1973 20' CC Transom woes

[pianewman]

I've found a shop in the VA. Bch area (Coastal Fiberglass) to replace the transom, for much less than FL, and I can keep the boat closer to me. (I may not give it back to my 88-year-old dad, for many reasons, some of then quite selfish!) The repair person and I were examining the boat yesterday, and he commented that "No dealer should have hung that motor on there w/o checking the transom. It's in terrible shape", as he tapped and demonstrated that most of it sounded hollow, and showed me how much it all flexed when weight is applied to the motor. He was as disgusted as we are. Curiously, he was able to name the dealer (brand) shop that did it, although his experience with the brand was in the Va Bch area, not Bradenton.

So, while looking at the mounting, he questioned the height of the cavitation plate. Remember, this is a 1973, 20' CC, 450+lb., 150hp Mercury 2-stroke motor. Currently, the cav plate is almost 1" higher than the keel. Is this correct? The transom bracket (the part that LOOKS like it should hang on the cut-out)is about 3 inches higher than the cut-out, and the transom (which must have been replaced) is 25".

Thanks for input. He wants to know where WE want the engine mounted. He has his ideas, but wants our input.

[hermco]

Are you sure about those measurements?

[pianewman]

Private message sent.

[pianewman]

New transom in place. Mercury OptiMax150 Motor reset so the AC plate is exactly level with the flat of the keel.

MiragePlus 48-18278, 17p prop. Underway, top speed around 40+, 5200rpm.. At top speed, regardless how I trim it, the AC plate is buried (I can't see it, clear water) and I feel the bow is too high when trimmed properly. I'm aware that this motor is 150lbs heavier than the original motor(s) back in the mid-70s, but I expected, at full throttle, things would level out.

Any thoughts? Should I raise the motor a notch? Is this the proper prop for efficiency? I'm surprised how much lateral spray comes off the motor, at speed, unless I tilt the motor out a good bit.

Again, thanks for helping me out with this.

[hermco]

You should be able to go two holes higher.

[pianewman]

Thanks, Don. You've continued to offer me sound advice. I've just spent an hour reading the "performance" threads re: props and motor height. Wow, do I have a lot to learn!

I think I've got the correct prop, and will raise the motor. There's a Mercury tech where I've got the boat stored, and he's willing to go out with me and check things out, and will raise the motor for me, as well. I might also install the Hydro-Shield I've got sitting in the back of my truck, per Fr. Frank's advice. I've just got to get over the thought of drilling through the skeg of the "new" motor!

Once again, I'm so pleased to have all this knowledge available. Thanks, guys.

[FishStretcher]

Thanks, Don. You've continued to offer me sound advice. I've just spent an hour reading the "performance" threads re: props and motor height. Wow, do I have a lot to learn!

I think I've got the correct prop, and will raise the motor. There's a Mercury tech where I've got the boat stored, and he's willing to go out with me and check things out, and will raise the motor for me, as well. I might also install the Hydro-Shield I've got sitting in the back of my truck, per Fr. Frank's advice. I've just got to get over the thought of drilling through the skeg of the "new" motor!

Once again, I'm so pleased to have all this knowledge available. Thanks, guys.

I am happy with my hydro-shield and it has saved my prop from damage at least once this season. I suspect that dragging it thru the water might hurt my top speed, but maybe that is offset by the fact that trim seems great, even with a 4 stroke and a kicker on a 20 footer- about 430 lb total back there. And I am only pushing it with a 100 hp outboard.