Help with prop sizing on my new purchase

[Rswilliams13]

Hey guys, looking for some help choosing a new prop. I live at lake tahoe which is 6200' elevation, and just purchased an immaculate condition 1987 chris craft 210 Limited bowrider (scorpion hull) with a mercruiser 5.7L 260 and alpha one gen 1 drive. The boat was ordered to the marina here new in 1987, and the previous owner i got it from spared no expense and had the boat kept at and maintained by the marina/dealer since new. The boat runs like and looks new despite being 31 years old. I am excited on the new purchase, and installing a few upgrades. Here's the current prop specs/performance info:

14.5" x 19P 3 blade Mercury aluminum prop in decent shape
WOT 4200rpm (according to stock tach)
Top Speed at WOT 44-45MPH (GPS speedo app on phone) with just me onboard

So here's the question, I recently picked up a mint condition mercury vengeance 14x19P stainless 3 blade prop at a garage sale for $40 a few days ago figuring if it wasn't the right fit for my boat, i got a steal, and could resell it and invest in the right prop. So that's my plan. I figure I want to be closer to 4400-4500rpm WOT. The move to stainless and the 1/2" drop in diameter might get me there, but I have not tried the new prop yet. I went to install it, but it looks like i need a different trust washer or spacer to get it installed correctly. I am not sure it will give me what I am looking for either.

The boat will primarily be used for cruising around the lake to various beaches, and lots of water skiing and wake skating. Top speed is not a major concern, but with the cost of gas up here and lots of watersports, holeshot and cruise mpg are top priority. I am thinking a stainless 4 blade prop is the way to go. I am also planning on installing a set of smart tabs.

Not looking to spend a ton, so I have been looking at the solas HR titan 4 blade props. They are 14 1/8" diameter. the question is should I go 18P or 19P? Not sure how much rpm will be gained by the 3/8" lower diameter and move to stainless, then lost by the additional blade. Please let me know if you have any suggestions, or if I am on the right track. Thanks guys - Ryan

 

[Maclin]

The diameter will not be much of a factor in gaining or reducing RPM, especially when going from Aluminum to Stainless.

Conventional wisdom is that, pitch for pitch and same number of blades, going to SS over aluminum will drop RPM's as the SS will not flex as much and slippage is lower, engine load is higher.

In your case the RPM's would probably go down and the top speed be about the same.

But get what you need to install the Vengeance correctly and just try it, see what it does. That should be a cheap enough way to gain some insight into prop wizardry.

 

[Maclin]

Was thinking about recommendations, and Reread your goals for the boat...

At that elevation your engine seems to be straining a bit to get up to mid operating range. With your mentions of watersport and holeshot as being important, I think you need to go down to 17p. Cruising MPG is kind of at odds with the watersports but anytime you get the engine up into the higher end of the operating range things improve, even MPG.

Some just capitulate and get 2 props, one for towing and one for cruising. For towing in your case, probably a 4 blade 16p. You pretty much have a cruising prop now, but going down to a 17p would give you better holeshot and get to a higher RPM with probably the same speed. A lot of your difficulty meeting those goals is that elevation. I imagine the best compromise for just one prop would end up being a 17p Stainless 3blade.

 

[jimmbo]

Run the Vengeance and see what it yields, rpm wise. I believe your engines WOT rpm range is 4200 - 4600