As I said -- you've built one -- the voice of experience is always
clearer than the voice of analysis. But:
#2 Wouldn't it have been easier and cheaper to buy a silicon bronze
left hand acme nut from our favorite supply house?
#4 Apparently you agreed with me, as the drawing shows 1/4" bolts and
you used 1/2".
#5 Right. I should have noticed that.
#6 Also, you apparently agreed with me -- he calls out bronze and you
switched to 17-4PH.
As to the philosophical question -- I love rowing or sailing our
twelve footer -- it's a real pleasure -- probably more so than your
Nester, as it's a no compromise boat. But on a daily basis, getting
in and out of a hard dinghy is a pain. Getting into one with SCUBA
gear on is almost impossible. It's one thing to love a hard dinghy
when you use it a few times in sheltered places; quite another when
you use it daily in relatively unsheltered anchorages where the mother
ship is moving up and down and the dinghy is also dancing, to a
different drummer, and you can't step on the gunwhale.
And rowing a mile to weather (15-20 knots) in Darwin in the morning
and then a mile back, also to weather, in the evening (wind seemed to
shift every day) would have been a real trial. Of course Darwin's a
worst case, but there were many places where the dinghy dock was half
a mile from our anchor.
Jim Woodward
www.mvFintry.com
Glenn Ashmore wrote in message news:JzPnb.106768$sp2.24480@lakeread04...
Jim Woodward wrote:
You've built one, while I've just looked hard at building one, so
you're miles ahead. Hands on experience beats analysis any day. With
that said:
1) I don't like left hand threads. I understand what he wants to do
-- put the clamp on with a normal, clockwise, forward motion, but I
think it's easier for the user to recognize that he wants to move the
rod toward himself and turn it accordingly. This is particularly true
if you're leaning over from the other half while doing it.
In an attempt to use off the shelf parts I built a test clamp using
standard RH threaded rod but there is something instinctive about
tightening anything from bolts to bottle caps clockwise. After I
noticed the problem I tried a mock up with a couple of boards on several
people. Everyone was confused by the RH thread.
2) I don't like left hand threads. It cuts down on your choice of off
the shelf materials. Not much, though, as you could use a silicon
bronze acme nut and 18-8 SS rod. (Running 18-8 threads in 18-8 nuts is
a bad idea as it tend to gall, but the 18-8/silicon bronze combination
used to be common in turnbuckles -- now we just put up with the
occasional galling of a modern all SS turnbuckle)
I turned LH Acme threads on the rods. Not hard to do and you have a
little smooth rod out at the handle end so you don't scratch your
fingers. Also turned a tapered spigot on the clamping end to align the
washer. The only down side was that the LH acme tap for the clamp plate
cost $90 but I have used it several times for other things.
3) I don't think they're beefy enough. 1/2" rod will bend when
someone stands on them. And I would use an acme thread.
That is really a non issue. The bolt is in almost 100% tension and only
protrudes 2". Someone would have to jump up and down on the handle to
bend it.
4) I don't like the mount of the attaching plate (The plate with the
keyhole). The clamp will tend to pull it away from its hull. It only
has to pull away (or bend) a little and you have a gap between hulls.
I would prefer a longer clamp screw and the attaching plate on the
inside of the other hull. This will complicate watertightness, but
it's worth it.
The Keyhole plate is through bolted with 1/2" FH bolts with a 1/16"
backing plate on the other side. It will not move very far without
ripping out the bulkhead.
5) I would through bolt the clamp plate. Never wood screw anything
under load.
The clamp plate is being pressed into the bulkhead when under load. The
screws are there just to hold it in place when it is not being used.
6) I'm suspicious of the end of the clamp. You're pulling against the
weld, which is a weak spot. Another reason to go up in size and
switch the clamp screw to 18-8.
Actually if properly done with 1/8" thick washers and a short spigot on
the end of the bolt the weld will be in shear rather than tension. The
whole design will be much stronger than bolts and wing nuts used on most
designs I have seen. I did change to 17-4PH rather than 316 for the
bolts. 17-4 is much easier to machine and is about twice as strong as
316. Same corrosion resistance as Nitronic 50.
7) The 3/16" clamp levers will be bent in no time.
Now that is a possibility but your hand will be hurting long before the
lever bends.
The real disadvantage of the Gerr clamp is the setup time on the mill
and lathe. The first clamp cost about $400 but you can knock out the
rest for under $20 each.
And, finally, nesting dinghys are over-rated for the voyager. We had
an Avon 3.15 rollup and a beautiful 12' rowing/sailing dinghy on our
circumnav. The Avon did all the work -- stable, dry, non marring,
fast (with nine hp) to shore which was as much as a mile away. Easy
to beach and to mount wheels to take it above the tide (1/4 mile in
Darwin). The hard dinghy was a joy to row or sail, but was strictly a
toy. Rubber duckies owned the voyaging market then and, I'm sure,
now.
That is more of a philosophical question. It depends on your
preferences. The nesting dink will get in the water faster than a
deflated roll up and for the more organic oriented rows much better.
Also the cost of a DIY nester and a nice pair of Shaw & Tenneys is about
half that of a roll up and motor. For those of us who will run out of
boat bucks just about the time the mother ship is launched that is a
very attractive feature. :-)