Through hull interfaces - propulsion - rudders

Hey all, I have been working slowly in the background on the design of a long endurance ocean going vessel. I have it all pretty much together other than how you achieve your wet interfaces.

My experience is that, even if you use a strong copper antifouling, rudder shafts and propulsion shafts start to gum up with sea life.

I have looked at stuffing boxes, magnetic couplings grease feed systems, etc.

Stainless rudder shafts in brass tubes with a large clearance appear to be the best bet so far for steering. The servo can be inside a waterproof enclosure with a rubber boot around the connection rod.

I still haven’t found an answer for propulsion. Even if you use a magnetic coupling to keep water out, the coupling to the propellor still runs through bearings. Again, stainless in brass with clearance can work as it is low RPM.

So, has anyone else got ideas on 1. How to keep the water out. 2. How t stop them clogging up with marine growth.

Hi! I can answer you as a sailboat owner, I am around here a few months as I intended to install Ardupilot in my real boat! have few months ahead before real testing as the components have just arrived, and slowly putting together my design!

You don’t have to worry about marine growth on the rudder and propeller shafts. Nothing will grow on them unless they remain still for some time. First soft grass appears after 10-15 days, so no problem for a vessel that continuously moves. Do you have a different experience?

I think it’s easier to use a small bilge pump with a float switch for emptying any water coming in from the propeller shaft. Investing in a drip-less shaft seal is a lot more expensive option and I don’t know if they exist for a tiny diameter shaft.

Another option is to have your propeller shaft entering the brass stern tube much higher than the water level, so theoretically water will never get in!


Thank’s for your response. is that your experience? 10 or 15 days?

May be different here we are in Australia, near the Great Barrier Reef - stuff grows so quickly.

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