Grip wrote:
Hey Richard,

When I started boating the rule was water+air temp should equal 100
degrees before needing extra protective gear.

That's one of the most dangerous "rules of thumb" out there, as there
isn't any combination of temps equaling 100 where it's safe to not wear
immersion clothing.

Some in our club claim 120 respectfully.

This level is closer to realistic, but still not enough. Any such rule
is too much of an over-simplification to be useful or safe.