Hi Micah,
The first thing that I'll say is that I've got no real life data about electric sailboats that are this large, so anything that I say here will be theoretical speculation. That said, let me take a stab at it.
First, I looked up data on a few 55' steel yachts. It looks like you would be dealing with a LWL of about 45' and a displacement between 30 and 40 tons. Based on a number of different rules of thumb, I'll peg your 3kt power demand to be around 2.5kW. If that is the case, then a 5kW drive system (about $4000-$5000) should suffice for low speed cruising (max speed around 4kts).
Let's call "all day" 12 hours. At 2.5kW, you'll need 30kWh to run at that load for 12 hours. If you want half of your power to come from solar, you shoud have at least 3kW of total solar panel capacity. That works out to be fifteen 200W panels, each panel is roughly 3' x 5', so the array would be 225 sq ft. (15' x 15'). Finding that much space for solar panels might be problematic. The panels would cost about $12,000 US and weigh about 500 lbs.
You'll also need at least 15kW of usable battery capacity. Let's examine some options:
In flooded golf cart batteries you would need almost 30kWh of rated capacity to supply 15kWh to a 60% depth of discharge. these batteries would weigh about 1300 lbs and cost about $3200 US.
In AGM batteries, you would need 24kWh of rated capacity to supply 15kWh to a 70% depth of discharge. These batteries would weigh about 1200 lbs and cost nearly $5900.
In Lithium (LiFePO4) batteries, you would need 20kWh of rated capacity to supply 15kWh to 80% depth of discharge. These batteries would weigh about 500 lbs and cost about $8500.
To recharge the 15kWh from a regular diesel engine with a 1800W (150A x 12V) alternator dedicated to recharging, it would take almost 12 hours to replace the energy that was missing from the batteries. Of course, the alternator should be matched in voltage to the drive system.
All of this data is centered on cruising at 3kts under power alone, no sails. You could decrease the size of the panels by increasing the size of the bank, however, you should be getting an idea of what this project might cost.
So, could this work? Perhaps. Is it complex, heavy and expensive? Yes. Could it be worth it? That is up to you.
These figures are all guesses, but if you did the conversion, you may find that they are fairly close.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
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> Micah Broussard sent this post, but it landed in my personal email account:
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> ===== Message body =====
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> Hello all, i have been lurking for a while and following the postsbtrying to gather some information on electric drive options and this seemed like as good a place as any to jump in.
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> My better half and i are considering options for a full time cruising retirement on a fill displacement boat, something like a diesel duck, steel in the 50 to 60ft range.
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> I plan to have enough of a diesel to drive the boat and meet or needs from getting from point a to b.
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> What was interesting to me way how well the solar seemed to help with the zodiac so i ask would it be practical to have an electric drive as a backup drive that i could employ when our speed is not important and when the sun cooperates. I understanda i will need a propulsion bank but how much wouold that need to be if i motored electric with a large solar aray during the day then perhaps motor and recharge the back over the evening.
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> Money is important, don't have endless funds to buy equipment but i can justify more solar panels and batteries if they will save me from buying more diesel down the road.
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> So if a decent cruise speed with a diesel is 5 to 6 knots, what size motor would i need to get the boat to 2 or 3 knots on EP and what size bank and solar panel would be needed to keep it going all day?
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> Make sense to anyone?
>
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