Fireboat 48 - a problem

Discussion in 'Jet Drives' started by aisha0808, Sep 8, 2009.

  1. aisha0808
    Joined: Sep 2009
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    aisha0808 New Member

    Hello guys.
    Im very new to this forum and got a problem. Any ideas will be welcomed.
    The big issue with this fireboat 48 (manufactured by Metal Craft Marine) it is the dirt collection
    Basically this boat have 2 pump that r sucking up the dirt but the grills are too big and marine roapes or plastic bottles are getting stucked into it so the cleaning have to be done manually.
    Now, i've been asking the manufacturer for a solution/idea and they never replied.
    Someone propose a smaller holes grill but that will affect the intake of the water.
    Someone else propose bigger pumps but they r sooo expensive.

    Im not an engineer so Im not sure if i explained correctly but plz guys i really need help on this matter.

    http://www.metalcraftmarine.com/html/firestorm_4648.html here u can see the boat im talking about.
     
  2. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Oh, your explanation is clear enough, the problem is very well known with water jet operators, and is a good reason to stay away from jets. It surprizes me that the jet supplier, Hamilton, has not responded to your signals!

    The objects you mention are mostly more or less floating debris, which is following the hull bottom into the jet entrance. As you correctly notice, any reduction of grating openings will have a detrimental influence on the jets. What can be done is a stretch of the inlet tunnel, so that it will reach down below the hull bottom to form a "collar" outside the boundary layer.

    This way, it is not collecting the debris that follows the bottom surface as easily as without this "collar". However, it is not a foolproof method, and the problems you might have with long algae will not be cured. Anyway, matching the shape and areas of this inlet is extremely critical for good performance, and must be done with due consideration of the flow necessary for the operating jet .

    I have designed a few special intakes along these thoughts for coastal fishing vessels; to be honest, it works far better than the originals (even in ice conditions), but it is certainly not "the complete solution" (which is to go for CP propellers....). You are welcome to mail me directly if you need further assistance.
     
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Castoldi, an Italian jet maker, uses a movable intake grid that can be operated by a large lever. It cuts plastic and wood.
    The system is used on police patrol boats and military craft and seems to work quite well; I do not know if it can also cope with ropes and nets.
     
  4. baeckmo
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    baeckmo Hydrodynamics

    That's right, and there are more movable grids around in the jet world; they are ok with reasonably "stubby" objects, like a log or a shoe. The real challenge are the floating nylon ropes, plastic bags, salt water ice, condoms aso.
     
  5. anthony goodson
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    anthony goodson Senior Member

    baekmo CDK are you sure you are answering the question asked, it would seem that aisha has a problem with his fire pumps ,not his propulsion jets, just an observation
     
  6. baeckmo
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    baeckmo Hydrodynamics

    You're quite right Anthony, my "inner screen" was instantly showing the familiar blur of mixed leftovers so often seen in a jet intake, and the reaction from my reptile brain was immediate.

    To my defence please note that the "Metalcraftmarine" are bragging about their fancy and supreme mudboxes protecting the fifi pumps, so my associating to the propulsion pumps is not totally in the blue!

    Now, we have to wait for Aisha to put the spell on us.......CDK, come hold my hand...
     
    Last edited: Sep 9, 2009
  7. anthony goodson
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    anthony goodson Senior Member

    Your interpretation may yet be proven right baekmo ,it was just an observation
     
  8. DJC
    Joined: Nov 2009
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    DJC New Member

    A product that is just coming to market designed to address the problem of jet intake fouling is the patented Fin Cutter System. It is a two stage system which clears both the intake screen and the impeller of virtually any debris drawn into the jet. It can be operated at any boat speed, no need to stop and backflush. The screen for the system also flows 10% to 15% more water than the original screen.
     
  9. anthony goodson
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    anthony goodson Senior Member

    If the problem is that bad ,use another propulsion system
     

  10. drmiller100
    Joined: Feb 2009
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    drmiller100 Junior Member

    stomp grate is the traditional solution for river boats.

    If a fellow had a "spare" pump, he could turn off the plugged pump and use pressurized water to clean the intake screen.

    basically, you would mount a nozzle inside of the intake to backflush the screen.
     
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