Running short shaft???

[nathanhooper]

Hey guys, not sure where to put this one, but you all have been very helpful in the past so I am going to stick it here.

So I decided to rebuild my Chrysler the right way and in doing so wanted to get another motor for the meantime. I found a nice, not very used, 50 horse short shaft.

Well, my transom is about 21 inches. Now I have been researching this for a while now and I cannot seem to find the answer to the question I am looking for.

The question is, will it be ok to run it IF I am only going to run it half throttle, or "under planning" speed? I hope that clarifies what I am asking. I am not looking to replace permanently the short shaft on the boat, just want to allow me enough time to fix my motor right, but allow me to get out and do some fishing.

Would it be better to build a set back plate of some kind and mount it on that? How far above the bottom of the boat can I get away with for just motoring around?

I know that most answers are to get a different motor, or get a different boat, but is there something I can do to allow me the short term use of this motor? I got a good, good deal on it. It is a 1968 Merc 500. If that helps decide what to do.

Thanks guys.

 

[Frank Acampora]

Re: Running short shaft???

If the hull is a deep vee, she is going to draw at least 6-8 inches of water at rest. Yeah, you could use the Merc, but you need to keep the hull at displacement, and even at that, if you go too fast, there is still the possibility of starving the prop.

It's kind of like towing a 30 footer with a passenger car--yeah, you can do it but you won't be happy. If you are just moving it in the driveway, you can get away with it.

 

[nathanhooper]

Re: Running short shaft???

Not a deep V, tri-hull up front to almost flat bottom on back. Don't know what you would call it actually. It has a semi-v shape at the rear. Its a trophy brand boat.

Yea, I get what your saying on the hauling thing. lol. If the boat were a deep v, would it be better?

 

[nathanhooper]

Re: Running short shaft???

would putting a add on cavitation plate on the motor help with running it at displacement speeds, or would it cause it to want to get on plane?

I have one laying around, but I am not going to mess with it if it would cause more harm than good. I am getting prices on an extension kit for the merc.

I watched a guy yesterday running at displacement speed, not sure why he did not plane, he was in the middle of a wide open area. I am sure there are many reasons why he didn't, but my question is does it hurt to just run around at those speeds? I watched him, and he was not going to slow, in just a couple of minutes he was out of sight.