So you have DS clone as a boat, but with a mast (and presumably stays?) from an actual DS.
Nobody here really knows your boat, so it is possible that the hull of your boat is shallower, so that chain plates are further from the tip of the mast, but it seems more likely that the mast is simply a bit too long. Let's see what we can figure out from your new measurements and picture.
If you look at your picture, it shows a small platform for the mast step, surrounded by a wider platform (flat blue). There seems to be an access panel (white) indicating that there may be considerable distance between the platform and the actual hull.
I would have expectd the mast to be too high above the deck because of that, but your mast-tip to partners measurement is within 2-3" of expected (the standard measurements, other than that for the mast rake, are all based on the top of the sail track, not the actual tip of the mast).
On a DS, the nominal value for the luff of the sail is 20' 6" and another 2' 0" to the top of the deck. With those values the
bottom of the boom clears the deck by ~16 to 18", (For my mast that works out to about 29-30" for the distance deck to mast step but each mast may be adjusted to the actual height of the mast step). From your mast tip to partners number it looks like you are within 2-3" of the target.
I'm attaching a drawing from the DS Handbook of a few years ago. This gives various lengths in reference to the deck level.
- Drawing-7.1.JPG (45.13 KiB) Viewed 19147 times
(The "band 3" in that figure is how high you can possibly raise your sail, so it's practically at the end of the mast track, if you want to relate it to my measurements. Band 2 is at the top of the boom, and my 16-18" "clearance" agree with that, if you add the width of boom itself: to get to the 24" in the diagram).
You should also be able to confirm whether your shrouds are attached to the mast at the expected position (22' 6" minus 15' 3" equal 7' 3" from the end of the mast track). Likewise the spreader brackets (15' 3" minus 7' 8" equal 7' 7").
If they are off by 13", either the deck layout of your boat is really different (that is 13" taller from the chainplates - which I don't believe based on the pictures) or your shroud attachments were moved. Based on the diagram, you should confirm their location.
If they are attached in the right place, but still come out short, you could have super wide spreaders. From what I remember that was not the case. Or they are mounted too high, so that the upper part has a steeper angle. Still 13" would be a huge discrepancy.
In summary, what you are trying to do is match the configuration above the deck level as per the diagram. If you are able to match that, then you can use standard DS sails and you will have enough clearance for a boom vang.
Looks like your mast is approx the right length relative to the deck level, which is good and after you have confirmed you shroud positions you should be able to figure out whether they need to be moved or are just too short for some reason.
Hope this all makes sense if you apply it to your boat.