No, they most certainly don't approve of spun props during a race. However, from a purely technical point of view, spinning the prop to cancel the drag is no different than a feathering prop. It's just difficult to ensure there is no "throttle abuse". However, if there were an controller setting for "electro feather", then it would just be matter of getting the RCs and various organizations to accept a feathering algorithm, and handicap accordingly. Imagine having a 3-position key switch connected to the controller: Off-On-ElectroFeather.
Much as there is more than one way to calculate true wind, there will be more than one way to set the "no-thrust" point on the throttle. Perhaps one way involves reading only the current to the motor and RPMs. Another way would integrate the STW NMEA sentence from the instruments. SOG shouldn't be used since it doesn't take currents into account.
Tracking mAmps/RPM may provide a good indicator of thrust. As soon as the curve starts tending up (prop starts loading up) you know there's too much power in the system and the throttle should back off a little.
Alternately, if you knew your speed through water precisely, then you could spin the prop at a precise RPM to match your prop rotation to the water speed. A piece of seaweed snagging on your sensor's paddle wheel could slow you down, so I would just add STW to the first method as an absolute upper band of RPM.
The important thing for even considering getting the concept of electro feathering accepted by a racing organization is that it has to be done without human input or control. Feathering props feather and folding props fold once the shaft stops spinning. Any electro-feathering would have to happen with no more than a mode-selection switch that tells the controller to spin the motor somewhere faster than regen but just before thrust is generated. There is probably a doctoral thesis in fluid dynamics in here somewhere :-)
Cheers,
/Jason
I'm not sure why the race committee would care if one was regenerating. I'm even less sure why one would want to as it would slow the boat.??
Surely, even spinning the prop to cancelling out the drag shouldn't be permitted. Do they really let you do that?
eric SV Meander
---In electricboats@yahoogroups.com, <mike@...> wrote:Jason,
Check with James to see if you will have RPM numbers when under power? If so that will help you. On my boat when I spin the propeller under sail and I notice that the rpm will continue to rise slowly without moving the AMP draw number off of "0" until I get to about 170rpm. That is telling me that I am pulling so little power that it does not register on the very precise and accurate monitor. If I calculate the forward speed of the 15X12 3 blade pro p at that time I will see that I am just about matching the speed of the water column accounting for current and SOG. I gain about 1/4 kts doing this and I attribute it to "eliminating prop drag". If I give the system more power, greater than "0" amps the boat will increase to about 1kts over the first 10amps or 400rpm. I find that I can spin the prop at the most about 550 rpm before I usually impact the sail foil. I will tell you that in our light wind sailing here in Southern California I do this a lot in the summer when not racing because it is more fun to go a little faster and certainly makes tacking a lot easier.
I would be very curious to find out what the racing community would say about the ability of the electric boat to store speed in the form of regenerative power under sail to be used later. I suspect that it would be a very quick NO!
Mike sv Fluke
Electric Yacht of Southern California
__._,_.___
| Reply via web post | Reply to sender | Reply to group | Start a New Topic | Messages in this topic (7) |
.
__,_._,___
No comments:
Post a Comment