Magnus effect steering

(1)

'I

FEB. i93k

ARCHi1-By John I Borg

in the continuing search for great-er safety and increased efficiency in

workboat design, all of the tradi-tional components and systems must be re-scrutinized, in this article I shall compare conventional steering by means of rudders with a new dy-namic steering concept, based on a physics principle called the "Magnus Effect.''

The area of workboat design most in need of improvement and innova-tion is Steering, particularly at low speeds. This is evidenced by the

re-Borg is princ'pa! naval architect of 18W Indus tries of Houmo. L.A. This per wa first pii. senfed at the recent Work Boat Show in New

Orloons,

r.t i'

cent crop of thrusters, squirters, ar-ticulated rudders, and piggy-back, fullswivcl propeller units displayed in living color on the pages of your favorite marine journal. All of these devices share a common characteris-tic: their complexity is more than compensated for by their inefficieri-cy.

It is well known that mankind's

favorite steering device, the rudder, has many inhement faults. You can steer a boat with a hockey stick if the boat is moving fast enough, but it is riot very effective at low speeds. The

rudder tends to act like a "flap'

when moving astern, building up heavy forces on the rudder stock and tiller arm or quadrant.

A rudder in action when viewed

Lab.

_{v. Scheepsbouwkurid}

1nische1-jescTfl

Deift

New steering concept utzes cylinder

in p!ace of conventional fiat rudder

f

w;sr,j

_c"

'-p

L.i

from above develops "lift'' in ti:

fashion of an airplane wing, but as the rudcr snie is increased '.vi h re-spect to !ie shtp's directic.a rtvei.

the component of force normal to the blade moves in a rearward direc-tion until a critical angle is reached.

then the r..vcr ''strils'' ae.J

into a brake. This tends to dampen

the forward nioLion of the hull so that more power is required to main-tair speed, and fuel is wasted.

Addi-tionally, as the rudder is stroked

through its seventy-or-so degree arc

from hard over to hard over, it con-tinues to turn the ship in an undesir-able direcricro, resuRne. iu oversee, pensation the

helrc "'

more fuel Finally, propebers, are rather ra

(2)

I'vi.4)i IU..) LlIcZ)t'

Conftnued

dages and are expensive to Construct and repair.

MANY DEVICES ON MARKET

Until now, "trick" steering and

propulsion dcvces found on the

markct were all developed with the intent of supplementing or replacing the medieval rudder. Most of these

coutraptioris suffer from a ease of acute awkwardness and an

over-abundance of right angle drives that

devour precious horsepower and fuel.

The prcbiern, then, Is to design a maneuvering device that is more ef-fective at all velocities; does not cre-ate addincna drag while developing its turning force; stops tunctioning

the instant the desired heading is

achieved; is difficult to damage, yet eas to construct and repair; can be retrofitted on an existing vessel; is

equally effective in the ahead or

astern direction; cart be installed on both how and slern; uses little energy to accomplish its role; and requires

no more machinery space or draft

luan a conventionaf rudder steertng system.

('' '

.LJi Li i

T'''7

t

It is clear that the solution has to be hydrodynarnie n nature. You do not save energy by adding more power units to your ship, nor by increasing the number of aopendages. The key is the geometry of the rudder itself, combined with a physical phenomen-on that was not obvious to our Baltic forebears who conceived the rudder idea nearly a thousand years ago.

The Magnus Effect rotor consists

of a cylinder having circular end plates, and is installed in place of the conventional fiat rudder. As the ves-sel moves ahead or astern creating a flow around the cylinder, a turning force at right angles to the direction of travel can he developed by

rotat-ing the cylinder in a clockwise or

anti-clockwise mode. [he niagni-tude of the turning force is a

func-tion of the velocity of the flow and the peripheral speed of the cylinder rfacc. When these become equal, a

low pressure zone develops on the side of the rotor that is traveling in

accord with the direction of how .As

'-the relative speed of '-the rotor

in-creases, so does the ''lift.'' When the surface velocity becomes four times

the flow velocity, the lift to drag

ratio is about nine to one. The ratio is less than two to one for most con-ventional rudders in the "hard

over" position.

TREMENDOUS FORCE

Thus, we have a device that can produce a tremendous turning force

with a minimum of drag. In other

words, it does not act as "brake" in the fashion of traditional rudders.

The Magnus Effect rotor needs

only sufficicnt torque to overcome bearing and surface friction forces, so the power requirements are quite low. Further energy savings are real-ized because the rotor can develop maximum turning force or return to

-,

s..-..

TRASH APRON

MUS vs EXSi

kU<

PERFORMANCE COMPARISON

CURVES FOR A _{LOWER END PLATE}

(3)

-- --.- .- .. .. .... - ..-. . .- ..

--.

.-'. -4DRVE HOUSING WELDED TO VESSEL STRUCTURE 1ROTOR

--COtTC

zero in a matter of a few seconds. The long delay of a typical rudder as it sweeps through 35 degrees of arc is not encountered.

The majority of Magnus Effect

steering systems pr000sed thus far

have been hydraulically actuated. However, for large vessels, it may be advantageous to utilize variable-speed, reversible dc electric motors. Indeed, Magnus Effect may be the only practical way to steer a super-tanker electrically.

As for vulnerability to damage, it

is difficult to visualize anything stronger than a cylindrical steel col-uinn. It is a large weldinent that is simple to construct when compared

with the elaborate, semi-balanced

airfoil configurations now in use. With respect to safety, the same redundancies of power sources and drive units can be used with Magnus Effect steering as with the conven-tional style. Furthermore, the new

?

/1

0 450 R.P.M. @10 Knots 450 R.P.M.

-

@9 Knots 450 R.P.M. @8 Knots 450 R.P.M @7 Knots 450 R.PJv. @6 Knots L130 R.P.M. @5 Knots 344 R.P.M. @4 Knots 258 R.P.M. @3 Knots 172 R.P.M. @2 Knots 86 R.P.M. - @1 Knot

method has the advantage of not locking itself into a turn; in the e-.ent of power failure, it is automatically ''centered'' due to its symmetry. WORKBOATS BENEFIT MOST

The virtues of Magnus Effect

steering, p:reiculrly for the

work-boat fleet, begin to add up rapidly. In the operation of pushboats on the inland waterways, drag-procuc-ing flankdrag-procuc-ing rudders may be elimin-ated. Bow steering for a difficult-to-manage string of barges i availahle either in the form of the

self-pro-pelled, radio-controlled

"Bow-master'' unit, a twin-hulled bow tow-boat that may he. manned and used in the normal fashion for greater

versa-tility, or the ''strap-on'' portable,

retractable rotar steerer. Tie Ia;tcr

resembles a utility Loinpany

''post-hole digger," but it

will produce turning forces ' a mere 2D -orsc-power that would he equivalent to

those of a 200-horse-power mrusting de',-ice, and it does not beceme "water starved" velocities in excess of three knots.

Au ideal atDiicati.ri

for Magnius Effect steer-ing is it's installation on double-ended ferry ves-sels. Here again, bow steering would he avafi-able at full ahead speed, paying a dividend in

greater maneuvering safety while crossmg busy waterways and dockine.

Other categories of

workboats that woud

obviously benefit from the increased efficiency of Magrius Effect steer-ing are self-propelled hopper dredges, dock-ing tugs, integrated tug barge units,

firccats,

and tov,ed sea-going barges. Large, difficult-to-maneuver, seagoing vessels could also era-ploy these devices as auxiliary or emergency control.

FIIST USED AS "SAILS" Historicelly, the rnarir.e

first became aware of ftc '. Effect in the year 1926 wtiC't man Inventor named Anton Flettncr

'-V

.'

I.

r'-

'\.r"-'

.J

COV7O!AL

(4)

L I 60 !jI

-

C' "V" L.. Continued

outfitted a vessel with cylindrical, - electrically rotated sails and voyaged to New Ycrk. The demonstration was e great success, but the tirning was off. Fossil fuel propulsion was cheap then, and the age of sail had passed.

znus

(P roposd) Rotor (2)

Tug

aow

We have turned Flettncr's dream boat upside down and rro.luecd an extremely efficient steering system that

is appropriate for the

''fuel-hungry'' times ahead.

RESEARCH COMPLETED Inspired by a review of the Flett-ner experiment and by an awareness of the need for more effective steer-jug, particularly on the inland water-ways, SSI, Inc., an affiliate of TBW Industries, Incorporated of Houma, LA, began a research program

con-i

.

rttii ft v

c*w1

gter!rir

(ExisI hig) Rdthr (2) lnring Potor (2) (Propo.ed) (Existing) drag, hardover42

FOC

\

c.\

\ \ ry'H"

cerning the subject.

In early August 1979

tests of

model cylindrical rudders were con-ducted at the Lockheed Ocean Lab-oratories lowing Basin in San

Diego. The hydrodynaniic theory

was verified and a practical formula for steering application was derived.

Inspired by this success,

immedi-ately following the tests, U.S. and foreign patent applications were filed. Although still in the preliminary stages of development, naval archi-tects and workboat operators alike

are showing marked

in-terest in this new concept.

Early this year the

first Magnus Effect rudders were retrofitted on opera-tional pushboats for field evaluation. Immediately following this study, it is in-tended that the systems will be available on a produc-tion basis.

We feel certain that Magnus Effect steering

will soon become

com-monplace throughout all

zones of marine activity

and that the safety and

economic benefits of

this simple and efficient

steering device will be felt industry-wide. MfL

fOW

.Ns\

V

MARINE ENGINEERING/LOG "4 9')U od s 1crce,

poonds poil

dr,

0 pounds

52 1,042 622 126 560 4,G6 2,242 9,372 5,02 1,1 5.045 4 .c.O 16,700 9,980 8,5(X) S ' ₂₈₀₃₆ _{lS,Sf 3} ₃₁₃₅ 14,013 0 310 39,600 22,400 4./'is) 20,000 361 52,900 30.600 5,400 27,600 433 66,652 39,t10 8.024 35,873 9 450 79,800 51,200 10,400 45,800

40

92,236 y) ,.n 12....38 6.051 D C7lCN G T?AVEL

.ciximum

'n'

ciru