Mr Sealey spent the whole of his conventional working life at Christian Salvesen, ending up as managing director of a firm that grew from whaling to become one of the biggest fish in Scottish business.
His time at the company, remnants of which were swallowed up by Norbert Dentressangle in 2007, involved learning the ropes in trades that were staples of the old economy.
"Part of my training was to spend, altogether, nine months at sea on a factory ship learning how they worked... That led to all sorts of exciting things like learning how to mend nets, to gut fish. I worked in the engine room, drove the ship."
Over the past two decades, the former one-company man has enjoyed encouraging the emergence of a heap of firms in areas of the new economy ranging from software to medical devices, by contributing cash and know-how.
Along with estate agency entrepreneur Mike Rutterford, Mr Sealey founded what became known as the Archangels investment syndicate in 1992.
There was nothing new in private investors backing firms, but Mr Sealey and company forged a new path by pooling the resources of successful people of means to make collective investments.
Participants provide what has been dubbed "bleeding edge" capital for early-stage firms that may be too small or young to obtain funding from banks or venture capital firms.
The group, which celebrated its 20th anniversary in October last year, has backed 79 firms to date.
The total invested by members of the now 120-strong syndicate is now £74 million. With co-investors, the amount provided totals £174m.
Sitting in the syndicate's offices in a handsome square in Edinburgh, the 77-year-old recalls getting the angel bug after making an investment in the city's Caledonian Brewing Company.
"When I retired in 1990, I was asked to look at a little company that some friends were involved in – Caledonian Brewing Company – and I got a bit involved in it. I fell in love with this idea of a little company that you could put your arms around. It only employed around a dozen people at the time."
He continues: "I was trying to help it managerially in the first instance and then it needed a bit of cash, I realised, so we raised a bit and put some money into it."
After deciding to seek other interesting opportunities, Mr Sealey soon learned that angel investing could be a high-risk game.
"I got involved, not very successfully I have to say, in a little restaurant on the High Street called Les Partisans."
What became Archangels had its roots in a meeting with Mike Rutterford, to whom Mr Sealey was introduced by influential lawyer Sandy Finlayson.
Mr Rutterford was looking for things to do after selling his Stuart Wyse Ogilvie estate agency business for more than £16m in 1987.
"He had a bit of cash in his pocket. I'd retired from Salvesens and taken a bit of cash out so we talked about it and Sandy introduced us to our first investment, which was a company called Optos."
The investment in the Fife-based company was made on the basis of very basic information provided by Douglas Anderson, who developed innovative retina-scanning technology.
"There was certainly no formal business plan," Mr Sealey said.
Archangels supported a series of fund-raisings completed by Optos before the firm eventually floated in 2006.
"Optos is a very good story. It explains a lot of what we do. We back a person and an idea and in general... we are patient investors. We are there to see the business succeed not in for a quick buck."
As word spread among advisors and banks, Messrs Sealey and Rutterford roped in friends and contacts to help broaden their reach until they arrived at the point where they felt help was needed, and appointed someone to help appraise and monitor investments. "To put it crudely, it sort of growed. We were keen on it, we liked it... I persuaded my old Salvesen chairman to join us, Sir Gerald Elliot. Mike encouraged one of his friends to join us, Eric Young. So we started to build up a little group."
The founders had no idea that they were laying the foundations of a syndicate that the Cambridge University science graduate believes has had a real impact in Scotland.
"What the exciting thing about it is from my point of view is, first of all, it has grown and it is, I believe passionately, a very important contributor to the growth of the economy. Young companies are where jobs are coming from and the new technologies are coming from."
The model works because Archangels provide "patient capital" and also draws on the experience and connections of backers to provide vital practical help for investees.
"What we provide is not just cash – it's what the Americans call smart money."
While angels unashamedly want to make money on their investments, Mr Sealey notes they invest alongside promoters of the companies involved.
"We always put it in as straightforward equity."
He does not disclose details, but notes participants have been pleased with the returns made on successful investments like Optos.
Three companies have been floated on the Stock Exchange and Archangels has made 11 trade sales, nine of them profitable.
While 39 investee businesses have failed, the money involved represents about 12% of the total cash invested by Archangels. The existing portolio of 26 firms includes five companies that are currently profitable. Some are paying dividends.
Mr Sealey is pleased many others in Scotland and further afield have been encouraged to follow suit.
"We have helped other people start and encouraged others and there are now more than 20 angel groups in Scotland, quite a few of whom we have had involvement with."
Angel investing may be worthy but it is never dull. "Both of us in our working lives have had a lot of fun out of our work, and being Archangels is fun."
Mr Sealey stepped down from the Archangels board two years ago but sill plays an active part in promoting its work.
Since "retiring" in 1990, he has also found time for stints on the boards of companies such as Stagecoach Holdings and chairing public sector bodies such as Edinburgh Healthcare NHS Trust.