Cav plate height for Zodiac Mk4

[Projectile]

Over on the Evinrude owner's forum, I've received posts from one of the moderators who is an Evinrude dealer that confirm that ETECs tend to have shafts that are up to or around 2 inches longer than the standard 15 inch length for short shaft and 20 inch length for long shaft. He's even posted photos of an ETEC 40 that had twisty clamps to secure the engine to the transom that were removed because that engine had to be bolted so much higher on the transom that they were useless.

As much as I love the way this ETEC 30 looks, weighs, and runs, this shaft length discrepancy is a real PITA. I specifically chose a smaller engine to be able to use those twisty clamps rather than bolting the engine to the transom (among other reasons, too).

[Projectile]

Raised it a little over half an inch ... made a little bit of difference, but bow still plows in and bow steers as I accelerate beyond a slow plane. I guess I shouldn't have expected much since the cav plate was 3 inches below the transom to begin with...

There's a little over a quarter inch of potential engine raising to go before the clamps won't fit on the mounting plate. I doubt that will make *the* difference.

It looks like I'm going to have to bite the bullet and try bolting this engine to the transom, but what if that height isn't appropriate? D'you just keep drilling holes?

[camelgas]

you can buy a height adjustable mounting plate that only needs one set of holes. cannot think exactly where I saw it advertized now.

[Peter_C]

Originally Posted by Projectile

bow still plows in and bow steers as I accelerate beyond a slow plane.

To me that sounds more like a trim issue. Let the engine trim "up" a little by have it move away from the stern of the boat. It will cause the bow to rise more too. Kept further under the boat trimmed in the bow will be forced down. There are many situations where bow down is good. Power trim is very nice to have but rare on small boats.

I believe the poster above is taking about jack plates.

[SIBRider]

This is about simpliest solution Mini Jacker
150lb weight limit though but you can still use clamps.

They have better options: Manual Jack Plates, CMC Manual Jack Plate, Manual Boat Jack Plates | T-H Marine but that's going to be bolt on. Although I don't see much problem bolting on piece of 1" plywood then using clamps.

I certainly have similar issue as projectile with my F470 I'm going to try one of the later.

[camelgas]

Thats the ones i was thinking of in the second link. As they are fully adjustable only one set of holes in the transom are needed, after this it should be easy to set up the motor height.

[Projectile]

Thanks, Peter_C, but I've tried all of the trim positions available. As I trim the engine away from the transom, the problem gets slightly better (but still horrible), and is then replaced by severe cavitation, so there must be more to it than that.

[SIBRider]

Originally Posted by camelgas

Thats the ones i was thinking of in the second link. As they are fully adjustable only one set of holes in the transom are needed, after this it should be easy to set up the motor height.

Been thinking about it more. On concern is with 18" transom motor need to be offset back quite ways 4"+ for sure otherwise clamps will rest of top transom. Not sure if it's such a good idea to push mount so far back. Will increase cantilever load considerably.
Back to drawing board.

[camelgas]

The motor clamps will end up at least 1.1/2 " above the top of the transom, so only minimal offset backwards would be needed.

[SIBRider]

My cav plate is 3" below transom. Clamps center are about 2" below mount. Add for some material around it's prob about 3". So the practically be resting if not offset far enough. I wouldn't be able to move down if need to. Most of jack plates you can buy offset 4" or more back anyway.

[camelgas]

so why not remove the hand clamps and bolt the motor directly to the jack plate that has the least offset backwards that you can find ?.

I cannot see that 3 to 4" backwards is a problem in this case.

[SIBRider]

Originally Posted by camelgas

so why not remove the hand clamps and bolt the motor directly to the jack plate that has the least offset backwards that you can find ?.

Well I suppose I could take out screws but not C-clamps themselves. Later are integral part of motor mount. Guess could cut them off but that's a bit extreme toward brand new motor. C-clamps reach about 4" forward and 3" down from mounting surfaces. Even screws don't look to be setup for easy removal. Handle and the cup are held in with flaring of shaft (again drill out/cut-off)

I cannot see that 3 to 4" backwards is a problem in this case.

Maybe but it's not a rib so shifting weight of motor back 4"+ will definitely change stress pattern on glued parts. May not matter don't know. Don't wan't to discover it was a bad idea somewhere far off-shore though.

[Projectile]

My dealer expertly built up my transom 2 inches with a large black steel plate. I was very pleased with the look and finish.

Unfortunately,though the problem is a little bit better, as I accelerate from a plane, the bow still digs down and I get lots of spray from the sides of the boat and she bow-steers to the left and right. It's impossible to get the boat to go straight. So though it is a little bit better, it's still a huge problem.

Plus ... get this ... now my engine cavitates/ventilates just going in a straight line on a slow plane and immediately as I make the slightest turn.

So the motor has been raised so much that it's cavitating/ventilating, and the bow-steering problem is not solved, which tells me that this is an inherent design flaw in the boat and not due to transom-length/motor-shaft-length mismatch.

My dealer could take out the plate that was used to raised the top of the transom and place it an inch lower. That would probably get rid of the cavitation/ventilation, but to what end? The boat is no fun with the bow steering problem.

(And yes, the boat and keel are properly inflated, changing the trim pin position doesn't help, and there is no weight in the boat to distribute, to anybody who might want to bring those up again as possible explanations/solutions)

[Locozodiac]

Hi Proyectile,

Sorry to read you still have severe tech issues with that boat/engine combo. Running lightly loaded or solo is probably what the sib doesn't like at all. Probably much confy fully loaded with max HP engine. Go boating with your dealer so to know that model seems to have too many flaw design issues.

Happy Boating

[Peter_C]

Originally Posted by Projectile

Unfortunately,though the problem is a little bit better, as I accelerate from a plane, the bow still digs down and I get lots of spray from the sides of the boat and she bow-steers to the left and right.

~ changing the trim pin position doesn't help, and there is no weight in the boat to distribute, to anybody who might want to bring those up again as possible explanations/solutions)

Every boat I have ever owned or driven that had adjustable trim made a dramatic effect on bow rise. With a motor heavily trimmed up the bow should fly high in the air. Do you have a new picture showing engine height of the cavitation plate to the bottom of the boat, and also a side picture showing the trim setting?

[Projectile]

Peter_C,

Before I raised the motor, trimming the engine back would raise the bow out of the water when accelerating to a plane considerably. I needed much more throttle to get the bow to come down to a plane. But once it planed, the bow would still get pushed down as I accelerated beyond planing speed, and the engine would start to cavitate because it was trimmed so far back that the back end of the cav plate was at or above the water.

Since raising the motor, it cavitates in a straight line with the trim position all the way down. Trimming back will only make it cavitate *even more*.

I can send you a picture, but what it will show is that my cav plate is about 3/4 inch below the bottom of the transom trimmed all the way down.

[Projectile]

Originally Posted by Locozodiac

Hi Proyectile,

Sorry to read you still have severe tech issues with that boat/engine combo. Running lightly loaded or solo is probably what the sib doesn't like at all. Probably much confy fully loaded with max HP engine. Go boating with your dealer so to know that model seems to have too many flaw design issues.

Happy Boating

Thanks, Loco.

I will not sell this boat to an unsuspecting buyer on the second hand market and pass this problem onto them. That would be the wrong thing to do.

I am hoping that Zodiac and/or Defender will help to to arrive at a solution.

[simsy]

Sounds like the full length of the keel of the boat is concave, making the water suck the boat down when at speed.

[rigi36]

It's not a cavitation plate

[bartiny]

Originally Posted by rigi36

It's not a cavitation plate

Just an "observer" on this thread but;

does it matter what people call it we all know "where it is and what it does"