Transom height vs shaft length

[Shockley]

Yesterday, I finally had a chance to take my new boat out. It is a 15'4" Eldocraft Spirit I. I already owned a 15HP Johnson from a previous boat. If you have read some of the other posts about this boat, you will remember that everyone, including me, agrees that the 15HP is too small for this size boat. When we got it inot the water, it would run well at idle to 1/4 throttle. The engine ran perfectly, however any more throttle and it would aerate the prop.

With that being said, my questions have to do with transom height vs shaft length. The transom height on this boat is 20" on the nose. From the bracket to the bullet point is a little over 23". Is this a 20" shaft? Do I need a 25" shaft? Do I need a jack plate to get it farther away from the transom?

Those are immediate questions I have. I am going to probably bite the bullet and upgrade to a new 40 or 50HP outboard as I am finding it very difficult to find a used one that is not as old as me. I just want to know what I need to be looking for in shaft length and jackplate if needed.

Thanks,
SDS

 

[tashasdaddy]

Re: Transom height vs shaft length

you do not measure to the bullet. you measure from where it sit on the transom to the AV plate just above the prop. Older motors measured 17-18 inches were short shaft, for a 15 inch transom new short shaft measure 15 inches. older long shaft measured 22-23 inches to the plate, new motor measure 20 inches for a 20 inch transom. clear as mud?

 

[Shockley]

Re: Transom height vs shaft length

Tashasdaddy, this is a 1988 model so it is probably a short shaft. I will have to measure when I get home. So do you think I need a 20" shaft on this boat? This would explain why the motor was aerating, I guess. The point of the bullet measured 2-3/4 inches below the centerline of the hull. If I am correct the AV plate needs to be on or right below the centerline. Is that right?

 

[tashasdaddy]

Re: Transom height vs shaft length

even or 1 inch above the keel.

 

[Shockley]

Re: Transom height vs shaft length

If I find a reasonably priced short shaft motor, can I use a jackplate to lower it to the desired level?

 

[tashasdaddy]

Re: Transom height vs shaft length

does not work well. you have to set it back so far, to be able to tilt the motor. also taking a chance of swamping the motor on a quick stop.

 

[Shockley]

Re: Transom height vs shaft length

Thanks for your help. I'll go back to the drawing board. I am having trouble finding a motor for this boat. I can buy a new boat for the price of some of these motors if I go new. I'll keep looking.