Water Jet Bow Thruster

Discussion in 'Propulsion' started by ytquest, Nov 25, 2012.

  1. ytquest
    Joined: Oct 2005
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    Location: Hendersonville,Tn.

    ytquest Junior Member

    I would like to pick a few engineering brains about useing water jets for a bow thruster system and if practical where to find some spec's for nozzle size and pressure requirements.
    Thanks for any info.
     
  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    For many years I sailed a 25 meter boat with a waterjet bowthruster.

    The system worked .

    It was very complicated and a major problem was the huge sea strainer needed to filter the volume of water needed. Harbours are full of junk, plastic bags and whatnot. Many times the sea chest clogged.

    When modern, small yacht size thrusters, appeared on the market we cut it out and replaced it with a hydraulic thruster.
    Unless you have some special idea Id forget the waterjet and go conventional.
     
  3. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    There was a company marketing a waterjet thruster that was quite simple. There was a high volume water pump belted off the engine and two manual hydraulically operated valves that diverted the water port or starboard.

    Michael has a valid point about strainers and junk.

    I would think someone could easily cobble together one.

    I did a quick search and turned this up:

    http://www.jetthrusters.com/

    http://www.sopacmarine.com.au/Portals/3/pdf/thrusters/WillDo Jet Thrusters.pdf

    http://www.omnithruster.com/Welcome.html

    And one last thing which I was reminded of when I saw the last link, it does not matter if the nozzle is above or below the waterline, the performance is the same.

    Steve :rolleyes:
     
  4. michael pierzga
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    michael pierzga Senior Member

    Consider the inside diameter of the pump output plumbing . HUGE, and made of steel, plus the valve system to thruster port, starb and idle. Lots of stuff.
     
  5. ytquest
    Joined: Oct 2005
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    Location: Hendersonville,Tn.

    ytquest Junior Member

    Thanks for the info Keysdisase and the input Michael. I am not very fond of putting a 9" hole on each side of my bow.
    I have run my Garden designed Force 50 for 22 years with out one but find that every now and then a small push on the bow could make the difference between having to make a second try.
    And take into consideration the loss of hull speed due to drag from the tube or external unit. Let's face it 7.5 to 8 knots is about max hull speed for me. Most Mfg. estimate a loss of 1 to 1.5 knots due to the tunnel.
    Guess I will have think on it.
     
  6. Frosty

    Frosty Previous Member

    I shudder at the thought of cleaning and antuifouling an underwater thruster.

    Spend the money on some driving lessons.

    You don't need a thruster , on a bigger boat 70 up just get the bow tied up and pull back.
     
  7. ytquest
    Joined: Oct 2005
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    Location: Hendersonville,Tn.

    ytquest Junior Member

    Don't really need lessons after 22 years of running her, but with 8' of freeboard on the bow in a blow single handed. It would be nice to keep the bow from falling off before I get there.
    Did not always live this far inland, just came up raise my son after he was shang -haied away.
    But thanks for the advice Frosty.
     
  8. Frosty

    Frosty Previous Member

    If its nice weather and the sun is out and tourist walk the dock I may take a bit of time and place it bang in the dock before releasing lines .. But if it not I get the bow tied up first . The stern is where the prop is so I can do anything I want with that bit.

    Ive seen 40 footers with B thrusters and still make lash up.
     
  9. ytquest
    Joined: Oct 2005
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    Location: Hendersonville,Tn.

    ytquest Junior Member

    Know what you mean, fixed the gel-coat and glass on many of them. CH-CHING
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Look into drop down bow thrusters. They don't have a hole, so no drag.
     
  11. ytquest
    Joined: Oct 2005
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    Location: Hendersonville,Tn.

    ytquest Junior Member

    Thanks Par, I have and they are a better alternative to tunnels but both tube and tunnel have high initial, installation and maintenance cost associated with the products. I was looking for a cost effective alternative. (no free lunch)
     
  12. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Drop downs are complex, heavy ,expensive, high maintenance and will take up your complete forepeak. They always interfere with proper anchor chain storage and can instantly be damaged if you pick up a mooring line while maneuvering or you retract a fouled rope into the unit.

    Tunnels are robust and hide inside your hull.

    Id be surprised if you loose 1kt with a well installed tunnel.

    When looking thru the different offerings choose the most powerful unit for your application.

    What happens with a thruster is that it changes your seamanship and docking routine. Different options open up, like spinning the boat on its keel in a very tight harbour or singlehanded docking . Important that it can actually do the job.
     
  13. Frosty

    Frosty Previous Member

    I agree with what you say michael about the drop down --possibly the first time that I have.

    Except a single engine boat can also be swung on its keel without a thruster.

    There is info on the internet on fairing a thruster port and it is important. I dont think losses are even 1 knot.
     
  14. watchkeeper

    watchkeeper Previous Member

    Best bow thruster in the world for leisure craft is a deckie or youngster in an 3m RHIB with 25hp OB
     

  15. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    That what I use... an all purpose deckie with a pair of flippers.

    Foolproof and cheap
     

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