There is a commonly used DiY tool that is worse than useless on a boat. If you have one, throw it away now. What is it?
It is a common hand tool - no electricity involved
The problem it causes is not a safety issue
Worse than useless. If you did use it you would cause big problems - do NOT use one on a boat
It is very commonly used by chippies, kitchen fitters, plumbers, etc since time immemorial
Someone fitting out a boat on dry land might find it OK to use, but I doubt it. Once the boat is in the water it would lead to serious errors in fitting out.
A last cryptic clue - Would a confused viper sell it?