They appear to be speaking trumpets, which were essentially early versions of megaphones. Your first image I can't trace to an artist so I have no idea if it's contemporary or not. Pyle was an early 20th century artist and most of his paintings dealing with the 18th century are anachronistic.

However speaking trumpets were used during the 18th century. For example there's this detail from a satirical cartoon depicting the US Congress on board the Constitution (full image here).

The person filling the role of a coxswain is using something that clearly appears to be a speaking trumpet.

There's a 17th century text with the long name of An Account of the Speaking Trumpet, as It Hath Been Contrived and Published by Sir Sam. Moreland Knight and Baronet; Together with Its Uses Both at Sea and Land. Printed in 1671 it's a history of the speaking trumpet.

I should point out that speaking trumpets weren't used to give orders on deck. They were used when two ships came into contact with each other and wished to pass information along to each other.