T-Pain Is On A Boat: Re: [Electric Boats] Desiderata

Saturday, August 9, 2014

Re: [Electric Boats] Desiderata

Hi Eric,

Thank you very much for taking time to respond to my enquiry.

It is great to hear first hand experiences.

How do you recharge the batteries on your boat? Are you plugged into shore power every night?

We don't use our engine for propulsion very much, as we tend to sail everywhere. The regenerated power is more to run domestics plus Autopilot when we are passage making.

I was certainly disappointed in the amount of propulsion regen you quoted. Though we do manage to average 7/8 knots when sailing, so would be at the upper end of your figures.

We have disguised one solar panel on the coach house roof, but do not wish to spoil Desi's line by putting up solar arrays.

Kind regards

Stuart Armstrong

+34 619135390

On 7 Aug 2014, at 01:39, "ewdysar@yahoo.com [electricboats]" <electricboats@yahoogroups.com> wrote:

Stuart,

Given the displacement of your boat (30 tons!!), you should be considering at least a 30kW drive. If you choose a 96V system, your max power draw will be more than 300A. Even if you do not regularly operate at those levels, your system should be engineered for it. Even a 144V system should be built for 200A loads.

I noticed that you "must" have your system provide regenerative power. Regen in boats will not deliver what most people would consider acceptable. Sailing at 6kts, you will be lucky to get 100W of regen. That is 0.7A for a 144V system, less than a typical trickle charger. At 8 kts (how much time do you spend sailing while averaging 8 kts?) your regen might be up to 400W, or almost 3A @ 144V. What does than mean? Let's say that you use 15 minutes of half power (15kW) getting out of a marina, that's 3750Wh. Sailing at an average of 8 kts, you'll replace 400w every hour, so it will take more than 9 hours to replace the 15 minutes of power that you used in the morning. Average 7 kts sailing speed and the recharge time gets closer to 19 hours.

There was a well published electric conversion a few years back that had articles in at least one of the glossy magazines. 3 years later, the owners converted the boat back to diesel, citing their extreme disappointment with the real world regen results. This later story was published again in the glossy mags and reflected poorly on the electric boat community in general. I believe the root cause of the unfulfilled expectations rests with the vendors that promote REGENERATION!! as a good reason to convert to electric.

It has been my experience and the experience of others in this group that in typical displacement sailboats, regen is a surprising bonus when it occurs and might be suitable for recharging house batteries, not traction batteries (much higher voltage). Fast and light, large catamarans have been more successful with regen and large monohulls like yours (maybe) might get a little more, but there are few examples to collect any significant data points from.

So rather than leave you with unrealistic expectations of how this might work, I think that you should adjust your requirements and consider solar as a more viable, silent alternative (plus it works at anchor or in the marina). Personally, I struggle with how to incorporate that kind of visible technology on a classic boat design like yours or mine, but that's my issue. Others are willing to make the compromise.

Just some things to think about...

Fair winds,
Eric
1964 Cheoy Lee Bermuda 30, 5.5kW Propulsion Marine drive, 8kWh LiFePO4 batteries.
Marina del Rey, CA, USA