hi to you all, I do own a nacra 18 square equipped with a spinnaker and a square top mainsail with an inter 20 carbon mast. The boat is great but I have a hard time with my pointing ability. I am 250 pounds; to go as fast as the F18, I have to give them at least 5-7 degrees upwind. Getting the leeward hull nose deep in the water help a bit, but that is not enough. What should I look as far as tuning. I have been sailing for 15 years and this is my third boat but the very first unirig. So I guess I am missing something; anyone can help me.

how hard are you sheeting the main, how much down hauil. what wind conditions do you suffer most.

we need more info!!!

In the quest for more info, what are your mast settings, Spreader rake, diamond tension, resutling prebend, and mast rake? Mainsail?

Generally, pointing is all about leach tension.

With things being 'non-standard' I would check a few things before looking to the finer points of tuning. Check the hulls are parallel, all foils are in good order and the rudders are correctly set up to lock down in line with each other(sight leading edge to leading edge) and check the alignment(toe-in).
The Inter 20 carbon mast is designed for a heavier boat and crew weight and consequently is stiffer than you may normally choose for your configuration. I am sure the Inter/Nacra 20 sailors can give you a base setting for prebend. You may require more prebend than base with your setup. Was the sail cut specifically for the mast/boat configuration? If not get a sailmaker to check over your rig. He should be able to establish any changes needed to the luff curve suit the mast. Additionally a softer boltrope and/or powerful downhaul may help compensate for the stiff mast.
With the platform straight and the sail matching the mast you can then look to balance the rig. If the mainsail has not been carefully matched the drive from the rig could be anywhere in relation the lateral resistance.
Mast rotation - With no jib to deflect air around the back of the mainsail a unarig is much less tolerant of poor trim. You just have to work at it to find the sweet spot.
Don't trapeze too early to keep the windward hull out and be very wary of trying to measure performance against F18's if you maybe in their dirty air.
No easy fix really. Things might not be far off, but with non-standard you just have to work through the whole boat.

Cheshirecatman

thank you Scooby for your reply. The wind condition that I suffer the most is light air and it is worst if the water is choppy. Down Haul has been tried anywhere from soft (few wrinkles on the mainsail) to the point where the wrinkles just disappear. Sheething is relatively soft because when I sheet hard, I feel I'm ''chooking'' the boat

Chris, since I suffer the most in light air, and the boat don't seem to have a lot of drive in theese conditions, the settings I use are the one recommended for heavy crew on the nacra 20 class tuning guide: 1.5'' spreaders rake, diamond tension to give 1'' prebend. I don't have the tool to measure the diamond tension. Although you may think theese settings are excessive, I do not trapeze before 15 knots.

Denis,

are both leeward and windward telltales flying when you have problems with speed/power? Do they stop flying and stall when you let off the downhaul and sheet?
What is your mast rotation like, and your leech (leech telltales flying or stalling)?
You write you have been sailing for 15 years so I assume the telltales are all flying, but I have to ask just to make certain we are on the same field.

What cats or boats have you sailed earlier?

cheshirecatman, the hulls have been measured and are parralel. I never had a look at the rudders being in line, I will check that out next weekend. Toe in is about 1/16".
I am not sure about the mainsail matching the mast. I have seen some f18 guys hoisting the main out of the track, putting the boat on the side,then sheeting in and making sure the curve of the sail would match the mast curve. I have done such a test but I felt I would had to put a lot of prebend on the mast to get a good match and therefore resulting in a flatter mainsail loosing the power that I desperately need in light air. May be my understanding is wrong, or the procedure to chek the match is wrong. please let me know.
mast rotation: although I did play quite a bit with the angle, I would not say that I can feel a lot of difference. Would there be possible to install some telltales somewhere to help me to find that sweet spot.

Denis, more draft in the sails in really weak winds results in proportionally more drag, making you a lot slower. I always got the best results with flat sails in really weak winds. 1-2 m/s. When it gets to 3-4 m/s and some chop more draft is needed for best performance. Just my general experience.

For mast rotation, where is your mast spanner/rotation control arm/lever pointing? To the daggerboard or between the daggerboard and corner of rear beam?

Rolf, I never had a real check to the telltales behavior while letting the downhaul off and sheeting. Thanks for the clue, I will check this next weekend. Mast rotator is usually pointing at the rear end of the daggerboard for light air.
The mainsail was manufactured by Elliot Pattison (Nacra sail suppliers in North America, I believe). I have 2 windows for the telltales. one at the first third and the other one at 3/4 of the sail(just slightly higher than the spinnaker hound).
Now let me give you a snap shot of the telltales behavior in light air. To get decent speed, I usually bear off until the lower telltales are streaming aft, if I get closer to the wind and the windward telltale start to lift, the boat get deceptively slow.
Now here the pictures: both lowers telltales streaming aft, top windward top telltale lifting and leeward one streaming aft (not enough leech tension?), both leech telltales flying backward to leeward (to much leech tension?)
So I wonder if I read the telltales correctly because at this point they get me quite confused. Would appreciate your input.
I previously owned a hobie cat 18 and a nacra 5.2

I agree Rolf, but what about light air and choopy water?

Since nobody else has mentioned it, where is your outhaul?

Do you have a Loose gauge?

How far aft is your mast raked? Remember that Uni's should be raked more than a sloop.

Denis,

what windrange do you define as light? I say that 0-3m/s is light and go flat in that range. You will probably experience that the telltales will more or less demand a flatter sail in that range becouse the wind separates from the sail easier. This is even with some chop. The reasoning is that even if it takes longer to accelerate with a flat mainsail, there is just no more energy to get from the wind even with a main with more draft. Does that make sense?
In more wind and chop I want more draft, becouse then I need more power and can use it to accelerate faster after busting through chop. In more wind and flat water, the sail have more draft after manouvering and while accelerating, but is flattened for more speed after a while (changing gears)

In light winds I ignore the lower telltales. It is the top telltales where the wind is strongest and possibly skewed to the surface level wind I sail in.

By your description of the telltales I would hazard to guess that you have too much draft in the sail up there. I have no experience with the sail/mast combination!

I would try more pre-bend, more downhaul and more sheet until the telltales are streaming (leech telltales acting up/indicating separation 50% of the time)

If I am wrong, I hope the gurus will let us both know.

Denis,

the 18square you have, is it the one NACRA put togheter quite recently on a special order? I read something about that a couple of years ago and suddenly it came back to me. It was a lovely boat in the pictures I saw. How much does your boat weight and do you have a strategy for righting it alone? (I dont want a discussion on solo sailing and righting, I am just curious about your boat).

Rolf is spot on with his advice. I would suggest that the spreader angle in increased to allow you to play with pre-bend settings without making the mast over stiff 'sideways'. You might be suprised at how much extra pre-bend you actually need. If afterwards you find that you do have to have to stiffen it up sideways (auto depowers too much in the stonger stuff) you can then adjust the balance between spreader angle and diamond tension accordingly.

Cheshirecatman

Hi Will, the outhaul is positionned so the main is about 3 to 4" away from the boom in the middle. Unfortunately I don't have a loose gauge, but I sure can borrow one at the club. Any numbers?

Rolf and Cheshirecatman, thank you very much for your valuable inputs. If I read correctly, the only thing that I really went against your suggestion is the prebend and also more spreaders rake. OK I will work around theese settings during the weekend and let you know if you don't mind.
now Rolf I need some clarification when you say the telltales demand a flatter sail; Is this means top telltales streaming aft and leech telltale 50% of the time acting up?
Cheshirecatman, is my way of checking the match between sail and mast is wright? If so, should it be the starting point to define the prebend that I need?

You are wright Rolf, this the boat. I don't know the weight of the boat but, because we had to increase the thickness of the aluminum on the cross members for stiffness, I suspect the boat to be 5 to 7 kilos heavier than the 170 kilos claimed by Nacra. I have a 9 feet power bar to right the boat. This is something that I have builted myself. It works quite allright since I was able to recover once from a turtle (complete upside down). This power bar also had some weight!

I would try more downhaul as a 'first easy fix' to see if I was able to get both leeward and windward telltales to stream properly when the leech telltales break 50% of the time. If you get better speed and pointing that way, I would start changing my mast setup to make it match the luff curve.
If the sail was made for you, the sailmaker can probably help you with some figures to get you into the ballpark for spreader rake and tension. E/P sails are good guys from what I know about them.


I never liked the tension meters/gauges. I always measure spreader rake by releasing tension before putting a batten from tip to tip on the spreaders. Measure distance to the luff track. Then tension the spreader wires and tie off the halyard to the boom. Measure the distance from the (now tied on tight) halyard to the mast track at the spreaders. This is your spreader rake and pre-bend when done the old fashioned way.

The way you described on hoisting the main outside the track and comparing curves is good. The real proof is when you go sailing though.

The flatter sail will get you better airflow over the sail and more leech tension. It should result in better pointing and speed. Please keep us posted and study those telltales. They tell us all we need to know to get the setup right, but it takes some brainwork



I am not certain if I understand the question. What you just wrote above is the ideal trim for max power for least drag.
What you wrote earlier was that the top windward telltale lifted and the leech telltales stalled (separation in front of the leech). The latter description sounds like there is too much draft in the sail for the windspeed. Perhaps I can answer more fully if you try rephrasing your question.