I have made an order for a 450R for my Phantom 25 V bottom. Its a 1985 model UK offshore race design. No steps - ol style runner.

At this moment I have a 400R on it. Best speed is 89 mph with a Max5 25 prop at 7,060 rms. 1:1,75 gear ratio. Most of the times we end up at 88 mph at 7,040 rpms, which translates to 7% slip. Which is good for a classic V hull design. I run the propshaft 2 inches above the bottom. The trim is fairly neutral and boat runs high and flat.

With the 450R I estimate a top speed with a Max5 27 to approx 95 mph. Mercury offers Max5 with 15,25 inch diameter and 15 inch diameter. Merc advertise 15,25 to have less slip. The question is if the 15,25 will be faster than the proven 15 inch diameter, since its most likely will give more transom lift ...

What do you think?

Cheeers, Toffen