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1984 Boston Whaler Outrage 18 re-power:

In May of 2017 I decided to re-power. I had a 2003 Bombardier Johnson 150 two stroke mounted on the 1984 Outrage 18. Wonderful motor - but not fuel efficient. After extensive research, I chose a 2017 Mercury 115 Command Thrust. The install is complete and I have put a few hours on it. Not enough to give a complete breakdown on everything but I can tell you all that I really like it so far. I chose the Mercury over other brands for many reasons: 1) I like the fact that I could swing a V-6 class prop on the motor. In fact I just transferred the prop from the legacy two-stroke. A 14.5” x 19” prop. At WOT I get the same performance as listed on Boston Whaler’s published performance data for the same motor on a 2017 Montauk 190 with a 14 3/8" x 19" prop. I realized this performance at sea trial with the technician at the helm and ¾ tank of fuel. Same with me alone with a full tank of fuel. 2) Weight. The legacy two-stroke 150 tipped the scales at 370 lbs. +/-. 2017 Mercury 115 CT is almost the same. There was no way I was going to have a 150hp class four-stoke installed on the boat because of the weight. I’m located in St. Augustine Florida and the Atlantic Ocean is a large water body. Couldn’t see myself navigating the St. Augustine Inlet and Atlantic offshore swells / waves here with that weight hanging off the transom. 3) Ease of maintenance. 4) The Mercury is made in America.

I will give an update on more specific performance / economy matters as I put more hours on the motor. Pics coming soon to my personal page.

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Peter,

Thanks for the preliminary report. The Merc 115 CT sounds like a good match for the Outrage 18. When you get it all dialed in and put some hours on the new rig, could you please share some of the performance data? E.g., speed vs rpm, top speed, fuel economy, etc.

My interest is more than academic. I have toyed with repowering my 19 Outrage II with the 115 ProX/S version of this engine. But even though I have the same hull as you, my boat has a different interior and is heavier. So I'd love to hear wht sort of "numbers" you are achieving withthe 115 CT. Thanks!

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JRP,

Will do. Give me a couple of weeks on that. Thanks for the reply.

Peter

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Without knowing the make and model, this size is meaningless. Prop sizing is like women's clothes sizing. No two brands are the same. One brand's size 6 is another's 8 or 4.

We are spoiled that a XL is an XL.

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Peter,

Of course, more specifics would be helpful, but I'm not sure your prop info is completely meaningless. We do at least know that you are able to use the same prop that you previously used with your 2.6L V6 2-stroke engine, and apparently with satisfactory results. That is impressive given you are now operating a 2.1L I4 4-stroke engine, albeit with the beefy CT gear case.

However, despite the good results so far, and whatever the prop specifics are, it would just be dumb luck if it's the best match for your new rig. Very likely one of Mercury's new stainless offerings would be a better choice. Hopefully some of our resident prop experts (Finnegan, Tom Clark, Phil T, etc) can offer some suggestions! But the more data and details you can provide, the easier it will be for them.

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Solus prop. 14.5" x 19". Aluminum.

Aren't prop sizes standard across the board in the boating industry? If not, tell me. Fact based response please.

After 5 hours of break in I am seeing less then 3 GPH overall. Wow.

More to come. Thanks All.

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At what speed? Idle?
At what RPM?

The starting point to select a prop from a given manufacturer, is to have the boat loaded in an average state.
Meaning not light and not heavy.
Then the WOT RPM's should fall within the manufacturers specifications.
You have not given us any of this info and you cannot compare this to any other boat model like you have above. Period.

Load your boat in a medium state and give us the WOT RPM's and also the WOT RPM's the manufacturer recommends.
We can start from there.

Nothing is going to be perfect.
When running light on fuel and other weight, the motor could go beyond the WOT RPM's
When running heavy the boat may not be up to the recommended RPM's
There is a happy medium.

Once you select a prop that falls within that range, and the motor is mounted at the correct height, you can then test the overall performance and fuel economy.

Running a 115hp on an Outrage 18' will not have the longevity as running a 150hp on that same boat.
A 115hp will have to work harder at more RPM's to keep it up to the same speed as the 150hp. Thus the 115hp may be also burning more fuel.
Big misconception is thinking a smaller motor will give a boat better fuel economy.
Maybe at idle speeds but not at identical cruising speeds.

Good Luck and keep us informed.

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Elaelap ran a F115 on his Outrage 18 out of Bodega Bay in California and did some hard core offshore fishing. He loved it.

For him it was a stern weight issue.

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Peter -

Let me clarify.

Size is measured in inches. Diameter and pitch.

Prop performance is not universal with size due to the different blade geometry and materials.

Aluminum props are not as efficient or as durable as Stainless Steel.

If you talk to a prop shop and ask them if a Yamaha SS x by x will perform the same as a Solas or Turbo or Powertech SS x by x, they will say no or maybe depending on the models.

Call Ken at PropGods @ 941.735.5808 if you want to talk to a professional prop guru.

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Today I did a performance test. One person on board (Me). I tipped the scales this morning at 155 lbs. 60 gallons of fuel in the tank. Two anchors in the bow locker totaling 30lbs. +/-. A roto-molded cooler in front of the console weighing approx. 30 lbs. Cooler empty. No other gear on board. One battery located under the console. Wind was 5-7 knots coming from the Southeast. Tide was running so I did two passes along the same stretch of water in the ICW just South of St. Augustine. Outboard set at level trim. Here are the results of the two passes averaged. Measured with my Simrad Go7:

650rpm 2.5 knots
1000rpm 3.5 knots
1500rpm 5.0 knots
2000rpm 6.1 knots
2500rpm 7.4 knots
2750rpm 8.75 knots
3000rpm 10.9 knots
3250rpm 15.4 knots
3500rpm 19.7 knots
4000rpm 22.5 knots
4500rpm 26.5 knots
5000rpm 29.7 knots
5500rpm 32.5 knots
5950rpm 36.0 knots WOT

These results are eerily similar to Boston Whaler's published performance data for a 2017 Montauk 190 with same motor - slightly different prop. Please refer to their website for that published data. I cannot provide fuel burn rates as my gauges are Mercury analogue.

Peter

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Great stuff, Peter! Thanks for the efforts and sharing it with us.

At mid-range cruising speeds, the closest match I see with the Montauk 190 data is at 4000 rpm (Montauk 190 is doing 22.0 knots @ 4000 rpm).

At that rpm, BW shows an mpg of 5.33 (4.63 nmpg). I assume you would be darn close to that, which is impressive.

But even better, at 3500 rpm the Montauk achieves only 17.5 knots, and you are getting 19.7 knots. So if you burn the same amount of fuel (3.5 gph), your best fuel economy should be nearly 6.5 mpg at around 23 mph (or roughly 20 knots.)

How big is your fuel tank? You might have trouble using it up!