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Q&A: Leaky Shafts, Prop Walk, Lubes for Sliders

Your technical questions answered by some of the most experienced trawler minds on the water.
Grand Banks 42

Grand Banks 42

Q: On my Grand Banks 42, the rudder post at the stuffing box is pitted and allows a very small amount of water in the boat. I might pull out a couple gallons of water every three or four days. Sometimes after a week of not turning the rudder, the leak almost stops. 

Is it worth doing something about it? If the rudder is in otherwise good shape, can the shaft be fixed? (As in welded or ceramic coated and turned?) Is there a type of packing material that works better than others? And can this be done with the boat in the water? —Eric Paulsen

Eric: Since Grand Banks switched to fiberglass in 1973, I’m assuming you have a good ol’ wood-hulled boat, but I’m not sure if your rudder is bronze or stainless steel. If it is bronze, then I would want to remove the rudder and check the shaft for any signs of dezincification. Good bronze will have a golden yellow color. Any pink splotches would indicate that the zinc in the original bronze alloy has leached out. This condition will dramatically weaken the rudder stock, and the best solution is to replace the rudder.

If your rudder is stainless steel, again we’d want to disassemble the rudder and inspect the shaft, but we’re looking for something different.

When stainless sits in water that doesn’t move for long periods of time, the water can become deoxygenated. The oxygen in the water helps to protect the hard shield that forms on the outside of stainless steel that actually makes it resistant to corrosion. Once that shield is gone, the stainless can freely corrode. So, if you have pits in your rudder shaft, the question becomes how deep the pits are, and what is going on inside the shaft where you can’t see. I’ve cut open severely pitted shafts to discover what looks like termite trails.

If the pitting is truly limited solely in the area where the stuffing rides, then you may get lucky and be able to use a slightly longer or shorter stuffing box hose and relocate the stuffing to a cleaner spot on the shaft.

Your first priority is to keep the seawater on the outside. We have used epoxies to repair minimal scratches or pits, but haven’t welded or used ceramic coatings on shafts. I’ve always considered the epoxy fix to be temporary. I’m unaware of a packing material that would seal a pitted shaft. Packing can usually be changed in the water, but it is difficult to inspect a shaft properly with the rudder in place. If you suspect pitting, I’d recommend pulling out the rudder to be sure it isn’t compromised. —Max Parker, Technical Contributing Editor


propwalk-opener-spread

Q: I really enjoyed Tor Pinney’s article entitled “Prop Walk” [October 2020]. I have been a mariner for 50 years with only outboard-motor experience. I have a single 250-hp outboard on my 25-foot aluminum boat with a tall cabin that acts like a sail in the wind, so docking in tight quarters can be challenging. Never knew about prop walk before. A couple of questions: I have a right-handed prop, so am I going to benefit approaching the dock on the port side or starboard side to maximize prop walk in reverse? Also, with only a single outboard, do I augment prop walk by turning my outboard maximally to the dock prior to initiating reverse, or turn it to neutral position, or leave turning away from dock, which is where it would be in forward approaching the dock? —Donald Lillegard

Donald: Thanks for your comment. Regarding your questions, note how the sixth paragraph begins: “However, if a prop shaft is perfectly parallel to the water’s surface, as in sail drives, there is no prop walk at all.” I probably should have written “as in sail drives and outboard motors,” as this exception applies to them as well. Except when motoring in very shallow water, outboard motor propellers are usually trimmed so that they’re parallel to the water’s surface, neutralizing any paddlewheel effect. Even if you intentionally tilt your motors, you’ll likely achieve much better control in reverse by simply aiming the prop in the direction you want the boat to back. All of which is to say, I doubt whether prop walk applies to your boat. —Tor Pinney, Author


Cruisers-Cantius-48-sliding-glass-door

Q: I wonder if you agree that white lithium grease is any good for sliding doors on my boat. I’ve got a Cruisers Cantius 48 with two sliding Opacmare stainless steel doors. I’ve had good luck keeping them running smooth with the grease and am interested in your thoughts. —Peter C.

Peter: This choice often comes down to silicone grease vs. white lithium. While they are similar, there is one important difference: White lithium grease is petroleum based. Petroleum-based products can harm rubber and plastic components, while silicone will not. If your sliding door track has no plastics or rubber, then white lithium is a great choice. —Steve Zimmerman, Technical Contributing Editor

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