In shipbuilding, a beetle is just a big wooden mallet.  One version is used with
a horsing iron for driving caulking materials into seams.  A horsing iron is a 2
handed caulking iron - you stand back and hold the iron in the seam, and the
beetle wielder gives a couple of stout blows, then you move down the line a
couple of inches.  I have done this and it is very tiring. Looking for a
demonstration of this, I ran across a video of Joe Chetwyn.  I worked with Joe
when he led the team caulking the Kalmar Nyckel in 1997 and he looked exactly
the same as he does in this 2011 video.  The horsing iron and beetle start at
2:40

https://www.youtube.com/wa
tch?v=yE3qVxBykyY ps://www.youtube.com/watch?v=yE3qVxBykyY>

Another version of the beetle in the shipyard is a piece of 8” or so log on a
handle with iron bands to keep it from splitting.

I have told this story before but it is one of my best memories of shipbuilding.

When you caulk a boat, the cotton and oakum (on a bigger boat you use both) are
driven in very tightly - you can see from the video of the two-handed beetle.
The first step is to complete the caulking with the smaller tools to get it in
place, and then to drive every inch with the larger tools.  On the Kalmar Nyckel
there were 2 sets of horsing iron and beetle and it took 3 days to complete this
last step.

Over the course of the 3 days, the sound of the mallet hitting the iron changed,
becoming more clear and resonant.  By the end, the hull was ringing like a bell
with every blow.
 
Ed Minch