I recently had lunch with a friend named Hans who owns a very nice 54-foot offshore sailboat. Hans does some pretty serious miles, with a bunch of trans-Atlantics and countless voyages from Nova Scotia to the Caribbean in the fall, and back home in the spring, to his name. Hans shared that he was considering replacing the house bank on his boat with lithium batteries to dramatically increase the effective bank size from its already large capacity, about 800 amp hours at 24 volts (1600 amp hours at 12 volts). When I asked why he would take this expensive step, he shared that his goal was to reduce generator run time from its current several hours a day when sailing offshore. (Hans has two AC generators, one of 3.8 kw and the other a monster 14 kw.)
Really?My first thought was that increasing the bank size would not decrease generator run time since the amp hours used have to be put back eventually, regardless of bank size.
OK, I Get ItBut then I started to see his logic for his typical four to six-day passages: Nova Scotia to Bermuda and Bermuda to the Caribbean, and return. In this case a massive house bank (lithium or not) would increase the chances that he would not have to disrupt his sailing with long and frequent generator runs since:
- He usually goes alongside at the beginning and end of a passage and so can be fully charged before leaving and then recharge from shore power on arrival.
- These passages typically, or at least often, include some motoring with the attendant battery charging.
We Gotta ThinkHans' story is interesting because it illustrates how each of us needs to really think about our usage profile before selecting battery type and capacity, not just:
- Make a decision based on some rule of thumb,
- or what someone else has done,
- or just assume that a bigger bank is always better.
- Spends a lot of time at anchor and rarely goes alongside.
- Regularly makes longer passages of a week or more in the trade wind belts where motoring is much rarer.
Big MoneyI digress, back to Hans. Of course, all of this assumes that he is willing to spend the some US$10,000 to US$15,000 that such a lithium bank and associated modifications of the boat's electrical system would cost, not to speak of the added complications and fragility of lithium. (See Further Reading.) None of which he was keen on.
A Simple and Cheap SolutionGiven these drawbacks, we chatted a bit more about other ways to solve his problem, during which I asked:
How about if you could reduce generator run time to half or even a third of what it is now for less than 10% of the cost of lithium and with minimal complication and installation hassles?Hans perked up and allowed how that would be a perfectly acceptable solution.