We had a lovely whale-watching ride 2 Decembers ago with Capt. Andy -- I don't remember any turbulence but I usually take a half-dose of Bonine/Dramamine just in case. We got great photos of the coast and whales - the skipper was scrupulous about keeping the legal distance. ^

Now, with a 12 and 16 yr old I'd also suggest doing one of the sea kayaking tours along the southern coast. It's very safe if they are swimmers (life jackets worn at all times). My boys were that age when we took them. Since both had plenty of canoeing experience (not absolutely required), they were in their own kayak. They scooted ahead of the rest of the group about 30 yards and were joined by a pair of dolphins that came up and played with them, circling the kayak, swimming ahead and darting back etc. It's difficult to get teenagers to demonstrate awe in front of their parents, but this did it! If you really want to see the coast line up close, this is a great way to do it.