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Captain John
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Discussion Starter #1
I still have the question to ask, I know this might start something so Sorry In advance!


Why is it that everywhere you go there is always a Monohull, like at boat shows, or on TV when they are talking about sailing in general why is it that they never talk about Multihulls! They all talk about how much heal is in sailing but they never talk about the other side of the sailing world! I always say why sail slow when you can sail fast? Life is to short! Can someone clear this up for me, i don't care what boat show you go to if there is a Monohull there should be a Multihull! The consumer is so miss-lead, don't get me wrong the heal is a thrill, but speed is better!;)
 

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Telstar 28
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993 Posts
It really depends on what you're trying to do. Multihulls have some advantages and disadvantages compared to monohulls, and a lot of how severe those advantages/disadvantages are depends on the exact design you're looking at.

For instance, a lot of the charter market catamarans have trouble sailing in light air and have trouble tacking. This is because these boats were designed with the charter market in mind and are fairly low performance designs, with smaller sailplans and relatively high windage to accommodate a floating condo interior.

Compare them to a high-performance cruising catamaran like a Chris White Atlantic 48 or Gunboat 48, and you'll see some serious differences in the design and performance characteristics of the boats.

What are the advantages of a cruising multihull?
  • They sail flatter, which means they're more comfortable in many conditions and often safer. It is harder to fall off a 20' wide catamaran that heels less than 10˚ than it is to fall off a monohull that is 12' wide and heeling 25˚.
  • They're often faster than comparable LOA monohulls
  • They often haver far more cabin space than comparable LOA monohulls
  • They generally have a quicker motion than monohulls—which some people tolerate better
  • They're often designed to be close to unsinkable, since the materials they're made of are often lighter than water.
  • They often can gunkhole and sail/anchor in shallower waters than comparable LOA monohulls due to having relatively shallow draft.
Disadvantages of multihulls:
  • They can't support as much food, water, cargo or equipment as monohulls of equal LOA.
  • They're more weight sensitive than monohulls—when you're carting around several tons of lead, what does a couple hundred more pounds of gear matter. :)
  • Badly designed ones don't sail well in light winds or tack well.
  • Badly designed ones generally don't sail faster than comparable LOA monohulls
  • They don't self-right—however, monohulls sink—this is basically a wash, with an advantage to the multihull, since I'd rather be on a floating upside down boat, than a boat that is right-side up and sitting on the bottom of the ocean
Myths:

There is a long-standing myth that multihulls can't sail to windward or tack well. This is obviously false. The Polynesian islanders explored most of the southern Pacific, and much of it to windward. Also, Dennis Conner's Stars and Stripes pretty much put the whole idea that multihulls can't point and can't tack to bed.

There's also a myth that catamarans or trimarans are less expensive boats than monohulls of comparable LOA. That's basically pure crap. Think about it, you're building two or three hulls and the structures to connect them. A multihull can often be a less expensive boat for a given performance specification, but given the same LOA, the multihulls are generally more expensive, not less.

As an example, my relatively slow cruising trimaran often passes 40' monohull sailboats. The monohull sailboats that are as fast as my 28' trimaran are many times the cost of it. However, compared to some of the boats with comparable LOA, it is probably slightly more expensive.

Then there's the myth that multihulls aren't seaworthy. This is also pure crap. A properly designed and constructed multihull is very seaworthy. If you don't believe that, see the most recent speed records for sailing around the world and see what they were set by. Most of them are set by trimarans. This myth comes from the period when many were home-built, using cheap materials and poorly constructed. Many of the multihulls from that time were and are junk.

Different types of multihulls:

There are basically three types of common multihulls. They are the proa, the catamaran and the trimaran.

The Proa:

The least common of these is the proa. A proa is a boat that consists of a main hull with a single smaller ballasted outrigger. Most do not have a bow or stern in the traditional sense, since the outrigger is kept to windward. The boat is not tacked, but shunted, where what was formerly the bow becomes the stern and the rudder is moved from one end of the boat to the other.

Generally, the proa has a crab-claw sail and the mast, by design is in the center of the main hull. A crab-claw sail looks very much like an oversized lateen rig with a boom added.

The Proa generally has the least cargo carrying capacity of the three designs.

The Catamaran:

Catamarans are boats that have two equal size hulls and a bridgedeck connecting the two hulls. The hulls are often asymetrical mirror images of each other and can have shallow keels, centerboards, daggerboards or a combination of keel and board of some sort. They generally have dual rudders, one on each hull, and in the case of large cruising catamarans, often have dual engines and props.

Catamarans, generally, have the most space of the common sailing designs—monohull, catamaran and trimaran. However, they are weight sensitive, and utilizing all the stowage space they provide can hinder the boat's performance.

Many people are first introduced to catamarans in the form of sport beach cats, like the Hobie Cat. This is somewhat misleading, as the characteristics of a beach sport cat and a cruising catamaran are very, very different. A sport cat has a very high sail area to displacement ratio and is extremely easy to capsize. They go like a bat out of hell, and capsize if you look at them cross-eyed. A cruising catamaran, especially the larger ones have extremely high initial stability and righting moments and are very, very difficult to capsize if sailed properly.

There are basically two different schools of thought for cruising catamarans. The first is like those designed by James Wharram, one of the catamaran design pioneers. Most of his catamarans have little or no structure on the bridgedeck that connects the main hulls. In many cases, his boats are designed with two hulls that are connected together in a somewhat flexible manner. All of the accommodations are in the two hulls.

These boats often have fairly decent sailing characteristics, since they don't generally have the windage created by a bridgedeck cabin. Stars & Stripes was designed much along these spartan lines, but with a very rigid bridgedeck and hull structure for performance reasons.

The other school of thought is the solid bridgedeck design with a cabin over the bridgedeck. This can be taken to extremes that result in very poor performing boats. However, most modern catamarans come from this school of thought. Compromises have to be made to balance performance and accommodation. Things like sufficient bridgedeck clearance, beam, cabin height, draft, and such are all important and need to be balanced depending on the design's intended use.

Some boats have a solid bridgedeck from bow to stern. However, this is less common in modern designs, since having an open design for the forward third of the bridgedeck seems to have significant benefits—so you'll generally see some form of nets or trampolines forward of the main cabin on many more modern designs.

The beam of a modern catamaran is often 50-60% of the LOA. Generally, the smaller the LOA the higher the beam to length ratio is, but there are exceptions, like the Tony Smith designed Geminis, which have a relatively narrow 14' beam. This was done to help allow the Geminis to be kept in a single slip, rather than requiring them to use two slips or an end slip.

The Trimaran:

The trimaran consists of a large main hull and two smaller outriggers. Often, the outriggers or amas, have sufficient buoyancy to float the entire vessel in and of themselves. The hulls on a trimaran tend to be fairly long and narrow, and as such, the trimaran often has the least space of the three common designs, less than monohulls of equal LOA. They also tend to be more weight sensitive than catamarans and monohulls.

The trimarans are basically divided into two categories, IMHO. There are racing designs and cruising designs. The racing designs are often designed to have one of the two amas airborne when under sail. They're often very light and very fast, with little in the way of amenities. The cruising designs generally aren't designed to have any of the hulls leave the water, and are a good deal slower due to the greater wetted hull surfaces.

A good example of the two different design philosophies are the Corsair 28 and the Telstar 28. The Corsair 28 is about the same LOA as the Telstar, but has a much smaller and lighter cabin. The Corsair 28 doesn't have standing headroom in its cabin, and is designed with a portapottie and camping stove as standard accommodations. The Telstar 28 on the other hand has almost 6' of headroom throughout most of the cabin, a head with holding tank, and a proper propane stove/broiler, optional refrigerator and sink. The Telstar also has a bit less sail area than the lighter Corsair 28. One is clearly a racer and the other a cruiser.

Of the cruising trimarans, there are basically two different schools of thought. One, like the older Jim Brown designed Searunners, has accomodations in the wingdecks that connect the main hull to the amas. These boats are far heavier and have much more windage than the more modern designs, like the Chris White Hammerhead 54, which has all the accommodations in the main hull. There are some boats that bridge these two designs, like the Dick Newick designs, which have much smaller solid wingdecks with very limited accommodations and space contained within.

Trimarans, often have better sailing and performance characteristics than do catamarans. They generally sail a lot more like monohulls, since they heel a bit more and can often pivot on their main hull.

Many of the smaller sport designs, like the Corsairs and the Telstar, fold to allow them to be trailerable without disassembly. However, the folding design generally sacrifices interior space.

The beam on most trimarans is about 60-75% or so, but there are extreme examples, like BMW-Oracle's new trimaran which has essentially a square footprint, with a beam to length ratio of 100%. :)
 

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For those who like slips and docks, as opposed to moorings, mutihulls are not really an option. They take up too much darn room.
 

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Telstar 28
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993 Posts
Quorning and M&M both make a nice boat... the GB66 is wicked fast but costs two arms and a leg. The Quorning DF1200 is a nice boat, and only costs a leg. :)
 

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Captain John
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Discussion Starter #6
Quorning and M&M both make a nice boat... the GB66 is wicked fast but costs two arms and a leg. The Quorning DF1200 is a nice boat, and only costs a leg. :)
SailingDog.

You really know your boats, i will never know them like you do! Thanks for all that, but still i think its not right that all you hear about is monohulls.;)
 

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Telstar 28
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993 Posts
I've been lucky enough to get a ride on a Gunboat 48... I'd love to try a GB62 out, but they're just ridiculously expensive. Quorning makes a really nice boat, probably the nicest of the production sport trimarans...but they're priced to match. :) I've spent a long time sailing and researching multihulls. :)
 

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Captain John
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Discussion Starter #8
I have sailed on a F24 and a 27, 28, I really like the whole design of these boats. This is what i grew up on, ABBOTT 33 - SAILBOAT PORTAL (specs. English)

Since we could not stand up on this boat, and the beam was not even 9 ft. Maybe this is why I like the design of the F-Boat! I would like to sail on other multihulls but its hard to do when you do not know anyone, that has one.. I would love to have GUNBOAT, those are so nice looking!
 

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Sailingdog, thanks! Many, many thanks. Multi vs. mono is the ever-returning debate, and it is so nice to see a post that balances and (almost) exhausts the issue from the outset, it saves so much time. If I hesitated for a moment, it was at your statement "The Quorning DF1200 is a nice boat, and only costs a leg." All I can say is, you must have very expensive legs! I travelled all the way to Antibes (France) to view a second-hand DF1200, and it was beautiful, but at more than $650,000 for 40 feet of narrow space I now call it my lucky escape that someone bought it first.

Monos do not dominate all sailing shows, it is location-specific. In the end, choices seem to come down to sailing area, i.e. winds, ports and possibly temperatures.

Perhaps the most common stupid argument is that "they" are faster than "them." The gaps are so huge between a racing tri and what you can get for cruising, and an Open 60 compared with your long-keeler, that you might as sensibly buy a Honda sedan because you heard the Honda F1 wins races.
 

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Telstar 28
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Osmund—

Glad to help. I try to write a fairly balanced post, as I've sailed on both Monohulls and Multihulls, and like some of each.

Under some conditions, I'd have a hard time running down Gui's DC1200, but I could easily pick a course where I'd kick his butt... a few 6' deep sandbars would guarantee that... given his 10' draft. :) I won't have the interior space of Cam's Tayana barge, but could probably run it down in most conditions... :) So, you really have to consider what you're looking for in a boat. For some people, a multihull just won't do...for others it is going to be the best choice.

And yes, my legs are very expensive.... :D
 

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My first ride on a multi was a small Hobie. My friend didn't have much in the way of sailing skills. We were just trying to keep the mast pointed towards the sky:eek: , but we had a great time. That was over 35 years ago.

Zip forward to 92, and I was getting ready to leave S.F. on my 30ft. mono. I took several day sails on Adventure Cat. A 55ft steel day sailor. I had gone several times, and the owner let me drive the boat down the city front, and across S.F. Bay. We had small rooster tails off the sterns at 18 1/2 knots:eek: . I looked at the owner, and told him that when I grow up I am going to get me a cat. I said it jokingly, but it ended up true.

Anybody who sails on a good sailing multi will always appreciate the experience. I have never experienced a problem with getting a berth, or been charged more for the fact of my width. I am part Hawaiian, so I have to be a wee bit prejudice....;) ...i2f
 

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Picnic Sailor
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ImASonOfaSailor,

You will be pleased to know that down here in OZ, the Multi's are getting a pretty fair deal. The last Sydney Boat Show was full of the damned things. I recall several multi's showing, Seawind, Lightwave, Perry and Tasman are 4 that spring immediately to mind i am sure there were others. Seawind particularly nearly had more going on than Beneteau.

SD Great Post. I have often just dismissed Multi's as an option for low to mid budget cruising, I have been looking around however and found a few interesting boats, do you know of or have anything to say about the Seawind 960?
 

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How do multihulls ride vs. mono's?

In waves and/or high winds - how would you compare the riding characteristics of multi's and mono's? Don't have any experience on a multi, other than a Hobie...
 

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Telstar 28
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993 Posts
I'm not surprised, the Aussies and Kiwis have had a fairly strong showing in the multihull contingent. I can't comment on the Seawinds, except in a general way, as I've not sailed on one. They seem to be fairly well regarded boats, not of the floating condo variety, and seem to have fairly decent sailing performance. I've had a chance to walk about a Seawind 1000XL a couple of years ago, and liked the fit and finish of the boat... but didn't get a chance to sail it. If you look at the specifications, and the photos, you'll see that they don't have the massive freeboard of some of the floating condo-type boats.

Here's an image of the Seawind 1000xl and 1160 courtesy of the Seawind site.





and compare it to the Lagoon 380, photo courtesy of Lagoon Catamarans:



and you'll see what I mean about the difference in profiles... the windage on the Lagoon starts with the hulls, which have pretty high freeboard. The windage on the Seawinds is really mainly the bridgedeck, which is pretty far aft. This means that the Seawind will likely tack far more readily than the Lagoon. BTW, the Seawind 1100 is about 32' LOA, the Lagoon 380 and the Seawind 1160 are about 38' LOA.




ImASonOfaSailor,

You will be pleased to know that down here in OZ, the Multi's are getting a pretty fair deal. The last Sydney Boat Show was full of the damned things. I recall several multi's showing, Seawind, Lightwave, Perry and Tasman are 4 that spring immediately to mind i am sure there were others. Seawind particularly nearly had more going on than Beneteau.

SD Great Post. I have often just dismissed Multi's as an option for low to mid budget cruising, I have been looking around however and found a few interesting boats, do you know of or have anything to say about the Seawind 960?
 

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Hello, everyone!

I'm new in general. I have been looking around and found lots saying about stability and speeds but nothing about comparing displacements. So how do the hull designs compare in terms of:
-dead weight to full load weight with same total loading capacity and same power or engine.

If you can link to some papers, that would be great also.
Sorry, if this has been asked before.
 

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Telstar 28
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993 Posts
There are far too many variables in design to allow anything like a simple comparison of displacement to load capacity and engine power...

Even among monohulls, there is a very broad range of weight bearing and performance characteristics for a given displacement. A high performance, foam-cored construction racing boat with a high aspect keel with bulb may have the same displacement as a much shorter LOA full-keel, heavy displacement solid glass laminate boat. However, the former might have greater load carrying capacity due to the greater water plane area and still offer much higher performance.

This is even more complex when you consider multihulls. For instance, on a catamaran, given the exact same hull configuration, one may be a full-bridgedeck with salon and pilothouse and the other could be a open bridgedeck with all accommodations in the hulls like a Wharram design, and the two boats would have very different load carrying and performance characteristics.

Likewise, you could take two identical sets of 34' hulls and build one boat with a narrow beam, similar to an Iroquois or Gemini catamaran, and the other with a much wider beam, and the two boats would have very different characteristics.

Some multihull designs do not tolerate overloading to any significant degree, where others seem to do fairly well when loaded down.
Hello, everyone!

I'm new in general. I have been looking around and found lots saying about stability and speeds but nothing about comparing displacements. So how do the hull designs compare in terms of:
-dead weight to full load weight with same total loading capacity and same power or engine.

If you can link to some papers, that would be great also.
Sorry, if this has been asked before.
 

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I see but isn't structural mass still a good measure?

I saw multihulls are said to capsize forward, as I understand it this is because of the sail and mast. This is rather a mechanical problem and design of a specific ship. For example if the mast is much taller than ship length than it will capsize in the direction of the wind. A solution would be making the ship longer or maybe devide the center hull into forward and aft hulls (diamond).

I wonder are there actually any ships in diamond configuration?
 

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Telstar 28
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No, because weight or mass for the sake of mass is not necessarily a good thing. For instance, making a solid glass hull thicker adds strength and a lot of mass, but you could get the same strength for much less mass by going with a cored-laminate instead of solid glass.

Yes, a heavier boat is often more stable...but if the weight is added in the wrong place, then it can make the boat far less stable. As an example, one of the posters on this forum has a steel boat that has the water tanks located just under the deck. This boat is far less stable than it would have been if the tanks were located just above the keel, since the mass of the water has effectively shifted the center of gravity upwards.

Another example—adding an in-mast furling system adds weight aloft. Say adding one to a boat adds 100 lbs aloft and the mast is 60' high. That means that the 100 lbs. aloft adds about 3000 ft.-lbs. of torque when the boat is rolling. If the keel is 5' below the waterline, and the center of gravity is roughly at the waterline, to offset the addition of this furling system, you'd need to add 600 lbs. of mass to the keel—or the boat will be more tender with the in-mast furling system than it would have been without it.

Also, the scantlings on a multihull are going to be somewhat different than the same LOA monohull, especially since the multihull doesn't have to support the mass of a heavy metal keel.

As for a multihull with four hulls in a diamond configuration... doesn't make much sense at all. First, the load carrying capacity would be much lower than one with two full length hulls (a catamaran) or one with a full length hull and two smaller outriggers (a trimaran). Second, the engineering would be a nightmare, since your dealing with a greater number of forces in more directions than if you have two or three substantially similar hulls—you'd give up a lot of rigidity for very little benefit.

It is pretty easy to badly engineer a multihull... look at the "Tin Can" trimaran. From this top-down view of his concept—it is obvious that David Vann is an idiot.



The crossbeams (or akas) on his trimaran are primarily an "X-shaped" set that meets in the center of the main hull. This means that the amas (or outriggers) have about ten times the leverage, since the crossbeams are about 30' apart at the ama and only about 3' apart at the main hull, and that any twisting force on the boat will likely cause the akas to fail at the point they attach to the main hull—which is indeed the problem Vann ran into.

If you look at most other trimaran designs, the crossbeams are generally parallel and spaced as far forward and aft on the main hull as is reasonable, reducing the leverage the amas have on the main hull to close to one-to-one, as seen in these images:







Finally, I'd point out that many multihull capsizes are actually not capsizes per se but caused by the boat pitchpoling after stuffing the bows into the back of a wave. This is one reason it is generally wise to leave a multihull a bit aft-heavy.

On cruising sized multihulls, pure wind powered capsizes are very rare and generally are caused by human error more than anything else. They're generally caused by the captain and crew pushing the limits of the boat and having her overcanvassed for the given conditions.

Multihulls, unlike monohulls, generally reef for the AVERAGE PEAK WIND SPEEDS, not the average wind. The reason for this is very simple—a multihull CANNOT bleed off much of the excess wind power of a gust by heeling, only by accelerating—so it must have the sails configured for the average peak wind speeds. However, unlike a monohull, a multihull is generally pretty light and doesn't have the inertia to resist accelerating during a gust, so it is a huge disadvantage to have the slightly lower amount of sail area up.

Cruising sized multihulls also have enormous initial stability... an order of magnitude greater than that of a similarly sized monohull. This tends to damp out any but the greatest movement. For instance, in an anchorage, if the wave period is just right, you can often get monohull boats rolling side-to-side a considerably amount. This doesn't happen on cats and tris in the same anchorage as they can't "store" the energy of the rolling waves in their keels.

This lack of inertia often works against multihulls under certain conditions, especially when the conditions are heavy, short period chop with very light winds. The chop tends to stop a multihull because there isn't enough inertia or wind for the multihull to power through the chop.

I see but isn't structural mass still a good measure?

I saw multihulls are said to capsize forward, as I understand it this is because of the sail and mast. This is rather a mechanical problem and design of a specific ship. For example if the mast is much taller than ship length than it will capsize in the direction of the wind. A solution would be making the ship longer or maybe devide the center hull into forward and aft hulls (diamond).

I wonder are there actually any ships in diamond configuration?
 

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Well, I read that post, but my question was for a general understanding of the matter.

Yes, a heavier boat is often more stable...but if the weight is added in the wrong place, then it can make the boat far less stable.
I understand but it's always difficult to do it right in practice.
Finding the center of gravity of your boat... Can I assume it's usually designed to be where the mast is or somewhere along it?

As for a multihull with four hulls in a diamond configuration... doesn't make much sense at all. First, the load carrying capacity would be much lower
Well, if the hulls are used as feet for deck structures like the SWATH....
So they all could be of the same design, and with the big deck structure it's easier to have them rigidly fixed. Virtually a big ship on four feets. I guess it would be very big for better deck to hull structure ratios, and many tension structures.

It is pretty easy to badly engineer a multihull... look at the "Tin Can" trimaran.
Yeah, concentrating the forces you want to reduce in one point is counter productive. :laugher

Finally, I'd point out that many multihull capsizes are actually not capsizes per se but caused by the boat pitchpoling after stuffing the bows into the back of a wave. This is one reason it is generally wise to leave a multihull a bit aft-heavy.
I also read in the wikipedia about that but somehow I don't quite get that bit.
Is there a visual explanation around?

However, unlike a monohull, a multihull is generally pretty light and doesn't have the inertia to resist accelerating during a gust, so it is a huge disadvantage to have the slightly lower amount of sail area up.
This is similar to vessels being to fast and lift off, too. I would imaging adding controlable hydrofoilers/wings to increase downward force for increased resistance in bad sea may help.
Or maybe watertaking bags underwater for increased mass but with no boyancy (or the reverse...maybe not). Don't mind my random ideas.

Cruising sized multihulls also have enormous initial stability... an order of magnitude greater than that of a similarly sized monohull. This tends to damp out any but the greatest movement.
How about underwater control surface. (Let's ignore port draft restrictions)
Hmm, reading all this I have the impression that ship technology isn't as advanced as aeronautics yet. But then aeronautics get lots of development money.

Btw. thanks for all the insights.
 
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