how do you explain this?

[ryanr623]

1991 regal 17'
4.3 merc 2bb

Old prop - 14x19p maybe a few nicks, 45 mph @ 5000rpm WOT

New prop - 14x21p 45mph @ 5100rpm WOT

Unless both my tach and Speedo both speed being accurate I am lost. 21p gets on plane immediately just like the 19p

 

[steelespike]

Re: how do you explain this?

i do suspect some problem with tach or speedo or both. If we had a gps speed It would help a little,
with an accurate speed.
Some cells have a gps app
also would help if you can find your gear ratio on the out drive.

 

[Texasmark]

Re: how do you explain this?

Same prop material and brand name.....like alum Solas for example?

 

[r.j.dawg]

Re: how do you explain this?

If your tach is accurate, you need to get your WOT down. Should be 4400 - 4800.

 

[QC]

Re: how do you explain this?

Maybe the 21 is really a 19 or visa versa? Does seem odd even with Tach and speedo issues. When those things are off, they are usually off the same as opposed to variable. I wouldn't discount any possibility too much though. need to verify everything, including the prop itself. Not sure how you'd do that. Is it marked as a 21? Or boxed as a 21? Hopefully both.

 

[jestor68]

Re: how do you explain this?

They're both the same pitch?

 

[jimmbo]

Re: how do you explain this?

Diameter, rake, cupping, number of blades, and blade area could all be factors here. An uncupped 21 inch will be similar to a cupped 19 inch. The 19 could have a solid grip on the water while the 21 is blowing out.

 

[Texasmark]

Re: how do you explain this?

They're both the same pitch.

Does sorta look that way.

 

[bnicov]

Re: how do you explain this?

The 19p prop was probably knocked a bit out of whack since you mentioned it has some nicks in it. The way to find out is have a prop guy put it on the die bench and check the pitch of the blades.

 

[ryanr623]

Re: how do you explain this?

one was definitely 19 and one was 21. I ran serial #s just to be sure. both were Michigan match

 

[r.j.dawg]

Re: how do you explain this?

I've got 14 x 20 four blade aluminum's on my Alpha's and my WOT is 4500-4600 RPM @ ~45mph. Granted, my boat is 10 ft longer and around 8000lbs, and I have twin engines, but I have never had any performance problems.The PO got rid of the 13.75 x 21 stainless 3 blade props and it made all the difference in the world. I'm thinking that one of your props has a spun hub maybe??????