New Pitch Prop (?)

[pgottshall]

I got my 25hp Bass Tracker-17 tuned up a couple weeks ago, and it starts & runs great. The motor had a really-trashed 10x13 aluminum prop, and ran about 18mph. When the prop was new, 24mph was normal.

So, I ordered a new stainless 10x13 prop. Problem is, the boat would now go only 8mph (tough on Lake Shelbyville!), and the engine RPM's was about 1/2 what I'm used to.

I took it back in, and they told me I needed a different pitch, as the engine was lugging. They put on an 11-pitch, and said the boat went on plane & ran good.

I'm concerned that I just lost 20% of my speed, and confused why it ran good with the trashed Al prop.

Can anyone explain this to me?

[Jerry Blake]

Sounds like there's something wrong with the motor if you can't get the same RPMs with the same pitch prop. Might check to make sure the throttle is opening all the way - maybe the cable needs adjustment.

[zwalls]

I got my 25hp Bass Tracker-17 tuned up a couple weeks ago, and it starts & runs great. The motor had a really-trashed 10x13 aluminum prop, and ran about 18mph. When the prop was new, 24mph was normal.

So, I ordered a new stainless 10x13 prop. Problem is, the boat would now go only 8mph (tough on Lake Shelbyville!), and the engine RPM's was about 1/2 what I'm used to.

I took it back in, and they told me I needed a different pitch, as the engine was lugging. They put on an 11-pitch, and said the boat went on plane & ran good.

I'm concerned that I just lost 20% of my speed, and confused why it ran good with the trashed Al prop.

Can anyone explain this to me?

good question!!

if there is nothing wrong with the engine or fuel delivery system then here a formula to figure out what pitch you need!

divide the MAX RPM's the motor should be run at into the current rpm's and multiply that times the pitch you have and that will give you the pitch you need assuming there is nothing else wrong!!

hope this helps!!!

[pgottshall]

Thanks. I really don't think there's anything wrong with the motor, as it's running very smooth, & they checked the cable for me.

[Cane Pole]

on line pitch calculator. works good too. went thru the prop crap last year.

Propeller Calculator / Prop Calculator

[Barnacle Bill]

Its NOT the new prop if its the same size.

[CRAPPIEHUNTER68]

What prop did you end up with?

[Eeyore]

I believe if you switch to stainless, you need to drop a size in pitch.
Might be worth seeing if you can borrow a lower pitch prop to try out

[Barnacle Bill]

I believe if you switch to stainless, you need to drop a size in pitch.
Might be worth seeing if you can borrow a lower pitch prop to try out

Not on a motor that small. Besides 1" change of pitch = a change of 200 RPM. I strongly believe he is dropping a cylinder under load.

[Eeyore]

Not on a motor that small. Besides 1" change of pitch = a change of 200 RPM. I strongly believe he is dropping a cylinder under load.

I don't know enough about boats to say whether its the same for small engines, but I read that 1" pitch change = 200 RPM.
I'm not allowed a fishing boat, family has to be able to enjoy it as well, so I'll settle for my old 120 HP runabout really need to save some pennies and fit a trolling motor to it