Alsphere in Venice
by Captain Tork Buckley
Excerpted from The
I waited on the dock of The San Clemente Palace
on the Venetian Island of the same name. The hotel is an amalgam
of old and new; a Camaldolesi monastery in 1131, latterly during
the Austrian occupation a hospital for the insane, now a luxury
hotel. I arrived by traditional Venetian water taxi, but I would
depart on an Austrian, prototype vessel of radical design. Challenger
II is Alsphere Engineering’s 14.45-
m demonstrator for a new hull concept: Displacement Glider.
hull shape echoes the retro idiom of the hotel: a near vertical
stem recalls a New York commuter boat, but like the hotel the
underlying hardware is very advanced.
The hull is formed of two elements – a
relatively wide ‘keel’ containing the propulsion
machinery and a virtually flat-bottomed hull with a slight wave
shape. Alsphere refer to the keel as the “displacement
keel” and to the rest of the wetted surface as the “planing
The vessel’s keel has relatively narrow
width compared with length, yet 75% of the displacement occurs
here. At 19 kt top speed this DG hull cheats the displacement
hullspeed limitation that restricts top speed to around 11 kt.
Alsphere’s Martjaz Peterman explained,
“Wave systems produced by the two elements cancel each
other out in the optimum speed range”. The shapes of two
elements are optimised for flow, e.g. the keel continues to
The result: a minimal wake in the optimum speed
zone: for this hull 9 to 19 knots. A wake represents lost or
wasted energy so a smaller wake equals greater efficiency. Alsphere
claim a potential reduction in fuel costs of 30%. Further cost
savings are found in a lower power, thus lower cost, prime mover.
graph of shaft power V speed shows significant speed advantage
over planing hulls through the range, optimised in the middle
and diminishing at the either end. Against displacement hulls
the advantage simply gets larger as you go faster. Of course
the displacement hull has reached hull speed in the middle of
the DG hulls’ speed range. Another advantage claimed is
that the interior usable volume is 20% greater, as machinery
– tanks etc – are in the ‘keel’.
Danny Lenard of Nuvolari-Lenard design endorsed
this, stating, “For yachts of 12 to 20 m . . . improved
efficiency, and minimal wake with maximal interior volume (from
such a hull) are very interesting”.
For larger yachts efficiency savings are impressive;
a hypothetical 59-m yacht based on an existing style above the
waterline, with DG technology below, reduces propulsion power
requirements at 15 kt from 2,908 to 1,060 kW. Unfortunately
it’s clear that there would be less usable interior volume
than in conventional displacement design. Unless operational
area requires minimal wake it is unlikely mega yachts will use
Commercial operation is different; a 40-m crew
boat for the Gulf of Mexico oil fields is in build with a modified
DG hull drawn by Louisiana naval architects AK. Suda Inc. The
main attraction for this operator is fuel savings with an added
bonus of ride comfort; wake reduction per se is of no interest.
Challenger II features an unusual construction
technique: interlocking extruded aluminium ‘planks’
minimally welded, caulked then faired. That Pinnacle construction
system is another design of the DG hull inventor, Theodore Eder.
In this system the vessel needs no frames. Formers are used
during construction and were left in place on the original (open)
Challenger II. Once the superstructure was fitted, Mr Peterman
told me, they could have been removed.
Alsphere do not wish to be boat builders; they
propose to license construction to other builders.
difficult to assess how our market will respond, both to such
innovative design and unusual commercial approach. Danny Lenard
is enthusiastic too about the styling possibilities; construction
may be from any material and as all the hydrodynamic ‘work’
is done below the waterline, the hull above can be in any style:
traditional, modern, ‘picnic’ boat; here form need
not follow function.
Minimal wake (above right) is of less interest
to such yachts at sea; however, in areas like the U.S. Intracoastal
waterway or Europe’s inland waterways there are benefits
where speed limit criteria are ‘no wake’ rather
than ‘x knots’.
It was not by chance the Challenger II was trucked
to Venice after construction in Vienna; Venetian authorities
expressed interest in replacing the ACTV Vaporreto fleet with
a limited-wake vessel. However, as the inventor points out it
is the smaller high-speed vessels such as those used by the
emergency services that damage la Serenissima the most.
Challenger II’s motion underway is not
unpleasant but certainly odd; Danny Lenard described it as gliding;
to me it was similar to a catamaran. There is negligible roll,
pitch and yaw or heel when turning. Claims of minimal wake from
9 to 19 kt are valid. As expected below 9 kt the wake is as
for a displacement hull. The boat is quite stiff, understandably,
as on this empty prototype almost all the weight is below the
water line. She turns well, though steering is heavy, and manoeuvring
as well as draft (deep, compared with a planing hull) must be
considered disadvantages. The keel has considerable lateral
resistance; bow and stern thrusters are required to manoeuvre
transversely. Around 15 m LOA is required to gain the 20% extra
interior space single engine operation; there is no room in
the keel for two engines. Indeed there is little room either
side of a single engine.
The Displacement Glider is an unusual design
that will certainly find a niche in yachting, though perhaps
it will find a larger application in commercial shipping where
wake damage is a serious, in many cases unanticipated, problem
for high-speed ferry operators.
reproduced with the kind permission The
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