Comments on a few fibers in this thread:
My 7.5 hp Johnson outboard
develops a measured 125 lb static thrust in forward and 60 lb in reverse at wide open throttle. I think the gear
ratio is the same in forward as in reverse. At least in my memory the gears in the lower end look the same. I have three props for the engine
(all different), and I can not remember which was in use when I did the measuring this summer.
3HM35F has a 2.14 ratio in forward and 2.50 in reverse. The 14% lower prop speed for the same engine
speed in reverse should reduce the speed of the water
exiting the propeller
by 14% and also reduce the weight/time of the water
exiting the propeller
by 14%. It is sort of a double whammy on thrust. In addition the blades of the prop seem to have a bit of an airfoil shape that might not like reverse. I have not measured the static thrust in forward on the boat.
On page 222 in Earl Hinz, "The Complete Book of Anchoring
and Mooring" 2nd rev ed, static thrust ranges from 20 lb/hp for displacement
hulls, to 15 lb/hp for semi-displacement hulls, and to 10 lb/hp for planing hulls. (1) The book never says forward or reverse. (2) I'm guessing that the differences in the table are due to the use of props really designed for use at cruising speed being used at zero speed. (3) On the next page after talking about powerboats with twin 200 hp engines, he says, "Sailboats faced with storm conditions at anchor may want to seek the services of a powerboat to help them powerset their anchors before the winds arrive."
Digging through a coffee can full of high shank feet years ago looking for a 1/4" cording foot to make the piping on my boat cushions
, I found a foot with a zig zag hole and two side-by-side tunnels under the foot. The owner of the shop said the foot had been used to sew the ropes together in thousands of the loops at the end of the guy lines of army shelter-half tents. So, at least the US army machine sews eyes in small diameter lines.
I got a great eBay deal on my 0-2000 lb Dillon dynamometer by mispelling dynamometer "dynomometer". (I can't spell.) A seller also could not spell, and I was the only bidder. I bought it for a song to watch the loads on my anchor line in a breeze with and without an anchor riding sail.
In the Bahamas
with clear warm water, I many times find my 44 lb Bruce with only one ear buried by my reverse. Three times after a front, it has completely dug in with only the shank partly showing. I am guessing that the wind
pulls harder than my engine. (I am a 34' Pacific Seacraft
It might be fun to walk a marina dock
with a dynamometer in hand asking the people in the cockpit
with a drink in their hand to try reverse at full speed with the tension gauge tied between their bow cleat and a dock
cleat. You could get a bunch of reverse/thrust data and maybe some dock cleat strength data. You might do the same thing with anchored boats, but it might not be as much fun.