Is external rudder a good idea? - Page 3 - SailNet Community
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post #21 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

I too don't understand how a transom hung rudder relates to weather helm

Surely that is a function of the force exerted by the sails and the resistance of the keel and rudder.

Putting the rudder further back on the transom increases it's leaverage compared to an inset rudder, so the force required to move the tiller should be less. I think anyway.

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post #22 of 57 Old 07-04-2013 Thread Starter
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Re: Is external rudder a good idea?

Thank you all very much for the input, it was of great help.
I will allow my self to summarize the different opinions, if another kind soul has the same question, and comes across this thread.

1. It is an advantage with one less hole in the boat to worry about
2. Provided that the rudder-mounts are properly sized (as with any ruddertype), it is a completely safe setup
3. A lot of very seaworthy (and "blue water") boats has this setup
4. Weather-helm is not related to the way the rudder is mounted
5. It might be a challenge to mount an outboard motor if so desired
6. A lage wave crashing from behind, could induce higher stress to the ruddermounts
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post #23 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

7. In an anchorage or marina it is also a bit more vulnerable to getting bashed by another boat, et cetera.

8. If you pay slip/moorage fees based on the length of your boat it will cost you a few more bucks/month.

Never forget them. Do something to prevent it from happening again.
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Last edited by SlowButSteady; 07-04-2013 at 03:11 PM.
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post #24 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

Quote:
Originally Posted by krisscross View Post
Transom mounted rudder makes it harder to steer (especially in strong wind when going upwind) compared to all other types of rudders. That can be counteracted to some degree by reducing sail area and having a long tiller. I have a 20 foot boat with transom mounted rudder (Mirage 5.5m) and that is my observation. I made a longer tiller for it, which was a very easy job. Some people make an extension to their regular tiller, which they put on only in rough weather, so there is more room in the cockpit.
Certainly the helm may feel "heavier" on an outboard rudder, but that is purely a result of the unbalanced nature of the rudder. Some would prefer to say the outboard rudder has more "feel". Weather helm is a completely different problem. Weather helm is when excessive rudder ANGLE is required to keep the boat from rounding up. It has nothing to do with whether the rudder is transom mounted or not. It has everything to do with sail trim, rig tune, heel angle, etc. If anything, theoretically, a transom hung rudder would be more powerful than the same rudder hung under the boat because it is a greater distance from that fulcrum that is the keel so it provides a greater mechanical advantage. (Of course there will be those that would argue that the outboard rudder loses efficiency because it doesn't have the bottom of the boat providing an "end plate" effect.... but we won't go there!)

There are a great many high performance boats that use outboard rudders, and I can guarantee you that they don't suffer from any kind of weather helm inherent to the rudder design! Look at the J-24; if anything they suffer from chronic LEE helm and they have outboard rudders!

More practical considerations:

My last boat was a race boat with an outboard rudder, and that allowed me to remove my rudder so that I didn't have to put antifouling on it. I just stowed the rudder below! If your rudder gets damaged, you can remove it for repair with the boat in the water.

If your rudder gets fouled with seaweed or a crab trap line you can easily see it and clear it. On a rudder hung under your boat the rope could get jammed between the top of the rudder and the hull, requiring a swim to clear.
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post #25 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

Quote:
Originally Posted by Morild View Post
6. A lage wave crashing from behind, could induce higher stress to the ruddermounts
That's a fallacy based on the stern supposedly protecting the rudder from behind. Unless half your stern is dragging in the water, a large wave crashing from behind will put just as much stress on an inboard rudder except that the stresses aren't visible from the cockpit and are transmitted into the rudder tube instead (not "felt" at the tiller so much).

Because it isn't protected by the stern, a transom-mounted rudder is certainly more likley to be damaged if you're not careful whilst reversing into a marina pen or when launching off a trailer (in which case you'd damage your stern instead), but, as ST pointed out above, for most people the advantages of being able to more easily fix a transom-mounted rudder outweigh any apparent disadvantages created by the location.

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Last edited by Classic30; 07-04-2013 at 07:54 PM.
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post #26 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

Al my designs have out board rudders as I consider it the only intelligent place to put a rudder on an offshore cruiser. As the Pardys pointed out "They put rudders on the back of a plane instead of the middle for good reason."It drastically simplifies self steering and inside steering, or autohelm steering via a trimtab on it's trailing edge, making such systems exponentially stronger than any of the options available for inboard rudders.
I see no real advantages for an inboard rudder on an offshore boat ,and can't understand why so many designers make that obvious mistake.
Lack of offshore cruising experience among them may be one reason.
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post #27 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

I was reading about Black Feathers the other day, the Cal 20 that successfully sailed the solo transpac in 2008.

His rudder failed a good ways out (fiberglass fatigue, supposedly) and he was able to replace it easily with some wrangling. He pulled the broken rudder out of the gudgeons and was able to wrestle the old wooden one back into place, allowing him to continue on as normal. The process didn't sound easy, but it was accomplished without a jury rig or serious issue.

Granted, the Cal 20 is basically a big dinghy and most of the larger boats I've looked at with outboard rudders would be substantially more challenging to repair at sea if something failed (e.g. Flicka, Westsail). It still seems to me that, even with those boats that have massive rudders in place off the transom, if something failed, the repair would be easier than dealing with something run through the hull.

It's also easier to inspect, which is a big plus to me.
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post #28 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

The outboard hung rudder can have one serious fault: at higher speed and when a boat is well heeled over such a rudder can easily 'ventilate' or 'suck air down along the lower pressure side of the rudder' and the rudder will/can lose ALL control depending on the amount of ventilation.

Couple this with a helmsman who doesnt understand 'weather helm' requiring more rudder angle to overcorrect for adverse helm; include the vulnerability to 'ventilate' ........ and you can expect an unexpected 'pirouette' / unexpected rounding up as a worst case scenario in your future.

Stern hung rudders can easily 'ventilate'.
Totally submerged rudders have great difficulty in 'ventilating'.
Advantage - submerged rudders
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post #29 of 57 Old 07-04-2013
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Re: Is external rudder a good idea?

Quote:
Originally Posted by Mechsmith View Post
Weather helm is a function of how the rudder is hung. If the extended line through the center of the hinges goes through the effective center of of the rudder there will be no weather helm.
This statement is just wrong. No recognition of the how the center of effort of the sails, keel area, etc. affects weather helm. It has almost nothing to do with the relationship between the center of the rudder area and the hinge location.
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post #30 of 57 Old 07-05-2013
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Re: Is external rudder a good idea?

Quote:
Originally Posted by RichH View Post
The outboard hung rudder can have one serious fault: at higher speed and when a boat is well heeled over such a rudder can easily 'ventilate' or 'suck air down along the lower pressure side of the rudder' and the rudder will/can lose ALL control depending on the amount of ventilation.

Couple this with a helmsman who doesnt understand 'weather helm' requiring more rudder angle to overcorrect for adverse helm; include the vulnerability to 'ventilate' ........ and you can expect an unexpected 'pirouette' / unexpected rounding up as a worst case scenario in your future.

Stern hung rudders can easily 'ventilate'.
Totally submerged rudders have great difficulty in 'ventilating'.
Advantage - submerged rudders
That's complete rubbish, Rich.. C'mon, surely you know that.

Any modern boat that is is "well heeled" will have enough of the rudder exposed to 'ventilate' and potentially broach very soon thereafter if the helmsman isn't careful. You don't have to compete in many races or look in many books to see that.

If a single-rudder boat is so badly set up that the rudder doesn't "ventilate" to some extent at full heel, then dragging the tail around a racecourse won't win you any races either.

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Last edited by Classic30; 07-05-2013 at 12:51 AM.
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