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1976 Sport 15
The boat weight with accessories + me = 900-1200 lbs

2001 Mercury 40 hp 2 stroke
gear reduction 2:1, 13x26
5000-5500 RPM @ WOT
Best top speed ever: 31.7 mph
Average top speed (@WOT): 27mph

The prop on there now is an aluminum stock prop. I am not sure about the pitch. I want to know the proper size I need to achieve the best top end, but not take forever to reach plane either. I ran numbers through a formula from another Whaler site but I'm not positive on how to interpret the answers. I know the answer is in MPH, but what else do I have to consider?

I'm looking at these Mercury Vengeance propellers. At $400 a pop, I want to make sure I'm making the right decision. Anyone cabeesh this info?

http://www.propline.com/Select-Boat-P..._40_HP.htm

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What year engine? I ran a 17 pitch on my 2003 Merc 40 two stroke on my 1972 13 and was easily over 40. Probably 42. use the XHS exchangable hubs system and the props are much cheaper and easy to switch out.

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2001

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AD, you're running a 15' boat with a 40hp. You're not going to get much faster than you are already going with a different prop. You've indicated that your WOT RPM is 5-5,500 which is right in where you should be.

Also, spending $400 on a new prop is crazy especially since you'd not see that great of a performance enhancment. There are props on ebay and craigslist all day long that are of equal quality for much less money than $400.

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True. Most guys run a 70 on that hull

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your right and that's what I was thinking. problem is i still dont know what pitch and size to look for as far as a replacement. those 400$ are too expensive for the performance i'm goingt o get, true.

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Without some precise data of WOT RPM and speed, it is difficult to calculate the pitch of the propeller you have now, but we can take a guess.

If you hit 30.7 MPH at 5500 RPM, for example, that suggests you have a 13" pitch propeller. 27 MPH at 5250 would suggest a 12" prop.

I suspect the latter is the pitch you have.

If the aluminum propeller you have is a Mercury prop then it is probably either their 10-5/8" x 12" (part #48-73134) or their 10-3/4" x 12" (part #48-816702) prop.

You could remove the prop and read the part number to know for sure.

The Mercury Vengeance would be a good choice for a stainless steel model. I would recommend the 11" x 12" size (part #48-855856)

There is no reason why you should have to pay $400 for that prop. Shop it around.

An even better choice of prop might be the Stiletto Triad 3.5 in the 10-1/2" x 12" size (part # C802312). I can get you one of those complete with hub kit for $225.

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You can also buy the older pressed-in rubber hub Triad II for the close-out price of $195, delivered. Boat Owner's World has these on sale:

http://www.boatownersworld.com/Props/...series.htm

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thanks for the input Tom. I looked on the prop hub between the blades and saw a string of numbers that didn't seem to make sense, but the last set of digits was "14P". Could this be the pitch? Or is this just the s/m number?

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14P means 14" of pitch. The number preceding it is the part number. Give me that number and I can verify which propeller you have.

I am surprised to hear you have a 14" pitch prop. Assuming it has not been damaged or modified, the prop is slipping more than I would expect.

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Here's the number, and the specs are in my shop manual for this prop.

48-816706 A40 14P
10 3/8"
14"Pitch
3Blades
Rated for typical Gross weight of 1200-1800lbs
Boat Length 15-17'
26-32 MPH

According to the chart in my shop manual I can install a 10" diameter prop with a 16" pitch and get 30-36MPH. But its rated for 700-1200lb gross boat. The 15 is 600 and plus me and everything else I might fit under this weight. Am i thinking right on this? What am I sacrifcing?



The current prop does have some damage to it. The edges are a bit chewed up and knarly.

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No, that is not what the manual is telling you; it does not work that way.

What the manual is saying is that *if* your motor could turn the 16" pitch version, then the boat speed would be in that range.

If your motor turn the 14" pitch prop to within the specified WOT RPM range, then increasing pitch would only decrease the RPM an reduce speed.

OK, 48-816706 is the Mercury 10-3/8" x 14" (large blade area) aluminum prop, one of two 14" aluminum props they make.

Certainly if the edges are dinged and chewed up a bit, your boat's performance will suffer. You definitely want to go to a good stainless steel prop which will have the added benefit of not getting so chewed up.

You could try the 14" Vengeance, but I suspect it may be a bit too much prop for your boat. I would recommend a 13" Vengeance or the 13" Triad as the best fit and performer.

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Okay so what kind of performance should I expect from the 13" pitch? same, less, or more top end speed? Also, what diameter should I look for in the 13" pitch?

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You should expect a little more top end speed, better acceleration and fuel mileage with a new propeller. The new stainless steel propeller will also last MUCH longer.

You don't decide what diameter to get, the propeller designers have already done that for you. Once you decided on the model of propeller and pitch, the diameter is a given.

The 13" pitch Vengeance has a 10-1/2" diameter.

The 13" pitch Triad also has a 10-1/2" diameter.

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I have the same motor with this prop on originally-

48-816706 A40 14P
10 3/8"
14"Pitch
3Blades

I have the Sport 13 (2001)

I changed it to a 13 pitch and get better performance for heavier loads.