Anti cavitation plate is lower than the, "Keel" 2" is this OK?

[AllenMercury45]

Hi, I have a 1969 Glastron 15' boat, With a 1960 45 Hp Outboard, the lower unit has an addapter kit on it that is 6" long. It came off of a Pontoon boat. I bought it this way. The Anticavitation plate is about 2" lower than the bottom of the transom. It works OK, but puts out quite a Roster tail. It looks cool, but , I dont know if it's OK to run it like that. I feel it might be causing quite a bit of drag on the lower unit, and don't want to put the stress on the transom, or with Gas being so expensive these days I dont want to spend more for that of course either. Should I install a,"spacer" , to bring the motor up, to get the anticavition plate aligned with the Keel?
Thanks for any input concerning this.
A M 45

 

[64osby]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

If you could post a picture that would help.

But from everything I know and have learned here, the anti cavitation plate should be about 1" above the bottom of the boat as a starting point. Having a 6" adaptor might not allow you to move the motor up high enough.

And yes it sounds like your stressing something.

 

[wire2]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

I've had 2 o/b's, and 2 i/o's, all of them had the anti-cav plate lined up perfectly with the keel. That rooster tail looks flashy but that's lost thrust. You're losing efficiency and speed. So there's actually less force on the transom.

 

[Home Cookin']

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

it won't do any damage; it's just not efficient. Consider replacing the motor instead of cracking open one that is 50+ years old.

 

[metriccrescentwrench]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

I'd call what you're seeing "spray" rather than a rooster tail (which is produced when the prop pierces the surface of the water - typical on higer performance hulls - watch drag boat racing on TV if you ever get the chance). You're not damaging or stressing anything, just costing yourself speed due to increased drag. The prop puts forward force on the lower unit, the increased drag is basically acting directly opposite the thrust which just results in less force being applied in the forward direction. I also agree with the suggestion to consider a different engine. OR ... maybe look into a jack plate.

 

[Chris1956]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

Can you raise it 2" on the transom, and still bolt it to the transom? The antivenitlation plate whould be even with the base of the hull.

 

[JB]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

As the members say above, the plate should be about 1" above the bottom.

BTW, It is correctly called the anti-ventilation plate. It has no effect on cavitation; that is a prop condition issue.

Good luck.

 

[BF]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

With an old 1960 motor, it could well have a water pickup above the plate (the newer ones are below), and probably in the leading edge of the exhaust flange behind the prop. My old short shaft OB's measure about 18" from the inside of the transom clamp to the anti-ventilation plate. That is the correct length and puts the av plate below the keel, and the side water pickup in the water when on plane. But, for my 25 hp, if I don't shim the motor up 1/4-1/2", it does spray a bit up to the sides. With a shim, the plate & water pickup are still in the water on plane.

Since your motor sounds like a "long shaft" version with the extension, I imagine it's made for a 20" transom... since it doesn't sound like it's 5" long, I'd guess your boat also has a 20" transom.

If I'm right, I don't think you'd want to lift the engine that much (3")... but a little (try 1/2") would probably do the trick for the spray.

 

[steelespike]

Re: Anti cavitation plate is lower than the, "Keel" 2" is this OK?

1960 45 hp must be a West Bend or McCulloch?
As it is it's just a little inefficient.Your motor will use about 4.5 gallons per hour at wot(wide open throttle).whether pushing a house boat or a race boat.The key to fuel savings is speed;the faster you get from here to there the less fuel you will use.Just being able to raise the motor 2 to 3 inches could add 2 to 3 mph under ideal conditions.It would also likerly improve handling.
If the motor was correctly propped for the pontoon it will need to be propped for the Glasstron.
If the prop is wrong you could ruin the motor.