In the waiting of proper weather, here is a table that was derived while studying McCready ring value of various sailplane, with various wing loading. It gives you an equivalent additional Mc Cready setting to be representative of polar change due to waterballast.
This is the result of numerical investigation filtered by the “TAR”* method. For sure your marvelous onboard computer knows better…
The objective is to provide simple figures, easy to memorize, per family of glider (Club class/15m/18m/20m/unlimited), to be used with “Standart Mc Cready ring” (like the good old time).
Example : today I fill my LS6 with 80L of water. I should consider increasing by 0.4m/s my McCready setting due this additional wing loading – on top of other setting (80/100*0.5m/s=0.4m/s)
Don’t hesitate to use this “enhanced rule of thumb” !
(& keep in mind it is always more efficient to have a McCready setting “a bit too less” than “a bit too much”…)
* “TAR”=”That’s About Right” method – i.e. there is a certain dose of approximation in all this.