[Mister_M]

Originally Posted by gap

Obviously you have never been on a sailboat. With that little degree of freedom, a jib sail can make a modern sailboat to move almost against the wind direction

https://en.wikipedia.org/wiki/Sailing_into_the_wind

You're right, I would not be able to "drive" a sailboat. But can this puffer be compared to a thin and light sailboat ? And I was not aware of the extra sail that you mentioned in a previous post.

Originally Posted by gap

Ambient light is not the same as direct sun light. While I will agree with you that the sea bottom won't reflect as much light as atmoshpere and sea surface, I think that for our purposes this difference can be ignored

I was not talking about the sea bottom, but about the direction from which may come direct sun light (which obviously can't come from the sea bottom).