Great Bay Race

[Bill Roberts]

Hi Guys,
It sounds like you all had a real blow out at the Great Bay Race. There is one thing I don't understand. Why does an 8.5ft wide boat beat a 12ft wide boat in righting moment limited conditions. I also noticed that some H20s beat the 22s on corrected time. What's going on???
It seems like you guys do fine in light and medium winds, 5mph up to 15mph, against all competition. Ladurini builds great sails. As long as you guys can hold the boat down and drive 100% of the sail area, everything goes good.

The problem seems to come when the wind exceeds 15mph and goes on up to 20mph with puffs even higher. This is the wind speed range where sails have to be depowered. You have to alter the shape of what Ladurini has built for you.

The root of the problem comes from the fact that the force of the wind varies as the square of the wind speed. At 10mph wind speed the dynamic pressure of the wind is proportional to 10squared or 100. At 15mph the dynamic pressure of the wind is proportional to 15 squared or 225. This is 2.25 times as much force per square foot of sail area as the sails were exposed to at 10mph wind speed. This is the wind speed where our boats become righting moment limited. At 20mph wind speed the dymanic pressure is proportional to 20 squared or 400. This is four times the force per square foot of sail area the sails were exposed to at 10mph wind speed and almost twice the force per square foot of sail area the sails felt at 15mph wind speed.

So here we are. We are in 20mph winds and can drive only a little over half our total sail area. What do we do??? If we just luff/ feather/downhaul the mainsail and take the battens out of the jib, we are going to be very slow relative to our potential. So what can we do better?
1. Install 50% stiffer top two battens in the mainsail. No taper on these two battens. Make the top of the sail flat. This will drive the CE down in the mainsail and reduce the overturning moment. Install a 50% stiffer top batten in the jib to flatten the top of this sail and open the leech. Move the jib sheet attachment point forward on the jib clew plate to reduce jib leech tension and let the jib twist out at the top and be flat. You do the same thing to the mainsheet at its clew plate attachment point, move it forward to derotate the mast which reduces the overall camber of the airfoil which reduces the overturning moment from the mainsail and it lets the leech twist out. In general you are doing things to the rig and sails to reduce the overturning moment and "streamline the sails".

In winds up to 15mph we all can hold our boats down and drive 100% of our sail area and our boats go fast and everyone is happy. Sailing to windward in overpowered conditions, aerodynamic drag is a parasite.
Everyone can drive their sails in proportion to their max righting moment.
The bigger teams can drive more of their sail area and luff less sail area than the smaller weight teams. The sail area that is not being driven, cannot be held down, reduces boat speed to windward in two ways; it is a double hit! First we are not getting thrust out this sail area so there is a sail thrust loss. Second the wind is blowing across this undriven sail area and making aerodynamic drag. Sailing to windward the relative wind direction is only slightly off the bow. Therefore the drag from this undriven sail area is almost opposite in direction from the forward sail thrust component. Therefore this aerodymanic drag subtracts from the forward sail thrust and this makes the net forward sail thrust a smaller force. Therefore it is very important to "streamline the undriven sail area". So in 15mph winds with higher gusts, flaten the top of the main and jib with stiff untapered battens. Move the sheeting attachment point forward on the clew plates and flatten the top of the sails and make them twist off to leeward. Move the CE down in the sails so that the overturning moment is less. This allows the forward sail driving force to be greater and boatspeed goes up. Also a stiffer bottom batten in the jib is helpful in strong winds in that it will make the jib traveller car run further to leeward and this opens the slot and flattens the jib overall shape.

In 20 mph winds with higher gusts, "take the jib down". It is a parasitic drag that you don't need in these conditions. Today for off wind sailing we have spinnakers and the spinnaker will take you downwind as fast as you can control the boat. The jib is of no value downwind. Upwind in 20+mph winds, the boat is faster without the jib. Sailing to windward in these conditions with a battenless jib is super slow and the boat won't point.


I hope these tips help and I want to see you guys do better in the next high wind regatta. Make these changes and practice, practice, practice and you will do much better in the next race.
Good Sailing,
Bill

[Glen Marsh]

Hey Bill-
Just wanted to add to the comments you posted about the Great Bay Race. Concerning the hobie 20's , they have great ratings not to mention that they were sailed by good sailors, nothing more to say here about that..... Only one Arc22 w/spin finished the race the other sailed a different course because they did not have a spinnaker.

The other 20 ft. boat was the CFR20 sailed by Brian Lambert (not too bad of a sailor). The arc22 was just as fast as the cfr20 just not going as high because the whole no jib concept.....and the arc can not furl its jib.

While weight did help in these conditions, we had to foot off to keep the hull flying so not to slam into every on coming wave and thus giving up distance and angle. We do believe that weight plays a major roll in the performance of a boat. These corrections need to be used and used correctly. Just not applying a H3 to Base DPN and sail the race, but both weight and wind adjustments NEED TO BE USED. This should level the playing field and at this point the numbers can and should be adjusted. Speaking on thrust and size.......in the us sailing numbers h3 becomes less of a factor to no factor as wind increases. How would you suggest this issue be resolved???

[Bill Roberts]

Hi Glenn,
The ARC22 does not have a roller furling jib because sailing to windward with a furled jib is slow. A furled jib makes drag just like another piece of mast section 32 feet long going along for the ride along the jib luff. Been there, done that; it doesn't work.
You and Steve need to learn how, when and where to use your weight to advantage. Five hundred and fifty pounds on a 15ft lever arm is 8,250ft lbs of righting moment. Compared to 360 lbs x 15ft = 5,400ft lbs. That is 2,850 ft lbs more righting moment or 53% more righting moment than the average all male team. You guys can hike too hard and force the skipper to reach off slightly sailing to windward trying to keep the windward hull up. With you two guys just sitting on the windward hull with a 12ft lever arm, you are generating 6,600ft lbs of righting moment. That is a 22% advantage over the average size team in righting moment without using the trapeze.
As far as the jib goes: you need to practice taking the jib down out on the water. Roll it from the top down to the foot. Leave the tack and jib sheet attached and snug. Roll the jib up and tie it along the spinnaker pole with a couple of ties. This should be no more than a five minute job and neat. When you see that bay covered with white caps, JIB DOWN! I do not know if you are sailing with jib battens or not but the time when jib battens really pay off is in a stiff breeze. Without jib battens the jib blows up like the throat of a bull frog and you can't point and you have lousey speed. The jib becomes a net drag.
As for crew weight corrections: A big team has additional hull drag in light winds and the same sail thrust as everybody else. Therefore in light winds they deserve a break in PN. As the wind picks up to 15mph or so, things become more even. By 18 to 20 mph and up the big guys have an ever increasing advantage. In this wind speed range they deserve a hit; a PN reduction. Just the reverse is correct for light weight teams. In light winds where they have an advantage, they deserve a hit. In strong winds where they are at a disadvantage, they deserve a breakin PN, a higher PN.
The present US Sailing PN adjustment system doesn't do this. It is technically incorrect. I do not know where the present system came from. For sure it did not come from a reliable source. I have been talking to Darline Hobock about this.
Good Sailing and win this weekend,
Bill