[dishwara]

There is definitely a difference between the 15 2-stroke and 15hp 4-stroke. The 4-stroke is not going to have nearly enough power at low rpm to get you on plane with a big load so that the motor would finally get up enough rpm's to actually make it's full 15hp. I would compare the 15 4-stroke as far as planing power to a 10hp 2-stroke, or worse. I'm sure that some will disagree, but that's my experience with them. I did once own a nice lightly used 15hp 4-stroke Mercury and although it ran smoothly and quietly, it didn't have nearly the power that I was accustomed to with a 2-stroke 15hp. I only kept it for about 2 weeks and sold it.
A '53 15hp Superfastwin is relatively speaking, quite a powerful motor, and one of the faster. 15hp OMC's made. If it has been properly tuned with good compression and new ignition, it is very reliable. You are not going to find a 15hp 2-stroke or 4-stroke that will outperform the '53 15hp if they are all in good running condition.
From my experience, a 550 pound load on a lightweight 14'36" jonboat with a 15hp 2-stroke would have a hard time getting on plane, and max out about 19 or 20mph at best. My 2-stroke 15hp outboards go about 22mph on my boat (15'42" duracraft johnboat) with just me and a 6gal. tank of fuel.
Basically, I would check the compression on the '53 model and if it has around 105psi and both cylinders are within about 5psi of each other, I'd clean the carbs, replace the coils, plug wires, condensers, points, fuel lines, water pump impeller, and use it. If the lower unit leaks, it's about a $40 repair if you do it yourself. You might even add a fuel pump and use a single line modern tank for about $40, or install a pressure tank rebuild kit for about $30. If your motor has good compression and a good set of gears and clutch dog, fixing it correctly yourself would be the best and cheapest route to go if you want a 15hp motor.
Just an idea,
JBJ

[galeru]

I have a 1436 Tracker with a 7.5HP (detuned 15HP) Force and go out often with a 500# load, scoots along no problem and the fish finder speedo says around 23MPH. I've taken out another person at max load (or a touch over) and it would still plane, probably 18-19mph. here

[octopus]

Thanks for the information! I seem to keep coming back to the older 2 stroke idea. That probably is the right answer, I just need to find one in the next month before the season starts more

[nenolod]

Now throw in the fact that a new 15hp tohatsu or nissan motor can be purchased for about 2300 new online and it makes the decision even harder. Is a 2001 honda worth 1500 when a 2012 tohatsu is worth 2300?

[eedcxsww]

How much does your load weigh, total weight of everything added to the boat? I have taken my boat up to 9000' where the elevation is killing OB performance and the boat would only run 13-15mph. If you were only doing 13-15MPH flatland, either that 15HP Rude wasn't putting out 15HP or you were really overloaded. [links]

[RubyShemp]

Re: Motor recommendations for a 14' jon boat

[koskenkorva]

Both standard Jon boats and semi-v Jon boats come in the same size ranges though there are much more buying options, in each size class, for standard Jon boats.

[M.I.]

Below is a rough guide to the appropriate outboard motors for different sized Jon boats. [links]

[NegativeOne]

Maximum load: 320 pounds.

[senwoarn99]

By the USCG's sizing calculation a flat bottomed 1436 with a 15" transom will be rated for no more than 15hp. These boats are designed to be lightweight. Add all that lumber and you defeat the P.O.U. of a small aluminum boat.

[xscreenprotectorx]

120lbs. Consider you've probably got 200lbs of decking in there already plus your weight & your gear. all adds up fast in a small boat. [links]

[cardinalshark]

You can use www.NADAguides.com and look up outboard motors to search around and find the lightest motor for the size you're looking for. In the 20-25hp range you're looking @ 100-105 lbs for either a Mercury/Mariner, Yamaha or Tohatsu, but an evinrude will run

[Pilot]

18 foot Jon Boats average a maximum horsepower of 40-60hp. This is a larger range and more research should be done based on your specific model. more

[nrtr]

20+ foot Jon Boats can have 75hp+ and vary a lot more in their specs, customization, and design. Here are a few averages just to give you a baseline: more

[yebyen]

12 foot Jon Boats average a maximum of 5-7hp.

[worldoffer]

I have seen others recommend a formula for flat-bottomed boats that the maximum horsepower should be estimated by taking the length (in feet) multiplied by the width (in feet) and dividing that in half. Then subtract 15 from that figure and you have your max horsepower.