Outboard Tuning Question

I put a new to me tiller on my boat last summer and am unsure that I have it at the right height on the transom. Resulting from getting a new found rooster tail… Trimming the motor up after getting on plane, the rooster tail does diminish a little but is still present. I would have guessed that was a result of the motor being mounted too low on the transom.

It has been suggested to me that the cavatation plate should be about 1.5″ below the bottom of the transom.

Any guidelines for properly setting that up?

MT

Sounds low to me. I like to get mine set so at normal running speed with the motor trimmed to where it should be at speed, the cavitation plate is out of the water. Water hitting the bottom is good, water hitting the top is not. I had to raise my motor 2 holes to hit the sweet spot from where it was mounted by the dealer.

Be careful not to bend your transom when raising it.

The starting point is level with the bottom of the transom.

Where is it at now? I also set mine up level to just a touch high, though not as high as John but each boat is different.

This has a good explanation on motor height and has pictures of what it should and shouldn’t look like.

engine height

Great link John, I think that answered my question of the motor being a little low. The cav plate is roughly level with the bottom of the boat, and while running it is under more water than the link suggests.

When I raised my motor I gained about 200 RPM on the top end and about 1 mph. Not a huge difference, but the boat handles a lot better and my fuel consumption is lower. Not a lot lower, but enough to where I can see the difference on the fuel gauge.

I’ve noticed a number of these threads and I keep thinking to my particular situation when I read them. How do you go about raising the motor? Does the whole motor, mount, etc get raised? Doesn’t the “lip” of the motor need to rest on the transom of the boat? I am thinking my motor is a bit low, but don’t know how to go about adjusting it properly. The last thing I would like is my motor at the bottom of the lake.

The motor does not need to rest on top of the transom.

You can raise the motor using the trailer jack. Block the tires front and back. Lower the jack all the way. Put a block of wood under the skeg. Remove the top motor bolts and loosen the bottom ones enough that the motor can slide up and down. Raise the trailer jack until the top hole in the transom lines up with the motor hole you want to mount through. Clean the bolts and put new sealant on them. Install the bolts and add new sealant to the bottom bolts. Tighten the boats to the recommended torque. Done.

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The motor does not need to rest on top of the transom.

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If that is the case, I may take a look at adjusting the motor a little this spring. Thanks.

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The motor does not need to rest on top of the transom.

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If that is the case, I may take a look at adjusting the motor a little this spring. Thanks.

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Check where your motor bolts onto the transom. Years ago all motors had a slider on the bottom bolts but not anymore. Bigger Merc`s I know for sure don`t have the slide so all the bolts have to come out. That means the engine has to come completely loose from the transom so using the trailer jack does not work well. If you have enough people around to steady the motor then you can get by with it.

In my case, it is a 2003 Yamaha 115 4S on a 2002 Sylvan Excursion. Have been contemplating upgrading to a 150 but if moving the motor up a little improves performance a little, maybe I won’t.