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.