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  1. #1
    Join Date
    May 2001
    Location
    Broken Brexit Britain
    Posts
    55,916

    Default Sternthruster problems - advice?

    In the 5yrs I've owned my current boat I have had recurring problems with the sternthruster, specifically failures of the electric motor and electrical control box attached to it. The control box has been replaced and the motor rebuilt but now it seems the motor has failed again and it is beyond repair. Both my bowhruster and sternthruster are Sidepower units and have the same 13.1hp motors. I have never had a problem with the bowthruster so I know there is no inherent problem with the motors

    The problem with the sternthruster is that the motor sits at the aft end of the boat (obviously!) in a separate bilge compartment under the bathing platform



    This compartment always has water sitting in it despite my best efforts to keep it dry and obviously any water tends to migrate to the aft end of the compartment when the boat is on the plane. This means that the sternthruster motor is often sitting in water or being splashed with water. No wonder it keeps failing

    There are 2 questions I wanted to ask

    First, I approached Osmotech in the UK (Sidepower agents) for their advice. They suggested I replace the standard motor with an IP motor ie one that is protected from moisture. Unfortunately Sidepower do not offer a like for like IP replacement for my 13.1hp motor and Osmotech have offered a 10hp motor but suggested that it will give similar thrust to my existing 13.1hp motor if I also replace the existing 4 bladed prop with a new 5 bladed one. I'm not sure I believe this. Any comments?

    Second, I want to make further efforts to keep this bilge compartment drier. I have already replaced the hatch seals and the rudder stock bearings and I am really at a loss to understand where the water is coming from now. The mechanic who replaced the hatch seals swears blind that the new seals are not leaking because he's sat inside the compartment with the hatch closed and had somebody else spray water over it. There is no sign of any leaks from the rudder stocks either. There is quite a large bilge pump in the compartment but it cant empty all the water. I am thinking about fitting an additional small bilge pump to get more of the water out but that still doesnt tell me where its coming from. Any ideas? There is no connection between this compartment and the engine compartment forward of it

  2. #2
    Join Date
    May 2001
    Location
    Bucks & St Raphael SoF
    Posts
    1,485

    Default Re: Sternthruster problems - advice?

    Hi Mike, I have the same problem with water sitting in the same place and am also not sure where the water is coming from. I had assumed it was excess rainwater, but the hatch seals are OK. The 2 thoughts I had were 1 - a weep around one of the bolts that joins the platform to the hull (unlikely) or 2 - I know the water from cockpit drains around the engine hatch run through the BP and out the the back, and maybe there is a leak from here.

    My stern thruster looks to be in a similar position to yours and is boxed in - i think it's a Vetus unit, and haven't had any problems caused by moisture, but I'm not sure on their power rating, or quality!

  3. #3
    Join Date
    Jul 2014
    Location
    Lincoln
    Posts
    257

    Default Re: Sternthruster problems - advice?

    Is there any way to build a small enclosure around the stern thruster to prevent the water moving/splashing on the motor?

  4. #4
    Join Date
    Oct 2007
    Location
    Belgium
    Posts
    4,882

    Default Re: Sternthruster problems - advice?

    fwiw,
    this summer I've replaced the old and broken 4 blade propeller from the bow thruster
    with a new 6 blade prop,
    6 blades is now standard at Vetus, they don't claim anything about the thrust, they claim (and it gives) less noise compared to the 4 blade.
    my feeling is that the thrust is the same, for sure not more then before.

    regarding the moisture,
    boxing the existing motor seems a good solution

    do you really need a stern thruster ?
    I don't have it never missed it

  5. #5
    Join Date
    Jul 2003
    Location
    River Itchen, Southampton
    Posts
    7,320

    Default Re: Sternthruster problems - advice?

    Quote Originally Posted by mikef View Post
    In the 5yrs I've owned my current boat I have had recurring problems with the sternthruster, specifically failures of the electric motor and electrical control box attached to it. The control box has been replaced and the motor rebuilt but now it seems the motor has failed again and it is beyond repair. Both my bowhruster and sternthruster are Sidepower units and have the same 13.1hp motors. I have never had a problem with the bowthruster so I know there is no inherent problem with the motors

    The problem with the sternthruster is that the motor sits at the aft end of the boat (obviously!) in a separate bilge compartment under the bathing platform



    This compartment always has water sitting in it despite my best efforts to keep it dry and obviously any water tends to migrate to the aft end of the compartment when the boat is on the plane. This means that the sternthruster motor is often sitting in water or being splashed with water. No wonder it keeps failing

    There are 2 questions I wanted to ask

    First, I approached Osmotech in the UK (Sidepower agents) for their advice. They suggested I replace the standard motor with an IP motor ie one that is protected from moisture. Unfortunately Sidepower do not offer a like for like IP replacement for my 13.1hp motor and Osmotech have offered a 10hp motor but suggested that it will give similar thrust to my existing 13.1hp motor if I also replace the existing 4 bladed prop with a new 5 bladed one. I'm not sure I believe this. Any comments?

    Second, I want to make further efforts to keep this bilge compartment drier. I have already replaced the hatch seals and the rudder stock bearings and I am really at a loss to understand where the water is coming from now. The mechanic who replaced the hatch seals swears blind that the new seals are not leaking because he's sat inside the compartment with the hatch closed and had somebody else spray water over it. There is no sign of any leaks from the rudder stocks either. There is quite a large bilge pump in the compartment but it cant empty all the water. I am thinking about fitting an additional small bilge pump to get more of the water out but that still doesnt tell me where its coming from. Any ideas? There is no connection between this compartment and the engine compartment forward of it
    I Used to fit sternthrusters Mike and we used to build a dam around them as Richard suggests as a matter of course. It's the only way IMO. The operation of a bilge pump float switch is a foreseeable event no matter how many seals you replace and you don't want it to cost you a k (ie a new motor!)

    Just epoxy in some marine ply or some GRP offcuts if you can get them. About 6" high will do the trick as your pump will be shouting at you long before that's inadequate.

  6. #6
    Join Date
    Jun 2011
    Location
    Volos-Athens
    Posts
    4,911

    Default Re: Sternthruster problems - advice?

    boxing it in, wont it create heat dissipation issues?
    OK, it's stern so wont be used alot, but still, no?

    I recon cheapest solution would be a hydraulic pump on the PTO on one of your engines, 2 pipes to stern and modify the housing to accept a hydraulic motor

    cheers

    V.

  7. #7
    Join Date
    May 2001
    Location
    Broken Brexit Britain
    Posts
    55,916

    Default Re: Sternthruster problems - advice?

    Quote Originally Posted by vas View Post
    boxing it in, wont it create heat dissipation issues?
    That was my concern but if Elessar says its OK I will do that. I dont use the sternthruster a lot. Its more a nice to have rather than essential but I hate having anything on the boat which doesnt work!

    I cannot imagine that a hydraulic solution would be cheaper although if I was speccing a boat from new I would certainly go hydraulic

  8. #8
    Join Date
    Oct 2007
    Location
    Belgium
    Posts
    4,882

    Default Re: Sternthruster problems - advice?

    Quote Originally Posted by mikef View Post
    That was my concern but if Elessar says its OK I will do that.
    pls realise that Elessar proposes the smart solution to make a "dam" = wall around the motor,
    not a fully enclosed box,
    then, heat is no isuue, I'm just not 100% sure if this is enough protection against moisture "spray" inside that compartment

  9. #9
    Join Date
    Jun 2011
    Location
    Volos-Athens
    Posts
    4,911

    Default Re: Sternthruster problems - advice?

    Quote Originally Posted by mikef View Post
    I cannot imagine that a hydraulic solution would be cheaper although if I was speccing a boat from new I would certainly go hydraulic
    I'm pretty sure the "motor" you'd have there would be really peanuts (couple of hundred euros?) The PTO adapters etc is another mater though

    Quote Originally Posted by BartW View Post
    pls realise that Elessar proposes the smart solution to make a "dam" = wall around the motor,
    not a fully enclosed box,
    then, heat is no isuue, I'm just not 100% sure if this is enough protection against moisture "spray" inside that compartment
    +1


    cheers

    V.

  10. #10
    Join Date
    Apr 2011
    Location
    Boat- Western Med
    Posts
    5,444

    Default Re: Sternthruster problems - advice?

    When on the plane and bouncing about .....
    1- May the rear box section flexes and looses it static seal your guy tested out ?
    2- the lid move and thus water ingress ?

    Fix
    Is there any way of mounting the motor higher ( accept the water ingress in a chasing tail kinda way ) ......
    Longer shaft , belt n pulley , chain n sprockets ?
    I,am writing this without the benefit of a pic of the existing set up / arrangement in the box .

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