Torpedo hull

[Hondaen]

Hello :)

I`m a electro engineer, but i`m facinated of marine designs.

Can a marine engineer give me som input/comments? I have toughts of some hull designs, but I lack the knowhow to predict if they have a "life" or not:

1. Torpedo hull design.

Two "torpedos" with propulsion are located 1 meter below water surface. They travel leveled with automatic boyancy systems.

Each of the torpedos have two struts holding up a frame, so persons can ride on the "boat". With this design, waves are minimalized. Will this design give us fast and econimic hulls? :D

2. "Ski" design.

Two long skiis are mounted at each side of a boat. They are twice the length of the boat, maybe longer. Main goal is so rice the boat from the sea and make a vessel that plan. Scnd goal is to lengthen the boat, so it can travel faster in heavy sea, as it "cuts" the amplitudes of the waves.

Ok, sorry my bad english, but what do guys think? :)

[timothy22]

#1 seems to be an excellent idea.
http://en.wikipedia.org/wiki/Small_Waterplane_Area_Twin_Hull

Don't know about #2

[messabout]

One of your Universities, in Norway, has an acknowledged school of naval architecture. One of the teachers is famous for his books, and particularly for vessels of unconventional design. The author is Odd Faltinsen. Perhaps you could contact that college for advice or counsel. ( I hope I spelled his name correctly)

[PAR]

It's much more efficient to skip across the water's surface then bore through under it. Early submarines, where power resources were quite limited, understood this particular trait, doing as much of their passage making on the surface as possible, where they could travel at 2 to 3 times their submersed speed.

The second concept has obvious issues, like docking, boarding and exiting, "tripping", having one "ski" out of phase, strength/weight limitations from a cantilevered set of ski supports, etc.

Hydrofoils are a way of getting the boat out of the water, above the harshness of existing sea conditions and dramatically increasing efficiency. Unfortunately, just like most else in yacht design, they have a negative side to weigh against the other compromises in convoluted concession that eventually develop into a design.

[marshmat]

It's much more efficient to skip across the water's surface then bore through under it. Early submarines, where power resources were quite limited, understood this particular trait, doing as much of their passage making on the surface as possible, where they could travel at 2 to 3 times their submersed speed.
True, to a point.... those early submarines, though, had hulls shaped like those of surface craft, with the ability to submerge being secondary. Since they had to run the diesels to get any kind of range, and so little power was available in electric mode, it was best to design them to run on the surface except when attacking.

Now, the US and Russian navies still refuse to say exactly how fast their nuclear subs can go, or how deep. But it seems to be generally accepted that they're the fastest boats of their size in the fleet, by a fair margin. The catch- they can only go fast when they're submerged, and the surface wave system taken out of the equation. On the surface they suck, but in their natural environment, subs can be shaped for remarkably low drag and no longer have the speed constraints imposed by dragging along a surface wave larger than your ship.

1. Torpedo hull design.
Two "torpedos" with propulsion are located 1 meter below water surface. They travel leveled with automatic boyancy systems.
SWATH, the rather awkward name for this type of hull, is a setup seen now and then for special purpose applications. Our Coasties use them for charting, among other things- with very small waterplane area, they're not very susceptible to wave action and so you get a very stable platform to work from. Unfortunately, it's hard to get the hulls deep enough to get rid of the drag-creating surface wake system, without also introducing excessive draught (thus lots of groundings), limited load carrying ability (because of the small waterplane) and structural complications (many SWATH ships have suffered fatigue damage in the strut-bridgedeck joint because of the enormous moment arm being applied on a very narrow strut). So the stability gains are real, the possible efficiency gains still a pipe dream.

2. "Ski" design.
Two long skiis are mounted at each side of a boat. They are twice the length of the boat, maybe longer. Main goal is so rice the boat from the sea and make a vessel that plan. Scnd goal is to lengthen the boat, so it can travel faster in heavy sea, as it "cuts" the amplitudes of the waves.
So, sort of like a wave-piercing trimaran, with very long, slender amas? That could work..... reminds me a little of the BMW/Oracle America's Cup trimaran, although that thing is designed more to carry a flippin' huge sail than to be comfortable. Make them planing hulls.... that could cause some issues with ride harshness, and I'd question whether that would be the way to go. Since you're already talking long and thin, sticking to displacement mode might give a smoother ride without much of a drag penalty. The annoying and destructive dynamic instabilities PAR mentions would have to be very carefully analyzed. (And I'd hate to see the marina bill for docking the thing.) But it might be neat to see it tried.

[Guest625101138]

Hello :)

I`m a electro engineer, but i`m facinated of marine designs.

Can a marine engineer give me som input/comments? I have toughts of some hull designs, but I lack the knowhow to predict if they have a "life" or not:

1. Torpedo hull design.

Two "torpedos" with propulsion are located 1 meter below water surface. They travel leveled with automatic boyancy systems.

Each of the torpedos have two struts holding up a frame, so persons can ride on the "boat". With this design, waves are minimalized. Will this design give us fast and econimic hulls? :D

2. "Ski" design.

Two long skiis are mounted at each side of a boat. They are twice the length of the boat, maybe longer. Main goal is so rice the boat from the sea and make a vessel that plan. Scnd goal is to lengthen the boat, so it can travel faster in heavy sea, as it "cuts" the amplitudes of the waves.

Ok, sorry my bad english, but what do guys think? :)

You need to decide what you want to do with the boat. Existing boats look the way they do for practical reasons.

SWATH type craft will outperform other displacement craft providing the hulls are deep enough. Typically about 3 diameters deep. The optimium shape has a slenderness ratio of 8.

I built the boat pictured to test viability. The big issue is static stability. The pictured boat was pedal powered and even with the widely spread outriggers it took me over an hour to work out how to mount it. The buoyant "submerged" hull has a powerful tendency to want to get to the surface. If I accelerated at even moderate rate the front outrigger would rise over 2m high until the from of the "submerged" hull was at water level.

The boat did ride like it was on a cushion of air, totally immune to any waves up to 0.4m high.

I learnt about the need for three diameters after it did not perform as I expected and made quite large waves. The main hull was less than 1D below the surface. If it was set any lower I would have needed to wade neck deep to mount it and then try to climb up in some way.

So as Matt points out the concept is sound but there are many issues to resolve satisfactorily. If you google SWATH you can get ideas.

Rick

[Hondaen]

Hello

Thank you for all replys. They where all very informative. :)

Rick: Very interesting project you have. Wish I could have seen it in real life and tryed it myself.

I guessed that it would be a big problem with boyancy. However, I had this idea using electronic microcontrolles to controll the up/down movement of a vessel, by the use of servos and mini fins.

You get powerfull calculation in a very little package, full PID regulation is possible for cheap. Offcourse it is hard to develop and fabricate if you are unfamiliar with theese things, but mayebe it would have worked.

Thanks :)

[Shore_Fisher]

I am looking for a small, transportable, near-shore, fishing boat design. To fit my requirements (2 people, side-by-side fishing, camp on-board) I need a very beamy conventional design that just gets too big to be easily transportable. I'm not interested in high speed, but want the best efficiency I can get.

I was thinking that this type of 'twin torpedo' design, with a flat, 'party boat' style deck well off of the surface may be good for me. If I could design the hulls and sponsons (?-The bits that break the surface and connect the hulls to the deck) in some removable fashion, I may even be able to get a 'car-topper'.

I was wondering whether it is possible to use pumpable water ballast in the submerged hulls to adjust hull depth on the fly. Empty and above the surface for launch/shallow running, and well down under the surface for 'cruise'. I am assuming that this would require the sponson buoyancy to be substantial enough to affect overall buoyancy, but would this size of sponson just negate any benefits of the submerged hulls?

I was also thinking that a height-adjustable deck-to-sponson connection could allow adjustment to accomodate different wave heights and fishing down close to the water.

What does anyone think?

[Guest625101138]

Efficiency and added ballast are inconsistent. The most efficient boat will be the lightest you can make within a given size envelope.

Eliminating reserve buoyancy in the hulls with ballast will make it very sensitive to load shifts. It will have tendency to roll and pitch in the extreme by small movements on the deck.

You also need to set a speed range as your definition of high speed may be different to others.

The most efficient submerged buoyancy is achieved with a single hull having slenderness ratio of 8 and sitting at least 3 diameters below the surface. This can result in intolerable draft. Going to two submerged hulls negates the efficiency benefit. Twin hulls are used to improve ride quality on larger SWATH craft but does not do anything for efficiency.

Rick W

[BMcF]

Hello


I guessed that it would be a big problem with boyancy. However, I had this idea using electronic microcontrolles to controll the up/down movement of a vessel, by the use of servos and mini fins.

You get powerfull calculation in a very little package, full PID regulation is possible for cheap. Offcourse it is hard to develop and fabricate if you are unfamiliar with theese things, but mayebe it would have worked.

Thanks :)

In fact, active micro-processor-based control of pitch, roll and (often) heave is a characterstic feature of all of the most successful SWATH ever built (successful in terms of maximum stability and minimum motions). Nearly all use two forward control fins (canards) and two aft control fins (stablizers).

So your idea has obvious merit..since you basically 'thunk up' what is a very accurate description of many SWATH in service today.

[jehardiman]

1) SSP Kaimalino, circa 1968

http://www.geocities.com/dthigdon/dynamics/ssplift2.jpg

2) HYSWAS Quest, circa 1975

http://www.geocities.com/dthigdon/dynamics/quest.jpg

or RV Triton, circa 2005

http://upload.wikimedia.org/wikipedia/en/3/31/RV_Triton_bow.jpg

[Guest625101138]

John
The reference to Quest is appreciated. This boat is a larger version of what I hoped to achieve. This video shows it in operation:
http://www.youtube.com/watch?v=kRuUtOmMGR0

The initial part with the pedal powered boats show similar problems to what I experienced.

The submerged section is very similar to my submerged section and is probably the optimum for fully submerged operation. In flight it seems closer than 3 diameters to the surface so would make some waves.

My idea was to use the wide set outriggers on foils to provide good inherent static and dynamic stability so I did not need to go to dynamic control surfaces. This aspect was discussed after my initial experience but it adds complexity and more wetted surface.

The main issue for me was the draft but the idea has merit if the load does not change much and there are deep berths and moorings available.

The ride quality is outstanding compared with any other craft with maybe exception of full foil. Also the single hull used on Quest would be more efficient than any other displacement craft. The advantage over foils is that you have something solid and streamline in all planes under the water although it would not have much propensity to climb over solids obstructions.

Rick W

[BMcF]

"2) HYSWAS Quest, circa 1975" uh..make that about 1995, at least. The young engineer on the deck, Danny J., was barely in to high school yet in 1975.;)

[jehardiman]

"2) HYSWAS Quest, circa 1975" uh..make that about 1995, at least. The young engineer on the deck, Danny J., was barely in to high school yet in 1975.;)

I have no idea when that picture was taken, or even when Quest was built, I guessed the mid to late 70's, but the HYSWAS concept pre-dates my Senior Design Study ('83-84) as I went through most of the David Taylor data on HYSWAS and SWATHs from the '60's and'70's at that time. The TAGOS-19 (ordered 1986) class is basicly identical to my design study SWATH because thats what the data converges to. My advisor decided that a nuc sub based HYSWAS was a little out there for a design study.

Edit; OK, Googled it up, earliest HYSWAS paper I could find was 1976 (which seems about right), Quest was built in '98.

[BMcF]

I have no idea when that picture was taken, or even when Quest was built, I guessed the mid to late 70's, but the HYSWAS concept pre-dates my Senior Design Study ('83-84) as I went through most of the David Taylor data on HYSWAS and SWATHs from the '60's and'70's at that time. The TAGOS-19 (ordered 1986) class is basicly identical to my design study SWATH because thats what the data converges to. My advisor decided that a nuc sub based HYSWAS was a little out there for a design study.

Edit; OK, Googled it up, earliest HYSWAS paper I could find was 1976 (which seems about right), Quest was built in '98.

Good stuff. I've worked with the DTRC guys who pulled off the original Kaimalino project. In fact, that was where the first active control system development came from...what we still base ours on today.

HYSWAS was the gleam in the eye of one John Meyer for a very long time before he finally got that demonstrator funded (John believes that everything should have foil lift and done right, never any hull left in the water.:D ) The young fellow in the deck in that pic cut his teeth working with me on SWATH and SES controls before moving on to tackle the HYSWAS control problem with MAPC. They did a fabulous job on the craft.

[Guest625101138]

I have no idea when that picture was taken, or even when Quest was built, I guessed the mid to late 70's, but the HYSWAS concept pre-dates my Senior Design Study ('83-84) as I went through most of the David Taylor data on HYSWAS and SWATHs from the '60's and'70's at that time. The TAGOS-19 (ordered 1986) class is basicly identical to my design study SWATH because thats what the data converges to. My advisor decided that a nuc sub based HYSWAS was a little out there for a design study.

Edit; OK, Googled it up, earliest HYSWAS paper I could find was 1976 (which seems about right), Quest was built in '98.

The video I linked to advises the vessel was factory complete in July 1995.

Rick W

[narf2600]

I too am a computer engineering student and have been thinking of trying to construct a small computer controlled swath boat with automatic buoyancy compensators in the hulls. I’ve read a lot of other threads and was thinking of pm-ing BMcF to see if he would give me advice (thanks for your other post about swaths, very interesting), but I saw this thread and decided maybe it would be more useful to post it here. I’m sure I could handle the controls part but had some questions regarding the hull / design itself.

My dream goal would be to build a very small long range ocean capable boat, I’m thinking slightly smaller than 10 meters. I want to make it as tough as possible for the size, basically a nutshell. How would such a small swath behave? From what I’ve read I believe it would provide a stable ride up to moderate seas, but how would it handle a storm or other undesirable situation? I’ve read other post stating they can’t be made self-righting. It seems as if maybe swaths perform very stable until they are overtaken by waves to the point of capsizing? Any advice/links appreciated, there is very little info I can find about this topic!

[BMcF]

The smallest manned SWATH I ever 'played' with was built by SOS and had one of Doc Higdon's last analog computer stabilization packages installed. It was 34' LOA if I recall correctly, and served as a camera platofrom for ESPN during the America's Cup back in '87 (?..is memory serves).

The exceedingly tender nature of the SWATH is really evident when dealing with such a small version...getting people on and off at the dock required some coordination and she also ballasted down considerably to increase the stability at rest.

Underway..rock stable and very sea-capable little craft.

Fully stabilized SWATH vessels share a problematic trait with stabilized hydrofoil craft; their remarkable seakeeping performance can (and have) lead an operator in to trouble because there is nothing to indicate a worsening of sea conditions in a progressive or gradual way. You can operate yourself right in to serious and immediate trouble. The 'limit sea state' appears suddenly as a brick wall.

Including the sensors and related control algorithms to support a 'wave contouring' mode of operation is done for some. However, there is a 'grey area' between sea conditions where platforming control is both desirable and possible and the high sea conditions where 'contouring', or following the local wave slope, is the only means of survival.

[narf2600]

Thanks. So do you personally think there is a better, more seaworthy hull for the size? Is my idea practical at all? I plan on using dc motors, one in each hull, perhaps the batteries and fuel/water as well. Rough estimate of 8 meters long with .5 meter diameter subs, fiberglass. I'm thinking of just building 1 submarine and see how that goes. Rather than the double cat like design mine would be more 2 cylinders with some buoyant arm holding them to the main hull.

[Guest625101138]

Thanks. So do you personally think there is a better, more seaworthy hull for the size? Is my idea practical at all? I plan on using dc motors, one in each hull, perhaps the batteries and fuel/water as well. Rough estimate of 8 meters long with .5 meter diameter subs, fiberglass. I'm thinking of just building 1 submarine and see how that goes. Rather than the double cat like design mine would be more 2 cylinders with some buoyant arm holding them to the main hull.

The only merit would be ride quality. It will have a lot of wetted surface so a lot of drag.

I practical terms it will need a couple of mtres of water to operate so you will not be able to get close to shore although nothing different to a deep keel yacht. How do you get to a motor or wiring if something fails while at sea?

Rick W

[Ad Hoc]

BMcF

Yes well noted. That is often the problem with SWATHs, knowing when rough is rough! I was on sea trails of a SWATH many years ago, we were out in a hurricane, over 100knots of wind, the Ariel eventually blew off it was that bad! Only problem we had was turning owing to the high windage. From memory we heeled about 22 degrees during turns in those winds, other than that though, she was smooth as a babies bottom!

In answering the original question, the speed of a pure SWATH is related to the Monk Effect, excessive pitching, hence why SWATHs, pure SWATHs are stabilised for pitch.

My colleague designed currently the worlds fastest SWATH, some called it a MWATH, owing to its slightly greater WPA. We have designed/developed a 40knot waterjet SWATH several years ago, just waiting for a client to say "I want one", original client back out last minute, typical!..trouble is powered by GTs so very very expensive and limited application!

[marshmat]

It seems to be rather difficult to get a small SWATH form to work well. Between the waves-over-the-deck issue and the weight shifts of crew moving around, I think there's a good reason why we don't see many SWATH ships under 15-20 metres or so.

The Canadian Coast Guard has some for hydrographic survey: http://www.ccg-gcc.gc.ca/eng/Fleet/Vessels?id=1095 Reported to be very, very stable and excellent platforms to work from. (I haven't seen one in action yet, but I've come across a few videos- they are almost completely unaffected by waves.) But note that they're only intended for coastal use in ice-free conditions. They run for shore if things get nasty.

I share Ricks concerns about draught and access to the hulls in an 8-metre-ish SWATH. By the time you get enough waterplane to be able to even get one arm down there, you're already almost a conventional catamaran.

[Ad Hoc]

Marshmat

The smallest SWATH my colleague and I have designed has been 21m LWL, but there is the small is too small aspect when considering a small SWATH. The main being as you pointed out movement of personnel would mean a very active ballast system being required which adds weight, so the tubes become larger, then deeper draft and so on and so forth...so there is law of diminishing returns when considering a small swath.

Not sure what you mean about a 'conventional catamaran' with respect to waterplane area, when "getting one arm down"...

[marshmat]

Thinking in terms of, in an 8-metre boat, for the struts to be narrow enough that it behaves like a SWATH instead of like a normal surface-floating catamaran, you wouldn't be able to get to anything in the pods. If you make the struts wide enough to get more than one hand in there, it wouldn't be a SWATH anymore.

[Ad Hoc]

If it is just 8m, then why would it matter if you can't get easy access via the struts?...since 'just an arm' is hardly sufficient to perform proper maintenance on any equipment below in the tubes!

This is what design and being a client is all about. Accepting compromises. A SWATH a true SWATH is the ideal choice for seakeeping, but for speed, or cost etc, it is not. Next time you buy a car, is it for its speed, its weight or its functions or its price?!

Everything in design comes at "a price"..whether one is willing to accept the compromise or not, allows the design to be realised. Horses for courses. Focusing on one aspect of a complete design to say it is flawed is not 'designing'!

We can of course scrutinise and criticize an 8m design SWATH, but if that is what the client wants and is prepared to accept the compromises, then who are we to argue?

[Ad Hoc]

sorry forgot to add

what is your definition of a SWATH then, if you feel allowing a hand to pass between the struts renders the design "something else"..?

[narf2600]

Thanks for all the input.

As far as maintenance, if something fails inside one of the subs then I would not try to repair it while at sea. While not ideal, the boat should be able to get by with just one dc motor. All the computer controls, wiring, etc will convene in the main hull. The only thing that could fail in the sub is the motor itself, or structural failure. My idea right now is the sub will be completely encased except for an opening for wiring/tubing in the middle and an end cap where some type of tray can slide out which holds all the equipment.

As far as the depth, that shouldn’t be an issue. The buoyancy could just be increased where it basically becomes a pontoon boat. This situation wouldn't be ideal either, but I don’t see it being a problem temporarily if it needs to pass shallow water.

My main concern or thought is still: if it is possible to build this design, how well could it handle a storm. Again, my main design goal is to make the toughest small boat possible. Everyone says this is the best design for seaworthiness, which makes sense in semi-rough conditions, but if the boat is overtaken by one bad wave I don’t see how it can recover. This would be true too for larger vessels also though so perhaps that isn’t as big of a problem as I foresee it to be? It just seems the natural tendency of the swath would be to flip over and stay there.

[jehardiman]

My dream goal would be to build a very small long range ocean capable boat (SWATH), I’m thinking slightly smaller than 10 meters. I want to make it as tough as possible for the size, basically a nutshell. How would such a small swath behave? From what I’ve read I believe it would provide a stable ride up to moderate seas, but how would it handle a storm or other undesirable situation? I’ve read other post stating they can’t be made self-righting. It seems as if maybe swaths perform very stable until they are overtaken by waves to the point of capsizing? Any advice/links appreciated, there is very little info I can find about this topic!

Small
Long Range
Ocean Capable
SWATH

Choose any 3, but you are never going to get all 4. As has been well pointed out in some of the above posts, SWATHS are geometry and weight critical in respect to thier hydrostatic and hydrodynamic properities. Get too far off the necessary relationships of length, seperation, buoyancy, waterplane, variable load, and fineness and you will have a poor performing vessel. FWIW, SWATHs basicaly fall into 3 LOA sizes, a poor performing 15-17m range (some that are called SWATHs in this size are really cats), a 25-30m size, and a 60-70m size. These sizes are not arbratary, they are based upon construction, strength, maintaince, and envrionmental constraints. Additionaly larger SWATHs beneifit from the Law of Cubes, which normally hamper fast vessels. One additional note, because a SWATH depends on it's geometry for it's performance, fuel consumption, tankage, and ballasting is a primary design driven.

My main concern or thought is still: if it is possible to build this design, how well could it handle a storm. Again, my main design goal is to make the toughest small boat possible. Everyone says this is the best design for seaworthiness, which makes sense in semi-rough conditions, but if the boat is overtaken by one bad wave I don’t see how it can recover. This would be true too for larger vessels also though so perhaps that isn’t as big of a problem as I foresee it to be? It just seems the natural tendency of the swath would be to flip over and stay there.

Actually, capsize is the least of your worries. SWATHs are very inefficient structurally and a balanced SWATH design will most likely fail structurally or take a plunging wave before it can be hydrodynamicly loaded sufficiently to cause an actual capsize or the more likely pitchpole. You must understand that the interaction between static and dynamic response in a seaway of a proper SWATH is very different than a normal vessel.

In short (~1.5 LOA or less) waves a SWATH "platforms" the waves, i.e. it rides over them without heave using it's large mass to WP to prevent motion. In this mode, there is no need for active control and the control fins are zeroed to provide damping. This is very different compared to monohulls or catamarans which can only platform waves much smaller than LOA.

In long (2 LOA or more) waves on the other hand, a SWATH has be forced to "profile" the waves using active control. This is because the vessel is slow to rise to the wave due to the high mass inertia in pitch compared to the small WP. Without active pitch control to force response, it would be impossible to build sufficient crossdeck clearence

Because of the realities of sea spectra, open ocean SWATHs need crossdeck clearences of 2-4+m. Smaller SWATHs cannot acheive these clearences within weight and strength considerations and conesquently have much poorer performance.