Rob
We need 2 to 3 hours of sunlight to restore the batteries to full capacity following the 15 to 20 minutes it takes to get clear of the marina and hoist sails.
Completely recharging the 8kWh would take two days of good sunlight with 600W of panels. We could fit a lot more panel area and use the panels for motor sailing but for just weekend use the 600W will be enough. I have some panels that are semi-rigid to fit to a curved deck but Peter's are standard roof mounted panels.
The boat is out of the water now and Peter will be getting quotes to repair. He hopes to be able to get different rudders and improved mounting by negotiating once he the initial quote. He plans to work on the bows and seal the outboard well before it is put back in the water if the yard costs are tolerable.
I have been looking at rudder options. If we put a flat plate on the blade top that has width starting at the thickness of the blade at the shaft and angling outward at both sides at 20 degrees we should ensure the rudder is always fenced against the hull so this overcomes the instability we get and the reduced effectiveness once the top of the blade is away from the hull. That means we could consider blades with larger cord.
Blades probably thicker sections although I have not yet looked at where cavitation will start. Also streamline sections with a sharper trailing edge. Existing rudders are more like a series of flat panels and the trailing edge is about 20mm wide; 10mm radius.
I am also looking at winglets on the bottom of the blade. These would be formed on a plate 300 wide and 200 long with leading edge raked at 30 degrees and a 20% thick cambered 16 series section. Plate bolted to the bottom of the rudders.
Aim is to get rudder blades no more than 600mm below the hull but having better performance than the existing rudders.
The rudder shaft tube would be stainless rather than PVC. 600mm high bulkheads fitted 300 either side of the shaft. The core to taper from the bottom of the shaft tube to the bulkheads replaced with solid glass. The top of the tube supported in a horizontal bulkead between the two vertical ones and the sides of the hull.
Overall this arrangement can be made strong enough to support the weight of the windward hull off the rudders. The blades are likely to still fold back if they hit something solid at speed but they should survive a heavy grounding on an inclined bank.
Rick
On 31/01/2013, at 11:38 AM, Rob Denney wrote:
Thanks for that. Very impressive.
If you have 400W of solar panels, will 2 hours of (bright) sun fully charge 8kWh batteries?In bright sun, could you motor at 4.5 knots (4kWh) without battery use?Hope it proves reliable, as this is a significant jump in auxillary motors, imo.robOn Thu, Jan 24, 2013 at 3:31 PM, Rick Willoughby <rickwill@bigpond.net.au> wrote:
Rob
We have total nominal stored energy of 8kWh. This is more than I initially planned because the second set of cells have higher capacity than the first. They were slightly cheaper in terms on $/Wh so were better value. Both systems are completely isolated electrically. On the one occasion we ran one bank down to allowable minimum voltage we got about 5% more charge into it than the nominal capacity. So I suspect we can safely pull out the 8kWh although you do need to be conscious of the battery state similar to any fuel tank. The difference is the energy source is ubiquitous whenever there is light in the sky. The panels drop output when clouds are overhead but still significant output.With clean hull and low wind we got 4.5kts with 4kWh - I was aiming for 5kts. We were doing 3kts with total of 1.5kW this week. I did not measure the power drain at full speed of 6.5kts but it would have been over 10kW total from the two batteries. So range depends on the speed you are prepared to move along at. We can steer with the rudders using only 500W on both motors - about 2kts. We can spin the boat in its own length using motors alone.So far only the small battery is being charged with solar power. It is connected to 4 x 50W panels that were at hand. The intention is to get 2 x 200W panels for the larger battery. There is room on the cabin top for more panels but at this stage there will be ample capacity with total of 600W for day sailing getting in and out of the marina and any anchorages. Our little trek across the top of the bay this week used about 20% of the battery capacity but we sailed more than half the 6nm round trip.In good sunshine the batteries will be recharged in a few hours after motoring out from the mooring.The 200W panels cost $1/W so they are tremendous value these days. I have some 100W semi-rigid panels for my solar boat that cost $2/W. They were attractive due to their low weight of 3.85kg and ability to fit neatly on a curved surface. These can be fitted on a low trafficked deck or cabin top and walked over with feet or soft shoes.The durability of what we have built can only be tested with time and use but it has already made the proa more user friendly. The total weight of thrusters, batteries and controls is roughly the same as the 60HP outboard, its mounting, controls and fuel tank. The solar panels are extra weight but worth it when you consider the convenience over liquid fuel.There is a 2.5kW petrol genset on board at present that is used for power tools but also provides emergency charging capability.As you know this boat has a lot of windage and it is something that concerns me with regard to open water operation. It is not too hard to build a light boat with materials available these days but windage becomes an issue for performance and ultimately survival.RickOn 24/01/2013, at 3:01 PM, Rob Denney wrote:Also keen to know how long the batteries last on a charge at various boat speeds and how long they take to charge with the solar panels.Rick Willoughby
Rick Willoughby
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