Bow Thruster Anomaly

[CaspersCruiser]

Last Monday, July 17th, I launched my 2012 R27 for a shakedown after it had been stored indoors since concluding my Florida panhandle cruise at the end of February. Everything worked well for two hours of cruising until maneuvering into my slip. I was in the middle of the fairway starting the 90° turn into the slip when I activated the bow thruster. It paused for a moment and then made a spinning noise. Not fast as I expected to hear with a sheared pin, although, thankfully, I have never heard a thruster run with a sheared pin. But it did spin and did not produce thrust.

The next morning, as planned, I cruised an hour back to the launch ramp and trailered the boat. When I pulled it out of the water, I looked in the bow thruster tube expecting to see a stick or piece of stray dock line stuck in the prop. There was nothing but a small bit of limp water growth. No sticks, no dock line.

I went to the helm and had an observer watch the prop as I bumped the thruster. They reported the prop turned at speed. That was encouraging, but head scratching.

I returned to the thruster tube and checked the security of the prop. It spun freely, but there was about 1/8” IN-OUT play of the prop hub on the shaft. I checked the stern thruster prop and found its prop hub had only a minuscule amount of IN-OUT play.

Last year when I had the boat at Huckins Yacht in Jacksonville for service, they replaced the bow thruster prop. I wondered if they had simply failed to sufficiently torque the prop nut when installing the new prop. By the way, the new prop made a marked improvement in thruster performance.

I talked with Ray Lavoie at Imtra about this issue and he discounted that the prop was loose and said that it was likely that the pin had sheared and was only partially engaging. Well, today I used a long ratchet extension and socket (13mm) and it took a surprising amount of torque to secure the prop hub nut.

To anyone who may try this procedure, per Ray Lavoie, the bow thruster prop has to be blocked while applying torque to the prop hub nut or the whole prop hub and prop turns when torque is applied. I used a piece of scrap quarter round long enough to pass all the way through the prop to the other side of the thruster tube. (To my darling wife—“See dear, there IS a reason I keep all these pieces of scrap wood in the garage!”)

Has anyone out there in Tugnuts land encountered a loose thruster prop hub nut? I’ll find out if this resolves the issue when I next launch the boat.

 

[BB marine]

The shaft is splined. The nut holds the the prop on it does not drive the prop onto a taper. In my opinion having the nut loose will only cause it move on the shaft. There is a washer that needs to be installed and then the nut. I tightened the nut until all end play was removed. The end play is not causing the prop to not spin. I would agree with the tech the pin is sheared.

 

[CaspersCruiser]

I would agree with the tech the pin is sheared.

The “Wizard of Tugnuts” has spoken.

Time to find that spare shear pin.

 

[NorthernFocus]

It takes very little torque to spin the prop out of the water. So even with a sheared pin there can be enough friction to spin the prop in air but not when submerged.

 

[CaspersCruiser]

It takes very little torque to spin the prop out of the water. So even with a sheared pin there can be enough friction to spin the prop in air but not when submerged.

Understand completely. Wishful thinking on my part. On the older classic R27s with air conditioning, the bow thruster is located under the air handler and bitch to access.

 

[CaspersCruiser]

To bring this thread to a close and for future readers making forum searches, the issue in the bow thruster was a sheared pin. The vessel is a 2012 R27 Classic with a Side Power SE-30 bow thruster.

Nothing was ingested into the thruster prop to cause the brass pin to shear. The pin just wore out and failed. There were a lot of brass shavings on the gear leg and thruster motor mating surfaces. The shear pin is located on the thruster motor.

As best as I can determine, the pin had seven years and approximately 700 hours engine hours use. Stainless steel shear pins are now supplied by Imtra, the company handling Side Power thrusters. I had a spare brass pin, but elected not to install it. Instead, I ordered the stainless pin.

My 2012 boat is equipped with air conditioning and it is the split system used on early model R27 Classics. The air handler of the split system is positioned above the bow thruster and complicates access. A the description of how to change the shear pin in both the Side Power stern and bow thruster is in the thread link below. I found it very helpful.

viewtopic.php?f=5&t=2013&p=45161&hilit=bow+thruster+shear+pin&sid=3c3ab1a2c4a86d5cbbe24fb97143e289#p45161

Tools that make the job easier:

1) Chapman 1/4” ratchet wrench with 6mm hex bit. One should have been supplied in the Side Power documentation when your boat was new. If you don’t have it, one can be bought from Imtra or Chapman.

2) Snap ring pliers to remove and install the snap ring that secures the shear pin on the thruster motor shaft.

3) An inspection camera to view the position of the U-slot on the gear leg to which the shear pin on the motor mates. It is impossible to see the U-slot otherwise. Without a camera, the U-slot would have to be aligned by feel. The U-slot and the shear pin have to be aligned when the motor is mated back to the gear leg.

Using the inspection camera, I was able to align the U-slot in a precise horizontal orientation relative to the threaded bolt flanges on the side of the gear leg. Then before installing the motor back on the gear leg, I precisely aligned the shear pin with the bolt holes on the side of the motor. It was very gratifying when the motor mated to the gear leg perfectly on the first try.

If your boat doesn’t have air conditioning or if it is a later model with a combined air conditioning system without the air handler installed over the thruster, an inspection camera is not needed.