Pump jet propulsion system in russian submarines

chinggis wrote:

kumbor wrote:

Big_Gazza wrote:

kumbor wrote:If inflow to pump jet is constructed properly, with sufficient opening at the fore end, pump jet is easily cleaned by simply reversing pump jet! Otherwise, classical propeller must be stopped and divers sent to free the propeller of clogged objects. That`s what I think. May be i am wrong!?

No chance.  Suck in a fishing net, and you won't rid yourself of it by reversing prop rotation.  By the time you know you have a problem the net will be well and truly ingested and entangled beyond hope.  Divers in the water will be needed as a minimum, and that a bit of a problem on a combat mission

Britts use pump jet for over 25 years. Are there any practice how to deal with clogging, if it occured, or if it was admitted!

Ship is going into shipyard with floating dock, workers remove clogging material, put new paint on ship, repair what is not repaired last time and when everything is finished, ship sail away, workers got pay and all live in happiness There is no other options because you need special tools and cranes and in many cases you do not have in on ship because it is big, heavy, cumbersome and you dont need it in 99% when ship is sailing.  

I am starting from similarity in comparison with low power commercial waterjets / pump jets. American PBRs in Vietnam (with Jacuzzi waterjets), as well as many modern yachts with similar propulsion, if waterjet got clogged with seaweed, simply reversed their waterjets, and in vast majority of cases the propulsion gets free of undesirable objects. Such practice was widespread in ex yugoslav navy also, with class 620 LCUs, powered by two MTU 8V331TC of 900hp each and two Castoldi waterjets! I`ve heard about such practice from their commanding officers, professional military mariners.

I know that big submarine and surface ship waterjets are different and more complex in many ways, but the principles should be similar, I think. Reversing cannot always help, but in some situations can help.

I would think an inlet guard on a pump jet would make more sense to prevent the problem in the first place... design it so that when reversed the propulsion system blows air back out of the inlet and blows away all the problem material...

But as BigGazza said... they have them on their Borei SSBNs and not on their SSNs... think that might be a clue that they don't want them on their attack subs...

GarryB wrote:I would think an inlet guard on a pump jet would make more sense to prevent the problem in the first place... design it so that when reversed the propulsion system blows air back out of the inlet and blows away all the problem material...

But as BigGazza said... they have them on their Borei SSBNs and not on their SSNs... think that might be a clue that they don't want them on their attack subs...

Waterjets / pumpjets works in the water, so "the system blows WATER back when reversed!

I know that big submarine and surface ship waterjets are different and more complex in many ways, but the principles should be similar, I think. Reversing cannot always help, but in some situations can help.

Can we also categorically state they have pump jet propulsion systems on the Borei SSBNs and one of the Kilo class SSKs... the latter was for testing, which was tested thoroughly, so the issue is clearly not that they don't know how to make them or can't afford the technology...

Their reasons might be as simple as when operating in northern waters there is a chance of water freezing inside the pump jet and jamming the whole propulsion system, or hiding for long periods amongst ice fields is a problem for pump jets as you need an external propeller to chomp up ice so the sub can move in places western subs might have problems with.

I mean we see that British ships have problems operating in warm water because they need colder water to cool their engines with... you really don't know these things for sure until you test them... and the Russians clearly tested them.

GarryB wrote:

I know that big submarine and surface ship waterjets are different and more complex in many ways, but the principles should be similar, I think. Reversing cannot always help, but in some situations can help.

Can we also categorically state they have pump jet propulsion systems on the Borei SSBNs and one of the Kilo class SSKs... the latter was for testing, which was tested thoroughly, so the issue is clearly not that they don't know how to make them or can't afford the technology...

Their reasons might be as simple as when operating in northern waters there is a chance of water freezing inside the pump jet and jamming the whole propulsion system, or hiding for long periods amongst ice fields is a problem for pump jets as you need an external propeller to chomp up ice so the sub can move in places western subs might have problems with.

I mean we see that British ships have problems operating in warm water because they need colder water to cool their engines with... you really don't know these things for sure until you test them... and the Russians clearly tested them.

Their reasons might be as simple as when operating in northern waters there is a chance of water freezing inside the pump jet and jamming the whole propulsion system, or hiding for long periods amongst ice fields is a problem for pump jets as you need an external propeller to chomp up ice so the sub can move in places western subs might have problems with.

Sorry, but i think that subs are not projected, neither constructed to lay still in the water. If water freezes within pump jet than a whole sub would be stuck in pack ice and made useless. i have never heard of such case in the history of submarines.

The Akula class (NATO codename Typhoon) was designed to hide under thin areas of arctic sheet ice and surface through that ice to launch its missiles... I would expect newer designs would at least use the ice to hide around... and SSBNs mission is not to constantly move around all the time... its mission is to remain hidden but able to receive instructions when needed... if it hides on one side of an iceberg then at least it is protected from one side...

When the Germans were designing tanks they had the brilliant idea of overlapping the wheels as that spreads the weight and reduces gaps between the wheels where enemy penetrator rounds could go through to penetrate the hull side.

In practise mud and snow and ice got in between the wheels during driving during the day and overnight it all froze solid and the vehicle could not move at all in the morning.

Something might sound like a clever solution, but you need to test it to see if it is all good or if there are any problems with the new technology.

They adopted it for the Borei class SSBN which suggests it is useful for the places they operate and they way they operate... the fact that the new SSKs and SSNs and SSGNs don't have pumpjet systems suggests there are some serious issues for certain tactics and methods of use or perhaps locations that make a normal propeller more suitable.

GarryB wrote:The Akula class (NATO codename Typhoon) was designed to hide under thin areas of arctic sheet ice and surface through that ice to launch its missiles... I would expect newer designs would at least use the ice to hide around... and SSBNs mission is not to constantly move around all the time... its mission is to remain hidden but able to receive instructions when needed... if it hides on one side of an iceberg then at least it is protected from one side...

When the Germans were designing tanks they had the brilliant idea of overlapping the wheels as that spreads the weight and reduces gaps between the wheels where enemy penetrator rounds could go through to penetrate the hull side.

In practise mud and snow and ice got in between the wheels during driving during the day and overnight it all froze solid and the vehicle could not move at all in the morning.

Something might sound like a clever solution, but you need to test it to see if it is all good or if there are any problems with the new technology.

They adopted it for the Borei class SSBN which suggests it is useful for the places they operate and they way they operate... the fact that the new SSKs and SSNs and SSGNs don't have pumpjet systems suggests there are some serious issues for certain tactics and methods of use or perhaps locations that make a normal propeller more suitable.

I agree. pr.941 Akula SSBNs were specially projected to surface even through 2m ice. Borei pr.955 is much smaller, with less capability to surface through pack ice, but places with difficult ice situation are a common operation area for russian subs in general!

They had special instruments to find the thin areas of ice... I think they called them Polyanas or something for the Akula to surface and break through... perhaps now they have special explosives to shatter the ice above the smaller lighter subs so they can surface and still fire their missiles.

I seem to remember images of deltas sitting on the surface in a solid ice field with their high missile structure on the subs giving them good clearance for a launch... though to be fair they might just have been drawings by US intelligence... it was 30 years ago...

GarryB wrote:They had special instruments to find the thin areas of ice... I think they called them Polyanas or something for the Akula to surface and break through... perhaps now they have special explosives to shatter the ice above the smaller lighter subs so they can surface and still fire their missiles.

I seem to remember images of deltas sitting on the surface in a solid ice field with their high missile structure on the subs giving them good clearance for a launch... though to be fair they might just have been drawings by US intelligence... it was 30 years ago...

I think that explosive charges are not used or rarely used to break ice, though old straight running torpedoes can be used for that purpose. Ice free sea "lakes" are polynyas - полыня, accented on the last syllable. Special "ice sonars" are also used. All russian subs in service can launch missiles submerged down to 50m depth at least. Missile itself can break some ice thickness also.