Annie Hill wrote:
I think you're being a bit pessimistic there, Erik.

That's me... :)

Alan Jones wrote:

I did want to point out that we owe it to JRA that we met up!

That's great to hear.  Here in NZ the junkie community is very supportive and helpful and, indeed, we've all become very good friends.  It's good to know that people are meeting in person as well as online.

I trust that we will hear about the first junket in that part of the world, once these two sails are made and rigged :-)

Erik and Evi Menzel Ivey wrote:

Hey Alan - I am guestimating the total weight of all the parts could be close to 1000 lbs.  That includes the tabernacle, structural deck/hull reinforcements, master, counterweight, sail, and running rigging.  The hul lshape  is certainly ideal for load carrying, but that still seems like a lot.  Thoughts?

Also, you think the sail need to be above the pivot when you drop the master?

Erik

I think you're being a bit pessimistic there, Erik.  Alan's all up weight is 485 lbs, the tabernacle, shouldn't weigh more than 100 lbs and the deck reinforcement would amount to no more than a sheet of 12mm ply, which is 22kg - about 45 lbs.  The 320 sq ft sail I made for Fantail weighed about 20 lbs, alloy battens are about 0.4kg/m, which is about 5 ozs per ft and an alloy yard doesn't have to weigh much either.  I shouldn't have thought he'd be adding more than an extra 300 lbs to the mast and counterweight. 

I'm planning to put my mast in a tabernacle and I'd certainly want the sail above the pivot at all times.

BTW Alan, you could taper your topmast more: mine went down to 3 inches and  is still going strong!

Hello Everyone and Happy New Year!

For Autarkia, I have decided to make a hybrid mast with the lower 20 feet constructed of 6 inch Schedule 40 aluminum pipe.  This pipe is made from 6061-T6 alloy, and the O.D is 6.625 inches (168.275 mm) and has a wall thickness of 0.28 inches (7.112 mm).  A 20 foot length weighs 131.28 lbs.

The upper section will be made with fir, laminated up from the pile of leftover 2 by 4's I have left over from the build.  This section will insert into the top of the pipe by around 18 inches, and will be bonded in with epoxy.  I'll taper it down to 4.5 inches at the top, and epoxy fiberglass it.  This section will weigh around 50 lbs at 12 feet long including the inserted end.

The whole mast will weigh around 185 lbs with fittings and will be 30 to 32 feet long depending on my final sail design.  The pivot in the tabernacle will be about 5 feet up from the bottom, leaving 25 to 27 feet above the partner (tabernacle pivot).

The bottom of the mast will have attached a lead counterweight weighing in the vicinity of 300 lbs, that I will cast from a pile of tire weights I have already.

I worked out the counter balance as follows:  The weight of the aluminum mast above the pivot point will be 98 lbs.  The center of balance of the pipe will be 7.5 feet up from the pivot so its moment times the arm will exert 738 ft/lbs with the mast horizontal.  The wood section's center of balance will be 19.5 feet up from the pivot, and with the wood section weighing about 50lbs, will exert 975 ft/lbs.

Add the two - 738 ft/lbs plus 975 ft/lbs and we get a total of 1713 ft/lbs to counter balance.

If we take the weight of the mast below the pivot point (32.82 lbs) and put it's center of balance at 2.5 feet down the mast when horizontal, we get 82.05 ft/lbs. That still leaves us with 1713 - 82 = 1631 ft/lbs to counterweight.  But if I can get a lead counterweight at the bottom of the mast that weighs around 300 lbs, then I can generate 300lbs times 5 feet or 1500ft/lbs.  That leaves around 131 ft/lbs to overcome manually to raise the mast.  Pushing down on the weighted end will only require about 26 lbs of pressure to raise the mast!

I have more details on this blog post:  https://junkrighouseboat.blogspot.ca/2017/01/mast-design-with-counter-weight.html