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Author Topic:   Dauntless 15 with 50-HP
joz posted 06-07-2015 07:33 PM ET (US)   Profile for joz   Send Email to joz  
This morning I took out my [Dauntless 15 with 50-HP] for the third time since I've owned it--a beautiful calm morning. I wanted to see how it would perform with just me [and 6-gallons of fuel], and get some numbers. Here's what happened: At WOT, [the boat speed] was running about 30 to 31 MPH, at engine speed 6000-RPM. With a slight trim, I hit 32-MPH, and RPM jumped to 6,200. It's a 1995 50 horsepower Johnson, and the manual says WOT is between 5,500 and 6000.

Is 6,200-RPM going to hurt this engine?

The propeller on the engine is 13-3/4 x 15. The manual suggests a 13-1/4 by 17. Anyone have this boat with a propeller they love? Should I not run [the engine] at 6,200-RPM? Thanks for any help!

dg22 posted 06-08-2015 11:01 AM ET (US)     Profile for dg22  Send Email to dg22     
That is a hard question to answer especially with a 20-year-old motor. I'd find a prop that keeps your WOT RPM within the range and keep the 15-pitch prop for pulling skiers.

Tom W Clark posted 06-08-2015 11:36 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
6200 RPM is not going to hurt you motor if you hit it during testing.

If the propeller is aluminum, you will definitely get improved fuel economy, fast speeds, and better handling if you upgrade to a well fit stainless steel propeller.

I recommend the 13-1/4" x 13" Stiletto Advantage (Yes, yes, I know it is less pitch that what you have but your current prop is slipping 14 percent and the Advantage will yield about -5 percent calculated prop slip)

Be sure the motor is not mounted all the way down on the transom, it should be mounted two holes up thus:

o <-- Mounting Bolts Through This Hole in Motor's Bracket

joz posted 06-08-2015 11:47 AM ET (US)     Profile for joz  Send Email to joz     
HI Tom, Thanks for the suggestion. Did you mean 13 1/4 x 13? And yes, the prop is aluminum. What is your opinion on the factory recommendation of an Aluminum 13 1/4 x 17 Prop? It's not a ski boat, I will use it for fishing and cruising with my wife and small kids, and we may pull them tubing now and then. I will look in to the stiletto, though I know they're expensive.
Tom W Clark posted 06-08-2015 11:54 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Yes, I meant to type 13-1/4" x 13"

Where do you see a recommendation of 13-1/4" x 17" and what model of propeller is being recommended? Propeller size depends on the boat and your needs so there can be no singular propeller recommendation.

"Expensive" is relative. The Stiletto Advantage 4.25 can be had for $270, delivered with hub kit.

joz posted 06-08-2015 12:08 PM ET (US)     Profile for joz  Send Email to joz     
The manual I have for the engine, factory manual, is for a 1995 Johnson 50, 60 and 70 HP engine. On the specs page, it indicates WOT operating RPM at 5000-6000 for the 50. For propeller size, it says 13 1/4 x 17 for all three engines but refers you to a page in the manual that says exactly what you did, that it varies depending on boat and use. The prop is an OMC prop, and I called a dealer and they said that the prop I have on it now, the aluminum 13 3/4 x 15 has been replaced by a 13 1/2 x 15, and it will have an all new hub kit. I read somewhere that by increasing pitch, I could bring the RPM down a pinch where it may get me under 6200. But the diameter would also be smaller. I assumed the 15 was the happy middle, but I just don't want to damage the motor. The other issue is that the current prop is slightly damaged, and the pitch is surely filed down a little in order to smooth out some of the knicks that were on each blade. I don't think calling it a 15 pitch anymore would even be accurate. At the end of the day, I was looking to replace the prop anyway since this one was a little warn.
tedious posted 06-08-2015 12:09 PM ET (US)     Profile for tedious  Send Email to tedious     
Joz, the additional cupping on the Stiletto will act like about 2" extra pitch, so while it may sound strange (and Tom can speak for himself) the 13-pitch will likely work out well for you, especially giving your stated usage model.

Good props are not cheap, but the Stiletto Advantage is one of the least expensive stainless props out there, and also a very good one. I'm sure you spent a lot on your boat, so spending just a little bit more to make sure it performs as well as it can makes sense, especially if you are looking to keep it for a while.

I like to predict speeds just for fun, so I am going to guess that the prop Tom recommended will have you hitting 5800-5900 RPM trimmed out, at a speed of 34-35 MPH.


Tom W Clark posted 06-08-2015 12:28 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I am going to change my recommendation to a 13-1/4" x 15" Advantage 4.25, but only because this boat should be much faster than it is now.

Factory test data for the 1990s I have here show the Dauntless 15 doing 36.3 MPH with a 40 HP Mercury four stroke and 35.9 MPH with a 40 HP Merc. In both cases the notes show the boat weight as "Heavy"

I think 36 MPH is a reasonable goal, and you'll need the 15" Advantage to get there.

Tom W Clark posted 06-08-2015 12:29 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
...36.3 MPH with a 50 HP Mercury four stroke...
joz posted 06-08-2015 12:38 PM ET (US)     Profile for joz  Send Email to joz     
And you're confident that it will run within the RPM range and not reduce performance as others suggest on this forum? It would be a shame to spend that money and not be able to return the product. That is my fear.
Tom W Clark posted 06-08-2015 12:40 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Who is suggesting reduced performance?

Why wouldn't you be able to return or exchange the propeller?

joz posted 06-08-2015 12:46 PM ET (US)     Profile for joz  Send Email to joz     
In my search for the perfect prop, I've clicked on many links of people suggesting their stiletto actually lowered RPM too much. More threads indicate that you're right, I'm just being cautious. As far as returns, once a prop is used, most places don't accept returns. On iBoats, the prop you recommend is $351! Not including the hub kit which I couldn't find. Where would you shop for both the prop and its hub kit? 36 MPH would be sweet! I wonder if marinas stock test props that they would rent to customers to mess around.
Tom W Clark posted 06-08-2015 12:50 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I predict a 13-1/4" x 15" Advantage 4.25 will yield 35 MPH at 5700 RPM, if the motor is two holes up on the transom.

Be careful what you read and who you listen to. Some know more than others...

iBoats is not known for good deals on propellers. I can supply you with a prop for much less then that. Shoot me an email:

joz posted 06-08-2015 01:03 PM ET (US)     Profile for joz  Send Email to joz     
Gonna have to check my transom when I get home! I'll be in touch if/when I decide to pull the trigger. Thanks for your advice.
crabby posted 06-08-2015 05:19 PM ET (US)     Profile for crabby  Send Email to crabby     
Make your move soon, Stiletto props will soon be tough to find.

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