Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades - SailNet Community

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  #1  
Old 11-03-2012
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Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

I installed my 185TT steel thruster tube and attempted to install the thruster. The thruster prop cannot be installed on the shaft when the drive assembly gasket that is provided is installed between the drive unit and the tube. Without the gasket the prop can be fitted with the bottom contacting the tube. Prop clearance to the bare steel in the tube is about 1/24th of an inch total or 1/48th all around if the prop is centered. This is without any primer or bottom paint on the steel. Apparently my only option is to cut down the prop at the wide ends of the blades with a consequent and significant loss of performance.

Any experience out there with this model with a steel tube? Apparently there is a shortage of engineering talent at Lewmar. Other installations that I have looked at have 1/8 to 1/4 all around clearance after primer and bottom paint have been applied. Cutting 1/8 to 1/4 off the wide ends of the prop probably takes out 10% or more of the blade area and thrust.
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Old 11-03-2012
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

cutting the blades in any way is going to result in an out of balance rotating mech.....it will not last long at all, and has the potential of destroying itself and the motor and the housing in short order

Something is amiss, installed wrong or defective....

best to chase down Lewmar or an installation tech familiar with this model.
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Old 11-03-2012
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

I have no personal knowledge of this (why should that stop me from commenting?) but it seems that the tube is too small or your prop is too big. Someone grabbed the wrong part at the factory / someone ordered the wrong part / some else screwed up?

I doubt you would be successful cutting that prop, without destroying the whole unit in short time. I would guess with the proper equipment and talent, the prop could be cut but why? Something is wrong. Fix the original problem, don't create new ones.

Lewmar can't help??
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Old 11-03-2012
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

Not a wizard of physics or hydrodynamics but I wonder what actually happens to the diameter of the blades when spun under water. Will the blades flex creating more room between them and the pipe because of the resistance of water? I do appreciate that there should be more space when installing the blades. It looks like a either a crap design or the wrong parts were put together at Lewmar. Good luck and see you later at Cariga's.

Last edited by FarCry; 11-05-2012 at 09:52 AM.
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Old 11-03-2012
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

Not that I know anything at all, because I don't, but I think most props go out of balance about one week after they hit the water due to growth on a blade or chips here and there. Just a though in case you have no choice but to grind a 1/4" away.
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Old 11-04-2012
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I have the same model thruster installed in a fiberglass tube on a new to me Beneteau. The prop was heavily fouled and I purchased a new prop instead of trying to clean the original. I installed the new prop just prior to launching and found the same problem. Not having any time to research the problem I ground down the edges of the prop as close to even as the other blades. As careful as I was to get the blades even I am sure it is out of balance. When I compared my grinding to the original props grinding my grinding was much more even. I figured the balancing was not critical as any growth would also cause balancing problems. I completely forgot about me having to grind the prop in order to fit. I am going to contact Lewmar to get their input on this.
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

Thanks georgec -- I have sent a request to Lewmar Product Support and will try to get someone on the phone on Monday. I downloaded a copy of the prints on the Lewmar site to try to determine the design diameter of the prop but cannot open the files. Tube ID is 7 9/32 inches so prop diameter should be about 6 7/8 to 7. It is about 7 7/32.
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Old 11-04-2012
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

If I'm understanding the OP; The Gasket is the problem? It is possible the MFG, has a torque setting for the bolts. That would compress the gasket and give the prop the clearance needed. I've encountered this situation in air moving equipment. The deflection of the shaft only needs to be very very slight to cause misalignment. If the tube is out of round, or the mount has been flexed he may need a new tube.
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Old 11-05-2012
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

Unless or until Keith shows up to respond, no the gasket is not the problem. No the steel tube is not of round nor has the mount been flexed either, all good theories however. Yesterday he found another boat in the yard with the same bow thruster. The tube was the same diameter but the blades were a smaller diameter. This really looks like a problem with the parts that Lewmar supplied in their package. I just hope they resolve it quickly as Keith wants to confirm that steel can float very soon...
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Re: Lewmar 185tt Bow Thruster Install - Clearances/Cutting off Blades

Spent a half an hour on the phone with Lewmar US and UK. General denial response. Asked UK for the design diameter of the prop and they did not have a drawing! UK has agreed to send a drawing when they find it.
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