Jack Lines

[Robbie.g]

Just guessing, but Brion may have been expressing the fact that jack lines on the deck have two features;
1. even if your tether (connecting you to the jackline) is the shortest it can be and still enable you to move, it is still long enough that you can still be tipped outside the guardrails.
2. The loads on the jackline and the anchors for such are under considerable load if you tip over the side, especially if the line is pre-tensioned.
I'm presupposing that deck jacklines follow the very common, running down the side decks, fastened at or around the forstay tang and at a padeye aft of the turning blocks.

Whilst a jackline that is inboard, (as near to the centerline of the boat),have some more helpful features; because of the layout of may boats means that the jackline can also be quite high for the first part to the mast, you would therefore have a shorter tether. A solution like this means that in the event of a slip, you would be more likely to stay within the confines of the guardrails, and out of the ocean. Further, as the jack line is split in to 2 (along the lines of cockpit-mast and mast - forestay tang) the forces on the anchors would be lower, as each leg is shorter and the jackline will probably not need to be under the same kind of tension as a deck mounted version.

It's all in the 'Bible'.....

Regards