1989 Outrage 22: Engine Mounting Height Change; Propeller Change

[Palomino]

I have a 1989 OUTRAGE 22 with a Yamaha F250 XB. The engine mounting height is the lowest possible position. The propeller pitch is 15. The boat has bottom paint and a T-top. During testing the boat had 80 gallons of fuel, two adult men, and heavy gear aboard. The maximum boat speed was 45 to 46-MPH with an engine speed of 6,000 to 6,200-RPM.

A recent boat trip was to go 30-miles offshore in seas of 4 to 6-foot height, which entailed 8-hours underway. The total distance was about 95-miles. The engine was run at full-throttle for 15-minutes. The fuel economy for that trip was 2.75-MPG.

FUTURE PLAN
I will change to a 17-pitch propeller and raise the engine mounting height to the highest possible position. I am told this should improve the fuel economy and increase maximum boat speed by 2 to 3-MPH.

[Moderator's note: this post was appended to a different discussion on another boat seeking advice on various engine combination for repowering, but had been inactive for over a year. The post has been moved to become its own separate discussion.]

[jimh]

I will...raise the engine mounting height to the highest possible position.

Until readers learn how many sets of holes are provided on your engine, your description of the engine mounting height is impossible for readers to interpret. Some engines have four sets of mounting holes, and other engines have five sets of holes. You should describe the new engine mounting position in terms of how many "holes" the engine will be mounted above lowest position.

[jimh]

A friend has a nice OUTRAGE 22 with a 300-HP E-TEC. It is a 52-MPH-or-faster boat. On that basis, your OUTRAGE 22 with 250-HP should be be able to hit about 47 to 48-MPH, or about 2-MPH faster than you are getting now.

[Palomino]

CLARIFICATION OF ENGINE MOUNTING HEIGHT CHANGE
The Yamaha [F250 XB engine transom mounting bracket] has four [sets of ] holes. I moved [the engine] up one hole. Now [the engine mounting height is] two-holes-up [from lowest possible position ].

PROPELLER CHANGE
I changed the propeller to an SST 17-pitch from an SST 15-pitch. The boat speed at wide-open throttle is now [around] 50 [unspecified units of speed but we will assume statute miles per hour, MPH], where before [with the 15-pitch propeller] it was between 45 and 46 [MPH*].

TEST CONDITIONS
[During testing on October 10, 2025 the boat speed was] 51.5 [MPH*] with 1,000-lbs of load including fuel, but there was a current. I [did not include the weight of the T-Top] in my [figure of] 1,000-lbs load.

FUEL ECONOMY
At wide-open throttle the fuel economy is 2-MPG.

At 38-MPH the fuel economy is 3-MPG [but this is] not a fair comparison [because my prior report of] 2.75 [MPG apparently with the 15-pitch propeller occurred] in the worst case [conditions, which were] four to six [feet tall] head seas [whereas the 3-MPG outcome occurred ] in the [unidentified waters referred to only as] the sound and [sea state was] light chop.

ENGINE SPEED
With the 15-pitch propeller [the engine speed at full throttle] was 6,000 [RPM*]. [With the] 17[-pitch propeller the engine speed is now] 5,750 [RPM*].

CAVITATION
There is no cavitation.

ACCELERATION
[The time for acceleration from a standing start at full throttle onto plane has decreased] noticeably, but it was already strong [before the change in propeller pitch].

[Moderator’s note: the asterisk indicates assumed speed dimensions where none were indicated.]

[Palomino]

B.D. helped me some with propeller selection using on-line chats. His engine is mounted all the way up [again, there is no way for readers to understand the engine mounting height when described this way].

[The experience of] operating [an OUTRAGE] 22 at [speeds over] 50 [MPH*] was interesting. My 18-footer [had boat speeds of] 48 to 49 [MPH*]. I felt more in control with the 18-footer than [I do now] with the 22-footer.

[jimh]

I [did not include the weight of the T-Top] in my [figure of] 1,000-lbs load.

The influence of a T-Top on maximum boat speed is not just from its added weight. The surface area of the T-Top creates drag from wind resistance, and the force of wind acting on a surface increases exponentially with wind speed. So the T-Top exerts a double penalty on boat speed.

There is no cavitation.

You probably are referring to propeller ventilation. Propeller cavitation is entirely different from propeller ventilation. The effect of cavitation on the propeller would be seen in the appearance of small corrosion on the propeller blades.

For more information on ventilation versus cavitation, see this presentation by Lenny Rudow on youTube at

Boating Tips: The Difference Between Cavitation and Ventilation
https://www.youtube.com/watch?v=5bj5kjh3l9o

[jimh]

In the initial post in this thread, the engine mounting height was described:

I have a 1989 OUTRAGE 22 with a Yamaha F250 XB. The engine mounting height is the lowest possible position.

In a follow-on post, the engine mounting height was changed, and the change was described as follows:

I moved [the engine] up one hole.

If you start at the lowest possible engine mounting height, and you raise the engine higher by one set of mounting holes, the engine mounting height position is now described as "one-hole-up." However, Palomino contradicts that by next saying:

Now [the engine mounting height is] two-holes-up [from lowest possible position ].

At this point, readers do not have a clear understanding of the engine mounting height.

In order to convey clearly to readers the engine mounting height, please use the terminology that is described in detail in a separate article, written nine years ago with the hope of preventing confusing statements about engine mounting height, at

Engine Mounting Height Nomenclature
https://continuouswave.com/forum/viewto ... ?f=7&t=739

When providing performance information, the value of the information decreases if there is ambiguity about important elements in the data. For a comprehensive summary of performance testing data that should be provided in order to give a full report about the observations, see

Template for Reporting Performance Data
https://continuouswave.com/forum/viewto ... f=7&t=9422