Hi Bill,
My first response is that you re tackling a very difficult project, but we can break it down into managable pieces. We'll use the Sun-Cat 46 as a baseline to see how feasible your proposal is.
The Sun-Cat 46 promo info is typically big on nice photos and short on performance data. Let's see what can be deduced from the info that they do provide....
Things we know: the boat has two 8kW drives, two 23kWh battery banks, 6 kW of solar panels and cruise speed of 4.9kts. Less useful is the battery only cruising range of "up to 8 hrs". What we're looking to figure out is how much energy it takes to drive the boat at 4.9kts.
We're going to have to make some assumptions. The battery boxes are isolated and vented, so I'll assume that they are flooded cells. I'll pretend that the 8 hour range is at 4.9kts (probably optimistic). Using that info, 46kWh of flooded cells will last 8 hrs to 100% depth of discharge with a 94A load. That's 47A per drive. So 4.9kts is 4600W.
Based on that, let's examine your stated requirements. You want enough battery to cruise at 5kts for 24 hours. You'll need at least 110.4 kWh of battery capacity. If you used Trojan T-105s, you would need 80 batteries that would weigh 5000 lbs and cost about $12,000 US. Lithium would cut the weight almost in half to 2800 lbs and cost about $46,000 US.
Lets assume that you average 8 hours of motoring per day (some days more, some days less) If you want to collect all of that via solar, then you'll need to collect about 37kWh per day. In the Caribbean, stationary panels that are oriented the right way collect an average of 5 times their rating per clear day (more in summer, less in winter). So you should have about 7.5kW of solar panels to support the average 40nm of cruising per day. How big is a 7.5kW array? I'll use a Sanyo HIT-225A01 home solar panel to give a rough estimate. Each panel produces 225W, is 63" x 32" x 2", weighs 36 lbs and costs $770. You would need 34 panels to hit the 7500W rating. The 34 panels would weigh 1224 lbs without mounting structures and cost $26,000 US. Arranged in a 6 x 6 array with one less in the first and last rows, the array would be 31.5' long and 16' wide.
If you're aiming for the SunCat 46 specs, you've used up 6200 lbs of the total 14,000 displacement (that includes the weight of the boat too) and $38,000 of your budget on flooded batteries and the solar panels alone. I included all of my assumptions and the math so that you can adjust your requirements if needed. I spec'ed readily available components, if you can find better for cheaper, your chances of success go up.
The only magic bullet that will make a significant change to the calcs is much more money. Then you might be able to find bleeding edge technical stuff that might save weight or improve performance.
If this hasn't scared you off already, then you can start digging into the details that you asked below, but I thought that looking at the high level requirements would be a good place to start.
Fair winds and calm seas,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Galstaf" <richard@...> wrote:
>
> Hey folks,
>
> I have posted occasionally but follow the discussions on the list with great interest in advancing battery and solar technology.
> I am still looking to build my live-aboard cruiser in the 40-60 feet size range.
> I know most of you guys are sailors, but the knowledge of solar and battery tech would be applicable.. so I am looking for recommendation on recreating this German solar boat on a budget. This is pretty much exactly what I want, a solar powered catamaran.. no sails, no regen, etc.
> Please check this out
>
> http://www.solarwaterworld.de/index.php?id=69&L=3
> http://www.solarwaterworld.de/fileadmin/pdfs/SunCat-46-prospect-english.pdf
>
> My current idea is to take a used aluminum or Fiberglass passenger ferry preferably with a blown motor(s) and strip out the engines and seats and convert it to a live aboard with electric power and a large solar array over the entire top of the boat.
> This will be augmented with a larger genset when needed for emergency reasons.. but ideally the genset will rarely need to be started.
> I would want battery storage to allow for 24 hours of cruising at around 5 knots.
> The boat will be designed to hop between the islands in the Caribbean, and this should allow plenty of time for the array to top up the batteries if consumption has exceeded the solar array capacity.
>
>
> So.. if this were *your* project, what would you recommend for brand and sizing the electric motors, what brand and type of batteries would you buy (Lithium or equivalent technology), what controller and what and where would you get the solar panels from?
> How tall would you make the vessel, what should I consider in terms of weight and positioning of the array?
> Is there a practical way to make an array of this size "directional", i.e. follow the sun.
> The more detailed you can be the better. If you know of someone else that has put together a non-sailed cruiser in this sort of size range and has a blog, that would be awesome too.
> I want to keep the cost of the whole project considerably under $100K. :-)
>
> Many thanks!
>
> Kind regards,
> Bill
>
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