OUTBOARD SHAFT LENTH QUESTION

[Breakin"even]

I was interested in one of those 115 johnson outboards recently posted. my tinny is shallow with a 20" or 21" shaft now.
could I get away with the johnson that has a 25" shaft.

 

[ericl]

could I get away with the johnson that has a 25" shaft.

Depends on what "get away with" means to you. It will at the least cause the boat to ride differently (prop has a longer fulcrum & bow will tend to rise) and will create more drag. There may be other negative outcomes, but I expect that VERY few have tried this experiment

 

[Breakin"even]

I guess the only option would be to raise the transom 5", the corners of the transom are 5" higher
than the center now and mabye filling in the lower area strait across could work. I damaged the
transom slightly on a log and was thinking about reparing before repowering. Or keep looking for
a two stroke with 20" shaft.

 

[Corey_lax]

I was interested in one of those 115 johnson outboards recently posted. my tinny is shallow with a 20" or 21" shaft now.
could I get away with the johnson that has a 25" shaft.

Lots of drag. No fuel efficiency.

I guess the only option would be to raise the transom 5", the corners of the transom are 5" higher
than the center now and mabye filling in the lower area strait across could work. I damaged the
transom slightly on a log and was thinking about reparing before repowering. Or keep looking for
a two stroke with 20" shaft.

sandwich it with aluminum. Nice that you can weld it on completely. I have to bolt mine because it’s a fibreglass boat.

 

[Fisherman Rob]

You sure your tinny will safely take a 115?

 

[Silvercreek]

Just raise it up in the bolt holes. You can probably get 3 or 4" higher like that. I don't think that extra few inches would make too much of a difference in drag. But a 115 on a tinny?

 

[Brett McK]

Correct me if im wrong im no expert. But The older 17’ Lifetimer runabout my Dad and I run has a brand new 60hp Merc on it. Thing rips above 5000rpm. I mean you could put a 70 on it but a 90 or a 115 would be overkill IMO. You have to take into account the outboards weight. Thats why my old man and I chose the 60 over the 70 or 90 was the smaller block saved a tone of weight in the butt end. If you have a serious “tinny” like 20’ plus maybe a 115hp would be okay but that doesnt sound like a lot of transom for a heavy motor that dips when accelerating...

 

[Breakin"even]

You sure your tinny will safely take a 115?

It has a Mercury 115 stack 6 now that runs great but the lower unit is leaking and the tinny is rated for it . That been said I allways sugest passangers hold on when accelerating.

Just raise it up in the bolt holes. You can probably get 3 or 4" higher like that.

I'm not sure what you mean by that, the motor sits on top of the transom. Please explain how I can raise the motor? All your info is greatly appreciated.

 

[Breakin"even]

If you have a serious “tinny” like 20’ plus maybe a 115hp would be okay but that doesnt sound like a lot of transom for a heavy motor

My tinny 18' lund Alaskan and I agree with you. It rides rough in choppy weather so i am usually ride at half throttle or less depending. This boat was desinged during the 2 stroke era and cannot handle the weight of most 4 stroke engines. I found the yammy 70hp 4 stroke is the only one in its class with the weight simmular to the old Merc. which would be enough for the chuck. I have reservations about buying new and still having a marginal boat on the ocean.

 

[Silvercreek]

It has a Mercury 115 stack 6 now that runs great but the lower unit is leaking and the tinny is rated for it . That been said I allways sugest passangers hold on when accelerating.


I'm not sure what you mean by that, the motor sits on top of the transom. Please explain how I can raise the motor? All your info is greatly appreciated.

On the motors they have usually 4 bolt holes on the transom bracket. If you bolted it through the bottom bolt hole that would raise it up. I was thinking the bolt holes were an inch apart but I just looked on a cad drawing for a Yamaha 150 and there closer, there's only 2.25 inches difference between the top and bottom holes. I'm not sure if that's a standard thing or not. But perhaps you can get a new hole through the transom a bit higher aswell.

 

[Breakin"even]

Thanks Silvercreek i will look into this.

On the motors they have usually 4 bolt holes on the transom bracket. If you bolted it through the bottom bolt hole that would raise it up.

 

[sly_karma]

Have a look into a jack plate as a possible solution too. Easy to raise the motor 4-6" with a jack plate.

 

[Breakin"even]

Have a look into a jack plate as a possible solution too. Easy to raise the motor 4-6" with a jack plate.

I looked at a jack plate for an easy fix but my boat has little free board and i'm not sure
how much moving the motor off the transom onto the plate will effect that. I did remove
my kicker from the transom to a bracket and that lowered the boat in the water.

 

[sly_karma]

You are right to be wary of a change in balance caused by moving the outboard back off the transom. Some jack systems offer just vertical extension and zero or minimal setback. I installed a jack plate from Vance Manufacturing that is working very well and uses top quality materials. I see in their lineup they also have this vertical extension bracket:
https://www.vancemfg.com/static-jack-plate-5-inch-vertical-extension-p/jjp123419.htm

 

[Breakin"even]

I see in their lineup they also have this vertical extension bracket

Thanks sly_karma that looks like a great solution, there site had no canadian dealers, where did you get your bracket?

 

[sly_karma]

Direct from Vance. Shipping was ridiculously fast.