was originally designed as a Triple Spreader Rig, is this the setup you have? The triple spreader rig is very touchy and I think it would be quite hard to explain in this forum how to properly adjust the diamond wires so I would rather have you call Tom and discuss the tuning/rigging of this mast with him.