Recently a story hit the headlines that really upset me. It was of the two people who died and the others who received life changing injuries as a result of a boat propeller. If you not familiar with what happened here is a link
Basically the family enjoying the ride fell overboard, the kill switch was not engaged and so the boat started to circle around them and eventually the propeller of the outboard motor cut them to peices. I thought it was a terrible story that stayed with me for a long time.
I know nothing about boats but while watching a really old James Bond movie and seeing a propeller I was suddenly struck by a thought. Why don't boat propellers have guards. It's too obvious! If you saw an electric fan in an office there is no way you would expect it not to have a guard. Just because the prop is underwater does it logiacally make any difference? I thought not, so I did a quick search on Google to see if I was missing some fundamental point- perhaps they collected seaweed or otherwise malfunctioned with a guard.
Infact the reason boating propellers don't have guards is far more sinister. The industry resist it. According to the http://www.propellersafety.com/ there has been a long running debate where the manufactures have thwarted attempts at legislation and come up with some amazingly stupd studies (that people can drown if they get sucked into a guard - like that is worse than getting hacked to bits).
Like many things in the world, this is plain old capitalisms fault. It would drive up costs to add a guard, so the idustry will resist for as long as it can, and in the absence of legislation (which the manufactures lobby against) people will continue to die needlessly.