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post #1 of 89 Old 02-01-2008 Thread Starter
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Skeg hung rudders

We've all heard the mantra about skeg hung rudders protecting the rudder. Some recent comments from Jeff, I believe, have caused me some thought on the matter. Is that a really valid advantage or just a shibboleth. Sort of like the perception that one could not have a fin keel for offshore work, until the Cal 40 came along and obsoleted the full keelers in offshore racing?

My own perception is inclined to think that, in a fin keeled boat, one is most likely to strike or snag an underwater object with the keel about 99% of the time before ever getting to the rudder. And most all transom mounted rudders have done without a skeg since time immemorial as well.

Thoughts?

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post #2 of 89 Old 02-01-2008
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post #3 of 89 Old 02-01-2008
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Good question Sway,

When we chose our current boat we were looking for a modified fin keel with a skeg hung rudder because that was a desireable trait by concensus opinion. Your observation that most collisions will be on the keel also makes sense but bouyant logs may have the ability to to bang the rudder on the bounce. My common sense tells me that a skeg hung rudder would seem to be sturdier just having that second reinforcing pivot point down low and that it would help take a lot of wear off the upper bearing surface. Our current boat sure is a lot less manueverable than our previous spade rudder boat through.

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Last edited by erps; 02-01-2008 at 11:04 AM.
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post #4 of 89 Old 02-01-2008
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I missed Jeff's comments, but PROPERLY designed I have few qualms about the structural integrity of spade rudders for coastal or even offshore sailing. But in recent years I've noticed an increase in reports of spade rudder failures from boats sailing off-shore. So due diligence is the key if you plan to go off-shore with one, to make sure it is a sound design.

The responsiveness of a well balanced spade rudder is a pleasure, especially for daysailing or racing, and docking under power (particularly in reverse). But on longer trips it can grow wearisome and can be more work for the crew or an autopilot/windvane. They do not generally want to steer straight of their own accord, necessitating a fair degree of attentiveness at the helm.

As an all round compromise, I prefer a skeg-hung rudder, with the prop in an aperture: For the protection it offers from collision with floating debris. For it's tracking ability. For it's resistance to snagging pot warps.


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Skeg hung rudders tend to track straight with very little helm input. On our boat, we can walk away from the helm without even tightening down the clutch and the boat will hold it's course long enough to mind a sheet or traveller, or duck below to grab gear. If we lightly tighten the helm clutch we can go forward to tend a sail. For longer periods, our autopilot (when the d*&@ thing works!) doesn't have to work very hard to keep the boat on course.

We pretty well sail through the Chesapeake crab pots without worry (we don't deliberately run them over, but don't get worried about doing so either). Having snagged pot warps on both spade rudders and bulb keels, it's not something I want to deal with when I have a boat load of kids aboard.

Sure there are downsides to the skeg-hung rudder. More wetted surface area (drag). They do not generally steer nimbly in reverse. They usually are not balanced like a spade rudder, so they do require more effort to turn (but with the mechanical advantage of a wheel it's less noticeable.) However, it is this lack of balance that makes them hold their course with little input, so it's a trade-off.

Also, it IS possible to design a balanced skeg-hung rudder, if that is an important priority in the design brief.

_____
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post #5 of 89 Old 02-01-2008
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Billy Ruff'n has a fin keel and spade rudder. The hard things we've hit struck the keel first and, fortunately, never damaged the rudder. We have had lobster pot warps get fouled up in the small slot at the top of leading edge of the rudder. That probably wouldn't have happened with a skeg hung rudder. If I had built the boat (I'm owner #2), I'd probably ask for a skeg rudder. It wouldn't turn as quickly, but I'd sleep better offshore.

I thing the real risk with a spade rudder is that it breaks off or falls out of the boat. This risk is mitigated with good engineering and design and robust construction, but it's real. I met a couple that lost their rudder 300 miles offshore -- shaft broke, rudder went south, water started coming in. They stopped the leaks but eventually lost the boat. After three days of working the problem in 15 ft seas and really strong trade winds the dog had gone crazy and the wife was not far behind and the skipper (a retired Coast Guard master chief) gave up. They were taken off by the a Columbian tug boat and had to scuttle the boat. Their insurance company sued the builder, in the process discovered lots of other problems with rudders on that model that hadn't been adequately resolved, and recovered the loss. Might have been different with a skeg hung rudder????

P.S. Actually, I sleep pretty well offshore -- the rudder stock is a solid 4" diameter bar of stainless steel with two 5/8 through bolts holding various things in place, where it penetrates the hull the structure is very beefy, two quatrants bolted to the stock. The rudder isn't going anywhere.

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post #6 of 89 Old 02-01-2008
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Having a somewhat longer than normal rudder and keel, I believe I may have something to say.

My present boat, would I cross the ocean with it? No I wouldn't, it would be a short but very demanding crossing.... Would the boat cross the ocean, yes it would, in fact its even good for a circumnav if needed to. A fast one at it...but not a calm one. Not a relaxing one.

Question here is would I do it? NO..my keel and rudder were designed and installed with one objective only. Performance. That is the objective of these designs..performance..

Then you sacrifice sturdiness and ease of operation for weight and speed. If its heavy it aint fast, if its fast, it aint very sturdy...

Mind you, another point...the fact that my boat is sailed hard in conditions where most will be coming home or reefing, at loads you can't imagine, forced us to increase sturdiness without affecting weight, enter the carbons kevlars etc...

So in reality while the boat has a sturdy keel and rudder, the forces it is subjected to are also greater. Either on impact as well as in motion at higher speeds.


With my boat, where I sail I worry not with groundings, but I do worry with fishing pots and other...I have the added problem of a staright keel and a bulb in the end...

I have passed pots that passed the keel and snag the rudder...so with my boat, you really need to see where you're going.

Most pots have the lines at surface or near it, so when they hit, they hit the upper part of the rudder shaft, so its not a big problem.
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Thanks, Alex. A nice primer on the nature of prudence versus defending one's boat choice at all cost.

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post #8 of 89 Old 02-01-2008
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Perhaps a partial skeg with the screw in an aperture is the best compromise. The rudder would be supported much lower and consequently stronger than a spade rudder. It is less wetted area than a full skeg giving performance and the rudder couldo be shaped so that some of it extends forward of the hinge allowing it to be more balanced. I would be particularly good if the portion extending below the skeg was designed to be sacrificial so that, in the event of a major blow, it would just break off leaving the portion above the skeg to steer with. The screw in the aperture would be well protected.

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Which, taken at the flood, leads on to fortune;
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Is bound in shallows and in miseries.
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post #9 of 89 Old 02-01-2008
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ditto what JP said!

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post #10 of 89 Old 02-01-2008
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Quote:
Originally Posted by Giulietta View Post
I have passed pots that passed the keel and snag the rudder...so with my boat, you really need to see where you're going.

Most pots have the lines at surface or near it, so when they hit, they hit the upper part of the rudder shaft, so its not a big problem.
In your case, the saildrive itself acts as a small trap for whatever avoids your keel. But you are right...I had to keep a very good eye out at dawn for those Portuguese net floats...they are all over the place, and I can easily see that snagging one at a high speed could cause a lot of problems.

I also agree that your boat could cross the Atlantic. But your crew would look like they had pissed off Mike Tyson by the end of it.

Having said that, for what is essentially a race boat, it is well-balanced. You can tell by the way it tracks easily and how the various sail sets don't impart a lot of weather or lee helm. It's a little alarming to the uninitiated to see light through the hull beside your seacocks, however. That was my introduction, you'll remember: up close and personal with your defective plumbing!
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