Rudder Modifications

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Greetings,
Re: Post #25. Is there a propeller missing on the end of that shaft or am I missing something?
 
O C Diver said:
Not sure what data you're looking for.
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I was just saying that because someone feels a modification has made an improvement, doesn't always mean it's so. Especially if the modification was made by the seat of ones pants.

And I'm not speaking to any one person here directly. Just making an observation.
 
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funangler said:
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.
Click to expand...

Now thats impressive. I can spin twins on a 180 easily, but thats the first time I have ever seen a single screw do it. Any chance of a couple pics on the steering cylinder attachments at full turn?
 
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 did. Given the same set of circumstances again, I would wait until I am sure it wasn't just a new boat owner that didn't know the handling characteristics of the new boat.

I have the same problem now. We now have out first twin screw and I am FIGHTING the urge to install a bow thruster until I figure out how to really handle her in different conditions.
 
Tom....don't fight too hard....


To me the better reason for a thruster on a twin screw boat is when you lose one, some boats are dang near uncontrollable on one screw.


Sure the braggarts will say...'No problem...it can be done"...well so can a lot of things "be done", but why struggle and take the chance.


Getiing used to twin screw is just practice and unlearning some old habits to a point. My own 10 year old son and many other kids who have never even drove a car learn a twin screw pretty quick and pretty good. That's not a slam if it's taking you a bit...it's that "seeing through different eyes" that may be taking the problem. You will get it and twins will make some tough docking situations seem like why aren't all boats twins (that's for the argumentative, which is better types). :D
 
Therapy said:
I have about 38 degrees and to get any more I would need a bigger steering ram, 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.
Steve
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I am not an advocate of more than the std 70 degree rudder swing altho several here have good reports. To increase rudder swing, you don't need a longer ram. You need a shorter rudder arm. Just move the hole towards the rudder stock slightly and you increase your angle. 38 degrees should be enough tho. How is adding to the rudder (anywhere) going to give you more angle??
 
Thanks Brooksie.
While I've recomended increasing rudder deflection numerous times in the past the following comes to mind.

I have 90 degrees of rudder deflection and it never occured to me that my larger than normal ram cylinder had anything to do w the 90 degree deflection. Well the more deflection you have the less torque will be applied to the rudder shaft? I have a very large ram and helm pump for a 30' boat also w a very big rudder. Not to mention three turns L to L. Knowing that I may not now be as eager to recomend it to boaters w normal sized steering systems. I also have noticed in 7' quartering stern seas that my system handles the large rudder forces fine. So at this point I need to say that a steering system w a faster rudder (large deflection) will need the whole system powerful enough and robust enough to handle the increased loads and I have no idea if the average system can do it gracefully. I installed the oversized steering system for other reasons and it came in very handy when I increased the swing to 90 degrees. So if one goes to the wide swinging rudder w decreased mechanical advantage (as I did) the whole system needs to be strong enough to handle the increased forces.
 
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manyboats said:
Thanks Brooksie.
While I've recomended increasing rudder deflection numerous times in the past the following comes to mind.

I have 90 degrees of rudder deflection and it never occured to me that my larger than normal ram cylinder had anything to do w the 90 degree deflection. Well the more deflection you have the less torque will be applied to the rudder shaft? I have a very large ram and helm pump for a 30' boat also w a very big rudder. Not to mention three turns L to L. Knowing that I may not now be as eager to recomend it to boaters w normal sized steering systems. I also have noticed in 7' quartering stern seas that my system handles the large rudder forces fine. So at this point I need to say that a steering system w a faster rudder (large deflection) will need the whole system powerful enough and robust enough to handle the increased loads and I have no idea if the average system can do it gracefully. I installed the oversized steering system for other reasons and it came in very handy when I increased the swing to 90 degrees. So if one goes to the wide swinging rudder w decreased mechanical advantage (as I did) the whole system needs to be strong enough to handle the increased forces.
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Good point.
 
When I fit the boat out preparing to move to Alaska I installed a new engine, rebuilt trans and lots of other stuff. The Capalano hydraulic steering was one of the up grades.

But Willard put the two holes in the rudder horn so the original push-pull cable steering must have been strong enough as I have not made my rudder larger.

When I had another Willard 30 skipper aboard I turned around (180) in a fairly narrow fairway and he got very nervious. Thought he was going to throw into reverse w/o my permission. He was reaching for the levers. We cleared the stern of the big seiner w room to spare.

One of the reasons I went to hydraulic steering was for a lighter steering effort. It turned out considerably heavier and I think it's due to the two large hydraulic units and the larger seals. Seal friction is the cause IMO.
 
Greetings,
Mr. TB. "Slight" thread drift...Having been aboard your previous vessel and seen the modifications/upgrades and excellent quality of your work (and Bess's), I would think you will never suffer an engine loss short of an unforeseen catastrophic failure thus negating the need for a bow thruster in the situation suggested by Mr. ps (post #35) although anything is possible. Save your pennies for that craft beer hobby you enjoy...Practice, practice, practice...um, sorry, I mean practice maneuvering...
 
Therapy said:
Absolutely, I will add as much as I can to the front of the rudder to keep it balanced.
Thanks
Click to expand...

Therapy, this is what I did and the difference was night and day. The rudder was about 350 square inches before and 609 afterwards. All of the addition was after the shaft as I did not have room in front to add any. I could not tell any difference in the stiffness of the wheel. It felt the same as before. First pic is before the second is after. I would do this mod again in a heartbeat.

DSCN7025.jpg

DSCN7159.JPG

DSCN7070.jpg
 
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When I was researching doing this I read that as a rule of thumb the rudder should be 5% of the underwater profile of the boat. I estimated as close as I could that the profile of my boat was about 99 square feet. That would mean the rudder should be about 5 sf. The original rudder was about 2.4 sf. After the mod it is 4.2 sf. I was afraid of going any larger. It turned out to be sufficient. It tracks straighter and the turning radius is like I said day and night difference. We used to be at a marina that I had to make a 180 to get into the slip. Before I would have to stop and back up at least once (sometimes twice) to make the turn into the slip. Afterwards I could just make the turn without even trying.

It amazes me when I think about the previous owners put up with the handling of this boat for 34 years and an $800 mod totally changed the boat.
 
I do not recall EVER hearing a person complain that their rudder is to big.

Steve
 
READY,
Where did you read rudder area should be 5% of hull profile? Was a certian type of boat called out like FD? Sailboats and power boats faster than trawlers I'm sure would need different numbers.

I'm a natural born modifier and frequently go there. My ideal rudder would be even bigger than what I have w hydraulic power steering and a 90 degree swing. I really don't need a better rudder but lighter steering effort would be welcome.

For roughly displacement speeds it's really hard to imagine a rudder too big. Just need it strong enough and w high enough control power. One needs to be careful not to back so fast that the forces become so great on the rudder that it takes the helm out of your hands and slams the rudder against the stops. That could cause some damage. A bigger rudder should have a stronger system and more power or mechanical advantage to control it.
 
Could somebody please explain the theory behind the angle iron on the aft edge of the rudder? This seems like it would cause significant drag and violates much of I thought I knew about hydrodynamics.

Thanks,
RR
 
Dave Gerr goes into the how and why of thistle, Maclear and other rudders work, read chapter 13 of Dave Gerr's Boat Mechanical Systems book..

The elementary level I get is when they are hard over, the feather acts as a thrust reverser (Like a jetski) when the prop wash hits the aft edge it kicks the water farther around.

Maybe I need to re-read it too..

Stu
 
manyboats said:
READY,
Where did you read rudder area should be 5% of hull profile? Was a certian type of boat called out like FD? Sailboats and power boats faster than trawlers I'm sure would need different numbers.

I'm a natural born modifier and frequently go there. My ideal rudder would be even bigger than what I have w hydraulic power steering and a 90 degree swing. I really don't need a better rudder but lighter steering effort would be welcome.

For roughly displacement speeds it's really hard to imagine a rudder too big. Just need it strong enough and w high enough control power. One needs to be careful not to back so fast that the forces become so great on the rudder that it takes the helm out of your hands and slams the rudder against the stops. That could cause some damage. A bigger rudder should have a stronger system and more power or mechanical advantage to control it.
Click to expand...

I don't remember exactly but I saw it in several places, one I believe was an article be Dave Gerr but I have slept since then. I am sure it was in reference to a non planning hull. My understanding is the faster the boat the smaller the rudder needs to be.
 
The last bit of angle in the rudder is past 90 degree and the water thrust follows it. My boat goes backwards when hard over to starboard. I put it hard over and shift forward the trust kicks it off the dock and backs up. What is hard to get use to is you have to straighten the rudder to stop going backwards.
 
Therapy,

Look into articulating rudders. We've seen a few of these installed on Nordic Tugs with good outcomes. Check this video from BEI.

Home Page
 
READY,
Since you saw it in several places it's probably a rule of thumb like a max of 35 degrees rudder swing. And one can inject variables to make adjustments. Like longer boats may need more rudder than shorter boats and boats that carry their draft far into the ends may need more rudder. But it sounds like a good rule of thumb. Thanks.
 
" My understanding is the faster the boat the smaller the rudder needs to be."

True

However most boats are slow boats when docking so some require crutches.

Bow thruster is common , our Launch has a "backing rudder".

This is a bronze cone that looks like a megaphone mounted in front of the rudder on its own shaft . A link to the rudder swings it in the same direction.

Angle iron in a T on the rear of the rudder helps in close quarters with no noticible extra drag at displacement speeds.
 
FF said:
"

Bow thruster is common , our Launch has a "backing rudder".

This is a bronze cone that looks like a megaphone mounted in front of the rudder on its own shaft . A link to the rudder swings it in the same direction.
Click to expand...

The general definition of a backing rudder is a set of flanking rudders forward of the prop. Do you have an image of your device?
 
Do you have an image of your device?

No sorry , but the megaphone is in C/L in front of the prop. USN 50 Utility boat

Dont know a US Navy site that might show it, sorry.
 
So it is a "wake equalizing duct"? Is it mounted higher than centerline of the prop shaft?
How big is the skeg? Usually those are needed when the prop loading is light on the top due to turbulence caused by the skeg or other gear. It does not turn though.

https://www.caeses.com/forum/index.php?/topic/228-design-of-a-wed-wake-equalizing-duct/

If you're talking about something that is aft of the prop, and pivots with the rudder, that's a thrust diverter. I guess it could be mounted forward of the prop but I've never seen or heard of one like that. Also, it would impair the water flow to the prop during forward operation...
 
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Fast Freds is a backing rudder. It is on many navy small boat designs. 3 different sizes of personnel boats, utility boats etc. It shares characteristics with a flanking rudder but it is not independent of the steering rudder, a drag link connects them. Flanking rudders have their own control and are operated separate from steering rudders. You read mixed reviews if they work well or not. Some guys love them, others thing they are a waste of time.
 
My experience with that design is they don't work until you move at least 3 kn backwards. It's a scary as hell until you realize how good it can be.
 
There are several other aspects of rudder size, design and use.

The initial rudder size is what the rudder post, ram(s) and power system are made of and capacity. Changing rudder size often wears out the system prematurely. By 'wears out' I refer to rams developing seal leaks, pumps dying (usually at inopportune times) and rudder stocks shearing. Also autopilots being under capacity to handle the increased ram load/feedback.

So while you may need larger rudders, usually actually USING the rudder fully and applying lots of goose at the opportune time is the most effective way to make your boat do what you want her to, well.... that and practice.

On the other blog mentioned recently, there is evidence of the problem. It was noted to NOT touch the rudder when manuevering. This is actually referenced in several 'yacht handling' tome's. It is not always correct.
 
Sailor of Fortune said:
Some guys love them, others thing they are a waste of time.
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Flankers......
I am of the opinion that ALL boats should have them. Having worked a boat with Flankers for 12 years they are the cats ass. Great to learn on (was a training boat) even more handy to let others learn on because it increases the amount of 'OOPS, I waited too late to do that' recovery time, and awesome to get out of tight spots with.

BUT, as you said, some guys just don't get the hang of them, or use them optimally. (or care to learn)

It seems to me that boats with Flankers that aren't used are being operated by people who don't take the time to actually learn how useful they can be, and are 'bashful' to take advantage of every tool in the tool box. Part ego, part ignorance.
 
Flankers are fine for displacement boats...beyond that I'm not sure just how much help/hindrance they are at speed. I suspect bad as rudder size goes down very proportionally or even disproportionately with speed.


Also...just increasing rudder size doesn't necessarily mean premature anything...you do have to consider all the components in altering a design..but often components aren't all that precise to begin with. A total system changeout is hit or miss as many have discovered just because one component is altered.
 
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