Motor Height with CMC Break Away Mount

[blackshear]

I am running a 30 hp Tohatsu on a 1648 jon boat with a CMC kick up plate, which puts the motor about 5" off the back of the transom. Normally I would run the motor with the cavitation plate about 1" below the hull but with the 5" offset shouldn't I raise the cavitation plate so it is at least flush with the bottom of my boat?

 

[lckstckn2smknbrls]

The rule I went by was for every inch of set back you can raise the motor .25" above the bottom of the hull. In the end my motor was about 2" above the bottom of the hull.

 

[blackshear]

I raised the motor as high as I could and can only get flush with the bottom of the boat. I called T-H Marine who make the CMC break away mount to see what suggestions they might have. They recommended that I replace the break away mount with the two piece jack plate and raise the motor as much as 3" to 4" above the bottom of the boat. He was very vague about how that would effect the performance of the boat. Right now I have a porpoising issue when I try to lift the bow for a smoother ride. Anyone have any experience with jack plates on smaller (1648) jon boats?

 

[lckstckn2smknbrls]

It will take a lot of experimenting to find where your combo works best.

 

[RaisedByWolves]

It will take a lot of experimenting to find where your combo works best.

Yep, I’ve been messing with my motor height for over a year now and I’m currently building a jack plate.

Granted I’m cheap and only buying things like props when I can find a really good deal on a used one, but I’m narrowing it down.

 

[wmk0002]

Hey Blackshear, just went back to your post history and saw where you went from the Yamaha F25 to the Tohatsu 30. Did the Yamaha quit making oil for you?

 

[turbotodd]

depends on the hull but I've run 4" lift with no issue with 5.5" setback.

 

[blackshear]

Hey Blackshear, just went back to your post history and saw where you went from the Yamaha F25 to the Tohatsu 30. Did the Yamaha quit making oil for you?

The F25 had gotten much better and only made oil if I did a lot of idling, which I understand is a common problem for most all four strokes. I traded mainly because I wanted a little more speed and liked the tilt/trim feature of Tohatsu. With only 10 hours on the Tohatsu I can smell gas in the oil with it as well and I guess it will get better as it gets broken in like the F25 did. I really miss some things about the Yamaha but overall I’m happy with the Tohatsu.

 

[turbotodd]

I went and played with mine some yesterday. I was at 4" lift and tried a couple different borrowed props, and lifted the engine higher. It's on a war eagle 548, F25C. With the normal setup, 12" Turbo hotshot lifted 4" even on a CMC PT35, I was happy with it. Decided to try for more since I found a guy with different styles of props.

I could get another inch of lift, by using a 4 blade 11" that had a good bit of cup added, but the problem I ran into was that it would run so high, it would partially uncover the water pump inlets--water pressure would drop way off. Speed-wise it was exactly 1 mph faster, 35 vs 33.9. Big deal. Tested a PT SRA with some cup, 11", on the fuel cut at 6200 and change, 33.0 mph avg. Others were really disappointing in one way or another. He had a ron hill cleaver that I tried as well but had to remove the trim tab for it to fit, and while it performed decent on the top end and would run as high as I wanted it to, it came out of the hole like poo, hard to actually get it on plane. Once up it did ok, speed about the same rpm on the high side, with a low-water pickup it would probably do ok but I aint about to do all that. Stuck my turbo 12" back on and called it a day at 4" of lift. Still runs right at 33mph with a chop, at 6180 with an acceptable holeshot. PT&T helps tremendously in that area; I can get it on step then trim it out. Could stand to work on the hull a little as it tends to porpoise but I just trim in slightly until it goes away. ONly other issue is I have a pull to the starboard side that I can't get out. Wants to pull the motor out of my hands at full throttle and the little tab is adjust all the way as far as it will go. Ran out of motivation to play with it any more or I'd have figured out a way to adjust a little more.

one thing I did do on mine was to remove most of the weld bead just to the port and starboard side of keel. They put a bead across the entire back of the boat, where the bottom meets the transom. It serves to reduce porpoising and you can reduce it's size a little but you will also induce some porpoising if you take off too much. I removed a lot of the bead just to each side, and left it intact everywhere else. That in itself picked it up quite a bit. It was a noticeable modification for sure.

 

[RaisedByWolves]

I went and played with mine some yesterday. I was at 4" lift and tried a couple different borrowed props, and lifted the engine higher. It's on a war eagle 548, F25C. With the normal setup, 12" Turbo hotshot lifted 4" even on a CMC PT35, I was happy with it. Decided to try for more since I found a guy with different styles of props.

I could get another inch of lift, by using a 4 blade 11" that had a good bit of cup added, but the problem I ran into was that it would run so high, it would partially uncover the water pump inlets--water pressure would drop way off. Speed-wise it was exactly 1 mph faster, 35 vs 33.9. Big deal. Tested a PT SRA with some cup, 11", on the fuel cut at 6200 and change, 33.0 mph avg. Others were really disappointing in one way or another. He had a ron hill cleaver that I tried as well but had to remove the trim tab for it to fit, and while it performed decent on the top end and would run as high as I wanted it to, it came out of the hole like poo, hard to actually get it on plane. Once up it did ok, speed about the same rpm on the high side, with a low-water pickup it would probably do ok but I aint about to do all that. Stuck my turbo 12" back on and called it a day at 4" of lift. Still runs right at 33mph with a chop, at 6180 with an acceptable holeshot. PT&T helps tremendously in that area; I can get it on step then trim it out. Could stand to work on the hull a little as it tends to porpoise but I just trim in slightly until it goes away. ONly other issue is I have a pull to the starboard side that I can't get out. Wants to pull the motor out of my hands at full throttle and the little tab is adjust all the way as far as it will go. Ran out of motivation to play with it any more or I'd have figured out a way to adjust a little more.

one thing I did do on mine was to remove most of the weld bead just to the port and starboard side of keel. They put a bead across the entire back of the boat, where the bottom meets the transom. It serves to reduce porpoising and you can reduce it's size a little but you will also induce some porpoising if you take off too much. I removed a lot of the bead just to each side, and left it intact everywhere else. That in itself picked it up quite a bit. It was a noticeable modification for sure.

This may seem silly, but are you sure you’re angling your anti torque fin the correct direction, or is it completely out of the water?