Visiting Isla Floreana in the Galápagos Archipelago

Caution, Engineers at Work

Nine of Cups at anchor off Puerto Velasco Ibarra. I took this picture from shore in front of the Wittmer hotel.

Back on the boat, David and I put on our "engineer" hats to figure out why the battery performance has been so poor lately. The house battery bank consists of three 8D batteries (behemoths, at more than 150 lbs each) and one smaller battery, all wired in parallel. The battery bank has a very large theoretical capacity which should be adequate for our needs. However, we've noticed lately that the battery bank seems to get depleted quickly and we have to run the engine more often than desired to recharge.

One thing Marcie has already discovered is that the refrigerator performance could be greatly improved by adding extra insulation; she now puts a blanket and some cushions on top. Sailing in the tropics, the reefer compressor used to stay on all the time, but with the extra insulation, the compressor actually shuts off now and then (plus the refrigerator stays colder). Since the refrigerator is powered by the battery bank, the improved efficiency will help the battery last longer. The freezer also has a problem with icing up and needing frequent defrosting, so somehow humid outside air is getting into the box.

David and I spent the afternoon examining the battery bank and charging system, following wires, testing components, and performing experiments. Based on our studies, we reached two conclusions. First of all, we could be a little more aggressive in charging the batteries, by boosting the voltage produced by the alternator. This in turn would increase the charging current and recharge the batteries at a slightly faster rate. The most important discovery was that the alternator regulator only stayed in absorption mode for about 40 minutes, before tripping to float mode. During absorption mode, the alternator produces significantly more charging current to recharge the batteries quickly. Once it trips to float mode, the alternator delivers much less current (basically, a "trickle" charge). The switchover from absorption to float always occurs after 40 minutes, even if the batteries haven't been fully recharged and no matter how long you run the engine.

We both figured that our large battery bank (with well over 800 amp-hours of theoretical capacity) would not be adequately recharged with only 40 minutes of absorption time, so we need some way to extend this part of the charging cycle. As it turns out, there is an easy way to do that: just turn the regulator off and on while the engine is running. This causes the regulator to restart and provides another 40 minutes of absorption time. David installed a toggle switch and we'll toggle it every half-hour while the engine is running, to see if this does a better job charging the batteries.

I took these pictures ashore to show boobies diving into the water (it's not necessarily the same booby each time). The first picture shows the booby slowly cruising overhead while peering intently into the water.

Spotting something of interest, the booby begins to wheel into an attack dive.

Plunging rapidly, the booby starts to fold its wings.

A streamlined booby about to enter the water.

A dart-like fully-streamlined booby.