S.A./Disp. is listed in two places on each boat form and appear to be different number for the same category? On the Com-Pac 23 MII it shows 16.90 (Rig and Sail Particulars) and 19.28 (Top area general data), which number is correct and why the difference in the numbers?
This link:https://sailboatdata.com/sailboat/com-pac-23-mk-2 has both numbers the same.(Maybe they fixed it after you pointed it out?) You could also figure out the number for yourself, though it calls for more than just taking the SA and dividing it by the displacement:https://en.wikipedia.org/wiki/Sail_Area-Displacement_ratio
Not a huge deal but I would like to know which is correct, many other boats I have looked at are very close but the Com-Pac is a large difference. I guess I will just calculate it and see which is closer and use that block from now on.
Thanks for taking a look.
General information: So far the Rig and Sail Particulars section has been the most accurate.
Re-checking the form I now see what you mean. It may be that the 19.28 number is based on the reported sail area of 250 square feet, while the 16.90 number is calculated from the measurements taken from the actual spar dimensions and 100% of the foretriangle, which add up to 219.15 square feet. Drawings and pictures show that there is some overlap to the jib, so the two numbers would seem to reflect two different things. The one to use depends upon what you’re looking for. Actual practical performance based on the usual sail area of the jib and main (overlapped jib and probably some roach to the main, and so bigger, at 250 sq’) or theoretical performance based on just the triangular areas of the spars and forestay - smaller, at 219.15 sq’.
I guess I am looking for accuracy and consistency, I have been checking several boats that I am considering and almost all of them the difference in the numbers is off by very little (example: 0.02 or so) when I found a big difference with Com-Pac a warning light went off. When you start using things like “reported” I have to ask reported by whom? From my understanding the Com-Pac 23’s generally reflect more of the 16.90 from what I have been reading, which is fine for my use but a person could be very disappointed if you didn’t check it out by reading from multiple sources. It’s ok, I created an easy to use formula to check, it now takes me longer to find the boat spec’s than it does to run the formula. Thank you for looking at this, I completely missed the S.A (reported).
Hello Kevin, Paul is correct. the difference is the reported sail area from the builder vs the 100% fore triangle determined by the rig measurements. Builders will often use a head sail bigger than 100% to report upwind sail area.
So it is more likely for the boat to actually perform to the “reported” standard, since that is based on the real sail area of the boat under sail? Using the 100% foretriangle figure automatically makes fractionally rigged boats look like poor performers, which may not actually be the case.
I guess you can say that. As you know, performance varies depending on the sails. Reported sail area is based on actual sail area. While nothing is 100%, builders tend to report SA based on their standard sails. Some will report using a Genoa to improve the performance number. Because you can always change sails, this is not necessarily the better number to use to compare boats. Using the rig measurement is better for that.
Also, keep in mind the other half of the equation, displacement, is almost always “light” which is with permanent equipment installed but tanks empty and without previsions, crew, etc. To my way of thinking reported displacement should be to the designed waterline but that is not always the case.
Using the rig measurement to compare boats sounds like a made-up number that has no relation to reality. For example, we only use our #3 jib (100%) when it’s blowing more than 20 or so knots, steady, and we’re headed upwind. Less wind, or on a reach, we’ll use our 150% genoa. Most of the time we use the genoa, because most of the time around here it blows less than 20 knots. How do you think the boat performs most of the time? If we were to use the 100% jib 100% of the time, we would not perform as well. Comparing us to other boats this way would make us look bad. Comparing us to other boats using the sails we (and they) actually use would provide a truer picture of real performance under sail. Why not compute SA/D based on a triple-reefed main and storm jib? Because it obviously wouldn’t provide a useful guide to performance under sail in normal conditions. Using the “reported” figures seems like it provides a more valid comparison.
I see Paul’s point but if you compare all boats using the same criteria (rig measurement) wouldn’t that be the best for comparison. You can’t compare actual sailing as each individual would/could use different sails for the same conditions depending on what sails they have, can afford and sailing experience thus creating differences even when comparing the same boat. Maybe I’m wrong but I would think comparing the same data for each boat (rig measurement) would be the best for getting a good base comparison of what could be vastly different boats. In my case not too different but there are a couple that are designed to be a little faster under sail and the rig measurement also shows that.