The calculations in sailonline’s performance loss system are a bit complicated. Sometimes it’s really handy to know how much you will lose as the result of some manoeuvre. This is why I made the Sailonline Performance Calculator ^{[1]}.

The calculator should be pretty self explanatory, but let me explain some of the quirks.

So, to calculate the performance loss, you will need to enter your twa before the turn and after, and your performance just before turning. Because of the calculations, you also need to enter what boatspeed you will have on your new twa. This is the boatspeed you would have with 100% performance.

All numbers except *time lost* are based on serverjumps of exactly 10 seconds. Since the serverjumps are not that regular, the results of the calculator can be off by a tiny bit.

Time lost is calculated as follows: imagine a boat sailing the same course as you, but with 100% performance. At the point that you reach 100% performance you’ll be behind the other boat. *Time lost* is the time it takes you (at 100% speed) to cover the distance between the two boats.

When executing multiple course changes before you recover to 100%, you can use the optional “time to next DC” parameter. This will give you some extra info. Again, all numbers except *time lost* are based on server jumps of 10 seconds.

*Time lost* is calculated a bit different, not using 100% speed, but the speed at the moment itself (when your performance is not fully recovered yet). The distance between you and the imaginary boat without performance loss is also not yet at it’s maximum.

This *time lost* parameter is meant to help you adjust DCs. Suppose you need to tack for a mark, and then round the mark before your performance is fully recovered. Then you can set a DC for the tack, and set a provisional DC for the mark rounding. Put the number for the tack (first DC) in the calculator, and add the time difference between both DCs in the *time to next DC* field. The result you get at *Time lost to next DC* show you how much you have to delay your second DC to compensate for the performance loss. You can double check by measuring the distance between both DCs (first DC: tack, second DC: rounding) and comparing that with “distance to next DC”.

If anything is unclear, or if you miss something (for example, performance increment per minute) in the calculator, let me know.