Sounds like you are running 19 props, right?
A new set of props can set you back some serious bucks. If you could get someone to let you borrow a set of 21s, it would be interesting to try them out on your boat. With 300 Mercury horses on the back, you should be able to run into the upper 40s or low 50s - but your current props are going to over-rev the engines to get there.
I think the V-6 Merc 150s had a max operating RPM of 5500 - but the 175 went to 5800 - that's how they got 175 out of the 150!
A lot of people say the 2 litre (121.9 cu.in.) V-6 Merc will run all day at 6000, but I just don't buy it with the stock rods and pistons. I had a 'Rude on a hydroplane hull bass boat a few years ago and would run it up to 6200 WOT from time to time, but it was going so fast it would scare you. I almost never (well rarely :twisted: ) ran that thing wide open, but it literally screamed at 6200!
I would check with some marine places and see if anyone has a set of 21 pitch props for a V-6 Merc around - maybe they would let you try them out and take your old ones in trade if they work.
Just don't hit anything with the loaners...
Good luck and see ya on the water!
