Engine height... Excessive spray from right and left of the engine.

jhetrick55

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I have a 100hp 1972 johnson that I think may be sitting too low on my boat. There seems to be excessive spray both right and left of the engine especially at cruising speeds (20-30mph). I tried attaching some pics, not sure if it's working. The cavitation plate seems to be about an inch below the hull. Is that typically where it should be? Seems like it maybe should be in the neighborhood of an inch above the bottom..
 
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jimmbo

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That combo, you could raise the engine(your drop-in brackets should be the ones with multiple holes) so the Anti-Ventilation Plate is flush with the Hull bottom, when it is Parallel to it. If you are running a prop with cupping and/or higher Rake, you could even raise it further, but it might ventilate while getting over the hump onto plane, and Power Trim was offered on that engine, do trimming in on take off isn't an option. Speaking of which, which hole do you have the Tilt Pin in? Having it in too close to the boat can cause a lot of spray, as the AV plate is making a Trough/Trench in the water
 

Joe Reeves

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Sighting the engine and rig on a trailer... the cavitation plate should be parallel with the keel.

The cavitation plate should be approximately 1/2" to 3/4" below the keel at the transom... not to exceed 1".
 

Sea Rider

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Post a pic of lower leg shot sideways showing both horizontal plates...

Happy Boating
 

oldboat1

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Maybe a transducer kicking up spray on one side, speedo pickup on the other?
 

jhetrick55

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Thanks for the input, everyone. Sorry for the delay. Yesterday we adopted our son, Nicholas, so I have been a bit busy. The transducer and speedo pickup are on the same side of the boat, so I don't believe that is the issue. I finally did get some pictures of the engine height from before I moved the cavitation plate even with the keel. I don't have any pics with it even, but I know it is even. Gonna give that position a try for a bit and see what happens. If worse comes to worse, I will try another position.
 

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Sea Rider

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Have you checked the lower leg side water splash by looking out transom at wot ? If not, how have you determined so ?

Check this out :

If rear hull is clean while water flow exits flat out at speed, the only possible way to achieve side splashes is when water flow bangs/skims lightly above the upper water def plate (X) side seen on pic, If that's so, raise the motor one notch and test again, visually check if the splash has gone.

That setting it's ideal for top water performance when having deck load evenly distributed and motor trimmed right for combo to ride parallel to water surface at wot. Motor, prop must be in top operation to achieve said condition.

Ideal LU-Transom Height.JPG

If water flow skims right under or very near the (yellow line) much better, best prop thrust on any water cond. From a spot on LU/transom height optimization can go straight to a prop maximization if wanting to better anything boating you're not plainly satisfied with. Report your findings...

Happy Boating
 

jimmbo

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If water flow skims right under or very near the (yellow line) much better, best prop thrust on any water cond. From a spot on LU/transom height optimization can go straight to a prop maximization if wanting to better anything boating you're not plainly satisfied with. Report your findings...

Happy Boating

What?!

If water is anywhere near the yellow line at speed, the engine would need raising about 3 inches. Those Slots/slits you are calling 'Exhaust Ports', are the Water Discharge/Drain Ports.

To the OP. You could raise the engine an inch, if using a Cupped AL prop, or 2 inches if using a SS
 

Sea Rider

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What?!

If water is anywhere near the yellow line at speed, the engine would need raising about 3 inches. Those Slots/slits you are calling 'Exhaust Ports', are the Water Discharge/Drain Ports.

Really, what's the problem if being exhaust or water discharge ports ? Both needs to be covered with water under the yellow line, if exposed flow will pass very near AV plate, on rough water cond, tight close turns prop will aerate. To me those ports are relief exhaust ones, if air exposed motor sound will be highly increased while prop aerates as mentioned.

Just sit motor a bit higher till the splash stops and voila!!!

Happy Boating
 

oldboat1

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And to confuse things further -- the water pump is about where the X is. At slow speeds or idling in neutral, the water depth should be safely above that point (probably fine with the current engine height imo).
 

jhetrick55

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I seem to have made sense of the posts ;). What I did was raise the engine about an inch. Everything that needs to be covered is covered and on my last trip out two days ago, no more side splashing. I'll keep an eye on everything but for now the issue seems to be gone. Next time out I will get more pics of how it sits in the water and running WOT as well.
 

Sea Rider

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Was just a matter of sitting the motor at a larger transom height. Check if at the new current motor height the prop doesn't aerate on choppy, windy water cond and at tight close turns at speed... How many holes up were needed to achieve one inch higher from previous setting ?

Happy Boating
 

Joe Reeves

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I seem to have made sense of the posts ;). What I did was raise the engine about an inch. Everything that needs to be covered is covered and on my last trip out two days ago, no more side splashing. I'll keep an eye on everything but for now the issue seems to be gone. Next time out I will get more pics of how it sits in the water and running WOT as well.

There'ya go!... Good for you. :)

One thing you should do though..... That model has a two wire warning horn which serves one purpose only... to blare out steady and constant if the engine starts to overheats. The easy test to make sure that warning horn is active is to ground out that overheat sensor, the TAN wire you see sticking out of the cylinder head, then turn the key to the ON (engine NOT running). That small act should make the warning horn sound loudly,

NOTE that the warning horn sounds before the engine actually overheats... but if it is ignored beyond that... well suffice to say that's not a good idea! :)

Let us know if all is well.
 

Faztbullet

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Both needs to be covered with water under the yellow line, if exposed flow will pass very near AV plate, on rough water cond, tight close turns prop will aerate.
No Sea ..does not need covered or cause any aeration problems.
jhetrick55 glad your on the water and fixed...
 

jhetrick55

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So, I moved the engine up three holes. Forgot to get pictures, but ran it a bit this weekend and still the same good results. I haven't tested the overheat sensor but again, ran this weekend with no issues. Thanks for the help, everyone!
 

Joe Reeves

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Jhetrick55... Just as an after-thought, those holes just above and to the rear portion of the anti cavitation plate..... They're not exhaust holes. That is the thermostat relief port. Nothing comes out those holes until the thermostat opens, then water flows out those holes. Watch those holes sometime when you're running on a flushette... very easy to tell when the thermostat opens,or is stuck shut... or open.

The exhaust relief port(s) are the two holes at the top rear portion of the long exhaust housing between the powerhead & lower unit. There is another (inner) exhaust within that long housing of which water fills between the two, and those two holes allow the excess to escape so as to prevent water entering the powerhead. Without that cooling water between the two housings, that paint job would be burnt off on the engine first run-out.
 

Sea Rider

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No Sea ..does not need covered or cause any aeration problems.
jhetrick55 glad your on the water and fixed...

Sorry Faz, will never know as OP has not raised his motor ENOUGH for flow to skim right above AV plate. Lower leg should be tested on rough water cond along tight turns at speed to determine if with prop eareation or not so your comment is useless as the OP has already solved the splash issue...

Happy Boating
 

jhetrick55

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Well, let's settle down a bit :). I did run the boat over the weekend and did have some rough water and did plenty of turns. Boat ran as well as it has since I've had her and no longer have an issue with water spray right and left. Again, wish I remembered pictures and/or video, but I had such a good time with a boat seemingly running great that I spaced it.
 

Faztbullet

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Need to learn your engines and how they function Sea....OP said three holes, that will put AV plate close to level with bottom of hull where it should be...
 
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