Mast anti rotation on a N570 (boomless)?

What's the best way to limit mast rotation on a boomless cat. I have a N570 with an NACRA Inter 18 CF mast. At least, to the best of my knowledge that's what it is, it's 30' 4'' tall from halyard sheave to base. No Anti rotation control arm installed.

Can I buy something likeTHIS, and fabricate something?

I can think of a few ideas with the control arm above. With two linens running to the front beam, to two cam cleats mounted on port and starboard side of the mast. With the control arm either facing front or back. I don't like the back idea since it would be close to the tramp and in the way. I also am not sure about it only having one mounting/rivet hole on each side, which would allow the control at to move up and down after installation on the mast.

Any good ideas? I'm sure someone already figured out a good solution.

When you have a boomless main you don't need to limit mast rotation. You need to induce rotation using that rotator arm. Don't rivet it to the mast but through bolt.
Buzz

The Dart 18 use a line from the main clew to the mast spanner. A little crude, but works.

I need to limit mast rotation going upwind, I also don't have a problem needing to over rotate the mast downwind since I run a spinn. Good idea on not riveting, looking closer at the piece from Murrays I see it has a 1/4'' hole for NACRA, so a 1/4'' through bolt should work well.


Does that work?

Very unusual to need to limit rotation when boomless. the back edge of the mast needs to point at the shroud upwind, but sheeting in the sail combined with the jib slot pressure forces it more fore/aft. the only reason darts have the line is to rotate the mast on a gybe

I'm not sure why I need to, but on an upwind leg the boom certainly seems to be rotated too much, it has a very sharp angle to the sail. Looks to be over 45deg to the hulls, and forward of the shrouds. That is with a lot of main sheet tension. If I force the mast to be more straight by pulling on the diamond wires I can get the tell tails to flow on the inside of the main sail and the angle seems to line up better with the rest of the sail shape.

In light wind it's right with the sail "baggy", but in heavier wind 15kt plus I feel I need a flatter sail and less rotated, pulling on the downhaul flattens the sail but the rotation is now too much now in relation to the flatter sail curve.

Maybe I got it wrong but it certainly appears to be over rotated in heavier wind with a flatter sail.

The spanner can be mounted where the mast base is already riveted/bolted and then the control lines are led to fairleads and cleats mounted on the main beam. I don't have one on my boat though and seem to do fine in 15-20kts. If you are not already doing this, you should move the clew/outhaul inward and that will help flatten too and usually results in a little less rotation with the sheet tight.

The 5.5SL that I had used a track along the foot of the sail. A car ran on that track that the mainsheet system hooked to. Less rotation upwind meant the car was pulled forward on the track running along the foot of the sail (It had a line and cleat that adjusted where the car was on the track). The track only ran for about 18 inches or so on the foot/aft end of the sail.

I have a good picture, but it is too large a JPG to post - but this was standard set up on most 5.5 SLs.

This is probably what I need to do, attach main sheet further in on the sail to flatten the sail and pull the mast straight. The problem is that I lose tension on the square top and the sail inverts...

Could you email the pic to me?

kronquist (AT) hotmail.com

Bjorn

I sent 2 pictures. Post them if you can compress them.

It worked really well, even under load - it may have been an "upgrade" for the 1994 Alter Cup boats (I think it was 1994)...

It was a pinhead main, so your comment about leech tension may be a factor.

Yes- Use that mast rotator through the bottom of the mast with a bolt and a large. reinforced grommet through the trampoline behind the rear beam, ala my Flyer "A" cat- you will then place 2 more grommets near the outer edges of the tramp for the limiter line to exit on each side- after exiting it will cleat in a small cam cleat mounted on the hull on each side. On the Flyer (single person boat) the cleat is near the shroud where all the other control lines are led, on your sloop you will have to think about where to mount. Another option using the same "spanner" is ala my LCD "A" cat- mount the spanner with a bolt through the front and back of the mast (you will have to bend the spanner to make it wider- you could cut off the bottom of the mast track- back to the "web" and I would to use that flat surface. Then you mount the spanner to left or right, your choice, and then put 2 farleads on the front beam on that side- positioned about 2" apart as I remember- so one is inside the end of the spanner and the other outside- oh, and mount a SS strap on that side of the mast about 6-12" up from the spanner or use some fitting on the mast for a small strong line to the end of the spanner to hold it up- this keeps it from dropping down and hitting the fairleads as you tack/jibe. A line is then led from a cleat on the front beam on one side- through the fairlead closest to it, through the end of the spanner (or a small block shackled to the end) through the other fairlead to a cleat on the other end of the front beam. Of course you could lead to turning blocks on the beam and back somewhere to cleats if desired.
Hopefully this is understandable, but if you need pics both boats are home and I could get some pics if you need them-
Having sailed a 5.0 for 17 years but now on squareheaded boats I understand your dilemma!

Kirt

I would not mind some pictures of that.

I rigged the boat this weekend and took a bunch of pictures, without wind the mast does not over rotate, and part of my problem is probably the main clew position. With the downhaul full on for a flat sail I spill the square top, using the outer main clew hole I can keep the square top powered up with more downhaul than I can with the main sheet further in. But this causes the mast to over rotate.

Bjorn

Bjorn-
Will try to get some pics in the morning and post- It's dark out there right now!

Kirt

My problem with the mast rotation was the clew position, with it further in, the sail flattens and the sail shape is correct. My new problem is that I have no "tension" on the square top and it inverts.

I did not use the inner hole before because of this, but even with the outer main clew hole the square top inverts as soon as it blows more than 5-7 or I use any down haul.

You might try adjusting the batten tension, I'm not sure how much it will help though.

The previous owner of your boat (or at least the only N570 I've sailed with that had a carbon mast) seemed to do pretty well in the wind range you are talking about without ideal crew weight.

After I got the boat I got a new sail. So I'm not using the old sail that came with the boat.

I'll do some more research on the issue. I did try the battens very tight and loose and everything in between. But I just can't ger the top to firm up.

Bjorn-
Hopefully these photos will help - if I can get them to post! Sorry the boats aren't set up- just have photos of beam/tramp and mast bases. BTW my LCD A cat was set up boomless but did come w/ the mast rotator- and this was before pre-bend days! Note the front of the mast is pointing up- the rotator is on the port side so the end of the rotator lies between the eye straps to the port side of the mast ball.

Kirt
I'll have to post the Flyer photos on the next post-

Should be the Flyer tramp w/ mast base- apologize for the plastic- but you should be able to see through it- note the green line to the end to keep the rotator from dropping down and on the tramp note the grommet with blue line- goes under tramp and note exiting near shroud through clam cleat.

Hope this helps-
Kirt