another pitch question

[ajp1977]

Whats up all..my first post...what I have is a 50 hp Yamaha motor. It is a 2 stroke and the wot on the motor is 4500 to 5500. the motor sits on a 16' lowe big john...ave weight is probably around 750lbs. I currently have a 10 3/8 x 13 aluminum prop on it..My question is can I go to a 15 pitch prop to improve top end speed, or at that weight am I gonna be runnin to low of rpms? Couldn't find the correct chart on the Yamaha website or on this one. Thanks

 

[anzomcik]

Re: another pitch question

What is your current WOT and GPS speed

 

[ajp1977]

Re: another pitch question

Ran next to another boat with a speedometer and it said we were doing 30mph. We didn't have a gps and I still don't. Im not sure how to figure out the rpms at wot.

 

[Sea Rider]

Re: another pitch question

You must install a tach or a cheap induction tach, go for a wot spin on flat calm glassy no wind waters with you alone and lightly loaded boat. Check achieved wot rpm and see if inside stated min-max wot rpm numbers for that 50. Will know is under or over propped, can play with prop pitches to run at the nearest 5,500 rpm at wot.

Don't play with prop pitches blindly you can screw your beloved engine. Standard props, usually medium pitch delivered with engines will perform well, but must be tached if planning changing them, new pitch selction is not a guess issue.

Happy Boating

 

[jestor68]

Re: another pitch question

How about this.

Using the Merc prop selector, and the following weights, it recommended:

Boat/motor=700, people/gear=250, 12 gal gas total weight=1018 Recommended 17 pitch. Add another person(250) it dropped to 15 pitch.

Bear in mind this assumes a motor in like new running condition to handle the 17 pitch.

Since your motor is not new, I'd recommend not going more than 15 pitch.

Using a 9% slip factor, the 30 mph and your gear ratio comes out to about 5000 rpm.

 

[ajp1977]

Re: another pitch question

Thanks for the advice. I do like that merc prop selector, and I now realize it makes sense to install a tach as to seeing how important it is.! thanks again