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Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Friday, March 16, 2012

Three Approaches to Rudders for Barge/Scows

A rudderless ship is a ship in trouble.
Traditional


There are a BUNCH of different ways to design and mount rudders, most of which can be adapted to barge/scows. Here, I'll talk about three basic approaches.

The basic problem is that barges tend to be very shoal of draft.

A high aspect ratio rudder (taller than wide... I'm speaking in profile view, here) has to extend below the hull, where it is exposed and vulnerable. Low aspect ratio rudders (wider than tall) need to gain area by spreading very wide, indeed, which increases leverage burden (heavy helm).

But there are  many approaches with easy, DIY, and workable solutions. The following are three, core approaches, from which many variants are possible.


Barn Door Rudder
Barn door rudders are traditional on many barges. Skeg hung, they are almost impossible to manage with a tiller. Most often, they use a wheel system, with line purchase running from the corners of the transom to a hole, high (styling is arbitrary). If you want a wheel, this system is cheap and robust.

A similar system is used by traditional cat-boats, but using a wheel controlled tiller. Should the wheel system fail, they can be extended for full tiller steering. They look pretty nice, too.

Note that, in plywood, box barges (such as TriloBoats), the skeg's shape is identical to the plywood off-cuts from the sides. They can be brought inboard and beefed up with timber before bolting to the hull. A variant would be to extend it a bit with a rudder post mounted vertically along the full length of the transom and skeg.

When taking the ground, with this type, be sure that the rudder isn't going to hang up on even a slight hummock or small rock... that will generate a LOT of stress as the boat settles.


 
Post Rudder with Bottom Plate
Post rudders are often used in sharpies. Their advantage is in being protected by the hull from forward and above. Drawbacks include piercing the hull (need a well or water tight post housing) and needing clearance to drop it down and out when servicing. I'd think this would be particularly useful in center-cockpit layouts, shortening the distance between helm and rudder.

This one has its post set at right angles to the plane of the bottom... as it turns, it's edges remain snug to the hull without widening gaps. Particularly at the leading edge, this helps keep weed and such from jamming.

It is balanced, meaning it has some area forward of the post (line of rotation). This greatly reduces strain on the helm, and allows much more area than would otherwise be comfortable. Typically, a tiller would be fitted.

When underway, the bottom plate keeps water from spilling off the lower edge, increasing the rudder's efficiency. I've heard a rule-of-thumb that the added efficiency is the equivalent of adding one side of the plate vertically to the bottom of the rudder. Bottom plates would surely help with barn door types, too.


KickUp Rudder
KickUp rudders come in numerous styles. This one is my personal favorite, and what we've used on all our larger boats. Essentially, there is an upper and lower piece (the blade), overlapping in a circular bearing plate. At its center, a heavy bolt with washers serves as a pivot. A tiller is fitted to the upper piece. A retrieval line is fixed to the blade and cleated high.

Advantages are that they can be lifted completely clear of the water, when not in use. The relatively fragile blade is dismountable, for easy maintenance. They can be high aspect, extending below the hull, but will kick back and up if run aground. In heavy, floating weed, we lift it clear and propel/steer with the scull.

This one is balanced, allowing the rudder to be oversized (nice positive effect and adds to lateral plane). The forward tip of the blade, when the rudder is kicked back near horizontal, is just a bit less than the draft, allowing steerage in any immersed position. The aft-set lower tip, and continuous curve (no flat section at the bottom) will roll the boat forward if we've forgotten to pull the rudder, and we settle down with the tide (purely theoretical, of course!).

The lower tip of the rudder needs to be weighted. Pouring lead or zinc works ('spent' zincs are easy pickin's around many grids or yards). We found some commercial, paired zincs that we cross-bolted in place... they're not as streamlined as inset metal, but much easier to work with. If you use zinc, consider epoxy-coating to keep it inactive.

If we're really booking, off the wind, the rudder may kick back some from water pressure, despite the weights. We have a little hook on the rudder post, low and forward, to catch the retrieval line and lock the blade down. We try to remember to undo it before approaching shoal water.

One thing that's worked well is cutting a circle of close-cell foam, and using it to pad the bearing plate. This keeps the whole thing perfectly quiet (can get clunky, without, in slop and bobble).


Planning out the rudder,  it helps to include the mounting arrangements. Winging it, later isn't at all easy, as close fits work best. Consider walking around a boat yard or marina (the funkier the better), trolling for ideas. Lots of good stuff on the net.

I see a lot of plans (on the net, especially) that look great on paper, but seem pretty non-KISS. Even something as simple as housing cheeks on a kick-up rudder are harder and more expensive to build, and often swell or warp, creating problems. Long and ingenious holes bored through the body to lead control lines are hard to waterproof and inspect. Be ware!

One mounting system we really like was first seen on James Wharram catamarans.

Matching, thwartship holes are drilled and faired in the rudder-post and leading edge of the rudder, both of which have been faired to half-rounds.

Light line is fixed low (stopper knot, among other methods)  laced from the bottom up, tensioning as you go, in figure 8s (e.g., through post to port, lead aft and between post and rudder to rudder starboard side, through that hole... repeat, alternating sides). Fix high (cleat or somesuch).

The 8s need to be kept from slipping, to keep rudder and post in-line. Wharram fills the holes with epoxy, and drills out if replacing. We prefer shouldered screws through the line, just in case, so we can do and redo.

This system is absolutely quiet (the line cushions all moving parts), with no metal to fatigue. Since it's rolling, as the rudder works, rather than sliding, there's almost no friction. LUNA's line was looking great after 12 years! If there ever is a problem, it costs a few bucks for more line.

One variant we saw was alternating hinges of heavy webbing, crossing from one side, between rudder and post, to the other. All the advantages, with possibly easier attachements and less initial work (no holes to drill and fair).

*****

When laying rudders out, I usually just eyeball it. There are several theories as to how much to count toward a boat's balance, how big they should be, how deep, what shape.  But looking around traditional designs, the variation is huge, and all seem to steer the boat.

If anything, I would err on the large size. You can always cut it down. You can't have too much steerage, and the downside consequences of too large a rudder - even among optimal theorists - aren't drastic. You can, on the other hand, have too little, and that's a problem!

One consideration is the angle of the rudder post. If raked aft (traditional, and our preference), the rudder will want to swing to center. This means, all things being equal, the boat will tend to go in a straight line when you let go of the tiller. If vertical, it's neutral - less help, though when making way it will tend to center. If raked forward (reverse transom), it wants to flop outboard - a true pain in the neck.

So pool your options, build your rudder and set your course!


15 comments:

  1. A good post full of good ideas. I built a Wharram tiki 31 some 25 years ago now and the rudders were fixed in that manner. It was a bit fiddly to make but it did work extremely well, no play, no noise. A system I cetainly would use again. If memory serves, the lines were 5 or 6mm polyster. It was cheap, efficient and easy to make.

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  2. Yeah, thanks: gotta lace Lunas rudder back on in April. Didn't take a pic before I cut the last bit off so have been wondering how to do it. Considered special steel hinges but off that finally and back to the lacing on.

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  3. Hi Dave, A question... Do you have rudder cheeks on both sides of the rudder blade, or only on one side with a big bolt doing the work, it seems like a simple way to go?

    You are so right on the importance of a big rudder, I sailed a few dogs with small rudders that were turned into thoroughbreds by increasing the rudder size and balance, more control in all conditions and much faster.

    As an experiment I added a small delta shaped wing to the bottom of my rudder and she feels a lot happier in strong winds, and more responsive in light airs. Now she will not round up in a gust, unless I let her, whereas before a big gust could cause her to round up unless I dumped the main.

    Cheers

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    1. Hi Ben,

      We use the one upper piece of the rudder, overlapping the lower blade on one side (I'll call this 'open design').

      That's either no cheeks, or one big cheek, depending on what you call a cheek. I tend to think of cheeks as plates added on to two sides of the main affair, either to reenforce, or, in the case of a kick-up rudder, to house.

      We tried a housed, kick-up rudder on ZOON... It worked okay, but there was lots of friction chafe. It eventually started to rot deep in the housed slot where paint had been worn away (way hard to repaint). Saw that open, bearing plate style, somewhere, and never looked back.

      The one consideration is that the open design only bears at the top or bottom of the plate (the radius) rather than at top AND bottom (diameter) of the housed style. Thus, an open design of equivalent strength should have a bearing plate with twice the diameter of the housed version.

      Those plates definitely help... I've seen some housed kick-up rudders that have their cheeks carried low, like a standard, shallow, aft hung rudder, but each half-plated on its respective side. The kick-up (unplated) extends that downward.

      We've considered that sort, but are always finally seduced by the ability to entirely clear the water with the rudder.

      Dave

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    2. Thanks Dave, interesting about the rot, never even thought of that. Just got to get my head around the asymmetric weirdness of it!

      I would guess your fully kick up design would shed kelp reasonably well, and putting plates might on the bottom might not? Is kelp a problem up your way?

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    3. Hey Ben,

      Asymmetry is something I have to brace myself for, even now. ZOON (ex Bolger LONG MICRO) had an off-center mizzen mast. A visitor to the build site walked several times around the boat (which has many odd features), saying nothing. Finally he burst out, "I can accept all of this... EXCEPT that OFF-CENTER MAST!!!" It worked out great, BTW.

      And yes, kelp is common up here (but I wouldn't say a problem... it's DELICIOUS!).

      The KU rudder does shed kelp pretty well, but will bog down when overloaded... it'll kick back far enough that the 'hook' enters the water and starts to pick up weed. It's easy enough to lift and clear it.

      But in heavy weed (and little wind), we tend to lift the rudder clear and steer with the scull.

      We try to move in line with the streaming kelp, and not across it, preferably going with it and not against it. But like the song says, "Ya can't always git whatcha wa-ant!"

      As far as plates go, the main reason we don't add them on the KickUp blade is that the don't stay horizontal if sailing in shallow water. As soon as we 'cock it up' in a shoal zone, the plates become brakes. If we had housing down to below the waterline, we could add plates to that.

      Dave Z

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    4. ha, funny how I can accept the looks of traditional off center hatches and outboards, which are both very dangerous, but part of me is horrified at masts and foils being off center or lopsided, though I fight that part pretty hard... Could the hook on the KU rudder be rounded so kelp slides off easier? I guess I am a bit paranoid, remembering getting tangled up in kelp in the beagle canal, it damn near stopped us dead! We just managed to limp clear of the kelp Forest, and untangled the rudders with a boat hook. Then with much reving in ahead and astern finally we had the prop clear. Nasty, and I was glad it was flat calm and daylight.

      What is that kelp recipe?

      Cheers

      Ben

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    5. Hey Ben,

      OC masts work amazingly well... kind of proa-like.

      I think that hook could be rounded... it would have the advantage of shedding weed when cocked, but would catch weed that managed to ride up and over it (waffle, waffle)... so far, we've left it sharp (tight to the bottom when down).

      Left sharp and rudder down, a loop of weed kicks the blade up, and the weed slides down. Since there's little weed in close and shoal (when we sail with it cocked), we don't catch much on the hook, anyway. So we've kept it so far.

      Lots of ways to prepare kelp... love to pickle bull kelp slices (2 parts vinegar to 1 part water and spice to taste). Or roll the fronds and slice to make 'noodles'... steam 'em and top with anysauce. Or stuff and bake. Or saute with other greens. Or roll dried leaves around rice+ for sushi. Or add to ramen soups. Or...

      8)

      Dave Z

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    6. yeah, gotta re-condition myself and try an OC mast one day. Kelp spaghetti sounds yum. Cheers

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  4. "Shouldered screws"? I build things, and yet I can't say I've heard of them.

    "We prefer __shouldered screws__ through the line, just in case, so we can do and redo."

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    1. Sorry... sloppy term. By 'shouldered' I mean any screw with a portion near the head that's unthreaded (the threads will wear the line). This would include woodscrews, small lag screws, various deck or sheetrock type screws and so on.

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  5. I replaced the kick-up rudder blade on my sharpie a few years ago. I went with an oversized, balanced design, which made steering a lot easier. The blade extends forward a bit to achieve the balance, so ballasting it to keep it from kicking up when underway was not an option. Instead, I rigged a downhaul using a "fool's purchase" with a long, stretchy 1/4" nylon line on a 4-part purchase to hold it down, making it so that the line is the weakest link of the whole system. If I run aground (and neglect to uncleat the downhaul) the line stretches, the blade kicks up, and nothing bad happens. I really should do a proper write-up on this design some day...

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    1. Hi Kollapsnik,

      One element that works well for the 'weak link' is a hook made from a strip of light metal (peened around a rod to fair the crotch). If there's a strong hit, the metal straightens and dumps the line.

      Now that I think about it, maybe a zip tie would work around the line and to an eyestrap?

      Problem is it's difficult to reset. We're playing with a rigid hook mounted on a ply friction plate (friction set by wingnut), and can be reset quickly. Hopefully try it out this season.

      Phil Bolger used sacrificial dowels between the fixed and kick-up parts. About the size of a pencil, they'd just break when forced... a small box was kept handy, and could they can be replaced in a jiffy. That worked pretty well if ya can keep track of the spares! 8)

      Many ways to rig the cat...

      Dave Z

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    2. We're thinking about a downhaul for our new boat (WAYWARD). One thing we tried and worked well on ZOON was a light nylon downhaul pulling UP near the fwd edge of the bearing plate (leverage is the horizontal distance from the pin to the line's attachment point).

      We located a compromise between a strong enough pull with only a little stretch, and a 'spill point' within they nylon's 20% stretch zone.

      It could supply quite a good resistance to kick-up, but if the rudder struck heavy weed or bottom, the nylon would stretch... rotating past the bearing plate's 6 o'clock, it would then relax uphill in the kicked up position.

      Took a little math, trial and error to get right, but then worked like a champ.

      As I recall, we used the retrieval line, but now can't remember how we got that to work. Maybe I'm confusing with the metal strip approach.

      Dave Z

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  6. Hi Dave,
    Can you recall/describe how the webbing was attached on the rudder you saw that used it instead of line?
    Thanks,
    Everett

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