Ok, I'm going to put my 2 cents in here...the information that i speak of here is the farthest from scientific and I'll have to say that I'm certainly no class racer or racer at all for that matter, but hopefully it will be worth something to someone.
To start, buying stock sails is probably the smartest move considering it will keep your boat class legal and at the same time not aid in the diminish of the resale value of your awesome boat(there are lots of H20 class racers out there or potentials there of).
There are only two H20's at the lake where we sail, one is mine and the other is my friend's. I probably have two and a half years of experience over my buddy in cat sailing. We are both relatively new to the H20 all together.
Even though I don't class race, I would say that I am very critical person when it comes to sail trimming. I watch those tell tales like a hawk and really keep an eye ball on sail shape and laminar flow using a couple sets of tell tales on each sail and of course some leach tales as well, to keep from being over or under sheeted. My buddy is not quite as critical as me yet, and I am positive that he would agree. He's just has a slightly more casual approach and is newer to cat sailing in comparison.
Now, my buddy and I have sailed our boats side by with stock sails and single handed. And once again I'm sure he would agree, that using my more developed experience, I have caught him on the lake and then proceeded to pass on the same course and heading once or twice all in casual fun...once again only because of the experience that I have over him on the 20 and in cat sailing in general.
However, towards the end of the season, Mel had purchased some new sails from Chip @ Whirlwind after deciding that he wanted to pump up the looks and performance of his boat to some degree. The main being a pentex square top radial and the jib a pentex radial cut, like the stock jib but different material.
Naturally we had to put them to a test, one like we've done before...Flying in formation!
On the second or third outing with his new AWESOME looking sails, we spent about two or three hours following each other on the lake trapped out, on various courses mostly close hauled, footing and reaching as well. On this day it was warm and the wind was pumping an average of about 10-12mph to my recollection (perfect for single handing a 20). However... something was different! Now, let me just say that when we sail together, we sail close enough , usually, to where if we yell, we can hear each other. On this beautiful day... the very best I could do was only keep up with Mel. I don't think I ever could close the gap and on certain instances he would pull me and there was nothing I could do about it. All there was for me to do was to become even more critical to the action of all my indicators trying adjust and re-adjust to try to make up some ground. It came down to me simply just cutting the course slightly, once in a while enough to keep up and stay with in a reasonable distance. At this time, Mel had no tell tales at all, no yarn and no wind indicator.
I do realize that there are many other factors to this equation and that some were not talked about and also not even considered while in action on these two boats.
Does there appear to be a performance difference between Mel's rig and mine considering the before and after bench testing? I would have to agree.
The other Question in my mind would be..if it were possible to take identical H20's, put identical sailors on them with the rigs I referred to earlier in varying wind conditions and on the same course ...would there be an advantage with the squaretop rigged sailor's boat? I believe yes, in most cases. Even in heavier wind! why though? As we've heard others opinions on that a squaretop's center of effort being moved upward some, all the while making the vessel more over powered beyond the half way point up the mast, contributing to being less than a benifet... A PROPERLY CUT and condtionally TUNED squaretop main sail, will handle heavier winds or respond to a "puff" by opening up its top half/third leech or roach to automatically spill some wind(because of the leverage of the cord of the "squaretop"). This action helps to relieve the sudden heeling moment due to the extra area way up high which makes the squaretop not a hinder, but a helpful feature in most cases.
I do have experience with a mylar squaretop on an H18 of my own. The main thing I noticed, even though I was less experienced then, was the feeling that the boat heeled less in any case or that the boat felt as though it calmed down or "was calmer", compared two the stock sails used prior, especially when the wind started to peek.
In conclusion, I think that if a squaretop in general were a design of decreased efficiency, you wouldn't see them all over the world. I realize that this is not free efficiency though, It takes know how, a good design, and the ability to properly tune it for the conditions to get extra help out of it in most situations.
What I mentioned above is what seemed to be blatantly clear at the time of the comparison. On the other hand, If there was to be considerably more wind speed that day and lets say that all mechanical settings were left the same for both boats. Mel's boat may have been a CRAZIER ride!! BUT, we all make adjustments to the conditions more or less. I still think he would of had the advantage and using tell tails would only add to his benefit of course.
Again, this was just un-scientific experience between some average joes in reasonable conditions. This opinion is only worth what it cost you.
Get the factory sails if you see your self selling or class racing in the near future. Get a trick square top from Chip for max performance or for pleasure sailing. I've had personal experience with two sets of his sails. I was very impressed both times, in the quality of craftsmanship and materials used, not to even mention that both times that the sails were ordered, they arrived in exactly 3 weeks! Also, check for your self on prices from other manufactures. He will amaze you there too.
I will keep my stock sails always, in case I ever sell my boat. You can bet as soon as my paychecks stop getting smaller, I will be ordering a new set for my self. I feel as though I've experienced the difference in more than one way..and I'm sold on the performance!...Obviously!!!
98 Miracle 20 + magnum wings