Look for a book:
Peter D Jeans, Seafaring Lore and Legend: A miscellany of maritime myths, superstition, fable and fact, McGraw-Hill, 2004. ISBN 0071435433
Some editions of the book may use the title From Noah’s Ark to St Elmo’s Fire: Seafaring Lore and Legend.
Jeans wrote that ship-builders set a representation of a star in the end of bowsprits and ‘sail booms’ as ‘a sign of the old-time seafarer’s faith in the Pole Star as the guiding star for his ship … a sort of backup for the eyes of the figureheads once common on the bows of sailing ships’.
Jeans continued: ‘the stars may also be reminiscent of early seafarers’ beliefs in Castor and Pollux, in the constellation Gemini, as protectors of those who go to sea’. Jeans wrote that Castor and Pollux, in the form of twins in the crew of the Argos captained by Jason, had protected the Argos during a storm. After that, according to Jeans, mariners sought spiritual support from Castor and Pollux during bad weather.
Jeans book can be found in many second-hand bookshops for around US$3.
You can also read it on Google Books (look for the section sub-titled ‘Guiding Star’ on page 310).
Cheers
Bil