i used to have a friend whose commercial troller had a ferro-cement hull. The humpbacks used to love to come up and rub their backs against it as he was trolling on la Perouse. I'd get a call on the VHF--"Help Tom--I'm being f#$#ed by a whale!" I'd look over and his boat would be rocking back and forth with a humpback snuggled alongside. he sure had some good whale pics, tho.
T2