torgue for articulated rudders

[Singleprop]

Hi All,

I am looking for information or a webside that has rudder torque calculations/formulas for an articulated rudder (flap rudder).

I have found several regular rudder calculations on the net, but nothing discussing the effect that the flap has.

The question is how much extra torque is required when the rudder is deflected at 35 degree (then the flap is at about 45 degrees)?

*

 

[FF]

Not sure the torque would change ,

the difference is after 35 deg a flat rudder will stall, the articulated claims to still turn , rather than becoming a speed brake.

Most boat rudder tabs are not balanced , as is done for aircraft control surfaces.

To be sure of a proper sized steering setup I would simply add the tab to the rudder area , and calculate rudder area with that.

Look at ,,,,.wikipedia.org/wiki/Kitchen_rudder

*

Any tabed rudder must be locked somehow to use reverse, never an easy task.


-- Edited by FF on Tuesday 31st of January 2012 05:29:36 AM

 

[Singleprop]

I am pretty sure that adding another 10-20 degree deflection or so ( created by the flap) to the normal 35 degree deflection of the rudder will require a more powerfull helms pump, cylinder and rudder construction.
But is there an easy way to calculate this? ..or just add, say 30 % to the calculations?
I checked the bible (Dave Gerry, boat mechanical systems handbook), couldn't find any relevant info......maybe it is as you say, just add the flap area to the rudder area...

On the other hand, we are not talking about a flat plate rudder since it just would not make sense to invest the extra money to get an inefficient flat plate flap rudder - it would have to be a profiled rudder...

 

[Singleprop]

I'm not convinced that a flap would have to be locked when reversing.
Firstly, it's not really possible to lock a flap.
Secondly, the rudders are in operation all over the world - they work.
Thirdly, the way to handle a reversing would be to deflect the rudder a bit less so that it doesn't stall.

 

[pull]

The information you are looking for is available, but it will cost you 20 bucks.

It is contained in a 3 part series that Dave Gerr wrote for ProBoat dot com.

Additional details and calculations are in a 2 part article written by Eric Sponberg on shaft strength calculations, also in ProBoat.

Go to Proboat and register for the one month access to the archives, search for Gerr and Sponberg and learn all you need to know..

Interestingly, Gerr concludes that a McLear/Thistle rudder beats an articulated flap rudder hands down.

Mike

 

[Singleprop]

Thanks, will check it out.

I have not read the referenced article but I would expect that the "rudder competion winner" depends on what the rudder is designed to do: i.e effective at high speed, effective at low speed maneuvering, effective at towing, effective at sailing, effective at motoring, effective on autopilot etc, you get the picture.

My requirement is low speed maneuvering with a bow thruster.....so that I don't crack the paint on the neighbor, but also the better response when on autopilot (I expect that a smaller rudder deflection is required - due to the flap - and that it will mean that the autopilot has an easier job). But not sure......

 

[windmist]

Have you checked with this company - http://bayviewengineeringind.com/*?

They made my articulating rudder for my Mariner Seville 37 and they have a lot of experience and could answer any of your questions.* When I had the boat built, I had the factory install a bigger helm pump then was normal.* Everything has worked well for 3 seasons now.

Ron

 

[Conrad]

And another site that might be helpful...

http://www.rudderpower.com

 

[FF]

There is quite a difference between an articulated rudder , and a rudder with a trim tab/control surface.

The tab is usually partially balanced and is hooked to the rudder with linkage to provide "power steering".

If mostly one speed is used the power steering works well,steering with either the rudder or just the tab,

for sailboats where the speeds will vary , the tab gets the auto pilot or air vane input and positions the rudder.

In reverse the tab must be locked or removed.

In reverse the articulated rudder will be curved backwards which may create oversteering .

Perhaps on a twin , where rudder position is less important in reverse it might be useful.

 

[RickH]

I have a printout of the Dave Gerr article and while the discussion on various rudder types is very complete, there is no data on figuring out additional loads for articulated rudder.* After a lot of research, I went with the McLear "thistle" rudder for our tug.* Single screw, no bow thruster, but had a GREAT improvement in low speed handling as well as better response on the autopilot while cruising.** Best $ 200 I ever spent on the boat.

Rick Haverstock

*

 

[FF]

Best $ 200 I ever spent on the boat.

AND no moving parts!!

KISS

 

[nwboater]

I have an articulating rudder on my Willard 40 trawler. It too was fabricated by Bayview Engineering WA and I consider it the best, most useful addition to my boat. After installing the new rudder, we took it*out for a trial run. Immediately, I*noticed that the hydraulic steering couldn't keep up with the job.*I decided to increase the size*of the pump cylinder and ordered*the next*size up*in bore and stroke. The original pump was a*Wagner*but I*changed to*Jastram*ordered through*HamiltonJet. (It was not necessary*to change the helm pump or resevoir).*After the change*over,*no more chattering, and four years later I'm still amazed by Northstar's remarkable maneuverability*in close quarters while*running dead slow. **


-- Edited by nwboater on Thursday 9th of February 2012 05:18:31 PM

 

[Codger2]

nwboater wrote:
*After the change*over,*no more chattering, and four years later I'm still amazed by Northstar's remarkable maneuverability*in close quarters while*running dead slow. **

******** Do you happen to have any photos of the finished product? I've been toying with the idea of doing that for about two years. Also, I'm told it's pretty expensive. Did you find that to be true?

 

[RickH]

When I posted last night, I guess that my brain cells were not fully engaged.* I did a write up on the thistle rudder project for the Sundowner owners group.* If anyone is interested in the particulars, here is the link to that article:

http://www.sailangle.com/group-forum/topic/id/1871

Rick Haverstock

*

 

[windmist]

you happen to have any photos of the finished product? I've been toying with the idea of doing that for about two years. Also, I'm told it's pretty expensive. Did you find that to be true?

_______________________________________________________

I would guess that you would pay around $5 grand now but you should call Jamie Wells at BEI for a quote. He's a very approachable guy.

Ron

Some pictures:

 

[nwboater]

Guru, I don't have a good picture* to post here, but mine looks exactly like that on "Windmist". Three years ago I paid $5000, including the yard bill. Bayview Engineering*owner, Jamie Wells, is a*good*guy and can talk you through the process, including cost. Also, he designs and ships these rudders around the country*-- easy to install.

 

[Singleprop]

http://exchange.dnv.com/publishing/RulesShip/2001-01/ts303.pdf

*

found this document that has a little info about rudder torque - page 9-10. As far as I can judge the flap area has to be added to the rudder area as was mentioned earlier - but special considerations are required - but not specified.......need an NA.

 

[Singleprop]

"special considerations" seem to be to double the torque compared to a regular flat balanced rudder.

This is in line with Kobelts and Bayview Engineerings actual calculations - which came out the same.