Motor Boat & Yachting - January 2016 UK

BOAT MASTER NEWTECH

JANUARY 2016 79

Putting aside naturally

stabilised multihulls and the

more esoteric forms of

stabilisation such as flopper

stoppers (aka paravanes)

there are now six types of

stabilising systems you can

choose from, comprising:

OGyros Now available for boats

as small as 30ft (e.g. Seakeeper

3DC, MBY September 2015) gyros

are terrific when the boat is at rest.

No external drag, but their

effectiveness typically reduces at

higher speeds;

OConventional fins These

provide stabilisation under

way but not at rest. Available

with hydraulic actuators but

also with smaller and lighter

electric motors;

OZero-speed fins Also electric

(e.g. CMC fins, MBY March 2013)

and hydraulic, these larger fins

waggle rapidly to provide a boat

with stability at rest as well as

under way. Zero-speed fins are

ultimately likely to eliminate

conventional fins;

ODMS AntiRoll When the boat is

at rest, DMS’s high aspect zero-

speed fins (MBY February 2014)

flap like bird wings instead of

waggling around their shafts as

other fins do, so they should be

more efficient;

ORotorSwing The oddball of the

stabiliser world (MBY August

2015) these spinning shafts (see

picture above) appeal particularly

to users of shallow inland

waterways because they can be

folded flush with the hull;

OHumphree The latest system

reviewed here which combines

the full attitude control of

Humphree’s top interceptor

system (Active ride + CTOS

co-ordinated turn) with electric

zero-speed fins.

30 SECOND

BRIEFING:

STABILISER ROUND UP

With compact electric actuators and fi ns made partly from carbon fi bre, Humphree
claims its system is at least 25% lighter than the competition

Humphree’s new system

links fast acting interceptor

tabs with electronic fi ns for

superior stability under way

and at anchor. The fi ns are

designed to break off without

breaching the hull structure if

they hit something solid

generators and/or alternators need to
feed the batteries the better.
Humphree’s assertion that the
system controls pitch, as well as roll
and yaw, needs qualifying. Any fin
system will reduce pitching to a degree
simply because of the vertical damping
effect of having a pair of immersed
plates amidships, resisting being pulled
up and down through the water.
However, I talked to Humphree’s
technical guru, and the company is not
claiming that pitching in waves will, or
even can, be eliminated. The pitch it
refers to could be more suitably
described as the bow-up, bow-down
running trim, which the interceptors
continuously optimise as fast as they
can based on what the boatbuilder and/
or owner has told the system is best.
With under 1-second from fully-up to
fully-down, that is extremely quickly,
and it naturally has a damping effect on
pitching in more general terms.
One question is why Humphree did
not combine its interceptors with a gyro
instead. The effect of
Humphree’s
interceptors can
be felt down to
around 15 knots,
but to exert their full
degree of control normally
requires 20 knots or more.
Likewise, although we all know how
effective gyros are at zero speed, I’ve
been on boats where their efficacy has
started to tail off at speeds as low as 10
to 12 knots. So although it wouldn’t
always have been the case, combining
Humphree’s interceptors with gyros
might have left some boats with an

uncomfortable control gap in the

middle of the speed range.

QUICK AND EASY INSTALLATION

Humphree’s new system allows us

to raise two issues that we’ve not

had the space to discuss with other

stabiliser tests and reports (see 30

second briefing for a round up, right);

namely noise and the electric versus

hydraulic question.

Describing its 24V DC electric

actuators/motors as ‘ultra fast’ implies

some sort of speed-of-response

advantage, but frankly the hydraulic fin

systems I’ve tested have been so

brilliant anyway that I reckon this is an

irrelevance. More pertinent is probably

how the boatbuilders perceive the

installation advantages of being able to

dispense with a hydraulic system and

simply run (albeit chunky) 80A power

cables and tiny control wires. And

notwithstanding the varying sizes of

different actuators (hydraulic and

electric), it is likely that an all-electric

retrofit would be easier than a hydraulic

one. But it will vary considerably

between boats.

As for the ability to run Humphree’s

fully 24V DC system without help of the

generator (as Seakeeper’s new 3DC

can) that is a varying benefit. Under

way, generator and alternator noise

would normally be swamped by the

engines, so no big deal. Anchored in a

quiet bay, it would be great to run

silently from the batteries alone. But

when that anchored use is extended to

the high current draw situation that

zero-speed overnight operation would

entail, who knows whether a typical

battery bank would cope?

Noise is an issue to which there

seems to be no definitive answer. I’ve

heard owners of both electric and

hydraulic systems claim that their

system is the quieter one. This suggests

that much has to do with the particular

installation. I’ve recorded hugely

different sound levels on similar boats

powered by identical engines.

Sometimes it’s been obvious that

sound insulation was the key, but

structure borne noise can be a big

factor, and that can be an elusive thing.

Hopefully we might be able to answer

some of these unresolved questions

soon, as Humphree hopes to have a big

cruiser for us to test towards the end of

this year. Watch this space.

Contacts http://www.humphree.com