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Up date on testing Persistence.
It's lengthy.
Read at your OWN RISK!
Today I did the second wet testing on
Persistence. In the first test I found several things that needed tweaking
and had my first floating experience. In this test, like the last, the sub
was tether to the trailer where it could float a little, but only a little,
above the deck of the trailer.
The most needed corrections found
in the last test was repitching and reducing the propellers. All
three of Persistence's propellers are three bladed. The rear and largest
prop, is bronze. I made a jig to hold it, and a tool to fit the blades
with a three foot long T-handle. With the prop firmly held in the jig it was
relatively easy to twist each blade by hand with the three feet of
leverage. And I'm not that tough of a guy either! I twisted
them flatter to reduce the pitch. The harder part was twisting each
blade the same amount. Another jig to measure with did the trick.
After reangling the blades I put the prop on a
shaft mounted in a lathe and spun it, tapping a little here and there
to true it up as close as I can. After that, I turned some off the back
side of the prop the reduce the blade area and then hand ground each blades
edges back to what I thought looked like a proper shape. After the
reshaping, I used the lathe and a long shaft to balance it at 2000
RPM. The job took several hours and "persistence." (Did I really say
that?)
It's was only a guess on how much to alter the prop
but I got lucky. Today's test found it was exactly
correct. I couldn't get it any closer if I knew what I was doing.
Last time the thruster drew 110 amps and it should have been 70 amps. This
time it drew 69 amps on the nose.
I cooked the speed controller last time
testing. The 110 amps was just to much. I thought I had the needed
parts in the shop but didn't. They are now on order and may be here for
the launch. If not, it's full power, or off. It's now HOT WIRED to
the relays!
I altered the smaller side thrusters
similarly. They are both aluminum props and, as I found out, they don't
take a bending as much as the bronze ones do. I bent them a little but not
much since I started a small crack in one of the blades. Nothing
detrimental but a good warning. These props are of the weedless type so
they have long tails. I removed some of the tail and reshaped the new end but
apparently not enough. They drew 30 amps last time and now draw 27
amps. I need to trim them down to 20 amps. Guess I'll reduce them
some more.
The air leaks I found around the bolts that
passed through the MBT's last test were all fixed with some silicone gasket
sealer. No problems there now.
I also added some weights to the interior of the
sub and am now closer to a diving weight. On this test it floated lower in
the water and settled firm to the trailer deck with about eight inches of the
conning tower above the surface. The last test I couldn't get it to settle
that deep with all ballast tanks flooded. I now have about 500 pounds of
removable lead inside the sub. I may add some of that to the drop weights
later. In hind sight, I could have added eight inches to each battery pod
and two more batteries.
I built my MBT venting according the Kittredge
design. A design that was used of both K-250's and K-350's so I'm pretty
sure it's as it should be. But, when I flood the MBT's for the first time
they vent smoothly and evenly. They vent well, as long as you
keep the sub trim. I found I have to monitor both forward and aft
tanks as they get closer to full other wise the sub pitches forward or
aft trapping the remaining air in the higher tank. I'm guessing more
practice at keeping trim will fix this problem.
The other thing I noticed was that ones a tank
was totally filled and water runs into the lines it doesn't vent
as smoothly the second time. If I refill the tanks with air it expels the
water but if only a little air is added to level off, it doesn't vent
properly. I think I'm trapping water in some parts of the piping and
unless I generate enough pressure to force it out, it's trapping air
behind it. As I said, Captain Kittredge used this design for years so It's
probably something I'm doing but It does point out the need to never let vent
lines trap water. I hope practice solves the annoyance.
So there you have it, if I haven't bored you
to death already. The LONG story!
I'm still on for an actual launch on Sunday June
6th.
Thanks for listening. I would really
appreciate any recommendations or advice from anyone diving a K
boat. Geez, I'd sure hate to flip the darn thing over or sit stuck to
the bottom on the maiden voyage. :-(
Dan H.
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