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geohan 12-17-2002 05:04 PM

Not Very Smooth Racing Bottom
 
I wonder if the detrimental effect of an "orange peel" bottom surface isn''t a bit overrated in any racing competition less than one-design boats, dry-sailed in the national or perhaps regional championships. I don''t know, I''m just asking but my thinking is that the effect may be small compared to missing a wind shift, or a puff or misplaying the currents. Perhaps I''m just trying to ease my conscience for not having a 600-grit-sanded and burnished underbody. (My wife seems to have lost her interest in sanding boat bottoms and I never really had the urge in the first place).
Do any of you know of or have quantitative data of the speed differences between orange peel and polished bottoms? Bethwaite claims (High Performance Sailing, page 252) to have measured a 2% drag increase due to an invisible but just-detectible-to-the-touch, road film over the polished bottom of a high performance 18-foot dingy towed at 2-kts but doesn''t say how much it decreased its speed. Can one get there from here?
Smith in "How Sailboats Win or Lose Races" reports his towing experiments. In one case a Small Point One Design, (19 1/2-foot, 2300# displ., 400# outside ballast keel, round bilge) was test towed with a rough bottom condition (No marine growth but"...paint ridges on her rudder, grooves in her iron keel, and caked paint along her topsides) between one and six miles per hour to develop a speed(y) vs. drag(x) curve. A similar curve was developed after she was "...carefully sanded, all cracks and keel gouges filled, and her entire bottom given two coats of clear epoxy paint". The bottom was then further smoothed and polished. The smooth bottom was faster by an average of 200-feet per mile. That equates to 3.8% faster for a gain of 227-feet per NM or 24-seconds per NM at 5-knots.
Now consider this: Two boats on a beat cross closely and continue on opposite tacks at 5-knots boat speed and 45-degrees off the true wind direction. In only 1.4-minutes they will have diverged 1000-feet(1) with both on a Line of Equal Postion which is perpendicular to the true wind. Now a 15-degree wind shift will cause the boat on the side to which the wind shifted, to gain 366-feet(2) sailing distance at the other''s expense. At 5-knots this amounts to a 44-second(3) gain or loss.
One lesson here is that when two boats on a beat cross on opposite tacks, ONE OF THEM IS GOING THE WRONG WAY! The other lesson is that it is better to have even a grossly rough bottom than to miss a 15-degree wind shift more than once every two miles. If you have a rough bottom AND miss the shifts, you should probably reevaluate your program, but a little bit of orange peel shouldn''t be catastrophic.
Ok guys, rip it up! Cheers, George
(1) (1.4-min)(500-fpm)(cos45)(2-boats) = 1000-feet
(2) (1000-ft)(sin15)(cos45) = 366-feet
(3) (60-spm)(366-ft)(500-fpm) = 44-seconds

Jeff_H 12-17-2002 05:33 PM

Not Very Smooth Racing Bottom
 
Bottom preparation really comes into play in two separate conditions, very light air and in gusty winds. In light air the difference is very noticable and comes into play when it makes the difference in how much speed you can build by way of apparent wind. What happens in light air is that as a boat builds up speed its also builds up apparent wind and with this building of apparent wind comes more speed and with more speed comes more apparent wind until the drag on the boat becomes large enough to stop the boat from increasing in speed. In these extreme light winds a boat with a smoother bottom will get up to speed quicker and hit a higher speed. This higher acceleration can means minutes coming out of a tack and will also allow the faster boat to place itself more strategically on the racecourse.

In gusty conditions, a boat dispurses the energy of a gust in two ways, accelerating and heeling. Acceration is good because it is faster, and with more speed there is less leeway and less rudder angle required. When you heel the opposite occurs, Leeway increases and rudder angle needs to be increased which can often actually reduce speed. Here again the increased drag of a rough bottom means more heeling and less accelleration. Not good!

I don''t do a full blown racing finish on my boat but I do have it sprayed and sanded after application. On my smaller boats I would use a hard bottom and burnish afterward, if nothing else but for the pyschological need to eliminate a rough bottom as an excuse for a poor finish. 8^)

Jeff

Jeff_H 12-17-2002 05:35 PM

Not Very Smooth Racing Bottom
 
And another thing, while sailing the wrong way can really hurt you on the race course, you are probably not the only one who chose the right side of the course so you still need boat speed to walk away from the guy who went your way.

Jeff

Sailormon6 12-18-2002 09:51 AM

Not Very Smooth Racing Bottom
 
George Ė The detrimental effect of a bottom that is poorly prepared for racing isn''t overrated. It really is very detrimental. The question is, "How much do you want to win, and can you be satisfied racing without winning?"

You compare the adverse effect of a foul bottom with the adverse effect of missing a windshift or puff, and then you contend that a tactical error is more harmful than a foul bottom. There are flaws in that reasoning.

First, at your present skill level (regardless of whether you are highly skilled or less skilled), there is very little that you can do, in the short term, to stop making those tactical errors. You canít just choose to stop making mistakes. Over the long term, you can acquire more knowledge and skill and reduce those errors, but you canít do it now. A foul bottom, however, can be corrected immediately. If your opponentís boat is capable of achieving its maximum potential speed, and your boat is not, and if you canít stop making mistakes, how do you plan to beat him?

If you are presently much more skilled than your opponents, you are less likely to make tactical errors than your opponents, and you can beat your less-skilled opponents even though your boatís bottom and keel are not race-prepped. Dennis Conner has been credited with being able to use a slower boat to beat a faster boat. That can only be done when there is a considerable differential between the skill levels of the skippers and crews of the two boats, and with a little good luck, as well. It takes a lot of skill to overcome the hard reality that a faster boat will always beat a slower boat, unless the skipper and crew of the faster boat prevent it from doing so through human errors.

If your boat has less raw speed than your opponent, you cannot usually win by sailing in the same conditions as your opponent. If you sail in the same winds and currents as your faster opponent, he will beat you because of his superior speed. That means you are forced to split from your opponent, and go off hunting stronger winds and puffs, or a favorable slant on the wind. If your opponent is smart, heíll cover you wherever you go. If he doesnít cover you, itís still very difficult and very risky to go hunting wind. After all, you are trying to find enough wind to overcome the disadvantage of having less raw speed. If it was easy to do, everyone would be doing it.

As Jeff H. points out, a foul bottom not only reduces your maximum speed potential, it hurts more every time you move your rudder.

I donít have any quantitative data, but I raced my boat in a national regatta in 1983 after meticulously preparing the bottom and fairing the keel, and it was clearly the fastest boat on the water. (After developing a big lead in the first four races, we finished second in that regatta because of an equipment failure two legs from the finish line in the last race.) Superior speed allowed her to get better starts, to draw ahead of the other boats and into clear air on the windward leg, to outpoint them, to round marks faster, to tack more efficiently and to accelerate back up to speed more quickly, and it enabled her to maintain better speed and to coast farther when sailing off the wind or in light air. In short, it helps you all the way around the course every time you move the rudder, and it helps when you donít move the rudder. When you make a tactical error, raw boat speed even helps you recover from the error. I raced her in the national regatta three times since then, and, in each instance, can see a clear relationship between the results and the adequacy of my work in prepping the underwater surfaces.

All that having been said, whether you expend that much effort to prep your bottom is your choice. As I get older, arthritis prevents me from prepping the boat as I used to, but it is still very satisfying to race, in club races, in the middle of the pack, mixing it up with the other sailors, yelling rules at them and occasionally getting a little lucky and out-foxing them, beating them to the finish line. In some ways, itís even better than winning regularly. You donít have to do all that work if you are enjoying racing without winning all the time. Itís no sin, you know.

shuttdh 12-18-2002 10:19 AM

Not Very Smooth Racing Bottom
 
While we are on the subject. How important is it to have a barrier coat underneath antifouling paint if the boat is in the water 8 months out of the year?

geohan 12-18-2002 03:12 PM

Not Very Smooth Racing Bottom
 
Jeff: Thanks for your reply. I agree with what you say but am stuck with somewhat limited resources and need an objective way to spread them around. If the difference between orange peel(say 80-grit) and smooth underbodies amounts to more than 6-seconds per mile, perhaps the new jib could wait another year. My original use of the term ''orange peel'' probably wasn''t a good choice since as Max suggested we do use a smooth roller and tip it out but without any further sanding.

geohan 12-18-2002 03:34 PM

Not Very Smooth Racing Bottom
 
Sailormon6: Thank you for your remarks. We certainly agree that smooth bottoms are better. It''s the smoothing that''s the rub.
To put it all in context, our venue is a 30-boat, mixed-fleet club racing under PHRF. My wife and I race a 30-foot, 9700# Mercator with a tall rig, and do quite well in light air when getting from one cat''s paw to the next is the name of the game. Being quite a bit the most senior on the course, we certainly don''t domnate but manage to win often enough that we aren''t taken for granted and seem to provide a nice ''high'' for those who can best us. This makes it fun for us and for them which may not be a bad thing. Our aspirations are to remain interesting competition and to "tweek''em" when they aren''t looking! We admit this doesn''t do much for advancing the sport but trust it is not a disservice. Now thanks to your last paragraph we may even be virtuous----naw. Cheers, George


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