The Steamboating Forum

I am looking for a 26-32 X 32in pitch prop. does it matter if it is RH or LH? I suppose this boils down to the question of whether RH Or LH direction is the correct or preferable direction for engine rotation. My engine is a Navy K. This is a two cylinder compound engine and I believe that engine should have a "primary" rotational direction (though i don't know which it should be). Or for that matter any compound, should it have a "primary" rotational direction?
Does this further reduce to the question of "primary" rotational direction for a ninety degree crank?
My wife and I have long ridden a tandem bicycle. I thought (engineer) it would be good to have the cranks ninety degrees out of phase. This would give four pulses per rotation. We rode this way for a long time. I pondered the cycling term "don't pedal in squares, pedal in circles". i believed this was a basic postulate for cycling. If a person "could" pedal in circles, it would be true. But the human leg can only extend with power and thus circling is but a lofty goal which clouds the physical reality which is that we pedal just like a two cylinder ", non compound, steam engine. womp-womp-womp-womp. if we could pedal in circles, the mass of the wheels wouldn't matter. since we can't, the mass of the wheels is the most critical factor to speed.
page two, My stroke force is much greater than my wife's stroke force. Therefore, i set my crank a few degrees ahead of hers so that i initiate each power stoke and she follows a little longer through the bottom.
Here is the difference between the tandem bike and the four cylnder steam engine. SLIP!!!! My bike has no slip, but my boat prop does. whomp-slip whomp-slip . Prop efficiency mandates smooth input force.
Sooo, there is a "primary" rotational direction for a compound twin engine. Which direction is it?

You always want to have the crossheads of the engine in compression when the engine is running ahead. The crossheads of the Navy K are on the port side, so a right hand prop (that turns clockwise when viewed from astern) is the one you want.

WOW!!
I will be all night trying to picture "cross heads in compression". I am not giving up yet. but help me a little?

Further, you know some things about the Navy K. I need to gain some of your knowledge about it.

Yes, the K has a single sided cross head and it is on the port side. i'm not telling you, i'm confirming my visual. The downward stroke compresses the crank and pushes against the face of the cross slide. is that right? is that part of the understanding?

Yes, going forward, on the down stroke, the crank is to starboard, so if the crosshead guide wasn't there, with the piston pushing down, the angle of the wristpin joint would cause the piston rod to bend to the port side (toward the missing crosshead guide). Likewise, on the up stroke, the crank is to port, so if the crosshead guide wasn't there, with the piston pulling up, the angle of the wristpin joint would cause the piston rod to again bend to the port side (toward the missing crosshead guide). In both cases, with the guide there, the angle mentioned above compresses the crosshead against the guide, which is what you want.

Going astern, the forces are reversed, and the wristpin joint is trying to bend the piston rod to starboard on both strokes, which would put the crosshead in tension, trying to pull it away from the guide.

Often with single guide engines, the astern guides only have about 1/2 of the bearing area of the forward guides, so an engine with a left hand prop would be wearing out the crosshead bearing surfaces twice as fast.

Whoa, Boy! Just when I start to think that I know a little bit about steam engines (thanks to lurking on this forum!) along comes a post like this one and I realize how little I know! Not discouraged yet, but certainly humbled. A greatly informative thread. Thanks much!

What amazed me was that the whole conversation and conclusion happened while I was in bed and asleep!