Is it possible to lower the transom tub?

I have a 24' Fisher pontoon that my wife and I resurrected. It was quite a project, and we found a number of things that would indicate that the previous owner, whom I shall call Knucklehead, was lazy, and/or never had the right tools or supplies to do things right. We wound up stripping the boat down to the deck, and rebuilding the whole thing.

My latest discovery is that the motor (1995 60HP Mercury Bigfoot long shaft) is sitting too high, even though Knucklehead said he had the tub 'custom made' just for this boat. According to my research, the cavitation plate should be about even with the bottom of the tubes. It sits 7 1/2" above that. The motor is sitting as low as it can go on the transom.

I was thinking that I could buy some z-bar or channel, and lower the whole tub about 6 inches. Bolt the z bar or channel to the bottom of the deck, and bolt the transom tub to that. Would this be a good idea? Or am I setting myself up for more problems?

I will upload some pictures as soon as I figure out how to make them smaller.

Any ideas?

Jack
South Florida

Re: Is it possible to lower the transom tub?

Here are some pictures I took today:

The "custom built" transom tub


Transom tub, showing the height of the motor relative to the tubes. The straight-edge is touching the bottom of the tubes.


Another view of the straight-edge


Rear view of the transom

Re: Is it possible to lower the transom tub?

i think your reserch is flawed a bit putting the cav plate even with the bottom of the tubes would be a bad idea it would then sit too low in the water i think that is for a plaining hull as opposed to a displacement set up if you look at the water line on the pontoons your motor sits plenty low in the water for it to be effective if you still want to lower it i would sugest using a jack plate if you get too much length on the tub brackets it might effect lateral strength when turning not to mention tha it would put the tub down into the water witch would hamper performance and could alow water to flow into the tub when on plane

Re: Is it possible to lower the transom tub?

Cooter's points seem valid. What caused you to research motor height? Poor performance? Prop ventilation? Difficult to steer at high/low speeds?

kazeej said:

My latest discovery is that the motor (1995 60HP Mercury Bigfoot long shaft) is sitting too high, even though Knucklehead said he had the tub 'custom made' just for this boat. According to my research, the cavitation plate should be about even with the bottom of the tubes. It sits 7 1/2" above that. The motor is sitting as low as it can go on the transom

Click to expand...

Is the motor running in it's correct rpm range at WOT? Maybe you need to re-prop, rather then move the motor.

Re: Is it possible to lower the transom tub?

jbcurt00 said:

Cooter's points seem valid. What caused you to research motor height? Poor performance? Prop ventilation? Difficult to steer at high/low speeds?



Is the motor running in it's correct rpm range at WOT? Maybe you need to re-prop, rather then move the motor.[/QUO

+1 ^^^ Did you water test the boat before you bought it ?

Click to expand...

Re: Is it possible to lower the transom tub?

Cooterdude
I don’t think a jack plate would do the job. They are not recommended for lowering the motor, and they will only lower it 3-4 inches. I need at least 6.
I agree with you about the length of the tub brackets and the lateral strength. That could be why I couldn't find anyone who has done it .

Cooterdude and jbcurt00

There was a lot of difficulty in steering, especially at high speed (this boat will run 18 to 22 mph by GPS, depending on conditions). But this was because the steering tube on the motor was badly corroded inside. Even sitting on the trailer, it was hard to turn. I replaced the steering tube, and now I can move the motor by hand, just by pushing it from side to side. I couldn’t do that before.

Here’s what started the whole motor height research thing.

I want to put a trolling motor on this boat. Mainly to move the boat around when fishing, or just slow cruising, and have a way to get to shore if the big motor dies. I found the Minn-Kota EM series trolling motors that mount on top of the cavitation plate. They require 13” from the cavitation plate to the water surface. I only have about 8”. Knowing the history of how Knucklehead did things, I started looking for information on the correct height of the motor.

I found many opinions about motor height on pontoons. I finally found some pictures of two different toons that showed their motor mounted much lower than mine. That’s when I started considering lowering mine, if possible. If I can’t lower the motor, I will have to resort to putting a trolling motor on the front, and lose some of the room front deck. I want to avoid this, if possible.

I hope to take it out this weekend, so I can see how the steering performs under real conditions. If I do, I will be able to get more info on the RPMs at WOT.

Please keep in mind that, although I rebuilt this boat from the deck up, I have almost no experience with pontoons, so I could be (and probably am) completely off base with this. I appreciate any advice you guys can give me.

Jack
South Florida

Re: Is it possible to lower the transom tub?

When you go out let some one else take over the wheel for a bit and look at where the cav plate is really running, it should be just below the surface of the water by a few inches, 1 to 3 inches is about perfect, if its to deep you will lose performance. In your pictures it looks like it is about right to me. It should not be below the bottom of the toons by any means, that will cause excessive drag and will drop your top end a huge amount.

Re: Is it possible to lower the transom tub?

Engine height on a pontoon isn't nearly as big of a deal as it is on a mono hull boat, you want ti deeper than on a mono hull boat because the water behind the boat is so torn up from running between the tubes.

I agree with others in that your engine looks to be just about right and I will bet at rest in the water you will have very close to the 13'' you need, the boat doesn't float on top of the water especially being a pontoon, probably 1/2 your tubes will be submerged so you should be good.

I would take the boat out and measure it in the water before I moved a motor pod, that could go really really wrong, lots of forces involved there.

Re: Is it possible to lower the transom tub?

Well, we're not gonna make it out this weekend. If we don't make it next weekend, it will be a while. Thanks for all the replies. I will report back when I have some more info to share.

I am never disappointed when I ask questions here. You guys rock!

Jack