1990 Mariner 8HP long shaft- SLOW!

[Duckbill]

I've got a new (to me) 12' semi v alum jon boat with a 1990 Mariner 8HP long shaft on it. I just put a new 9" pitch prop on it. I know the long shaft will slow it down some, but this thing will only do 12-13 mph and won't get on plane unless I put everything in the front. Does that sound right? I used to have a 9.9 Merc on my 12' flat bottom and it was a rocket ship.

 

[crazymanme2]

Move your tilt pin up a notch or 2.A long shaft can slow you down alot.

 

[Duckbill]

Thanks for the reply Crazyman.

I've heard folks talk about a manual jackplate. Would this be something worth looking into?
I would basically be lifting the motor 5" or so. Does this kind of thing work on small aluminum boats or is the transom generally to weak?
Obviously, I would want to build my own. Those jackplates are expensive.

 

[cyberflexx]

TH Marine mini jacker that I had once purchased was around $100 bucks.. if you can, i'd go with that, its pretty solid and can be drilled easily..

83 bucks here...
https://www.jmsonline.net/mini-jacker.htm?source=googleps

 

[lckstckn2smknbrls]

I got my TH mini jacker on ebay $42 including shipping. It was brand new.

 

[Duckbill]

Thanks guys. I imagine you could fabricate something similar if you had the material. Of course, if I found one for $42 shipped I'd be all over it.

 

[Duckbill]

OK! Upon further review, I have discovered that I have an extra-long shaft ( in most cases this would be a good thing :mrgreen: ).
So, my cavitation plate is around 8" below the hull :shock: . It's no wonder this thing is slow :roll: . Do I need to waste my time with a jackplate of some sort? I'm thinking that 5" is the highest I would go because I have a thin walled transom. Should I just live with it until I decide to sell it and get a short shaft?

 

[free jonboat]

really? i have a 4 hp mariner longshaft on my 10 footer and with just me in it it will push 20 mph.

 

[Brine]

really? i have a 4 hp mariner longshaft on my 10 footer and with just me in it it will push 20 mph.

Are you running nitrous? :LOL2:

 

[Duckbill]

really? i have a 4 hp mariner longshaft on my 10 footer and with just me in it it will push 20 mph.

That's a screaming little machine. I'd love to get 20MPH with my 8HP.

 

[free jonboat]

really? i have a 4 hp mariner longshaft on my 10 footer and with just me in it it will push 20 mph.

Are you running nitrous? :LOL2:

ha ha ha no... i only weigh like 110 and i have a really lite boat 8)