drive shaft lengths

[fishhead]

Got a 250 ox66 yamaha on a 20 foot 1980 enchanter with a new balsa core and floor. Had the motor then got the boat. The motor has a 25 inch shaft and the old hydraulic jackplate is blocked off at the highest position. Boat runs unreal with a 25 pitch lazer 3 blade but I lose water pressure at 70 mph on the speedo. Seems like getting a 20 inch shaft would be pointless cause if the motor could come down a hair once up on the pad, maybe I wouldn't lose water pressure. The old jackplate did work for a while and the boat would chine walk wildly unless it was jacked up all the way so that's why I blocked it off cause trimmed down she still jumps out of the hole. Need a new lower unit and was wondering if now is the time to convert to a 20 inch shaft. What would be gained with a 20 incher?

 

[john lamon]

not sure about the shaft length but you should get a set of scoops for your water inlets, that will cure your water pressure problems.

 

[ndaniels]

The 20" shaft would bring the weight of the powerhead lower and it should be easier to balance it (chine walking). I've heard thats not always true because of the gyroscopic effects of the spinning motor parts. I don't really think you'd see a difference either way on that hull. At one time I was looking into an allison ss and thinking about going with a short midsection on my omc and asked some experts about it- that was the awnser I got (makes sense).

I'd go to the 20" because it would look better on the boat. You could also cut a 25" shaft down to work on a 20" mid, I'd think. Main thing is coming up with the shorter midsection. I'd go with a scoop or plug the top couple of holes on the lower to keep water psi. I have no idea if the yamies have a water scoop available like the mercs (omc doesn't).

 

[john lamon]

I have no idea if the yamies have a water scoop available like the mercs (omc doesn't).

Not that it matters for him but I've used the merc scoops on an omc and it worked just fine.

 

[fishhead]

never even heard of scoops until yesterday. Had read about nose cone low water pick ups and knew that was not what I wanted. Do the scoops create much drag? The previous owner of the boat had a 20 inch merc on it and advised me to be aware on turns that the outboard side of the boat will jump up. I had experienced that as a kid with my 15 foot glastron and actually liked it. With my 25 inch shaft motor jacked up, the boat always turns flat and is extremely stable with the 250. Who knew? Another advantage I see with the 25'er jacked up is having the powerhead up high and further out of the water so it is less apt to get wet on stops especially out in the Gulf around the pass here in Pensacola. The guy who did my balsa core sold checkmates in the 70's and he is the one who got me all conscientious about the looks of my power setup. I think I'll stick with a 25 inch shaft and save $695 plus $25 shipping on a 5 inch gearcase extension kit. Got to get some scoops. Thanks for the replies.

 

[john lamon]

The scoops don't create any drag, there more of a flat plate the goes over the inlets and forces water in, like ndaniels I don't know if yamaha make em, here's a pick of a my merc scoops.

 

[timbaso]

hey i have a 79 enchanter with a 97 250 ox66 25 inch also. i want more speed have u done anything to urs mod wise?? how does it run with that 25 pitch prop i have a 21 n i onluy go barely 60. i also need a jack plate does it make a big difference?? n i dun under stand how having the motor jacked up make u chine walk less ?? pleaz explain...