Oldest high thrust outboard

I’m a big fan of the older Johnnyrudes, but building a small outboard cruiser and will need a high thrust motor. I don’t think there were any pre-80’s but I could be wrong. I think the old Sailmasters were geared and propped the same and just had longer shafts, but could also be wrong(maybe they did spin a bigger prop?).

Whats the oldest high thrust I could find and how hard would it be to locate?

Talking 5-15 horse or so.

Thanks.

Jbo

 

I'm not aware of any, but you didn't indicate the HP range you were looking for.

In the larger motors there were V4s that came with the larger gearcase, which could allow a larger lower pitch prop.

The late 90s 4 strokes were junk, but I don't think you wanted something like that.

 

In the mid 80's I had a Ranger (Mull) 26 sailboat with a Yamaha 9.9 4-cycle long shaft high thrust. Electric start and alternator. Very quiet and more than enough thrust.

 

I tried, but spell-check got me. LOL

5-15 “HORSE”, not hours.

Jbo

 

Yamaha F9.9A introduced in 1984.

The stock Evinrudes from 1974 onward had the same gear ratio as today's Merc bigfoot. Fifteen horse 1974 - 2005 ran 2.42 gears.

https://www.kirschbaum.at/ki_prop/pdf/2015/RPM Chart.pdf

 

The gear reduction ratio is only part of it, the larger diameter prop is more important.

 

The real issue is structural. The mounts and gearcases and upper chasses aren't strong enough to run high thrust on longer legs for longer periods of time. The old pre-looper Evinrudes that had the V4 powerhead on a V6 chassis had the right idea (140hp on the same chassis as a 225 V6, IIRC). The prop sizes are limited by this. Maybe the best thing to do is find an Evinrude 25 that takes an 11" prop and just put a 15hp powerhead on the thing. But realistically, I think if you are propping for 6 knots (10 ft/s) and looking for a normal slip at WOT of about 20ft/s, a 9.5" prop works just fine. If you want to cruise the Caribbean all winter with it, maybe you can save two gallons going with a bigger prop, but I kinda doubt it. At anything less than ten HP, the bigger prop will be less efficient, and I put-putted around the Caribbean at around 4 hp in my 38'er.

 

There was a OMC 9.9/15 sail version that had a vented extension so you got the thrust back in reverse, they had plenty in fwd so not an issue.
Putting one of todays high thrust 4 blades would make a good engine assuming it doesnt make too much thrust for the transom clamps?