H18 rigging/tuning tips

I got my 83 H18 (with SX wings) out on the water for the first time this season (only got it out 4 times since I bought it last year) and want to work on fine tuning the rigging and getting it set up better. I will not be racing but still like to go fast. For background I have been sailing for decades on many different boats and did a fair amount of racing on small boats when I was younger and sailed a H16 & 18 for fun in college. I am also an engineer and a bit of a geek.

Here are my questions, I appreciate any help you experts can offer:

1. Mast rotator - how is it effectively used? My understanding is that when you let the mast rotate more you get a fuller sail for more power and can limit the rotation some to depower the sail in heavy air. Please explain how I would use this to tune the main sail and when I would use different settings.
2. Downhaul - I have the original stock 1983 downhaul with a broken pulley and cleat. I have been just running the line through the tack and back and forth to get multiple purchase and then just tieing it off to itself with some half hitches. I am thinking of getting the power downhaul 5:1 from Murray's Marine. I understand I want more downhaul to depower the main in heavy air and I think this would do the trick. If anyone has a used one that is similar for sale, let me know.
3. Mainsail trim - I have a newer sail (3-4 yrs old with very little use) and the original all aluminum mast (no comptip). Is the newer sail cut for the comptip and therefore not the right shape for the all aluminum mast? The sail seems very full near the top even with all the downhaul I can get.
4. Batten tension - The battens about 2/3 the way up on the main seem to have a lot of bow to them. I have them just snug when the sail is down but when I raise the sail they really give a full shape.

Thanks for the help

1 & 2) When you talk about powering up or down the sail, basically what you're talking about is modifying the sail's draft (depth) to suit your power needs (deeper=more power, flatter=less power).
If you lay your sail out on the ground, you'll see that the luff is not straight, it's curved. When you hoist this curved edge up a mast that wants to be straight, and you pull on a little downhaul, what happens is the mast bends a little, the sail material firms up and a pocket forced into it due to the difference in curves between the mast bend and the sail's luff curve. The more tension you pull on the luff (downhaul), the more the mast bends. As the mast continues to bend, the more closely it matches the luff curve of the sail and so the less pocket is forced into the sail (i.e., the sail becomes flatter). If the mast is bent to the point that it exactly matches the luff curve of the sail, the sail will be dead flat (more or less).
So adjusting your mast rotation, diamond wire tension, and downhaul are all related because they affect where and how much your mast bends. The tighter your diamond wires and the less mast rotation you use, the less your mast will bend and the fuller your sail. Less diamond wire tension and more rotation will allow a flatter sail.
Having a powerful downhaul really is the key to bringing this together and allowing you to take full advantage of your sail's range and your mast tuning. The stock 3:1 system simply is not powerful enough to get the most out of your sail. I run a 6:1 with dual exit blocks so the downhaul can be easily adjusted by the crew from the wire.

3) The cut of the latest 18 sails is probably optimized for the comptip mast. The comptip is more flexible than an all-aluminum mast tip, so it bends more easily meaning that more shape is required in the upper portion of the sail to compensate for increased bend. When you use this sail on a stiffer, all-aluminum mast, it's not surprising that you are getting more draft up top. There's not really a whole lot you can do about it unless you want to take it to a sailmaker and have them take out some of the draft. You could also try running stiffer battens.

4) Batten tension, there aren't any real tricks here. Snug them up enough so that the wrinkles are taken out along the batten pocket. Changing the tension has very little effect on performance other than making the battens difficult to "pop" across if you set them too tight. Again, the reduced bend of the all-aluminum the mast tip is going to force more draft into the upper section of the sail. Stiffer battens or having the sail re-cut would be your only options for flattening the top of your sail if you can't achieve the desired shape through mainsheet and downhaul tension.

sm

These posts are really helpful! One area that I'm still trying to get my arms around is the difference between "power" and "speed". Please correct me if I'm wrong, but my understanding is more sail draft = more power and this bigger pocket helps pull your boat along. But a deeper, more powerful draft does not always translate to speed, does it? Example: I've seen it posted that heavy winds call for more downhaul (flattened sail). Is this because the skipper wants to control the speed of the boat when it's blowing (i.e., "throttle it down") or because "de-powering" the sail in heavy winds actually makes the boat go faster? Thanks guys!

It might be better to look at it in terms of power vs. drag (not speed). Really what you're trying to do is get the boat into the double trapped, windward hull just kissing the water, position as soon as possible (upwind of course). In light wind, You want to maximize the power of the rig, even at the expense of drag, in order to achieve this position as it will provide the highest top speed (as a general policy).

Once you reach the fully trapped position, you switch into drag reduction mode. Any increase in windspeed should be compensated for by flattening the sails and then reducing their angle of attack. Step one - sheet in all the way (you should already have been doing this), Step two - tighten downhaul until bottomed out, Step 3 - travel out until at hiking strap, Step four - roll up jib.

All the while, your need to take note of the balance of the boat. If the helm feels really heavy, or the boat is flying up and down all over the place, then you probably need to make an adjustment.



Depowering through the use of downhaul in high wind makes the boat go faster. Applying strong downhaul tension in conjunction with strong mainsheet tension causes the top of the mast to bend which causes the top of the mainsail to "twist" open. This has several benefits including reduction of drag because of reduced tip vortex drag as well as lowering the CE of the rig. Lowering the CE of the rig allows the boat to carry more power for a given crew weight since the power is applied lower, so there is less heeling moment. Windsurfers have known about the benefits of twist for about 20 years, look at any modern windsurfing rig from behind and you will see that it is heavily twisted (if rigged properly).

sm

Thanks a bunch, SM, I understood everything you wrote. Now, to put it all into practice! If I'm being honest I kind of jumped into things head first last year when I got my "new" boat on the water. Looking back I didn't spent nearly enough time on these critical tuning details. For example, I have a stock downhaul system that I never really even bothered with other than to crank down to the point I was confident my bolt rope would stay seated in the lower track. I never once adjusted the downhaul when I was on the water. And I now know my shrouds were set up way too tight (I broke an anchor pin early on and I was concerned I'd break another one if I allowed for the needed rotation slack, the importance of which I also failed to understand). Oh well, I'll get there. Maybe this summer I won't get passed by a H16.