Twin Rudders

[HVYJimmy]

Hi Guys
looking at a boat with twin rudders . it has the propeller in the center .
Pros and cons? I imagine it should steer well when traveling , but would it be disadvantaged in maneuvering in a tight Marina ?


Cheers


Jimmy

[u4ea32]

For nearly all boats, and certainly all cruising boats, twin rudders are a styling exercise. If you dig the style, fine. But recognize its not a good thing, just a stylish thing.

Practically, they are a bad idea and many race boats that had them switched to single rudders. The feel of the helm is generally ruined, more drag, and less control under power as there is no prop wash on the rudder blades.

And since the thing that usually fails with steering is the quadrant, cables, and pulleys, such twin rudders provide no effective redundancy. Worse, because the rudder blades are not protected by the keel, and there are two of them, you have a MUCH higher probability of rudder blade damage, and of the rudder ripping a big hole in the bottom of the boat.

If you have a boat with an EXTREMELY wide ass end, then it might be useful to have such rudders, but note that many race boats fit this description and today almost none (besides IMOCA and Mini 6.50) use twin rudders. A decade ago, perhaps, but many of those have been converted back to single rudders at great expense.

While wide sterns are the current fashion, and do result in the maximum interior volume that will fit into a marina slip, it is a lousy shape for motion at sea, and especially bad for performance: the increase in wetted surface and displacement is significant, and two rudders makes this even worse.

Again, you might see some race boats with very wide sterns, but that is to achieve maximum stability within a box rule with a large number of crew. Simply inappropriate for cruising.

But the do sale well, even if they don't sail well. Much easier to sell such a boat at a boat show. They seem like the house you left when you drove to the boat show.

As you can guess: personally I would take a pass, and look for a more suitable yacht.

[chrisr]

a major problem with twin rudders (not mentioned above) is their tendancy to pickup weed, ropes n other junk. single rudder is tucked behind the keel and gets some protection

on the other hand, twin rudders mean more control as the leeward rudder is well immersed and still nearly vertical

on balance imho the inherent complexity is not something you want on a cruising boat

cheers,

[slug]

Originally Posted by HVYJimmy

Hi Guys
looking at a boat with twin rudders . it has the propeller in the center .
Pros and cons? I imagine it should steer well when traveling , but would it be disadvantaged in maneuvering in a tight Marina ?


Cheers


Jimmy

Twins need a much larger turn circle so they are clumsy in port

The reason you use twin rudders is sailing characteristics

The leeward rudder is very efficient

To boat tracks better and as a result autopilots are more effective

Twin Rudders For Blue Water Cruising | Humphreys Yacht Design

[Mag3]

well put.

there are some good reasons to have them. The vanity part spoken of above is the dual steering stations... that's the crazy stuff...

doubles the failure points
doubles the complexity
doubles the electronics usually
takes lots of space...

Originally Posted by slug

Twins need a much larger turn circle so they are clumsy in port

The reason you use twin rudders is sailing characteristics

The leeward rudder is very efficient

To boat tracks better and as a result autopilots are more effective

Twin Rudders For Blue Water Cruising | Humphreys Yacht Design

[daletournier]

I wonder how many of the above posters have actually sailed modern boats with twin rudders any decent distance?

Many European boats now have twin rudders and despite what some above say there are some good reasons for it, not just vanity which is a ridiculous comment, liking the look of your boat dosen't mean you are vain!

One benefit is that modern hull shapes are faster, they also surf more. You probably arent going to see a old passport or Han's christian surf in ocean swells at 12 knots +.

Now, my not so radical shaped hull ,but much more modern hull than the boats above will surf at decent speeds, sometimes in the mid teens,, one of the downsides of surfing is you do at times come off a wave a little wrong and the rudder isnt able to bite as well as you like due to the heel, this is when twin rudders are great. The leeward rudder becomes more effective giving you greater control. The older hull shapes dont really benefit from this as they dont all surf as well, they often have fuller keels, theres always trade offs, choose the tradeoffs that you prefer.

Twin rudders are a natural part of evolving hull shapes. These modern hulls sail better and arent more uncomfortable than older boats, as guys with old boats will have you believe, often due to their greater form stability they are more comfortable.

Like all things ,boat design has evolved and some dont like change.

[daletournier]

Originally Posted by Mag3

well put.

there are some good reasons to have them. The vanity part spoken of above is the dual steering stations... that's the crazy stuff...

doubles the failure points
doubles the complexity
doubles the electronics usually
takes lots of space...

How about redundancy? My twin wheels have separate cables, chains etc, therefore if theres a cable failure I stil have a whole other wheel...hows that a bad thing, crazy thing or ridiculous!

[daletournier]

Originally Posted by slug

Twins need a much larger turn circle so they are clumsy in port

The reason you use twin rudders is sailing characteristics

The leeward rudder is very efficient

To boat tracks better and as a result autopilots are more effective

Twin Rudders For Blue Water Cruising | Humphreys Yacht Design

Before I posted with my "leeward rudder is more effective, particularly when surfing" I hadn't read your post...so yes I obviously agree, it's a big improvement in sailing characteristics having twin rudders particularly with modern cruising hulls.

My next mono will have twin rudders with a bow thruster.

[daletournier]

Originally Posted by u4ea32

For nearly all boats, and certainly all cruising boats, twin rudders are a styling exercise. If you dig the style, fine. But recognize its not a good thing, just a stylish thing.

Practically, they are a bad idea and many race boats that had them switched to single rudders. The feel of the helm is generally ruined, more drag, and less control under power as there is no prop wash on the rudder blades.

And since the thing that usually fails with steering is the quadrant, cables, and pulleys, such twin rudders provide no effective redundancy. Worse, because the rudder blades are not protected by the keel, and there are two of them, you have a MUCH higher probability of rudder blade damage, and of the rudder ripping a big hole in the bottom of the boat.

If you have a boat with an EXTREMELY wide ass end, then it might be useful to have such rudders, but note that many race boats fit this description and today almost none (besides IMOCA and Mini 6.50) use twin rudders. A decade ago, perhaps, but many of those have been converted back to single rudders at great expense.

While wide sterns are the current fashion, and do result in the maximum interior volume that will fit into a marina slip, it is a lousy shape for motion at sea, and especially bad for performance: the increase in wetted surface and displacement is significant, and two rudders makes this even worse.

Again, you might see some race boats with very wide sterns, but that is to achieve maximum stability within a box rule with a large number of crew. Simply inappropriate for cruising.

But the do sale well, even if they don't sail well. Much easier to sell such a boat at a boat show. They seem like the house you left when you drove to the boat show.

As you can guess: personally I would take a pass, and look for a more suitable yacht.

And they dont roll gunnel to gunnel ddw like the hull shape you prefer.

[Fore and Aft]

I completely agree Dale. We had twin rudders on our yacht. She sailed like she was on train tracks when that leeward rudder was vertical. But coming or leaving the marina without a bow thruster was a nightmare. Two years we had twin rudders and then one broke when we accidentally run aground. That did not stop us cruising for another week, after much debate we installed a single swing up rudder. Now in the marina we go where we want at any speed. If our yacht was a fixed keel I would have installed a bow thruster.
As for the wide stern, I am not smart enough to argue there disadvantages. But considering for 80% of the time we are not sailing I am happy to spend the other 20% of the time dealing with the design faults of a wide transom.
Dale I think you are wrong about evolving hull shapes. I swear when I was in Hong Kong maritime museum last year they had models of old junks with twin rudders.
Cheers

[daletournier]

Originally Posted by Fore and Aft

I completely agree Dale. We had twin rudders on our yacht. She sailed like she was on train tracks when that leeward rudder was vertical. But coming or leaving the marina without a bow thruster was a nightmare. Two years we had twin rudders and then one broke when we accidentally run aground. That did not stop us cruising for another week, after much debate we installed a single swing up rudder. Now in the marina we go where we want at any speed. If our yacht was a fixed keel I would have installed a bow thruster.
As for the wide stern, I am not smart enough to argue there disadvantages. But considering for 80% of the time we are not sailing I am happy to spend the other 20% of the time dealing with the design faults of a wide transom.
Dale I think you are wrong about evolving hull shapes. I swear when I was in Hong Kong maritime museum last year they had models of old junks with twin rudders.
Cheers

Those chinese, ahead of their time!

I'm not even in the" big cockpit is a liability at sea camp", not only is a big cockpit more comfortable at anchor , it's also more comfortable during a long ocean passage!
We head off next week to Tahiti, approx 3,200nm with 3 onboard, I guarantee you that not once will any if us say "I wish the cockpit was smaller".

And in regards to it being a liability if you cop a wave ,I disagree with this as well. I've filled the cockpit 3 times, alot of water, each time due to a partially open transom the water disappeared very quickly, much quicker than if I had a couple of scuppers.

The most comfortable thing about a modern hull is "you spend less time at sea"

Btw ,if you have a remote vhf mike in the cockpit and it says "submersible " ,they're lieing..... I know they dont like floating..lol

[Misbehaving]

Listen to Bob Perry in his recent Sailing Anarchy interview, newer type of designs are better than old slow double enders with full keels. As explained above, there's a reason why double rudders are more common, it's due to the hull design.

[slug]

Originally Posted by daletournier

Before I posted with my "leeward rudder is more effective, particularly when surfing" I hadn't read your post...so yes I obviously agree, it's a big improvement in sailing characteristics having twin rudders particularly with modern cruising hulls.

My next mono will have twin rudders with a bow thruster.

Everything is a compromise

The fastest hull will always be the narrowest hull . The issue with narrow hull is stability ... they need lots of ballast . This makes for a heavy boat

To overcome the ballast issue you add form stability ...beam

A boat with much beam aft can’t sail with a single rudder on centerline

As the beamy boat heels , it’s rudder comes out of the water and is no longer effective . The rudder must always be wet

To overcome this you go with twin rudders ... a lightweight boat with high form stability and good rudder control

It’s also a compromise

A beamy boat , one who substituted beam for keel ballast has very much wetted surface ... in light wind and choppy seas they stick to the water like a suction cup . It’s common to artificially heel a beamy boat up to 10 degrees to leeward ... shift water ballast, crew weight ... In light wind , to reduce wetted surface

Also Light boats... beamy boats .. have great interior volume , but they don’t like to be overloaded . Once the transom edge is submerged the hull sticks to the water like glue ...slow

Modern, beamy boats are for special people who can cruise and obey the design rules

I believe the better design choice is the middle ground ....moderate beam, moderate displacement , moderate draft , single rudder


He’s

[Snore]

To the OP----

When I was doing charters there was one boat in the fleet that had twin rudders. So I regularly got to compare the characteristics of single vs twin rudder.

Yes the twin rudders seemed to track nicely. When moving forward, at speed, she seemed to turn as tight-if not tighter than the single rudder boats.

Slow speed handling required different skills. On modern boats (and most older ones) the prop wash (thrust) is directed at the single rudder. Therefore, from a standstill, if you put the rudder hard over and put the boat in forward gear, the boat will turn in the desired direction. With a twin rudder boat, this doesn't happen. From a dead stop, rudder hard over and engine placed in gear-The boat will not start to turn until there is enough headway for the rudders to have an effect. The only way to compensate for this is a bow thruster. How often is this an issue? In my case everytime the vessel was taken out of her slip. It could also be a factor when waiting for an opening at the fuel dock, picking up a mooring ball, or a bridge opening. Is it a deal-killer? Nope!


If I was counseling someone looking at a double rudder boat, my recommendations would be

1. be sure the thruster is the largest size recommended by the manufacturer. If you are going to need the thruster, the last thing you want is for it to have marginal thrust or overheat.
2. don't hesitate to use the thruster! But do so in moderation. 3)on many boats if the forward water tank is empty and the midship tank is full, the thruster will capitate. Test the boat at the dock so you know if this will happen - and avoid doing so.
3. on many boats if the forward water tank is empty and the midship tank is full, the thruster will capitate. Test the boat at the dock so you know if this will happen - and avoid doing so.

Other posters have accurately captured the other positives and negatives.

[daletournier]

Originally Posted by slug

Everything is a compromise

The fastest hull will always be the narrowest hull . The issue with narrow hull is stability ... they need lots of ballast . This makes for a heavy boat

To overcome the ballast issue you add form stability ...beam

A boat with much beam aft can’t sail with a single rudder on centerline

As the beamy boat heels , it’s rudder comes out of the water and is no longer effective . The rudder must always be wet

To overcome this you go with twin rudders ... a lightweight boat with high form stability and good rudder control

It’s also a compromise

A beamy boat , one who substituted beam for keel ballast has very much wetted surface ... in light wind and choppy seas they stick to the water like a suction cup . It’s common to artificially heel a beamy boat up to 10 degrees to leeward ... shift water ballast, crew weight ... In light wind , to reduce wetted surface

Also Light boats... beamy boats .. have great interior volume , but they don’t like to be overloaded . Once the transom edge is submerged the hull sticks to the water like glue ...slow

Modern, beamy boats are for special people who can cruise and obey the design rules

I believe the better design choice is the middle ground ....moderate beam, moderate displacement , moderate draft , single rudder


He’s

Absolutely, everything is a compromise BUT some compromises are better than others.

I've said this in other threads, this forum is very USA eccentric, if it was european centric you'd often see very different comments, Europeans have not only accepted modern naval architecture, they've fully embraised it. Its US cruisers that are stuck in the "old is better" think.

As I said earlier, many that have opinions on modern boats , boats that have twin rudders, inmast furlers etc have never sailed them therefore they actually dont know if they are comfortable or not.

I used to refer to the "he has a old Bob Perry mentality " still stuck in the glory days of made in Tawain .....I'll never say that again now that I read Mr Perry is all for modern hull design and twin rudders.....looks like I had a opinion that was outdated time to change it.