One of the first items I had to replce on my newly acquired 30' were the missing or frozen hatch knobs. I went to the Bomar web site and West Marine. Both had the knobs at $10 per knob. I found replacement knobs from McFeely's at $1.03 each. The Bomar hatches are 5/16 #18 male and female knobs. One of my goals is to post the replacement parts that I find for others to take advanatge of.