Propping a 140 Merc on Checkmate

[sludgeguy68]

Finally got the trim working properly late in the season and I'm trying to find the correct prop size. I also tried to learn how to drive it properly in that short time, so I probably don't have everything optimally set up, but it would be great to get the jack plate at an optimal height and try another prop for next year

At WOT I'm at around 4800 with the prop having a good "bite" and little/no rooster tail. I can keep trimming up to get my recommended RPM (5800), but I can hear a clear difference - like a propeller plane noise, I'm assuming that's the prop ventilating?

I can top out at around 48 MPH on the GPS

1985 Checkmate bow rider, 18'
1978 Mercury 1400 140hp inline six
CMC jack plate
19 pitch prop - not sure how to interpret the other numbers on it: 155 2510
carrying very minimal gear (1 battery), boat should be light. doesn't seem waterlogged at all

Is there a better prop for better top speed/gas mileage?
Thank you

 

[jestor68]

Re: Propping a 140 Merc on Checkmate

It sounds like you are trimming out too far and ventilating the prop badly if you get a thousand more rpm with no real increase in speed.

At what rpm are you getting 48 mph?

What sort of prop(al or SS) are you using?

 

[dan02gt]

Re: Propping a 140 Merc on Checkmate

How much set back do you have with your jack plate?
What is your engine hight measured in how far the center of the prop shaft is below the pad?
Any idea how much the hull weights?

Without knowing more I would have to guess that a Tempest Plus 21p would be a good start set 4" below the pad. If you have the small gear case you could run a Laser 2 or Trophy Plus with the small hub.

 

[Bamaman1]

Re: Propping a 140 Merc on Checkmate

We used to run a 1979 17' Checkmate with a Merc 115 hp with a 19 and 21 pitch props--depending on what we were going to be doing that day. We were getting over 48 mph on the smaller motor without jack plate.

But the jack plate throws another dimension in that the engine needs to be at the exact height for the purpose intended. Try to use a GPS speedometer, not the one that came on the boat.

You might want to see if there is a prop shop in your area. If you buy from them, their expertise is free. Or, try to find an experienced boat dealership that has done plenty of high performance setups.

I'm in agreement with dan02gt above in what props to start with.

This is something that has to be done at the lake. Some prop shops will let you take 3 props for demo, and buy the best for your purpose. The tach and speedometer speak to which prop is best.