Belt drive

[Rich47]

How does one go in reverse using a belt drive? I have been thinking about the question off and on as I am planning to build a three ton steel sailboat with a 6 hp Yanmar diesel from a genset as an auxiliary. I recall reading in Donald Street's book The Ocean Cruising Yacht that belt drive in yachts was quite common in the "old days", presumably before World War II. It was said that the practical limit for power transmission was 5hp per belt, and that any more rquired multiple belts. The schematic drawing showed a bank of ten belts. There was no mention of arrangements for motoring in reverse.
My current notion is to mount the engine with the crankshaft transverse to the propeller shaft, with a pulley on either end of the crankshaft, two pulleys on the inboard end of the propeller shaft, two belts and two pairs of idler pulleys/belt tensioners that would redirect each belt the 90 degrees required to drive the shaft. If you can picture this in your mind, brief consideration will show that one of the belts when tightened will turn the prop in the forward direction, but with that belt loosened and the other engaged the prop goes in the opposite direction. There is no twisting of the belt in a figure eight (which would be a different means of reversing direction that would be necessary if both belts were driven off the same end of the crankshaft).
The advantages of such an arrangement would include
1) No precise alignment of the crankshaft, transmission shafts and propeller shaft is necessary, so no shims and feeler gauges and micrometers and worry over that. The angle of the propeller shaft with horizontal is not critical as with conventional gear transmission and engine in line with the shaft.
2)If the thrust bearing is aft of the drive pulleys on the propeller shaft, a belt can be replaced with minimal efffort/ no disassembly at all.
3)Both ends of the engine are easily accessible; indeed the whole engine can be unbolted and removed for repairs quite simply, and reinstalled equally simply.
4)There are no gears and no lubricants and nothing is in danger of burning up except the belts, which are relatively inexpensive and easily replaced as mentioned.
5)The reduction ratio can be chosen by varying the drive pulley diameters, can easily be changed if experience demands, and could even be different for forward and reverse.
The limitations are imposed by the requirement for belts that can twist through 90 degrees. This would seem to limit the application to low power and vee belts.
Dos anyone know if anything like this has been tried (particularly if it failed)? What would be a practical way to fabricate a thrust bearing so that the spinning propeller sends the vessel forward rather than simply pushing its shaft towards the engine? Would pillow blocks on the crankshaft ends be necessary to avoid side loading the engine bearings?

[duluthboats]

Reverse and more with the Kitchen rudder. http://boatdesign.net/forums/showthread.php?t=418
Gary

[Rich47]

Thanks for the fascinating tip! This device is for a powerboat though, not an auxiliary sailboat. Still, I enjoyed reading the thread.
Just what is your quotation from Weston Farmer supposed to mean? I only know that he was a yacht and workboat designer in Minnesota. I was fortunate enough to acquire by chance his inscribed copy of Claud Worth's classic book Yacht Cruising.

[duluthboats]

Rich,
1. I think with some creative thinking a Kitchen rudder would work on a sail boat.
2. “The hand feeds the mind” was Weston’s way of saying you have to do it before you really understand it. For years I had a quote hanging in my tool box “To know you must do”, this was a translation, author unknown and source unremembered. Than I read Weston. It’s a slow way to learn but for me the only way.
3. There are other work arounds for reverse using pulleys. But if you want to keep things really simple I would suggest a paddle.
4. I was born in WI and grew up in MN, I just moved to the west 8 months ago, after
50 plus years in MN.
5. Welcome to the forum!

Gary