C & A Thomason, based on the island of Yell in Shetland, has secured £22,200 from Highlands and Islands Enterprise with a further six-figure sum coming through a grant from the European Fisheries Fund.
The expenditure on new equipment allows the business to develop new mussel sites at Copister in South Yell which will increase capacity.
The on-board sorting equipment also means the mussels can be categorised before the boat goes back to shore.
The company is retaining its existing three staff with three more part-time positions being created.
Christopher Thomason, managing director, said: "The new harvesting vessel and equipment will make operations more efficient and increase mussel production.
"This is vital for ensuring job security and creation in an island community like Yell, which is remote and fragile."
David Priest, development manager with HIE, said: "The new work boat will help increase production, turnover and jobs based in Yell and this will be a useful boost to the local economy."
The boat is being built and commissioned this year and is due to enter service in 2014.