Rudders with Endplates

[sharpie]

I was wondering if anyone here has had experience with shallow rudders with endplates on them. Bolger uses them on some of his designs and I think that Dias used a fancy one on a recent boat. Do they work well enough to consider making the move from a kick-up rudder? Is there a specific formula for determining the submersed area?

[Ian McColgin]

And that boat in Chatham featured in the last year by out host. The end-plate shape and angle is actually very subtle and sophisticated. Unless your a genius who know all that foil shape numerology, tip turbulance theory, etc. figure you might well make the boat worse. Even if you've an NA bud, better make the rudder with a kind-a slot on bayonet fitting to take different end plates to test. Not only shape, but attack angle. The damn things are just horizontal.

[sharpie]

I can consult an oracle, can't I??

[Stu Fyfe]

Bolger designed my Redwing end plates on the rudder as well as the bilge keels and 2/3 of the keel. They were designed so the plates would prevent the keels and rudder from digging into the mud/sand. They work well for that purpose. In addition, Phil felt that they would also aid the shallow rudder. I'm not sure exactly how they work, but Phil once told me that they work like the elevators on an aircraft. Bolger suggested that they might give a catboat such as a Beetle an advantage as well. I'll have Redwing with me at the WoodenBoat Show if you'd like to see what they look like.

[landlocked sailor]

I put one on my Nimble 20. The drop-down rudders on these boats are notorious for breaking. I just sized mine so it looked right; seat of the pants engineering and it works well.


Rick

[sharpie]

Thanks, folks. Stu, I appreciate the offer, but will not be making it out that way. Rick, thanks for the pics. That gives me some visual clues to begin fiddling.

[donald branscom]

Vortex reliever. whatever. The guy that discovered this feature which is now on most airplane wings was not an engineer. He just started throwing paper airplanes out of the window of his sky scaper office and one day he noticed that when he bent the wings up on the ends the plane did not stall ,instead it just glided down smoothly. The story was on 60 minutes TV program.

Now if you want to know more go get CA Marche"s book
THE AEROHYDRODYNAMICS OF SAILING.

Water is 12 times more viscious than air so take that into account. That fin cannot slant back more than 57 degrees.
Tug boats use these kind of devices too.
The one on the photo posted of the NIMBLE looks about right.

[mcdenny]

Practical Boatbuilder had a multi-part article on rudders a while ago.

http://www.proboat-digital.com/tcpro...at/inbox/33422

Lots of good info on fancy rudders.

I built a thistle rudder with endplates for my launch as I wanted to minimize size (less draft and better shaft angle while still tucked under transom.

Here's a pic of my rudder

[Bobcat]

I have such a rudder on my Bolger-designed Bobcat. It works well. It's nice to have a rudder that it is no lower than the skeg when I am coming into the beach.

[Woxbox]

I made one that looks a lot like Rick's for my Searunner 25 -- I used the rule of thumb that you need to maintain the total rudder area -- so the bottom plate should make up for the depth cut off, or the replacement rudder needs to be wider to compensate along with the end plate.
At any rate, I was surprised to find that there was no loss in performance at all. I did keep the old one on board, just in case, but never needed it.

[paladin]

They are properly called "splates" and are used to reduce tip vortexes...the "fluid" moves over the control surface and slides off the end...the splate redirects the fluid over the control surface....the effect was used on the 1940's and later Beechcraft Bonanza's and the Cessna model 310's but they found that making tip tanks the proper shape and dimensions they could also extend the range and stability of the aircraft.

[Ilker]

Hello all,

have searched the forum but couldnt quite find the result that I was hoping so I would like to post my question to a relative old topic.

I have built my 28' displacement boat. I know about the displacement speeds etc but I was hoping to minimize the squat effect on the transom hopefully by a modification on the rudder.

looking at the Glen pic above and my links below, what do you guys think of a horizontal stabilizer - elevator?

any specifics to it? where to place and why?

I highly appreciate any info.

Thanks,

http://gallery.bateau2.com/displayim..._display_media

http://gallery.bateau2.com/displayim..._display_media

[CapnJ2ds]

Had a mate with an extended Hartley "Tahitian" which was very hard-mouthed and gave a fair bit of trouble with stress on the actual steering mechanism. He was going to add 150mm or so to the trailing edge of his steel-plate rudder in an attempt to fix the problems. I was a bit worried that it would exacerbate them, especially the strain on the mechanism, and persuaded him to add an end-plate on the bottom of the rudder, about 150mm each side. It was just another piece of flat plate, with the leading edges angled back about 40 degrees. Worked well; the boat became more docile and the steering mechanism gave less trouble.

Always best to experiment with someone else's boat, eh?

[CapnJ2ds]

Further to my #13 above, and having had a look at your pics, that's a plate rudder you have there, so it shouldn't be hard to weld an end-plate on the bottom, or to hack it off or alter it if it doesn't work as hoped. Reckon you could start with (Guess) 300mm sticking out each side (i.e. 600mm total width) and see what happens.
Much wider and you might need bracing struts? Leading edges should be angled back a bit.
Dunno how much it'll affect squatting though - if your boat is a displacement hull, it's gonna squat regardless if you push it.

[Ilker]

Thanks for the response.

2 videos of test rides to make it more visual underway...

I know the displacement hull factor but I just want to minimize it if I can...

http://vimeo.com/11580828

http://vimeo.com/11005700

[CapnJ2ds]

Nice looking boat - seems to be quite handy too! But I don't really see a squatting problem, she seems to be doing just fine.

[Ilker]

it is very responsive to steering..

but main problem is my swim platform in in water when underway.

see the pic, where it is quite high docked but at 6,5-7 knots it is all in.. that is what I am trying to avoid.

http://gallery.bateau2.com/displayimage.php?pid=43297

[donald branscom]

I would not do that.
Those end plate designs often can really get stuck in the mud!!

I also do not think it will help with the "squat".

Move more weight forward instead.

[Ilker]

I have tried that.. I have added 420 kgs of steel blocks under the forward berth..

[Jamie Orr]

I was wondering if anyone here has had experience with shallow rudders with endplates on them. Bolger uses them on some of his designs and I think that Dias used a fancy one on a recent boat. Do they work well enough to consider making the move from a kick-up rudder? Is there a specific formula for determining the submersed area?

I've been sailing my chebacco for 12 years with a rudder with a depth of 12" at the post and a plate 12" wide with the forward edge of the wings cut back at 45 degrees, the trailing edge straight across. Very similar to the Bobcat. I've never had a problem steering in any condition (the worst is running in 20 -25 knots there is a significant weather helm as the sail, all on one side, tries to turn the boat). The rudder depth equals that of both the skeg and the short shaft motor so damage from hitting the bottom is a non-issue.

Jamie

PS The rudder post should be vertical or the plate will create turbulence when turning. Also,there is frequently some movement up and down from wave action when anchored which can be annoying when trying to sleep. I solve this by looping a line under the tiller at the post, pulling the rudder up to the limit of its travel and fastening the line to a cleat on the mizzen (right behind the rudder post).

[Chris Ostlind]

Do you have pictures of your setup, Jamie

[Chris Ostlind]

Some years back, aeronautical engineer and avid multihull sailor, Tom Speer, had this to say on rudder endplates/T-foils:

Date: Saturday, 21 December 2002 2:22
Subject: Re: [multihull_boatbuilder] Transom hung or spade rudders?

>On Friday 20 December 2002 04:34, Jeff Wynn wrote:
>...
>> Would winglets at the bottom of the rudder yield a similar result? I'm
>> thinking of the kind you seen on the new jets to control the vortices
>> off the tips of their wings.
>
>The Moth and I-14 dinghies are already using T-foil rudders to good effect.
>There are advantages in pitch damping and pitch trim as well as effective
>span of the rudder.
>
>Endplates don't automatically double the effective span. They effectively
>diffuse and move the trailing vortex away from the main surface, but they
>don't eliminate the vortex wake. And they add additional wetted area. So
>the trick is to get the improvement in effective span without getting a net
>loss due to the winglets themselves.
>
>These articles talk about designing winglets for sailplanes. Similar
>principles would apply to designing winglets for rudders and keels,
although
>the detailed requirements would be different.
>http://www.mandhsoaring.com/articles/ostiv97.pdf
>http://www.mandhsoaring.com/articles...et_Testing.pdf
>http://www.soaridaho.com/Schreder/Co...k_Winglets.htm
>
>In general, however, if you're only looking for an increase in effective
span, you can get the same benefit with less wetted area by simply extending the surface. If there's some restriction on span, then it makes sense to branch out with a winglet.
>
>Cheers,
>
>--
>Tom Speer
>F-24 Ama Deus

[JimConlin]

Damfino's rudder planform was compromised a lot for shallow draft.
It occasionally stalled at low speeds.
It's a good foil (NACA0012) and doesn't ventilate at the top, so the best available fix was an endplate.
It was fabricated of 1/4" G10. The extension on the back was also intended as a get-back-on-board step.
I noticed an improvement in low-speed steering.
I doubt that the added drag could be measured.

Sorry for the grunty pic.

[Binnacle Bat]

If the only goal is to reduce squat as you approach hull speed, I would think that trim tabs at the bottom of the transom would be simpler, more effective and not add any undue stress to your rudder.

They can also be made adjustable so you can find the right angle to get the lift you need. The fancy ones come with hydraulic pistons so you can adjust them underway from the bridge.

Allan