Tournament 307 - proper engine height?

[jlflynn1]

Just bought a 2009 307. First time Grady owner. Besides the marine inlet sea cock issue, I’ve noticed when I trim the engines down (3 clicks), I noticed they really kick up a lot of spray (more on port engine) and drench the side of the engine cover. When I trim up 6!or 7 clicks, no issue. However I am wondering what height other 307’s have their engines? My engines are about 7/8” off the transom. See video below of spray.

https://youtu.be/YqYqqh9_yoc

And pic below

 

[DennisG01]

Generally speaking, the anti-ventilation plate should be skimming across the surface when on plane. If your plate is buried, then it is too low.

 

[jlflynn1]

The plate does seem buried a bit....I would think that these engines would have been mounted correctly coming out of the factory....but with a first year model, maybe they made some adjustments the following year.

 

[DennisG01]

You're making an assumption, though, that a previous owner didn't mess with it. Raise them up a hole or two and experiment. IF the anti-vent plate is buried, you know that the engine is too low, for sure.

 

[glacierbaze]

Doesn’t look like any wear marks on the adjacent holes. I think that historically, most manufacturers mount the engine as low as it will go, and it’s in the ballpark, even if it’s not a homerun. Maybe there’s a safety issue or a liability issue. Next time you’re at a boat show, look to see where most of the engines are mounted.

 

[DennisG01]

Doesn’t look like any wear marks on the adjacent holes. I think that historically, most manufacturers mount the engine as low as it will go, and it’s in the ballpark, even if it’s not a homerun. Maybe there’s a safety issue or a liability issue. Next time you’re at a boat show, look to see where most of the engines are mounted.

Good catch.

Here's another "general" rule of thumb that you can easily check. For every 1' that the engine is mounted behind the end of the hull, the anti-vent plate should be mounted 1" higher. But again, this is just a general guideline.

 

[jlflynn1]

I took another pic of my engines cruising at 4400 32 mph at one click past half on the trim. It certainly looks like the vent plate is buried. I also noticed on my buddies 283 release his twin 250’s are mounted 1 hole higher than mine. Granted my beam is 1 foot wider. Nonetheless, I sent an email to Grady and am awaiting their recommendation.

 

[seasick]

The hole used is not an absolute reference. The initial rigging position, according to the Yamaha rigging guide::For planing boats, the anti-cavitation plate should be positioned to the boat transom bottom or slightly higher" ( for displacement hulls the cav plate should be even to 1 inch lower than the transom bottom edge at the center line of the motor)

Toe out should be checked too. One way to get an idea if your toeout is close to spec is to look at the wakes of the motors . The wakes should run into each other (merge) at about 25 to 50 feet behind the boat at cruise.
The settings of trim tabs can greatly affect the ride height of the boat/motor so just looking at where the cavplate is may not tell the complete story.Often fine tuning the tabs has more effect than raising or lowering the motors mounting hole. Finally, this is true especially for lighter and smaller hulls,when someone goes aft to look at the cav plate under speed, the added weight of that person can affect the plates depth.

The bottom line is that it is not easy to just look and determine if the mounting height is optimal. Although trial and error can help, it is a pain to have to readjust the mounting height.
The better approach is to ask similar boat owners what the measurement is from the cav plate to the bottom edge of the transom ( even, lower or higher and by how much) with the motors trimmed parallel to the transom. Find out what their goals on performance are, they may be different from yours. Perhaps hole shot performance is important, maybe its cruising efficiency. Ask what props are rigged and how happy the captain is with the setup.

 

[jlflynn1]

Thank you for the feedback Seasick....what does check for "toe out" mean?

As for the trim tabs, I assume you mean the Bennett tabs....I have them set at "0" for this test. No trim. Unless you mean the zinc trib tab just above the prop....(I think that is what it is called)

 

[DennisG01]

I'm sure Seasick meant "trim" tabs, not the anode.

Google "toe out" - you'll probably come up with references to tires, but it's the same idea. Think "the opposite of being pigeon toed".

There's too much splash going on in the picture, making it hard to tell. Did you look at the anti-vent plate height in relation to the hull as mentioned above? This will give you a good general idea. A straight edge off the hull bottom works well.

 

[seasick]

Thank you for the feedback Seasick....what does check for "toe out" mean?

As for the trim tabs, I assume you mean the Bennett tabs....I have them set at "0" for this test. No trim. Unless you mean the zinc trib tab just above the prop....(I think that is what it is called)

For twin motors, the usual setup is for the front of the motors to be slightly farther spaced to each other than the rear of the motors. In other words, the motors are angled in a bit towards each other at the rear. That setting is what causes the wakes to cross. If the motors are aligned straight to each other, the wakes look like two lines. If the motors are closer at the front, the wakes will diverge or spread out.

To check measure the distance from the center line of leading edge of the lower unit to the leading edge of the other motor.
Now measure the distance from the center line of the cavitation plate to the other cav plate. The second measurement should be a little shorter ( an inch or so)

 

[glacierbaze]

Old school method was to run straight down a smooth body of water at speed, and have a second person disconnect the motor that was not tied directly to the steering cable, or cylinder. The free motor would find its own track of least resistance, and you would adjust the linkage to that position, and reconnect.

 

[seasick]

Old school method was to run straight down a smooth body of water at speed, and have a second person disconnect the motor that was not tied directly to the steering cable, or cylinder. The free motor would find its own track of least resistance, and you would adjust the linkage to that position, and reconnect.

I have heard this before but to be honest, I would be scared to death to disconnect a motor linkage while under speed. I have searched for some scientific explanation as to why that method would work but haven't found one yet. If you know of any, please post a link.