Hi! As you are an expert in the domain, do you know if my method to generate personal password seems secure?

Typically, instead of memorizing a lot of random password, I memorize only one password and for each website I use the password:

sha1(password|domainname)

Until here nobody give me a clear answer, and therefore I assume it is secure while not any flaw is discovered.

And more precisely, I use

sha1(password|number|domainname)

because, if I fear my password was discovered, I change it by incrementing the number.

I would be very grateful if you mind answer my question. Thanks!