Especially on a boat. 5 minutes is enough to turn them red(and dead), but not enough to cook them through. It does take a big kettle to cook 4 medium to large lobsters. We keep one kettle large enough to steam two, and many other smaller pans, nested inside.

What I like about grilled lobster, especially on a boat, is it's much more civilized to eat and a lot less mess. The mess is in splitting, cleaning and draining the carcass(in your sink). After grilling, the lobster is delicious.

Steamed in the shell, is not my favorite way to prepare lobster, unless you're on a lobster dock, over the water, on a wooden picnic table.

Where you eat lobster is as important as how you cook it.