2001 Dauntless 16 repowered with Yamaha F115B

Optimizing the performance of Boston Whaler boats
rsantiago
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2001 Dauntless 16 repowered with Yamaha F115B

Postby rsantiago » Tue Sep 05, 2017 10:54 pm

Hello to all,
I posted a few weeks ago in the GAM section that I repowered my Dauntless 16 with a new Yamaha F115B engine and a Solas Titan HR 4 13.25x15 propeller. The following is performance data that I recorded today regarding this boat and engine configuration. Speed readings were taken from GPS and RPM readings were taken from a digital tachometer.
RPM SPEED (MPH SOG) Gear Ratio: 2.15 Full Throttle Range: 5300-6300 RPM
1300 4.6
3600 19
4000 23
4500 27
5000 31
5500 35
6100 40
The DAUNTLESS 16 would plane at approximately 4000 rpm and would remain on plane at about 3600 rpm once I throttle back. I find that a nice cruise range to be anywhere between 3800 rpm and 4500 rpm depending on sea state.

Using fuel refilling and distance travelled I estimate that fuel burn is around 5 miles per gallon over the range of operation between refills. I don't have a fuel flow meter, but have used this method for sixteen years with my previous engine with consistent results.

In general, the Solas 4-blade propeller gave me a better acceleration from standing start, excellent mid-range acceleration, smoother entry, and better rough water handling relative to a sixteen foot boat. Boat speed of 40 mph feels awfully fast in this boat and I won't be reaching that speed often!

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Phil T
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby Phil T » Wed Sep 06, 2017 10:35 am

I went back and re-read your thread.

Your performance reads very LOW.

Bob (GoldenDaze) showed his results for a 115 as breaking 42-43 with a 4 blade Trophy plus. A 3 bladed prop is even faster.
cf: http://continuouswave.com/forum/viewtopic.php?f=4&t=2453&p=14603#p13961

Why the 4 blade prop?

Where is the engine mounting height?
cf: http://continuouswave.com/forum/viewtopic.php?f=7&t=739

I would think you would want to be at least 2 holes up.

Having the right height and prop is not about WOT speed as much as getting the engine to run at the proper RPM's at all speeds.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

rsantiago
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby rsantiago » Wed Sep 06, 2017 11:42 am

Hi Phil--I also read the thread by GoldenDaze and thought I would get similar results.

On my boat, the engine is mounted two-holes up. The boat also has bottom paint in good condition.

With a three-blade Yamaha 13 x 17 the boat ran too bow high and was struggling to plane. That didn't happen with the 13 x 17 propeller on the previous engine, an F100 with a Doel-fin.

I wanted to avoid putting a Doel-fin on the new engine and went with a four-blade propeller after reading several threads here. Using the Yamaha Prop Selector on Yamaha's web site I narrowed it down to a 15-pitch propeller. The slip calculator shows a 1-percent slip at 40-MPH and 6000-RPM.

I went with the Solas Titan 4 propeller based on decent reviews I read online and decent price for a stainless steel propeller at $244. Also, the Trophy Plus propeller that GoldenDaze used was a 17-inch pitch versus the 15-inch pitch I am using. This could also have an effect on top speed.

jimh
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby jimh » Wed Sep 06, 2017 12:57 pm

A calculated SLIP factor of 1-percent is probably too low to be true, and that usually comes about because the pitch of the propeller was understated in the calculation. The four-blade propeller you have that is marked 15-pitch is probably acting more like a 16-pitch. Pitch ratings are not universal and in complete congruence among all propeller makers and all models, so it is not surprising that your performance testing produced such a low SLIP calculated value.

The outcome of the re-power and propeller selection sounds good to me. If the four-blade makes the top boat speed a few MPH lower, but gives better all-round results, then so be it. It is rare day that you run any boat at maximum throttle for long stretches, unless you are in a race or some sort of competition where speed is the most desirable aspect of performance.

jimh
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby jimh » Wed Sep 06, 2017 1:07 pm

Regarding fuel economy, there are many variables that affect the combination of engine, boat, and propeller to produce fuel economy. In the engine there is a parameter known as brake specific fuel consumption or BSFC. BSFC measures how efficiently the engine converts fuel (by weight) into output power. The interesting aspect of the typical internal combustion gasoline engine is its BSFC is not a constant--far from it really. BSFC varies according to throttle position, engine speed, and load. Data about BSFC is just about NEVER published for an outboard engine. But we can learn from looking at other engines whose BSFC data is published. In those engines we see that there are certain operating points for the engine in which the BSFC will peak, that is, the engine will be the most efficient at converting fuel into power.

The problem in a boat is to get that peak in outboard engine BSFC to correspond to a good cruising speed for the boat hull. And at that speed we would like the propeller to be operating at its most efficient point, too. If all this aligns, then the boat, engine, and propeller work at their optimum point and the result is really great fuel economy.

You can chase this point by trial and testing of propellers on a given boat with a given engine, looking for some combination that gives improved fuel economy. But, of course, to find it you have to be able to accurately measure fuel economy, and to test in nearly identical conditions.

I pursued this sort of testing for a while, but once I found a propeller that worked well, gave good all-round performance, and got decent fuel economy, I gave up further testing and just went boating. Maybe I left 1-MPH of speed and 0.1-MPG of fuel economy still waiting to be claimed. I don't care. I just enjoy the boating with what I have.

Sounds like your DAUNTLESS 16 is at that point. Enjoy boating.

rsantiago
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby rsantiago » Wed Sep 06, 2017 2:21 pm

Jim,
I agree with your assessment of good all-around performance. I feel that I have reached good operating norms for my boat, thanks in large part to this forum and those who contribute comments to it.

Thanks to all for their input.
Happy Boating!
Ralph

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GoldenDaze
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby GoldenDaze » Thu Sep 07, 2017 3:47 pm

Hi Ralph, your speeds look about 2-3 MPH lower than mine across the whole RPM range. To me, that suggests that your prop pitch is a little low, and indeed it is a bit lower than mine. I'm a little surprised that you aren't hitting more than 6100 RPM at wide open throttle.

That said, overall your performance seems pretty solid, and since I can count on both hands the number of minutes I've spent over 40 MPH in 14 years with my boat, I probably wouldn't get too worked up about top speed. If your boat is fast to plane with a full tank of fuel (45 gallons, which is a lot of weight on a 16 footer), then your lower pitch seems justified.

Enjoy!

-Bob

rsantiago
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Re: 2001 Dauntless 16 repowered with Yamaha F115B

Postby rsantiago » Sun Sep 10, 2017 10:02 pm

Bob,
Thanks for your input. It was valuable in making my propeller decision. I'm not too concern with my top speed and really more impress with how the boat handles in a stiff chop with the 4 bladed prop. The boat rides over the waves and has less of a tendency to get airborne. Even when I catch a little air the landing is softer for an overall improved ride in head seas. Once again, thanks. By the way, the data taken was with a full tank of gas.

Ralph