25" shaft on a 20" tramsom???

[fishtales]

I bought an older 21' Grady-White with a 20" transom, I have a 185HP Johnson with a 25" shaft. Can I use it and how will it affect performance???

 

[Frank Acampora]

Re: 25

Re: 25

You can use the engine but the prop will be way too deep in the water. Lotsa drag, lotsa backpressure. The engine won't develop max hp. and the backpressure will be so high that it may stall at idle. Stalling at idle happens to some rudes on bass boats that sit real low in the water.

Buy yourself a jackplate or build up the transom 5 inches with marine quality plywood. Plate it with heavy aluminum (at least .080 thick aircraft quality, not soft plate) on both sides and reinforce the motor well with angles and plate in the corners. Use a lot of through bolts and fender washers. If done correctly, you will be able to hang anything on there.
If you want to see an example, go to Chrysler Crew, join the help forum and look up Frank's boats in the photos. I raised that transom 5 inches and you could drive a truck into it without breaking it. The photos are actually in a Crysler Crew album sponsored by yahoo but I can never get there except throught the help forum.

 

[tashasdaddy]

Re: 25

Re: 25

my first concern is putting a 400 lb engine on a 20 " transom. launch the boat regularly loaded, and get someone to sit on the transom to equal 400lbs. if that works out, an adjustable jack plate is what i would use.