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Author Topic:   15-footer's Propeller
44z posted 04-17-2011 08:59 PM ET (US)   Profile for 44z   Send Email to 44z  
I've just purchased a Sport 15 with [1999] Mercury 60-HP two-cycle three-cylinder engine. I'd like to replace the beat-up propeller with a stainless steel propeller. I'm looking for an all-around propeller that would be able to pull up a skier but also handle just one person full speed in flat water. Does anyone have an idea of propeller type and pitch?

On a related note, as far as motor height goes, do you recommend that the cavitation plate be flush with the bottom, or higher or lower?

jimh posted 04-18-2011 08:53 AM ET (US)     Profile for jimh  Send Email to jimh     
The three-blade propeller is probably the best propeller for all around use.

On a small and very light boat like a classic Boston Whaler SPORT 15 the top speed will be very dependent on the load and weight on the boat, and it will be impossible to find a propeller that will give optimum performance under the two very different loading conditions you have set out. When the boat is lightly loaded and has only one person the speed potential will be very much greater than when the boat is pulling a person water skiing. There is no propeller that will give the optimum performance in both those situations.

You can estimate the propeller pitch after you have determined the top speed potential. For a lightly loaded SPORT 15 with 60-HP the top speed will be about 38-MPH. Now find the recommended maximum engine speed and the gear ratio of your engine. Then enter those parameters in the propeller calculator at

http://continuouswave.com/cgi-bin/propcalc.pl

Enter a SLIP of 10-percent. The calculator will return a propeller pitch.

dgoodhue posted 04-18-2011 08:56 AM ET (US)     Profile for dgoodhue  Send Email to dgoodhue     
Definitely higher. It should raised 2 or 3 holes depending on the prop.

As for the prop, the ideal prop for top speed and ski is going to be different props. You may be able to ski behind a top speed prop. What is your current wot rpm and pitch of your prop? Also , you will want correct the engine first before buying a different prop.

Tom W Clark posted 04-18-2011 10:58 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
[quote]...an all-around propeller that would be able to pull up a skier but also handle just one person full speed in flat water[./quote]

My entire teenage recreational life was spent fooling around in boats, Whalers especially, and this is all we did. We never used anything but one propeller, so yes, I think it is entirely possible to find a well fit prop for your dual needs.

For a Sport 15 with a 1999 Mercury 60 HP two stroke, I recommend a 10-1/2" x 12" Stiletto Triad 3.5 propeller with a C-011 hub kit.

You can buy one brand new one with hub kit and have it delivered to your door for $200 or less.

If your motor is mounted all the way down on the transom, as dealers often did back in the day, I suggest you raise the motor two more bolt holes, or in other words, mount it so there is about 1-1/2" of space between the top of the transom and the motor mounting bracket.

jimh posted 04-20-2011 11:29 PM ET (US)     Profile for jimh  Send Email to jimh     
It is possible to find a propeller that will be able to pull a skier, but it is very likely impossible that a single propeller will be optimum for each of the two very different situations you described. Hitting top speed when the boat is light and has only one person aboard and having the best acceleration when pulling up water skiers are situations of rather significantly different loading. The smaller the boat the less the over all weight and the less horsepower reserve available. The addition of the load of a skier to a very light 15-foot boat cannot be ignored. It will affect the performance. If you had a 6,000-lb boat it might not notice a water skier, but a 500-lbs 15-footer certainly will.

The best way to discover what propellers will do on a particular boat is to actually test them. That's your next step.

Tom W Clark posted 04-21-2011 01:36 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
It is obvious that no propeller will be optimal for both the quickest possible acceleration under a great load and achieving the highest top speed with little load.

Of course, that is not what 44z asked.

He asked for "an all-around propeller that would be able to pull up a skier..."

and

"...also handle just one person full speed in flat water."

The propeller I've recommended will accomplish both of those goals quite nicely.

Owtrayj25 posted 04-21-2011 12:19 PM ET (US)     Profile for Owtrayj25  Send Email to Owtrayj25     
Perhaps we should debate what "full speed in flat water" means? Is this suppose to mean the absolute top speed a Sport 15/1999 Mercury 60 HP engine is capable of, or the top speed of the Sport 15/60 HP Merc with a given propeller, presumably the propeller that will allow the boat/engine to achieve its maximum speed?

I see no barrier to accelerating to full speed on flat water with any propeller, provided the boat is not over powered.

jimh posted 04-22-2011 09:29 AM ET (US)     Profile for jimh  Send Email to jimh     
Every propeller will cause a boat to reach its "full speed" if one defines full speed as the fastest speed the boat can reach with that propeller. That is not much of a criterion and does not lead to much insight in propeller selection.
Tom W Clark posted 04-22-2011 09:50 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I agree. However, that is not what 44z asked. I believe he is asking for a propeller that will not allow his motor to exceed its redline at WOT if only one person is aboard and the water is flat. In other words, a propeller for having fun and going fast.

The propeller I have recommended will allow that.

We can argue the semantics of the first post, but why not let 44z explains what he wants if my interpretation is incorrect.

I note that so far here in this thread, which is a simple request for a propeller recommendation, that there has been only one recommendation of a propeller offered.

Owtrayj25 posted 04-23-2011 08:22 PM ET (US)     Profile for Owtrayj25  Send Email to Owtrayj25     
[No propeller advice given]
jimh posted 04-24-2011 11:07 AM ET (US)     Profile for jimh  Send Email to jimh     
Contributors who want to parse language perhaps can continue amongst themselves in private email. The topic here is propellers. So far I don't see any bad advice given.
44z posted 05-03-2011 10:35 AM ET (US)     Profile for 44z  Send Email to 44z     
I appreciate the insights you guys are providing for me. First, my mechanic tells me that if I raise the motor 2 holes (from flat on the transom) I risk cavitation on turns. He is a bit leary of raising it. Second, on prop selection, I am less concerned with pulling an adult skier and more interested in speed with 1-2 people while still having enough acceleration pull up a 125 teenage skier. Finally, does anyone see anyway I can get the boat to 40 mph without radical moves? Thanks again.
Tom W Clark posted 05-03-2011 10:39 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
4z -- Your mechanic is wrong; the propeller will not cavitate if the motor is two (or even three) holes up. Have him give me a call if he has questions.
Tom W Clark posted 05-03-2011 10:41 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Yes, I think 40 MPH is entirely possible with the three cylinder Mercury two stroke 60 on your Sport 15.
geo15sport posted 05-03-2011 04:47 PM ET (US)     Profile for geo15sport  Send Email to geo15sport     
What prop would you recommend for my 1987 Johnson 70 on my sport 15, same needs as 44z. I'm running the original aluminum 13X19, still in like new condition. I've read where you indicated any prop over 20 years is really outdated, my motor has always been adequate pulling up adult skiers and top speed, but I'm from old school and don't know any better. Would new prop be money better spent than a manual jack plate? I'd like to raise my motor to third hole and still be able to turn sharp, is that possible? Right now motor's all the way down and I have to remove it from transom just to replace steering cable.
44z posted 05-03-2011 06:03 PM ET (US)     Profile for 44z  Send Email to 44z     
Tom, I have looked on several web sites but can't find a Stiletto Triad 3/5 with c-011 hub kit delivered for $200. Could you point me in the right direction here? Also, when I use the Prop/RPM/gear ratio/speed Calculator and plug I come up with a recommended 13-14 inch pitch prop. Do you a 14" is a little high for my 15' with '99 60 Merc? Thanks.
Tom W Clark posted 05-03-2011 06:16 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
geo15sport -- Good question for a new thread.
Tom W Clark posted 05-03-2011 06:23 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
44z -- Here is one source though the new style Triad 3.5 is priced way out of line. I suspect that is a "typo" on their web site but at any rate they are selling the old style (rubber hubbed) Triad II for $195, delivered.

http://www.boatownersworld.com/Props/stiletto/stiletto_triad_series.htm

I just orderd one directly from Stiletto though they were out of stock on the Stiletto brand. They sent me a Turbo Hot Shot (same as a Stiletto Triad) in the 10-1/2" x 12" size.

I'm going to use this for some testing but it will be available after I'm done in a couple weeks. If you can wait, I'll sell it to you for $200.

If you are going to size a Stiletto Triad using a propeller calculator, you need in input a slip value of zero *or* take the result you get and subtract one or two inches of pitch. Either way, you'll want a 10-1/2" x 12" Triad/Hot Shot.

44z posted 05-03-2011 08:52 PM ET (US)     Profile for 44z  Send Email to 44z     
Tom,
Sounds great. Let me know when you've finished your testing and if you have any new insights on my situation please pass them along. Thanks.

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