Thanks for the suggestion Tom and i believe that you are correct. IF a prop was maximized for propulsion efficiency and you reversed it then it would be maximized for regen. A prop cannot be maximized for both forward and reverse propulsion and i have the feeling that for all prop designs the reverse efficiency is not even considered. Whatever you can get from reverse you get and no one worries about it at all as ANY reverse efficiency is simply good enough.
Certainly I would use LEDs and indeed every possible means of reducing electrical demands.
Props can always move a boat in reverse and reversing the prop would have the result of using whatever thrust is normally used for reverse in the forward direction. Again since very minimal forward speed is needed the trade off to get the improved regen is a very good one.
I'm pursuing the goal of being energy independent on the boat. A tri has the best possibility of doing this because it takes so little energy to move them in the first place. I'd always seek to recharge via solar, wind and regen(still wind) while falling back to shore power when it was extremely available or a diesel DC gen for extraordinary circumstances.
A prop powered up to the point where it only provides say 5 watts of recharging power is simply not detracting that much from the boats speed under sail. As one adjusts the controller so as to provide more and more regen the drag increases. At some point one attains the maximum regen possible for the prop/sail plan/hull combination. At that point if one could suddenly add another ten square feet of sail the regen and speed of the boat would naturally increase to a new and higher point of balance.
I don't yet know how to predict what the balance point between speed and regen would be for a given system but the above MUST be true.
I think that there is a misconception common within this group that speed produces regen but that simply cannot be the case. A certain minimum speed undoubtedly needs to be reached to spin any prop but after that the energy that can be removed from the prop is directly related to that being put into it by virtue of sails (or whatever) driving the boat through the water.
If one will take as given that 3 knots will allow regen to begin then how much power can be removed at 5 knots is completely dependent on how much power is driving the boat. An aircraft carrier could have a prop the size of an automobile and produce kilowatts of power at 5 knots but a small sailboat might not be able to produce 20 watts at the same speed because at the very second one attempted to produce more the speed would decrease.
Two things seem fairly clear to me. One, the speed of the boat WILL be affected by the amount of energy one attempts to siphon off and into a battery bank via regen and two, the more power there is driving the boat then the more power one can siphon off before the speed reduction adversely affects the ability to generate the power.
There will always be a balancing point where regen is maximized and that has to be a balance point between sail plan (driving force) and hull drag plus regen drag. Speed doesn't produce regen but rather the driving force of the sail does.
If you had a row boat and contrived to place a 5hp engine plus enough weight to create a 200 lb load in the boat and then placed a regening prop into the water sufficient to slow the boat to say 5 knots then you would be producing say X watts of power.
If you then doubled the hp to 10 but adjusted the weight so as to remain exactly a the 200 lb load it would then require a larger regen prop to slow the boat to the same 5 knots producing Y watts of power. Every watt of the Y-X power would be from the added 5 hp as all else would be constant.
Just another way of saying that the speed of the boat has nothing to do with the regen but rather it is the power that is being put into the boat propulsion that determines the regen that can be taken out.
Which is to say again, bigger sail plan equals more regenable power.
Just thinking on paper here. Thanks for you patience. :-)
I STILL think you are right with reference to the reversing the prop idea. IF the prop were properly maximized for propulsion then reversing it would yield a prop properly maximized for regeneration.
I've never read anywhere what the efficiency of a prop in reverse is and perhaps i will go look for that now. Do you have any idea?
From: tom_f22wanabe <tom@triatic.ca>
To: electricboats@yahoogroups.com
Sent: Friday, October 12, 2012 10:03 AM
Subject: Re: [Electric Boats] regen, displacement, sail plan, hull form....
I suggested that reversing a prop would be a cheap way of improving the regen efficency. But just that, a cheap way of proving the concept, as opposed to building a custom regen prop. I any case the taper would have to be machined the other way and the prop would then be ruined if you want to use it in the normal direction.
As others on this list have pointed out before - any gain in regen efficiency will probably be more than offset by the reduction in driven efficiency.
Brown and Marples were trimaran pioneers for many reasons but mainly because a tri could cut the time spent on passage. They liked outboards for power because they were lighter and could be completely raised out of the water and they recommended minimum electrics to reduce weight. Brown would not slow the boat down on purpose.
IMHO: an efficient feathering prop on a trimaran, use LEDs and switch a big power drain like a water pump to manual and you might make up all the power you gain by using regen.
Tom
--- In electricboats@yahoogroups.com, Michael Mccomb <mccomb.michael@...> wrote:
>
> i completely agree that a larger prop will be needed... Â i believe all the boats currently trying to get regen are configured in such a way as to maximize the efficiency of the motored propulsion rather than the regen.... if one reverses that notion because one doesn't care if the propulsion is slower due to an inefficient propulsion oriented prop then fitting out with a prop to maximize regen is possible.... Â i'd be perfectly happy with 5 knots total headway out of a tri as that would give me the ability to get out of a mooring AND sufficient headway to maintain steering control
>
> the larger prop will produce more drag, more regen and will require being turned when not regening in order to maximize the speed under sail.... Â shouldn't take too much juice to turn a prop up to where it is merely no longer producing much drag
>
> i had a fellow suggest that the correct configuration for a regen prop would be a normal highly efficient prop mounted backwards.... Â intuitively this seems correct to me.... Â a well designed and sized Michigan Wheel for instance when mounted backwards would give somewhat crummy forward propulsion but should give great regen..... Â any thoughts on this perspective???
>
>
> ________________________________
> From: "matwete@..." <matwete@...>
> To: electricboats@yahoogroups.com; electricboats@yahoogroups.com
> Sent: Thursday, October 11, 2012 10:00 AM
> Subject: Re: [Electric Boats] regen, displacement, sail plan, hull form....
>
>
> Â
> Regen has been implemented on several boats whose owners are on this list. Â I've not heard anyone talk about getting more than 100 watts or so out at displacement speeds. Â So I think there's a high bar to cross to get even 200 watts, let alone 500watts. Â At most, the prop will see effective water speed that is perhaps 70% of that flowing under the boat. Â At such speeds, you'll need a huge prop to get the power you're looking for.
>
> From my HTC Sensation 4G on T-Mobile. The first nationwide 4G network
>
As others on this list have pointed out before - any gain in regen efficiency will probably be more than offset by the reduction in driven efficiency.
Brown and Marples were trimaran pioneers for many reasons but mainly because a tri could cut the time spent on passage. They liked outboards for power because they were lighter and could be completely raised out of the water and they recommended minimum electrics to reduce weight. Brown would not slow the boat down on purpose.
IMHO: an efficient feathering prop on a trimaran, use LEDs and switch a big power drain like a water pump to manual and you might make up all the power you gain by using regen.
Tom
--- In electricboats@yahoogroups.com, Michael Mccomb <mccomb.michael@...> wrote:
>
> i completely agree that a larger prop will be needed... Â i believe all the boats currently trying to get regen are configured in such a way as to maximize the efficiency of the motored propulsion rather than the regen.... if one reverses that notion because one doesn't care if the propulsion is slower due to an inefficient propulsion oriented prop then fitting out with a prop to maximize regen is possible.... Â i'd be perfectly happy with 5 knots total headway out of a tri as that would give me the ability to get out of a mooring AND sufficient headway to maintain steering control
>
> the larger prop will produce more drag, more regen and will require being turned when not regening in order to maximize the speed under sail.... Â shouldn't take too much juice to turn a prop up to where it is merely no longer producing much drag
>
> i had a fellow suggest that the correct configuration for a regen prop would be a normal highly efficient prop mounted backwards.... Â intuitively this seems correct to me.... Â a well designed and sized Michigan Wheel for instance when mounted backwards would give somewhat crummy forward propulsion but should give great regen..... Â any thoughts on this perspective???
>
>
> ________________________________
> From: "matwete@..." <matwete@...>
> To: electricboats@yahoogroups.com; electricboats@yahoogroups.com
> Sent: Thursday, October 11, 2012 10:00 AM
> Subject: Re: [Electric Boats] regen, displacement, sail plan, hull form....
>
>
> Â
> Regen has been implemented on several boats whose owners are on this list. Â I've not heard anyone talk about getting more than 100 watts or so out at displacement speeds. Â So I think there's a high bar to cross to get even 200 watts, let alone 500watts. Â At most, the prop will see effective water speed that is perhaps 70% of that flowing under the boat. Â At such speeds, you'll need a huge prop to get the power you're looking for.
>
> From my HTC Sensation 4G on T-Mobile. The first nationwide 4G network
>
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