Rudder Trim (Up or Down)

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Re: Rudder Trim (Up or Down)

Postby jeadstx » Mon Sep 23, 2013 3:23 pm

I noticed the forward rake with my original rudder head. Can't remember if I still have the forward rake with my new rudder head.

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
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Re: Rudder Trim (Up or Down)

Postby Tipster1 » Mon Sep 23, 2013 7:17 pm

Thank you Chris and John.

If rudder is raked forward to a neutral position, how do you know if you are getting any lateral resistance from it?

I like a slight weather helm because I know I am getting some lift from the rudder and it feels safer. Neutral helm feel creepy, and as I said before, I can't pump the rudder to get another foot closer to dock.
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Re: Rudder Trim (Up or Down)

Postby GreenLake » Mon Sep 23, 2013 10:08 pm

Even with a (partially) balanced rudder blade you can still get weather helm.

Weather helm simply describes the tendency for your boat to round up when you let go of the tiller. The balance in the rudder would only reduce the force needed to counteract the weather helm. The weather helm as such comes from the fore and aft distance between center of effort and center of lateral resistance. Moving the CLR forward would increase weather helm, but tilting a rudder a few degrees does not shift the CLR by enough (at best, it shifts it by half as much, realistically even less due to the contribution of the hull).

The way you balance the boat is by sail trim and change in mast rake. Reefing the main or raking the mast a bit less, or moving it forward if stepped on deck, would decrease weather helm.

That said, balancing the rudder blade can reduce the force required to turn it and that can rob you of some of the feedback, but you will be getting the lateral resistance.

Looking at the photo, I can't convince myself that the rake is substantial enough to create a fully balanced rudder. Looks like there's more of the chord behind the line through the pintles than in front of that line. Same goes for sculling - there should be enough asymmetry there to allow vortex separation at the trailing edge....
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Re: Rudder Trim (Up or Down)

Postby Alan » Mon Sep 23, 2013 11:36 pm

+1 on what GL said, based on my recent experience on Lake Tahoe. I kept having to deal with bigtime lee helm, even with the headsail furled and the main rigged and a very mild breeze blowing. It was to the point that the boat kept turning by itself, and I had to turn it back with the motor, and even at that it was a constant struggle to keep the bow from turning away from the wind.

How can this be? I asked myself, while mentally reviewing everything I'd read here about boat balance, and mast rake, and lee helm vs. weather helm, and center of lateral resistance vs. center of effort, and, and...aha. I'd forgotten to lower the centerboard. Which meant, of course, that the boat was pivoting around the rudder, because it was the only source of lateral resistance, and it's way the heck at the back of the boat. Once I did lower the centerboard, the problem vanished, so it's reasonable to assume that the rudder was giving lateral resistance and the centerboard counteracted it.

I'm about 99 percent certain (too late and too dark to go out and rig the rudder to check) that my rudder has the same forward rake mentioned here. Shouldn't matter, at least in regard to boat balance.
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Re: Rudder Trim (Up or Down)

Postby Tipster1 » Tue Sep 24, 2013 7:53 am

Yes, GL, I definitely agree that my rudder isn't angled so far forward as to make it completely balanced around an extension of the pintle line. When I am able to use rudder blade controls I'll be able to fool around with this on the water and I suspect that a partly raised rudder will give me more sculling-power.

This got me thinking ("Oh, No." says the crowd), If a rudder blade were perfectly symmetrically balanced, which I assume to mean that there was as much area in front of a line extended down from pivot point as behind that line AND the boat had a weather helm for safety, meaning without correction the boat turns into the wind, then you would have to be steering off the wind to maintain course. That would increase drag, so I guess a totally balanced rudder would be a bad idea, theoretically, unless you want to re-tune the boat and give up weather helm.

Right?
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Re: Rudder Trim (Up or Down)

Postby GreenLake » Tue Sep 24, 2013 11:49 am

Tipster1 wrote:I suspect that a partly raised rudder will give me more sculling-power.

It'll be interesting what you discover. Now if you could replace your rudder with something that's a bit flexible, like a diving fin....

Tipster1 wrote:If a rudder blade were perfectly symmetrically balanced, which I assume to mean that there was as much area in front of a line extended down from pivot point as behind that line AND the boat had a weather helm for safety, meaning without correction the boat turns into the wind, then you would have to be steering off the wind to maintain course. That would increase drag, so I guess a totally balanced rudder would be a bad idea, theoretically, unless you want to re-tune the boat and give up weather helm.


To the entire system (the boat) the angle of the rudder blade to the centerline of the boat is what matters. Where the pivot is (as seen from above) doesn't matter. I bet you could even move the rudder a few inches to either side and the effects would be second order at best.

So, we should be able to separate the balance of the rudder blade from the balance of the boat (weather vs. lee helm). You describe both of them accurately, but the drag from correcting for weather helm exists whether or not the rudder blade is balanced.

A slight amount of weather helm, requiring a small deflection of the rudder blade (and causing a small amount of drag) is preferable to neutral or lee helm - others have stated that here, so I don't need to repeat it. So, as long as your boat is rigged and trimmed to give only a small bit of weather helm, you are fine and the little bit of drag from that is expected. Balancing your rudder won't add to (or take away from) that drag.
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Re: Rudder Trim (Up or Down)

Postby jdoorly » Wed Sep 25, 2013 7:05 pm

If you have some way of locking your tiller another good way to check your balance on a beat is to lock the tiller at your normal weather helm position (hopefully around 3-4 degrees) and then steer the boat using your mainsheet. Pull in to come up and let go to fall off, and be one with the universe...
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Re: Rudder Trim (Up or Down)

Postby Tipster1 » Thu Sep 26, 2013 8:59 am

Great discussion, here. In my youth I had a boat that was so nicely balanced that I wrapped the main-sheet around the tiller and would relax in the back and sheet out and head up in the puffs with one hand only. Still imagine that, with normal rudder design (not a balanced blade) you can sail straight with rudder straight in line with CL of boat and still have safety of weather helm, since without tension on the tiller, rudder will swing to windward and boat will head up.

As far as flexible foil or flipper on rudder, windsurfers at the expert level, either in straight line formula racing or rapid maneuvering wave sailing talk about fin flex and how they can feel difference between stiff and flexible materials. And they are all fiberglass. At my level, key is a good shape to the fin to prevent cavitation, maximize lift, and minimize drag. Good fins start at $150.00.

Has anyone ever installed an oarlock on the back of a day-sailor and tried to scull it into a dock? Seems like it would be doable.
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Re: Rudder Trim (Up or Down)

Postby jeadstx » Thu Sep 26, 2013 12:41 pm

I have used the rudder to scull the boat for a couple hudred feet before. It was in dead calm. I also have oarlocks mounted in line with the end of the CB trunk for use with oars.

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
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Re: Rudder Trim (Up or Down)

Postby dannyb9 » Thu Sep 26, 2013 12:54 pm

i would add that heel has a great effect on helm pressure. the more you heel the more powerful the helm 'torque' becomes because the underwater shape becomes more asymmetrical. the boat wants to head up as it heels, a great safety feature. in many boats, if you heel to windward the boat will want to bear off. there is some level of heel (close to no heel) that will result in a neutral helm. racers are always looking for this 'balance point' because pressure on the rudder is drag. most of us like to have slight weather helm so we can feel the balance of the boat. totally neutral helm is hard to maintain because the boat may veer off the wind in lulls and if youre trying to go to windward, youre losing ground.
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Re: Rudder Trim (Up or Down)

Postby GreenLake » Thu Sep 26, 2013 2:23 pm

Tipster1 wrote:In my youth I had a boat that was so nicely balanced...

I have sailed my DS in moderate airs without touching sheet or tiller, using a bungee to hold the tiller in position (pull to both sides, but with a slight "give" due to the elasticity of the bungee). After trimming the sails and setting the tiller, I could cleat both sheets and just sit on the rail (not hike) and watch the boat sail itself. It would luff up in gusts and fall off a bit in lulls but always return to the same angle relative to the wind (close reach or sailing a bit free, if I remember correctly). Lasted for a good part of an hour, until the wind died.

I don't know whether the slight give in the system from using a bungee rather than a line to hold the tiller was essential or not, that just happens to be the system I used. If it was not, even a fully balanced rudder should have worked the same. I think of a balanced rudder like power steering. You need less force, and you may not get the same feel of the road, but the car responds the same to steering input. Same with boats, balancing the rudder by having part of the foil forward of the pivot just affects how hard you have to work the tiller, not how the boat reacts to the same tiller angle.

There are self-steering setups that link tiller and mainsheet. For any of those, the force required to turn the tiler (and the distance the tiller travels at the point where the link to the mainsheet connects) would presumably affect how the pull on the mainsheet changes with tiller deflection (and vice versa). You might need a method to amplify or reduce the effect of the tiller in order to trim such a system. In my case, I found out that fixed trim (mainsheet not affected by tiller) was perfect, and a slight "give" in the tiller arrester may(!) have been beneficial (don't know).
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Re: Rudder Trim (Up or Down)

Postby Tipster1 » Thu Sep 26, 2013 5:24 pm

More interesting thoughts here. I definitely want to rig a tiller tamer or lash it completely and try sailing standing up to see what I can accomplish applying windsurfing skills.
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Re: Rudder Trim (Up or Down)

Postby jdoorly » Thu Sep 26, 2013 7:55 pm

A balanced spade rudder is usually a NACA0012 airfoil (9/28 Edit by jd- Error: A CB is usually NACA0012, A rudder is usually a NACA0010). The rudder post needs to be located in the rudder's widest place. That position is 30% aft of the leading edge and its a happy coincidence that that position is the perfect compromise between lowest drag, highest lift to windward, and helm feedback.

I have a TillerPilot auto helm and I just modified my tiller keeper to an adjustable clamp style like the Tiller Tamer (my wooden "On/Off" design tended to jam up in humidity). I use the keeper way more than the Pilot. The Pilot doesn't like weather helm or even me walking around on the boat. If I change from one side to the other, seated in the cockpit, the Pilot changes course 10-15 degrees! But the clamp works great for short periods or longer ones if not moving around too much. And, the clamp can be set 'in between' so you can just grab the tiller and steer, then let go again for awhile. Mine takes a bit less than one turn to go from 'off' to full 'on' so it's very handy. That's a function of the bolts threads per inch and the rope size. I used a 1/4-20 bolt. The metric threads are finer so more turns needed. The rope I used is 3/16" double braid. I have factory horn cleats on the stern decks and the rope runs from the starboard one (held with a bolyn) through the port one to a rolling hitch. I'm thinking of dumping the hitch and adding some bungie as the arc of the clamp/tiller cannot be duplicated by the straight (taught) rope so there is always some looseness creeping in.
Last edited by jdoorly on Sat Sep 28, 2013 9:59 pm, edited 3 times in total.
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Re: Rudder Trim (Up or Down)

Postby GreenLake » Thu Sep 26, 2013 10:03 pm

On my DS1 I took two fender washers. I drilled two small holes into the "ring", so now I have three holes in a row in each. I screwed the washers into the wooden coamings from the rear using one of the new holes, and the other projects below the coaming and can accept the hook of a bungee. So now I have a bungee that goes straight across a bit below the tiller. I take a bit of shock cord and make three turns around bungee and tiller and then tie the two ends of the cord to each other. Three turns give me the desired level of friction. With that the bungee is able to hold the tiller, but if I want to override, I just have to push a bit harder and the bungee will start sliding through the lashing until it settles at the new set point. I can even do a crash tack without having to first adjust or loosen anything.

When I don't want to use the system, I can rotate the washers out of sight.

On a DS2 one would have to mount some eye-straps somewhere. But they would have a big advantage over the stern cleat in that they would allow the pull to be in a more advantageous direction.

I have since sailed on a boat with a commercially available tiller tamer and found it no comparison.
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Re: Rudder Trim (Up or Down)

Postby Tipster1 » Fri Sep 27, 2013 9:47 am

@ GL - meaning, it wasn't as good as your own system?
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