Engine mounted too low?

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#1
95 Adventure 208
05 Yamaha F200

I think my engine is mounted too low. I've posted before about my top speed being not what others are getting. The anticavitation plate is underwater. In the picture we were going about 24-26 KTS at 4500 RPM. I didn't think to get a picture while we were sitting still...

Also, is this a known issue about engine height on these boats? This boat used to come with a 150 2 stroke, now I have a 200 4 stroke. If they used the same mounting height, couldn't that throw off how the boat performs with the added weight to the rear? Just a thought.
 

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Ky Grady

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#2
I think you're headed in the right direction. Cav plate should be about an inch higher than the bottom of hull when trimmed straight up and down. Grady rigging is usually second hole down from top. On my 228 with bracket I'm top hole on bracket and 3rd hole on motor and this combination works well. SmokyMountainGrady raised his one hole and helped with his performance on his 4.2 F250, he was re-rigged in top hole which was too low.
 

SmokyMtnGrady

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Hey Lt, I gained about 100 RPM on the top end. I also noticed slightly better midrange RPM and less drag. My motor keel is mostly out of the water when trimmed all the way up. Grady says hole 2 so it's what we did.
 

Lt.Mike

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#6
Hey Lt, I gained about 100 RPM on the top end. I also noticed slightly better midrange RPM and less drag. My motor keel is mostly out of the water when trimmed all the way up. Grady says hole 2 so it's what we did.
What did that work out in total wot speed increase? Did you notice and tendency to blowout easier when trimmed?
Just asking now as down the road I’m sure at some time to encounter an issue that this info will help with.
Thanks!
 
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#7
Do you think the added weight of a 4 stroke has any effect on this? Would 200 lbs of front ballast be an option or something worth looking into? I've been a lake boat guy all my life and that's always a solution to right the boat for a skier or wakeboarder.
 

seasick

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#8
Do you think the added weight of a 4 stroke has any effect on this? Would 200 lbs of front ballast be an option or something worth looking into? I've been a lake boat guy all my life and that's always a solution to right the boat for a skier or wakeboarder.
The added weight will make a difference. You would see that at rest where the stern sits lower and maybe even the scuppers are at or below the water line. Most likely when you stand aft and look over the transom, the scuppers may be partially submerged The weight also affect the angle of the hull and trimming ability may be limited. On later year 208s you will see that at one point the dry hull weight increased by about 200 pounds. It is suspected that was due to ballast added up front to compensate for the added motor weight. Since the hull sit a tad lower, more area is in contact with the water and that adds drag and drag saps thrust.
The added weight also needs extra horse power to match the 2 stroke motors. A 200hp 4s will equate in performance (speed) to the older 150 2s.

The early F200s also have different torque curves and you may notice that the time to plane takes longer than with the 2s. If top end is not your goal but low end performance is, a 4 blade prop will probably help.
 
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SkunkBoat

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#9
hmmm....motor is bolted to a 25" transom....same holes....same 25" shaft length....
distance is the same regardless of weight...
On plane- the water is at the keel level regardless of motor or horsepower
Unless the distance of the cavitation plate is physically lower than the old motor's, I don't see how the old motor didn't look the same as the picture ...when on plane.


hmmmm....unless a bracket set back from the keel throws that thought in the garbage...hmmm.....


don't mind me...I got lost thinking.....
 

SmokyMtnGrady

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#10
I called Grady when I repowered. Actually, KY visited my house noticed my motor was mounted on the top hole position by the installing dealer. I could never get it to reach more than 5400 RPM. KY noted to me his 3.3 liter 225 was in the 3rd hole. So, I researched it. When Grady installs the 4.2 liter f250 on the bracket they install it on the 2nd hole down from the top. Based on that data I moved my motor 1 hole up.

The lesson here is Grady White customer service will be glad to help you figure this out too. They still make your boat and I would ask their opinion or should say professional engineering advice as the builder what would they do, you know WWGWD. Lol.
 

seasick

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#11
One interesting fact that I stumbled into regarding the bolt hole locations is that the ABYC specs state that the first hole (highest) should be 1 7/8 inches below the cap plate. The spacing on the motor holes are usually 3/4 apart but I don't know if that is a standard.
 

seasick

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#13
A couple of things to note about the original photo.
Just the fact that you have leaned over the back to take that picture will push the motor lower into the water. Therefore the photo may not truly represent the running conditions
Secondly, the added weight of that 4 stroke will also push the motor lower but keep in mind that the cav plate height relative to the hull plane doesn't change. If you move the motor higher, you may run into a situation where the water flow to the prop is reduced since in effect the transom may be partially disturbing that flow.

Physics is physics. If you add weight, the hull will sit lower but not necessarily the same across its length. The bow will actually sit higher and the aft lower that it did before the motor change
Before moving the motor, play with the motor trim at different speeds to see if there is a sweet angle for your hull. Adjusting trim tabs will help also.

Adding ballast up front would correct some of the hull angle issues but adding weight will add drag and that will affect the performance specs..