Raising the transom and outboard motor mounting questions

[twr7cx]

I currently have an early 90's Mercury 60HP outboard on my boat with a shaft length of 520mm (20.47244 Inches) measured in accordance with:

I believe this is what is commonly refered to as a Medium Shaft and are usually generally around 20"'s long.



I'm looking to put a larger HP motor on the back of the boat (90HP), most of which are only available with a Long Shaft (25").

Now I realise that there are a few options for doing this, but I am looking to have the transom built up rather than using a jack plate due to a couple of issues I am currently experiencing:
* in reverse, water washes over the back where it is dipped down for the outboard fitting.
* steering to the left is limited and compromised due to the steering arm fouling on the body. You can see from the pictures below that the steering arm has already been cut shorter and welded by the previous owner. You can also see in the pictures below that it is hitting on the boat as there is a mark in the fibreglass.




So what I'm looking to do is to have the transom built up by 5"'s in order to be able to fit a Long Shaft outboard on and also resolve the above mentioned issues.

A couple of questions though:

Is my current outboard sitting in the correct position (refer to picture below)?



At present, the mounting clamp bracket does not touch the top of the transom. Is this an issue?

 

[Frank Acampora]

Re: Raising the transom and outboard motor mounting questions

Raising the transom five inches is not an issue and if done correctly will be as strong or stronger than the original. I did mine by adding the proper thickness of plywood and keying it into the original fiberglass. I coated it to preserve it and then covered it with .080 hard aluminum I currently have a 125 mounted on it with no signs of flex.

Engines do not necessarily need the mounting clamps to touch the top of the transom. In fact many engines run better with the cavitation plate a little but above the bottom of the hull. This requires raising the engine on the transom.

If you go to the Force forum, you can see photos of the boat in a post titled: "Has anyone used a 19 or 21 pitch prop on a Force 85"

I will try to post a few better photos later.

 

[Chris1956]

Re: Raising the transom and outboard motor mounting questions

There is no such thing as a "Medium Shaft" length. A 15" Shaft length is shortshaft, a 20" shaft length is Longshaft, and a 25" shaft length is X-longshaft. 30" is XXL.

There are usually 90HP motors available in the longshaft, however, newer motors tended to have the X-longshaft.

If you want to raise the transom, decide on a design that is real strong. If you are uncomfortable with the design, find a longshaft motor.

 

[Frank Acampora]

Re: Raising the transom and outboard motor mounting questions

Here you go: This is a hull with an original 15 inch transom that I raised to 20 inches.

 

[109jb]

Re: Raising the transom and outboard motor mounting questions

Which side of the boat is the steering wheel on?

Looks like from the engine pictures it would be on the left based on how the steering cable comes out the right side of the tilt tube. Not suree about Australia, but here in the USA, the steering wheel is usually on the right and the cable exits the left side of the tilt tube.

Is the splashwell area larger on the left side of the motor?

It appears it might be in one of your pictures in your album. If so, could the steering wheel have been moved to the left side by the previous owner? I'm thinking that the steering wheel should be on the right and more area in the left side of the splashwell is to accomodate the steering linkage.

 

[twr7cx]

Re: Raising the transom and outboard motor mounting questions

Which side of the boat is the steering wheel on?

Looks like from the engine pictures it would be on the left based on how the steering cable comes out the right side of the tilt tube. Not suree about Australia, but here in the USA, the steering wheel is usually on the right and the cable exits the left side of the tilt tube.

Is the splashwell area larger on the left side of the motor?

It appears it might be in one of your pictures in your album. If so, could the steering wheel have been moved to the left side by the previous owner? I'm thinking that the steering wheel should be on the right and more area in the left side of the splashwell is to accomodate the steering linkage.

Steering wheel is on the right hand side - same side as steering wheels are on on vehicles here in Australia.

Splash well is the same size both left and right.

Steering tube runs down the left side of the boat and enters the splashwell from the left side. I suspect that the boat may have previously had cable steering (i.e. a cable running down each side of the boat).

 

[109jb]

Re: Raising the transom and outboard motor mounting questions

I see. That cable routing is different than I have ever seen. Doesn;t really matter I suppose, but the cable normally runs down the right side of the boat and enters the splashwell from the right. If the splashwell is the same both side it shouldn;t really matter.

It looks like the boat is fiberglass and the transom is pretty well sealed in there. If I were to extend the transonm up, I personally would want to remove the existing transom and replace it completely with one that is taller. That's a lot of work. If I were in your shoes I think I would just keep searching for a 20" shaft motor. For the steering problem, I would cut a little fiberglass where the cable is hitting and then make a fiberglass repair. Basically make a cavity for the cable to go into. As for water coming over the transom, as long as it is just in the splashwell area I wouldn't worry about it other than to make sure the rubber boots the wiring and sterring cable come through are in good shape. That is essentially what the splashwell is there for. Good luck.