Thanks for the assessment, Rich. Some clarifications:
1. the vang's connection to mast is higher than the absolute base of the mast
The attachment point is just above the mast collar. In the photo, the vang is loose and you can see the lower set of blocks just above the bowline in the jib sheet. It's as low as it can go.
2. From the pic, and I may be wrong, but I see a 5:1 vang being used
I was wrong when I wrote 4:1, that was the original configuration. In the photo, it's 6:1.The 2nd set of blocks are obscured in the photo.
the 'tail' of the vang seems to be running along parallel to the mast; and if so, the 'tail' is generating NO 'down' force
That's true and could be reconfigured to go to the mast collar turning blocks. The manufacturer ran the lines that way for neatness, I suspect. Good idea.
A vang that makes a 45° angle with its boom will generate 40% more 'downforce' than a vang that makes a 30° angle intercept.
Agreed. The angles are horrendous. But if I move the boom attachment point forward to get 45 degrees, then the moment arm on the boom will be reduced. So I think that I will solve one problem and create another.
Your last paragraph is the most helpful. I'll look at when and how I apply vang. Thanks.
I really think that all it does that is useful is to hold up the boom
True. The spring in the rigid vang is fighting the 4:1 or 6:1 block arrangement, reducing the down power. Rigid vangs are poor "vangs", IMO. They're mostly boom holder-uppers.