Re: Jet drive conversions
After using outboard jets for 35 years, here are some things I have learned:
1. They are mostly a bolt up to replace the lower unit. Look at the Outboard Jet website.
2. They will add 5" to the drive length. This means a short shaft will need a 21" transom and a long shaft a 25" transom.
3. They will reduce effective power by about 40%. Actually a little less at very slow speed and a lot more at 20 mph or more. They will be a lot slower than a prop. I had a light 16 foot flat bottom river boat (like a jon) with a 135 merc and maximum speed was about 28mph.
4. They will cavitate at times and can be hard on crankshafts. Particularly with straight 6 mercs.
5. The 35-40 OMC engines are not great for power with a jet. They are rarely used. They are ok on a light 14' jon with 2 people. A 50 hp 4 cylinder merc works well as do the 3cyl and v4 omc engines. Most all V6 engines work pretty well.
6. They are expensive. I would look for the jet unit at a good price then find the motor for it. Anything at or under about $500 for the jet is probably a fair deal if it is in decent condition. Older motors are common,
used jet units are not.
7. The only moving parts are the drive shaft, the impeller and a single bearing. The big problem with older units is wear between the impeller and the housing. Newer units have a replaceable liner. Do not but an old one without it unless you know what you are doing.
8. The boat is critical. It needs to be light, and have a large mostly flat planing surface. Mostly you need a job boat style or something sort of similar. Deep V's do not work well nor do most fiberglass boats because of weight.
9 They are a lot of fun when running water 5" or 6" deep.
