Toffen
07-10-2006, 01:15 PM
Hi!
I trust you all are well.
Got my Phantom 25 with twin Merc 2.5 EFI SS engines on water this week. We are still tuning it in, but some testing has been done. The engines are mounted 19 inches centre to centre, and propshaft is 1,25 inches below the bottom. 2 inches of setback. Gear ratio is 1:1.87.
I have tried a pair of stock Bravo 1 28 pitch x 15 1/4 diameter props without went holes, and here are the results:
Holeshot: The boat jumps into plane without breaking loose.
4.000 rpms = 53 mph gps
6.300 rpms = 84 mp gps
Above 6.300 rpms the rpms increase, but not the speed. Lots of power left, but the boat needs more bowlift, and the prop loose grip of the water and ventilates.
My theory is that the Bravo 1 lift the stern too much due to is large diameter and 4 blade design. The effiency at 4.000 and 6.300 rpms indicates that the engines can be mounted higher if I can get hold of props with better bowlift / less stern lift.
I will test a pair of stock Mirage Plus 27 pitch tomorrow. Several Phantom offshore racers from the past have reccommended this prop together with Choppers as a good choice for top speed runs.
What do you think?
Cheeeeers and thanks!
Toffen G
A happy boater :)
I trust you all are well.
Got my Phantom 25 with twin Merc 2.5 EFI SS engines on water this week. We are still tuning it in, but some testing has been done. The engines are mounted 19 inches centre to centre, and propshaft is 1,25 inches below the bottom. 2 inches of setback. Gear ratio is 1:1.87.
I have tried a pair of stock Bravo 1 28 pitch x 15 1/4 diameter props without went holes, and here are the results:
Holeshot: The boat jumps into plane without breaking loose.
4.000 rpms = 53 mph gps
6.300 rpms = 84 mp gps
Above 6.300 rpms the rpms increase, but not the speed. Lots of power left, but the boat needs more bowlift, and the prop loose grip of the water and ventilates.
My theory is that the Bravo 1 lift the stern too much due to is large diameter and 4 blade design. The effiency at 4.000 and 6.300 rpms indicates that the engines can be mounted higher if I can get hold of props with better bowlift / less stern lift.
I will test a pair of stock Mirage Plus 27 pitch tomorrow. Several Phantom offshore racers from the past have reccommended this prop together with Choppers as a good choice for top speed runs.
What do you think?
Cheeeeers and thanks!
Toffen G
A happy boater :)