Michigan 14.5/17 vs Solas 14.8/17 performance difference

[Heloguy]

Hello everyone! This is my first post, and I would like to begin by thanking each of you for your wonderful insight throughout the years. Thank you!! I have a 1991 vip open bow 18.5 foot ski boat. 115 hp 3.0L mercruiser with alpha one gen 2 drive. WOT range 4400-4800. I recently replaced my Michigan wheel 14.5/17 aluminum prop with a Solas 14.8/17 amita 3 aluminum after reading favorable reviews for the latter. The mw prop suffered damage after a losing fight with some rocks. The Michigan prop ran 4800 rpms wot at 43 mph gps with full fuel and 2 souls fully trimmed out. The Solas revved to 5100 rpm wot and 38 mph gps under the same conditions, lake, fuel, trim, and souls 1 week later. No other mods between other than prop. I assumed that the new prop would be very similar in operation with a possible increase in performance due to design, but that is not the case. It pulls great on the holeshot, and ventilates at about the same trim setting as the mw would. I double checked the ratios stamped in each prop again and they are as advertised. Any ideas as to why the big difference?

 

[steelespike]

When calculating a props performance some of the numbers are actual.
prop size,drive gear ratio,gps speed. rpm and slip numbers are harder to come by.
The calculator says you can't go 43 at 4800 rpm. Assuming the 43 is correct then
if we guess slip at 12%(usually in the low double digits) we get about 6000 rpm.to make 43
43 would normally occur with at least a 21" prop.@ about 4800.
The Solas @ 5100 and 38 mph calculates at about 7% slip, unusually low,
I think due to an erratic tach.I'm betting the Solas actual slip is closer to the low double digits I suggested
And the rpm higher.The tach and on board speedo are always suspect especially on an older boat.
On a well setup 3.0 18 ft.boat a 17" prop would be used for water sports with a load of people in the boat
With the proviso that it will over rev with a light load. I used a 2.00 ratio for both props yours
may be somewhat different but no matter as long as we are just comparing prop results.
We are assuming the 43 wasn't affected by a current or tide.
The 17" Solas performed as you would hope keeping in mind both rpms are suspect.