Does anyone have a good algorithm for using a password template/seed for different sites? Choosing a template, say 5_h_7_s_9_j, and replacing the _ with charact

Does anyone have a good algorithm for using a password template/seed for different sites? Choosing a template, say 5_h_7_s_9_j, and replacing the _ with characters from the site's name works (and you could increment the characters or whatever), but if anyone gets two of your passwords it's pretty obvious there's a pattern and it's not particularly hard to work out the relationship between the site name and the password.