Maybe you'll get lucky and the chain plates will all be the same. That was the case on my boat. They should be the same side to side unless the anchor points are significantly different. A quick inspection and measurement should tell you if they are. You could pull both of the cap shroud chainplates at the same time with halyards to something secure on the deck replacing the shrouds. Then do the lower afts or fwds respectively. The mast will stand just fine with only either the fwd or aft lowers in place.
Yeah, i've been thinking about this over the past few days.
Ill be at the boat this weekend. Ill be taking detailed measurements to see how different the chainplates are from one another.
I'm thinking ill be doing the chainplates in a "quadrant" style sectioning.
The process for chainplate install/reinstall will be as follow:
Quadrant 1(remove, have fabricated, reinstall):
Lower aft port
Lower aft starboard
Quadrant 2(remove, have fabricated, reinstall):
lower fore port
lower fore starboard
Quadrant 3(remove, have fabricated, reinstall):
Quadrant 4(remove, have fabricated, reinstall):
Quadrant 5(remove, have fabricated, reinstall):
With the lowers, I will be doing both sides at one time. I also plan to loosen the tension on the lower fore/aft shrouds just a touch as well, while leaving all mast head ones as is.
While the lowers are being fabricated, since all my running rigging is new as of 2014, I will be using halyards for main and jib as support. If i feel the need, ill also add some other halyards to increase support.
Once lowers are completely replaced, fore and aft, I will then work on the uppers at a single time, being port and starboard, all the while using halyards to give the structural support(using 1-3 lines for the support lines).
Then i'll proceed with the bow shroud, I am also thinking I will loosen the stern shroud just a touch and crank down on the supporting halyard as well.
The same process will occur for the stern shroud as we did on the bow, just the opposite end of the boat.
Once all of that is complete, I have enough compelling evidence that I do NOT need to lower the mast to replace the shrouds. The shrouds will be done one at a time, not in quadrants like the chainplates.
I will be doing the lowers first, then the uppers on both port/starboard, then will proceed on with the bow and stern shrouds.
As long as I feel confident that the chainplates and knees are in good shape, and the lower shrouds are also in new condition (I will be using the stay-loc or something similar) I am confident that due to the minimal lateral forces, especially on a clear not windy day and being in a marina, it is perfectly safe to do with the mast in place.
This also is on the condition that after goig up and down the mast for inspections, i see no evidence of issues that need addressing. Given that i do find something that I feel untrust worthy about, the mast WILL be pulled for further inspection and repairs along with shroud replacements