89 Cobra w/ 50HP Force: Trim & Prop Question

[mikehayes]

I recently changed out my Prop from a 11 14/ pitch to a 10 and 38/ pitch. The reason I made the switch was because my boat was acting as if the hub was spun and I changed out due to suggestions from your website. However, I do not have an RPM gauge to check what I am running? The only thing I know is I am having a better time getting out of the hole and planing, but I lost speed due to the drop in pitch. I was running about 30 MPH when I was using the older prop when it worked now I am lucky to get 25 mph. I indicated to my boat dealer that I wanted more power and he sold me the lower pitch prop. I am not sure I gained power but I am disappointed in the loss of speed. Can you tell me the recommended pitch on the prop for my motor?

Another issue is I do not have power trim on my boat, I have 4 hole settings to adjust the trim of my motor with a bar that slides into the holes. This is a pain in the rear but I am dealing with it as the power trim kit is $$$. Can you tell me when I should use which holes? For example, when I have my wife and two kids on the boat it has a difficult time coming up to plane, are the bottom or top holes better when loaded and what is best when it is just one or two people.

Thanks,
Mike

 

[roscoe]

Re: 89 Cobra w/ 50HP Force: Trim & Prop Question

Can you tell me the recommended pitch on the prop for my motor?

That is determined by the rpm you can reach at wide open throttle (wot).


Having trouble deciphering your prop sizes.

You need 2 numbers, the diameter, and the pitch.
Such as 11 diameter x 13 pitch
Or 10.5 x 11 p

the 11 14/ and the 10 38/ numbers don't make sense.
Could you double check the numbers?

Anyway, a a prop with a lower pitch, will give you a better hole-shot, and shouldn't effect the top speed TOO much, unless you have gone too far.

If you are having trouble planing the boat when the family gets in, you do not want to use a higher pitch prop.


The trim settings are a bit of trial and error for each boat/motor/load situation.

Generally, the bottom holes will get you on plane easier.

 

[JB]

Re: 89 Cobra w/ 50HP Force: Trim & Prop Question

Post this question in the Prop Forum.