Not quite
Hi Morgan,
Not quite so.. The "I" is the dimension from the top of the jib halyard sheave (as you say) to the "BASE OF I"-NOT the base of the mast. "Base of I" typically is very close to the shroud bases, or chainplates, on the deck. This is true on all boats (in terms of the "base of I"). On all boats, the actual base of I is a line just below the chainplates (I am using the chainplates as a reference for this discussion), but is not a point on the boat which can be physically identified-it is only the engineering drawings. When we sailmaker types measure a boat for sails, we use the base of shrouds as a base of I-just so we can compare it to the sailplan we have at the loft. If this dimension is 1-2" less than the sailplan indicates, we can confirm we are talking about the same rig. We then take all of the other measurements (luff length, base of mast, track locations, etc.) to make the sail fit properly (we hope!).
In the case of the E 27 with a deck stepped mast, the "I" will be longer than the distance from the sheave to the base of the mast by roughly the height of the cabin top-something in the order of 12-14" I would think. The standard "I" is indeed 32.5 feet, but that should be a longer distance than from the sheave to the base of the mast (mast step on deck). In the case of a keel stepped mast, the overall mast length will be longer than the "I".
The ONLY time the it would equate to mast length (but there is no technical correlation) would be in the case of a deck stepped mast which had no cabin top or any crown in the deck (totally flat deck).
And there you have it..
S