I have a copy of part of an original drawing of the paddle when of the John H Amos and it says the paddle wheel has a mean diameter of 18' 6".  As I can't read anything else on the drawing size wise can someone tell me what this means?

Graham

Hi,
    I believe  it is the diameter  measured between midpoints of the opposite blades

  Tom

The way I understood it when I was an apprentice was that if you had a tube the mean diameter was the the point half way between the outside diameter and the inside diameter.  In paddlewheel terms I assume it means the point between the inside and outside diameter of the floats.  Which, of course. in a feathering wheel would be the pivoting point of the float.

Looking at the GA drawing in "British Steam Tugs", which scales correctly for length and beam (from its printed scale - the original at 1/4" would be better), 18'6 would be too large to fit in the paddleboxes.  The wheels are drawn with an overall diameter of 16' with the floats pivoting on a pitch circle diameter of about 13'3.

Odd to find such a difference - I wonder if "mean diameter" in this case refers to some calculation of the wheels effectiveness, perhaps a comparison to a standard with fixed floats?