Sailboat rudder design

[Ericson38]

Originally Posted by Doug Brown

Our rudder is a partially hung spade rudder on a skeg.

The problems with it were the lower rudder bearing, which fit into a shoe on the skeg. From the factory they were poorly attached and the shoe would fall off causing the rudder to break.

Other problems were the upper rudder stock was solid 1-3/4" stainless, while the lower rudder stock was 1-3/4" & 2" stainless tubing. This was done to save weight.

The fiberglass rudder blade was made in 2 parts and basically "glued" to the rudder shaft tabs, and the blade would come "unglued".

These were generic problems made when the boat was originally designed.

Plus with the rudder stock within the blade design you can't inspect the stock or tabs or the fiberglass joint to see how everything is survival over the years.

Since we are going to be going to very out of the way locations, we had a new solid stainless steel rudder made - much like on fishing boats and power boats. It is made out of 1/4" plate SS - no foil section. It does have re-inforcing ribs that foil sections could be added to at a later date, but we have found that it works fine as is.

The SS rudder shape has the same exterior outline as the fiberglass one.

We extended the solid 1-3/4" rudder stock to the full length of the rudder blade and changed the design of the lower rudder bearing into a bolt on 2-piece bearing. Since the overall rudder assembly is extremely long, we installed a shaft coupling right above the rudder arm so the rudder can be removed in 2-pieces - the blade from below and the upper shaft from above.

Since we have a SSB, I was able to use the rudder plate as out ground plate and the SSB performance has greatly improved. Since the rudder is 2-piece, we were able to weld a emergency tiller fitting directly onto the upper rudder bearing and rudder shaft.

The new rudder steers very easy and controls the boat better than the old fiberglass one. Plus it is extremely easy to work on/remove/maintain the new rudder.

Since everything on the new rudder is solid 316 SS, it wasn't cheap, but compared to other rudders was not to outrageous - and it will never break. Design, material and fabrication came to about $10,000.

Surely gets the job done. How do you antifoul it ? How much does it weigh ? You are saying it controls better than the foiled shape one, even though it has the same area and planform shape? I would not have thought that would be the outcome, unless the other one had the post turning inside the armature (broken loose internally).

[Lokiyawl]

The hybrid rudder design on the Taswell makes a lot of sense to me from a hydrodynamic, balance and appears to be a structural improvement over a free standing spade. I would worry some about the rudder being disabled in the event that something got jammed in between the bottom of the skeg and the balance portion of the rudder, has this ever happened on your boat? I have seen some attempts using a faired pc. that covers the opening when the rudder is straight which I assume would help.

Interesting that you mentioned the Hylas 49 rudder since my current interest is the Stevens 47 (same underbody as I understand) I have been asking a lot of people about the handling of these boats. To date, no one has made any complaints about the boat having a heavy helm despite the lack of any balance in the rudder which I suspect may be more due to the balance of the hull than rudder design but that is only my guess. I like the fact that the entire rudder is supported by a robust skeg and the fact that the entire blade may benefit from from a delayed stall due to the interaction with the skeg. I say "may" because the lower portion of the skeg on this boat is quite narrow and I am unclear if there may be a minimum chord width for the skeg to ensure this benefit, does anyone know for sure? I would be very interested in input from anyone that has sailed one these boats on the rudder effectiveness during difficult conditions.

BTW, I recently found a book entitled "Marine Rudders and Control Systems" which seems to have a lot of good information on rudders of all types along with test data.

James

Originally Posted by Ericson38

"The balance of a spade also gives a light helm as long as the bearings don't bind at speed due to the rudder flexing. A hybrid rudder (semi balanced), half skeg/ half spade works well but is more complex overall."

Bill Dixon was doing this on the Taswell line. To counter this, the Tayana 52 (Perry) and Hylas 49 (Stephens) don't have any part of the rudder forward of the post, so the skeg goes down to the bottom of the rudder.

[Ericson38]

Perry's Norseman 447 skeg also tapers down at the tip-

45 norseman 447 384

I haven't had any problems with mine yet, but in the Chesepeak, I dont' want to be boasting about it.

My neighbor's Hylas (extended Stevens 47/Hylas 47) skeg does taper down quite a bit at the lower tip, so much so that I think that the skeg is bronze at the shoe at quite a way back up towards the joint where it meets the hull.

I have only read great things about the Stevens 47 sailing capabilities. My friend's Hylas is still on the hard this year.

[Don C L]

[QUOTE=Lokiyawl;1905716]The hybrid rudder design on the Taswell makes a lot of sense to me from a hydrodynamic, balance and appears to be a structural improvement over a free standing spade. I would worry some about the rudder being disabled in the event that something got jammed in between the bottom of the skeg and the balance portion of the rudder, has this ever happened on your boat? I have seen some attempts using a faired pc. that covers the opening when the rudder is straight which I assume would help.


Yes it is wise to have some kind of faring to prevent anything from jamming below the gudgeon on a balanced rudder. At least in my area kelp and crab pot lines will snag in there. Maybe I am in the minority but for cruising I just think if anything can go wrong, it will. There are very strong spade rudders, or unprotected skeg hung rudders, but once you see one bend or snap or snag a crab pot, or an anchor line, at least for me, I start to see rudders as "cruising" rudders and "racing" rudders.

[Ericson38]

[QUOTE=Don C L;1910210]

Originally Posted by Lokiyawl

The hybrid rudder design on the Taswell makes a lot of sense to me from a hydrodynamic, balance and appears to be a structural improvement over a free standing spade. I would worry some about the rudder being disabled in the event that something got jammed in between the bottom of the skeg and the balance portion of the rudder, has this ever happened on your boat? I have seen some attempts using a faired pc. that covers the opening when the rudder is straight which I assume would help.


Yes it is wise to have some kind of faring to prevent anything from jamming below the gudgeon on a balanced rudder. At least in my area kelp and crab pot lines will snag in there. Maybe I am in the minority but for cruising I just think if anything can go wrong, it will. There are very strong spade rudders, or unprotected skeg hung rudders, but once you see one bend or snap or snag a crab pot, or an anchor line, at least for me, I start to see rudders as "cruising" rudders and "racing" rudders.

The line will first pass under the keel, and then along the prop shaft, pass under the strut boss, and finally (land on) hit a line cutter (unless I'm not motoring )

[Jman]

Never thought of Doug's approach. But I have a few questions.
How do you keep it clean of growth?
All the additional drag has to have slowed you down - is that why you feel more in control?
Do you feel all the turbulence through the the wheel?
10k - that is an investment....




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[Doug Brown]

For Jman -

I coated all of the 316 stainless steel with 2 coats of Interluxe epoxy and then a tie coat of clorinated rubber before putting on 4 coats of bottom paint.

You can clean it with a piece of carpet. It has 3 circular zincs per side on it.

I think it has less drag than a shaped rudder since it is thin - basically only a 1/4" thick. The re-inforcing ribs are also only a 1/4" thick and are basically in the water flow stream so they don't add much drag.

The boat was designed as a fast cruiser and still does OK. We're happy with 120-nm a day, but she easily gets 130-135-nm on a reach without a lot of drama.

All of the shaking and shimming that the old rudder had is gone and the feedback is now excellent.

However, as guessed, it is heavier. Our original fiberglass/ss rudder weighed 145-lbs, this one weighs 180-lbs - which was actually pretty close to what I figured it would weigh (I thought 168 without the re-inforcing ribs and the rudder post not going all the way down to the bottom of the rudder blade).

316 stainless isn't cheap and you need some big machinery to make something of this size. Our original quote was in the $3 -4,000 range just for the rudder but we made a lot of changes and the price of 316 went $$$ UP during the construction period. We also had new bearing holders and bearings made - all of which added to the cost.

As I remember we had 4 plywood rudder blades cut for fitting on the boat to insure that everything fit, and although costly to do, when we cut the 316 using the same CNC pattern that we used to cut the plywood, everything fit perfectly.

Biggest plus (other than it works so much better than the old one) is that it is a tank and extremely easy to work on, inspect and remove. If I break it, I have a lot of other things probably going really wrong too!

And you sleep very well on long passages not worrying if the rudder is going to break. It's worth a lot to me and my wife to not have to worry about it breaking.

Everything is a comprise and we think that at the end of the day the pluses outweighed the minus.

[Jman]

Doug,

I am glad it is working for you! As for drag - ever seen an airplane or car with no fairing in recent years? Thin does not equal no drag. What about the huge vacuum behind the rudder post? Unless everyone else is wrong...

If you cover it with rubber and anti fouling - where does the grounding come from?

You started it - just wondering...


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[Lokiyawl]

You see lots of metal plate rudders on workboats and they obviously work. My take is that a thinner rudder will of course have less drag at a 0 AOA just as a hull with a more narrow beam will. Thin plates do however stall at a slightly lower AOA than thicker foils. From what I have learned so far, the optimum thickness ratio from the standpoint of operating at the largest deflection angle without a stall is about .15. The structure of most fiberglass rudders that I have worked on are all welded stainless and the weeping rust stains worry me. While I probably would not use a flat plate rudder on my own boat, I can see some big advantages in this solution with regards to being able to inspect all of the welds/metal structure to be sure that it is structurally safe.

James

Originally Posted by Jman

Doug,

I am glad it is working for you! As for drag - ever seen an airplane or car with no fairing in recent years? Thin does not equal no drag. What about the huge vacuum behind the rudder post? Unless everyone else is wrong...

If you cover it with rubber and anti fouling - where does the grounding come from?

You started it - just wondering...


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[Doug Brown]

OK, here is my thinking on drag.

I should note that I am fully aware that my "barn door / commercial fishing boat rudder" is not a hydrodynamic beauty. But the flip side is how many commercial fishing boat rudders have you ever seen broken, compared to how many yacht rudders have you seen broken?

My max speed, like when the boat falls off the edge of the earth, is 7-kts. If we are doing 5-kts, which is pretty much our average speed over 30,000-miles, how much drag/lost of speed can possibly be occurring? Maybe 0.1 or 0.2 kts? 0.5 kts?

My rudder has maximum movement of something like +/- 25-degs (it is a Whitlock Cobra steering system) and from what I have seen of the Autohelm 3000/steering wheel movement over all those miles is probably 95% of the time the rudder is moving less than 10-degs to keep the boat on course - probably more like 5-deg or less. So how much drag can be occurring at a 3 to 5-deg rudder angle 95% of the time? Not enough for me to care about.

I think the safety aspects of the construction far outweigh 0.1 or 0.2 kts. Besides, when we change from a fixed 3-blade prop to a feathering 3-blade prop we gained between .5 to 1.0 kts (depending on wind conditions), so I am still to the plus side.

As to using the rudder as our ground plate, I checked with a couple of local, knowledgeable certified SSB people and read the ICOM book on grounding plates and they all said - basically - that it was the "surface area" of the metal mass that was the important thing, and that the surface being painted or covered did not effect the performance. ICOM says that you can use your keel as a grounding surface too.

I think most people don't use the keel as connecting the antenna tuner to the keel would be a nightmare to do since you need a large surface area connector - ie something thin and flat - to make the connection. Usually 2 - 4 inch wide copper strips.

On mine I went to flexible woven copper grounding straps that are made for HAM radios set-ups. I used two that are 1-1/4" wide, so in effect each cable is 2-1/2" wide. Having 2 cables, I get the 5" (see previous picture of my tuner and rudder post). Another advantage with the cables is that they can be made with fitted ends so the attaching bolts fits and fastens well.

Anyways, right or wrong, that's my thinking. So far I am happy, it seems to be working well and I think the pluses outweigh the minuses. I am not interested in getting that last 0.001 knot out of the boat, am happy with 5-kts and a comfortable safe ride.

[thai ree]

Doug,

That's an awesome rudder design. it took me several hours of searching to actually find a stainless rudder online. I could have driven to newbern faster, im on the hard in holden beach, nc. I'm a welder/sailor in need of a new rudder for my 1980 morgan 382. I'm considering fabricating a 316ss rudder thats basically the same naca0012 foilshape as the original. my design difffers from yours slightly in that It would consist of 3 scantlings welded to the stock then welding bending sheeting on the slip roll to weld around the stock and scantlings. Im unsure of whether completely weld the rudder closed or allow water to flow thru via holes thru the top and bottom and scantlings. I don't want to end up with corrosion on the inside, which is basically why im need of a new in the first place. Are you still happy with your rudder after a couple years, did you ever end up modifying it to create a foil? Thanks for posting the pics.

[Doug Brown]

Hi - I had thought about enclosing the rudder, which is one of the reasons the re-enforcing ribs where put on. But after a lot of thought I decided to keep it open: 1. to be able to fully clean it 2. to be able to following inspect it 3. to be able to change the zincs on it 4. if enclosed, the other skin will deteriorate from the water flow over it. One of the self-steering units has a skinned rudder blade and they suffer from this corrosion problem

When I made this rudder, it is basically a 100% copy of the original rudder,except it is "flat". Since it was flat and heavier than the original rudder, I extended the front leading edge about 1/4" to give some extra power for turning the rudder when using the Autopilot 3000 unit.

When everything was done (rudder, new lower bearing, indexing the rudder shaft so it turned the same amount in each direction) it was just incredible how easily the rudder turned and how well the boat performed.

One giant mistake happened when it was being made in that they cut the rudder shaft in the wrong location and a propeller shaft joiner/coupler had to be installed so the needed extra length could be added. Other than the $500 I had to pay for the coupler, it actually worked out well as I can now remove the rudder blade without having to have the boat lifted up in the air, or digging a 3-ft deep hole under the rudder blade to remove it from the boat.

A couple of months after building the rudder and the haul out, we one day decided we didn't want to go sailing anymore (we had been doing it for 35-years) and sold the boat. The guy that bought her really loves her and keeps her in the same slip that we had her in. We live about 3-miles away from the marina so see him alot and have gone sailing on her a few more times.

I should have done the new rudder years ago - it made that much of a difference.

Since you are a welder, you'll be able to make a new rudder much cheaper. We used a 2nd hand power boat prop shaft for out rudder shaft - a big cost savings. We had the rudder blade cut from a single piece of 1/4" ss using a plywood pattern that we made. We then fit the plywood "blade" to the rudder stock to check all the dimensions and once we were happy with it used the same computer points for the water jet cutter to cut out the ss blade.

It was worth the hassle, not sure about the expense ($12,000), but it came out about as bullet proof as you can make a rudder.

Doug Brown