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Screen or Grate on Bowthruster tunnel

Discussion in 'Technical Discussion' started by Zeke, Feb 14, 2014.

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  1. Zeke

    Zeke Member

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    Jun 14, 2010
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    Location:
    New York City
    We recently hauled the older 100 ft motoryacht which I run. It has a shipwrights bowthruster installed in an 8" FRP tunnel. One of the two gratings was missing. It seems that nobody I can find sells screens/gratings for thruster tunnels. Do most bow thrusters have these or no? Does anyone have a recommendation where I can get one or is it safe to run without? We have presumably been running with a missing gratings for a while.
  2. NYCAP123

    NYCAP123 Senior Member

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    The boats I run are a bit smaller, but I've never seen a grate or screen over a thruster tunnel. Seems that would make servicing difficult.
  3. Mark Woglom

    Mark Woglom Senior Member

    Joined:
    Jan 30, 2011
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    Live in Gilford NH. Boat in Sarasota winters, New
    I have Max Power 225 electric thrusters on my boat. Twice, I've lost a propeller blade on the bow thruster. (There are duplicate 3 blade "props" on both sides of the "prop shafts".)

    I never noticed a problem, such as the sensation of a locked shaft, or a vibration from a missing blade. In both cases, the missing blade was reported to me by the diver that cleans the bottom of my hull.

    I don't have any sort of debris filter, such as a grate or screen. Part of me thinks there should be a filter, and part of me thinks the blades are junk. I'd bet on junk blades, because the thruster doesn't get that much use, and it certainly doesn't get used in a debris field.

    I don't recall ever seeing thruster tunnels with debris screens, but I'm normally looking at boats from above the water line.
  4. Old Phart

    Old Phart Senior Member

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    I dunno
    Hmmmmmm.

    Have you contacted the mfg?

    Read feature #4, regarding servicing, while in the water.

    Bow and Stern Thrusters


    P.S.- Ask about their Custom designed Stator Screens, too (ask about feature #6 on website).
  5. Capt J

    Capt J Senior Member

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    If they're Vetus bowthruster props. It's corrosion. Water gets between the plastic bow thruster propellor and the brass hub, that puts pressure on the plastic propellor and eventually splits it.
  6. Caltexflanc

    Caltexflanc Senior Member

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    Sep 25, 2011
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    Location:
    North Carolina
    That's not the problem the OP has, he is missing a screen not the prop. And the guy missing blades said he has a MaxPoewr BT. A couple of times I have toured the Jarrett Bay yard when there were 150 or so big boats in there for hurricane haul out, and looked at all the hull forms and configurations. I can vaguely recall a BT screen on one boat, maybe two. . The only fear I can imagine needing one for is if you are regularly picking up moorings where the pennants drop below the ball and you are concerned about sucking one up. Or the occasional bow line that gets accidentally dropped in the water. Seems to me a screen fine enough to prevent that would also lessen thrust (?)

    By the way, I believe Vetus fixed the mentioned corrosion problem a few years ago with their new prop design.
  7. Capt J

    Capt J Senior Member

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    Not from what I've seen.....The new prop is the same material but just a 3 blade instead of a 5 blade or 6.

    A screen small enough might restrict flow, unless the opening is larger than normal, but the biggest issue is it might create cavitation. I'm sure if the boat is out of the water a welder/fabricator can make what he needs. I've seen verticle bars, but never a screen. Also that would make it really hard to clean barnacles out of there. I was replying to Mark who I quoted in my earlier post.
  8. Capt Bill11

    Capt Bill11 Senior Member

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    I don't like screens or grates on my tunnels. I always take them off.
    Now if I was running in an area were the water was filled with debris all the time I might feel different. FWIW, in all my years of running boats with thrusters I've only had something get in the tunnel and lock up a prop once.