You've actually jogged my memory. I've seen people claim that an aluminum yacht may act as a Faraday cage, so to that end, I'm sure a mostly steel tug boat would do the same. Excellent!

I found that Faraday cage claim. Also, I wish I had an extra $5m around to pick up one of these yachts.

http://www.setsail.com/lightning-strikes-and-how-to-prepare/