Increased engine spray after engine raised

Optimizing the performance of Boston Whaler boats
coxmd
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Increased engine spray after engine raised

Postby coxmd » Mon Aug 22, 2022 11:25 pm

I have mounted a 2001 Yahama 90-HP two-stroke-power-cycle engine on my 1989 Montauk 17 at an engine mounting height of two-holes-up from the original mounting at lowest possible position. An engine mounting height of two-hole-up seems common for this boat-engine combination. The A-V plate is located about 1.5-inches above the hull bottom at the keel. When the boat is on plane at 22-MPH most of the A-V plate is above the water flow.

After the change in engine mounting height, an increase in V-shaped spray coming off the lower unit of the engine can be seen. There is a SONAR transducer mounted on the Starboard side of the transom, but the spray pattern is symmetrical.

From what I read online, the typical fix is to further raise my engine another mounting hole.

Q1: since I already have the AV-plate above water while on a plane, have I not already maximally raise the engine?

When on-plane I've trimmed the engine up to the point just before I hear increased ventilation. I never get to the point of porpoising.

Jefecinco
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Re: Increased engine spray after engine raised

Postby Jefecinco » Tue Aug 23, 2022 10:07 am

I recommend raising the engine one more hole. I've enjoyed bet performance when the A/V plate is virtually at the water when cruising on plane.

Since it requires little effort and no cost to raise the engine why not give it a try?
Butch

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Phil T
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Re: Increased engine spray after engine raised

Postby Phil T » Thu Aug 25, 2022 12:20 pm

Greg--I agree, go up one more hole.

Reshoot video. A few seconds longer next time.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

jimh
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Re: Increased engine spray after engine raised

Postby jimh » Fri Aug 26, 2022 9:52 am

coxmd wrote:Q1: since I already have the AV-plate above water while on a plane, have I not already maximally raise the engine?
To know when you have achieved the maximum generally requires enough experimentation to observe that the last change produced a reduction instead of an improvement in the outcome. You won't know if three-holes-up mounting height is better than two-holes-up mounting height until you try it.

The short motion picture view of the V-spray does not appear to show symmetry to me. More spray looks like it comes from the Starboard side of the transom, where the SONAR transducer is located.

I don't believe the goal in engine mounting height is to eliminate spray. The general goal in engine mounting height is to optimize boat speed and acceleration. Some spray from the leading edge of the gear case moving through the water is inevitable. The foil above the anti-ventilation plate is called the spray deflector. Perhaps on this particular engine the spray deflector is not doing its job.

If the performance goal is to achieve the maximum possible boat speed at full throttle in calm seas, then generally the higher the engine mounting the better, as long as the engine water cooling pressure is maintained at proper level.

For every boat there is a different pattern of use. In some cases, the boat is always used in protected and calm water. If the boat is used in rough water and large waves, a very high engine mounting height may not be the optimum.

coxmd
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Re: Increased engine spray after engine raised

Postby coxmd » Sat Aug 27, 2022 10:56 pm

Jefecinco wrote:I recommend raising the engine one more hole.
You called out my laziness, I pulled out the Harbor Freight engine hoist and raised it "all the way up", to three-holes-up, which looks unusually high after being used to seeing the engine mounted all-the-way-down for so many years.

LINK to photo

Phil T wrote:Reshoot video. A few seconds longer next time.
New videos:

The A-V plate is now fully clear of the water. Appreciate the spray on starboard side is absent on port side: https://photos.app.goo.gl/LVxRkk4sFmUhvf8K7

Spray is now only on the starboard side, presumably from the transducer; to capture the spray pattern in the recording is difficult: https://photos.app.goo.gl/xJEQrBF18V4f3HW16

jimh wrote:For every boat there is a different pattern of use. In some cases, the boat is always used in protected and calm water. If the boat is used in rough water and large waves, a very high engine mounting height may not be the optimum.
This is part of my struggle. I use my boat on both the Connecticut River (which can be smooth and pond or lake-like) and on Long Island Sound which typically six-inch to one-foot chop, but can have larger seas with storms. For now I've optimized for calm conditions, and I'll have to see if excessive ventilation occurs in rougher conditions. The nice thing for now is that I used all the resources from this site and properly created new holes that will allow me to drop the engine back to two-hole-up mounting without much fuss.

Thanks all for your help.

Now to address my excessively deep SONAR transducer mounting.

jimh
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Re: Increased engine spray after engine raised

Postby jimh » Sun Aug 28, 2022 7:12 am

Re the SONAR transducer mounting as seen in your very clear photograph: the transducer is too low. For a bit of advice on transducer mounting see:

SONAR Transducers
https://continuouswave.com/whaler/reference/sonarTransducer.html

Re the engine mounting at three-holes-up and the position of the Anti-Ventilation plate relative to the water flow as seen in your most recent recording: the A-V plate looks great. As long as you don't have problems with the propeller ventilating in rough seas, you should be done adjusting engine mounting height.

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Phil T
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Re: Increased engine spray after engine raised

Postby Phil T » Sun Aug 28, 2022 11:22 am

C -

You are really close.

The boat wake is nice and flat with minimal spray. Excellent. I think you have nailed it.

As for the 'ducer. It is not terrible. While you can play with it a bit, I think it is reasonable.

As for ocean conditions, you are, again, on track.. See how the boat handles in the snot. You may need/want to go down one hole just to ensure good grip and eliminate ventilation. (Another excuse to spend hours out on the boat)

When rigging my 1991 Outrage 17, I raised the engine to "3-holes up" but lowered it to "2-holes up" due to ventilation in high speed sweeping turns when in swells.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003