Dauntless 16 re-power

Optimizing the performance of Boston Whaler boats
Lupi
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Dauntless 16 re-power

Postby Lupi » Mon Aug 27, 2018 11:31 am

Hello,

I am still using my Dauntless 16 with the stock Mercury 90-HP two-stroke-power-cycle engine. I'm happy with the current settings:
—stainless steel Stiletto 13.25 x 17-pitch propeller
—engine mounted 3-holes-up

Compared to the stock setting (aluminium black max 13*19 and only 1 hole up), performances and riding are significantly improved. I know that 90 hp is a little bit just, but the settings, resulting from good advices received on this forum, made a very good compromise and performances are largely acceptable, even loaded with people.

But,... this engine is now 20 years old. I know that it can breakdown @ anytime. If I was to replace the engine, I would go to 115 hp. The offer is quite large, but in my area (peninsula in Britanny in France), I have dealers for Mercury and Yamaha. I would prefer to go Mercury because less expensive and their 115 hp is the lightest on the market (360 lbs). Yamaha makes 390 lbs and I know that weight on the transom is really key for this boat.

Did anyone experienced the 115 hp from mercury on that boat ? Ideally I would like to re-use my Stiletto prop, and given its features, it can only go to small gearcase, so CT models and sea pro models cannot be chosen. Then two options :

- regular 115 hp (max 6000 rpm and gear ratio of 2.07)
- Pro XS 115 hp (max 6300 rpm and gear ratio of 2.07)

With my 90 2 troke, I could reach 40 mph @ 5500 rpm wot with gear ratio of 2.33. My Stiletto prop is running like a 19 even if it is a 17 pitch.

Should the 115 engine be mounted as high on the transom ? I know this boat is very particular because of its weight sensitivity on the transom and engine dealers always follow manufacturers recommendation with engine height and prop selection that are not adequate with this boat, reason why I took advices here and why I request again good recommendations.

Thanks a lot in advance

Luc

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Phil T
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Re: Dauntless 16 re-power

Postby Phil T » Mon Aug 27, 2018 12:33 pm

There have been many threads on this subject.

This one is only weeks old.

http://continuouswave.com/forum/viewtopic.php?f=4&t=2453
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

Lupi
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Re: Dauntless 16 re-power

Postby Lupi » Mon Aug 27, 2018 1:18 pm

Thanks,

I've basically read all the threads, even in the old forum, but my question was about the new Merc offer in 115 hp range. All threads relate different engines.

Jefecinco
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Re: Dauntless 16 re-power

Postby Jefecinco » Tue Aug 28, 2018 11:15 am

Lupi - As a former Dauntless 16 owner I agree that engine weight has significant impact on the 16. For that reason the most critical factor for me would be engine weight. Given the different gear ratios and HP of the new Mercury engines your Stiletto propeller may not be the best choice but finding another propeller should not be a problem. I would mount the new engine at the same height as your current 90 HP Mercury.

I believe you will find the performance of your Dauntless with a 28% HP increase to be significantly improved.

Is the Pro XS an Optimax engine? If so, I would opt for the quieter less complicated "regular" version.
Butch

Lupi
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Re: Dauntless 16 re-power

Postby Lupi » Wed Aug 29, 2018 4:26 am

Thanks Butch,
Much appreciated

Both regular and Pro XS are based on same platform : 4 cycle engines, 2.1l, 115 cv. Weight 359 lbs. Optimax range seem to have been discontinued (at least for Europe).

So, we have same engines, but the Pro XS is supposed to have more (hidden) HP. Talking with my Merc dealer, it delivers a true 127 HP. Redline 6300 vs 6000 rpm for the regulat 115 hp.

I was guessing that my Stiletto 17 pitch could do the job on one of those two even with 2.07 gear ratio. When I do the prop selector on the Merc site, they propose, among other, the laser II 19 pitch that I know turns like a Stiletto 17. Now, I have a doubt because I remember I chatted with a member of the old forum who had same boat (Dauntless 16) but with the former 115 HP two stroke that was a strong engine with a redline @ 5250 and gear ratio @ 2.07. He was using a Michigan rapture 17 stainless steel, so basically same features than the Stiletto and he put a fin on the jackplate. He reported 44 mph @ 5000 rpm.
Given this, I tend to think that my Stiletto 17 would be too much and not adapted to the new 115 hp Mercury that operate with gear ratio 2.07 but at higher rpm. That confirms what you said.

What is sure is that the engine should be raised on the transom with the combination of a good SS propeller that can operate close to surface.

Thanks again

Lupi

jimh
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Re: Dauntless 16 re-power

Postby jimh » Wed Sep 05, 2018 10:49 am

Re the Mercury re-branding of certain OptiMax engines to be ProXS engines: this odd name change seems to have ended, and so has the OptiMax engine line.

Lupi
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Re: Dauntless 16 re-power

Postby Lupi » Fri Sep 21, 2018 10:59 am

I've looked at the large gearcase models of the mercury 115 HP 4 stroke (CT models) that may be a good idea for the dauntless 16.

Compared with small gearcase, the gear ratio is 2.38. I did a quick prop selector on Mercury web site that ended, for SS props :

- Mirage plus : 23/24 pitch
- Tempest Plus : 23/24 pitch

I know nothing about those props, but I would tend to think that if the engine has to raised at the maximum on the transom, the prop should have a lot of rake which I do not know between the Mirage or the tempest is the most appropriate. Do anyone has experienced those props?

Thanks

Lupi

jimh
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Re: Dauntless 16 re-power

Postby jimh » Sat Sep 22, 2018 8:58 am

Lupi wrote:Do anyone has experienced [a Mercury MIRAGEplus propeller]?


I have been using a MIRAGEplus propeller on my boat for about nine years.

Lupi wrote:I do not know between the Mirage or the tempest is the most appropriate.


The MIRAGEplus propeller is a large-blade-area three-blade propeller without much rake, intended for boats that are typically larger and heavier than a 16 DAUNTLESS.

Predicting which propeller will produce the best results on a particular boat and engine combination is difficult. Actual sea trials with the various propellers is really the only way to discover which one works best. I don't think there have been too many tests conducted with a 23-pitch MIRAGEplus on a 16 DAUNTLESS to refer to. You might be the first to try that propeller.

In my experience with actual testing compared to the suggestions produced from the Mercury propeller selection website, I have found that the pitch suggested has always been too high for my application.

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GoldenDaze
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Re: Dauntless 16 re-power

Postby GoldenDaze » Mon Oct 15, 2018 12:59 pm

Lupi, while your engine is much newer than mine, has a different gear ratio and almost certainly a different torque curve, you might consider the Trophy Plus prop. I did a comparison of several props on my 160 Dauntless some years ago, see http://continuouswave.com/ubb/Forum4/HTML/004868.html, and I've been very happy with the Trophy Plus since. Given the difference between my 2.07:1 gearcase and the 2.38:1 gearcase you are talking about, that suggests a change from 17" pitch to 19" pitch, all other factors being equal.

-Bob