Correct spelling, explanation: in most cases -ible is the suffix applying to words of Latin origin. Visible comes from the Latin word visibilis, therefore it applies to this rule. Moreover, there is an unwritten rule saying that words with the suffix -able will be left with a full word without the suffix (for example renew → renewable), while words with -ible will be unfinished without the suffix. Visible is one of such words, therefore visable is incorrect.

Definition of tried:
adjective, one that can be seen
I couldn’t see that sign. I wasn’t well visible.
On the basis of visible signs and symptoms, we can assume pneumonia.

Incorrect spelling, explanation: because of the Latin origin of the word, the suffix that we use is -ible (there are some exceptions but generally that is the rule). There is also an unwritten rule saying that the suffix -ible is used for words, which are left unfinished if we take away the suffix, and -able is used for those which are in their full form without the suffix (visible without -ible is not an actual full word form). Therefore visable is a wrong spelling and the correct one is visible.