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Old 08-05-2016, 13:04   #1
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Looking For Thoughts On Building A Balanced Rudder

My previous 30ft sailboat had a spade rudder - it was amazing for maneuvering in a tight spot such as the marina. I recently bought a new to me 34 ft boat with a skeg rudder that is not balanced (see attached image). I was a little shocked the first time I was maneuvering in a marina on how unresponsive it was when backing up.


It occurred to me that I could possibly someday redesign the rudder to be a little more balanced. The little information that I could find suggested that the forward area should be 18%.

I know that this is a big project and should probably be redesigned straight from the rudder stock and that the connection points should be beefed up.



But I am hoping that those with more knowledge than I could chime in on the pros and cons.

The boat is built in 1980 from a Ted Brewer design - Aloha 34.


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Old 08-05-2016, 18:40   #2
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Re: Looking For Thoughts On Building A Balanced Rudder

It makes sence these days, to reduce power consumption to autopilot by having a semi balancing/balancing the rudder.
But on a skeg hung rudder such as yours how will you get more area in front of the rudder stock. If you do put area under the skeg and get your 18% in front of rudder axis, it would become a collector of all sorts of crap in the water, (weeds, ropes etc), and more prone to damage.
I suppose you could shorten your skeg and put some area of your rudder under the skeg, without protruding in front of the leading edge of skeg. But you would have to restore strength to the bottom pintle.
If you take off a bit of area on the leach of the rudder, it may help your reverse manoevering but with some loss of forward control.
Spade rudders are made with more massive Rudderstocks, I do not recommend you remove the skeg.
So many headaches, in my opinion skeg hung is stronger, but less manoeverable.
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Old 08-05-2016, 18:51   #3
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Re: Looking For Thoughts On Building A Balanced Rudder

Little bit of rudder theory, the centre of effort is roughly 25% from the leading edge of the rudder, so the lever is the distance from centre of rudder stock to C of E. when the C of e is at the rudder stock it is called balanced.
However when the vessel is reversed the c of e is now towards the back edge of rudder, the lever is now comparitively massive, and the likely time the wheel/tiller will be pulled out of your hands.
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Old 08-05-2016, 20:05   #4
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Re: Looking For Thoughts On Building A Balanced Rudder

Of what material is the boat (especially the skeg) built? Makes a difference in how easy it would be to make the mods.

We have a pal in Tasmania with an Adams 13 that he built. Saw him one day with the boat on the slip... skill saw in hand! He proceeded to saw about half of the skeg off. He then basically added that skeg material to the leading edge of the rudder, creating a partially skegged, partially balanced rudder. He said that it improved steering going in both forward and reverse directions. The material in this case was timber with glass over ( I forget if it was strip planked or cold molded, but some form of modern timber construction). He added a new gudgeon and pintle just above the balance area, but made no changes to the rudder post.

Obviously, he had the advantage of having built the boat himself, with all the knowledge of how things were done that this includes. However, it also shows that the general principle is sound. In your place, I'd be doing a lot of investigation into your own construction before sawing anything off!

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Old 09-05-2016, 08:56   #5
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Re: Looking For Thoughts On Building A Balanced Rudder

Try this when reversing :
Use a 1-2second burst of full power & then neutral.
Repeat this until boat is "coasting" fast enough for rudder to bite water & steer.
Never leave gear in reverse while backing. Leave in neutral.This avoids prop walk & ,in your case,excess water pressure on rudder.
A sailboat will coast a long way.

Cheers/ Len
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Old 09-05-2016, 09:11   #6
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Re: Looking For Thoughts On Building A Balanced Rudder

While a balanced rudder may do nothing for reverse steering, I have built several with the 18% area forward fans found them twitchy. Difficult to steer straight. Finally settled on 10% area forward. Be careful. Structural issues here
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Old 09-05-2016, 09:16   #7
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Re: Looking For Thoughts On Building A Balanced Rudder

hello all, thank you for your suggestions.

I wrote to the designer, Ted Brewer, he responded and said that it is feasible and may help with reversing. He also added that he has a set of drawings for the boat available for purchase - this I am excited about. if I decide to go forward with this I would certainly like to get a designer to draw something up - preferably the original designer if he's available.

I am not sure if I will attempt the alterations, but I am curious as what would be needed to be done and whether I have the time and skills required.

I do believe I have a reasonable mechanical aptitude and have an eye for the details but I have not attempted to create anything structural with fiberGlass as of yet.
I would assume that I would need to weld internal framework to the existing rudder stock on the leading edge and Glass that in . Mr Brewer mentioned that it may be prudent to put a guard out in front for weeds etc.

With respect to boat handing strategy - I do usually give a reasonable burst in reverse and allow the boat to glide back and allow the inertia of the boat to swing the bow to nearly the intended direction before engaging forward. But it's different with all boats I am sure and it's a product of the wind , current ,inertia and other factors that contribute to the final vector.

Brad
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Old 09-05-2016, 09:24   #8
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Re: Looking For Thoughts On Building A Balanced Rudder

Brad, I carved away a bit of keel (to make room for a bigger propeller) and replaced some of the area with more rudder, forward of the post. This 'balance' addition is less than the 18% that you mentioned. The difference in rudder 'feel' and performance was quite noticeable when the boat is moving forward but reverse performance was unchanged. Also, I closed the gaps along the top of the rudder and along the leading edge of the rudder (where it still has some keel nearby).

I am very pleased with these results and they were easy to perform on this metal structure. However, whenever someone breaks out the sawzall and starts experimenting/modifying their boat, they must be fully prepared to accept total failure.

Steve

On Edit: I see you are in touch with the designer. That should alleviate much of the failure aspect.

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Old 09-05-2016, 10:18   #9
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Re: Looking For Thoughts On Building A Balanced Rudder

Bradpb, before you do surgery on your boat you may want to try learning to adapt to your skeg rudder.

My boat with a moderate fin keel and skeg hung rudder steers well moving forward but not so in reverse. Nevertheless, I can maneuver in reverse with good results.

The water flowing past the rudder is what gives steering control. In forward the water from the prop which is just in front of the skeg flowing over the rudder provides the moving force for steering even when the boat has little or no way on. In reverse the prop causes little flow over the rudder. There is little flow over the rudder until there is considerable way on. That leaves no steering control in reverse at very low speed.

I've learned that I can control my boat only in forward. But I can still steer backing. To back up I use reverse with the helm centered to begin momentum. When I need to change the direction of my movement aft I shift into forward, turn the helm hard over, give the throttle a short bust which kicks the stern over before creating forward momentum. Then I center the helm and go into reverse again to continue moving back. I repeat as needed. It becomes natural with a little practice. It is much easier and less expensive than major surgery on your boat.


S/V B'Shert
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Old 09-05-2016, 10:45   #10
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Re: Looking For Thoughts On Building A Balanced Rudder

Ted is a very competent designer. Messing with what he has done is not advisable unless you have commensurate knowledge of naval architecture!

As someone else said, the 18% Area forward of the stock is likely to give you grief, and you might like to reevaluate your reaction that the boat is "unresponsive" since you are basing it on prior experience with a spade-ruddered 30-footer having something like 2/3 the displacement of the Aloha. TrentePieds is spade-ruddered and 30 feet - 25 LWL - and she is downright squirrelly.

Being squirrelly is an intrinsic consequence of the "fin keel and spade rudder" that became fashionable forty years ago because some people thot they could have it all in a "cruiser/racer". Bei mir, that is bilge water. In a cruiser you want the ability to track without being squirrelly. The behaviour of the boat when making stern-way is of lesser consequence, and something you adjust to. If you helm different boats on a frequent basis you have to be sufficiently adaptable to accommodate to the particular boats' behaviour, and it isn't difficult.

In brief - very brief - you anticipate the "propeller walk" by positioning the boat as the forward way comes off her and she goes dead in the water so she will be on her intended course by the time she has sufficient stern-way to steer by the rudder. The first boat length, or so, of stern-way the propeller walk will dominate. Then as way comes on her and you ease the throttle the rudder becomes dominant.

Just another trick to learn :-)

There are also serious structural considerations involved in what you propose. You shouldn't do it without taking the matter up with Ted. Ted has retired, but he lives just four blocks from me. If you insist on doing this thing, I could, if he gives me prior permission, put you two in touch.

TrentePieds
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Old 09-05-2016, 10:47   #11
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Re: Looking For Thoughts On Building A Balanced Rudder

"Balance" depends on where you define it. For the pintles it means equal weight and effort distribution. For the water flow, its the maximum area for leveraging the water flow with the boat's movement. For some folks it means a rather neutral helm(hopefully with a little bit of weather helm. All these are in conflict with each other to a degree. Healing of course complicates the issue. Designing a rudder to help backing up will likely produce a lousy rudder for going forward.

Usually you can learn to use quick and fast thrusts to get the butt end to go reasonably where you want it to go. In fact, if you have your rudder hard over to port and give full forward throttle burst, the stern(rear of boat) will slide to starboard. Using this idea you can crab your way to the dock. These are one or two second actions to move the hull, not to go anywhere.
Let someone like a fisherman show you how its done in fishing boats like a lobster boat. Same principle. Easy to learn, but takes practise.
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Old 09-05-2016, 11:22   #12
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Re: Looking For Thoughts On Building A Balanced Rudder

TrentePieds, thank you for the information. As I said before I'm not convinced that I want to do this - i do appreciate the information and knowledge from all that have answered my post.

I did write to Mr. Brewer earlier and he said that he is no longer in the design business, but he is willing to indicate on the drawings that I am ordering from him where a possible cut line would be.

thanks
Brad
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Old 09-05-2016, 12:48   #13
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Re: Looking For Thoughts On Building A Balanced Rudder

I feel your pain Brad. At least you are going in with your eyes wide open.
I did a rudder mod on a spade as opposed skeg, for stalling. Refoil to a naca profile (110%). Cut out rudder tube for a an AP lever. Turned into quite a project, installing ruddershaft gland. Great results to windward but reversing suffered.
Now have to use deblen's method for reversing.
Don't care, rather have the windward performance and a light rudder.
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Old 09-05-2016, 12:49   #14
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Re: Looking For Thoughts On Building A Balanced Rudder

Here's what I did to get a balanced rudder. The boat turns like a fin keel racer, backs up with control and has a light helm.
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Old 09-05-2016, 13:00   #15
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Re: Looking For Thoughts On Building A Balanced Rudder

cottonsail, thanks for the pictures and Information. It's nice to see a completed project. It doesn't appear from the pictures that you have added very much area on the leading edge with such positive results. I love the idea of just adding a block of wood at the bottom.
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