If you haven't noticed, there is a war going on in Ukraine with large quantities of explosives readily available. Failing that ANFO is cheap and easy to make Nobody but you is proposing to use a rowboat. A long timer is trivial to make. They have new inventions now called rope and magnets that make it easier to lower the explosives and attach them to the pipeline.
You would use anfo for underwater demolition? How does moisture affect ammonium nitrate?
What type of booster would you use?
The outer pipe line is encased in concrete. How would magnets work under water on concrete?
