Picture this — you're walking along the beach and come across a washed-up shipping container chock-full of goodies.

You can hardly believe your luck, and begin to grab everything you can get your hands on.

But is it legally yours now?

That was the question being asked earlier this week when a shipping container washed up on Moreton Island.

To the disappointment of many, it was empty, but the question remained — who can claim the maritime property that ends up on our beaches.

Turns out it's not as simple as finders, keepers.

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Enter the law of salvage — the rescue of a ship or cargo from danger at sea.

Simply put, it's the service of a volunteer to save salvable property from loss or damage.

Performance of a successful salvage entitles the salvor to financial reward from the owner of the rescued property.

Maritime lawyer John Kavanagh said when it comes to salvaging there are a few boxes that need to be ticked:

It's in danger — There has to be some risk to the maritime property, otherwise there's no saving it from that risk.

There has to be some risk to the maritime property, otherwise there's no saving it from that risk. Be a volunteer — You can't be under any sort of duty or requirement to conduct a salvage. That rules out crew saving their own ship, as well as police and other emergency services tasked with saving property

You can't be under any sort of duty or requirement to conduct a salvage. That rules out crew saving their own ship, as well as police and other emergency services tasked with saving property Be successful — Historically salvage services have been rendered on the basis of "No cure, no pay". "Cure" in this context means that some part the ship or cargo was saved and "pay" relates to the value of the property saved.

"If you tick all those boxes, and you recover the property and saved it, you can go to the owner and say, 'I have possession of your property, if you pay me my salvage reward I'll give it back to you'," he said.

"It's one of the misconceptions of salvage you can just claim the item.

"I had a query this week from a fellow who has someone leave a vessel on his mooring. He's asking if he can claim salvage, obviously in his thinking that means he could just say the vessel was his. But that's just not how it works."

I've salvaged some maritime property — what's my reward?

It varies, depending on the value of what was salvaged, as well as how hard you worked for it.

John Kavanagh was a mariner before practising maritime law in Brisbane. ( Supplied: Pacific Maritime )

The harder it was to salvage, the more valuable the reward.

But it tops out at the value of the property.

"There's quite a few considerations, one's the degree of skills, the investment the salvor has put into saving it, time, effort, fuel, ships, people, and so on," Mr Kavanagh said.

"There's the degree of success. You may have saved it but you may have damaged it significantly in the process."

The value of the asset itself is also taken into consideration.

"If it's a $10 million ship, and it was in incredible danger and you had to exercise a great deal of skill, and deploy a lot of resources to save it, and you're entirely successful, then you could claim up to 100 per cent of the value of the property."

The other question you've got to ask yourself — will it all be worth it in the end?

In one case Mr Kavanagh handled recently, a ship broke free from its mooring at a yacht club in wild weather and started banging into other boats, causing damage.

"A couple of fellas saw it happening, jumped on their runabout and went out and got on board and looked after it, tied it up, secured it, and made it safe," he said.

"So they were volunteers, they had no obligation to do it, they just thought it was the right thing.

"They were successful, it was maritime property, and so they could claim salvage, that was the advice I gave them.

"The problem was they didn't exercise any special skill, it wasn't a complex job. Whilst they saved it, the danger wasn't all that great. The ship wasn't going to sink, it might've been damaged a bit more, but it wasn't that complex.

"While their claim was a good one, they were probably only going to get 5 to 10 per cent of the value of the property. Which once you've written a few letters and start a claim, the cost of doing it is probably not worth the cost of chasing it."

What's the difference between salvaging and theft?

That depends on your intentions.

"There are two elements to any criminal offence. The first is the mental element, the second is the physical element," Mr Kavanagh said.

"Physical element is the taking, you've taken the goods out of the container and you're keeping it.

Make sure your intentions are clear when salvaging, or you could be done for theft. ( Audience submitted: Ben Taylor )

"The fundamental difference between theft and salvage is intention.

"So if your intention is to salvage, and you take the goods and look after them, and then you contact the owner and say, 'I've salvaged your goods', that means you don't have intention to permanently deprive the owner of those goods."

He said attempting to contact the owner was "evidence of intention".

"Intention is invisible in anyone's head … but if you have evidence you reached out, you made enquiries, you found who the owner is and contacted them to tell them you've got their goods and they can have it back if they pay the salvage claim, then that's very clear that you had the intention to salvage.

"But if you just take them back to your home and keep them and don't tell anyone about them … most people would think you had no intention except to keep them."

Any famous stories of salvage?

One of the most famous examples would be the tale of the MSC Napoli.

Container ship MSC Napoli ran aground in 2007. ( Luke MacGregor: Reuters )

In 2007 the cargo ship was deliberately beached off England's south coast to prevent it breaking apart during storms.

About 100 containers fell off the ship and washed up on the so-called Jurassic Coast, a United Nations-registered World Heritage Site.

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"Initially intrigued and then delighted, local residents, followed by scavengers from all over the country, descended onto the beach and spent two days and nights frantically looting whatever booty they could get their hands on," ABC reported at the time.

"Motorbikes, spare car parts, clothes, make-up, nappies and even Bibles in foreign languages were all rapidly pilfered by grinning beachcombers in a crazed treasure hunt more akin to the days of galleons and pirates."

Mr Kavanagh said it was "an extraordinary event in every way".

"All this absolutely fantastic stuff dropped on the beach. And who's to say … it's a pretty fine line when the only difference between theft and salvage is intention."

What's going to happen to the shipping container on Moreton Island?

It'll be removed from the beach, eventually.

Owners Maersk Line said they were working on it with barge operators and local marine authorities.

"This is a complex operation with many factors to consider including barge availability, weather conditions, windows at local ports and more," a Maersk spokeswoman said.

"The container in question will be removed by barge to Fisherman's Island, to our container depot."