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Author Topic:   Prop advice on a 15

Cliff posted 05-08-2001 12:15 PM ET (US)
I know this has been touched on before and I apologize in advance for asking this question again but I can't seem to find the previous posting where it was discussed.
I have a 15ft whaler with a 1999 50hp yamaha with a standard aluminum factory 15 pitch prop that came with the motor.
The boat is really slow to get on a plane with just me in the boat(220lbs) and the top end doesn't feel like it is where it needs to be......if I add 3 adults and myself...forget it. The tach was wired incorrectly last season so I won't have a reading till I wet the hull in the next couple of weeks.....and I have a handheld GPS which will help with nailing down top end speed(I assume 35-37mph should be about right).
Should I go to a 17 or 19 pitched prop or buy both depending on the use?
Some pointers again would be great. Thanks
The Whaler Guy posted 05-08-2001 12:20 PM ET (US)
go with larger diameter and less pitch
Cliff posted 05-08-2001 12:29 PM ET (US)
Thank you
lhg posted 05-08-2001 12:46 PM ET (US)
I'd also recommend you upgrade to Stainless Steel. It will be more efficient.
jimh posted 05-08-2001 11:50 PM ET (US)
You really need a working tachometer to evaluate the propeller situation.
My 15-Sport (1976) has a 50-HP Merc (also 1976). The engine comes from the era of rating horsepower at the powerhead, not at the prop, so perhaps by today's standards it would be a 45-HP. It is also 25 years old, so maybe it is more like a 40-HP!
It had a 16-inch pitch 3-blade aluminum prop on it. When I got the tachometer installed I found the engine was only running to barely 5200 RPM. I was aiming for more like 5500.
I bought a 15-inch Merc BLACK MAX prop, another 3-blade aluminum but with cupped blades. (Diameter 10.125 inch). This got the revs up a bit, but I still felt the prop was too tall, especially with two adults aboard and all the gear, and in rough water.
I bought a 14-inch Merc BLACK MAX, and this has been the best prop so far. I can rev to 5500 rpm when lightly loaded, and the boat seems too handle better in rough water with the smaller pitch prop.
Of course, the pitch that is right is also a function of the gear ratio of the lower unit. I think the Merc is 2:1. Check what the Yamaha is before taking comparisons from these results.
Cliff posted 05-09-2001 10:35 AM ET (US)
Thanks again all for your reply's.....
anymore anyone wants to add is welcome since I am keeping a file on this for reference
Cliff
lhg posted 05-09-2001 02:13 PM ET (US)
JimH - What you really want on your engine is one of the brand new Merc Trophy Sport SS 4-blades. These are the latest for the small size 30-60HP gearcase. These are now being recommend for the new 13 sport w/40hp engines. But probably won't see many, since it is not in the "package" price (aluminum prop is standard) and runs up the cost. So Dealers won't sell it. And I don't think this prop is interchangeable with other brands, except possibly Yamaha. It is not a vented or bass boat prop! (Nobody with a bass boat would be satisfied with 60 HP!)
Propellers are like computers, fish finders and GPS. It's impossible to keep up without spending a fortune!
jameso posted 05-11-2001 02:02 PM ET (US)
I have a 15 with a 50 HP OMC, 17 pitch prop 11 3/4 dia, engine is raised a couple of inches and set back 4 inches,,great hole shot, almost scary and will at WOT my gps indicated 36/38.

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Author	Topic: Prop advice on a 15
Cliff	posted 05-08-2001 12:15 PM ET (US) I know this has been touched on before and I apologize in advance for asking this question again but I can't seem to find the previous posting where it was discussed. I have a 15ft whaler with a 1999 50hp yamaha with a standard aluminum factory 15 pitch prop that came with the motor. The boat is really slow to get on a plane with just me in the boat(220lbs) and the top end doesn't feel like it is where it needs to be......if I add 3 adults and myself...forget it. The tach was wired incorrectly last season so I won't have a reading till I wet the hull in the next couple of weeks.....and I have a handheld GPS which will help with nailing down top end speed(I assume 35-37mph should be about right). Should I go to a 17 or 19 pitched prop or buy both depending on the use? Some pointers again would be great. Thanks
The Whaler Guy	posted 05-08-2001 12:20 PM ET (US) go with larger diameter and less pitch
Cliff	posted 05-08-2001 12:29 PM ET (US) Thank you
lhg	posted 05-08-2001 12:46 PM ET (US) I'd also recommend you upgrade to Stainless Steel. It will be more efficient.
jimh	posted 05-08-2001 11:50 PM ET (US) You really need a working tachometer to evaluate the propeller situation. My 15-Sport (1976) has a 50-HP Merc (also 1976). The engine comes from the era of rating horsepower at the powerhead, not at the prop, so perhaps by today's standards it would be a 45-HP. It is also 25 years old, so maybe it is more like a 40-HP! It had a 16-inch pitch 3-blade aluminum prop on it. When I got the tachometer installed I found the engine was only running to barely 5200 RPM. I was aiming for more like 5500. I bought a 15-inch Merc BLACK MAX prop, another 3-blade aluminum but with cupped blades. (Diameter 10.125 inch). This got the revs up a bit, but I still felt the prop was too tall, especially with two adults aboard and all the gear, and in rough water. I bought a 14-inch Merc BLACK MAX, and this has been the best prop so far. I can rev to 5500 rpm when lightly loaded, and the boat seems too handle better in rough water with the smaller pitch prop. Of course, the pitch that is right is also a function of the gear ratio of the lower unit. I think the Merc is 2:1. Check what the Yamaha is before taking comparisons from these results.
Cliff	posted 05-09-2001 10:35 AM ET (US) Thanks again all for your reply's..... anymore anyone wants to add is welcome since I am keeping a file on this for reference Cliff
lhg	posted 05-09-2001 02:13 PM ET (US) JimH - What you really want on your engine is one of the brand new Merc Trophy Sport SS 4-blades. These are the latest for the small size 30-60HP gearcase. These are now being recommend for the new 13 sport w/40hp engines. But probably won't see many, since it is not in the "package" price (aluminum prop is standard) and runs up the cost. So Dealers won't sell it. And I don't think this prop is interchangeable with other brands, except possibly Yamaha. It is not a vented or bass boat prop! (Nobody with a bass boat would be satisfied with 60 HP!) Propellers are like computers, fish finders and GPS. It's impossible to keep up without spending a fortune!
jameso	posted 05-11-2001 02:02 PM ET (US) I have a 15 with a 50 HP OMC, 17 pitch prop 11 3/4 dia, engine is raised a couple of inches and set back 4 inches,,great hole shot, almost scary and will at WOT my gps indicated 36/38.