A ship is a horrible place to raise a family
To be clear, I am not saying the mixed-gender crews do not work, nor am I saying that it is impossible to design a ship in such a way to account for family life, just that historical ships lacked the space and privacy necessary for a properly functioning family unit.
The #1 reason you don't see nomadic sailors is because ships are way too confined places for families to live together for long periods of time. Men and women get along great for a few hours a day, but in general men are wired to need long periods of quiet focus which you can not get on a ship when confined with a large number of women and children. The male psyche is designed to 'abandon' his family so that he can provide for his family. Almost every sailing culture in history has had strong taboos about women being on board because of the variety of psychological problems this could cause in such close spaces.
Nomadic caravans worked out much better because the men could scout ahead, hunt, forage, or simply walk apart from the family because he is "ummm... in the forward guard, yeah that sounds like a good excuse."
This is why even the most maritime focused of cultures still maintained home ports to go back to, because they needed a place to raise their families which was not where they worked.
But even without an exact historical example, we can make some inferences about how this could work.
Vikings traded on unestablished routes
In the medieval period, ~90% of wealth was kept in tradeable/usable goods rather than currency. This means when vikings would sack a town, they would be taking tons of trade goods that they often did not have a direct need for. They also did not have the manpower to attack many of the towns they would find while exploring; so, when they came across larger towns or cities, they would often stop to unload their pillaged commodities for things that either had a more direct need for or silver coinage.
This meant that they were trading along unestablished routes because what they were really looking for were small poorly defended communities that you often had to go off the beaten path to find. They did not need to make the same profit margins on their trade goods as regular merchants because their commodities were generally "purchased at extremely discounted rates"; so, sub-optimal trading was okay.
How your scenario could have evolved
Vikings needed hometowns, but as history progressed, northern European towns got better and better at defending themselves. Historically what this meant was that vikings kept having to go farther and farther out to find easy targets, or they had to take bigger and bigger risks attacking better defended towns. This issue was actually what ended the viking age as viking simply became to big of an investment in time or risk to still be sustainable.
For a viking clan to remain viable past the 11th century, they would have to abandon the idea of having a home to go back to. Unlike most other European civilizations, viking women often had many of the same freedoms, privileges and responsibilities as men. They were trained to farm and fight and perform more masculine trades so that the village would still function while the men where away. This means that training women to also be sailors would not be a huge stretch for their social norms (as long as they are not sailing with the men).
This is where your ship convoy comes in. Convoys are typically combinations of larger less maneuverable merchant ships surrounded by smaller more maneuverable military escorts to protect them. By placing women and children aboard the larger "village ships" and allowing them to be fully manned and captained by their female crew, the men could meet their psychological needs by going out onto the smaller escorts while the families are kept safely in the middle. This gives your a situation more similar to a caravan where people can come together and segregate as needed. Now your fleet can explore (and raid) the whole world without ever having to turn back home.
As time goes on, this fleet would develop a far more comprehensive map of possible trade routes than any merchant company would have access to such that they could eventually stop raiding and just trade. Instead of connecting 2-3 major port cities and letting the cities make the man-in-the-middle profit of distributing these goods, they might interconnect dozens or even hundreds of smaller towns directly by knowing precisely what each town needs and when. At times the the fleet might park in a hidden alcove in a river delta while a dozen smaller escorts sail off in different directions with precise amounts of goods, to all of the little towns within 1-2 days. At other times the whole fleet might sail up to a major city with goods from a 100 different farmers, miners, and craftsmen around the world each purchased at the lowest price possible.
These trade routes would be so complex and inconsistent as to seem randomly nomadic, but to the enigmatic fleet elders it is a complex formula of precisely timed stops based on a deep knowledge of places that other merchants have just never gone far enough out of their way to know about.
Surviving against militarized trade competition
As L.Dutch points out in his answer, large trading companies in the late medieval and colonial periods turned to military force to protect their economic interests, but a post-Viking fleet like this is the last thing you want to compete with on that level. The fleet is not so large or spread out as to put the major trading lanes out of business, and the cost of fighting them makes about as much sense as the Seleucid Empire attacking Sparta. Win or lose, you are guaranteed to pay a bigger price fighting such a fleet than any profit margin you might hope to gain.
Surviving against storms
Storms are a constant danger on the deep seas when you are travelling direct routes between major ports, but this fleet would by its very nature stick close to shores and rivers so that they could hit all of those little towns, and in the process discover just where all the natural safe alcoves and smooth beaches are. This means they could pull up into safe places and/or anchor down during major storms such that they might lose a ship here and there, but losing the whole fleet with all hands would be much less likely than for a deep sea fleet. Even with all their ships in one spot.