Date: 2 July 2020. How Shaft Keys
Aboard Seaweed I have had the
"opportunity" to replace my shaft keys. The first time I did so for
the one on my propeller, I used a galvanized replacement. That
worked out just as well as you might expect. Abject failure was had.
Experience has imparted to me the importance of having spare keys as
a component of my parts inventory. Today I'll tell you what a shaft
key is, where to purchase same, and why I believe you should have them
aboard your vessel.
Shaft keys are
made of square bar stock. That means the piece is square, and "bar
stock" indicates that the item is solid versus hollow. Your shaft
keys are made of bar stock and should be stainless steel. Galvanized
steel will rust.
STOCK ↓ made of 303 Stainless.
I bought my square bar stock aka
Midwest Steel and Aluminum (763-582-1925) company. Four years ago they were
kind enough to cut mine to the lengths required. That was a great
benefit to me. This is something you should purchase in advance. It
is a low-cost item. Finding stainless steel is important.
You do not want to
"make do" with something that will rust in salt water. TRUST ME on
that. It will take a torch and a darn good welder to get the mess
free for replacement. Thanks to Rocky for his skills in freeing the
mess I created by Not doing things correctly when in a pinch.
To be perfectly fair, there was no local place to
obtain stainless bar stock. Without the item Seaweed could not move
so choices were made. I opted for galvanized, figuring "how bad can
Note to Self: When
asking how bad can something can become, I should have realized
things could get a lot worse than I initially imagined.
Shaft Lessons, the
whys and wherefores:
All shafts are robust solid metal.
Usually they are stainless steel though some high-dollar vessels opt
I keep spare SHAFT ZINCS
↑ inside mounted on
the shaft. That way they won't get lost.
Almost all boats with inboard propulsion have a shaft. The shaft is
a solid stainless steel or monel round bar. It spans between the
transmission and the propeller. The shaft size is dependent upon the
engine of the boat. More powerful engines generally have larger
diameter shafts. At one end of the shaft is the transmission and
Here is a photograph of a
↓ COUPLER. The coupler is
between the transmission and the
Side Note: that is the yellow handle of a
THRU HULL SHUT OFF VALVE
and an 8-gauge BONDING WIRE.
Mini Lesson on
Transmissions: The transmission has
gears inside. When moving forward on a single engine boat like Seaweed, the
gears turn clockwise. Reverse is the opposite. Now to connect all
those gears to the shaft there is a coupler. It joins the shaft to
The FLEXIBLE COUPLER is red. It is bolted between the
transmission and the regular coupler.
As I understand
it, the purpose of a flexible coupler is to be sacrificial. If I do
something stupid (hit something hard with my propeller) rather than
destroy the inner workings of the transmission, the red coupler is
designed to take the fall/break.
A mechanic back in Carrabelle
advised me to purchase
the flexible coupler. The cost was approximately $100.
The Coupler has a slot cut into it.
So does the shaft. The KEY
↓ (square bar stock) secures the two
The flexible coupler is secured to
the transmission. The "real" coupler is next in line. A slot is cut
into the shaft and an equal one is in the coupler. The KEY fits into
said slot. When combined, the key keeps the shaft in line. It turns
with the internal gears of the transmission.
Lower half of picture: White transmission, red flexible
coupler, real coupler, shaft, and two zincs.
The zincs are NOT
currently protecting the boat from electrolysis. Instead, they are
there to help keep me from sinking!!! When underway were I to hit
something hard enough to dislodge the shaft it could, theoretically,
fall out. Those two zincs will prevent that from happening. It's a
simple safety measure. The added bonus is that I always know where
my spare zincs are located.
Seaweed is a single engine boat.
My propeller is right-handed, meaning the prop turns in a clockwise
direction when in forward gear. In other words, right goes forward.
The gears inside the transmission turn. The coupler holds the shaft
in place so it can rotate the propeller. Without a key at the
transmission, the shaft
will not spin.
What you need to know: First, you
need to know both the size and length of bar stock your boat
requires. It is my experience that both ends (transmission and
propeller) are the same length. Yours may however differ.
Then, buy spares from the
Midwest Steel and Aluminum company. Phone: 763-582-1925
I was fortunate in that Midwest actually cut mine to the length
required. If you
don't know how much, simply order a one foot of the correct
diameter so you will be prepared. This is one of those items that
you don't need until you need it immediately.
shaft key problem. Part One.
transmission: When the aft end of your transmission rotates [
and THE GREEN AREA
→ ] and the
shaft does not, verify that your shaft key is okay.
At this point you should
Calder's for precise
directions, or hire someone. I paid for an engine mechanic to
This is not my area of expertise, thus I rely on Calder's. If
I had no other option I would do the replacement myself.
Still, in matters such as this I much prefer hiring someone
with both strength and experience.
Please know that
Calder's Boatowners Mechanical and Electrical Manual
4th Edition is amazing. It provides
exact directions on how to diagnose and fix almost everything on
a diesel vessel. That said, I'm not an expert at the mechanical
aspects nor do I have the physical strength to do what many men
can. Therefore, I hire both muscles and expertise as required.
I might not do the repair, knowing how
it should be done is important. This allows me to verify
that the individual I hire is actually doing the job properly.
Replacing shaft keys is not a normal maintenance
event. The key is generally replaced when you swap props.
NEW KEY INSTALLED
↑ just forward of the
The first key I broke was at the propeller end of my shaft. This
happened when Seaweed was more than 20 years old. I do believe this
was the original key.
shaft key problem. Part Two.
Propeller: I started the engine. After
warming her up for a few minutes I put
Seaweed into forward gear. Nothing happened. There was zero
movement of boat. First I opened the bilge and verified that the
shaft was spinning. It was, yet there was no movement of water
at the transom.
There are a couple possible
reasons for this:
Note: A line wrapped
around the propeller would cause the shaft to not turn
and/or vibrate horribly.
When something breaks I always hope
least expensive repair will remedy the situation.
My friend Ken is a diver. He
dove the boat, confirming the prop was
still attached. Ken was smart and also checked for my prop
key. Alas, that critical component was missing. In the process of my being
anxious to have a boat that moved under her own propulsion, I
made a mistake.
Locally (this was in
Georgia) I could find no stainless shaft keys so opted for a
galvanized one. How bad could it be? Let me tell you, that was
an AWFUL decision. The galvanized piece rusted and rather than
dissolving sealed itself to both the shaft and propeller.
Seaweed was haul out at St.
Marys Boat Services. The yard owner, Rocky, was able to heat up
the rusted galvanized mess with his welding torch and remove the junk I
had thought was "good enough". It was only because of his talent
that I was able to get underway again, this time with a
stainless key. Thanks again Rocky.
After installing the galvanized bar stock I went
shopping online for a real shaft key. My searches lead me to Midwest Steel and Aluminum
based in Minnesota. Because I knew the size and length required,
they kindly cut my pieces to size. Not having to cut stainless steel
was a Real Benefit to me. I now have spares. Shipping was prompt and
the cost was reasonable.
In conclusion, I advise folks to
purchase a foot or so of bar stock.
How to find your size:
Put your engine in neutral. Rotate your shaft.
It should turn by hand. Look next to the transmission until you see the slot
with a square
piece of metal in it. That is your bar stock. Measure across that span.
You now know your size.
As an aside, Seaweed has
a 1.25" shaft. I required 5/16" bar stock. A neighbor also has
a 1.25" shaft.
He uses the same diameter key as mine, though
he requires a shorter length.
Where to buy:
Please note that I am not being paid for this! I needed
stainless bar stock, could not find it locally, searched online,
found a company, and ordered via telephone. They cut it to the
length I specified and shipped it promptly. That's sounds like a
good company, so I share their information here:
Midwest Steel and Aluminum (763-582-1925) based in the United
I keep my stash in a locker, just in case a shaft key is
required again. I am ready.
This isn't a fancy "big thing" however it is critical
to the propulsion system of Seaweed. Without bar stock keys, my boat
could not move through the water.
BAR STOCK KEY
installed on shaft at the propeller:
This is life aboard Seaweed. I
love my home. She is the best.
Having a substantial
spare parts inventory is
important for my happiness quotient. Truly
I am blessed.
Thank you for reading. I
I'd love to know if others have had shaft key issues.
Do you have spare bar stock aboard your boat?
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In the Bilges,
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