20" or 25" Shaft?

[stang82]

Hi All...<br /><br />Getting ready to update my outboard and was wondering which shaft length I should go with. My boat is a home built tunnel deck boat with a V hull in the rear. Transom hieght is 21". The boat is heavier than the norm and I am currently running a 1967 Johnson V4 80 Hp with a 25" shaft. The engine performs fine, just not enough Hp/speed to put the boat up on plane. So, I'm making the change...

 

[Dhadley]

Re: 20" or 25" Shaft?

Standard transom height for a 20" motor is 20 3/4". Are you sure your 1967 motor is a 25"?<br /><br />Also, if it's a tunnel but the back is a V -- where does the tunnel end? Kinda hard to imagine...

 

[walleyehed]

Re: 20" or 25" Shaft?

We're not talking about a tri-hull are we???

 

[stang82]

Re: 20" or 25" Shaft?

Thanks for replies...<br /><br />It's not a tri-hull, but kinda similar. looking at the back of the boat, the V hull is in the center with air channels on each side between the V hull and the left and right pontoons. The boat is all fiberglass and the left and right sides of the hull are flat bottomed. To give you a better idea, if you are familiar with the hulls that you could plug a wave runner into it to power it, thats what this is. I believe it was called a Whisper Craft, but not shure. When I bought it, I decided to build a V hull where the wave runner would go, mount an outboard to it and made a deck boat of it. 3 and half years later I'm done, looks great, but just need to get the power right...<br />The Johnson is a 25" shaft, and after eye balling it this mourning, saw that the cavitation plate is at least 4 " deeper than the bottom of the V hull...

 

[Dhadley]

Re: 20" or 25" Shaft?

Ah! It's like a tri-toon or a pontoon with a center pod. <br /><br />Regardless, the motor is too low creating all kinds of drag. Its interesting that old of a motor was a 25". You may have to use a manual jackplate to raise it but its worth a try.<br /><br />Good luck!

 

[DJ]

Re: 20" or 25" Shaft?

Never seen one of that vintage with a 25".<br /><br />By your description, the 20" is the one for you.

 

[wilkin250r]

Re: 20" or 25" Shaft?

Since you have a non-standard transom height, I think you will be best served with a jack plate, whether you jack it up 4 inches and use a 25" shaft, or go down 1 inch and use a 20" shaft.<br /><br />Personally, I'd recommend the 20" shaft and a jack plate, as it may be difficult/expensive to find a jack plate with 4 inches of adjustability.

 

[stang82]

Re: 20" or 25" Shaft?

Thanks Wilkin250r<br /><br />Just sold the old Johnson thinking that I do need the 20" shaft. Once the engine was removed, I got the exact measurement of the transom from top center to the bottom V point and it's 19 1/4". Any further thoughts on set-up?<br /><br />Stang82