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Author Topic:   Prop size for 15 whaler

elvis posted 10-21-2013 08:16 PM ET (US)
Hi all...well, I just bought a rebuilt evinrude 48 2 stroke for my 15 whaler...I had been looking at a 70, but that deal fell through.
I hope to have it mounted by this weekend, and was wondering what kind of prop I should consider for the future.?
The current prop on this 48 is a 12-1/2 by 13. Is that pretty good for speed...top end, power...torque?
Is there a stainless or other size aluminum one I could get that would give the best all around performance? Just curious on the expert's suggestions.
Thanks!
dgoodhue posted 10-22-2013 09:06 AM ET (US)
Do you know what the gear ratio, operating rpm range of the motor is? I think those don't have power trim/tilt.
jimh posted 10-22-2013 01:48 PM ET (US)

quote:
"Is [a 12-1/2 by 13 propeller on a rebuilt Evinrude 48-HP outboard engine] pretty good for speed...[sic] top end, power...[sic]torque?
Torque comes from the engine and creates the ability to do work. (Horse)power is a measurement of the rate at which work is done. These are both characteristics of the engine, not the propeller. If your engine can accelerate its engine speed into the recommended full-throttle range, it will produce 48-HP.
Top end and speed are the same thing. Let us discuss speed of a boat with the cited propeller.
Speed of a boat is a function of propeller pitch and the propeller shaft rotation speed. It will be typical that a 13-pitch propeller can produce about 32-MPH of boat speed, assuming an engine speed of about 5,500-RPM, a gear ratio of 2:1, and a SLIP of about 5-percent.
To make boats go faster requires more power. More power allows for a propeller of greater pitch to be turned.
jimh posted 10-22-2013 03:21 PM ET (US)
In the REFERENCE article I wrote about the classic Boston Whaler 15-foot hull there is information from Boston Whaler about the speed potential of the hull with various amounts of engine horsepower. See
http://continuouswave.com/whaler/reference/15/
There is a suggestion that 50-HP will produce about 34-MPH at best. We can extrapolate to 48-HP and get around 32 to 33-MPH. This suggests that a propeller with around 13-pitch ought to be appropriate.
elvis posted 10-22-2013 06:33 PM ET (US)
Excellent and helpful feedback, many thanks. Sounds like this prop will do just fine. I'll run it in a couple weeks and let you know what it does.
Again, thanks much!
P.S. I found a SS prop...same size and pitch, and wondered if this would change the performance much from the aluminum. Just curious.
Tom W Clark posted 10-22-2013 10:00 PM ET (US)
You don't say what year your Evinrude 48 SPL is but I think they all use the same gearcase. The gear ratio is 2.42:1 and the redline of the motor is 5500 RPM. There is no way the a 13" pitch propeller will be suitable. If using an OMC/BRP prop you would want a 17" pitch.
You also do not ell us if the motor has power trim or not. The 48 SPL did not come with power trim and tilt but it was available from OMC as an accessory that could be retrofitted.
A good stainless steel propeller would be very beneficial to you and there are some very good aftermarket props available for that motor. Precision Propeller Industries, Inc. (PPI) offers two really good props that I think might work well. The Stiletto Triad/Turbo Hot Shot is one, the Stiletto Star/Turbo Pontoon 1 is the other.
The Triad/Hot Shot is offered in a special large diameter version designed specifically for the OMC/BRP 3.5" gearcase motors. The Star/Pontoon 1 model has alar diameter and very large blade area so it works very well for acceleration and stern lift, a benefit that may well be appreciated on a skiff without the benefit of power trim and tilt.
For either model of propeller, you would want the 15" pitch version.
If the motor is mounted two holes up on the transom and one of these props is used, I think 35-36 MPH is possible.
jimh posted 10-23-2013 09:18 AM ET (US)
On my Mercury 500 on my SPORT 15 the propeller was a 13-pitch and hit about 34-MPH. That old Mercury gear case must have been around 2:1 ratio.
It sounds like the OMC with its 2.42:1 gear ratio is designed to swing larger propellers, a "bigfoot" model of a sort.
elvis posted 10-23-2013 07:54 PM ET (US)
Hi Tom, Jim...
It's a 1991 and doesn't have power trim or tilt...all manual.
I hope to get it mounted and try it out soon...possibly this weekend but most likely next weekend. I'll let you know what I find out with this aluminum prop. Many thanks!
dgoodhue posted 10-25-2013 07:06 AM ET (US)
Your aluminum prop is two sizes too small. You can use it temporarily but watch your tach rpm; I wouldn't do any wot runs.
When you mount your motor don't mount it with blind holes. I would mount it 2 holes up.
Tom W Clark posted 10-25-2013 12:50 PM ET (US)
I agree with Doug. Do not mount the motor all the way down on the transom.
Tom W Clark posted 10-25-2013 12:52 PM ET (US)
I agree with Dave too ;-)
elvis posted 10-26-2013 04:43 AM ET (US)
Ok, 2 holes up, will do. Prob mount it today, I repainted motor yesterday, looks good...temperature outsidelower than needed, slow dry time, may have to wait extra day or so for paint to harden sufficiently.
So, if I understand the info right, a 13" pitch is too low,,,should maybe consider a 12-1/2 x 17" instead?
A
The motor was originally on a 22' pontoon boat, probably why the power. Prop vs speed prop.
Tom W Clark posted 10-26-2013 11:06 AM ET (US)
I am not sure you are quite getting it. Propellers are not generic pieces of hardware simply described by pitch and diameter. The size depends on exactly what model of propeller you are considering.
elvis posted 10-26-2013 11:37 AM ET (US)
My apologies, I thought my question was clear.
What size OMC prop have you successfully used (good all around performance) on a 1985 Whaler 15, with 1991 48 or 50 HP Johnson or Evinrude?
If not OMC prop, what Viper, Stiletto, etc have you used in a similar application?

dgoodhue posted 10-26-2013 01:11 PM ET (US)
I use a stiletto advantage on 89 15' whaler with a 70hp evinrude. I use a jackplate but its in the equivalent 3 hole version. I have power trim. My boat does 43-44 without trim and 47-48 with trim. The stilleto has a more lift than the cheap prop my boat came with and the OMC SST's I tried. My stiletto advantage is similar to the Triad by its fits your gear case. Since you don't have power trim Tom suggest a Stilletto star/pontoon (different name same prop) lfor additional lift. It sound like a great idea. The star can be bought in 12 x 15P for you application. I think they are a little over $200 new. If your looking to save a little bit of money you can buy used SST on eBay for $100. You would want 17P version for your motor. (Its probably around a 12" diameter).
Tom has tons experience with props and different whaler models. I would take his advice.
elvis posted 10-26-2013 06:34 PM ET (US)
Ok, sounds good. A 12x17. I'll start looking for one. Thanks!
Peter posted 10-29-2013 12:55 PM ET (US)
I had a 1988 Johnson 48 SPL on a 15 Super Sport. As I recall, the propeller was an 11 3/4 x 17 aluminum. The 48 pushed the boat to 36-37 MPH (GPS measured in multiple directions) with a single person on board. The motor was mounted all the way down on the transom using the blind holes and had no power trim or tilt. Other than a lousy idle, that was a pretty good motor for the 15 foot hull.
elvis posted 10-29-2013 05:57 PM ET (US)
Hi Peter, appreciate the helpful info. I mounted the motor last weekend, waiting on new fuel filter now and steering bar...link ... I forgot to order. One ahead of time, one is on the way now. Hope to assemble these 2 things Saturday and run it with the small prop...careful not to over rev.
Haven't gotten a 12x17 prop yet but watching a few on eBay, looks like $100 or so will get a new alum one.
36-37 mph is plenty good for this old guy in a 15.
Thanks again for the reply, I'm impressed by the wealth of info and helpful, courteous folks here. A+++
elvis posted 11-10-2013 03:24 PM ET (US)
Hi all...well, finally got the 15 on the water for a test run. I did not run it with the aluminum 12-1/2 x 13 pontoon boat prop, as some of you indicated that RPMs might be too high.
That said, I went shopping, and happened across a 12-1/4 x 15 stainless. The price was right, so I bought it and put it on. I had planned to get the 17 pitch, but this stainless 15 was so cheap in dollars I really had to give it a try.
I don't have a tach, but it sounded like RPMs were normal (or similar) at WOT to other whalers I've run, and top speed with 285 pounds of people, a battery, and 5 gallons of fuel in it was 32 mph.
Hole shot was excellent, too, and I was am very pleased with the acceleration from stop and the overall outcome.
I just bought the freshwater only motor, and the previous pontoon boat owner said it had a recent rebuild, and after running it I believe him. Steering was tight and smooth and overall it's a darn good setup, as the 15 rides great and is very fun....possibly my most favorite whaler to date.
Thanks for all your feedback and advice. Mom going to post another topic related to power trim.

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Author	Topic: Prop size for 15 whaler
elvis	posted 10-21-2013 08:16 PM ET (US) Hi all...well, I just bought a rebuilt evinrude 48 2 stroke for my 15 whaler...I had been looking at a 70, but that deal fell through. I hope to have it mounted by this weekend, and was wondering what kind of prop I should consider for the future.? The current prop on this 48 is a 12-1/2 by 13. Is that pretty good for speed...top end, power...torque? Is there a stainless or other size aluminum one I could get that would give the best all around performance? Just curious on the expert's suggestions. Thanks!
dgoodhue	posted 10-22-2013 09:06 AM ET (US) Do you know what the gear ratio, operating rpm range of the motor is? I think those don't have power trim/tilt.
jimh	posted 10-22-2013 01:48 PM ET (US) quote: "Is [a 12-1/2 by 13 propeller on a rebuilt Evinrude 48-HP outboard engine] pretty good for speed...[sic] top end, power...[sic]torque? Torque comes from the engine and creates the ability to do work. (Horse)power is a measurement of the rate at which work is done. These are both characteristics of the engine, not the propeller. If your engine can accelerate its engine speed into the recommended full-throttle range, it will produce 48-HP. Top end and speed are the same thing. Let us discuss speed of a boat with the cited propeller. Speed of a boat is a function of propeller pitch and the propeller shaft rotation speed. It will be typical that a 13-pitch propeller can produce about 32-MPH of boat speed, assuming an engine speed of about 5,500-RPM, a gear ratio of 2:1, and a SLIP of about 5-percent. To make boats go faster requires more power. More power allows for a propeller of greater pitch to be turned.
jimh	posted 10-22-2013 03:21 PM ET (US) In the REFERENCE article I wrote about the classic Boston Whaler 15-foot hull there is information from Boston Whaler about the speed potential of the hull with various amounts of engine horsepower. See http://continuouswave.com/whaler/reference/15/ There is a suggestion that 50-HP will produce about 34-MPH at best. We can extrapolate to 48-HP and get around 32 to 33-MPH. This suggests that a propeller with around 13-pitch ought to be appropriate.
elvis	posted 10-22-2013 06:33 PM ET (US) Excellent and helpful feedback, many thanks. Sounds like this prop will do just fine. I'll run it in a couple weeks and let you know what it does. Again, thanks much! P.S. I found a SS prop...same size and pitch, and wondered if this would change the performance much from the aluminum. Just curious.
Tom W Clark	posted 10-22-2013 10:00 PM ET (US) You don't say what year your Evinrude 48 SPL is but I think they all use the same gearcase. The gear ratio is 2.42:1 and the redline of the motor is 5500 RPM. There is no way the a 13" pitch propeller will be suitable. If using an OMC/BRP prop you would want a 17" pitch. You also do not ell us if the motor has power trim or not. The 48 SPL did not come with power trim and tilt but it was available from OMC as an accessory that could be retrofitted. A good stainless steel propeller would be very beneficial to you and there are some very good aftermarket props available for that motor. Precision Propeller Industries, Inc. (PPI) offers two really good props that I think might work well. The Stiletto Triad/Turbo Hot Shot is one, the Stiletto Star/Turbo Pontoon 1 is the other. The Triad/Hot Shot is offered in a special large diameter version designed specifically for the OMC/BRP 3.5" gearcase motors. The Star/Pontoon 1 model has alar diameter and very large blade area so it works very well for acceleration and stern lift, a benefit that may well be appreciated on a skiff without the benefit of power trim and tilt. For either model of propeller, you would want the 15" pitch version. If the motor is mounted two holes up on the transom and one of these props is used, I think 35-36 MPH is possible.
jimh	posted 10-23-2013 09:18 AM ET (US) On my Mercury 500 on my SPORT 15 the propeller was a 13-pitch and hit about 34-MPH. That old Mercury gear case must have been around 2:1 ratio. It sounds like the OMC with its 2.42:1 gear ratio is designed to swing larger propellers, a "bigfoot" model of a sort.
elvis	posted 10-23-2013 07:54 PM ET (US) Hi Tom, Jim... It's a 1991 and doesn't have power trim or tilt...all manual. I hope to get it mounted and try it out soon...possibly this weekend but most likely next weekend. I'll let you know what I find out with this aluminum prop. Many thanks!
dgoodhue	posted 10-25-2013 07:06 AM ET (US) Your aluminum prop is two sizes too small. You can use it temporarily but watch your tach rpm; I wouldn't do any wot runs. When you mount your motor don't mount it with blind holes. I would mount it 2 holes up.
Tom W Clark	posted 10-25-2013 12:50 PM ET (US) I agree with Doug. Do not mount the motor all the way down on the transom.
Tom W Clark	posted 10-25-2013 12:52 PM ET (US) I agree with Dave too ;-)
elvis	posted 10-26-2013 04:43 AM ET (US) Ok, 2 holes up, will do. Prob mount it today, I repainted motor yesterday, looks good...temperature outsidelower than needed, slow dry time, may have to wait extra day or so for paint to harden sufficiently. So, if I understand the info right, a 13" pitch is too low,,,should maybe consider a 12-1/2 x 17" instead? A The motor was originally on a 22' pontoon boat, probably why the power. Prop vs speed prop.
Tom W Clark	posted 10-26-2013 11:06 AM ET (US) I am not sure you are quite getting it. Propellers are not generic pieces of hardware simply described by pitch and diameter. The size depends on exactly what model of propeller you are considering.
elvis	posted 10-26-2013 11:37 AM ET (US) My apologies, I thought my question was clear. What size OMC prop have you successfully used (good all around performance) on a 1985 Whaler 15, with 1991 48 or 50 HP Johnson or Evinrude? If not OMC prop, what Viper, Stiletto, etc have you used in a similar application?
dgoodhue	posted 10-26-2013 01:11 PM ET (US) I use a stiletto advantage on 89 15' whaler with a 70hp evinrude. I use a jackplate but its in the equivalent 3 hole version. I have power trim. My boat does 43-44 without trim and 47-48 with trim. The stilleto has a more lift than the cheap prop my boat came with and the OMC SST's I tried. My stiletto advantage is similar to the Triad by its fits your gear case. Since you don't have power trim Tom suggest a Stilletto star/pontoon (different name same prop) lfor additional lift. It sound like a great idea. The star can be bought in 12 x 15P for you application. I think they are a little over $200 new. If your looking to save a little bit of money you can buy used SST on eBay for $100. You would want 17P version for your motor. (Its probably around a 12" diameter). Tom has tons experience with props and different whaler models. I would take his advice.
elvis	posted 10-26-2013 06:34 PM ET (US) Ok, sounds good. A 12x17. I'll start looking for one. Thanks!
Peter	posted 10-29-2013 12:55 PM ET (US) I had a 1988 Johnson 48 SPL on a 15 Super Sport. As I recall, the propeller was an 11 3/4 x 17 aluminum. The 48 pushed the boat to 36-37 MPH (GPS measured in multiple directions) with a single person on board. The motor was mounted all the way down on the transom using the blind holes and had no power trim or tilt. Other than a lousy idle, that was a pretty good motor for the 15 foot hull.
elvis	posted 10-29-2013 05:57 PM ET (US) Hi Peter, appreciate the helpful info. I mounted the motor last weekend, waiting on new fuel filter now and steering bar...link ... I forgot to order. One ahead of time, one is on the way now. Hope to assemble these 2 things Saturday and run it with the small prop...careful not to over rev. Haven't gotten a 12x17 prop yet but watching a few on eBay, looks like $100 or so will get a new alum one. 36-37 mph is plenty good for this old guy in a 15. Thanks again for the reply, I'm impressed by the wealth of info and helpful, courteous folks here. A+++
elvis	posted 11-10-2013 03:24 PM ET (US) Hi all...well, finally got the 15 on the water for a test run. I did not run it with the aluminum 12-1/2 x 13 pontoon boat prop, as some of you indicated that RPMs might be too high. That said, I went shopping, and happened across a 12-1/4 x 15 stainless. The price was right, so I bought it and put it on. I had planned to get the 17 pitch, but this stainless 15 was so cheap in dollars I really had to give it a try. I don't have a tach, but it sounded like RPMs were normal (or similar) at WOT to other whalers I've run, and top speed with 285 pounds of people, a battery, and 5 gallons of fuel in it was 32 mph. Hole shot was excellent, too, and I was am very pleased with the acceleration from stop and the overall outcome. I just bought the freshwater only motor, and the previous pontoon boat owner said it had a recent rebuild, and after running it I believe him. Steering was tight and smooth and overall it's a darn good setup, as the 15 rides great and is very fun....possibly my most favorite whaler to date. Thanks for all your feedback and advice. Mom going to post another topic related to power trim.