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Old 11-16-2012, 04:54 PM   #1
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Rudder designs

Has anyone tried different rudder designs on their vessel? If so, I would like to hear about them. Over the years I have run several designs on my Bruno-Stillman 35 (12K cruise) including flat plate (original), airfoil, wedge, split wedge (along shaftline), and contra split wedge before deciding on round nose airfoil w/ 20% balance and dam on bottom as the best compromise between minimum resistance, good low speed steering, & minimum "hunting" on the autopilot.
I am about to try and transfer what I have learned to my Willard 36 (6K cruise) which has a low aspect flat plate as std.

Any comments on your experiences would be interesting and appreciated.
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Old 11-16-2012, 10:15 PM   #2
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Sounds like you evolved into a really good rudder.

One of the advantages of going really slow is that not much tech is needed in rudder design. Just size and at 6 knots drag just isn't an issue.

I have a Willard 30' Nomad and have made one modification to my rudder that has worked really well. I increased my rudder deflection to 45 degrees each direction. A number of the guys on WBO talk about articulated rudders and other improvements. None needed. Just swing it 45 degrees each way and you'll be amazed. I accomplished this by changing the attach point on the rudder horn when I installed hydraulic steering.

Here I am w my rudder.

Eric
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Old 11-17-2012, 01:48 AM   #3
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I acquired a Masters 34, single engined semi displacement,with a flat steel plate no balance rudder, clearly a poor replacement on a well designed (Clem Masters) boat. A new rudder, using the plate as the base,was made in aerofoil shape, with a balance.
Turning performance improved immensely,showing the deficiency of the plate version.
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Old 11-17-2012, 02:54 AM   #4
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A lot of the boats on this forum seem to have small rudder designs, well mine anyway. Whether that is because a lot are twin engine configurations I don't know.

I look at yachts and full displacement boats turning at low speeds in full control of their boats, with the stern following the bow around, no fuss.

Then I look at the way we twin engine small rudder types, slide around a turn, usually not even using the helm, because we know at these speeds nothing with happen, it's all done with engines. In this situation the back of the boat pushes out and almost pivots a midship to effect the turn.It has always struck me that this is not good boat engineering.

I accept that obviously a full keel is crucial here, however a lot of our boats do have keels, some more than others, and as we usually don't exceed about 8 knots speed is not a major consideration as I understand it(which I probably don't), so are bigger rudders better?

Photo of the offending rudders.
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Old 11-17-2012, 06:00 AM   #5
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I can't imagine that the 36 willard needs much improvement in the steering department. If it does, you have covered all the usual fixes to be tried.
Your Bruno and Stillman was legendary among NE lobsterman for many years until greed took over and the building suffered-lawsuits ended the game. They only made a "bad" boat for two years.
Most trawler forum members will not be familiar with the B & S, except maybe Dave
Hawkins and maybe Art. I keep a weather eye out for a 42 Bruno at all times. I'm to cheap to pay anywhere close to what most people want for theirs!
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Old 11-17-2012, 10:08 AM   #6
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Eric, Thanks for response and suggestion. I will measure... I always assumed 35 degrees was a universally agreed upon figure. Funny, because "question everything" is my moto.

Bruce, Thanks. Fitting my rudder tight to the hull on top (3/8") & adding a dam (plate) on the bottom increased its power. So much so that I needed to change the sproket ratio on my AP.

Andy, Thanks. Yes rudders on twin screws do run smaller for sure. But then, less drag and the twins give added manoverability anyway. so good tradeoff. They would be more effective though if the top were up close to the hull. This would only work good on counter rotation props tho.

SF, Thanks. The Willard does handle well enough. I use it single handed.
It hs a FG covered, wood, flat plate rudder. A PO drilled through at the rudder stock (bronze) and put a bronze bar (3/8 x 3/4) down each side with 8 throughbolts. There is no thickness available to mortise these bars in. So I would like to fair them in fore & aft with filler getting a little airfoil shape in the process. The quirk is that the steering is harder to stbd. than port. I would expect the opposite as it is a LH prop... So I will make a trailing wedge that can be moved from side to side while in the water to try to balance
The Bruno is a fine boat indeed and their sad history & groundbreaking Supreme Court ruling is well known in NE. It is a Royal Lowell design. The 42, the original Bruno is a great boat indeen. Dick Bruno himself still has one and runs it to So. or Central America every year and as I understand it is a "missionary" for FG boatbuilding there. I do see a reasonably priced 35 once in a while but never a 42
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Old 11-17-2012, 11:27 AM   #7
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Lots of things become cast in stone for many reasons like what scope to anchor at and how much to deflect one's rudder. I often chart my own path and it's amazing how seldom I have trouble w going that route. Perhaps it's my Sagittarian luck but most all of my deviations are possible in degrees. I've got 2000hrs in ultralight aircraft and crashed very little. However I started on sand dunes and flew no higher than 4 or 5'. I flew unconventional ultralights and made unconventional modifications to them and have been known to fly unconventional as well. Skiers and dirt bikers that never fall down don't get broken bones but their skills never go beyond beginner either. Most of you know I'm very analytical and I don't do "crazy" things w/o a great deal of thought. Sure I flew hang gliders but there were a great deal of launching sites others would fly from that I never did.

As to the 35 degree rudder deflection (I thought it was 30) I think high speed planing boats should adhere to that but think about it ... what bad things can happen to you by turning your rudder more. Obviously it eventually becomes a better brake than a rudder. I reasoned my rudder would work at 45 degrees, adjusted it so and I have a boat that turns amazingly tight and has no downside that I know of after using a 45 degree rudder for 7 years. Life can be a little limited if you swallow all the rules of thumb and basic standards that come along.

My rudder is a bronze flat plate type that presumably came w the Willard and operated to 45 degrees I have no wants for more rudder performance.

Anybody have a picture of the elusive Bruno?

Please read the thread Profiles.

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Old 11-17-2012, 02:03 PM   #8
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Anybody have a picture of the elusive Bruno

Eric
Here's a 42 Bruno & Stillman for sale. Only one pic though.

And here's a 35.
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Old 11-17-2012, 03:30 PM   #9
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Brooksie,

Can you post some pics of the different rudder mods you have tried?

thanks
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Old 11-17-2012, 06:14 PM   #10
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bshanafelt, I may have some sketches of various things I have tried and maybe a pic of the final configuration and I'll look. But I'm in FL now and the Bruno is in MA. All of the modifications were made on the first rudder (airfoil) I made using polyester (Tigerhair) filler to add to and reshape as I went along. So once I had the new shaft and solid FG matrix I just added or ground off as needed. Goggle "contra rudder" & "contraguide rudder" they were used on some Liberty Ships and were claimed to increase efficiency by straightening the propeller vortex... I did not find this to be true for me but the again, except for GPS speed/RPM graphs I really didn't make the necessary tests. The split rudder which went with, rather than against the prop vortex I would think would offer less resistance. But that didn't prove out either (by my feeble observations)
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Old 11-17-2012, 07:17 PM   #11
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Twin rudders on a twin engine boat may look small individually but probably have as much or more surface area combined as the same boat with single prop and rudder.
A pivot point midships or a little forward is usual, that`s why you watch the stern leaving docks, maneuvering, etc
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Old 11-17-2012, 10:27 PM   #12
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I was working on a project that had a single screw and two rudders - I found it interesting that the rudders turned at different rates. The designer (Vripack’s Dick Boon) swore it was the best thing for this boat.
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Old 11-18-2012, 06:39 AM   #13
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"I found it interesting that the rudders turned at different rates."

Same as the front wheels on a car or truck.
Ackermann steering geometry - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Ackermann_steering_geometry
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Old 11-18-2012, 01:46 PM   #14
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Never saw the need to modify the Coot's rudder. It's a fairly big rectangle, is attached at two points to the hull (similar to Eric's Willard), and has a range of 40 degrees to either side of center. Works fine for the 7-knot, single-propeller boat.
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Old 11-18-2012, 03:33 PM   #15
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I look at yachts and full displacement boats turning at low speeds in full control of their boats, with the stern following the bow around, no fuss.

Then I look at the way we twin engine small rudder types, slide around a turn, usually not even using the helm, because we know at these speeds nothing with happen, it's all done with engines.
We chartered a single-engine GB36 before we bought the boat we have now, a twin-engine GB36. As far as I'm concerned there is no difference in steering between the two. While we use differential thrust when maneuvering two and from a dock or in and out of a slip I never use it at any other time even when idling through a marina or harbor. I use the rudders only and their response, at least in a GB, is excellent, single or twin.

Rudders move the stern not the bow, although most boats will pivot somewhat forward of the stern when rudder is applied. But you're really driving the stern around. So I never get the sense-- single or twin--- of the stern following the bow around as with a car. Instead the stern swings out thus aiming the boat in a new direction. GBs have fairly deep keels for this type of boat so there is never any sense of the boat sliding sideways to the degree that we get in our Arima fishing boat which has no keel at all and a fairly shallow-vee afterbody.

Now it may be that some twin-engine boats have overly small rudders. This can be the case with planing boats because rudders add drag and drag is what you don't want in a planing boat. The three rudders on an 80' Elco PT boat of WWII, for example, were sized to maneuver the boat at speed---- 30-40 mph. As a result, at slow speeds or idle speed the rudders might as well not have been there are all. They were virtually useless.

But I am impressed at how well our boat steers even at idle speeds. Its twin bronze spade rudders are fairly large. They are streamlined in cross section but that is just to reduce drag. They don't have any sort of airfoil shape to them. They have a slight degree of toe-in to them but that's just to eliminate any chattering or vibration in the steering gear which would be present if they were perfectly parallel.

First shot are our rudders. Second shot is the rudder on the Alaska limit seiner Spicy Lady. Nothing very sophisticated about it but I suspect it gets the job done real well.
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Old 11-18-2012, 04:12 PM   #16
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Mark says "Never saw the need to modify the Coot's rudder."

Big rudder ... big deflection ... works good at displacement speeds.
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Old 11-20-2012, 07:11 AM   #17
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"Rudders move the stern not the bow,"

The bow gets a differential pressure on either side , which causes the boat to turn.
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Old 11-20-2012, 08:05 AM   #18
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I posted about improved rudder designs a while ago. What came up was the thistle rudder design. Interesting design, google it and there is a wealth of information. What caught my attention is improved resonse for the auto pilot. it also provides better slow speed manuvering but with twin screws i don't have a problem there. If it could keep my auto pilot from chasing the stern of my boat on those difficult courses, it would be worth the work to install
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Old 11-20-2012, 08:34 AM   #19
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Has anyone tried different rudder designs on their vessel? .
Not me. I turn the wheel, the boat turns. I turn the wheel the other way, the boat turns the other way. I figure the people who designed my boat knew what they were doing. They built over one hundred of the same model before they built mine. If any changes were needed, they would have made them by the time they built my boat.
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Old 11-20-2012, 08:58 AM   #20
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Maybe practice with existing equipment would also be an option?......
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