Sea Level to Lake Tahoe - What Props?

[iboatmon]

My 2013 Cobalt 273 with 430 HP 8.2L Mag HO has a gear ratio of 1.81. Props are 1) SS, Merc 14.25 D, x 22.5P Rh 3 blade & 2) SS, Merc, 15.75D x 22.5P, Lh, 4 blade on a Bravo III drive. I am not sure why I have 22.5P props, since after looking at several posts here for similar mercs it seems most have 26P or 28P props, with that gear ratio.

Anyway I was wondering what a 4 blade BIII prop with a different pitch might buy me. I was out on Lake Tahoe (Elev 6225. ) and went WOT the other day with one other person on board and about 40 gal of fuel and topped out at 45 mph and 4500 RPM. I know I should get well over 50 MPH at sea level and run up closer to 5000 RPM. After looking at MerCruser's Website for selecting props, it looks like they would recommend 21P props for 54 MPH @ 4800 RPM. Seems a little optimistic to me, probably because they want to sell me a new prop!

Can any of you guys that know about such things tell me what prop I should have and what speed at WOT would be with that new prop at Tahoe?

Thanks!

[cmattj]

You’re perfect for Tahoe now if anything those numbers show a high slippage ( 15%) so is your speedo gps? Maybe it’s running behind a couple? Trim can play a role as more is better in WOT but may porpoise at lower cruise speeds.

As your down 60 horsepower in elevation inefficiency I would say a set of standard 24p once your at sea level and your power is back up.

Adding pitch now in Tahoe will make it strain. Your almost over propped now slightly. But just insure your blades have no edge wear or dents .

A set a used 24p will be a good find for when your on the Delta

[Big Block Power]

I argee with Matt. If you could find a set of 21's for Tahoe those might get you in the range your looking for. But your not going to gain as much speed that merc is saying. May stay the same or lose some.

[iboatmon]

Thanks Matt & BB. I need to do a better WOT test run with GPS, trim, etc., and report back. I agree that the 22.5P I have now is close to where I should be for Tahoe. I am Tahoe only, as I live here and don't plan to trailer to any other locations, so no interest in 24P.

Do you have any idea whether 4x4 props, instead of my current 3x4 props, would help? I do have a few minor chips, so I am thinking about getting new props anyway.

[cmattj]

Thanks Matt & BB. I need to do a better WOT test run with GPS, trim, etc., and report back. I agree that the 22.5P I have now is close to where I should be for Tahoe. I am Tahoe only, as I live here and don't plan to trailer to any other locations, so no interest in 24P.

Do you have any idea whether 4x4 props, instead of my current 3x4 props, would help? I do have a few minor chips, so I am thinking about getting new props anyway.

After you try another WOT and trim up for a 30- 45 second blast lets see if your slip numbers drop. Adding blades wont increase speed, just increase bite or reduce slip. Most Duo props set ups with clean blade edges seem to be 10 % or less.

Your current set up with a Prop shop just giving them a edge clean up will reduce cavatation and pick everything up. (speed and slip) Look forward to hearing your final test numbers.

[CaptainTom]

iboatman- I never switched the props on Kristine Marie. My WOT stats were close to 5000rpm and 51mph at Dallas elevation. That was not gps speed. I dug up an old picture:

8D03086C-2939-4EDB-8E76-6C3DA3537D33.png

[iboatmon]

After you try another WOT and trim up for a 30- 45 second blast lets see if your slip numbers drop. Adding blades wont increase speed, just increase bite or reduce slip. Most Duo props set ups with clean blade edges seem to be 10 % or less.

Your current set up with a Prop shop just giving them a edge clean up will reduce cavatation and pick everything up. (speed and slip) Look forward to hearing your final test numbers.

How do you determine the slip?

Oh, never mind, I found the Prop Calculator on the Web.

Thanks!

[iboatmon]

iboatman- I never switched the props on Kristine Marie. My WOT stats were close to 5000rpm and 51mph at Dallas elevation. That was not gps speed. I dug up an old picture:

8D03086C-2939-4EDB-8E76-6C3DA3537D33.png

Thanks Tom! Great to hear from you again.

That is what we got during the Slalom Shop Louisville Lake test in Dallas when I bought the boat, as well... about 50 MPH @ 5,000 RPM. Looks like I probably won't get much more top speed here at Tahoe, but I might be able to increase the WOT RPM slightly, to get into the appropriate range anyway, if I drop the pitch a little. As stated previously, I will need to do some more testing first.

[Big Block Power]

I can say all of the b3 guys that have switched to hill marine 4x4 have been happy. I can tell you me not so much with the Volvo set up. Still working on the numbers on it. I haven't had the proper conditions to run them hard this year. I can tell you I will never recommend them though.
You may gain hole shot and mid range.

[ADPIV]

I have a 2005 Cuddy 255 with the 496 and Bravo III Drive. Current props are 28P for Sacramento, I have been told to drop to a 26P, any ideas what would work best?