Dear __________,
Thank you for inviting us out on your boat this past weekend. The boys had a fabulous time wakeboarding, and Bob and I enjoyed spending a great afternoon with you and Gloria zooming around in the boat on the sparkling waters of the lake. Our picnic on the shore was also relaxing and fun, and it was just a wonderful day from start to finish. Thank you so much for including us on your boating excursion.
(YOUR NAME HERE)