You've gotten most, but not all of the following in the previous
comments:
1) Raising the sails increases the moment arm, which increases shroud
loads.
2) Adding weight increases the righting moment which increases shroud
loads.
3) Adding weight is to be avoided in a cat. This sounds like a major
increase.
4) Increasing the mast height reduces the shroud angle for the lowers,
thereby increasing loading on the lowers.
5) Reducing the shroud angle will require bending or replacing the
lower chainplates to match the new angle. Don't ignore this. (The
headstay and backstay have the same problem, but it's over at least
double the distance, so a toggle may be enough).
All of which suggest some careful analysis and, perhaps, bigger
shrouds.
Assuming you've done that analysis, and have determined that the
present wire sizes are still satisfactory, then I would:
1) Consider the age of the existing rigging, (I'm guessing this is a
used boat), and its remaining useful life. A complete replacement may
be in order soon anyway.
2) Consider cutting the long pieces of the existing rigging for use in
the shorter places, replacing only the longest pieces of wire, and
putting new terminations on the cut ends.
3) Look around for a used longer mast and buying its rigging or the
whole thing.
4) If you decide to piece out the rig with new two foot lengths, use
Norseman or StaLok rather than swaged fittings. A lot more money than
swaged, but a lot better quality. Then, some day down the road, you
can buy new wire and replace the two foot pieces with full length
pieces, reusing the fittings.
5) Easiest, and cheapest, would be to make extenders out of solid
stainless. Bob suggested round stock. He may have had the following
in mind, but I'll flesh it out a little. Get a second turnbuckle of
the same size as each existing one and approximately 24" long threaded
rod to match. Drill the ends of the rod for cotter pins. Take the
right hand thread end out of the existing and new turnbuckles and
thread them on the rod. Presto, you have a super-turnbuckle that will
span the gap. Get rolled threads on the rod -- if you buy the rod,
this will be almost automatic, but don't cut the threads with a die or
on a lathe. Use 316 -- it's not quite as strong as 303/304, but
corrosion is an issue here.
6) If you decide on the second solution, "just reweld the gooseneck 2'
higher", consult with the mast manufacturer. Many masts are made from
heat treated alloys that shouldn't be welded after heat treat and
there may be reinforcement inside the mast at the existing gooseneck.
Jim Woodward
<a rel="nofollow" style='text-decoration: none;' href="http://www.mvFintry.com" target="_blank">www.mvFintry.com</a>
"Evan Gatehouse" wrote in message ...
> Folks,
>
> First a bit of background. I'm considering buying a 40' cruising catamaran.
> It's an "open bridgedeck" design - without a bridgedeck cabin. I want a
> bridgedeck cabin so I'd have to build the cabin.
>
> To make the cabin fit I'd have to raise the boom. I have 2 solutions - just
> reweld the gooseneck on 2' higher, and trim the bottom of the mainsail.
> This looses me sail area which I am loath to do.
>
> The other solution is to raise the mast 2' (which is easy to do 'cause it's
> just stepped on a deck beam). But then all the rigging wires become too
> short. So I'm looking for ideas to extend rigging wires. So far I have:
>
> - replace most of the wires (7 at least would have to be done, not a cheap
> proposition)
> - short lengths of rigging wire with swaged fittings at each end -
> reasonably cheap but lots more potential failure points
> - short lengths of multiple passes of spectra or similar high modulus line -
> probably cheapest and lightest, need some custom solid aluminum thimbles to
> handle the lines
>
> I'd appreciate any opinions. Thanks, >> Stay informed about: extending rigging wires 
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