Preventing Thruster Shear Pin Failure

[scross]

A recent post reminded me of something I have been considering to reduce the chances of shear pin failure in both the bow and stern thrusters. I am curious if anyone out there has already implemented my idea.
Has anyone installed large mesh stainless screens on either thruster to prevent foreign objects hitting the thruster’s propeller?
Seems like a screen wouldn’t be too difficult to fabricate for the rear thruster as there are large flanges around the tunnel openings on both sides. Of course you would need the screen to be very firmly attached to prevent it from coming loose and getting sucked into the thruster prop. Since the rear thruster’s shear pin is the hardest to service, a set of screens there would have the most potential benefit.
A set of screens in the bow thruster would be more difficult to install because there’s no existing internal structure to which to secure the screens within the tunnel. It might be possible to secure the screens to the hull itself at the opening to the tunnel.
Thoughts everyone?

 

[S. Todd]

I would not want to reduce the effectiveness of my thrusters to solve "a problem" that I have never experienced. I suppose if I boated in waters that had way too much floatsam at the surface of the water I might change my opinion. How many thruster shear pins have you broken over how many hours of boating? The screens still would not prevent failure caused by rapid shifts in direction of the thrusters or operating them in waves that get them out of the water (both what could be termed as operator error).

 

[scross]

In 5 seasons of use we haven’t broken a shear pin. But it’s always a possibility of injecting an unseen “thing” into the thruster prop and having a problem. I’m pretty careful about thruster use but I’m not able to see everything all the time.
We still have a screen on the hull for the raw water intake and have never had a problem with growth or restricted flow due to it being there. The strainer catches the small stuff further down the line.
Our boat is only in the water 60 days a year in the PNW and I get a chance to inspect it in the hard every 2-3 weeks of use. So, I’m really not worried about build up on a thruster screen. The stainless screen I’m considering has a 1/4” to 1/3” mesh and the screen itself offers fairly low resistance.
After spending 5 hours replacing the macerator in the same area I know replacing the stern thruster pin is beyond my abilities as a contortionist. That would mean spending several hundreds for shop labor to replace a $10 part. That’s what I want to avoid.

 

[Red Raven]

Hi Al,

Consider yourself lucky for going so long without a shear pin failure. It is a pain to replace. Having said this I don’t think it is worth the Performace reduction a screen would cause. I would recommend that when it does fail you replace the brass shear pin with a stainless one. Your motor will still likely be protected by the thruster fuse. I have have blown both and the fuse is the far easier option to replace.

Curt