The Mariah Owners Club - Moving to a 17p -- what diameter would be a good place to start?

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Moving to a 17p -- what diameter would be a good place to start?

Hi All,

I'm currently running a 14.5" x 19p on the back of my 19' Mariah 1900s. It's a 4.3L Mercruiser, 195 horse.

At WOT, on very smooth water, I'm currently getting about 4500 RPM, so it seems a tiny bit overpropped. But mainly, I'd like to get a little more power on the low end for tubing, faster planing, etc. I don't really care about top speed.

So, I'm looking at a 17p prop. Should I keep the diameter at 14.5", or should that change also?

Re: Moving to a 17p -- what diameter would be a good place to start?

Hi abillmann,

Per the manual, your WOT RPM should be between 4400 - 4800 RPM so you're right in the ball park.

Since you're running at 4500RPM now, a 17P (keep the same diameter) would bring you right up to around 4800-4900RPMs at WOT. So you will loose a little top end, but the holeshot will be a little better!

WetWilly

Re: Moving to a 17p -- what diameter would be a good place to start?

In looking at props from Mercury and Michigan Wheel--and based on both of their recommendations--a 15" x 17p seems to be the choice. Does that extra half-inch of diameter matter much? I'm assuming that'll simply help the low end a tiny bit, and hurt the high end a tiny bit. Is that correct? Or should I really be diligent in getting 14.5" for the diameter?

For reference, the boat is a 19-foot 195HP 4.3L AlphaOne.

Re: Moving to a 17p -- what diameter would be a good place to start?

Hi abillmann,

Increasing either pitch or diameter will create more load on the motor and in your case, will reduce your holeshot, not improve it.

I used the Mercury prop selector based on your 1900's weight and the 4.3L, and it recommended a 18P (and diameters between 14.2 -15.5) for aluminum props and 17P (and diameters between 13.5 - 14.625) for SS props. I assume the range in diameter is due to differences in gear ratios, hull design and boat weight. Prop manufactures attempt to keep you within the recommended WOT as listed by the power system manufacture.

I still recommend that you just drop the pitch to 17P and leave everything else as it is if you're staying with an aluminum prop. I did the same thing, dropping from a 19P to a 17Pp aluminum on my 18.5' SeaRay 140HP 3.0L and the holeshot improved but the top end suffered as I lost about 5mph and the RPMs were over the recommended max at WOT so I just made sure to keep the throttle back just a little when running flat out.

Good luck,
WetWilly