bow thruster prop not engaging but motor is working

[Kevin White]

I was trying to get off a windward starboard dock and the bow thruster suddenly stopped working but the motor is still running when I hit the toggle switch. It's as if the prop became disconnected somehow, but, the prop is still connected. Has anyone had this happen? I'm about to go deep by removing the whole assembly and I'm hoping for an easy fix instead of $2000 replacement. Thanks

 

[S. Todd]

Sounds like a broken shear in. A relatively easy fix on a bow thruster. Access on the stern thruster is the issue. The owners manual shows the procedures for changing the shear pin.

 

[scross]

Keven,
Chances are that the shear pin has been broken. This is unfortunately a pretty common occurrence. Good news is that bow thruster is much easy to access and repair than stern thruster. New shear pins are stainless while the original ones were brass or bronze.
Check for any debris in the thruster tunnel. Anything getting caught in the blades can cause a shear pin to break. The other common causes are getting air in the tunnel during thruster operation or changing rotating direction with the control yoke to quickly.
Regardless of the cause, if it is in fact a broken shear pin then it is not too hard to repair. Good luck!

 

[Aquaholic]

Hello Kevin,
Same thing happened to me on my 2020 R23 with a Lewmar TT Thruster 110 back in December while we were a month on the water. It was ultimately not the shear pin, it was a loose prop. I checked the shear pin inside the unit while we were still on the water (you can get to the shear pin from the top of the unit inside the v-berth without having to pull the boat out of the water), but the shear pin was fine. I figured it probably wasn't the shear pin anyway since the thruster only failed in one direction. If the shear pin had failed one would think the thruster wouldn't work in either direction. Figured it was a loose prop.

It is an easy fix if your problem is the same as mine. My bow thruster has a plastic prop with splines and a set nut (along with a couple of washers and an anode). My set nut on the prop had loosened and so the prop would free wheel when pushing the bow to the port side but still worked when pushing the bow to starboard (because when thrusting to port the force was pulling the prop away from the shaft thus making the splines fail to grab; when pushing the bow to starboard the force pushed the prop into the shaft thus seating the splines despite the loose nut).

Because I had thought that the splines had degraded on my plastic prop I had ordered a new prop while we were still on the water in St. Augustine thinking I might get a diver to replace it - but the cost was high, the water murky, and the diver not very confident. So I postponed the repair until back home with the boat on the trailer. In hindsight I didn't need a new prop so now I have a spare.

With the boat on the trailer I simply unscrewed the set nut (keeping track of the washers and anode), pulled out the prop, doused the set nut and bolt threads with blue loctite 243 and screwed it all back together (after comparing my old prop to the new one and determining the prop was fine). The whole procedure is detailed in the Lewmar owners manual and is easy and straightforward. They have a torque recommendation and tell you not to over torque the nut -7.4 ft lbs for the 140 or lower. You'll need a wood dowel or something to hold the prop in place while loosening or tightening the nut. Also recommend shutting the power off to the thruster during the procedure to keep fingers intact.

Hopefully the loctite will keep everything tight (the manual didn't suggest that for the prop nut but I figured what the heck), if not I'll probably have to get a new nylon lock nut and washers and do the whole thing over. We'll be back out on the water in May and see how it holds up.
Regards,
Mark Hackett

 

[KKRCRACE]

I had the same problem last year. On my 2018 C24 the bow thruster stopped working and you could hear the motor running so I figured it was the shear pin but that was not the problem. It turned out to be the plug in the thruster itself had come out exposing the gears and bushing inside to the salt water. I had to pull boat to figure out what had happened. I Had to purchase a new one so I could get get back in the water. The thruster was covered under warranty but took about a month or more to get the new one.
KKRCRACE

 

[Kevin White]

Thank you all. I'll investigate and let you know. Hoping for a shear pin! 😀

 

[Kevin White]

Well, it was the shear-pin. The pin was in pieces and a lot of shavings. I was able to clean it up well and the boat came with brass shear-pins which I was able to replace. The compression ring was off but in perfect condition and the groove was perfect as well. I had to remove the motor because it was just to precarious to replace in the well. I was able to push the pin in with ease on the stern deck fish tank platform. Both the motor and the prop shaft turned with ease. Nothing was binding. I believe that I must have sucked in some algae/seaweed while trying to get off the windward side of the dock and it was just too much. I had to unwrap algae off the main prop as well. Lessons learned. I'm wondering of brass is a good idea. I understand that it probably safeguards the motor and prop shaft but it also seems like it wouldn't take much to shear it off either. Any thoughts?
Kevin

 

[S. Todd]

We had our R25SC for 6 summer seasons and over 330 hours and never replaced the brass shear pins due to failure. That said, the newer replacement shear pins are stainless steel which should be a little more durable. If it was me and I had one of each, I would use brass in the bow thruster and steel in the stern thruster ( just because getting to the stern thruster is challenging in the R25SC and the R27 classic).

 

[Wee Venture]

As previously mentioned by Al (scross), the new shear pins are stainless. If you order them from Imtra/Side Power now, that is what you will get. I would order several for spares and throw the brass ones away. The brass seems to slowly degrade with normal use.

John

 

[PanaSeaAh]

Agree with John. When my stern unit quit, I found the shear pin segments worn to a few thousandths thick near the groove and then sheared. the pin segments looked like they had been hammered flat near the grooves. After changing that one, I opened the bow thruster and found the same wear on the brass pin there, although it had not sheared yet. Replaced both with the Stainless ones from the manufacturer, and also now carry stainless spares. They are a pain, but much less pain than 1K clams +- for a gearcase.
Side bar: it took me a while to figure out the short 2" X 8" piece of lumber in the bilge under the stern thruster motor :?: . Then I figured out it was put there by someone else to hold up the thruster motor while the installer is contorted through the rear hatch and trying to line the motor up for the Allen screws with only one hand. Really helped.

 

[pwensinger]

Another side-power stern thruster post..... Lucille is a 2014 R29 -a "classic", new to us this year. We lost the stern thruster pin within an hour of operating the boat for the first time. The prior owner, responding to my email, said that the bow thruster shear pin had been replaced "numerous times" but he couldn't remember replacing the stern shear pin. It was just waiting for us.
Observations: Our R29 model has cabinets across the stern, not seating. If you pull up the floor of the port cabinet, you can look down on the thruster motor and the infamous hex head bolts. They are, unfortunately, about 2 feet away. I inserted the ratchet wrench into a piece of copper pipe (pounded flat) to make a long handle. This worked for the starboard bolt but not the port - not enough swing room. The post describing the use of a piece of board to support the motor is good advice. The motor is hanging from those bolts and they are a lot easier to turn once the weight is off. The bolts must be turned by alternating, a couple turns on the port, a couple turns on the starboard. Otherwise the heads and your tool run into the motor housing. I have two of the ratchet wrenches and extended both with the copper pipe adjusted to lengths optimizing swing. Ultimately, I found I could, with some discomfort, access the bolts from below. I weighed 135 pounds in college, now, at 72 I weigh 218. I could have used that 135 pound guy for this job. I hope this helps someone.

 

[griervictoria]

I was trying to get off a windward starboard dock and the bow thruster suddenly stopped working but the motor is still running when I hit the toggle switch. It's as if the prop became disconnected somehow, but, the prop is still connected. Has anyone had this happen? I'm about to go deep by removing the whole assembly and I'm hoping for an easy fix instead of $2000 replacement. Thanks

I have a 2014 R31S and had repeated shear pin failures in the bow thruster a few years ago. It was found that the thruster had not properly been aligned at the factory. It was corrected by Steve at Canoe Cove Mfg and has not been an issue for about 5 years now.