Prop questions for Yamaha outboard

[Old Crow]

I have a 2003 Yamaha 75hp carbureted four stoke on a 16.5' Lund aluminum fishing boat.
Currently the boat runs 2.5mph at idle (which I would like to slow down) and at WOT runs around 56-5800rpm (range is 5-6000 with a peak at 5500 if I remember right)
I damaged the prop the other day to the point it may be cheaper to replace.
The damaged prop is a 13.5dia x 15; I noticed the new 75hp EFI models run a smaller diameter but more pitch (13.25 x 17)

What effects would there be if I was to use this prop?

 

[Dhadley]

Re: Prop questions for Yamaha outboard

In theory, going to more pitch will produce faster speeds at the same rpm. Therefore if your idle rpm remains the same in gear then you'll be faster than the 2.5 mph.

What's your idle rpm now?

 

[Old Crow]

Re: Prop questions for Yamaha outboard

I'm going by memory, around 700

How does the smaller diameter effect things?
I was wondering; because of the smaller diameter and lower rpm's, mph maybe slower
and on the top end because of the increased pitch and high rpm's would load the motor more (increase speed/reduce rpm)

 

[junior1113]

Re: Prop questions for Yamaha outboard

most all props decrease diameter when increasing pitch. a 1/4" is nothing 1/8" a blade. you will lose about 350 rpms if you go with a 17. i think your numbers are good now with a 15.

i'd look for a good 4 blade 15 pitch. youll lose 150 rpms but performance will be way better. as far as idle speed if your @700 rpms. there isnt much can be done. tilt motor up when trying to idle slow.

depending how bad, effect of using a damaged prop could be expensive. it could couse a vibration which is sent through propshaft, and gears and seals could be affected $$$$$$$$

 

[Old Crow]

Re: Prop questions for Yamaha outboard

It was an Yamaha prop I damaged.

I have a Hustler as a back up but don't like it as much.
It's not as good out the hole. Takes longer to get on plane

Who makes a good 4 blade aluminum prop?

I'm thinking I'll just have my damaged prop repaired and balanced, should be around $80-90