Actually so did I and I counted the helmsman as sitting with feet in to the middle of the boat. Crew sits facing outboard with feet over the side. That moves 30% of the weight of a helmsman 3 feet inboard compared to crew. That is a lot of moment which you have to include and contributes the remaining 1/4 decrement of the effect of the helmsman.

L2

:: I did a reasonably careful measurement using this image:
::
:: http://express27.org/photos/2392.jpg
::
:: Assuming the boat is flat, A helmsman sitting at the
:: traveler has about 3/4 of the righting moment of a crew
:: hiking reasonably hard amidships. This means the
:: difference in total righting moment between an at weight
:: boat with a 300lb driver is less than 5% different than
:: one with 150lb driver.
::

:: -
:: -   ( 300 * 0.75 ) + 580 = 805
:: -   ( 250 * 0.75 ) + 630 = 817.5
:: -   ( 200 * 0.75 ) + 680 = 830
:: -   ( 150 * 0.75 ) + 730 = 842.5
:: -

::
:: With most drivers in the 150-250 range, I don't think
:: it's worth complicating the rules for a 2-3% difference.
:: I'll also submit this as evidence, that when it comes to
:: winning races there are more important things to worry
:: about:
::
:: http://express27.org/photos/640.jpg