Rudders, outboard or inboard

[Sailormann]

It would seem to me that a cruiser's first considerations should be simplicity and safety, not some “almost always more efficient” argument that really means nothing to a fully load cruising boat.

I think the key here is the "it would seem to me" phrase. There are a lot of people out there cruising who can afford to buy, insure and maintain boats with a lot of complicated, effort-saving systems. Who are we to say they are wrong...it's nice having hot water to shower whenever and for as long as you want to...

[Brent Swain]

Why did everyone believe the world was flat? Did their believing make it so?
I've yet to hear a valid reason for putting the rudder inboard on an offhsore cruising boat. I've read a lot of books on yacht design , being a designer myself for the last 32 years.
Donald Street asked many designers why they would rake a rudder post aft , when tank tests have all shown that it drastically reduces efficiency and reduces the stall angle ,and the only answer he got was "It looks fast and sells boats." I believe this is the main reason rudders on cruising boats are mostly inboard. Style over substance sells boats. It's naive and gullible to assume that because something is more commonly done, there must be a good reason for it. There must have been an equally good reason for everybody to believe that the world is flat, so it must have been true.
Having an outboard rudder lets me steer with a trimtab, so light that a six year old can steer in a big following sea, with only little finger pressure on the jog stick. A tiny auto pilot can do the same . So who needs a wheel?Steel tillers don't break.
Its like saying" cars are fine , but I need a buggy so I'll have something to tie my horses to."
Brent

[Brent Swain]

Inboard rudders also sell a lot of oversized ,power demanding autopilots , and the equipment to power them,and very expensive windvane steering systems so why wouldn't they put rudders inboard , for profit reasons.The incentive is obvious.
Brent

[rtbates]

Originally Posted by Louis Riel

I began cruising with an inboard rudder . I sailed a tank tested boat to New Zealand singlehanded, broaching continuously all the way.There I moved the rudder six feet further aft ,without changing the balance in any noticeable way. It became far more efficient.
Spending an extra ten thousand dollars on something which is far more complex and fragile, with no real benefits is stupid , period. An ouboard rudder is far stronger than any inboard rudder. You can make the pins as thick as you want with no disadvantage, and the rudder head can easily be made much stronger than any shaft you could fit inboard . Exposed ? To what? Is anyone suggesting that a piece of steel square tubing making up the rudder head ,6 inches by 2 inches can be dammaged by a dollop of water 6 inches by 3 ft? How much pressure does a 6 inch by 3 ft dollop of water exert? Not enough to dammage steel. The position of the rudder blade makes it no more exposed that one under the counter , unless one believes that what you can't see the sea can't see either.
Is a monitor hung off the stern less vulnerable than a steel rudder head of an outboard rudder? Hard to imagine anything flimsier than a monitor when it comes to impact resistance.
Yes I do lock my trimtab when docking. The locking mechanism lets me fine tune it for absolutly no helm.The further aft the rudder is the more efficient it, is especially when reversing. Further aft means more leverage on the hull. I believe tests which show any increased efficiency of inboard rudders may be tersting the rudder in isolation without considering the extra leverage of their being further aft.
I can easily unship my rudder for a paint job while the boat remains in the water.
The area of the trimtab going the opposite direction does reduce the effectiveness of the rudder by the equivalent of reducing the rudder area by the area of the trimtab, but that's a small price to pay for the simplicity and super reliability of trimtab steering.The reduction is negligible.
I've slid backwards down many a steep swell in 9 pacific crossings over 35 years . No problem .It only pushes the rudder post against the transom ,harmlessly.Only the bottom pin takes the load ,and that's overbuilt.
When I read in "Log of the Mahina", about the skipper having to tie a reef in the main ,almost permanently I lookd at the transom rake , perfect for an outboard rudder on a skeg and thought how much simpler that would have made the average Vega.
When I read David Lewis's book "Icebird " I couldn't help but notice how much easier his voayge would have been if he had got rid of that goofy keel attached rudder and put a skeg hung rudder over the stern, with inside steering hooked up to a trimtab.
Brent
Brent

I believe you're confusing efficiency with leverage.

[Seaquesta1]

Originally Posted by Louis Riel

Donald Street asked many designers why they would rake a rudder post aft , when tank tests have all shown that it drastically reduces efficiency and reduces the stall angle ,and the only answer he got was "It looks fast and sells boats." I believe this is the main reason rudders on cruising boats are mostly inboard. Style over substance sells boats. It's naive and gullible to assume that because something is more commonly done, there must be a good reason for it. Brent

If outboard hung rudders are so efficient, and reduce stall angle as you say, please explain why all leading race boat yacht designers place the rudder inboard. These designers live and breath speed and efficientcy and spend millions on researching all areas of yacht performance, Im sure that if outboard rudders were the panacea that you state, then they would have adopted it. There is nothing complicated or expensive with my inboard tiller driven rudder.

From a safety point of view, Ive had the stern on my boats clipped by other boats on several occations (or when not paying attention when reversing into marinas!). If id had a transom hung rudder, it would have been damaged, or rendered useless on several occations. Yet my inboard mounted rudder has never hit anything apart from my head when I've been diving.

Your also assuming that inboard rudders are always considerably more expensive! For Petes sake, its a piece of tube with two bearings in it! $100 tops!

[Efraim]

Originally Posted by Sailormann

There are a lot of people out there cruising who can afford to buy, insure and maintain boats with a lot of complicated, effort-saving systems.

I've just been reading about a Hanse 37.1 that sank off the cost of Ireland in 40 minutes due to rudder stock failure. The final report, that you can read here http://tinyurl.com/2tntq7 , makes for interesting reading, it mentions such things as, poor workmanship at Hanse, poor installation of an autopilot, and poor design of the boat itself. It noted that the aluminum rudder stock was roughly finished, the installation of a autopilot was poorly done, and that the boat had no watertight bulkheads.


It's obvious the boat owner had the money to buy such a boat, and could effort to add "effort-saving systems" an autopilot in this case, was probably insured, and who knows maybe the boat was still under warranty, however it turns out that those "effort-saving systems" contributed to the ultimate disaster, who would have thought?

What makes this even more interesting, is that while abandoning ship, the inflatable liferaft failed to inflate!

[Paul L]

What does this statement from the Hnase report mean?
"Aluminium does not have a fatigue endurance limit unlike steel."


Paul L

[Efraim]

Originally Posted by Paul L

What does this statement from the Hnase report mean?
"Aluminium does not have a fatigue endurance limit unlike steel."

From Wikipedia:

Some materials (e.g., some steel and titanium alloys) exhibit an endurance limit or fatigue limit, a limit below which repeated stress does not induce failure, theoretically, for an infinite number of cycles of load. Generally speaking, a steel or titanium component being cycled at stresses below their endurance limit will fail from some other mode before it fails from fatigue. Most other non-ferrous metals (e.g., aluminium and copper alloys) exhibit no such limit and even small stresses will eventually cause failure.

[Paul L]

That's interesting. So does this imply that an aluminium quardrant is doomed to failure at some point?

Paul L

[Efraim]

It means that non-ferrous metals have to used in appropriate situations as well as machined to high standards. The report in the case of the Hanse noted the poor workmanship of the machined rudder stock as a contributing cause to its failure, along with the poor installation of an autopilot system.
There doesn't seem to be much room for error, seeing that the issues in this case were microscopic in nature, nothing a regular visual inspection would have caught.
One can draw his/her own conclusion as to whether aluminum is an appropriate material for rudder stock or rudder components. Personally, I don't think that materials that require extremely close tolerances, or that can't take a little abuse are good choices for cruising sailboats, I would rather have something a little more forgiving.

[Brent Swain]

Originally Posted by Seaquesta1

If outboard hung rudders are so efficient, and reduce stall angle as you say, please explain why all leading race boat yacht designers place the rudder inboard. These designers live and breath speed and efficientcy and spend millions on researching all areas of yacht performance, Im sure that if outboard rudders were the panacea that you state, then they would have adopted it. There is nothing complicated or expensive with my inboard tiller driven rudder.

From a safety point of view, Ive had the stern on my boats clipped by other boats on several occations (or when not paying attention when reversing into marinas!). If id had a transom hung rudder, it would have been damaged, or rendered useless on several occations. Yet my inboard mounted rudder has never hit anything apart from my head when I've been diving.



Your also assuming that inboard rudders are always considerably more expensive! For Petes sake, its a piece of tube with two bearings in it! $100 tops!

Sure there is nothing complicated about your tiller driven inboard rudder , until you try to get a self steering arrangement on it, or an auto pilot big enough to handle the rudder instead of a trimtab, and the power source big enough to power it, or an inside steering method. Then it gets real complicated. Then having inboard rudders on cruising boats get exponentialy more expensive.
Like Donald Street said " trendy rudders look fast and sell boats. That is why they are done.
When you are trying to control a boat in a following sea, leverage is efficiency.
Build them strong enough and they wlil survive the odd ding from another boat etc,.
Leading designers of race boats have been known to rake ruder posts aft , which all tank tests have shown to drasticaly reduce their efficiency and increase the likelihood of stalling. Style over substance is what sells boats and makes them famous. Catalina 27's area good example of a very poorly designed rudder ,grossly unbalanced , done for style over substance priorities.
Brent

[44'cruisingcat]

Originally Posted by Seaquesta1

If outboard hung rudders are so efficient, and reduce stall angle as you say, please explain why all leading race boat yacht designers place the rudder inboard. These designers live and breath speed and efficientcy and spend millions on researching all areas of yacht performance, Im sure that if outboard rudders were the panacea that you state, then they would have adopted it. There is nothing complicated or expensive with my inboard tiller driven rudder.

Obviously all the race boat designers are stupid! As well as every single buyer of a race boat, or ex-race boat, eh Louis? Clearly there is only one boat designer on the planet who is not stupid!

Getting back to reality, one advantage inboard rudders have is that the hull acts as an endplate, helping to stop the rudder from aerating under load. Transom hung rudders under load can aerate, making them less effective. To counter this, a larger area of rudder is required = more drag.

Transom hung rudders are obviously closer to the end of the boat, and closer to the waterline too, so when the boat is heeled heavily there will be more tendency to lift out of the water. Again, to counter this a bigger, deeper rudder would be needed.

These factors do apply more to racing boats, though. For cruising boats transom hung rudders do make sense, but many cruisers are ex-racers, which is why so many have inboard rudders.

[GordMay]

Originally Posted by Paul L

What does this statement from the Hnase report mean?
"Aluminium does not have a fatigue endurance limit unlike steel."
Paul L

Auminum will always (eventually) fail under fatigue* (cyclical stress) loading, whereas (theoretically) Steel will not fail under fatigue loading, provided the stress level remains below the S-N curve.

* Fatigue is a process in which damage accumulates due to the repetitive application of loads that may be well below the yield point.

The significance of the fatigue limit is that, if the material is loaded below this stress, then it will not fail, regardless of the number of times it is loaded.
Materials such as aluminum, copper and magnesium do not show a fatigue limit, therefor they will fail at any stress and number of cycles.
For ferrous alloys such as Steel, the S−N (stress verse cycles to failure) curve flattens out eventually, so that below a certain endurance limit, failure does not occur no matter how long the loads are cycled.

See:

Strength ( Mechanics ) of Materials ~ Engineers Edge
Strength and Mechanics of Materials** -* Engineers Edge
Strength of Materials - Mechanics of Materials - Engineers Edge

[jjt]

In a moderate beam sailboat, the outboard rudder is more efficient because it is far away from the lateral center of effort. This means that less surface in the water creates the same momentum to turn the boat.

In a modern flat beamy sailboat the inboard rudder stays allways in the water (the outboard rudder looses steering surface when heeling, that's the reason why usually these boats have 2 rudders).

Racers designers draw sterns according to fourmula rules. Cruisers designers draw sterns according to sea rules.

It's not valid to generalize about outboard or inboard rudders. Each case should be evaluated in particular. Could be that one design needs an inboard rudder while in other design it's better an outboard rudder.

If we only consider simplicity, maintenance operations and strength, then outboard rudder is by far the winner, it's just not fancy.

[Butterman]

Without having read the other comments, the following is my idea of the various advantages and disadvantages of outboard and inboard rudders.

Advantages of Outboard Rudders:
1) Simplicity
2) Cost efficiency
3) Greater hull integrity
4) Less waste of internal space
5) Greater leverage on keel/turning ability(?)
6) Simpler to repair, replace, and inspect.

Disadvantages of Outboard Rudders:
1) Susceptible to damage from rear impacts.
2) Uses up space otherwise good for swim platforms, wind vanes, etc.
3) Can only be equipped on hulls with closed transoms(?)
4) Less sightly (opinion)
5) Extends overall length of boat without extending usable length.