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Old 01-24-2016, 08:48 PM   #41
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Absolutely, I will add as much as I can to the front of the rudder to keep it balanced.
Thanks
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.

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Old 01-24-2016, 09:04 PM   #42
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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.
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Old 01-24-2016, 09:48 PM   #43
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I do not recall EVER hearing a person complain that their rudder is to big.

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Old 01-24-2016, 10:05 PM   #44
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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.
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Old 01-25-2016, 12:29 PM   #45
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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
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Old 01-25-2016, 07:44 PM   #46
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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
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Old 01-25-2016, 07:55 PM   #47
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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.
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.
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Old 01-25-2016, 10:56 PM   #48
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Rudder Modifications

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.
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Old 01-26-2016, 10:42 AM   #49
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Therapy,

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

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Old 01-26-2016, 12:39 PM   #50
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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.
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Old 01-27-2016, 09:00 AM   #51
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" 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.
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Old 01-27-2016, 09:46 AM   #52
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"

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.
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?
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Old 01-28-2016, 08:25 AM   #53
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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.
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Old 01-28-2016, 08:38 AM   #54
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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.

https://www.caeses.com/forum/index.p...ualizing-duct/
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Old 01-28-2016, 08:39 AM   #55
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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.p...ualizing-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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Old 01-28-2016, 06:37 PM   #56
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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.
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Old 01-29-2016, 08:19 AM   #57
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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.
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Old 02-05-2016, 12:25 PM   #58
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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.
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Old 02-05-2016, 12:33 PM   #59
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Some guys love them, others thing they are a waste of time.
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.
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Old 02-05-2016, 12:41 PM   #60
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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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