New way of fitting bow thruster

Discussion in 'Boat Design' started by iceboater, Dec 25, 2012.

  1. iceboater
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    iceboater Junior Member

    We are in the process of designing a new 10m commercial fishing boat, and are interested in
    using new way of fitting bow thruster to our boats.

    I recently saw this (photo) at a boat show.
    The tunnel is half made in the mold and the tunnel bottom half is made from another mold
    and it looks like that piece is glued to the hull.
    I would like to use this method in our new mold and I am wondering if anyone building plugs or
    molds is offering this?

    If not, I think it could be a business opportunity for someone to make mold inserts with different diameter
    for truster tunnels like this, that could be cut to fit different lengths and V shapes.
    The concave shape aft of the tunnel could be separate peace to be adjusted to different hull shapes and then glassed
    to the tunnel insert to be inserted as mold in the mold in one peace, if boat is to have bow-thruster.
    The convex lib in front could be made with different materials after pulling the hull.

    The advantages I see in doing it this way are:
    Solid laminating in critical area of the boat.
    Solid gelcoat.
    Tunnel can be closer to the keel because of not needing to have
    space to laminate under tunnel.
    saves time.

    I have not thought of any disadvantages, but I would like to ask
    if anyone sees any problem with it or has experience with similar way of doing it?

    Thanks, Axel
     

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  2. SamSam
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    SamSam Senior Member

    I like the retractable bow thruster approach, it looks to have some advantages...

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I too like the drop down thrusters, particularly in canoe body craft where there's no fore foot to speak of. Some designs tend to be giant weed and debris catchers, such as the two you've shown, but others are much better in this regard.

    The reason to split the tunnel is fairly easy to understand, it permits demolding after layup. You'd never get it out of the mold other wise.
     
  4. tunnels

    tunnels Previous Member

    The idea is there but a completely manufactured drop in unit to fit the mould and then make everything as a part of the hull very little to no gel coat repairs like that one .
    Its a pretty disturbing shape but its far enough forward that maybe wont have an effect on anything by the time the water flow gets to the back!! :D
     
  5. michael pierzga
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    michael pierzga Senior Member

    I like the concept. Its the first time I have seen it. Installing a thruster tube is time consuming and prone to error.

    I cant see any disadvatages to your proposal. Even if the bottom fairing was damaged and fell off, the integrity of the boat wouldnt be comprimised.

    Im surprised that the idea is not already used on production boats.
     
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  6. wet feet
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    wet feet Senior Member

    I have seen a few of these installations and can appreciate the time removed from the process.I have to say that the few I have seen,as well as the one in the original post,seem to have quite large gaps between the mouldings.I also think the laminators who have the job of making the capping may find the job rather challenging.I would imagine the capping will fill with water over time,even if foam filled.
    The retractable thrusters are undoubtedly the best solution for minimum drag when not in use,but don't they look a bit delicate?They would also soon lose the drag advantage if the water in which the boat operates contains odd bits of rope or fishing net that prevent full retraction.
    I would prefer to mould the hull with the fairing for the tube included and just bond in a length of tube after moulding.Obviously this would require a mould designed to permit removal of the component or a centreline split.
     
  7. SamSam
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    SamSam Senior Member

    A large problem could be that not everyone needs a bow thruster or they don't want one because of the added cost and disruption of hydrodynamics. The vast majority of boats don't have bow thrusters, so building the mold with provisions for them (as in the OP photo) could severely limit the desirability of that hull shape and thus the usefulness of the mold. If you didn't want a bow thruster, you surely wouldn't want the huge hole and disrupted hydrodynamics of the hull shown in the OP photo.

    It seems like a solution to a problem that might not exist, and might cause bigger problems than it is attempting to solve.
     
  8. michael pierzga
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    michael pierzga Senior Member

    Hard to find a modern boat without a thruster. The client demands them. Makes sense to design the thruster into the structure at the beginning.

    Retractable thrusters are expensive, need experienced craftsman to install, high maintenance and fragile. The pivoting Hydromar ? thruster in the first picture will require many axel seal changes over its life cycle. The hydro motor is housed in the leg..a blown seal empties 50 liters of oil faster than you can respond to the low oil level alarm.

    Tunnels are the way to go on motorboats.
     
  9. Frosty

    Frosty Previous Member

    Michael has a --I think therefore it is ---syndrome.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Yup, I use them and fix them.

    This one cost 12 thousand to fix. Go with a tunnel thruster.

    http://[​IMG]


    [​IMG]
    image ru
     
  11. iceboater
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    iceboater Junior Member

    SamSam, I think you do not understand my description of how it is built.
    The half of the tunnel that is glassed with the hull is made on removable mold insert, so if the boat is not to have
    bow thruster you would not see anything but small imperfection in the gelcoat where the 2 bolts holding the insert
    where closed with clay.
    You mention disruption of hydrodynamics, which would not apply to our boat because at cruising speed of about 18-22 knots,
    we figure that the thruster is mostly out of the water.

    Drop down thrusters are not an option in our boat because the thrusters are used while hauling nets and longline and the ropes could be
    snagged on it.
     
  12. michael pierzga
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    michael pierzga Senior Member

    You should approach the thruster companies with your concept.

    It sounds like something that they could package with a thruster when selling 12 units to a production boat builder
     
  13. SamSam
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    SamSam Senior Member

    I see. Well, it wouldn't be too hard applying clay or fillet wax around the mold insert whenever you used it and the fit between the bottom part and the hull could easily be made much better.
    I would imagine the small flats fore and aft of the tunnel are/could be used to physically bolt the bottom half of the tunnel to the hull, allowing easier dis-assembly compared to gluing. But, maybe dis-assembly is not a concern.

    What is the purpose of the convex and concave shaping? To improve hydrodynamics or allow use of the thruster at higher speeds?
     
  14. iceboater
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    iceboater Junior Member

    Some others seems to have ---non contributing ---syndrome :)
     

  15. iceboater
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    iceboater Junior Member

    You are right, there is no need of dis-assembly.

    On that photo the convex and concave shape is bigger than I do it, but the purpose is to deflect water outward and prevent it hitting
    the aft part of the tunnel creating resistance and turbulence in the tunnel and even spinning the thruster prop in some cases.
     
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