[OMC-Boats] 68 Evinrude Sportsman 155 with short shaft OMC stringer drive

Ok guys, here's the deal. I got my 68 Sportsman from someone on the list, and it runs great. The bad news was that the outdrive's upper gearcase was toast due to no oil. I looked and looked and decided to try a 120hp OMC low profile drive (electric shift) on the boat since it would bolt right up. Now the differences between a low and high profile are basically 4" in length. With the old drive, the cavitation plate was about 2.5" below the keel (too low IMO). The new drive is about 1 3/4" above the keel (which I've read is ok depending on prop, etc).

I took the boat out today for a real test, and while it worked, I did not like it's performance. I decided to run the old beat up and chipped 14x17" prop from the old drive on the 4 cylinder 120hp short drive, and here's what it was like:

1. Rpm's came up too fast
2. Excessive blowout in turns, and some cavitation
3. Too quick to redline

Now, I did get her up on plane at WOT but it was in the redline. Made about 35 mph which is not bad I think. Now I did have my wife take the helm and run her up on power while I hung over the stern and watched the drive, specifically the cavitation (anti-ventilation) plate, and it was in the water fine, not riding too high, if anything too low. I think my drive depth is fine since I'm seeing the plate still in the water, but the angle of propulsion has changed, I'm working with a different gear ratio, and my prop might not be any good. Should I get a shallower or steeper prop? Have the prop cupped?

I would like to make this combo work correctly, it's a nice super clean drive with good shifting and a nice ball gear, and I like the idea of a shorter drive because I can lower it down in my driveway and most the way down trailering, as well as having less draft needed to operate. Additionally, the short drives are easier to come by. Sorry for the story, but any help would be great!

~Scott

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Received on Monday, 22 June 2009