Could use some advice on a new motor length

[Frankenfish]

Hey everyone, I have some cold feet and questions about buying a new motor.

For starters, I got my 1978 johnson running well, unfortunately like a horse that had bucked me off too many times, I lost almost all trust in it. Every time I ran it, I did more worrying, listening, and cringing at every noise rather than enjoying the ride and fishing. The market in Kansas is nuts for motors of that size right now with the run on outdoor equipment and I was able to get an extra $100 over what I expected out of it. All that equated to a sold motor to a happy customer.

My wife said she would rather buy a brand new motor than take a risk on used and I'm not one to talk her out of that opinion. Most shops in Kansas are primarily Mercury dealers so I feel most confident in that brand for service and parts availability. Boat's rated up to 30, but I don't feel the need to test that. I'm pretty set on a 20hp Merc tiller with electric start.

With the investment of a brand new motor, I have some cold feet and want to make the best and most future-proofed decision.

My question is on short shaft vs long shaft. My current boat is a 14ft Starcraft Seafarer with a 17" transom height which is a short shaft I believe. Were I to get a different boat in 10 years and want to move this new motor to that new shell, would I be better off choosing the long shaft?
Do I get a long shaft and small jack plate for my current boat?
Do I get a short shaft since that's what fits my current boat?
Do short vs long shafts retain their value better or have a better market should I want to sell it eventually?
I don't care much about speed, but I do care that it handles safely. Will the long shaft vs short shaft change handling in any detrimental ways?

Thank you all for any advice.

 

[DaleH]

Attached is a PDF for setting the OB height and ensuring it wears the correct prop.

Do you recall where the OB vent plate was in relation to the bottom of the hull on your old motor? The 'default' setting is even with it, but I find 1" above to be the best for small tin boats. This may be due to the setup axiom where one can raise their OB motor 1" for every 6-12" inches of setback from the transom.

Keep in mind some hulls are just 'off' ... like my current 14' skiff hull, with a short-shaft mounted on the transom cap, the vent plate is still too low; performance is not optimized. I just bought this boat back 6-weeks ago, and the wood could need replacing, so I'm going to raise the transom height over the Winter layover.

If set too deep ... which IMHO most OBs are ... you get excessive drag, slower speed and efficiency, excess spray and other non-optimized performance issues. To your questions:

Short or Long? - Depends ... I'd measure what you had or get spec from online manual and then measure to the OB of your choice, like a short-shaft, and see where the vent plate lands. Maybe the Dealer can opine.

Long shaft & jack plate?[/b] - If the short-shaft sat too deep, from above, this would be my choice.

Short shaft? - See those above ...

Short vs long shaft value? - To me it depends on the market. Inland with many lakes, ponds and small boat and shorts might have a significantly broader appeal. If near a saltwater environment, the long shaft might have a bigger market. But I'd never buy one based upon what the future marker would be, I'd buy it for the best setup and performance needed NOW!

Handling? - Provided both are setup correctly I think it is a wash. Yeah on boats the weight carried lower is best, but I don't see a few inches of motor set height being a big deal, as I sure wouldn't lose sleep over it.

.
View attachment Setting OB Motor Height and Correct Pitch Prop.pdf

 

[ktoelke54]

I can answer a couple of your questions. Tohatsu / Mercury shaft length guidelines say their short shaft motors will fit up to 17.5 inch transom. Your 17 inch transom should work great.

Adapting your transom to a long shaft is doable, at not to much labor or expense. And if your considering a long shaft boat in your near future, and would like to keep your new outboard, it’d be worth the effort. Otherwise, I’d go with the short shaft. Keep it simple.

As to which I would choose if two new boats were setting side by side, one short and one long, I’d take the long. I like the extra depth and see little disadvantage.

 

[GYPSY400]

I would also vote for the long shaft motor, you could modify your current boat with a jackplate or reworking the wood in the transom.
My newest boat is a long shaft and I love it for when the waves are coming towards the stern - be it trolling with the wind, or reversing into wind. Most new boats are long shaft anyhow.

I would also look into a 25, if your new boat is a 16ft, the 20 may not be enough.

 

[Frankenfish]

Thank you all for the advice. It's answered some questions and brought up others I wasn't aware of.
Judging off some old pictures, I believe the old OB was set near the correct height. If I were to go with long shaft and a jack plate, that would require a jack plate of at least 5 inches to set it near the old OB height, right? Maybe a bit more than 5" since DaleH mentioned extra setback requires it to be raised slightly higher.

 

[ktoelke54]

Thank you all for the advice. It's answered some questions and brought up others I wasn't aware of.
Judging off some old pictures, I believe the old OB was set near the correct height. If I were to go with long shaft and a jack plate, that would require a jack plate of at least 5 inches to set it near the old OB height, right? Maybe a bit more than 5" since DaleH mentioned extra setback requires it to be raised slightly higher.

Your math sounds about right to me.


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[JL8Jeff]

Thank you all for the advice. It's answered some questions and brought up others I wasn't aware of.
Judging off some old pictures, I believe the old OB was set near the correct height. If I were to go with long shaft and a jack plate, that would require a jack plate of at least 5 inches to set it near the old OB height, right? Maybe a bit more than 5" since DaleH mentioned extra setback requires it to be raised slightly higher.

Depends on if you get a jackplate or just a riser plate. The riser plate would bolt to the transom with no real setback like a jackplate. Here's the riser plate I'm referring to: https://thmarinesupplies.com/products/cmc-static-jack-plate-5-inch-vertical-extension The main thing I don't like about the riser plates is that it raises the center of gravity on the motor.