"Electricky Dicky" wrote in message
...
On Fri, 08 Sep 2006 22:58:51 GMT, "Adrian Smith" wrote:

What prop size for my narrowboat?

Hull: 70ft long 6ft 10 inches wide.
Weight: 10 tons

10 tons is 22400lb water is 62.5lb per cu ft
therefore boat displacement is 358.4 cu ft
Asssume length 65 ft and width 6.5 ft therefore area = 422.5 sq ft

358.4 divided by 422.5 is 0.848 ft = 10.18 inches draught


Engine: 48 BHP at 2800 (54BHP at 3000)

There is 11 inches between the centre of the shaft and the counter


Based on the above about 8 inches of the prop is out of the water!!!!
;-) No wonder it does not go ;-)

I currently have a prop with an 18 inch dia and 13 inch pitch. However the
engine never seems to struggle to turn the prop even when slamming in
reverse from full forwards.

Adrian Smith

Adrian sorry but your numbers do not compute.
Suggest that you check draught front and rear, your boat is more than
10Tons.
You also need gearbox ratio and distance from top of skeg to propellor
centre.

Richard

Nb "Pound Eater" Parkend G+S

I think I gave the Gear Box ratio in an update but it is 2:1

Just over 11 inches from centre of shaft to the counter/ Skeg.

mmm I had calculated approx 10 tons, anyway the draught is currently 23
inches. I'm going off to recheck my calculation now:-)

Adrian Smith