My wife, sons and I, have taken the In Side Passage cruise 3 times over the last few years and had a wonderful time each trip. Yes, a camera is a must and August is the perfect time.
There are a couple of suggestions I could make. Repeat after me - several times - Stitched panoramas.... Too much scenery for a single frame - regardless of how wide the lens is. Some practice shooting stitched will return wonderful rewards.
The other thing is bring a laptop or netbook. Down load your images and take a look at them. You will notice what you are doing right and wrong, very quickly and be able to correct the problem before you get home. I think that this would be especially important to your son. I did this on our first trip and it worked out well. Plus, in the evening you can all take a look at the day's shots.
I would also take a small backpack that you can carry the tripod, camera and lenses. It just makes it a bit easier we found.
.... and for the cruise, there are times that a DSLR is just a bit too much, a small P&S for the pocket works very well.
Just a few suggestions - and have a wonderful time....