The vortex (zone of turbulence) that follows all foils that are moving at any attack angle other than zero.What dead wood would there be on a fin keel boat?
Let me help your intuition.Intuitivly I am inclined to think that dragging a fixed prop requires more energy than one that is turning. There just seems to me that there is more slip with the free wheeling prop than with the fixed prop.
I think that the autogyro effect is different in that the autogyro has some control where the fixed blades would have the same resistance but would not lend themselves to control. The uncontrolled glide slope would be the same.
Yes, less cross sectional or less 'profile drag' because its not fully exposed to the slipstream ... the turbulence zone of the 'deadwood' is being 'pulled along' with the boat; hence, less parasitic drag on the prop if aligned vertically.Wouldn't a two blade locked vertical in an aperture see less turbulence & create less drag than one six feet behind a keel locked and not in a aperture?
Your transmission, typically of most marine transmissions, doesn't shift gears like a car. Instead forward and reverse are permanantly engaged by gears and there are two clutches. These are simple cone clutches in small transmissions. You push the cones for forward together and the thrust of the prop then helps keep them engaged. Same for reverse.What difference does it make whether
it's in forward or reverse? Either way nothing turns inside the transmission (at least for my Yanmar 1GM).
At just the right point of sail, a close reach, I can feel my wheel bucking and vibrating slightly as the vortex from the keel hits the rudder. Close hauled, there is enough leeway that the vortex misses. Farther off the wind, the vortex is not strong enough to be felt.Yes, less cross sectional or less 'profile drag' because its not fully exposed to the slipstream ... the turbulence zone of the 'deadwood' is being 'pulled along' with the boat; hence, less parasitic drag on the prop if aligned vertically.
At just the right point of sail, a close reach, I can feel my wheel bucking and vibrating slightly as the vortex from the keel hits the rudder. Close hauled, there is enough leeway that the vortex misses. Farther off the wind, the vortex is not strong enough to be felt.
Spinning props slow a boat more than a non-spinning prop. If you want to 'feel' the amount of work being done ... just measure the temperature of the spinning bearings and lubricating oil - the temperature difference is the result work!!!!
That wouldn't surprise me with an outboard prop. There are circumstances where freewheeling produces less drag. With common prop configurations in speed regimes close to their design propulsion speed, drag will be less fixed in most configurations. Unless you have a rigerous way of measuring, odds are on your side securing the prop and you'll be putting less wear and tear on the machinery.This seems to tell me less drag resistence in neutral?
Yes on all my fin keeled boats, with fixed props usually three blade, they have always sped up. This is not however an accurate method of testing as wind, current and other factors change. Usually when one is trying to eek out that last bit of speed they are also tweaking the sails etc. so this can not be relied upon as an absolute or accurate test because the measurable parameters are not fixed and are in a constant state of change with many contributing factors.Hasn't anyone just been sailing along and then lock the prop just to see the difference?
I occasionally lock my prop but if I want to go faster I unlock it.. My prop on the CS spins quite easily with a PSS seal & a two year old cutlass and will spin beginning well before two knots of speed through water. I will be measuring the exact "start spinning speed". On my C-36 & C-310 it began spinning at closer to 1.5 knots. I've actually had my prop spinning on the 310 while at a dock in Portsmouth NH with about a 2 knot +/- current.. I agree that some boats have more resistance than others and that friction resistance would cause more drag.Unless you have a rigerous way of measuring, odds are on your side securing the prop and you'll be putting less wear and tear on the machinery.
Changing angle of attack, conservation of energy, and other complex aspects of lift and the rotating foil that a prop is. The performance if aircraft props is directly applicable because their area and pitch are adjusted to match the differences in speed and fluid density. Aircraft with fixed pitch props do glide farther if the prop is stopped. However, it isn't done in practice because the pitching up of the aircraft to slow it enough to stop the prop after an engine failure loses more altitude and distance than the drag reduction gains.How do you move up the curve of friction resistance, starting at very freewheeling being more efficient, to the point of most friction, right before it stops spinning being the least efficient but then when it stops spinning it goes back to the least drag?
But when you are out of the water you have no water lubricating your cutlass or stuffing box. Mine is harder to turn on the hard too but still not difficult and I can spin the shaft by hand..Roger, on my boat when on the hard I can hand turn the propeller if I hold the blade tips but if I hold the shaft I can't apply enough torque to make it turn.