motor height, small fishing boat

[Mano del Sol]

On my little 12' Aluminum Starcraft fishing boat my transom is 16 inches top to bottom. The length of my motor from the top of the inside of the mounting bracket to the cavitation plate (if that is what it's called) is 18".

If I move the motor all the way up to where the thumbscrews are against the transom cap thingy I'm still about 1 1/2" below the hull.

Is there any that any of you know to get the motor up higher and should this even make a difference?

I'm still at least a few weeks away from mounting the motor and being able to do anything with the boat but I am a compulsive planner and this is bugging me not knowing!

Thanks!

 

[Reel Poor]

Re: motor height, small fishing boat

Does the engine mounting bracket have holes so you could mount the engine to transom without using the thumbscrews?

 

[Mano del Sol]

Re: motor height, small fishing boat

No it doesn't. It's just a clamp mount.

 

[CATransplant]

Re: motor height, small fishing boat

Hmm...I can't remember what motor you have for that boat. Typically, the smaller outboards have about an 18" length from transom to cav plate. I'm not sure why that is, but there it is.

Unless the engine you're mounting is going to plane this boat, I wouldn't worry about it. Your boat is the same as mine, I just hang the motor on it and go fishing. Maybe, if I find a 9.9, I'll worry about the mounting height, but for now, it doesn't matter.

You could add an extension to your transom, though, if you really need to. It's been done many times.

 

[Mano del Sol]

Re: motor height, small fishing boat

It's a 10 HP Johnson.

I don't think it's a matter NEEDING to, I just want to get everything installed as best I possibly can while I have it all tore apart. Seems kind of silly to rebuild the carb and ignition on the motor, rebuild and paint the trailer, replace all the wood, and probably end up re-painting the interior of the boat just flop the motor on there and go. I just wanna make sure it's as right as I can get it with what I've got, I don't think I am willing to modify my transom though.

And as I said, I didn't even know whether that 1 1/2" will even be significant.

 

[F_R]

Re: motor height, small fishing boat

An old 10hp Johnson, right? Those things were made to run deep. Raise it up as high as you can, it it makes you feel better and see how it works. Put a stick under it on top of the transom for a trial. But take precautions so it doesn't twist off of the transom and go for a swim. It will make a bit of difference in speed, but it also may cavitate. You just have to experiment.

 

[CATransplant]

Re: motor height, small fishing boat

I understand. As another poster said, those engines were designed to go on boats just like yours. You might be able to get another couple of miles per hour out of it by fiddling with the height, but that's probably it.

I've had a 10 hp on my boat, which is identical to yours. I mounted it down on the transom, like it was designed for. The boat scooted along very nicely, planing out easily, even with just me in the back seat.

I can't tell you the speed, but it was as fast as I cared to go in a 12' aluminum fishing boat. That's why I'm suggesting that you just hang that motor on the transom, with it sitting right down on the top. Take it out for a spin on the lake.

I'm betting you'll be quite happy with the performance of your tinny.

 

[Mano del Sol]

Re: motor height, small fishing boat

After doing a search I just might make a homemade jack plate thingy. It won't cost me much and it should be easy enough. The only issue I haven't seen in the other posts on this topic is what size and how many bolts to use.

The hull has the four #10 screw holes in it for the transom plate thingy but I suspect that those won't be enough.

 

[michiganmarty]

Re: motor height, small fishing boat

Mano,

I also have a 12 footer with the same issue. I added a 1" spacer to the top of the transom. The transom spacer really needed to be taller than 1", but the clamp screws would have run out of transom to clamp to. Without a whole lot of extra work, the 1" spacer was the easy way out.

By the way, the spacer did not make even the slightest bit of difference to how the boat performed. Now maybe if I raised it up until the cav plate was even with the bottom of the hull it would have, but that is an awful strong maybe.

You should seriously consider leaving the boat alone - forget the modifications. If you ever decide to sell the boat, most people will walk away from it since the transom was altered from the original design intent.

Besides, if the motor needed to be that high, I would think Starcraft would have designed it with a taller transom.

 

[BF]

Re: motor height, small fishing boat

on some older motors without thru hub exhaust, the water pickup is above the cavitation plate. My 25 hp OMC is like that. They need to be run with the cav plate lower than newer motors.

 

[michiganmarty]

Re: motor height, small fishing boat

on some older motors without thru hub exhaust, the water pickup is above the cavitation plate. My 25 hp OMC is like that. They need to be run with the cav plate lower than newer motors.

BF,

Good point. my 28 SPL E-rude is like that as well.

 

[Mano del Sol]

Re: motor height, small fishing boat

Well, not to nitpick but I was never going to modify the transom, just make and install a jack plate.

So, I have read in several threads that those motors were designed to run deep. If this is true then what are the reasons or advantages to running them that deep if a boat will run faster and plane out easier with it higher?

Is it because the water intake is right under the A/V plate?