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I am likely going to be purchasing a boat this weekend that has a 20in transom. I have measured my motor and it seems to be somewhere between a short and long shaft.... If I measure from the inside of the mounting bracket (where it contacts the top of the transom), to the bottom of the cavitation plate I get 17 inches. The way I understand it a short should be 15 and a long should be 20 when measuring this way. My estimation is that when mounted on a 20 inch transom 95% of the prop will be below the bottom of the transom (bottom of the boat). The motor I am using is under powered for the boat I am putting it on and so I don't think I will even reach "plane" at high speed... the water intakes should be submerged at all times if I am estimating correctly. This motor is also, only a temporary solution until I purchase a bigger motor later in the year. I read on a transom guide that you could be about 2 inches long or two inches short and be fine.
Can any boat experts give me some feed back?
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Not quite sure what type of boat expert you are looking for but your measurements and estimates sound funny.
The motor is either a short or long shaft. When measured properly, the short shafts are 15"-17" inches, and long shafts are 20"-22" inches. There are a few models with 25" inch shafts but that is of no concern to you.
I don't quite picture how you measured your outboard shaft length. Here is a link to a picture that does a good job of showing this measurement correctly.
[url "http://www.onlineoutboards.com/article_outboard_shaft_length.html"]http://www.onlineoutboards.com/article_outboard_shaft_length.html[/url]
If you measured yours the same way, and got 17 inches it is a short shaft.
Putting it on a 20" Transom is a very bad idea. It is a good way to put a motor to waste. The prop should be completely below the transom, otherwise it will not be balanced, even at low speeds. When it picks up speed it will not be able to suck up water for cooling. And how would you adjust the trim angle when you don't have enough length to work with. What's worse, your manuverability will suffer big time.
If you get into rough water with the 20" transom boat and the motor is running it will get real ugly. You will have no manuverability whatsoever.
It would be a shame to ruin a motor even if it is old and you are planning to get rid of it. Just about the only thing you will be able to do for the sake of saving the motor is going very slow, and always watching the water contact. That sure ain't no fun. It is possible to pull this off but I would never do it.
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I measured it just like in the link you posted and I get just over 17 inches. My prop is much further down from the cavitation plate than in the picture in the link, which is why the prop ends up below the bottom of a 20in transom. I read that the cavitation plate should be nearly level with the bottom of the transom, but could vary 2 inches in either direction. I definately don't want to ruin the motor, but if this motor will work for trolling around this summer I would be happy. It isn't going to go fast anyway, it is just a 5hp on a pretty large boat. 1-5MPH is what I am looking for.
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Yes, that is true about the cavitation plate. There are so many motors and designs that such a small difference does not take a big toll on performance.
As far as the prop being completely below the transom, I am very surprised. But on certain models it is possible. My main concern is that the motor will not always have a continues supply of water, depending on the situation. For trolling speeds it will work, but I would still not advise it. I just hope that you will be very careful and not allow the motor to run fast. And pay special attention to waves and whatnot. You don't want that prop or the wate intakes to be in the air. You would be amazed at what only a couple of seconds of "dry running" can do to the impellar area.
Though I would not put that motor on the boat you plan to buy I would tell you to check how everything looks at the ramp when you first launch. Tie the boat down and closely look at the transom area to see how everything sits. Then shake up the boat as if there is a wake or wave and see how everything is. There is no margin of error here. I would hate for that motor to get ruined. Then, when you get going watch what effect different speeds have.
With a all these precautions it is still gonna be dang hard to pull this off. There are always unexpected things on the water, and we as fisherpeople always get that urge to go just a little farther and explore more water. This is why you are going to be real limited in what you can do.
I am more of the cautious type and would not go for it. I would just wait for the new motor. You will have to drill another couple of new holes to secure the new motor to the transom, and the ones from your current motor might get in the way. You may not be able to fully seal them up, depending on how the new motor's mounthing bracket is. But if you decide to use the motor you have now, you could always use some marine sealent and plug them up.
Dang though, a 17 inch on a 20" Transom is gonna be tough. Dang.
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I pulled the trigger at Cabelas this weekend. I ended up getting a 14' Lowe, modified v. I was so surprised at how competitive their prices were, compared to all the other places in SLC and Logan that I checked. I saved enough between the boat and trailer, that I went ahead and bought a new outboard. Nissan 15hp. Can't wait to get out in it. I was going to get the 16' boat, but decided that since I go out alone quite a bit I didn't need that much extra room. Plus I usually only take 1 passenger and the boat holds 4.
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You made a wise choice. I have not had any problems with my Nissan Marine, except ordering parts for it, which is really the dealer's problem.
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]... I have been reading online about these older evinrudes. They were a little longer than normal because the water pump configuration was different.