22mm 2-blade nylon marine prop and solid-shaft drive

Hi gang, My focus lately has been with custom-built model boats.. powered by our little (.049) Cox engines. There isn't much to see on YouTube.. probably because of the inherent challenges involved with setting-up a small IC (glow) engine powered model. The Dumas company offers small boat kits and hardware for Cox engines.. but their kits are expensive and I think that most boat modelers today would be more apt to build a "RTR" electric-powered model because of the convenience.

Like many of us here; I'm a "tinkerer"... and prefer to take non-orthodox measures when it comes to my models. I enjoy the challenges involved with taking that approach. I recently sourced a jet-pump drive kit designed for a "380" brushed electric motor that I'm going to power with a Cox .049 reed-valve engine. Here's that thread.

That said; I recently searched Amazon for components to build a more conventional "surface-drive" (drive-shaft running in a stuffing-tube with exposed propeller) system for the same type Cox .049 reed-valve engine.

I found some propellers that looked promising. They were cheap.. and came with the option to run CW/CCW rotation.




Ten "pairs" for ten "bucks"...




There was the matter of how to "lock" the hub on a prospective "drive-shaft".. as they are not slotted for a "drive-dog". There's just a 1.9mm (.078") dia. through-hole.. and that's it. I did some researching on bicycle-wheel "spokes".. which are commonly 2.0mm (14GA)/2.3mm (13GA) sizes. The 2.0mm spoke has a shaft dia. of .078" and a threaded (2.2mm X 0.45mm thread) dia. of .0865" which seemed promising. They were also available in stainless steel.. which is a big plus for this application.




Ten spokes for eight bucks...




Once I received the components.. i proceeded to screw one of the props onto the threaded-end of the spoke. A tight "self-threading" fit.. which required chucking the spoke in my cordless VSR drill to "drive" the prop further onto the shaft. The hub's thickness is 10mm which is approximately the threaded length on the spoke.

The photo below shows a 1/8" OD brass tube (K & S) which has an ID of .096". That's too large for the spoke's .078" diameter.. so I need to source a tube that's a little smaller.. maybe having a 2.1mm (.083") inner diameter.




This should work well. There's no way that the prop is going to loosen on the shaft. Next step is to source a 2mm to 3.17mm adaptive coupling. I may even try to drill and tap a 2mm coupling to accept a 5-40 threaded stub-shaft for the engine side..

I like the reed-valve engines.. because they're capable of running equally well in either direction of rotation. Consider the possibility of building a twin-engine boat with counter-rotating propellers.. which would eliminate the "prop-walk" (paddle-wheel) effect. This is a possibility with reed-valve engines running these propellers.