1995 Outrage 24 Engine Mounting Height

Optimizing the performance of Boston Whaler boats
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Acassidy
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Location: Galveston, Texas

1995 Outrage 24 Engine Mounting Height

Postby Acassidy » Thu Jul 11, 2019 12:34 am

A 1995 Outrage 24 has a 2003 Yamaha 250 HPDI 30-inch-shaft engine. The engine is mounted at the lowest mounting position available. The person I bought the outboard from insisted on it being mounted as low as possible.

Using a straight edge to get the measurement, and with the [anti-ventilation] plate trimmed parallel to the hull bottom pad, the plate is 3-inches below the boat bottom;

I am borrowing a engine hoist and will lift up the outboard.

Four sets of mounting holes are available. If I understand correctly the vertical separation is 3/4-inch for each hole set.

By this math it seems like this Yamaha is very long for this boat.

The bottom of the hull is a rounded pad not a sharp Vee.

Q1: Should I move up the engine two holes (1-1/2-inch) making the [anti-ventilation] plate about 1-1/2-inch under the bottom?

Q2: Should I instead move up the engine three-holes making it at its highest position and putting the cavitation plate about 3/4-inch below the boat?

Q3: For anyone with c.1995 OUTRAGE 24 with a single (Yamaha) [30-inch shaft]engine: what is the engine mounting height?

Maybe I am measuring something wrong. Once I go to move the outboard I will measure it again to make sure.

My thoughts are that this is a heavy boat and is designed to make the outboard run deep and maybe I should embrace this fact and let it run deep and move the engine [to be mounted at two-holes up].

The propeller is a four-bladed aluminum Mercury-style 17-pItch. Top boat speed is 37- MPH at engine speed of 5,500-RPM. I am running this propeller as I add hours to the engine after the rebuild two-years ago. I am planning to put on a MIRAGE 17 propeller. I have MIRAGE 19. I plan to test propellers after I move up the engine mounting height.

The engine gear case is very deep while running, and I know the engine mounting height needs to come up.

This 2003 Yamaha 250 HPDI engine seems to be running very strong. I think the current [aluminum four-blade “Mercury-style 17-pitch] 14-1/2-inch diameter propeller is too small diameter, giving me poor efficiency.

The Mirage is 15-inch diameter and will be much better. Again, I have been using this [aluminum four-blade “Mercury-style 17-pitch] propeller to make it easier on the engine during break-in after the rebuild.

I really would like to move the engine mounting height once and be done.

Thanks for any help with this.
Archie

flymo
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Re: Outboard mounting height 1995 Outrage 24'

Postby flymo » Thu Jul 11, 2019 6:08 am

I am no expert on that boat, but your detailed measurements make it clear your engine is mounted way too low. I'm guessing your boat was designed for a 25" shaft engine, but I don't know for sure. In general, you want the AV plate somewhere around an inch above the keel.

In any case, best you can do right now is to raise it as high as you can. That will still leave you too low, but it will be much better than the current setup. I expect you'll find a huge difference in performance - the boat should get a bit faster, and the steering should be much lighter and more responsive. I don't know what your redline is on that engine but you may end up needing that 19-pitch prop.

Barring getting a new engine, you may eventually want to consider getting a jackplate to let you go up even more. A manual jackplate is not too expensive and will give you lots of flexibility.

Good luck, and please report how you make out with the changes.

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Phil T
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Re: Outboard mounting height 1995 Outrage 24'

Postby Phil T » Thu Jul 11, 2019 11:28 am

According to the specification sheet from Boston Whaler, the 1995 Outrage 24 does take a XXL, or 30", shaft.

As for your measurements, are you measuring down to the flat plate that is just above the prop and where the trim anode is installed? If so, has the transom been cut down? Would a photo help explain this?

Your target is to have the anti-cavitation plate to be 1 1/2- 2" above the bottom of the keel. Typically this translates to one or two holes up. This is also shown as follows:

top set of holes
0 <----"all the way down
0 <---- bolt here for 1 hole up
0 <---- bolt here for 2 holes up
0 <---- bolt here for 3 holes up

I would go for 2 holes up.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

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Acassidy
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Joined: Sat Nov 14, 2015 10:25 pm
Location: Galveston, Texas

Re: Outboard mounting height 1995 Outrage 24'

Postby Acassidy » Fri Jul 19, 2019 1:02 am

I plan to move the outboard this weekend. I borrowed a motor lift from a local fellow Whaler owner and I will move the boat to a flat surface to do the move.

The transom has not been altered in an way. It is all original. I was measuring down to [the hull bottom from] the top of the plate above the propeller where the anode is.

I measured the transom straight down and it looks to be just short of 30" (like 28-29 inches) and the outboard looks to be just a little longer than 30 inches. It is very difficult to measure the transom because the outboard is in the way.

Before I do the move I plan to measure it all again.

I may end up getting a manual jackplate in the future.

What are thoughts on sealant?

I used 4200 last time I installed it but am thinking Boatlife sealant for the reinstall.

What is the torque for the bolts and nut when I tighten them?

I am using Yamaha OEM mounting bolts.

Thanks again
Archie

jimh
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Re: 1995 Outrage 24 Engine Mounting Height

Postby jimh » Fri Jul 19, 2019 7:37 am

If the transom is designed for a 30-inch-shaft engine, and your engine is a 30-inch/shaft model, and if you want to change the engine mounting height only once, then you should probably move the engine to a two-holes-up mounting height from its present lowest-possible mounting height.

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Phil T
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Re: 1995 Outrage 24 Engine Mounting Height

Postby Phil T » Fri Jul 19, 2019 10:10 am

I never use 4200 or an adhesive. Always a sealant.

My preference is Boat Life brand.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115