Cool boat you have there! I felt some real envy when I read the article on your boat "back then". Good to have you here on the forum and please keep us posted on how you and the boat are doing

Either what they said...or the opposite. Most A cat guides explain it like this. If you can point well but the boat tends to not squirt in a puff, you need to flatten your sail. In order to not go over in a puff you have to point very high...your speed goes down, and you are pointing higher than your competition.
If, on the other hand, you have speed in the puffs (squirt) but can not point as high as the competition (especially in the lulls), then you need a fuller sail (more power).
Since you said you can not trapeze until the wind is up around 15 knots and you can not point, I think you need more power. With your boat you should be on the wire around 6. There are people that stop sailing at 15 knots and you are just now able to go out on the wire? Or do you just not go out before 15 knots?
The trick of lying the boat on it's side is to help you tune the mast. If, for example, you decide you want to have a flatter sail there are two ways to achieve this. You can crank on the diamond wire, or rake your spreaders back (or some of each). When you crank the diamonds you will get more bend up top and less down low. When you move the spreaders back you will get more bending down low. This technique helps tell where to adjust for your sail, not how much bend your sail needs.
Also, the square top is more sensitive to main sheet tension. Make sure you are in tight, especially above 5.

I've had that feeling before with an ali mast and I found the leech was pulling the top of the mast over when the mast was rotated. After that it was a compromise between mast rotation and mainsheet tension.
regards

i've been running pretty loose diamonds on my straight spreader 5.2 as i sail it; underweight, solo, on a generally light air lake without much chop or wave action

it sounds as though i should start experimenting with diamond tension as i could easily imagine that is happening to me when th wind does pick up...

Tight diamonds wont change what happens above the hounds and that's where my wing mast section used to lay over on the A class. Loose diamonds were the recommended setting on my 5.8, you could tell if it was too loose as the mast used to bend into the slot and the boat wouldn't point as well on the looser tack.

Spreader rake setting and diamond tension depends on the mast section (wing mast or conventional, alu or carbon). I know some A-cat guys who tried to dial in diamond tension from older trim sheets. At the end the diamond wires were torn out of the mast base. So I strongly recommend to ask somebody in your club or a good sailmaker, who has expierence with that stuff (i.e. has a similar boat (e.g. A-cat)). If not possible, post here some pictures of your sail+mast in different trim settings.

Apart from that, I think that the luff-curve-outside-the-track-matching method gives you way to much pre-bend and a too flat sail. You want to match the luff curve inside the track, with full mainsheet, downhaul and rotator pointed backward. That's your strong wind setting and at this time you want to want to match the luff curve to mast curve and hence have a flat sail. Just my 2 cents about pre-bend, maybe there are other opinions around.

Cheers,

Klaus

Hi Rolf,
I'm back from my sailing weekend and the tests results are quite encouraging. I did increased the prebend from 1" to 1.5" and went out sailing. Wind was very light, 3 to 5 knots, going upwind, I slowly cranked the downhaul by small increment pretty much up to max and that top leech telltale finally did start to stream about 50% of the time. Altough I'm pretty bad at the seat of the pant feeling, my pointing seems better(guys at the club agreed), but also I felt the boat was running a bit faster, that choking the boat feeling when sheeting hard was gone. My lower leech telltale was still hooked to leeward all the time so I tought I should try to increase sprearders rake to flatten a bit more this part of the sail.
Then back on the beach and up in the ladder to reach the spreaders to find out that the adjustments are seized up. I dont want to compromise my sailing season, I'd rather sail with a badly tuned boat than no boat at all. So that will be a winter project. I did measured the spreaders rake, I'm already at 2.5". Nacra 20 tuning guide recommend 2.6" for light crew. Since I'm all alone on the boat and the mast seem quite stiff, do you think it is safe to go beyond that recommended setting, may be 3".
I tried trough the site search engine to find out more about mast and sail tuning but I had a hard time to get good result. Any clue how to refine my search? I would really like to read about the subject.
Thank again for your help.
Denis

Hi Klaus,
since I did tried once that luff-curve-outside-the-track-matching method, I tend to agree with you saying it end up with an horrific prebend and that why I did not keepted theese settings. Now if I match the sail with the luff inside the track, I guess I have to measure the chord to depth ratio of the sail. What would be good numbers for flat sail and full sail? Should theese numbers be uniforms troughout the sail?
Now, stupid question; Can theese sail+mast pictures be taken on the beach. If not actually sailing, are they of any interest? Is putting the boat on its side would help? I' m afraid of your answer but I had to give it a try.

It's sounds positive. It will be interesting to see how things improve from now on. Did you try full outhaul to flatten the bottom? Almost everything adjustable on an 18-2 I had seemed to corrode and seize up in no time (quality issues?), anti-corrosion paste is a must. Can you make some cheap temporary (fixed length) spreader bars using cheap tube or get a local machine shop to thread you some? Good luck with the tuning.

Cheshirecatman

Great news Denis. Nothing is more fun than hearing success stories.

Agree on the pre-bend issue, sounds like you need substantially more pre-bend. I would have talked with the guys at NACRA about how much bend you can put in the mast safely, then found a combination of spreader rake and diamond tension that matched the sail and your conditions well.



I can not help you with any articles on pre-bend and sail setting. That topic is quite dependent on your equipment. In your case where you try to match your mast to your sail it is a matter of trying several settings and tuning for best performance to your conditions, boat and skills. When you can make all telltales fly in all wind conditions, you are getting close in my opinion. Then start finetuning for your best performance in your dominant conditions.

There is a lot of NACRA experience here and they can probably give you good advice on how far you can go with spreader rake and diamond tension. Is your mainsail a standard NACRA20 main?

Hi KMarshack,
from what I found this weekend, my sail was obviously too full below 5 knots.
May there is something wrong with the sail (the boat is a pretty weird custom combo) or myself, but sitting at the front beam on the windward hull at 6 knots, the best I can expect is to get that hull up in the air, laying my back out would be enough to maintain the proper attitude. Keep in mind the boat is 11 foot wide and I'm 250 pounds.
Thanks for your explanation about diamonds tension vs spreaders rake, It help me to understand a little bit more that mast prebend theory

Is there a reason you need to put the cat on its side to see the curve of the track and sail? cant this be done with the mast straight up?

Difficult to measure as the point of max curve is usually above the spreaders!!!!

i see now
thanks

Hi cheshirecatman,
the portion of the sail that I feel too full is just below the speaders rake and as far I couls see, the outhaul seem to have very little effect in this area. Here wheather had been very bad troughout the summer, It look better now and I hope It will continue trough the fall season. Boat is 2.5 hours away, so once I bring the boat home, I will work on these spreaders. Sailing and trying to catch those f18 guys is so fun, I dont want to miss a minute of it.
Let me tell you, I'm learning the frustating way about that anti-zeize compound.
Anyway,I feel a little less stupid and start to understand what to look for and I'm so excited with the weekend results, the goal now is to go out sailing and have a closer look on the effect of all theese onboard adjusments.
Thanks for your support

Denis

Hi Rolf,
I think my mainsail was a special order from the local agent to E/P, although I was never asked my weight, wind condition,etc. I have readed on another thread, you mention 10-12% for chord to depth ratio. Is 10= flat, 12=full? What about the location of that maximum draft, 35%? Same location troughout the sail?
After the sailing season, once I bring the boat home, I would like to play with the spreaders and diamonds adjustments trying to match the sail-mast and I start to believe that chord to depth ratio is probably the ultimate result I should look for. Am I wrong?
Thanks for your support

Denis

Really sounds like you need that extra pre-bend. If the tubes are not cracked you may be able to free them off with a couple of pairs of vice-grips, penetrating oil and maybe some heat. Otherwise get some new tubes asap (Murrays?), and for the sake of setting off a little earlier and spending an extra hour on the beach with the boat on it's side, tune it properly now.

Cheshirecatman

OK last question about putting the cat on her side... wouldn't that cause some bend in the mast from holding the mast head? Do you need a few people in different places to reduce bend (from being held sideways)

I ask because my cat is currently getting new diamond wire turnbuckles (the old ones were wrong/not adjustable) and i want to do this...

The weight the mast have to hold is almost zero, the top hull almost balance over the bottom hull. Put a chair or bench under the masttip and you are ok. I never put the boat on the side without diamonds though, if that is what you are thinking.
Take care that there is nothing on the ground to damage your hull as you pull the boat over on the side.

10-12 percent draft including mast is just a ballpark figure and not the answer to all your performance questions. There are too many variables like boat weight, crew weight, conditions, helming skill, trimming skill etc etc.
Max draft placement is much the same, dependent on skill and conditions. With max draft further aft you get better top end speed and pointing, but it takes more skill and less waves/chop to make it efficient.
Max draft should by my book be in the same position all the way up to the top on a uni-rig unless you have some unusual sailing conditions. Not so on a sloop rig.

Chord to depth ratio is a key for proper setup, but what you do on the water is far more important. I think you are more than ready to play with the settings and find what suits you best on the racecourse.
The above is of course just my unqualified opinions, I am neither a sailmaker or professional sailor, just an opinionated sailor
I would definately try to get my mast dialed in as soon as possible. What can be better than getting a good improvement in windward VMG just before the season ends, knowing that you have even more to improve the coming season? I would follow the advice of the good chesirecat