I did it and it was very wrong, my boat weighs about 1600 kg = 3527 lb, my trap speed is around 133mph, it said I had 647RWHP.
On the dyno at unigroup it says about 500hp ATM, so thats 150 stray horses my car does not have.
The ET one was at least partialy right with my 3527lb and 500 hp giving a 11.17, my best is 11.13, but the trap speed was 122, its missing the 11mph that I do have.