Load it up as you would use it for the sea trial. Full fuel tank and water tank and the number of people you'd generally have on board. If it doesn't perform as you like then you can back out. I know you'd then lose money on a survey and adding fuel to the tank. But you won't be the first to do that.
Another general tip to consider, adding to the above is that if you primarily boat in fresh water, due to the difference in bouyancy, the boat will behave as if it is like 10-15% heavier, needing more power to plane and top speed. At least, that is my experience and 2c.
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