CONTINUOUSWAVE

I have just acquired a 1987 SUPER SPORT 15. I intend to use the original 1987 Yamaha 50-HP two-stroke-power-cycle engine on the boat now; it's in good running condition.

I tested the boat when I bought it, but the tachometer was broken, so I couldn't get any good test data on the 10 x 15-pitch aluminum propeller, which was in bad shape. I want to buy a new stainless steel propeller.

[Somewhere] I have read conflicting information on propellers

What is a good all-round stainless steel propeller [for a Yamaha 50 on a SUPER SPORT 15]?

I want decent torque and decent speed.

The boat will primarily be used for pulling a tube or wakeboard and for exploring the bay. Thanks.

ASIDE: my first post.

Prop testing is a bit of art and science. Trial and error.

Read this thread. Especially comments from Fishnff and OverTheLine, two respected members.

http://continuouswave.com/ubb/Forum4/HTML/001733.html

Keep in mind Yamaha has two stainless prop options, painted and polished. The blade designs are not the same so the sizing will not be the same. Check with the dealer.

I would start with the 14" painted steel propeller.

If you don't have good retail support, I would reach out the Ken at Propgods. He knows props and whalers.
https://propgods.com/

Thank you, Phil, for the very good information.

A propeller does not create torque. That is the realm of the engine. Generally a two-stroke-power-cycle engine will have reasonably good low-engine-speed torque. Outboard engine manufacturers just about never reveal data about outboard engine torque. A propeller converts the engine torque into thrust to propel the boat.

For best all-round performance, an outboard engine should be fitted with a three-blade propeller. The propeller pitch should be chosen so the engine can accelerate into the upper end of the manufacturer's recommended range of engine speed for full throttle. Typically this will be a range of about 4.5000 to 5,500-RPM. Check the owner's manual for your particular engine to find the recommended full-throtlte engine speed ranges. You should be aiming for somewhere in that range when the engine is at full throttle. This will allow the engine to produce the maximum horsepower. It is typical for two-stroke-power-cycle engines to have the peak horsepower output occur slightly below maximum engine speed. It is also typical for two-stroke-power-cycle engines to produce more horsepower at low engine speeds than a four-stroke-power-cycle outboard engine, speaking generally.


Fig. 1. Power curves of two-stroke and four-stroke outboard engines from published data.

To not continue to use a damaged propeller was a good decision.

With 50-HP you can certainly get good results with an aluminum propeller. A steel propeller may give more ultimate top speed. Depending on the gear case on the engine, a steel propeller might be too heavy. If the manufacturer recommends steel propellers, then the engine should be able to use them. Steel will be more durable than aluminum. Steel will survive small impacts, while aluminum will not.