1986 OUTRAGE 18 Re-power

Optimizing the performance of Boston Whaler boats
sweetnut
Posts: 4
Joined: Thu Mar 23, 2023 10:11 pm

1986 OUTRAGE 18 Re-power

Postby sweetnut » Tue Mar 26, 2024 2:24 pm

I have an 1986 OUTRAGE 18 previously powered by [an Evinrude E-TEC] 115-HP engine. I plan to re-power the OUTRAGE 18 with a new made-in 2024 Mercury 115-HP FOURSTROKE engine.

This boat is my son’s boat. It will usually have three or four 16-year-old kids aboard.

My research indicates the maximum boat speed will be about 40-MPH.

My concern is the OUTRAGE 18 with a new Mercury 115-HP FOURSTROKE (not Command Thrust model) will be hard to accelerate onto plane with four aboard.

Q1: how will the OUTRAGE 18 perform with the Mercury 115-HP FOURSTROKE engine?

Q2: what will be the fuel efficiency of the OUTRAGE 18 with the Mercury 115-HP FOURSTROKE?

A step up to 150-HP is the next re-power option, but I think 150-HP would be excessive.

ASIDE

The E-TEC 115 produced “nice” [acceleration from a standing start onto plane at full-throttle with unspecified number of people aboard and other elements of gear aboard], but it needs expensive repair to get back to running condition.

jimh
Posts: 11869
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1986 OUTRAGE 18 Re-power

Postby jimh » Wed Mar 27, 2024 12:49 pm

Regarding performance, 115-HP is 115-HP, so the boat top speed should be the same. The E-TEC direct-injection two-stroke-power-cycle engine might have had a wider engine speed range at which it could produce its rated power that a typical four-stroke-power-cycle engine of the same displacement, so acceleration might be slower with the new FOURSTROKE Mercury—unless it has significantly more displacement that the E-TEC.

Fuel burn should be similar. The E-TEC used a stratified-charge combustion chamber to produce amazingly good fuel economy at lower engine speeds. The actual fuel economy you will realize will depend on many other factors, such as total boat weight, throttle settings, propeller choice, and how much time at high-throttle settings. Compared to the E-TEC there shouldn’t be much change in fuel used.

ConB
Posts: 248
Joined: Fri Oct 09, 2015 2:52 pm
Location: Suttons Bay, MI

Re: 1986 OUTRAGE 18 Re-power

Postby ConB » Wed Mar 27, 2024 5:34 pm

I am very happy with my repower of my 1987 Outrage 18 with a F150 Yamaha. I do not think it is excessive, and I like having reserve power for when I have six people aboard.

Con
!987 Outrage 18 / 2011 Yamaha F150
1969 13 / 30hp Johnson tiller

Lupi
Posts: 37
Joined: Mon Aug 28, 2017 4:28 am

Re: 1986 OUTRAGE 18 Re-power

Postby Lupi » Thu Mar 28, 2024 2:47 pm

150 HP is the max rating for an Outrage 18 of this era (if I'm not wrong). My brother used to have one with a Yamaha 150 HPDI (2 cycle direct injection). He could reach 50 MPH easily with four people.

But, he found the 150 HPDI was a bit too heavy. At dock it was obvious that there were too much weight at the transom. As this boat is not self bailing, there was always some stagnant water in the back, inside the boat.

If you are seeking for a 115hp, you should not get this problem as most of the 115hp in the market weigh less than 400lbs. The Yamaha 150 HPDI weighs close to 500 lbs.

If you are concerned with time to accelerate unto plane from a standing start at full throttle, maybe you can consider the 115 Pro XS Command Thrust. That model has almost the same weight as the normal model—just 4-lbs more—and it has the gear case of 150-HP engines. This gives you access to a wider range of propellers with large diameters.

sweetnut
Posts: 4
Joined: Thu Mar 23, 2023 10:11 pm

Re: 1986 OUTRAGE 18 Re-power

Postby sweetnut » Thu Mar 28, 2024 5:02 pm

Thank you for the replies.

I have settled on the Mercury 2024 115-HP FOURSTROKE (non command thrust)— second to availability and cost.

I believe the 115-HP engine will be fine on the boat.

Give me guidance on engine mounting height.

My own research indicates the Anti-Ventilation plate [should be even with the ] bottom of the boat.

Give me guidance on propeller selection.

jimh
Posts: 11869
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1986 OUTRAGE 18 Re-power

Postby jimh » Fri Mar 29, 2024 10:01 am

sweetnut wrote:Give me guidance on engine mounting height.

My own research indicates the Anti-Ventilation plate [should be even with the ] bottom of the boat.
Instruct the dealer to install the engine with the engine mounting height one-hole (0.75-inches) up from lowest position.

Whether or not the engine mounting height could be higher will depend on propeller selection.

jimh
Posts: 11869
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1986 OUTRAGE 18 Re-power

Postby jimh » Fri Mar 29, 2024 10:07 am

sweetnut wrote:Give me guidance on propeller selection.
The propeller should be a steel three-bladed propeller of proper hub diameter to fit the engine gear case.

The propeller blade diameter must fit the propeller aperture available on the engine.

The propeller pitch must be a suitable load for the engine to allow the engine to accelerate at full throttle to the engine’s maximum allowed operating engine speed when the boat is in its normal load condition that will be typical for the great majority of is running time.

The result should be the boat reaches its target speed based on power, weight, and hull design.

Mercury propellers are good designs, but at full retail price they are very epensive.

jimh
Posts: 11869
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1986 OUTRAGE 18 Re-power

Postby jimh » Fri Mar 29, 2024 10:23 am

To predict speed use the Crouch Method. I have implemented the Crouch Method in a calculator, the Crouch’s Calculator.

For power use 115-HP
For hull factor use 180.
For weight, you must add up all the weight on the boat. For a wild guess I will use 3,000-lbs.

The calculated target boat speed is then 35-MPH. Try it yourself at


CROUCH’S CALCULATOR
created by Jim Hebert

https://continuouswave.com/calculators/crouchCalc.php


To select propeller pitch you must input
ENGINE RPM
ENGINE GEAR RATIO
MPH
SLIP (set to 10)

From those four factors pitch can be calculated using a PROPELLER CALCULATOR. I have created a propeller calculator.

I don’t have a clue about your 115-HP engine gear ratio or maximum RPM.

I will take a wild guess and say the gear ratio is 2.33:1, and maximum RPM is 5700. The result is a calculated pitch of 17-inches. Try it yourself at

PROPELLER CALCULATOR
https://continuouswave.com/calculators/propCalc.php


ASIDE: how did you come up with a 40-MPH boat with only 115-HP? The only way that speed is possible is with a total weight of only 2,300-lbs.

sweetnut
Posts: 4
Joined: Thu Mar 23, 2023 10:11 pm

Re: 1986 OUTRAGE 18 Re-power

Postby sweetnut » Sun Mar 31, 2024 6:28 pm

The boat speed over ground exceeded 40-MPH on a cool April day in 46-degree [saltwater].

This 1986 OUTRAGE 18 was never bottom painted, always lift kept, so I assume [the hull interior foam was ] relatively dry.

Weights IN LBS
Hull 1250
E-TEC 380
Battery 50
Fuel 180
One adult 180

The breeze was slight. The tidal current was favorable. The boat ran very well.

The propeller was a VIPER 14 3/4 x 17-pitch.

This was a sea trial, so there was no anchor, no cooler, no lines, no chain, no gear.

jimh
Posts: 11869
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: 1986 OUTRAGE 18 Re-power

Postby jimh » Mon Apr 01, 2024 4:20 pm

Adding up the mentioned weights totals

1250 + 380 + 50 + 180 + 180 = 2040-lbs

which is extraordinarily light.

Adjusting the observed boat speed of 40-MPH speed over ground with favorable current of perhaps 4-MPH gives a speed through the water of 36-MPH.

Using the Crouch speed prediction method, for 115-HP, a Boston Whaler moderate V-hull coefficient of 180, and a boat speed of 36-MPH, the hull weight was probably closer to 2,875-lbs.

In any case, I am still very skeptical that an increase of 10-HP to 150-HP from 140-HP will add 8-MPH of increased boat speed.

Jefecinco
Posts: 1612
Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: 1986 OUTRAGE 18 Re-power

Postby Jefecinco » Tue Apr 02, 2024 10:22 am

A change in engine trim can have a significant effect on boat speed as can any change in engine mounting.
Butch