T&T: Hull Speed 20% faster and more economical, by new

[Rich Gano]

The US Navy (for all its perceived conservatism) has always been receptive
to new technology and currently has several vessels in service, not as
commissioned ships, but rather under the auspices of government-funded
research outfits, some more official than others.  Some of these are
university-sponsored groups.

One such vessel languishes here at a local marina across the bay from the
Navy base.  It is an odd looking aluminum duck with large deck-mounted
tanks, apparently for air storage.  It also has large air inlets in the
hull.  Apparently, the idea is to reduce hull friction by adding a layer of
air.  Somehow I imagine it would be allowed to berth at the base if it were
actually proving worthwhile.  It sits idle for "lack of funding" as best I
can tell.

While the Navy experiments with such things, hopefully not wasting too much
taxpayer treasure, the tried and true work horses of the blue-water Navy
carry the load of national defense at sea.  I help make sure that many of
them are indeed pumping a lot of air into the water under their hulls but
not for the purpose of friction reduction.

It is pretty difficult to come up with something that can be added to a
10,000 destroyer (good grief, my first destroyer in 1970 was 4,000 tons!)
that can help it's speed/fuel consumption, but we actually have a new/old
item that is helping.  Stern flaps (immobile "trim tabs") have recently been
added to some destroyers and carriers.  I'm not sure about cruisers and
frigates.  The thing helps to prevent stern squat as speed is increased thus
keeping the ship's trim more level, which decreases fuel consumption a few
percent as reported to me by the chief engineers and captains.  It looks to
extend several feet beyond the stern and is angled down a few degrees
(again, I am uncertain of the specifics).

A number of years ago, a shipyard owner acquaintance here in Panama City
took me for a ride in a heavy metal displacement mullet net boat he had
converted.  It was diesel-powered and maybe 30 feet or so in length.  He had
added a hollow fixed ring (looks like a kort nozzle) around the single
propeller.  Holes were drilled into the propeller side of this thing, and an
air passage allowed for free communication to a stand pip running vertically
from the keel to several feet above the deck.  He said the critical
measurement was where the vertical plane of the holes in the ring was in
relation to the propeller blade tips.  He had done something similar with an
outboard motor.

He took me out for a ride in the net boat and had the standpipe capped with
a thin piece of aluminum arranged to rotate over the opening.  He revved the
engine up to push the boat hard and had me go back and rotate the cover off
the standpipe's open end (it was difficult due to the strong suction).  The
engine immediately picked up a couple hundred rpm and vibration eased.  He
was able to pull back the throttle to the original rpm to maintain the
improved speed - I remember he claimed 25% fuel savings overall but at what
speeds and over how long a period I cannot say.  He told me his lawyer was
looking into patenting the item.  I have not spoken to him in a number of
years about what he may have been doing with the thing, but he is a serious
and professional shipyard owner.  He had built and owned some sixteen crew
boats operating in the oil patch off Louisiana when I knew him; so I'm sure
he applied his invention there if it was feasible.

Rich Gano
US Navy Surface Ship Silencing Program Trial Director
CALYPSO (GB-42-295)
Southport, FL