Rudder Modifications

Greetings,
Welcome aboard.

Learn to goose the throttle.

Therapy said:

I am new to owning a trawler and to this forum, I have a 32 transpac eagle, my boat does not turn very sharp mainly around the docks, the previous installed a stern thruster that works great when the wind isn't blowing. I recently pulled the boat to have some work done, and I am contemplating adding material to the rudder, to make it longer and increase the angle, this seems like an inexpensive approach and should not add much drag. Have any of you tried this? from what I have read trawlers have an unbalanced rudder with 20% ahead of the pivot point and 80% behind it, in my mind if I can maintain something close to this I should be fine. Can you offer any advice.

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It's not an unbalanced rudder if it has 80/20 split over the rudder post.

An unbalanced rudder would have 100% behind the rudder post.

What Bill said.

There have been a few in here that have modified their rudders with satisfied results...might try a google search for the threads.


Many different methods for adding metal to the rudder.. just depends on what you are comfy with.


Adding angle might help...that does have it's dangers if you don't understand the forces involved.

Same boat here. I have owned single screw boats since the 80s and find this boat needs a little more prop wash than others I have owned. For the first time single screw operator there is a bit of a learning curve. No plans to alter the rudder here. If you add to the rudder please let know how you like it. Cheers

Therapy,
How many degrees of rudder deflection do you have?

I modified my Willard to have 45 degrees each way. If you can call this modifing. There are two mounting holes in the rudder horn and I hooked the steering hyd cyl rod to the inbd hole ... the one closest to the rudder shaft.

I have no need for better rudder response now (and for the last 10years) but I know there's more to be had w articulated rudder trailing edge devices but it would need to be almost free for me to opt for more.

The Eagle and Willard are similar so that should give you what you want if your rudder is big enough. And I'm sure your boat isn't fast enough for the 45 degree rudder to be too much deflection. That would indeed be a concern w a faster boat but good to go as they say w a 6-7 knot boat.

Goosing the throttle is putting it mildly. You need to use the throttle like your mad at it.

Turn the wheel full left/right, hammer the throttle in fwd gear, quickly bring it back to idle ( that's goose 1). Shift to reverse, and hammer the throttle again to stop any fwd motion. Back to idle and neutral (goose 2).

Gooses come pairs and you have to be deliberate in both directions. Practice in open water with a bouy. Especially with wind.

I believe poster READY2GO added material to the rudder on his Marine Trader and is pleased with the results. He has a blog on it.

The trouble with some single engine boats (notably Taiwanese Tubs) is the rudder is designed for twins but the same design was used on singles.

I made three changes to Panope's rudder. 1 - Gap between keel and rudder closed. 2 - Gap between hull and top of rudder closed. 3 - The triangular shape added ahead of the rudder post provided an increase in size to the rudder and provided a bit of "balance".

The performance of the rudder was noticeably improved during close quarter maneuvering and "gooseing" (primary goal was to improve rudder power while sailing, which it did). Helm force was also reduced.

I wish I could have done these modifications "one at a time" so a determination could be made about which mod was responsible for the improved performance. It is reasonable to assume that the gap closing between the keel and rudder is not contributing to close quarter maneuvering as this modification is nowhere near the prop wash.

Steve

Steve,
I see your prop has a lot of rake. Can't remember what rake is good for or bad for. My present propeller has no rake. I think most props come w a little.

Here is a picture of a modified rudder that the builder of the Helmsman 38 tried. It worked well with a boat not exceeding hull speed but caused a vibration (as I recall) when getting on a plane. Notice the end plates and the "V" on the trailing edge. The previous rudder was just a flat piece of metal.

Shortly after I took delivery of the Helmsman 38, I replaced this rudder with an "Articulating Rudder" made by Bayview Engineering - Bayview Engineering Articulating Rudders Boats CNC Machine Shop Oak Harbor Washington.

Now that rudder made a BIG difference in moving the stern and was almost as good as a stern thruster.

However, my current Nordic 42 has stern thruster and I like it much better that the articulating rudder. My thoughts.

Eric, I'm not sure about the purpose of propeller rake. My propeller Diameter and Pitch was determined by a Naval Architect friend of mine. He gave the numbers to Osborne Propellers (Vancouver BC) and this is what they provided.

I must say, the propeller was spot on right out of the box. I can just make max engine RPM in calm conditions. I pulls like a tractor.

Steve

The Transpacific Eagle 32 was designed by well known NW designer Ken Hankenson for Glen L boats to be made in steel called the Union Jack. The plans for the Union Jack are still sold by Glen L. Transpacific Marine, a well know sailboat maker, asked him to design the Union Jack to be made with fiberglass. This hull has a slightly larger beam than many other 28 foot water line boats and therefore needs a little more throttle to swing the stern.

Several Monk 36 owners have modified their rudders similar to post 13. A 2" wide horizontal strip top and bottom, and vertical 2" angle iron on the trailing edge. A couple have added a strip welded to the trailing edge first to increase the rudder area. those I have spoken to report increased maneuverability docking and better tracking in following seas.

We did it on out first boat and it did help... a little. Mostly just in fairways, but other than that... Not a ton of difference. I think it just took me some time to get used to how she handled and work with what she gave me.

HOWEVER, in order to maintain balance of forces on the shaft, you should figure out the ratio of your current rudder fore and aft of the post and add material in the same ratio.

I don't know how long you have had it, but if it hasn't been very long, don't try to solve a problem that may not exist. It would be a waste of money IMHO.

I think I am going add 4" to the back of the rudder I will let you know if there is any improvement in close quarter handling.

Thank you all for your responses, Eric I have about 38 degrees and to get any more I would need a bigger steering ram, I have the boat up at Seaview in Bellingham getting a new drive shaft, So while its out of the water I want to get as much work done as possible, instead of changing the steering ram and adding a bigger hydraulic reservoir, I think I am going to add material to both sides of the Rudder, that should give me a few more degrees, and might even help in reverse. Thank you All
Steve

Therapy said:

I think I am going add 4" to the back of the rudder I will let you know if there is any improvement in close quarter handling.

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If it were me, add 1" (if that is the correct ratio) to the forward part of the rudder too.

Absolutely, I will add as much as I can to the front of the rudder to keep it balanced.
Thanks

I replaced the rudder in my charter boat (Bruno & Stillman) which was very inadequate. Consulted with several authorities (self proclaimed) and came up with the ratio of 25 to 30% of what is behind added in front for a rectangular shaped rudder. Mine is 28% and works effortlessly with mechanical steering (not hydraulic).

One of the points that was made to me about the leading portion was when hard over, the greater the length of the leading edge, the higher the percentage of water coming off the prop hits the rudder. Theoretically, if there is no leading edge, only half the water from the prop is hitting the rudder.

When adding more to the leading edge, remember to consider prop clearance for pulling the prop. Otherwise you may have to disconnect the linkage to turn the rudder enough to pull the prop.



Ted

Before you go about redesigning and replacing the rudder, satisfy yourself that the problem isn't something like insufficient hydraulic fluid and/or hydraulic ram problems.

We had a similar problem with a vessel we chartered in 2012. I thought the rudder was too small or some such thing but in hindsight I wondered if it was a problem with the hydraulic system as it's response was too slow. I guess I'll never know.

Jim
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I wonder how many people who have modified their rudders have any real before and after data with a good before baseline to prove the modification was of any real benefit.

Ever see one of these?
The US Navy thinks highly of them, this one is under a 50' Utility boat.
It is a reverse thrust rudder, it has a linkage to the main rudder and turns with it. Although it looks small, it is effective, as the cylinder has much more surface area than is apparent.
While you still have to "back and fill", the reverse burst is much more effective than without the device.

Capt.Bill11 said:

I wonder how many people who have modified their rudders have any real before and after data with a good before baseline to prove the modification was of any real benefit.

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Not sure what data you're looking for.

In my case, the rudder had almost no leading edge and was about 2/3 of the square inches of surface area of the new one. Without the leading edge it was difficult to turn as speed exceeded 6 knots. Backing was horrible (new rudder can't quite overcome all the prop walk, but pretty good). Do to the small surface area and no leading edge, you had to throw a lot of water at the rudder to kick the stern over. New rudder can back and fill with almost no throttle (bigger diameter prop also). The only trade off with the new rudder is that at 15+ knots, do to surface area, the rudder is a tad to sensitive ( takes very little movement to change course). This isn't a problem for the autopilot; I just need to be more precise.

Ted

To the OP. Just read Gerr's book.

Capt.Bill11 said:

I wonder how many people who have modified their rudders have any real before and after data with a good before baseline to prove the modification was of any real benefit.

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I have good data. However, it is described in sailing terms so not really applicable here.

Steve

If you look back through my post you can see what I did. I can make a near zero radius turn if I want with my single screw boat. Just google funangler rudder and that will lead to most of the post. There is also a video of the boat in action on YouTube.

Can't tell from the picture but rudders in front of the props are flanking rudders...very common of tug/utility craft.


Can be set up many different ways to spring into action...not always a direct connection.