Rudder Appendage

[lwarden]

Thank you Grumpyfng, Cosmopete and OCEANA for your report of the Eagle 40. We aren't quite ready to pull the trigger on a boat/life change and swap coasts for the Great Loop but this boat will be on our radar when we do. It seems to check a lot of the boxes for a couple doing coastal cruising.

For those interested in the Eagle, here is an article from Passagemaker from a few years ago:

https://www.passagemaker.com/cruise...eat-under-the-radar-option-for-trawler-owners

 

[steelydon]

Imagine my surprise when I saw that my eagle 40 was the subject of a topic. I appreciate the comments that have been made regarding the appendage and would like to make a few comments of my own. When I first bought the eagle the marina that I kept it in had very narrow fairways. About 50 feet. Entry was gained by coming through the channel then taking a 90° turn followed up within 100 feet another 90° turn in the opposite direction and then another 90° turn to line up with the slip. The original turning radius on the eagle required that I either use thrusters are back and fill. The appendage was added to reduce the turning radius which it did by about 50%. No more thrusters and no more backing. Concern was expressed about the pressure that the fins put on the rudder stock. The Eagles rudder stock is 2 inches and quite robust and it’s construction., very well mounted. there is no vibration underway and speed was affected by about 1/4 of a knot. I attribute this to the displacement of around 32,000 pounds wet and the slow speed that the eagle travels. The fins are about 40° and made of quarter inch stainless steel at a cost of about $60. The most expensive part of the install was drilling holes through the half inch rudder. Say what you will about Chinese stainless steel but I went through several expensive bits and a drill before turning the job over to the yard.

When the rudder is positioned for a turn the angle causes the propeller thrust to shoot out from the side, Almost thruster like. The surface area for both fins is approximately 240 in.² and does not interfere with backing. I would have done this the first time I had the boat on the hard but it took about three years before I decided to make the modification.

By the way the boat is listed on boat trader and and I would appreciate if one of you guys would buy her. Thanks again for the comments

Steelydon

 

[Steve1.0]

Out of sheer curiosity, has anyone ever heard of, or tried adding a third rudder, between the two existing on a twin screw trawler? Seems like it might help in a quartering sea.
My GB 46 wanders quite a bit, with her "frizbee" sized rudders. Keeps the auto pilot quite busy.

 

[steelydon]

Steve, I am certainly far from a naval architect. However, I think it would be easier to reach the size of your existing runners by adding flat stainless to them.

 

[steelydon]

Meant to say increase besides of your rudders.

 

[Steve1.0]

Steely, thanks for the reply!
Not so sure it would be less work. Dropping and modifying two rudders, while increasing the load on the mounting flanges at the same time.
Other than the cost of the associated new hardware, installation would be pretty straight forward. I'm good at drilling holes in my boat.

As any GB driver knows, the rudders have the same radius on both edges and the cross section of two "frizzbees" glued together.

A "proper" balanced, foil with a modest chord so as not to interfere too much when spinning about in a marina.

Hmm...

Seems more and more appealing as I type this.
Any naval architects out there?

 

[HeadedToTexas]

Very nice, Steely Don. Your maneuvering improvement is impressive.

My GB 46 wanders quite a bit, with her "frizbee" sized rudders. Keeps the auto pilot quite busy.

The rudder on our Mariner 37 is rather large (compared to a Frisbee anyway), but we still wander quite a bit and keep the autopilot busy, especially in a head or tail wind.

The "usual" advice for improving rudder response on this boat (or the Helmsman 38) is to add 4" to the front of the rudder. Anyone have thoughts or data on how that would compare to adding Schillings tails?

 

[HeadedToTexas]

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

Well that is certainly compelling data. Excellent article.

 

[garbler]

Your rudder appears to be close to balanced as is maybe a bit shy forward. Frequently I’ve seen skeg hung rudders with between 15-20% of the chord (width ) forward of the stock but honestly you need somebody a lot smarter than me to run the numbers so the area of the rudder blade is correct for your hull’s underwater lateral surface area. This is how rudders are sized. I do know though that too much blade surface fore of the stock can result in very light squirrelly steerage. Lots of factors to consider from lift, stall, cavitation and force. I will say it’s nice to see your rudder stock has a bolted palm. This feature makes unshipping a rudder so much easier though it costs more, very shippy.

Good luck
Rick

 

[Nomad Willy]

H to T,
Sounds like yo are trying to solve a problem w the solution of another.

Wandering is a stability problem and adding to the LE of a rudder contributes to instability.

Seems to me looking for an electrical/mechanical problem such as loose mechanics or not well matched electrical elements in your system would be a better place to look. Or even air in a hydraulic hose.

Or your rudder response helm to rudder deflection (think degrees). Your boat will wander if the wave action comes faster than you or your AP can make corrections for.

Looking at the rudder may be a waste of time.

 

[HeadedToTexas]

Could easily be, Eric. Much like my heading, I am wandering through the learning curve on this rudder subject!

Air in hydraulic lines could be as I do not recall this wandering behavior from my autopilot in years past. The autopilot does a far better job at holding a tight course in a beam wind than in a head or tail wind.

I also lost one of my two AP16 head units last year to corrosion on the video board. That should not be an issue though as the program is stored on the AC20 computer. Still, it's a change from last year.