This is not a single answer question. (corrected)

1st while sailing and at the dock  there should 0.0 Lbs (1.8 Lbs, or about half the weight of the spreader it self) of tension i.e they don't do (much) and it would be very hard to measure this almost no weight

2nd what is your weight and how close to the end of the spreader will you stand.  If at the tip then the tension will need to be at your weight when loaded  if half way then half your weight. (these tensions are when loaded, but when unloaded it needs to be 1.8# +/-)

SOOOOOOOOOOOOO they are there for the person who does not seize there uppers to the spreaders (the friction + seizing will hold 20 to 40# +/- both up and down) or for those who need to stand on them to spot ? reef's, sharks, and for whatever you would stand out on the spreaders for, ( you may want to leave them in place?) I stand near the mast = as close to the mast as possible = less than 6" from the mast which loads the tips at around 18#+/-. And I have never had any issues of movement.

I don't have them any more, I lost the extra (10 + Lbs up high = 60+ pounds on top of the deck ), about 6,000 miles back, and never looked back, I do not miss them at all.

Tim  I hope this helps you out, as weight up the mast in NOT a good thing.

Norm

Norm,

Your "seizing" ... is the upper shroud served and then seized to the spreader tip?  Service is an old world skill and application, but I think it would be as well or better than not served.

Plus service would reduce galvanic corrosion on the spread tip contact with the shroud.  I'm teaching myself the Liverpool splice and will be splicing my rigging, but I've also taught my self service to cover the splices and to make more decorative/aesthetically pleasing lashings etc. 

T. 

Norm,

I learned that concrete sealer is a great "tar" for service, and helps with chafe because it is very durable and UV resistant.  As in "Rigger's Apprentice," one may make the part varnish/part black paint slush too, but I'm actually a fan of the concrete sealer; which was recommended to me by a splicer on the East Coast.  If I could post pictures, I would of the finished splices and service I made for lifelines.

Liverpool splice is on 7x7 wire (or any wire with 6 strands wrapped around a core).  The 1x19 splice is another story.  This one starts from the same side as the 3-strand splice, but then is wrapped around standing strands (6 groupings of the 12 outer strands) similar to the Liverpool splice.

I had to make all the tools for service; including the serving mallet and serving board.  One can no longer find these things, so some ingenuity is required; which one may argue is what makes a good sailor .. :)

Thanks for the response!

T. 

EDIT:

I stripped and painted my mast, spreaders, and booms, and I found there to be galvanic corrosion in the spreader tips.  Now, it was not as significant as at the mast base (more salt water in these parts), but it was evident enough to consider isolation, as well as, fixing the spreader on the shroud.  I'm a fan of not having the lifts up there as well.