I am afraid that there are just too many Crew Agreements for you to get the records from them. You would need to employ a professional researcher. TNA will give you a list but these people don't come cheap.
http://www.nationalarchives.gov.uk/help-with-your-research/paying-for-research/If you look closely at his seamans "Ticket" You will see that he had no Royal Navy records. I doubt he was forced or pressed other than the need to sustain oneself. I doubt his father paid for or received any kind of monetary remunition.
Two books for you both available from TNA bookshop.
TRACING YOUR MERCHANT NAVY ANCESTORS by Simon Wills, Pen and Sword Books, ISBN978 1 84884 651 7
MY ANCESTOR WAS A MERCHANT SEAMAN by Christopher T Watts and Michael J Watts, Society of Genealogists ISBN 10 1 903462 51 7
In answer to your question re RELIANCE Looks like he was a seaman around 20/March/1843 on board the Arbroth registered vessel RELIANCE built in 1842 208 tons owned by her captain J Cargill and others.
Around 4/April/1844 seems, he was a seaman on board the Sunderland registered vessel HOUGHTON LE SPRING built Sunderland 1839 283 tons owned and captained by R Brown.
Merchant Seafaring by it's very nature was and still is a dangerous and precarious occupation. It is not an absolute science. Therefor researching Merchant Seamen, who for the most part were suspicious of authority and regulation, doesn't come easily. Take nothing as read and always try to obtain at least two original sources.