Your trig may be correct as far as the altitude is concerned but
practically speaking, you can rarely see anything 300 nm away.

I would agree they don't tend to come up on you in 10 minutes but it
may take a lot longer than 10 minutes to get to a safe
harbor/dock/anchorage.

Eric

(JAXAshby) wrote in message ...
There are lots of places where people sail and it's difficult to see a
thunderstorm coming

bull****. Thunderstorm clouds go as high as 60,000 feet sometimes, which means
they can be seen up to 300 nm away. Even 10,000 foot high clouds can be seen
up to 122 nm away. Can't see that coming?

And there are many places where the potential
exists every day in the summer

thunderstorms don't form inside of 30 seconds. You *KNOW* they are coming, if
one just pays attention.