I've put an aluminum propeller on my '77 Thunderbird 18' tri-hull in place
of the original stainless steel one. Old prop is a Mercury 48-73982A4, 13
3/4" diameter, 21" pitch. New prop is a Michigan Wheel Vortex 992005, 14
1/4d, 21p. It's attached to a Merc 165 I/O. On the original prop, top speed
was 45MPH indicated and cruise was in the neighborhood of 25-30 indicated at
about 3200-3500 RPM.

Anybody want to predict what (if any) performance difference I'll see on
Saturday when I take it for a spin?

My prediction is slower out of the hole, slower top end at mfg rpm spec
(42mph). WOT RPM probably won't change much due to the larger diameter prop
(pitch being equal). Cruise will be about the same.

--Mike

"Joe Blizzard" wrote in message
...
I've put an aluminum propeller on my '77 Thunderbird 18' tri-hull in place
of the original stainless steel one. Old prop is a Mercury 48-73982A4, 13
3/4" diameter, 21" pitch. New prop is a Michigan Wheel Vortex 992005, 14
1/4d, 21p. It's attached to a Merc 165 I/O. On the original prop, top
speed was 45MPH indicated and cruise was in the neighborhood of 25-30
indicated at about 3200-3500 RPM.

Anybody want to predict what (if any) performance difference I'll see on
Saturday when I take it for a spin?

"mgg" wrote
My prediction is slower out of the hole, slower top end at mfg rpm spec
(42mph). WOT RPM probably won't change much due to the larger diameter
prop (pitch being equal). Cruise will be about the same.

Had my boat out this evening. Your top speed prediction was dead on. I can't
tell much difference in acceleration or cruise.

Now to see if the new prop affects galvanic corrosion the way I'm hoping.

Thanks for the report. Good luck with the corrosion problem.

I'm out for a day on the lake with the wife and son tomorrow...can't wait.
I'm gonna put my 19p aluminum prop on to show my son what it's like to fly
out of the hole. He's gonna love it. I generally run with a 23p ss prop.
That keeps my rpms within the mfg spec @ wot.

--Mike

"Joe Blizzard" wrote in message
...
"mgg" wrote
My prediction is slower out of the hole, slower top end at mfg rpm spec
(42mph). WOT RPM probably won't change much due to the larger diameter
prop (pitch being equal). Cruise will be about the same.

Had my boat out this evening. Your top speed prediction was dead on. I
can't tell much difference in acceleration or cruise.

Now to see if the new prop affects galvanic corrosion the way I'm hoping.