CONTINUOUSWAVE

I'm looking at a used Whaler that looks in very nice shape, but has snaps installed just under the rub rail all the way around the boat for a snap-on cover. I assume a lot of drilled holes. Is that harmful to the boat?

Not at all.

Screw fasteners for snap-on receivers that are drilled into the hull sides are an abomination. The OEM weather canvas or cover was NEVER installed that way.

A cover that extends over the gunwale and covers the rub rail is normally held down by small hooks under the lip of the rub rail protruding part of the upper gunwale, and elastic or a draw string applies tension.

If the snap receivers or studs are screwed upward into the protruding gunwale from below, that is much better than going into the hull sides. But I would still worry about all the screws and holes in an area exposed to a lot of water and splash. They need to be well sealed.

While William J. Mills, the OEM supplier for classic Boston Whaler canvas accessories, used a few hooks and draw strings, many vendors do NOT use this system. Some use drawstrings or elastic.

The W. J Mills full cover retails for over $1k while other sunbrella boat covers, custom and semi fitted, retail for 1/2 that.

While there is a preference not to drill holes into a Boston Whaler, if snaps are already installed, it will not damage the hull.

The Mills cover for my 160 Dauntless installs with hooks below the rub rail. Measure twice, drill once!