Why am I going slow?

Today,  I still get the excited feeling off independence and freedom when I rig up my own boat, or hook up the Laser trailer and drive to an event, even though lately I am off the pace of the top guys locally, begging the question, are my tight pants really a problem?

I had a steak dinner with Andy Horton a few years back in Miami just prior to the OCR. Andy described the effect of his recent change in his Star boat design in meters at the weather mark, all other things being equal. Andy is a very talented (and analytical thinking) sailor. He also explained to me why footing in lifts (and designing the boats that way, with fuller bow sections to aid a speed build) is the key to winning in the Americas Cup boats, v5. I digress, (but actually that is as important as anything I have learned from anyone).

Here is my calculation for a Laser.

I am using something called Sail Area Displacement Ratio (also noted here as SA/D), something that seems to be used a lot to check a boats performance.

Sailor*Total Displacement*SA/D
215 397         20.91
210 392        21.08
205 387 21.26
200 382 21.45
195 377        21.64
190 372        21.83
185 367        22.03
180 362 22.23
175 357         22.44
170 352        22.65
165 347        22.87
160 342        23.09
155 337         23.32
150 332        23.55
145 327 23.79
140 322 24.03
135 317  24.29

Underlying Assumptions
Laser Weighs 130lbs
Spars Weigh   15lbs
Boards Weigh 15lbs
Rigging Weighs 10lbs
No allowance for clothing. You can take your naked weight 185, weigh your clothing and get 195.

First, compare that to a 175 Lbs all up and you get a difference in SA/D of 22.44-21.64= 0.8
.8 as a percentage of 22.44 is 3.56%

Second figure out the % advantage this turns into: a 175 lb sailor has a 3.56 percent advantage downwind and in light wind over someone who is 195 lb based on SA/D.

To complete the circle and get to Andy's turn everything in to meters concept: On a 1 km leg that is 35.6 meters, about 8 Laser Boat-lengths (assuming equal skill) (assuming SA/D is 100% relevant and significant)

If you double the difference in weight from 195 to 155 you get 23.31-21.64 = 7.16%

On a 1 km leg that is 71.6 meters, about 16 Laser Boat-lengths (assuming equal skill) (assuming SA/D is 100% relevant and significant)

So it makes sense almost universally people say 185 is the proper weight for the boat looking at the chart. Most boats have these proper weight ranges for a reason, here is a good example.

It also makes sense that technique and skill compensate for much of the difference in One Design sailing, so the weight range is able to be quite broad.