Steering
is a Science A machine that tracks
& maneuvers well is a pleasure to Operate! Any that do not are a hazard. We can improve your Vessel
Lowell W. Stambaugh /DMR
===================================
Hello;
You have entered the text blog of Lowell W. Stambaugh founder and principal
officer of Deflector Marine Rudder LLC since 1999. Presented here are a
collection of statements, short articles, and a few depictions intended to
explain rudder systems in general and Flap-Rudders in particular. Most will
restate some material you may have already seen as this collection spans some
years. Over time I intend, editing, should improve those features. I am sure
that if you plow through this material you will come away better informed.
I
do not know of any Mariner in the Western Hemisphere that has more experience
in this field than myself. I wish to thank those bold owners and operators who
have trusted my engineering to improve their vessels, initiating many fine projects.
Many though certainly not all, can be reviewed in the website pictures. Happily,
repeat orders for the next boat are the norm. We have been told that we are building the
best rudders available in the world. I think this is so. We avidly pursue any detail in current
understanding in this field in order to benefit our clients with the best
available. I hope you too will benefit from our work.
I
am starting this dissertation in very primary = basic terms and concepts. A
typical watercraft and aircraft (I understand banked turns) as well steer by revectoring a
flow stream. Most situations employ foils
to accomplish this pressure change. The device that accomplishes this is
typically located near the aft end. So it can be said that heading changes are accomplished by slewing the stern of most vessels. Like a fork truck, steering from
the back.
When a heading change or correction is desired
the helmsman angles the rudder panel = foil. As the hull and rudder advance
though the water, higher pressure from the water striking the forward
exposed side of the blade overcomes the consequently lower pressure of the
retreating side.
With
this established, I will state “that all rudders are foils”. So it is, that there are better foil shapes and
poorer performing shapes. The elongated
teardrop shaped foils are shaped so as to distribute the pressure more
evenly over the surface. This leaves flat plate surfaces as the poorer
performing foils. As conditions are dynamic
(meaning
variable) a Shape
Changing foil offers even more utility. A rudder is a traction
device. More is better!
How
much better? That word dynamic is a problem child. This means that exact
comparisons require exact condition analysis, extremely intensive study. For
simplification I will state conditionally that we are often likely to be able
to design a rudder system that will exceed the performance of a conventional
rudder by 2 ½ times effect.
How?
Perhaps you have noticed that our DMR rudder designs appear different.
By carefully applying scientific Hydrodynamic
principles. ( Hydrodynamics is the field we are speaking of here.)
There can be several features that differentiate a DMR High-Lift Rudder Blade from its’ inferior. Proper entry shape, sectional
shape, proportions, and proper placement are among them. Adding
a hinged 2nd panel to your rudder makes it a more versatile shape
changer. This effects a number of profound & usually positive changes.
Likely
you have not seen a turbine blade that is not cupped. A cup is formed at the hinge axis between
the main blade panel and the
trailing edge flap. This creates traction as tread does on a tire.
In a
rudder high pressure strikes the leading edge, but this pressure diminishes as
flow moves aft until
it can actually become oscillation creating buffeting if the rudder extends
back to far. Many who want more rudder lift add to the trailing edge of their
rudder blade. In most instances they did not get the desired increase in
performance for the reason just noted. The hinged flap however cups to create a
greater angle of attack resulting in a 2nd high pressure zone at the trailing edge! This is powerful.
Marine
steering goes back to paddles & oars. Fascinatingly my study shows me that
the Ancient Mediterranean steering oar was actually a very clever device,
better suited for its’ applications than much of what followed. Many of todays
watercraft were inflicted with inadequate rudders for their task. Most
experienced Mariners have had the experience of overtaking a vessel and
wondering just what heading they were trying to make. First one side is seen,
then a few moments later the other side
is in view in a great wobble -- continuously. Boats are designed to go ahead by
the bow, not push their side panel ahead. When this occurs the chine digs in
the hull rolls and a large portion of the forward thrust is consumed –
wasted creating discomfort & expense. The reason this is occurring is steering system inadequacies.
We
build modern machinery to eliminate this traditional inadequacy. Either the
rudder does not produce the power or does not move timely = quickly enough to
arrest the unwanted slewing off track. When this occurs I call it being out of phase. Your rudder has the task of
reacting quickly to the indication that you are veering off heading before this
becomes a substantial wobble. To do this the rudder must move quickly and poses
the power to arrest the hulls’ rotation early. (Later or weakly is being Out of Phase) Many of our customers
report that they transit more than ½ knot faster. That saves wear & fuel.
Quite a lot. Notice that our rudders’ flaps movement is inherently faster than
that of the main panel making them more effective at reacting in phase.
Happiness for you and your autopilot!
Our
customers must reset their autopilot to the lowest settings. When you go
straight the whole machine works less and your rudder does not need to make
high deflection angles. This is efficiency.
When
a conventional vessel intends to pull away from a dock face it is desirable to
rotate the stern out to clear any obstruction behind. When putting the helm hard over the DMR
equipped hull rotates rather going into a forward arc threatening whatever is ahead. The DMR flap angle produces a prop wash
vector abeam at approximately 90̊ from the forward axis of the hull rotating it
rather than propelling forward-- Efficient & easy, with reserve power to
overcome wind & currents as is needed.
Why
do so many boats have such marginal steering systems? Ignorance that is the
byproduct of historic/traditional limited view. To me the marine and more
recent aviation history of the world is fascinating. I collect books on those
subjects. I may yet write a book on this. Numberless sailors and whole fleets were driven
helplessly to wreck where modern understanding of rudder design might have let them sail closer to the wind and
survive. They did not of course have Stainless Steels, but relied on wooden
shafting which cannot transmit a much torque. We are fortunate in tools &
materials now.
As
we are the heirs of generations of experience. Today the stakes are high so it
is in our interest to make use of the best engineering for safety and waste
avoidance. At DMR our engineering is dedicated to this, best rudders.
When
I was a young commercial fisherman in Alaska wooden boats were the norm for the
fishing fleets. Boats handled wretchedly turning ponderously and often
requiring a constant hand on helm just to produce a ragged course. Stainless
steel was considered rare and impossible to work. Electro galvanic corrosion,
metallurgy, welding and cutting equipment was far less available, and not well
understood. (one year I fished a former sail boat) my own reaction to all this
entrenched antiquity was to become one of the earlier aluminum boat designers
& builders. In my own lifetime tremendous change has been made.
Interestingly
popularly the focus on rudder systems has generally lagged. To this day
designers and builders carefully select the propeller to be bought from
professionals, but often presume that they should copy a rudder they saw, and
build a copy of a copy that was designed in ignorance. This never served well.
One
consequence of the poor handling performance of many rudder equipped vessels is
the popularity of a great array of devices and alternative propulsion.
Thrusters, roll stabilizers, azumething Z-pellers, outdrives, and jets all owe at
least some of their popularity to this unnecessary frustration. Do not
misunderstand me all of the devices have their nitch and their deffiencies.
There
are several notable advantages of rudder equipped vessels, They are cost
effective and efficient in service. The inherent simplicity means service can
be accomplished more readily from a variety of options, using few patented
components. The power conversion factors favor rudders. Think of all that
spinning water imparted by the propeller blade. That rotation (swirl) is wasted
as it is unconverted to forward thrust. Divide that zone with a well shaped and
positioned DMR rudder and the spin is dramatically diminished allowing more
water to move directly aft as intended. Without the rudder there as in some systems the water
continues spinning aft. Jet pumps
have a collator to untwist the water, and this is why, single axis counter
rotating propellers are particularly efficient.
Longline
fishermen and tug operators particularly like that even gliding neutral our DMR rudder is providing
continued steerage. This is not the case for steered propellers and
in a rough seaway this makes a profound difference in ease of maneuver and not
needing “power on to turn”. Saves fuel as well.
Perhaps
you have noticed the another thing that makes a typical DMR rudder distinctive
is the “D” profile. I will state that curve is important, hydrodynamic, and
leave it hanging there to consider.
Let
me describe for you the motion and the mechanism that operates the DMR Rudder
Flap. When I first began experimenting with flapped rudder engineering I
devised and made models of 5 ways to drive the flap. I researched and found a
handful either patented in the past or from aviation. Then I studied what was
wanted I worked to devise, the ruggedest, simplest geometry, that could give
the least compromise, and have the least parasitic drag that could be easily
serviced. I call my selection the Western Fulcrum Pivot.
It employs a hardened roller (Rather like a cam follower) that drives a slotted lever arm.
Interestingly it makes more torque as the angle increases just as is wanted. It serves well and the roller
& pin are easily replaced though even this is seldom needed. We inventory
Pivot Roller assemblies in diameters of 1 1/8”,
1 ½”, 2”, 2 ½”, 3”, and 4 ½” which covers small vessels up through above 5,000 hp in tugs & trawlers.
1 ½”, 2”, 2 ½”, 3”, and 4 ½” which covers small vessels up through above 5,000 hp in tugs & trawlers.
Having
fished among other areas, the often dramatic weather conditions of the remote
Bering Sea, I understood that broken or inadequate is not appropriate. For this
reason I have always designed for long service, strength, and damage
resistance. Putting a hinge and a trailing edge flap at the back of your rudder
certainly adds to the complexity, However there is an interesting feature of
the Western
Fulcrum Pivot design is actually suspended from additional points at the very strong pivot pins. This has proved to
make them even more resistant to impacts.
I
fleetingly mentioned Galvanic Corrosion. All Mariners and persons making
decisions affecting vessel material selections should learn some of this
science. In short all metals a have electrical current potential relative to
other metals. This is the principle that makes the power of battery cells
possible. Notice that battery names are expressed as their component metals
Nickle/Cadmium or lead/sulfuric acid (sulfur is a metal) for example. Thus
corrosion has power. The selection of materials that are to be immersed in the
electrolyte seawater is critical, if you want to keep your equipment in service
it should be designed by individuals who understand this work, and use the
science in material selections.
A
number of materials are simply not suitable as components in corrosive
environments. This is so complex that it is not practical attempt a list
especially here. For your convenience I
am offering a simplified version of the GALVANIC SERIES TABLE. To understand
its’ use understand certain conditions. One is that most metals are used as alloys
= combinations of metal elements, and are therefore not pure. This shifts
things some. Two is that metals
can generally be grouped into families of compatible and less compatible. In general the further any 2 metals stand apart
on the chart the higher their electrical potential (difference in Voltage).
Note: most batteries in order not to self-destruct are limited to 2V per cell.
Very powerful.
Notice
that Bronze a useful & popular marine alloy that contains copper Tin &
Nickel, etc. As there are many copper family
alloys in popular use for fittings & parts in the marine world I
want to mention that faying copper atoms are an aggressive promoter of
corrosion of metals below it in e-V potential. This situation is very corrosive to Aluminum,
Steel, & Stainless steel alloys.
To
properly use the metals you need to understand that certain metals develop a hard shell
exterior oxide layer that
protects them as long as oxygen is available. These are the virtues of Alu,
& SS alloys. Steel however develops a layer that is soft & permeable,
and sloffs off. We usually choose metals
based on Strength, Cost, & Workability, or we would all use much more
titanium.
Understanding
anodic protection and passivation to control unwanted metallic destruction of
you valuable vessel will save you a lot of money. Notice active and Passive
phases of SS alloys in particular. Passivation is when a layer of oxidized
atoms has coated the metals surface slowing the electrical potential (like a
dead battery). What follows is from Wikapedia
Active
(Anodic) Commonly used marine metals in blue. The theoretical voltage in
Green.
1. Magnesium
2. Mg alloy AZ- 31B
3. Mg alloy HK-31A
4. Zinc (hot-dip, die cast, or plated)
5. Beryllium (hot pressed)
6. Al 7072 clad on 7075
7. Al 2014-T3
8. Al 1160-H14
9. Al 7079-T6
10. Cadmium (plated)
11. Uranium
12. Al 218 (die cast)
13. Al 5052-0
14. Al 5052-H12
15. Al 5456-0, H353
16. Al 5052-H32
17. Al 1100-0
18. Al 3003-H25
19. Al 6061-T6
20. Al A360 (die cast)
21. Al 7075- T6
22. Al 6061-0
23. Indium
24. Al 2014-0
25. Al 2024-T4
26. Al 5052-H16
27. Tin (plated)
28. Stainless steel 430 (active)
29. Lead
30. Steel 1010
31. Iron (cast)
32. Stainless steel 410 (active)
33. Copper (plated, cast, or wrought)
34. Nickel (plated)
35. Chromium (Plated)
36. Tantalum
37. AM350 (active)
38. Stainless steel 310 (active)
39. Stainless steel 301 (active)
40. Stainless steel 304 (active)
41. Stainless steel 430 (active)
42. Stainless steel 410 (active)
43. Stainless steel 17-7PH (active)
44. Tungsten
45. Niobium (columbium) 1% Zr
46. Brass, Yellow, 268
47. Uranium 8% Mo
48. Brass, Naval, 464
49. Yellow Brass
50. Muntz Metal 280
51. Brass (plated)
52. Nickel-silver
(18% Ni)
53. Stainless steel 316L (active)
54. Bronze 220
55. Copper 110
56. Red Brass
57. Stainless steel
347 (active)
58. Molybdenum,
Commercial pure
59. Copper-nickel
715
60. Admiralty brass
Now
that is a lot to take in ain’t it. Its length does not mean it is complete but
likely you can spot the alloys or alloy elements you have in use. There are
other charts that give the actual potential of the particular alloy. (remember
we use alloys mostly I doubt you are using much uranium) many on this list have
no place in a marine device. Manufacturers do not always Know best or have your
interest in mind it seems.
Here
is another Galvanic Listing from Penn Engineering
Anodic (least noble) Corroded Direction of attack Cathodic (most noble) Protected |
Magnesium
Magnesium Alloys Zinc Beryllium Aluminum 1100, 3003, 3004, 5052, 6053 Cadmium Aluminum 2017, 2024, 2117 Mild Steel 1018, Wrought Iron HSLA Steel, Cast Iron Chrome Iron (active) 430 Stainless (active) 302, 303, 321, 347, 410, 416 Stainless Steel(active) Ni-Resist 316, 317 Stainless (active) Carpenter 20Cb-3 Stainless (active) Aluminum Bronze (CA687) Hastelloy C(active) Inconel 625(active) Titanium(active) Lead/Tin Solder Lead Tin Inconel 600 (active) Nickel (active) 60% Ni 15% Cr (active) 80% Ni 20% Cr (active) Hastelloy B (active) Naval Brass (CA464), Yellow Brass (CA268) Red Brass (CA230), Admiralty Brass (CA443) Copper (CA102) Manganese Bronze(CA675), Tin Bronze(CA903, 905) 410, 416 Stainless(passive) Phosphor Bronze(CA521, 524) Silicon Bronze (CA651, 655) Nickel Silver (CA 732, 735, 745, 752, 754, 757, 765, 770, 794 Cupro Nickel 90-10 Cupro Nickel 80-20 430 Stainless (passive) Cupro Nickel 70-30 Nickel Aluminum Bronze (CA630, 632) Monel 400, K500 Silver Solder Nickel (passive) 60% Ni 15% Cr (passive) Iconel 600 (passive) 80% Ni 20% Cr (passive) Chrome Iron (passive) 302, 303, 304, 321, 347 Stainless (passive) 316, 317 Stainless (passive) Carpenter 20Cb-3 Stainless (passive), Incoloy 825 (passive) Silver Titanium (passive), Hastelloy C & C276 (passive) Graphite Zirconium Gold Platinum |
This
one lists many common alloys, so I included it.