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.
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)
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
24. Al 2014-0
25. Al 2024-T4
26. Al 5052-H16
27. Tin (plated)
28. Stainless steel 430 (active)
30. Steel 1010
31. Iron (cast)
32. Stainless steel 410 (active)
33. Copper (plated, cast, or wrought)
34. Nickel (plated)
35. Chromium (Plated)
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)
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
Aluminum 1100, 3003, 3004, 5052, 6053
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)
316, 317 Stainless (active)
Carpenter 20Cb-3 Stainless (active)
Aluminum Bronze (CA687)
Hastelloy C(active) Inconel 625(active) Titanium(active)
Inconel 600 (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)
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
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)
Titanium (passive), Hastelloy C & C276 (passive)
This one lists many common alloys, so I included it.