Evinrude Short Shaft to Long Shaft Question.

[thebigbuck]

I have a 1979 Evinrude 100hp outboard engine on my Charger tri-hull. I would like to know how to convert the engine to a longer shaft lower unit. Every time I turn the boat, it cavitates and I have to pull the throttle back, stop, and restart. It has done this since I can remember, I just always thought it was part of having a tri-hull. The prop is only half way below the bottom of the boat so I really think it was matched with the wrong motor to begin with. The engine runs great and I hate to get rid of it if I don't have to.<br /><br />Thanks for the help.<br /><br />Paul.

 

[ob]

Re: Evinrude Short Shaft to Long Shaft Question.

How tall in inches is your boat transom from top center to the bottom of boats hull?I don't know of too many tri-hulls that require a long shaft.Can motor be lowered any or is the transom bracket set as low as it will go.<br />At any rate it would be a lot simpler to just use a jackplate instead of converting the engine to a longshaft.Post back with transom height and motor bracket info.

 

[Boatist]

Re: Evinrude Short Shaft to Long Shaft Question.

TheBigBuck<br />I converted a smaller 1975 Johnson last year. I ordered the kit to convert from 15 to 20 inch. It came with all the parts and instructions. Only thing extra I had to get was some paint to match color. Can you lower your motor some? What is your transom height an current shaft length?

 

[thebigbuck]

Re: Evinrude Short Shaft to Long Shaft Question.

Thanks for the replies and advice. The boat is at the lake and as such, I will not be able to measure for another couple of weeks. I do believe it is mounted as low as possible on the boat. This is going to sound stupid, but what is a "jackplate"? If I was going to order the extension, where do I do that from?<br /><br />Thanks again for the help. This is an excellent resource for guys like myself.<br /><br />Paul.

 

[ob]

Re: Evinrude Short Shaft to Long Shaft Question.

Manual jackplate.<br /> web page

 

[Steve135]

Re: Evinrude Short Shaft to Long Shaft Question.

thebigbuck - going short to long is some work to do on a 24 year old engine. You might be in for some broken bolts and parts on the way which may or may not be fixable! I would see what is the cheaper way to fix the problem. May be the jack plate might be wiser.Or cut the transom out and fiberglass it. That can be done in weekend for 30 bucks!<br />steve

 

[Boatist]

Re: Evinrude Short Shaft to Long Shaft Question.

TheBigBuck<br />I ordered Kit from my favorite discount Johnson Dealer. A jack plate mount to the transom and motor mounts to it then you can move motor up and down with the plate. I would messure first and make sure some one has not raised motor to get more speed. Also another though is what type PROP are you running. Some props can be run as much as two inches higher and not cavitate. Usually these props are doubled cupped stainles steel.

 

[thebigbuck]

Re: Evinrude Short Shaft to Long Shaft Question.

Guys, again thanks for the help. I am going to go and measure next weekend and make sure of everything you have all told me. Also, I now know what a jack plate is and where to get them. That really looks like the best and easiest solution. I just need to measure and make sure that I have room to drop the motor a couple of inches and that all the steering linkage will still work okay.<br /><br />Thanks again for the great help and advice.<br /><br />Paul.

 

[bonitoman]

Re: Evinrude Short Shaft to Long Shaft Question.

I would buy an 8 inch or 10 inch setback plate. This is like a jackplate but does not go up like a jackplate. I just put my 110 Johnson that is a 20 inch shaft on a 25 inch transom. It runs great and the cavitation plate is about three inches up from the bottom of the boat. If you mounted your short shaft on a long shaft transom it would cavitate but by setting back 8 inches it will work. I would not convert your actual engine because of age and it is work. I know because I rebuild engines. You can pick up a setback plate for around $250 . Bobs machine in Miami sells them or you can go to a sheetmetal shop and they might be able to fabricate one for you. I would not cut the transom for one reason. What if your engine cracks a ring in two months? Your probabably going to replace that engine. Good Luck in your decision.