Sailjuice Global Warm up handicaps

Tide is an enormous factor in handicapping. There are a number of secondary effects that can effect one boat more than the other but the dominant one must be the speed of the tide relative to the speed of the boat. Fast boats have a much bigger advantage than slow boats. Slow boats have to travel further over the water to sail the same course.

Consider 2 simple examples using 2 boats on a broad reach. 

1)      Let’s assume that boat A can achieve 8 miles per hour while boat B can achieve 5 miles per hour in the same wind on the same course.  Let’s consider a simple I lap course between 2 buoys X and Y one mile apart with buoy X directly uptide from buoy Y. The wind direction is perpendicular to the tidal flow and the tidal flow is constant at 4 mph. Both boats start at buoy Y. Boat A sails to buoy X into the tide at 4 mph (8-4) and takes 15 minutes to cover the mile. He then turns round buoy and sails at 12mph (8+4) towards buoy Y and gets back to bouy Y in 5 minutes , so his lap time is 20 minutes . Boat B sails to buoy X into the tide at 1 mph (5-4) and takes 60 minutes to cover the mile. He then turns round buoy and sails at 9mph (5+4) towards buoy and gets back to buoy Y in 6.67 minutes , so his lap time is 66.67 minutes . I know I have ignored lots of second order effects but you can see that while on static water boat A  is faster than boat by 60% ((8/5)-1)on this tidal course he is quicker by 233% ((66.67/20) – 1). This is a huge difference.

2)      If we now consider the same course but with the tide perpendicular to the course and in line with the wind. If there was no tide boat A would travel from buoy Y to buoy X in 7.5 minutes but if the tidal flow is still 4 mph the boat gets taken 0.5 mile off course during that time. Similarly if there was no tide boat B would travel from buoy Y to buoy X in 12 minutes but if the tidal flow is still 4 mph the boat gets taken 0.8 miles off course. To do the analysis correctly you have to resolve the vectors  and take into account the impact on the boats speed of taking a modified heading to allow for the tide. Never the less you can see that simplistically the slow boat has to travel extra distance over the water than the fast boat – so not only is the boat  A faster than boat B by 60% but boat B has to travel further as well. If you resolve the vectors it amounts to about 14% extra distance for boat B but this takes no account of the reduced speed caused by the modified heading.

So how is this taken into account by the PY system?  The answer is it is not. All the data from all the clubs is considered and averaged so the RYA PNs will have some component of tidal data in their numbers. But it just causes more spread in the data from which PNs are derived. The SJ handicaps have effectively removed this for boats where there is enough statistical data from the inland results. Hayling Island Sailing Club have developed their own algorithm to make their handicaps more suitable for their tidal conditions. They treat the FF at 1023 as the pivot point and increase slower boats handicaps and decrease faster boats handicaps in a linear way with respect to the RYA PNs. The faster the boat, the bigger the negative correction.

In the case of Star Cross I guess that they have concluded that some of the descrepancies between the perceived speed of the boats such as the Laser and it’s RYA PN is bigger than is the case for adopting the SJ inland handicaps so they are planning to go with the latter. In the longer term despite their tidal flows being lower than Hayling it would be better to try and fit the data with a small tidal correction super imposed on the SJ numbers which penalises fast boats and favours slow boats.

The SCHRS system used for catamarans also ( I believe) has no way to allow for tides as it just considers the theoretical speed of the boat. Thus slow catamarans sail at a disadvantage to fast catamarans on tidal waters.