Bigsfish,
The weekend is coming up and perhaps there is a way to get some reasonable data without too much time or inconvenience.
In another post I think I remember that you have a large fresh water supply as well as a large holding tank capacity - if you combine that with your dinghy and a short trip with a 'bunch' of volunteer friends maybe you can get some confirmation without too much work.
Is this possible?
- Empty the water tank(s), pump the holding dry, drop the dinghy to the dock temporarily and take the boat out for a test run with one extra person and record your numbers carefully at WOT as well as a few other cruise points. I have used a digital camera to take a shot of all my gages in the past for this purpose but also have used preprinted sheets to fill in the desired data. This trip should not take long at all.
- When you return to the dock add back the dinghy, add back all the water as well as filling the holding tank with water (maybe 450-500 gal in your case). Get a bunch of people to join you for the next 'cruise' and copy the same tests you did above. The difference in weight should be in excess of #5,000 and the results will show how significant the weight gain is to the speed and rpm as the boat stands now.
Perhaps this will give you most of the feedback you need without the necessity of lugging off all your possession's , waiting for fuel changes, and removing and replacing 1,600# of lead.
I have had good results with this in the past - the only downside I have had was when I asked a young lady on the 'cruise' what her weight was. It of far better to not ask and just take a reasonable estimate.