therobzilla
Active member
Johnny,
You posted this statement in another post, I wanted to ask a question regarding this statement:
A 4 blade will not increase speed, it will take away from top end. Since it is a 76' model and does have the 2.41:1 gear case and RPM range 5500-7000k I would recommend a 3 blade 10 pitch prop if your putting it on a 12' tin. This would probably be a safe starting point to get some info. From there you can adjust in pitch to get optimum performance. But you have to start somewhere and cannot expect to get the perfect prop on the first try with out any data to go by. All we can do is give you an educated guess from our experiences.
If you can turn a 10 pitch at 6250-6500 rpm you should see numbers around 20-22 mph assuming a 15%-18% slip
I have this almost exact same condition, Johnson 1986 15 HP, on a 12' Gamefisher, this weekend I tested it and was almost exactly what you posted, 6450 WOT, 21/22 MPH 10 pitch 9.5" diam alum prop. Is this a good all around sweet spot for this motor and boat? Second question is a 17/18 % slip factor in a decent range, or is there room for improvement?
Have another post going with many more of the details here : https://www.tinboats.net/forum/viewtopic.php?f=4&t=31764&start=15
Thanks,
Rob
You posted this statement in another post, I wanted to ask a question regarding this statement:
A 4 blade will not increase speed, it will take away from top end. Since it is a 76' model and does have the 2.41:1 gear case and RPM range 5500-7000k I would recommend a 3 blade 10 pitch prop if your putting it on a 12' tin. This would probably be a safe starting point to get some info. From there you can adjust in pitch to get optimum performance. But you have to start somewhere and cannot expect to get the perfect prop on the first try with out any data to go by. All we can do is give you an educated guess from our experiences.
If you can turn a 10 pitch at 6250-6500 rpm you should see numbers around 20-22 mph assuming a 15%-18% slip
I have this almost exact same condition, Johnson 1986 15 HP, on a 12' Gamefisher, this weekend I tested it and was almost exactly what you posted, 6450 WOT, 21/22 MPH 10 pitch 9.5" diam alum prop. Is this a good all around sweet spot for this motor and boat? Second question is a 17/18 % slip factor in a decent range, or is there room for improvement?
Have another post going with many more of the details here : https://www.tinboats.net/forum/viewtopic.php?f=4&t=31764&start=15
Thanks,
Rob
