What Gregory said isn’t really applicable. When the sheet is cleated it doesn’t matter how much sheet is wrapped around the block as the cleat is “holding” the sheet, not you.It is also important how your block is mounted. If your block is mounted like the first picture, and you are pulling down into the cockpit, then only a small surface area of the line will actually be contacting the block. Whereas if you have a combo or system where the cleat is up higher, it will allow more line to contact (thus better grip) I wish i had realized this before mounting, but still works pretty good.
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I've always understood those to mean that the line isn't supposed to move until the ratio between the pulling side and the holding side exceeds the given value. That is, you'd need a force equivalent to only 1 kg to hold against 20 kg worth of tension on the other side of a "20:1" block. Obviously this can't be very accurate as it has to vary quite a bit with line thickness and quality.I don't know what the 10:1 or 20:1 means in this case, might just be marketing. Ratios only make sense to me in the context of a pulley system, not a single block.
In this example it actually isn't. When a line is cleated, it's irrelevant how much "grip" there is somewhere else in the system. The purpose of a ratchet block is to help with the holding and releasing of an uncleated line. (More or less what beldar just said.)It is also important how your block is mounted.