Rudder Attachment to 26M Hull

[seahouse]

BOAT – The right alloy of titanium is the ideal metal for use on boats wherever stainless is being used. It's what high-end, high-performance sailboats frequently use, and it's way more corrosion resistant than stainless in salt water. Titanium fittings and fasteners should pretty much last the life of the boat. I thought I wrote a post about this a year or so back (I just searched for it and couldn't find it- maybe another forum)... but it goes something like this...

The major reason it's not universally in use today on all sailboats (I think at some point in time it will be) is because the cost of the material has been kept artificially high by US protectionism, a vestige from WWII . It's a strategic metal for military applications, so the US manufacturers had a monopoly selling it and with no competition, overcharged the government and made huge profits, and had also no reason to invest to modernize their outdated production technology. When demand waned (recent decades) the more modern and efficient Chinese technology took over the market, and most US manufacturers went out of business. The price continues to drop.

Because its use has been artificially suppressed, the special fabrication skills needed (bending, forming, welding) for it are not as common, which adds to the present cost of using it.

There are online suppliers and fabricators for the stuff- send them your drawing and money, and they'll send you your parts.

-B.

[raycarlson]

An interesting side note, currently 95% of the worlds production of raw titanium ore is used to make TiO2 which is the color white in the paint, plastic and paper industries of the world.

[BOAT]

Ix- Thanks for your vote of confidence. Did the snugged pivot bolt on the spacers not solve the spreading of the rudder tangs problem?

- B.

Hey seahouse! I went to mastrebs to drink beers because his boat is broken and i forgot my rudder spacers there - I'm gonna go back for more beer but this time I will remember to bring the spacers back home (unless I have too much beer). And then I can tell you how the spacers worked out. We already know they make great beer coasters but i really want to try them out as rudder spacers.

(P.S. the rudder spacers that crikey uses make better beer coasters than your rudder spacers because they are the same shape as the beer mug but they look stupid on the rudders so i think i like yours better.)

[Ixneigh]

My brackets are bent because I sail with the rudders half up when I'm in shallow water. I'm not going to stop doing that since thats why I have the boat therefore I must strongerfy the system until it can cope. I've tried the spacers and what not but my gut, non-aerospace background, non-engineering degree instinct tells me they need to be twice as thick. The welds need to have nice fillets, unlike now, and the helm needs a solid bronze rack and pinion mechanism.
The top of the rudder stock needs a larger bearing surface.
The brackets are where I would start. If it had all that this thread wouldn't exist.
Ix

[BOAT]

I agree with Ixneigh - the rudder spacers are a great idea and we should all use some but in the end a strongerfy solution to the brackets is needed to make the MAC fully "Blue Water" capable.

What about cast aluminum?? Is that a PITA too? (I like pita bread, but I don't think that means the same thing).

[Crikey]

What I found (this was posted much earlier somewhere) was both rudders had a rearward factory setting. One of these is shown in the following image:

It may not seem like much but I'll bet you a beer on a coaster that that little difference could be calculated into a much larger loading than the vertical alignment I adjusted them to. Couple that with occasional extra rearward movement you sometimes get by a loose downhaul rope tie-off and there you have it - forces sufficient enough to bend or splay metal. I think the stock angle bearing bracket is engineered strong enough to handle the forces typically encountered under sail except when corrosion or looseness gets factored in. But the rudder petals sure want to flex.What I was after Boat, when I dropped them 2", was a bit more rudder bite similar to an IDA blade - but without the expense. Overall I think it has resulted in the same, or less overall drag because I don't stall them near as much as I used to. Add in all the other component slop and it used to feel like driving a car with shot ball joints. Not anymore...
The CD's were from an older picture and indeed were a PITA because they broke down pretty fast and caused even more friction. I've been using Brians (seahaus) material for two years now and will swear by them.
You'll notice the silly little under-power fins in the following pic:

This is what I was talking about earlier. To re-do these with a much larger type using a wrap around bracket that would also further stiffen the thin rudder 'petals'. Still waiting on the SS fatigue longevity info before I settle on what thickness to use.

(pardon the crappy graphic)

R.

[BOAT]

Okay, I get it now - that adjustment makes the rudders perpendicular to the surface of the water. Yes, if the rudders are not perpendicular to the surface there will be more rudder drag and greater forces on the rudder. I have not experienced this issue (yet) on 'boat' because 'boat' is still an relatively new boat and still is heavy to the rear - so my blades already track a little forward but as our boats get older and we add more and more 'stuff' to them they get more nose heavy and start to sit very flat on the water. When a stock MAC is flat on the water line it does indeed trail the rudders by about 1 or 2 degrees.

The rudder adjustment is supposed to take care of that but it's not able to go fat enough because the rudder itself gets in the way.

I just assumed if I got that nose heavy I would have to shave the rudder shank or re-drill the pivot hole to make up the difference to correct the angle - I never thought of moving the entire assembly.

That's interesting.

[Crikey]

Figure, the boat gets pulled (or pushed) nose down while under sail, whether running or reaching. That's the result of the drive of the sails to move it forward. The Macs broad stern results in extra lift at speed which altogether moves the angle of the rudders further rearward. Now the tip of the blade is taking the main force of the boat mass and the bending forces go way higher as you go faster. Mastreb could probably calculate the moments acting on the shaft.
(The rudder adjustment is supposed to take care of that but it's not able to go fat enough because the rudder itself gets in the way.)
That was pretty astute! Because I welded in stiffeners, I actually radiused a groove forward on the rudder nose.

The fibreglas seems pretty beefy at the top - hasn't cracked yet and it gives a better final stop to the down position than the small screw did before. The furthest blade in my picture is visually 90 deg with the hull rear.

It was fun backing the trailer up to my front ditch!

[BOAT]

This rudder tuning thing is really a lot more important than a lot of people realize. It can have a big effect on your speed. If for some reason you feel the boat is not tracking well or if it takes a lot of work on the helm to hold a line your first step should be to look at rudder attack. I check the rudder attack on 'boat' often and sometimes in the water using an underwater camera:


http://s1325.photobucket.com/user/boat2 ... 5.mp4.html

The forces on the rudder are more than some people realize. In some waters you are required to carry an emergency rudder. The sideways forces on even a small rudder are so powerful they produce enough pounds of torque to pull ropes and pulleys that can power equipment on board the sailboat. I have seen devices on boats that do things like steer the boat or wash clothing all from the power of water pressure on a small surface. I don't know how they work but I figure there must be a lot of pressure there.

If any of you have been on old trans-pac boats with those those wind vane (Gandolf) auto steering pilots wind vane things you should know that many of them work with a gizmo called a "servo pendulum" It's a device that uses the sideways pull on a rudder and turns it into a very strong force that can be powerful enough to steer a very large boat. Because of that same effect the new Hunter boats and others have those dual rudders that are at at steep angles to help reduce the effects of this "sideways" force.

http://www.selfsteer.com/products/monit ... ndulum.php

I'm not really any good at explainin stuff cuz I don't even fully understand it myself but mastreb or seahouse could probably explain better - but I have mentioned it before when I talk about the experiment my dad used to make me do when i was a kid on his sailboat and he would tell me to hold a whisker pole 4 feet into the water at 5 knots to show that even with two hands I could not hold the pole perpendicular to the water - the forces where too great. He was trying to get me to understand the lesson of drag and slip.

It's a HUGE amount of force.

[seahouse]

So to paraphrase, when you have adjusted the rudder stop screws so the rudders can tip all the way forward (forward rake), interference from the rudders themselves will prevent the stops from being reached?

It looks to me like it would not be possible (because of the limited range of the stop screws as well) to give the rudders forward rake anywhere near the point of instability (or damage) – the steering line of pivot will always end up “balanced”, well into the front half of the rudder. So it might be feasible to just set the rudders to rake as far forward as they can go (?), minimizing required steering force input and therefore stress on the mechanism, at the expense of “feel”. That's what you did Ross.(?)

What I don't follow is that the angle that the boat sits at in the water will affect this – the imaginary steering pivot line will always pass through the same place in the rudder no matter what the angle of the boat is.

The flow of water over the rudder surface will be at a different angle, but that's all; the servo effect and the balance of the rudders, and thus the ease of effort at the steering wheel shouldn't change. What am I missing?

Because of their streamlined shape (cross-section, not profile) the drag that the rudders make in the water moving straight forward is quite small, especially compared to something round, such as a whisker pole (by about 10X maybe for equivalent frontal area). Let the rudders drop straight down into the water from the full up position if you can. When they hit the water I would expect you to see them cut right through it like a knife; little drag.

Also, try releasing your rudder downhaul lines while motoring straight ahead at low speed, say 5 kts, and see how much they are pushed up by drag in the water. Not much I'll guess.

On the other hand, when moving in reverse, (and also when uphauling them, but their weight confounds this) the streamlined shape of the rudders becomes a great liability; the drag becomes much greater than even a round profile of the same frontal area.

But the forces than can be massive on the rudders are side forces, both from abrupt steering input, and water and wave action that can cause side-slipping with the mass of the boat behind it. In following seas and other adverse conditions I retract mine and use the motor in such and similar conditions. But that might also be because I'm a way more experienced powerboater than sailor.

Nice video BOAT, I get a 3.1415927 degree of forward rake measurement out of it.

- B.

[seahouse]

Ixneigh – Exactly where are you seeing bending in the brackets? Along the weld line, or along a vertical line little behind the weld, nearer to the rudder itself? Or maybe everything is just flexing on you? I am entertaining this, but my boat goes in the water for the season tomorrow (I hope), which might “quench” my progress on it.

-B.

[Ixneigh]

The bottoms of the brackets are flared out wards. I'm sure I'm not the only one this has happened to. I don't baby the rudders either, since on a sailboat or any boat, it's supposed to be strong. Full stop.
I'll pull them up if the boats drifting backwards into shallow water but that's it. I sail with them half up half down or anywhere in between. I'll drag them on the bottom unsecured, so they kick up if I hit something.
The system is marginal. We all know that. I want that fixed. Just like the person who's deck was cracking. In thst case it was cosmetic but it still bothered me every time I walked on it so I ground the deck down and added fiberglass so it didn't crack any more.
Don't think I don't understand the limits of the boat, since I do. And I'm fine with them. But within those limits there are still things that shouldn't be skimped on. If I'm blasting down wind a few mikes offshore at seven plus knots the last thing I want to think about is the rudders.

Re rudder stops, mine are as far forward as they can go , in fact the top end of the rudder is slightly scored from a bit of stainless on the bracket itself where they bear on. I have the coughunbreakablecough Ida rudders and the boat sails fine. With a jib in certain airs there is a very slight lee helm but I often sail with only part of the board down. I'm not sure where these complaints about excessive weather helm are coming from.
Please remember that my boat also has a set of skegs "temporarily" mounted on the bottom. I'm am quite sure these have an effect because in certain condition they make coming about harder.
Ix

[Crikey]

Brian, I don't think with the stock system I'd want to consider having the blades orienting forward of my right angle orientation. As you said, a rapid helm or broach would probably result in a fail or bend somewhere. However I'll give you a picture of a loading or running situation (thanks Geoff!) where the rudders can come rearward compared to the the water flow and encounter higher tip pressure when turned. Admittedly it's not very much! I get that the center of axis is carried through the nose area of the blade but angle it back and the mass of the hull is acting more on the tip. Ix is getting his bending from these forces.

My attempt to tune this area is to achieve as little drag as possible by minimizing the rudder angle applied through the helm. Even with the angle corrected to optimum the forward or rearward loading of the boat will change things by a number of degrees. My experience with using the sailing rudders under power has shown me they will come straight back if unsecured.
I suppose I will have to wait until I have a position sensor on an autopilot so I can really see what is going on.

R.

[BOAT]

Guys, you all know well that I am not a member of rocket science club. I think seahouse understood my demeanor about my rudder attack post when he made the joke that he estimated a 3.234 degree of forward attack on "boat's" rudders.

It was a joke.
(And besides, the leading edge of "boat's" rudders are exactly perpendicular to the waterline of the hull so the actual angle is 0.00 degrees . . . so there!)

The point I was making is this: If your rudders are too far to the rear it will have a negative impact on your boats handling. (It can be SEVERE! and also cause rounding up early because of sideways forces on the rudder tip if the rearward angle is extreme!). That's why HUNTER angles the rudders on their boats that have dual rudders.

That's why I used the Monitor Wind-vane Servo Pendulum gizmo thingy as an example. I was not trying to compare a rudder to a whisker pole!! I was showing that a sideways rudder has huge forces on it! It's not the leading edge "cross section" drag and (actually that's a discussion about "slip", not 'drag') whatever - that was not my point - my point is what happens to a rudder with a rearward attack when you turn it. It becomes more of a paddle than a rudder! And that same thing will happen even when you don't turn it just by making your boat heel over! When the boat tips sideways the improperly raked rudder is now presenting a paddle face to the water at the tip! There is enough power there now to turn your boat right into the wind! (I wish I was smarter as 'splaining stuff - my autism makes this all very hard to discuss).

I can see it in my brain but I can't explain it.

I would blow this off as stupid except that I have tried it myself on boat! One day out I was rounding up too soon and I was puzzled and then I found my rudder ropes were loose. I pulled the rudders back in tight and the boat went back to it's usual behavior of holding a course all by itself without me even touching the wheel.

[Crikey]

Good one Boat! Unfortunately I can't get your video to play - still trying. (How long did you hold your breath...)
That's why HUNTER angles the rudders on their boats that have dual rudders.
Do you mean outward? Mastreb talked about wanting to do that once. Too much re-engineering was involved to alter the stock configuration.
R.