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Date: 10 January 2020. Shaft and Propeller Keys.


Sometimes having just the right part can be the difference between a minor inconvenience and a major hassle. One such item that I keep aboard Seaweed are spare keys. No, not the kind of keys that go into a lock. These are made of square stainless steel bar stock. Having a couple of spares aboard your boat is a Good Idea.

SQUARE BAR STOCK ↓ made of 303 Stainless.

Company website: http://midweststeelsupply.com

The bar stock is used to make keys. Keys connect the shaft to both your transmission and the propeller. They are necessary to your propulsion system.

This is an item you will need at some point, especially if your boat is 20-plus years old. Get the proper size for your vessel. Seaweed has a 1.25" shaft. My bar stock is 5/16" solid square stainless steel. Each bar aka "key" is cut to 3.25" long.

A couple vessels away from me the fellow has the same 1.25" diameter shaft. His key for the propeller is 5/16" like mine. The key his boat requires is just 3" long. Knowing the proper length is important too.

This is the KEY that connects my shaft to the transmission:

You can measure the width of the key at the shaft/coupler connection. If I did not
know the correct length I would buy a one foot piece then cut my own when needed.

Frankly I'm not an expert on what your boat will require. Empirically (with just my boat and one other as a sample) for a 1.25" shaft the bar stock required is 5/16". This is something you need to verify for your vessel.

I chose to purchase from from the Midwest Steel and Aluminum company. There is no affiliate, no bonus back to me, etc. This is the place I found online back in 2016 and is still in business. I remember being particularly pleased with the service.

It is important to buy something strong that will
not rust. I chose to purchase stainless steel bar stock.


Midwest Steel [http://midweststeelsupply.com] cut the bar stock the exact length I needed to fit my Seaweed. I don't recall if there was an added fee for said service.

I labeled my spares with the details necessary to remember in years to come.

I have spares and know where I bought them. The written details make sharing said information with fellow boaters easy.

Every older boat should have at least two extra bar stock keys in the stash of spares aboard. Though not a first line purchase by any means, this item might just save the day. Finding stainless steel bar stock in a small town is nearly impossible.

I have sheared both the propeller key AND a few years later the key that connects the transmission coupler to the shaft. Seaweed was 30-ish years old at the time. Both I suspect were originals from when she was built in 1983. I say that because those keys were bronze.

That is life afloat. Seaweed is almost a Supply Ship by virtue of my having lived aboard her so many years. Like most, as things break I replace and purchase a spare. Most of us in it for the long term do the same.

Thank you for reading. Happy boating.   

Addendum: A follow-up article with more details about shaft keys has been posted. It is located here:

How Shaft Keys Work

Do you have spare bar stock aboard your vessel?
And, have you any opinion of stainless steel versus bronze or monel? I have a stainless shaft.

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