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Old 07-26-2022, 09:30 PM   #1
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Rudder Appendage

I was just browsing around Yachtworld and came across a Transpacific Marine Eagle 40 and noticed something on the rudder that I've never seen before. Can someone shed some light on what this modification is? Seems it must be related to low speed maneuvering but seems it would also create a lot of drag. I like the look of these boats but there isn't much on the web about them. If anyone has information or has owned one I would love to hear about your experience with them, appears like it would make a great loop boat.
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Old 07-26-2022, 10:35 PM   #2
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At the speed this boat goes the extra drag isnít that bad. With them the rudder is much more effective in turning the boat.
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Old 07-27-2022, 09:37 AM   #3
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search schilling rudder or fishtail rudder. There is a mechanical version of this idea too that retracts or extends the trailing edge for tight turning radius.
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Old 07-27-2022, 12:43 PM   #4
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It’s a fishtail rudder that works to increase the rudder effectiveness for low speed maneuvering. It does increase drag slightly but at trawler speeds is not too significant. A similar but more sophisticated version is an articulated rudder which has a vertical hinge such that as the trailing edge rotates based on rudder angle. It has very little increased drag in the straight ahead position.


[URL="http://https://www.passagemaker.com/technical/steve-zimmerman-right-stuff-articulated-rudder-
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Old 07-27-2022, 02:42 PM   #5
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3-5į is considered optimal flare on skeg hung slow speed rudders. Anything more creates more drag and load on the base bearing and rudder port than advisable. Iíve never seen the trailing edge flare so radical.

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Old 07-27-2022, 06:44 PM   #6
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Does it reduce rudder performance in reverse ?
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Old 07-29-2022, 09:01 AM   #7
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Thanks for the info. Seems like a pretty aggressive design, I would think an articulating version would be far superior.
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Old 07-29-2022, 09:17 AM   #8
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Thanks for the info. Seems like a pretty aggressive design, I would think an articulating version would be far superior.
But way more expensive and possibly more maintenance.
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Old 07-29-2022, 11:08 AM   #9
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Ted Hood designed and built several boats including 12 meter competitors that had ‘ trim rudders ‘ or articulating. They reportedly offered extreme fine tuning on fast sailboats and were considered desirable for those special hull and rig designs driving to weather. As I recall Herreshoff played with the idea and a few of the big Hand motorsailers had them. Complicated and expensive linkage

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Old 07-29-2022, 01:38 PM   #10
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The Schilling rudder attachment can’t help but cause an excessive amount of drag underway. The higher velocity propwash is bad enough w just a unadorned rudder but the pic shown by the OP shows a much higher than usual angle on the appendage that indicates that it could almost have been made w two pcs. of steel angle .. 90 degrees.

I would suggest that the OP take off the attachment (ideally after trial runs made w speed, rpm (never “rpm’s” as there is only one minute in the expression) so more is known by everybody about how much drag and speed (or fuel burn) is lost. It would need to be done carefully to be meaningful.

I approached the low speed maneuvering steering effectiveness by rigging the rudder mechanical configuration to increase rudder deflection to a high 45 degrees each way. A good articulating rudder would probably out perform it but at a fraction of the cost and effort. However a 45 degree rudder deflection is mot recommended for boats that run over about 10 knots. However it would only result in a very temporary loss in rudder effectiveness if rudder stalling should occur. I ran my Willard (FD trawler) for many years w the 45 degree rudder w/o any problem at all. Three turns lock to lock. The Willard 30 is a 6 knot (cruising speed) boat.

The best move for the OP would be IMO to consult w a NA.
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Old 07-29-2022, 02:06 PM   #11
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Quote:
Originally Posted by Benthic2 View Post
Does it reduce rudder performance in reverse ?
My Willard w “barn door” size rudder would steer in reverse fairly well. But requires the helmsman to hang on tight so as to prevent the rudder from going up against it’s stops w a hard thud or even “bang”. Could cause damage. My 25’ Albin steered backwards quite to very well at about 2.5 to 3 knots estimated. But I never let it get away from me as in locking the rudder against the stop.

I’ll offer one observation of the effectiveness of my 45 degree rudder that many can relate to. While approaching my slip (any of them that I had) I could go very close (allowing for stern swing) to the boats and pilings opposite mine and at the right moment go hard over w the helm. The boat made the 90 degree turn and I’d go on in w/o any “back and fill” at all.
Your boat may not respond quite as well as the Willard hull is better for turning than most boats having curved sides. And being somewhat wide and short.

With the OP’s schilling rudder the attachments IMO would almost certainly be less effective that the rudder w/o the appendages. One could also just extend the rudder. Best to do it LE and TE. Find the readily available proportional values of additions like 3/8ths” LE and 1.25” TE (usually expressed as a percentage LE/TE) … best to error on the too little on the LE. Just an example to achieve close to “balanced” rudder feedback.
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Old 07-29-2022, 02:14 PM   #12
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I donít think that the 2 pieces are 90 degree angle iron, probably closer to 45 degrees.
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Old 07-29-2022, 03:44 PM   #13
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I’d like to stress that rudder design and performance is a design aspect that needs more than just eyeballing and guessing. On trawlers of slow speed or semi-displament higher speed need the correct design and aspect ratio to work properly not create to much excess bending stress or tracking problems. The unbalance skeg hung rudder with little or no chord or surface area forward of the rudder stock is perhaps the simplest of designs while the balance rudder with a percentage of the chord or blade forward can require more math.

A properly designed rudder factors the chord or width, the span or height as if it were a hydrofoil or wing section. Flat plate rudders with exposed round rudder stocks on the outside do work but are very inefficient since the stock create laminar turbulance along the blade. Walk the boat yards and you’ll find the paint scoured off the sections of the rudder stocks. Truly efficient rudders on displ and SD hulls are tapered to the trailing edge and often flared 3-5į but most of all designed and built to ample scantlings.

A big slow turning propeller and a flat blade rudder though not optimal does indeed work as commercial fish boats can attest. They are common for one reason, cost. Unfortunately a good many offshore built budget trawlers seemed to have fitted up rudders the same way without doing the homework for displacement and semi-displacement rudder area formulas. My point is I don’t think it’s smart to tweak steering gear without professional design experience. Steering systems are just too critical and until you’ve lost control at the wrong time you’ll just have to take my word on it.

BTW I’ve never known a reputable builder or designer that would even touch a 45į hard over stop. On most power boats of the type we are dealing with are set up with 35į stops of 70į sweep. I’ve never heard that such a hard angle accomplishes anything more that stressing the rudder and it’s foundations.
However if you’re getting results and low speed then who knows but you still have live with 45į stops at any speed your dealing with.
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Old 07-29-2022, 04:29 PM   #14
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I think that a much more effective modification of a rudder would be to modify it to have a foil shape. It is commonly used on sailboats, in fact, I made one for my little sailboat. One of the issues is that when tacking with a flat plate rudder hard over the rudder work as a brake. The turbulence on the low pressure side of the rudder can reduce the speed so that tacking is difficult as the boat stalls out. The foil shape allows the water to slip around even when the rudder is at +45 degrees. A foil shaped rudder can also have a hydrodynamic advantage when going straight.

A common rudder shape for displacement speeds is a NACA 0012 foil. I wrote a blog about how I modified my sailboat rudder using Bondo for those who are interested. It could be done on a trawler without removing the rudder, although it would be three days in the yard and $300 in materials. For my little sailboat, it made a huge difference. Tacking improved because the boat then slipped around at slow speed and whipped around at higher speeds. Weather helm basically went away, which is saying a lot with a cat boat.

Whether it would be worth the effort on my trawler??? I have plenty of more important projects. However, the boat in the picture also shows a stern thruster, which means to me that the captain likely has control issues at the dock. In that case, a NACA 0012 rudder might be the simple fix. Probably heresy to somebody who has a $15,000 gizmo hanging under their swim step.
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Old 07-29-2022, 06:39 PM   #15
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Interesting info on a Schilling rudder replacement and comparison between stock rudder and Schilling on the same boat:
Fishtail Rudders Great harbour - Great Harbour Trawlers
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Old 07-29-2022, 06:54 PM   #16
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Marco and Stout have taken my earlier observations to the next level and are providing this forum with excellent information. Rudders can look simple but hydrodynamics donít lie. It behooves those with an interest to listen up and follow this advice

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Old 07-29-2022, 07:17 PM   #17
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Quote:
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I donít think that the 2 pieces are 90 degree angle iron, probably closer to 45 degrees.
Youíre right.
Steeper than Iíve ever seen though.
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Old 07-29-2022, 07:46 PM   #18
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Dave Gerr's book on mechanical systems has a great section on rudders, their design and the mechanics involved.
+- 35D is used as the max deflection mostly due to the loss of mechanical advantage as the geometry involving the steering arm angle changes. Other than that there is no magic to 35D
Whoever set up the OP's boat was really concerned about maneuverability. The fence on the trailing edge of the rudder and a stern thruster. I can't imagine that fence is adding much drag at low speed, though it is pretty clunky. Unless the boat has a real handling problem I'd be inclined to remove the fence and just use the thruster when needed. No reason to be anymore draggy than necessary
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Old 07-29-2022, 11:44 PM   #19
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Here is the fishtail rudder on Libra, a steel ship built in the Netherlands. I have no idea about drag but it sure makes close quarters pleasant. No stern thruster necessary.
(Someone really needs to address this forum software regarding photos. This is ridiculous already.......)
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Old 07-30-2022, 08:11 AM   #20
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Stella has large SS rudders with tapered fishtails. Cruise speeds are 6-8 knots, 3 turns lock to lock. The helm is responsive and autopilot control is smooth. With twin props, heavy displacement, and relatively low windage maneuvering in tight quarters is effective without thrusters and she easily pivots within her own length. Steering at very low speeds is 90% by shifting props at idle engine speed.
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