"One of the lesser known tools of the caulking trade was a "log of heat". This was an iron bar with a ball at each end which was put into the fire until red hot, and then placed into the pitch to keep it hot in the journey to the caulkers. (This tool soon became "loggerhead", and the term is still used today in describing two people who cannot agree!)"

MARITIME HERITAGE ASSOCIATION JOURNAL
Volume 6, No.3. September, 1995
Page 13

http://www.maritimeheritage.org.au/documents/MHA December 19...


"A loggerhead was a big chunk of iron, like a cannonball, with a long handle.
They were used by putting them into a fire to get them hot, then dunked into tar to heat the tar. The tar was then used along with flax or whatever, to make a caulk, which was driven into the ship's seams with a caulking iron.
I believe the term strike while the iron's hot has to do with getting the job done while the tar was still warm (the iron (loggerhead) was hot.
An additional term 'at loggerheads' which these days means at opposite sides of an argument, back then meant fighting with those loggerheads."

Cruisers Forum post #14
https://www.cruisersforum.com/forums/f129/sailing-idioms-223...


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Note added at 1 day 1 hr (2021-04-17 21:44:19 GMT)
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From The Concise Oxford Dictionary

"loggerhead - iron instrument with ball at end heated for melting pitch etc"
("pitch - tar distillation used for caulkin seams of ships")

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Note added at 1 day 1 hr (2021-04-17 21:56:10 GMT)
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Photograph here

https://en.wikipedia.org/wiki/Loggerhead_(tool)#/media/File:...