More prop or lower motor?

[leckbass]

I have an 18 ft aluminum boat with a 125 Mercury, I can't seem to get much speed out of this boat and I keep on going to bigger and bigger propellers. I've tried 17 18 19 and 21 in pitch propellers and the motor spins them too fast. That being said my prop slip number is close to 30%

How do you know if you should just go for a bigger propeller or lower the motor deeper into the water?

Thanks for your help

[morrcat33]

what speed does your boat plane out at?

[Bassmeister]

Lot's more info needed here.....motor height..engine rpms at wot, rpms getting on plane, just to start. Here is how to get your motor height ....Borrowed from the Champion Boats Forum.

[leckbass]

Lot's more info needed here.....motor height..engine rpms at wot, rpms getting on plane, just to start.

I know, I included all that information on the setup page a while back, but I'm not looking for complex setup Solutions I'm just looking for an answer of do I need to lower my motor or do I need to buy a bigger prop or how do I make that determination?

[leckbass]

what speed does your boat plane out at?

I could run on plane as low as 22 miles an hour

[RyanJ]

Do you have a pad hull or flat boat type hull?

[BassinPaPaw]

What kind of Rpm’s are you turning with that 21 prop?

[leckbass]

Do you have a pad hull or flat boat type hull?

It's not a pad, it's mainly a flat bottom some slight deadrise in the back but not much at all

[leckbass]

What kind of Rpm’s are you turning with that 21 prop?

I hit the max RPMs of 5250 and I still have throttle to go

[Jim1752]

Check tach accuracy Jim sheetz

[bassfisher444]

This will be good, been having the same problem with mine to some extent, can't get a prop that will hook up good at high speeds, I can turn a 24" pitch laser 2 prop to 5800 but only 45mph gps, which comes out to 20" prop slip, a 22" pitch laser 2 does the same thing, a 22" Powertech PTR3 runs 1-2 mph faster but still has the same issue, I have a manual jack plat but I am going to switch to an Atlas micro jacker so I can make fine adjustments while running to get it dialed in better.

[leckbass]

Check tach accuracy Jim sheetz

I checked it with a portable tachometer and everything matches up

[ksubasser24]

5250 rpm is to low. Should be turning around 5800.

[leckbass]

5250 rpm is to low. Should be turning around 5800.

Max RPM range is 4750-5250

[leckbass]

5250 rpm is to low. Should be turning around 5800.

Screenshot_20230328_214504_Drive.jpg

[cmclairday2]

I know, I included all that information on the setup page a while back, but I'm not looking for complex setup Solutions I'm just looking for an answer of do I need to lower my motor or do I need to buy a bigger prop or how do I make that determination?

LOL You're wanting a yes or no answer to an essay question.
The info you posted in the setups forum doesn't even apply anymore because it was a different engine. About all anyone could tell you with the information you've given is try it and see what happens.

[leckbass]

LOL You're wanting a yes or no answer to an essay question.
The info you posted in the setups forum doesn't even apply anymore because it was a different engine. About all anyone could tell you with the information you've given is try it and see what happens.

I will take all the measurements and repost the information, I was hoping not to muddy up the answer with all that additional information

[unknown angler]

Do you have anything disturbing water flow to the prop, like a transducer ?

[novakevlar]

If the prop is losing bite try a larger diameter prop. Can't just focus on pitch. Also certain props are designed to lift the stern, lift the bow, have more cup or rake etc etc depending on the hull type, wetted surface, weight, and desired performance. It's not a black and white answer so you need to provide more details to the group if you want a well-thought out answer. GIGO

[leckbass]

Do you have anything disturbing water flow to the prop, like a transducer ?

There is a transducer, but when I'm on plane it's barely touching the water and it does not leave any spray