Tentatively, they released it into the choppy waters off the coast of the Scottish town of Peterhead.
Ollie is eight and Harry is five, and the boat in question their Playmobil pirate ship -- a once prized possession that had been gathering dust at home.
But the voyage has taken it -- aptly named Adventure -- to Scandinavia and now on towards Cape Verde, having traveled through waters that have smashed far grander vessels than one measuring just 67 centimeters in length and costing $67 (£49.99.)
Its an unexpected voyage that has garnered attention from Copenhagen to Canada and from the United Kingdom to the United States.
The journey is part of an idea from their father Mac, who set his sons 500 adventures.
Currently, they have chalked off 208 with each one detailed on their Facebook page
but none have caught the attention quite like the Playmobil pirate ship.
"It started with the premise of a message in a bottle," Mac explains to CNN from the family home, "of sending a message from one country to another, to learn about how big the world is, and things like crosswinds.
"We didn't want to send a plastic bottle into the ocean as that's littering and sent the wrong message so instead we used a Playmobil ship that they no longer used and would have gone to a charity shop or something."
Voyage of discovery
To make it more seaworthy, the boys added a counterweight to stop it from flipping over and polystyrene to help it float. It then underwent testing in their local swimming pool and in open water before its main voyage.
But the Fergusons had no idea how the journey would play out as, on May 26, it was put to sea along with the family's contact details.
Their Dad recalls: "I half thought, it'd get caught up and spilled back onto the beach a few miles down the coast."
Instead, though, it traveled 390 miles to Denmark where it was picked up by a family, who contacted the Fergusons via Facebook with photos of them with the boat before returning it to the sea.
From there, it traveled to Sweden where it found its way into a tree, found by a woman in her boat who did some running repairs before setting it off on its latest voyage, this time to Norway.
"Partly because it was going to waste, we used the Playmobil boat but also as it was more eye-catching for people to pick up rather than leave it where it is," he says. "It's obviously worked better than it ever could have."
Its last appearance was in Norway, where it was found by a crew member aboard a conservation vessel a quarter-of-a-mile off the Norwegian shoreline.
"It made it to three countries in just about six weeks which is incredible," says Ferguson, with an infinitely more demanding journey now under way.
It was put on board the Christian Radich, a fully-rigged ship, and pushed into the waters towards Cape Verde in the Atlantic Ocean.
Lego in outer space
As for what the future holds, the family have no idea but the boys are still relishing it.
"It's funny as this is not even the most adventurous of our 500 challenges," explains Ferguson, who sent two Lego men into space 19.5 miles above earth with a GoPro.
"But of the 500, this one has certainly grown arms and legs, and it's certainly made the boys popular at school."
While they are enjoying the attention inside the school gates and watching themselves on television or reading about themselves online or in newspapers, they have "become rather blasé", according to their father.
Ferguson hopes the voyage might prompt others to set outdoor challenges for a generation of children plugged into tablets.
The 44-year-old, who has his own business working on adventures with children, says: "I'm not trying to make the boys Bear Grylls or Ray Mears but it's just to share experiences, and they're getting bigger and bigger, and more adventurous."