davefarmer said...
Note the distinction between rachet blks, which can be switched on and off with a lever on the side of the blk, and an auto ratchet that engages the ratchet mechanism above a certain load(often adjustable with tools). With a ratchet blk in the off position(light air), the sheave turns both directions easily. With the ratchet engaged the sheave only turns one direction(sheeting in), and when you sheet out the mainsheet, it slides over the non rotating sheave, adding friction that contributes to the holding power of the block.

An auto ratchet sheave turns both directions easily under low loads. As the pull on the blk increases, at some point the ratchet mechanism kicks in and locks the sheave in one direction. When the sheet is dumped quickly, the load is removed and the ratchet is quickly released, allowing the sheet to run freely( unlike the standard ratchet sheave that is still locked).

Quite different from both of these is the Oxen block, that locks the sheave and sheet positively with a quick release after sheeting in. And it remains locked, even without tension on the sheet, until the line is sheeted in again slightly and released.
These are sohpisticated, complicated blocks, that work very well in ideal conditions. They're very expensive, over $250, and require maintenance, and may not stand up well to dirty environments. And if they malfunctioned in an emergency, might not release at all, unlike either style ratchet blk where the line can run over the sheave even if it's locked.

I find all the Harken ratchet blks to be a bit stouter and more durable than the Ronstan units. Haven't tried the others. I use the carbo ratchamatics, which are the lightest that Hkn makes, on my cats with good results, but they may not be a durable as the others in the dirt. I have a 75mm standard ratchet on my elderly Fed 5 that's doing well after many years of hard use.

Dave