Fin & Rudder ratio

I have another simple question for the honnored panel :slight_smile:

Often designers speak of the t/c ratio of the fin and the rudder of the boat. Values like 6; 6,5 and 7 % are common but I would like to know how it’s calculated.

Is this a percentage of the max width of the fin/rudder or a percentage of the max beam of the boat, or is it something completely different ?



t/c ratio= thickness of a foil divided by the chord( fore and aft dimension of a foil)
Many designers favor low values -around 6%-7% for fin and even rudder sections.

Doug Lord
–High Technology Sailing/Racing