Timber jacks can be dangerous!!!
When lowering the load on a timber jack ALWAYS HOLD THE JACK LEVER AT ALL TIMES. If you fail to hold the lever it will flick upwards and may hit you, even crack into the side of your head!!!
This type of jack is usually only used to lift one side of the launch trolley when greasing the wheels, or to use on the hardstand trolley when removing or replacing rear wheels or when turning front wheels (providing there is no large load on the trolley).
Do NOT use timber jacks to lift boats in cradles!!!