T-Pain Is On A Boat: [Electric Boats] Re: Current state of affairs

Hi Jam.

1. Your panels might generate 750Wh of power per day (assuming little shading and latitudes <45). On a 72V nominal system that's less than 10Ah per 24 hours. That could be enough if you don't use much. If you're a weekend only kind of guy, then the boat could collect 50Ah while you're of "workin' for the man". If you're cruising, then the panels will cover a lot of house current but there won't be much left for your traction batteries.

2. Range is a funny thing. I made sure that I could motor over 20nm at 4kts (that's 5hrs). But the boat is considered a sailing auxiliary, the motor is a backup. When my boat was still diesel, I never burned more than 2 gallons in a weekend of coastal cruising, most of my time was spent under sail. Of course, I couldn't blindly accept such a limited range under power, so I bought a portable generator (mine is a Yamaha ef2000is, very similar to a Honda.), a backup to my backup. It weighs 50 pounds with a full tank and fits in a cockpit locker for transport. I have tested it by plugging my shore-power battery charger directly into the generator running on deck and have found that the generator/charger/electric drive combination will drive the boat at 4.4kts without any power from the battery bank. I've motored like this for an hour to prove to myself that it would work (it did) and when I slowed down, the excess power charged my batteries. Here's the clincher, in three years, including weekend passages over 30nm one way to offshore islands, I've never needed the generator. I don't bring it on day sails. I've got no solar or wind generation and regen is insignificant at my boat's speeds. But with 8kWh (160Ah x 50V) range has not turned out to be an issue. I didn't expect that, but that's the way that things have turned out.

It really all comes down to how you actually use your sailboat. If you typically buy 10 gallons of fuel a month to motor around, then electric drive may be too much of a compromise. But if you spend most of your time sailing, then electric may be a good fit. Converting my ketch to electric drive has worked out well for me. I had the opportunity to convert my F-27 trimaran to electric when my outboard died. Electric would have been more expensive, slower, less powerful, more complicated, heavier and would not have met my offshore racing range requirements. I bought a new 9.8 four stroke outboard for that boat. Different answers for different problems. One size does not fit all.

3. A quality drive system will end costing very close to what an internal combustion DIY re-power would cost. I don't suggest that anyone convert to electric to save money. There are plenty of other good reasons to go electric.

The regular system vendors that have been recommended many times on this list sell engineered solutions with predictable performance. They take a good deal of risk out of your conversion. Some folks here have put together good efficient systems from loose components or very basic kits, others here have not been as lucky. Some of the homemade systems end up needing some rework, reducing or eliminating the perceived savings.

Personally, I converted a number of cars to electric in the mid 1990's. with that experience, I chose a complete drive system from Propulsion Marine in Santa Barbara. The combination of motor size, gear ratio and recommended propellor were spot on. The drive unit is surprisingly small and simple. I could have fumbled around on my own for twice as long and ended up with a system that worked, just not as good as the one that I bought. By the time you add in all the small components that come with the drive system, the kits don't save you as much as you think. I think that whatever premium I paid for a complete solution was money well spent, it may have even saved me money in the long run.

My personal recommendation is for you to seriously consider Lithium (LiFePO4) batteries. They seem expensive, but they are honestly better batteries for our purposes. I know a number of people personally that have installed lithium batteries, along with a few other people in this group, and every single one is glad that they took the plunge. Of course, I've heard plenty of arguments from people that have never used them, and heard of people on the Internet that have had problems, but I know none of them personally. It's your money and your choice. I know that they are worth it to me.

That should be enough to think about for now.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, jam_jade <no_reply@...> wrote:
>
> It is Jam. Thank you for taking the time to calculate. I should have provided more details. My LWL is 26 and displacement 9t with a draft of 6.8ft.
>
> A couple of questions:
> 1. How well will my panels charge the batteries, say we go with what you predicted? They are not at ideal angles since they are the flexible kind and will be attached to the roof of the cabin?
>
> 2. The range. Most people boost it with a generator? At the time the suggestion was to keep my volvo as this generator.
>
> 3. Any good for source of components? Batteries, motor, controllers?
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> > Hi Jam (or is it Jade?)
> >
> > Things haven't changed too much in the last two years, in my opinion, LiFePO4 batteries are more accepted then they were when I bought mine in 2010, but they're about the same price as they were back then. PMAC motors and controllers are still the most common drive systems for your size boat.
> >
> > The general rule of thumb that has been confirmed in many different conversions done by various members here is 1kW of drive power for each ton of displacement. That amount of power typically can deliver 90-95% of theoretical hull speed.
> >
> > All of the design data that I could find for Alden boats before WW2 leads me to believe that they are essentially custom boats, with only one or two boats being built from a given set of plans. Minor tweaks were constantly included in each subsequent boat, so I don't have enough data to accurately predict your performance, but I'll give it a shot.
> >
> > A number of early Alden boats near your boat's size were built with LWL between 23' and 26' and the displacement was 8-9 tons. So I'm going to do some calcs under the assumption that your boat has 25' LWL and weighs 8.5 tons. My calcs for 25' LWL give a hull speed of 6.7kts. With 8.5 tons displacement, 8.5kw (11.4 hp) should drive the boat 6.4kts in calm conditions. If you choose a 72V system, full power would be 120A. 5kts should draw about 35A. Lithium cells like I mentioned above, in a 12kWh (160Ah - 75V) bank, would cost about $5-6k and weigh about 300 lbs. This bank would give you a usable range of about 16nm at 5kts. Slow down to 4kts and your range jumps to the neighborhood of 27nm. You could use AGM batteries or Flooded Lead Acid, but batteries that would deliver the same range will weigh 750-800 pounds.
> >
> > All of these numbers are based on the assumptions that I mentioned. If you can provide more specifics about your boat, I could dial in my predictions, but these are probably closer than you think.
> >
> > If you've got more questions, feel free to ask here on the list or you can contact me off list.
> >
> > Welcome to the list.
> >
> > Eric
> > 1964 Cheoy Lee Bermuda 30, 5.5kW Propulsion Marine drive, 8kWh Lithium batteries
> > Marina del Rey, CA
> >
> > --- In electricboats@yahoogroups.com, jam_jade <no_reply@> wrote:
> > >
> > > Hello everyone,
> > >
> > > I just joined your group. I did look into electric power about 2 years ago so my knowledge is a bit dated. I was wondering if you can fill me in with respect to what is the current state of affairs for an electric propulsion for my vintage sailboat. I have a wooden 36 ft 1935 John Alden with full keel. My old volvo 3B2 is in need of a change soon. I did the calculations a while back with a repower company and it turned out that I needed about 35hp to achieve the hull speed of 7 knots.
> > >
> > > Of course with a cruiser sustained power is a consideration. I do have 2 85W solar panels that I'll be installing soon so I guess that's a start.
> > >
> >
>