The future of batteries, solar, and electric motors....

[john61ct]

See, any propane freed within the hull sinks, filling the bilge.

So detectors, alarms, bilge blowers are reactive parts of the solution.

But the preventative measures are (should be) part of the original boat design, or require major refitting.

Yes people do it, but sometimes boom, even with military-level attention to inspection/maintenance checklists.

[BigBeakie]

Originally Posted by GTom

Depends how much you want to throw at your boat. On a cat, even a 2kWp solar (20 m2) and 2x1kW windmills are possible. Not saying economical or quiet (listening the wind generators in stereo...), neither that it provides full electric propulsion, but provided unlimited funds feasible, and might get you out of some awkward situations.

Personally I am with you, I don't think serious electric propulsion becomes a viable solution before we see those 90% efficient (500Wp/m2) solar panels and the energy density of the batteries doesn't go up 4-5x.

Btw, the Watt&Sea gear with 280mm propellers produces 400+W each at 8kts:


I fetched my fuel consumption guess from here:

The Watt& Sea is a nice unit, but certainly not the most efficient by a long shot.

The regen from the new Oceanvolt Servoprop is 1,800 watts at 8 knots from each motor. So, over 4 times the power output of the WATT&SEA at the same boatspeed. That obviously is a very useful amount of power under sail. At 7 knots it drops to 1,200 watts.

[BigBeakie]

The Oceanvolt Servoprop graph with actual test data points.

[Paul Elliott]

Originally Posted by BigBeakie

The Watt& Sea is a nice unit, but certainly not the most efficient by a long shot.

The regen from the new Oceanvolt Servoprop is 1,800 watts at 8 knots from each motor. So, over 4 times the power output of the WATT&SEA at the same boatspeed. That obviously is a very useful amount of power under sail. At 7 knots it drops to 1,200 watts.

I think we need to define efficiency. I would consider it being power generated vs drag. Do we have this data for either Oceanvolt or Watt&Sea?

[john61ct]

Drag while *not* in use would be most critical to me.

Worth giving up power output IMO.

Drag while in use, not so important?

[Paul Elliott]

Originally Posted by john61ct

Drag while *not* in use would be most critical to me.

Worth giving up power output IMO.

Drag while in use, not so important?

I think that drag in either case is a factor. I will be sailing whether or not I'm using the generator, and I would like to keep my speed up as much as practical.

[BigBeakie]

Originally Posted by Paul Elliott

I think that drag in either case is a factor. I will be sailing whether or not I'm using the generator, and I would like to keep my speed up as much as practical.

Certainly no-one would want to drag around a large 3 blade fixed prop all the time on any sailboat, that goes without saying. When you are not in regen with the Watt & Sea, you just lift it up out of the water. That's easy. With the Oceanvolt Servoprop, it is a variable pitch feathering prop that aligns with waterflow, and we all know a good feathering prop has insignificant dragfor a cruising boat.

But when in regen operation, the drag is about what the power generated value is. If at 8 knots boatspeed you are producing 400 watts of power, you'll have about the equivalent drag in resistance, ie, about 400 watts. If with the Servoprop you are getting 1,800 watts, you are getting about that much drag as well.

But the question is, how much will that slow down the boat? To answer that properly, you need to know A) the resistance curve for your boat vs boatspeed, and, B) the power generated by your sailplan at a given boatspeed.

When you look at both of these, you will see that that the amount of power needed to be produced by the sails to overcome water resistance at 8 knots is really, really big. For every knot of boatspeed the resistance curve just keeps heading up at a steeper angle > exponential not arithmetic progression.

By comparison, the amount of drag from regen is quite insignificant. It is about 1% to 3% when you run the numbers. I'm sure our engineer friends here can educate us on how to work that out?

That is why the users of Oceanvolt regen ALL report the effect on boatspeed is barely noticeable.

I also do not think, as some have proposed elsewhere in the Oceanvolt thread, that you need to be sailing at maximum "hull speed" in order for the regen not to slow the boat. This missed the point. The amount of regen drag is directly proportional to the resistance curve and the sail force required to overcome that resistance, andit is a small percentage of that wind force that you are deducting from the wind force vector. Hence, you don't slow down much.

Therefore efficiency in hydrogeneration is simply how much power do you get out for a given boatspeed. KISS