Robi said
"Us FL blade boys have been sailing the living co-hoots out of the boats. "

I am working in isolation up here. Not even another spin cat to tune with. So, I am begging. Have you FL boys come up with any mast rake, spreader rake, pre-bend numbers that would be useful for the Uni-Can? What about the spinnaker luff tension?

Bruce:
I run zero rake. If I were to measure from the bridle wires post the line ends practically in the middle between the rear port inspection access covers and the transom.

I run roughly 730 on the loose gauge for diamond wire tension.

As far as mast rake, spreader measurement etc etc, I have not fiddled with those settings yet. Hopefully this season I will start messing with that stuff to further understand it.

Bobcat,

I generally sail cat rigged (ie 1-up) and I'm running the following:

Mast Rake just to bottom bolt of the upper gudgeon:



The spreader is 28.25 inches from diamond wire to diamond wire at the spreader:


And measured perpendicular to the luff track is 1.875 inches.


I'm running #33 on the Loos guage (I understand that to be de-powered---ie more pre-bend); although I haven't played around at all with this setting.

What Robi said.

I posted this pic last year. This is about as far forward raked as I can get. I think that there is only 1 lower hole left on the bridle.


I think that I am running closer to Tback although not necessarily by choice. I should be going MAST UP next weekend. Weather helm wasn't an issue so I guess I can experiment with raking farther back. For science sake. But I do remember that there isn't much room before I blocktoblock.

Thats some serious rake. Isnt racking the mast aft better for higher winds?

Tback
I understand that you helped out at the Alter Cup. Did you retain any numbers from the mast tuning there?
I realize that it would be for the Glaser sails and 2-up but I'll ask anywise.

What did we learn about tying down the spinnaker pole?
Which reminds me. Do the mid pole lines on the Blade contribute at all? Beyond holding the tack halyard up? Do they stop some side to side wiggle?

Not sure about the Blade, but on the Spitfire the mid pole lines keep the jib centred, and help pointing up wind.

Mast rake was exactly where mine is ... at the gudgeon bolt.

I didn't tune the diamond wires ... but I recall them being set at #36-37 on the Loos Guage.

I believe the mid-pole lines contribute to keeping the spin pole centered and the one on the ring is to keep it from trying to spin/twist.

Referencing the spin pole tie down, originally used the blue loops with strong line (??brand??); one of these came untied during the practice race so they were all removed and the line was tied thru the bow hole and knotted (interestingly one of these came undone during races too). I think that Kevin was measuring 63.75 inches from tang to pole on each side ... this looked like it created a pre-bend of about 1 - 1.5 inches.

Bobcat,
The mid pole lines certainly helped to keep everything centered. The way the jib luff tension was run (to port bridle/hull intersection, then back to front beam) there needed to be something on the starboard side to keep the entire bridle/pole intersection from bending to port when the jib luff was loaded. We tied the port side first with the pole bent ever so slightly to port, then tied the starboard side tight to hold the pole as firmly as possible on the centerline. As to diamond wires, they were set at about 30 on the Loos gauge, in hindsight maybe a little loose, we weren't expecting quite that much breeze. I stayed on top of them, retightening as many mornings as time allowed. No one but me touched them during the regatta. If you have any other questions regarding how we set up the boats please ask, although I would not proclaim to anything close to an expert. We (Jake & I) decided how we wanted to tune the boats and I tried to keep them as close to those settings as possible during the event.
How do you like the boat? They look like a blast. I actually got to go out on the water on practice day for a few minutes to watch.

Not exactly. . . when we loaded the poles we measured 63" from the top of the bow to the end of the pole, hitches were tied at the pole end and the whole thing was loaded by lifting the front of the boat using the pole. This would set the knots and give about 64" form the bow top to the pole end, resulting in about 2" of prebend. Very similar to the picture of Bobcat's boat I believe. There was no line from the ring itself.

That is very low. I seem to remember Taipans run of 40-42 on the loos gauge. I don't use a Loos gauge myself so I don't know what I run. I just measure the mast prebend as that the same as knowing the diamond wire tension when the spreader rake and arm length are known.

Kevin, may I ask what you guys were exactly running as the spreader arm rake and spreader length. Up till now I've only encountered measurement in the way of " ... more then on the mast of the demo boat ..." As I don't know the settings on the demo boat these numbers don't tell me much.

If this info is not cleared for publication then I'll understand.

Thanks in advance.

Wouter

Note that Loos gauges are not well calibrated between instruments. E.G., I've check my diamonds with my loos gauge and measured 35 and then used another loos gauge and measure 38 on the same diamond. Just something to keep in mind.

Are these numbers for the old style Loos gauge (model A) or the new style gauge (pro)?

One more reason why I now prefer to just measure prebend itself and not (the indirect) measurement of diamond wire tension.

Wouter

I wouldn't worry too much about the diamond wires. I had a short conversation with Matt; the gist was that unless you're a champion sailor, other controls are more critical.

Speaking for myself, I had trouble shifting gears yesterday as the wind increased. The boat just didn't feel as good to weather as it did in the lighter stuff.

I'm convinced mast rotation is critical! If you're off, even a little, performance will suffer. IMO.

Pete,
In order for your other control lines to work properly, your spreaders and diamond wires must be close to right for your weight and sail shape. Get these in the right ballpark and then the downhaul and rotation will work for you. You guys really need to look to the A’s for rigging advice. Here is a quick synopsis from AHPC, Nacra, and Landy (as I understand it).
First, your sail maker has a hard time cutting a luff curve that is not smooth and a constant arc. Your mast will have a bending curve depending on the combination of the spreader rake and diamond wire tension. When you sail you must determine if you have good height (pointing) but poor speed (other boats squirt forward while your boat wants to heel), or if you have good speed, but lack height (everyone seems to point higher than you).
To go forward in a puff you need a flatter sail, to point higher you need more power (fuller sail). This is where the amount of pre-bend comes in.
The hard part comes when you realize that if you only adjust one parameter, your mast will not bend in the constant curve you sail has. Too much spreader rake and your mast will bend low and be straighter up higher, and conversely spreaders too far forward will give you a straight mast low and a curve up higher. So, first measure your pre-bend, spreader rake and diamond tension. For pre-bend string some fishing line from mast base to top and measure the distance to the track. (I place the mast on its side to negate gravity). For spreader sweep, place a batten or something across the wires at the spreaders and measure to the mast. A good sail maker can tell if your mast is not a good arc, but most of us cannot.
Tip: lay the boat on its side with the main up but NOT in the mast groove. Med sheet pressure and some downhaul and med rotation. Now look at the curve of our sail and the mast curve. Are they the same? (Play with sheet tension to get the sail close to the mast) If your mast has more curve down low your spreaders are too far back for your sail. If you just bring them forward you will fix the curve, but now your sail will be fuller (less pre-bend)…did you want or need that? (See above). If not, adjust your diamond wires to get back to the same pre-bend.
The goal is to have good power…first on the wire when the wind picks up, and still be able to flatten things out when it really starts blowing.
Hope this helps some of you.
Ken

Ken: Thank you very much. I'm sure it will help a great deal. I just have to digest it first. <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />

Copied and pasted your reply to a word document. I will print it out and work on my boat. Ken you are the man.

<img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" /> Jeez! Why didn't I think of that!?

Robi- pasted it into a folder I'm calling "tuning guide". Maybe when we do our next "Sebring" we can compare notes.