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.

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

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.

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.

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!

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

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.

Eric

manyboats said:

Anybody have a picture of the elusive Bruno

Eric

Click to expand...

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

And here's a 35.

Brooksie,

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

thanks

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)

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

"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

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.

Andy G said:

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.

Click to expand...

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.

Mark says "Never saw the need to modify the Coot's rudder."

Big rudder ... big deflection ... works good at displacement speeds.

"Rudders move the stern not the bow,"

The bow gets a differential pressure on either side , which causes the boat to turn.

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

Brooksie said:

Has anyone tried different rudder designs on their vessel? .

Click to expand...

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.

Maybe practice with existing equipment would also be an option?......

Greetings,
I think Mr.rwidman has hit the nail on the head. The manufacturer installed running gear that met the needs of the vessel. Sure, higher performance rudders probably CAN be designed but I don't think anybody here has a high enough performance boat to really gain a major advantage with a rudder re-fit.
A picture of a 1982 Penn Yan (now defunct company) boat with factory rudder...

Penn Yan: This is what I meant in my original post "split on shaftline" each 1/2 aligns with the propeller stream decreasing resistance. The contra rudder is offset the opposite way straightening the stream and reclaiming lost energy. I never had the equipment to measure 3-6% gains available.
Experimenters may be interested in this:
http://legacy.sname.org/sections/greece/DSME Energy Saving Device for GreeceSNAME(4distribution).pdf

I agree but how do you determine the angles to use? Anything is better than nothing at all? And can you factor in prop walk?

FF said:

"Rudders move the stern not the bow,"

The bow gets a differential pressure on either side , which causes the boat to turn.

Click to expand...

No, the water pressure, from the prop thrust and the boat's movement through the water, applies a sideways force to the rudder. That force is transmitted to the boat at the stern. This moves the stern sideways thus aiming the boat in a new direction. If your theory was correct you couldn't pivot your boat with the rudder and thrust if it was standing still. But every boat on the planet can do this.

The resulting swing of the stern and pivoting of the boat when it's going forward may cause the water pressure on one side of the bow to increase a bit which may add something to the turning moment, but it's not why the boat turns. It turns because you "re-aim" the stern.

manyboats said:

I agree but how do you determine the angles to use? Anything is better than nothing at all? And can you factor in prop walk?

Click to expand...

I held a dowel w/ 2 pcs. paper taped to it in front of a fan to get my angle which stayed constant with fan speed (as I recall) and which looks now to be about 2/3 of what Penn Yan used. I don't think prop walk is greatly affected. I never saw any difference in any of my various trials.

This maneuvering stuff is not rocket science peeps. We aren't trying to stay on strings of fish gear across a 40kt wind. We are simply putting small boats into places a couple of times per year. a little instruction and practice at the marina would serve 99% of the supposed handling issues. Why re-invent the wheel. Watch a commercial fisherman dock or un-dock and observe how they use gear and throttle. Most of us will not be as proficient, but nor do we need to be.

Sailor of Fortune said:

Maybe practice with existing equipment would also be an option?......

Click to expand...

Now where's the fun in that?

Probably not applicable to stinkpots like ours, but I added a 4" x 36" trim tab to the outboard hung rudder on a Cape George 36' cutter we sailed. The trim tab took ounces to turn, which in turn powered the much larger rudder. I could use the smallest, cheapest autopilot to turn the trim tab and hooked up a very simple and light weight wind vane that steered the boat to Hawaii and back with the tiller removed to get it out of the way. I was pretty surprised how well it worked....

Sailor of Fortune said:

This maneuvering stuff is not rocket science peeps. We aren't trying to stay on strings of fish gear across a 40kt wind. We are simply putting small boats into places a couple of times per year. a little instruction and practice at the marina would serve 99% of the supposed handling issues. Why re-invent the wheel. Watch a commercial fisherman dock or un-dock and observe how they use gear and throttle. Most of us will not be as proficient, but nor do we need to be.

Click to expand...

Who said anything about maneuvering?
Increased powering efficiency and less hunting on autopilot were the goals which prompted my experiments. These goals are actually somewhat at odds with improved low speed maneuvering.

I understand completely. It's the obvious thing to do. All boat rudders should be like this. But it's just too small of a detail to be bothered w when you're trying to turn a profit. I like the Sumnercraft keel too but I've never seen another boat w that keel. They saw they had the chance to deflect the water flow into the advancing prop blades to increase thrust and they did it. Perhaps the Sumnercraft designer had once been a jet engine mechanic.

But I too like those little fine tuning details. Makes a boat all that it can be.

Maybe if you had "hunting" issues with both the Bruno and the Willard, the auto pilot might be the place to look. Both hulls had many built so others would be dealing with the same problem.