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I had a query several days ago regarding an article I wrote for Cruising World magazine about batteries and battery banks. The fellow loved the article (Thanks!) but had a good question that I should share with everyone. It has to do with wire sizing, specificall the main cable from his boat battery to in his case a small outboard engine. On his boat the battery is located forward, I think under a berthing area and a rather long cable runs aft to his outboard motor. Keep in mind that in this case we’re talking about a small outboard engine on a sailboat, not that the type of boat makes any difference here. He was having trouble getting his engine to crank over with the electric starter.

OK, so the issue here is voltage drop, and wire sizing is the key. The little tables shown here come from my best selling book (small plug here) Outboard Engines, Maintenance Troubleshooting and Repair.

For larger engines, use this table:

Oh, and say, if you do use outboard engines, you need a copy of the above mentioned book. If you purchase it by linking to McGraw Hill  via my link in the left column of my home page here. Go for it! $20 well spent!

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