You can use a spirit level on boats, providing they don't move much - something over a few tons and it wil not heave about, in a quiet marina. Spirit level also provides a "straight edge" for marking out and so on.
Thats one of the most sensible questions I've ever read.
Personally - I have used a spirit level at home and I find they are fine as long as you put a brick on the lower end of the shelf to stop everything falling off. When I was at school which is rather more than a fortnight ago, I once made a set square - in fact I was the owner of the only 93.5 degree set square in the land and my right angles turned out just the same as any others - so I don't think spirit levels or set squares are much use really. My hedge looks really nice just now and is admired by all who pass by - did I use a spirit level - No.
QED
this fishing boat is about 20 foot long if that - and i know how a straight edge is used. They were definitely using the spirit level as a spirit level
If the boat was wobbly, there's a remote possibilty that they are totally daft, and you most certainly aren't. Weird eh? If you were a bloke, you wouldn't even need to ask this question, but are locked into a mindset of girliness and need training to break out of this mindset. You could consider driving round town abusing other drivers, occassionally making comments to self/SOH such as "look, typical- this one's going to turn right in a minute ...see?" and so on. Later, march into DIY shops and curse them for having such a poor selection of tools "Yes, a plumb line for goodness sake!" A starting point, when lending tools to neighbouring boats, make sarky comments like "and make sure it's got a return spring on it will you?".
look girlies know lots of boys' stuff. There were two guys working down in the engine room a couple of months, couldn't find the right size spanners. Tried looking everywhere on everyones boat but no success.
.... would it be whitworths spanners you're after, say I? and guess what?
Your talents are wasted on them pauline. I would been able to rip lumps out of my fingers with the nearly-correct spanners AND would have kept the swearing to a low volume so as not to interrupt your afternoon body-building sessions.