I'll start with an example of what we have right now.
http://www.nyteknik.se/multimedia/bilder/a...baten_webb_stor

Unfortunately the text is in Swedish but i think you get the picture. Its a group transport that can travel underwater crawl half submerged or go full speed at the surface. its called the Seal (something that makes it damn hard to research on the Internet, but we had one for testing at my base when i served.

Now what I am intrested in is a transport along the lines of the

http://en.wikipedia.org/wiki/Combat_Boat_90
or the
http://en.wikipedia.org/wiki/Jurmo_class_landing_craft

But with underwater capability.

Demands
1. 6h under water operation time.
2. 10 man (non diver) transport
3. 20m diving depth
4. 2-3 man crew (diver trained)
5. Ability to be "parked" on the bottom (crew leaves through airlock)
6. Ability to preform beach assaults
7. Semi submerged crawl capability
8. 35+ knot surfaced
9. Ability to spend prolonged times in the field as long as it has access to fuel.


Desired ability
2.1 16 or 20 man (non diver) transport
2.2 Under eater refueling capability
2.3 Small arms resistance or higher (12.7 perhaps)
2.4 Armament to support assaults and give capability against small boats and aircraft (This is probably better solved by escorts, but if you can do it go ahead.)

LOL.

Well our up engined CB 90 prototypes with ballistic protection makes 40 knots so it not that crazy. Damnit our torpedo boats from the 60s did 42 knots so it's not super crazy... Sure the boat working boat i give as an expel actually does almost 40 they say in the article that it does over 30 (and as usual they are being a bit shy with that sort of equipment. I have driven alongside it and it was alot faster than 30)

That being said 35 might still be a to high number but its decently not LOL high.

I don't think you can make the Stridsbåt go underwater...

35 knots is very fast. 30 knots or maybe even less seems more reasonable.

Well the design will obwiosly look more like the seal. It is hoever meant to fill the role of cb 90.

What is your relation to the cb90 since you call it stridsbåt B)

Technically, it's the Stridsbåt 1990 Halv pluton, but who's counting? :lol:

What you're saying, is that you want something that is half boat, half submarine, and can motor along at 30 knots (I doubt that you'll get 35+ knots). Like you said, you'll probably end up with something like an up-engined Seal, tbh. That system is really inventive in it's own right, tbh.

For a micro-sub it is LOL high.

And as said, you don't need to have a NS-designed plug for each hole. If there is a niche RL design that does what you want, you can always just use it.

How can it be LOl if the real thing does more?
It is the surface speed of a thing that is basically a RIB and they are usually allot faster.

Yea that is the basic idea. It is a slightly bigger seal there is however one big difference, The passenger of this thing are supposed to move from land to land through a frontal assault ramp. Only the crew will be trained divers.

Trouble is the seal is and underwater capable version of our group boats. I'm interested in an underwater version of the Stridsbåt 1990 Halv pluton.

The thing is I'm not planning to use this in NS I am interested in it from an engineering standpoint and because would usefully IRL. Since the small one can do 40 knots at the surface I thought well its slightly bigger so it should be slightly slower my fist guess was 5 knots, it maybe turns out to be ten? Who knows were doing this for fun and since its intrusting right?

I thought you wanted an armoured micro-sub with an airlock (as such presumably dry environment - you don't need airlocks if it's wet type), and not a CB90 as it is? You aren't going to keep CB90 capabilities without loss when making it into a sub. The Swedish 30-knot (not 40) thing you've linked is essentially more of an oversized DPV/manned torpedo than a boat which goes underwater.

Since you linked Combat Boat, which is actually a false translation of Stridsbåt. Of that weird finnish name Lamoni called.

Lay off, i'm part Finnish! :P

Okay lots of confusion here.


I think for VTC this comes from a bit of bad wording from me (As you probably understand English is not my primary language)

This is an understandable misunderstanding since i first only wrote

Now why did I take the CB90 as my main example? (The Jurmo does the same thing but for the Finnish)
What i meant is what a posted a bit further down

And you (understandably) interpreted it like this

I fully understand that it would probably loose some capabilities in the transfer that why i moved amour and armaments down from demands and halved the transport capacity.
It is however true that i want a dry enviorement for the transported soldiers, I don't know about the crew.

About the speed of the Seal

Since the article i sent you is from an regular Swedish magazine they haven't done that much digging and military companies doesn't really release the full specs for the public they simply had the figure 30+

Here we might have a case of my English letting me down, what I'm trying to say is that i have driven alongside it at 39 knots (actually the last stage prototype but that shouldn't be faster right?) An just for the record i was doing it in an up engined and armored prototype of the stridsbåt going full pelt the HC (the strb HC is the test model for the HS wich is also up engined but to a much smaller degree)

I hope i that cleared some things up. I have no interest in fighting over this i really only what to discuss if its possible and in that case how it should be done

I'll just repeat my self for safeties sake here

And if speed is the dealbreaker we can surely lower the demand on that

Shall we say 30 instead?



I must also just clear this up.

Cb90 (combat boat 90) produced under that name by doksvarvet is in service with the Swedish military callad Strb 90 H (Stridsbåt Halv pluton) It is used as an tranport for our brownwater operations units for example the Swedish http://en.wikipedia.org/wiki/Kustj%C3%A4garna (Where i served).

I don't understand what you are trying to say, this is starting to give me a headache. You can just take that Swedish hydroplaning manned torpedo and use it, what's the problem.

You can't make CB90 do things a manned torpedo does, it doesn't work like that. For one, you need to flood it to submerge, that Seal vehicle isn't watertight, it's filled with water when it's under. And you can't just go and do these things to a CB90. It's a dry design, you need a wet one.

Hehe this is giving me quite an headache to.

You will of course have to ad more ballast tanks (regular submarines are what you call dry designs if i am understanding you correctly)

I'll try to explain explain how i would try to design it (the reason i took this here is to is to get some new ideas about how to do it)

Imagine a slightly larger larger seal. With and enlonged troop compartment in the front. The compartment is pressurized and caries 10 troops sitting face to face in two rows with enough place for one man to move in the middle, it ends in a assault ramp (opening both up and down to give the transport a better shape in the water). Behind transport compartment and slightly raised is the "cockpit" were the driver and navigator sits side by side. I am not sure if this compartment is to be pressurized or not (I have been playing around with the idea of being able to use it as and airlock by equipping it with pumps and an overhead hatch thereby allowing the thing to be "parked" on the bottom (it can also be used to rescue troops via the hatch to the troop compartment) Under and behind the cockpit is the diesel and electric engines. Along the sides of the superstructure is ballast tanks to compensate for the increased lift from the compartments.

This is just the idea form the top of my head the only real submersible I've been a part in the design process of is a underwater sauna (that unfortunately lack combat applications)

No amount of ballast tanks will make CB90 go under. No reasonable amount.
You'd have to throw out any aluminium or plastic parts and replace them with steel, heavy, with excessive thickness. Make the hull of thick, excessively thick steel. Only then could you replace half the interior with ballast tanks and finally make it submerge. Needless to say, the result wouldn't be able to stay up on dynamic lift, bringing its speed down to Froude coefficient of 0.4, 0.5 tops.

Here goes your light weight and flying over the waves at 30 kts. Welcome displacement lift. It's not as much due to the weight of the pressure hull as to the fact that you can't then flood this compartment.

A flying DPV is only possible as a wet design, and even then it's a major achievement which you probably won't be able to replicate without copying.

These guys aren't wearing rebreathers to look cool, they are wearing rebreathers because the vehicle won't submerge unless it's flooded.

You don't understand. Ballast tanks don't make you less buoyant. They can't. They can't make you sink. They can only make your more buoyant, by being emptied, while underwater. That's it. Water inside and outside has the same density, so adding a tank filled with water has no effect on your buoyancy, other than the weight of the tank itself, which is better delivered with steel, lead or concrete.

That is why it's not supposed to look even remotely like the CB90 it's supposed to be a replacement for the CB90 but with some new capability's and some old removed.

There are several way to help the craft both go below the water and also to help it ride high on the surface. You could increase the size of the pontoons you could make overpressure ballast compartments you could also change the design to something more like a catamaran (with the ballast tanks and the pontoons being the parts that are under the water)

Remember the thing is supposed to be barley floating with the ballast tanks (at least partially) full of air (only the upper part of the cockpit is supposed above the waterline) Only with the pontoons full of air is the vessel supposed to be at the surface going fast. So your comment about the ballast tanks is a bit misleading since they are underwater even when filled with air the relatively they will make you sink when you fill them with water. And yes this means that the craft will be heavy enough to weigh down the passenger compartment. But you can make fast boats that are heavy, i wouldn't really call a commercial catamaran ferry slow (not the Nimitz class either)

I would just like to ad that I took this to these forums because i have no clear idea how (or even if) this could be done. I don't know how it will looks as i wrote above that design was just how i would try to do it from the top of my head. I will soon receive my master and I am already working part time as a product developer at the Defense institute in Stockholm (Försvarshöskolan) and i feel it is not an impossible thing to pull of. I took it to these boards because i felt it was an interesting thing to develop i would like to hear other peoples ideas. I'm doing this for fun and I don't feel any need to be here. I am actually enjoying it less the more I speak with you not because you seem stupid (you actually sound reasonably intelligent) there just seems to be an atmosphere that is devoid of constructive criticism.

Not really, all of that is useless.

You have to add weight, a lot of weight. And that weight will prevent it from planing.

Which is why it won't be able to go fast. Only planing and semi-planing hulls, nearly entirely above the water, are able to exceed a Froude number of 0.40-0.50.

It will still be too large and too heavy, with too much ballast and too small functional fractions, to go fast.

No, they won't.

Understand this: the water inside has the same density as the water outside. It's neutrally buoyant. You can attach a tank the size of Texas to your vessel, and all the water inside it still won't help you sink. Only solid ballast, with density substantially greater than water, contributes to your ability to submerge.

You should be able to understand the difference between large-scale, like A380 airliner, and heavy (dense), like a MBT, on your own. The modifications you need to do to a boat to make it submersible are of the latter kind. Some varieties of wet designs are an exception, and their unusual combination of qualities hinges on being what they are.


P.S. If you want to begin mentioning our qualifications, I actually do have some of relevant nature. I'm all for constructive criticism, but for it to be possible, the underlying idea has to be sound. It isn't here. You'd probably be enjoying it a lot more if you started off with a sound idea. It might be possible to implement by throwing lots of money at it and making lots of sacrifices, and shifting much closer to PMT, but not normally.

Here we go again, of course i will have to add weight

And yes the ballast tanks will relatively make it sink because if the weren't there filled with air it would already be sinking

If you then make the tanks the same weight as the water instead of lighter it will make the craft sink that's is exactly how subs work.

Why not even talk a bit about subs since this is a submersible the soviet Alfa class submarine does 41 knots submerged and that is so far away as you can come from a an that is as far away as you can come from a planing design. Would you also agree that that craft has the correct density required of my craft? Now just for fun imagine a catamaran design were I use two Alfas going just below the surface with a small superstructure obove the water connecting with some low drag component. Heck i can even place my boarding ramp on it and pretend I'm done. I have now built a stupid and to big version of my craft doing 35+ knots.

Can you see know that the idea is reasonable? Or are you just one of those guys who can't have misunderstood something?

Can't we just burry the hatchet, sorry for

We have differing wievs over the reasonability of someone maneging to produce a vesel being able to fullfill the things i posted. (Im not sure how to do it thats why i posted here) But since i have not been burried in a shitstom of people callong laughing out loud. There might be people that feel it is perhaps dooable beut are highly unlikely to start posting while the tread is going on like this.

So peace? We dont feel the same way about this can we stop saying the same things back and forward im quite surre noone of us gets any smarter from doing this.

Subs work slightly differently; this is what happens, but this isn't the cause. You sink because you are heavier than water, for that, your empty weight must exceed the combined volume of all dry spaces, multiplied by water density.

There are many ways to increase your empty weight, but in the end, all modern submarines end up adding ballast.

I see what you want to do. But the problem is that *first* you have to add empty weight, and only *then* can you manipulate the air space inside, i.e. your volume, to submerge or surface.

Now, what's the problem with that? The problem is that additional empty weight degrades your performance. Imagine CB90 loaded with so much lead that its weather deck is only barely above the water. This is what you'll get. Such a CB90 won't be able to plane on the water and do 40 knots. It will do maybe 12 knots. The added tanks are dead weight and dead volume; they don't contribute to your surface performance.

The key word here is "submerged". Drag is lower underwater. It can't do that on the surface. Although, it doesn't need to really.

Well, that low drag component will actually have a lot of drag at 40 knots. But suppose you avoid that, then you indeed get your craft.

For the low low price of two nuclear submarines with an exotic reactor type and their low low maintenance requirements.

You'd be better served by a single sub, at that.

The above is an exercise in insanity. From what I understand, it's *not* what you want.


To get the performance of a flying manned torpedo while adding a dry compartment you would need to substantially enlarge it; much more than by the size of the compartment alone; and all the while do so while keeping it light enough to be planing. It's not going to be worth it, it's easier to teach your teams to use rebreathers. Or even just give them open air from an onboard source, if you can live with the bubbles, although military rebreathers tend to be dumb low-performance designs that are almost as easy to use.


If you really want a somewhat silly crude design that does what you want, imagine 3 of these manned torpedoes connected together, like a raft. The central one is pressurized and dry, while the side ones lose the passenger compartment, navigation etc., but keep the engines, the lift-generating bottom and the tanks to allow the entirety to move at requested speeds. It will be thrice heavier and thrice bulkier, but won't get any extra speed or capacity, these side torpedoes are the price for keeping your guys dry.

Finally we are getting some were :lol: thanks for suggesting something close to what I am interested in.

Yea this is somewhat along the lines of what I'm after. I think it would be better to scale the two outer "torpedoes" to be able to lift the middle one over the water while the side ones themselves should be completely submerged (trying to keep the connection with the superstructure as low drag as possible when in surfaced mode) the main reason to break it up into a catamaran shape, is because just as you said regular subs are slow at the surface. There is two major reasons for this the first is that the shape of a sub is optimized to be used in a situation were the top and the bottom of the hull is meeting roughly the same amount of resistance, related to this is also the placement of the propulsion along the center axis (to avoid having to work against the engine push with the rudders all the time) this will decrease the drag of the vessel similar to the bulb on other non planing designs.

Again what you are saying is true you do how ever miss the point I'm after. I am sure you are familiar with newtons first law. Just because something is dens it wont be slow it will however be slower to change speed and turn. But just as you said doing it to a CB90 will make it slow because its a planning design and therefore relying on low density to ride high in the water thereby traveling mostly in a medium with much less resistance the water (air). But as both of us know its fully possible to make other hull designs fast in the water, and i never stated in my demands that i needed a planning design. Therefor I don't have that many problems with a heavy design. (It will be a bit more sluggish and consume more fuel but i can live with that)

I must however congratulate you on you estimation of what a CB90 does when its overburden. One time during my service when we moved way to many 81mm grenade launchers and ammo we were unable to achieve planning and were then doing almost exactly 12 knots B)

I just took that example to show that you don't have to make planning designs to have fast, and just to clear out the part about the tiny superstructure compartment extended on some rods from the subs sure it will generate some drag that why i said it would do 35+ instead of 41 but since it will be in the air i think it wont be to bad. Still it was just a lulz boat to show that the idea of a craft fulfilling the demands is possible.


Now i think i must explain why i am so damn interested in a dry compartment when it seems allot easier to use a wet design.

The reason for this is can be traced to the special need of brown water littoral warfare units like the one i served in. Imagine the Stockholm archipelago it one of the worlds largest archipelagos containing almost 35000 tightly packed islands usually covered in thick forest some marches and lots of cliffs and hills. This is the favored train of my battalion.
Established to defend the capital by performing guerilla warfare against invading soviet union by hoping round the islands in CB90s and we can set up almost anything on the islands and turn them into deadly fortresses we got lots of stuff man carried that you would usually have vehicle mounted just to make the islands a scarier prospect for the enemy: We got 12.7 mgs, AGLs 81mm mortars, SAM launching ramps we even have firing ramps for laser guided hellfires to deny boats access to the archipelago. After an attack we move double time to our boats and switch islands to avoid artillery. The boats are our lifeline Whit them we can fight for a week without resupplying (from hidden caches or friendly forces) and without them we still have supplies for three days and are stuck in a possible ordinance rain from heavy crafts in open water hoping for pickup.

So what does this mean?
Well we have loads of troops most of them carrying heavy loads when part of an grenade launcher group your equipment can exceed 100kg in weight so we are not that keen on lugging around a rebreather. And it is also loads of troops to train and equip not just some reccie dudes. Lastly I'm not to keen of moving the extra equipment in a wet design.

Why don't you use the damned CB90s then?
As I am implying in the under text of this thread the problem is satellites (and also UAVs) trying to find a boat that is lying in wait camouflaged or sprinting among the maze of islands is still like finding a needle in a haystack. The problem is that as soon as they receive information of an attack preformed form an island they just have to watch the footage until a transport leaves the island the follow it and destroy it. I don't know how many nations can do this right now but its not far away in the future.

This is were the demanded design becomes interesting. The ability to loose a tracking enemy and also to sometimes have the ability to move stealthy instead of fast when on the water. A final thing in the demand list that could prove interesting is the ability to park on the bottom as a way to hide the boat in a safe place.

Then why do i prioritize surface speed? Can't i just have a vessel that is fast underwater or why not simply slow altogether? The cornerstones of our tactics focus on speed and aggression when we attack, coupled with stealth in between. It is also usefully to be faster than the enemy when running away :). So why not do it under water? High speed maneuvering in the archipelago is hard enough during the night, if you do it underwater you will destroy your craft (in allot of places the depth wont allow it anyway).

Now i think i have described this almost to the best of my ability. Would you help me design a craft capable of this?
We could do it as suggested. With some work of course (Its far from a completed design) Or there might be a totally different idea that is better. I would really enjoy conjuring up a viable design with you since you know what you are talking about.

That will only give you 12-14 knots. Only dynamic lift can go further.

On water, it will be slow. You have to keep it above, which means that either it's displacing (limiting its speed, for this size, to ~12 knots), or it's dynamic lift, in which case it's constantly fighting its weight.

You can have it:
Displacement - Small and slow
Displacement - Large and slow
Displacement - Large and fast
Dynamic - Small and fast
Displacement/Dynamic - Small, slow as displacement, fast as dynamic

That's the ways you can have it. You need a very large ship to go fast in displacement mode. Either that, or a submarine (and it has to be pretty deep, more than its hull diameter), which still isn't as easily made fast as dynamic lift vessels.

You aren't really going to fit all that into a planing submersible with a dry compartment. All you are going to get is pretty much that Seal manned torpedo, except dry inside. With barely any space to even move your arms.

If you want more, you need either a wet design or a displacement one, and the latter is going to be slow, unless it's way too large for any landings.

At the point where satellites can actually find your boat, you have much bigger problems, like fighting off those flying mecha, or at least space-based lasers and robot helicopters. 24's way of using satellites is not based in reality.

Also, satellites are excellent at detecting shallow submarines, just in case you're wondering about what will happen to your design 50 years down the road.

Well, you've described what you want. However, it's not necessarily what you need. And if that is what you need, it looks like a case where you'd have to do with what can be done, which is a lot less than you need.

I've been contemplating making the Axolotl (Mudskipper's followup) submersible, however that would require some lulz ballast system that I just can't conjure. Doing reverse osmosis or distillation on seawater to get salt or very thick saline solution could work, but it's way too energy consuming to even consider with a non-nuclear vessel. Scraping the bottom for soil is another option, but either limited to low depths or extremely slow and still not suitable for blue water. With only water as ballast, you can't have lightweight and submersible in one.

Aw and i thought we were getting some were here

Please you cant seriously be suggesting this you can make smaller designs that are fast without making a planning hull. The reason you don't usually do it is because its cheaper easier and more effective to make planning designs. Give me a good explanation with its base in physics why its impossible, that a smaller design is more effected by rough se is not really a problem in an archipelago environment.

You are totally correct in stating that a non planning design will not be able to make beach landings wile getting as close to the waterline. That is not such a big problem as you might think, usually you might as well drop of and pick up troops along the cliffs, We only need the beaches when we make contested landings (that require high speeds and lots of firepower to keep troops safe) and if we are forced to do that the troops will have to wade in (we generally avoid it anyway since its so dangerous)

You conveniently "forgot" about the UAVs, but still your jokelike answer to brush it over actually pointed at one thing that might be of importance if we get allot of "robot" helicopter UAVs that can prove a challenge since we can't keep showing our location by shooting them down. Other than that i think we can safely say that a satellite log trace of our boats after contact is more of a problem than space laser and mecha :).

Detecting a shallow sub in brown water is allot harder than in a blue water environment. And finding vessels that will bee good in 50 years is quite hard.

Well do you really think every squad has all that equipment with them? Just like in the regular military we have many different units for different functions (thou we do cross train allot) It will more likely be one heavy weapon system per craft.

I find it quite fun that you keep reciting true facts that does not mean anything for the craft I'm interested in. I don't want a planning design, that's why weight is not at dealbreaker for me.

I'm saying you can't make small surface designs that are fast without using dynamic lift (planing, typically). The only way a small surface vessel can be fast is by using dynamic lift planing. Even SWATH doesn't solve the problem entirely.

The reason is that a vessel creates a wave as it moves through water. Froude number is a figure used to determine the character of that way. It's a bit complex, but, put simply, at Fr<0.15 there is no wave drag, at Fr<0.40 the wave drag is moderate, and at Fr=0.50 the vessel is trying to ride into its own wave, and the relative wave drag is maximum. At Fr approaching 1.0, the vessel actually manages to climb its own wave, which is known as planing. At this point, wave drag is rather reduced, and keeps close to constant further on.

The only practical alternatives to a planing hull are hydrofoils and hovercraft, but again both are examples of dynamic lift, and the difficulty of providing dynamic lift depends directly on your weight (unlike with static lift, which is natural).

See above. It actually *is impossible* for a surface vessel. Cheating like attaching a rubber duck to a sub nonwithstanding.

Nah, I'd be more worried about space lasers, followed by mecha, only them followed by satellite spying.
You need something like a million satellites to be able to cover any region where the combat is occurring (note: not the whole world, just any area) in near-real-time, and even that only gives you rough data, updated once a minute or so. And it's cheaper to outright buy out the opponent's country than to launch and maintain so many spy satellites.

Still pretty reliable really, when done from space, unless it's scraping the ocean floor. If anyone had enough satellites to do that, it would be a problem.

Then don't count on having a lot of speed, nor on being able to land this craft right on the beach without having to wade in.

What about detection from UAVs?

More of a concern, however their sensors and capabilities are rather limited. I don't see why aren't manned observation aircraft and helicopters seen as a much greater concern. We aren't at the tech level where you can spam the sky dark with UAVs, or, given marine combat ranges, a lot more of them than manned aircraft, and manned aircraft have better sensors, an extra eyeball type sensor, and engagement capabilities.

Thanks for posting Alenna since VTC conveniently "forgot" my

Anywa they could still pose a problem without spreading the entire archipelago with UAVs

The thing is this, the engagement ranges shrinks quite dramatically in an archipelago and you don't have to have that many UAVs. The whole thing that is dangerous is is that we can be follow after an ambush. So if the enemy commander only has to worry about routes were he will move forces. And he will generally be quite wary of using conventional aircraft. Due to our SAM batteries spread out along the islands and constantly moving around. (UAVs and High flying spy planes should be less afraid of this)


I'm sorry but you didn't answer why a boat suddenly becomes slow as it shrinks just because its not a planing design

I'll repeat myself

But it can still be done!

And since you seem to have such a problem with size right now I will give you an example of a small craft with the correct density to travel under water that manages to be fast at the surface good old torpedos. They are faster underwater because that is what they are built for. But since some models had problems maintaining depth when dropped from aircrafts they were often configured to run at the surface (there was even one torpedo that was fitted with wooden fins to get it to the surface fast)

How can a non planing small craft be fast having to work against a high froude number of maybe 0.8? Well in the same way a 15 year old catamaran ferry can do it (the stena voyager has a service speed of 40 knot and a record over 50) You simply need to provide enough power vs your resistance in the water (not really that strange) that is the reason fast non planing designs are usually narrow or multihulls (effectively narrow hulls placed side by side) the multihull being prefered because of stability.

So yes on a small design it would be simpler to make a planing design since its easy to do with light boats and that allows you to use a smaller power plant or simply make it ridiculously fast http://www.cigaretteracing.com/ if speed is what you are after.
But that still does not make it impossible to build a smaller fast non planing design.

There is no physical laws that states that a smaller design has to plan to be fast, physics only mean that the small design will probbably start to plan as you push more power onto it, unless its heavy or has hull shape that prevents it. If planing is the kind of dealbreaker you say it is i would like to know how there can possibly exist fast designs that doesent plan?

So surre the powerplant of a small craft that can push a non planing hull to 30 knots could probably push a plannig design to 45 maybe even 50 knots but it can verry much be done!

Because the Froude number is determined as Fr=v/(gL)^0.5, all metric, and the most Fr you can practically have in a conventional displacement vessel is about 0.45. Semi-planing GL can be a bit higher, and as it approaches 1.0, it's nearly pure planing. You can make your own calculations for your desired length.

Well, it isn't so. The reason you don't do it is because there are only two ways to exceed a Fr of 0.40-0.45 in a surface vessel. One of them is by employing dynamic lift (planing hulls, hydrofoils, hovercraft, WIG craft).

Another is wave-piercing, which is much more exotic, and involves actually moving your displacement part underwater, for instance in a SWATH configuration. However, this way has very deep draft, making it useless for beach assaults which you seem to want, and it's rather unsuitable for a submersible.

A conventional form displacement design can not do it, it will begin to climb its own wave, and as you apply more power, you only create a bigger wave and apply more of your thrust upward, and to break through Fr=0.50 it has to begin planing. It's physics.

No. You can be planing (semi-planing), or you can be wave-piercing, but a normal boat doesn't just exceed displacement speed limits in displacement mode because you throw a lot of power at it. It will become planing even if you don't want it to, only it will take an extreme amount of thrust to do that.

SWATH catamarans are in fact more fuel-efficient than planing boats. They don't defeat their limits by throwing insane amounts of power at it, they do it by hiding their displacement-producing section underwater. But the price for that is insane draft.

It can be done with a SWATH design. It can be done with a planing design. It can't be done with just taking an overweight (and we're not talking 20% overweight, we're talking 200% overweight) CB90 and sticking an enormous engine inside. Well, unless that engine is so powerful that it pulls this boat out of the water and sends it planing.

Aw man I never said i want a regular shaped hull design if you actually read my posts
Trinay

You will then se that this is a SWATH design

What have you said about those designs
VTC

Yes beach assault would be really nice.

Lets do some more reading and se if i consider it a dealbreaker.
Trinary

Oh do some more reading since you seem to have a tendency to dodge questions
Trinary

Then why do you keep on persisting
VTC

This shit is crazy you just we have been at this for almost a week and you keep changing what you consider as the problem and when you get proven wrong on something, you just ignore it and nag about something else. A day ago small boats could only be fast by being planing designs apparently that's not a problem any more, when you were wrong about the UAVs you just ignore them and for quite a long time you kept on insisting that you cant construct a vessel that cant sink and plan with a dry compartment even thou i kept repeating i don't want a planing design.

Can't some mod please remove or at least lock this tread, I don't ever want to post on this forum again but i find it hard not answer, because you always avoid answering the real thing and start speaking about something else. That being said this will be my last post

Your requirement 6 states:

You can't do it with a draft so deep that your troops can't even stand on the bottom and have to swim a long distance. It's also pretty ridiculous to submerge a SWATH, even if not theoretically impossible.

A non-planing, displacement design *can* do beach landings. It just needs a reasonably shallow draft. You can make it less than a meter. A far cry from about 3 meters it would take for SWATH. Or, you can go with a planing design, if you minimize dry volume. I've explained how to do it, a relatively wide design that maximizes planing area, with a cylindrical crew+engine container, and tanks outside of it.

I don't dodge questions, only skip ones where the best answer would be repeating the previous statement. It's how physics work, you either plan over the water, or move under the surface, or you adapt to wave propagation laws, in the latter case your speed becomes limited by your length.
If I haven't mentioned before, I do have an idea of what I am talking about in regards to these things; until recently it used to be my job. Most people here know that, so I didn't take into account that you didn't.

Small boats can only be fast by being planing or semi-planing. Wave-piercers (SWATH included) are so exotic I didn't even remember about them at first, and they still have a minimum size; you have to be larger than the waves you are likely to encounter, at least. That is not actually small. And the idea of considering a submersible SWATH for shallow water operations and beach landings is so outlandish I'd never think about it.
You are as free to come and go as anyone else, but that doesn't change the physics.

I'm sorry if I missed or misunderstood something you meant to say. I've been sticking by the original requirements listed, and the original prototypes presented, as well as common sense (i.e. the presumption that you don't want a 100-ton vessel that only carries a dozen troops, but rather something small, simple, affordable and easily transported).

Or just issue full body condoms to your troopers (waterproof overalls to keep their BCDs dry). Or, more practically, separate the water that enters the compartment by a thick durable film (you can make it a few millimetres thick, or more, multiple layers and stuff), allowing it to still mostly hug their bodies, but keep them dry. Then overpressurize the compartment, so as to keep their heads above the film level. Even if the film somehow fails, you can push water down by air pressure from above (think diving bell), although you'd still want them to breathe from regulators just in case. This will greatly reduce your buoyancy while submerged.

Add similar provisions to other compartments, for instance ensure that a water-filled bladder displaces fuel as it gets expended (though you won't be using fuel underground). Either eliminate every air space you can or provide a bladder to weigh it down if possible. An overall overpressure system will still be required, and will add weight and bulk, but not as much as if you kept a full dry design. Say... the swedish manned torpedo is 3.8 tonnes, you could have ~5.4 with same crew. It's a lot less than you'd need if you insisted on keeping a hard dry cylinder.

Although, seeing as they'll have to wade through water anyway (unless it's a hovercraft), I hardly see the big idea behind keeping them entirely dry. Although a full body condom (a primitive drysuit) can provide that pretty easily, with just their heads and necks above the water inside, and guns in aquapacks. Still breathing from regulators for safety. You can actually even make something disposable, to make taking it off easier. It will leak a bit, add some kitty litter on the bottom of the oversized shoes.

It will work just fine in the end, and the comfort gained by having a full solid dry compartment has a massive and disproportionate price in a vehicle like this.

Just as i was about to leave you answer with two good posts.

Well I will have to blame myself. I was being vague on purpose so that people would come with there own ideas. The boats were meant as an inspirations and to show what your designs were supposed to replace. Therefor I have never posted my own design (its not completed anyway and the reason I am here is to find some ideas. I would not like to post it before i have worked everything out yet but it is a wave piercing design in Roughly SWATH design (with the ballast tanks in the pontoons. Which i hope would be able "only" stick down 1,6 m under the surface.It would also be crappy in rough seas but that doesn't really bother me because waves can hardly become more that 2 dm valley to top in the archipelago.

1,6m That is hardly ideal for a beach landing since it will fore troops to wade trough roughly 15 m on a standard archipelago beach a(they are usually kind of "steep" under water" Still this is hardly ideal and one of the reasons i wanted to se what people would come up with here. I have toyed with the idea of a Inflatable floater under the main part of the hull (almost like some sick version of an airbag) that when used extends down between the underwater "pontoons" to lift the boat and also assist in slowing the speed in the final parts of an assault.

But contested beach assaults are hardly something we like they are the most dangerous things we do, and when performing guerilla warfare you rarely need to take something we will usually be content simply mortaring the island. When dropping of troops we usually do it going slow and dropping of by the cliffs (dry feet also keep troops happier). Another advantage of dropping of by the cliff is that after beach landing you usually have to pull the boats away with another vessel because they are all stranded and that is hardly practical for a regular drop of. Still if someone could find a smarter design i would be delighted.

You second post includes some really interesting ideas I was already going to do the fuel storage in a bladder surrounded by water when submerged (The Seal does the same thing) But you idea about separating water as it enters the compartment is great. Not sure how easy it is to make it able to hug against the passengers is a smooth and comfortable way however. But as I will try to explain bellow it will be useful even if its not pressed against the passengers

I'll just say something about the transport space. Se usually it will be totally packed the rack over the sitting troops full with assault rucksacks and the space between the troops sitting face to face being loaded almost to the roof with the big rucksacks extra ammo heavy weapons sweetwater containers extra rations etc all this kept in place by cargo nets.
And since we want to reduce the free dry space to keep it shallow draft (well reasonably shallow) This bag of water you are suggesting would allow the compartment to always weight like its fully loaded. This is great news since i only have to be able to sink buoyancy of the fully loaded troop compartment even when the transport is empty or partially loaded thereby allowing a reduction of permanent ballast

I see the practicality in a wet design but that transport compartment is the lifeline of the troops it is the home that remains the same during otherwise hard conditions its a place to tend your wounds to review upcoming operations to eat to store your everything you need to keep fighting a week without receiving supplies to fall asleep in your chair. But almost most important a place to recharge your batteries (in a double sense, well the actual batteries might not be the most important bit) I would say that the small dry compartment is worth its way to light weight in gold. That is why i would like to keep it dry.


Now I have a question for you since you have a history as a nautical designer. (I know allot about engineering but the submersible sauna we built at university is my biggest practical design experience when it comes to aquatic vessels) I do how ever know allot about well equiped guerilla style warfare in an archipelago environment.

The question:
If i do i quick digitalization of my unfinished design (no CAD yet just something quick) would you be interested in helping me finish it through some constructive criticism?

*Reaches out with the hand*

More like swim. You can't really wade through 1.6m unless you're unusually tall, especially while equipped.

It's not going to be comfortable, just tolerable. However, that idea is more applicable to a design based on the Seal. With SWATH you won't be as pressed for buoyancy reduction.

There is the EFV. Once they finish it, it's probably going to be the best amphibious assault vehicle - and it doubles as an IFV, providing solid fire support to the troops. EFV is substantially better in that role. Practically, you are trading an awful lot for the ability to submerge here.

I can. Just because I still don't find it practical, vs ones like EFV, doesn't mean I won't help make it less impractical.

I have waded through water that deep just keep you gun above your head and push on. Also factor in that when beaching a boat the water height will more likely be 1.4-1.5 since you push away allot of the sand and to some extent the boat is also lifted up by the sand.

You are totally correct as usual and as usual you also miss the point. So lets review what i said more than that.

And i you read bellow the quoted post you will se that what i really want is to have the "bladder" in the place were usually keep all our extra equipment.
So I guess it wont be that uncomfortable and certainly more comfortable than a wet design, and i also explain why it would be useful with a SWATH design.

The EFV is a great craft that will be really good at what it does (beach assaults and then moving inland) As i have tried to explain several times beach assaults will be a secondary function for this craft (thou on that it must still be able to do) the reason that it is a secondary function is that we rarely do it because we usually don't have to and it is dangerous (only the larger islands has one or two beaches anyway and i don't se the EFV climbing cliffs like troops from a boat)
Quite frankly I have tried to explain several times why a submerged boat would be very useful and the EFV would be reduced to a boat roll that is better preformed by a gunboat if it was forced to operate in the archipelago.
Remember this?

Il provide a air picture to make it a bit more clear

Sweet place huh? Its a deathtrap for troops not trained in it :)

I would actually really like your help cause you seem to be competent when it comes to boat design. But trust me I have good knowledge of what is useful in my preferred environment there is a reason that i will be called in as a sgt if we were forced to defend Stockholm B) It is probably quite hard to imagine how different it is if you have not served in such an environment since its miles away from regular amphibious operations.

How tall are you? At 1.6m, for an 1.8m tall man (a bit above average), there would be just 20cm between the tip of your head and the water level, even less if you count waves and less than exactly straight posture due to having to move. It will be gasping for air you intermittently get between waves rolling over you.

Even at 1.4-1.5 (although lifting the boat does nothing for the troopers below), it's much less favourable than assault with AAV (not even EFV), or just that Seal manned torpedo. If you tried that somewhere like V10, it would be marksman paradise. The only way to succeed here seems to be to come in unopposed, relying on stealth.

IIRC you referred to satellites and UAVs picking up surfaced boats. But as said, satellites can't really do that on a large scale, and UAVs aren't at that level of quantity. Remind me if there was another reason, this thread has got pretty long.


Anyway, if you are sure that is what you want, well, go through with it.

I am 186 and no one in my unit were under 180 but that doesn't matter you should be able to do it even if you are just 170 since it will as stated be more like 1.4-1.5

That is correct its is mealy a symptom of the fact that the boat is actually on more shallow water than its built for(in other words in the stated depth of 1.4-1.5m). Okay so why do i say that this is okay then well If we pretend that the boat only made it to 1.5 and the guy jumping out is only 1.7 you still got 30cm the reason for those extra ten centimeters is that in deep water you wade on your toes (we are not gonna be lugging the heavy rucksacks when doing a contested beach landing) so they should be able to make it ashore. And if one of the boats run into trouble, such as striking something underwater so that it is stranded to early, every solider is trained in swimming with his gun for a shorter distance.

Still that as hardly ideal but as I said in my last post

Contested troop landings are suicide that is why we almost never do them, so you are very correct in stating

But sometimes crazy things happen in war and you will forced to attack an island that we know the enemy is defending, usually we then turn to our hovercraft which are our best suited vessel for this sort of operation. Then we pray that the island we are attacking is has a beach if we are lucky because that means the vessels dropping us of will be traveling fast all the way forward a slow moving target with all the troops packed waiting for the assault ramp to lower is marksmans paradise. Either way we will drench the landing area in mortar AGL and 12.7 from surface vessels and nearby islands. Trusting in ride of the valkyries to keep us safe.

We don't want to do that! But its war and our main transport must at least have some capability in beach assaults.

So why do I want my transports to be submersibles?

The stealth part is really helped by the fact that it is a submersible, in the guerilla style warfare we are meant to preform stealth is our best protection and the ability to have a safe way to store boats inside the archipelago ("parking" them on the bottom) and it is also my prediction that we well in the forceable future need to be able to drop away from an eye in the sky (it could be a satellite, a UAV or a spyplane either way its bad for us)

You again stated correctly that

As i tried to say (here with UAVs as the example)

The strategic function of our littoral warfare forces are to deny a superior enemy direct access to Stockholm via the waterway. And if the just need a high flying spyplane (Or UAVs or satellites when they are capable of doing it) to track an ambushing force to a new island and then at the very least strand us on and island (swimming between islands is not hard at all, but its not a practical way to preform a war.)

I also feel that the ability to submerge will be the best way to increase survivability since the biggest threat for a sub that cant dive to deep depths are helicopters and remember.

And this applies the most to helicopters and since they are my biggest fear I feel submersion is the best way to protect my "lifelines"

So what I am trying to do here is using technology to create a unit specialized in attack from hiding and retreat to a new hiding spot as a way of defense. This is quite like another Swedish military vehicle that was quite effective in a narrow spectrum but worse the comparable vehicles on many other. This vehicle is the S-tank witch at least to me was effective in its roll in its time.

Don't ask me why i just wrote that. I stumbled over some documents about the S tank at work today i just thought about the similarities. Sure in my design its infantry doing the attack from hiding, but the vessel is a vital part of the concept when hiding against enemies with "eye in the sky" capability. When i think about it i guess i could post some of the documents here... (a part of it were already in English)