How to determine proper engine height?

[G8RDave]

I have a 2004 228 with an F225 (see sig). My Yamaha Fuel management system shows that my best mpg to be between 2.4 and 2.7. The Grady White performance data says it should be 3.6ish. Granted I have a hard top and I never boat in glass smooth seas, but still. I'm wondering if my motor is mounted a hole or two too low. Is there anyway to check without actually moving the motor from hole to hole? Where does everyone else have theirs placed? Prop is the factory 17M stainless. WOT trimmed out hits 6000rpms and about 43 mph. With gas prices going up so much every bit matters. Plus, I'd like the extra range in case I ever decide to motor down to the Dry Tortugas.

 

[BobP]

Is the boat on a trailer?

Get a staight edge and place it along the engine's anti-cav plate, like you are extending it to the hull, where does it meet the hull, height wise?

 

[G8RDave]

Yes, its on a trailer. I'll measure when I get home and post. If I recall correctly the plate should be one inch higher for every foot back from the transom, right?

 

[gw204]

Yes, its on a trailer. I'll measure when I get home and post. If I recall correctly the plate should be one inch higher for every foot back from the transom, right?

Yep, that's a good starting point.

The plates on my engines are about 1.5" inches above the hull bottom using the OEM bracket and that seems just about right. I had a friend watch them while running in a heavy following sea and he told me any higher and I would probably start blowing out.

 

[BobP]

Do this measurement when the straight edge is parallel to the keel, by trimming motor.

You may have to run a second straight edge off the the keel too, and see how the two are spaced apart, to be sure you are parallel. I guess you can also use a bubble level comparison, anticav plate vs. keel. I prefer the straight edge for this measurement.

For guys with twns, the hull reference is not keel, it's directly in front of respective engine.

 

[G8RDave]

Kinda hard to get exact measurements due to where my boat is stored, but it looks like the leading edge of the outdrive is 39 inches from the transom when the anti-cav plate is parallel with the keel and the anti-cav is 2 1/2 inches higher than the keel. Seems like it might be a bit low. Here are some pictures of how it is currently mounted.

How tough is it to raise it one hole? Will it really make any difference? Any draw backs? I've never had any issues with breaking loose even when trimmed all the way out (within reason of course).

Thanks!

 

[Curmudgeon]

If you're on a bracket, forget about any keel measurements. If you can turn sharply without "blowing out" the prop (RPM takes off with obvious loss of propulsion), it's not likely you're too high. Take the boat out with a helper and get it up to cruising speed, then look at the lower unit. The horizontal plate (some call it cavitation) should be "on top" of the water and only get splashed some. If it's not, you have room to raise it up. My Tournament 22/Honda 225 is setup with a "space" between the plate and water, and it will only blow out when lightly loaded and executing a max performance turn.

I wouldn't put too much emphasis on Grady performance numbers unless you can actually duplicate their conditions. Your T-top adds a good deal of weight and a ton of wind resistence ... :wink:

 

[JUST-IN-TIME]

I have a 2004 228 with an F225 (see sig). My Yamaha Fuel management system shows that my best mpg to be between 2.4 and 2.7. The Grady White performance data says it should be 3.6ish. Granted I have a hard top and I never boat in glass smooth seas, but still. I'm wondering if my motor is mounted a hole or two too low. Is there anyway to check without actually moving the motor from hole to hole? Where does everyone else have theirs placed? Prop is the factory 17M stainless. WOT trimmed out hits 6000rpms and about 43 mph. With gas prices going up so much every bit matters. Plus, I'd like the extra range in case I ever decide to motor down to the Dry Tortugas.

prop her to 58-5900 MAX!!!

yamis love 38-4100K

sux than yami never made a 18" prop