Thanks for your inquiry. I have not found any genuinely useful information for you but I can suggest an approach you can follow that will possibly answer your questions about your grandfather.
First of all, if your grandfather held the shipboard position of carpenter, he was definitely in the merchant marine.
I have found very little about SACAJAWEA to this point and nothing at all about your grandfather. I notice from your e-mail address that you are in Australia. That is interesting in that I suspect the ship operated primarily or exclusively in the Pacific. I did find that SACAJAWEA made at least one round trip from San Francisco to New Guinea in the period May-September 1944. There was only a partial crew list that I found with respect to this voyage and your grandfather was not listed, nor was the carpenter identified. From Google searches I found fragmentary indications that SACAJAWEA operated between Seattle and the Aleutian Islands on numerous voyages in 1943 and 1945 and also carried troops to the southwest Pacific in 1945.
It is very likely that your grandfather served in more than one ship during the war. It was very typical for the merchant marine crew of a ship to change completely from one voyage to the next. While one or more senior officers might remain with a ship for multiple voyages, the rank-and-file merchant mariners tended to move as soon as possible from a returning ship to a departing ship so as to keep earning pay. As soon as a returning ship reached its final destination, the crew drew their pay and at that point were unemployed. Since the same ship might not sail again for weeks, most crew members would immediately try to find another ship that required their services.
I suggest that you attempt to obtain a copy of your grandfather’s merchant marine service records, by contacting the U.S. Coast Guard. See this web page from the website I manage: http://armed-guard.com/searchmil.html. In particular see section A.2. Records of Individuals – Merchant Marine. You will have to contact the U.S. Coast Guard’s National Maritime Center in Martinsburg, West Virginia, USA. The Coast Guard was and is responsible for issuing certain documents ("seaman's papers") and officers’ licenses to U.S. merchant mariners, so they should have information about your grandfather. You will need to provide as much identifying information as possible about your grandfather. His service record should identify the ships in which he sailed and applicable dates, among other information.
Note that for the Coast Guard's purposes you are not next of kin to your grandfather (next of kin = parent, spouse, child, sibling). As such you personally may not be able to obtain your grandfather's complete service record. It would be best if someone else in your family who is next of kin could make the request for his service record, for example your father or an aunt or uncle, i.e., a child of your grandfather. You could do the leg work of preparing the request, researching information, etc., but it would be better if someone who is next of kin to your grandfather could actually sign any necessary document(s). If there is no next of kin, make the request yourself and hope for the best. There will be a fee for this service but the Coast Guard would not begin work without informing you of any charges.
SACAJAWEA was constructed in 31 days between November 28 and December 29, 1942, by the Oregon Shipbuilding Company, Portland, Oregon. She survived the war and was scrapped in Seattle in 1961. It is possible that she never sailed again after the end of the war. See http://www.shipbuildinghistory.com/shipyards/emergencylarge/koregon.htm and scroll to hull number 612. Also see http://www.mariners-l.co.uk/LibShipsS.html and scroll to the name of the ship.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website