AegerHant: It can be done. It's not easy, but you can create a trade route that will net you 2500-3000 echoes on each voyage. It's a little tricky and requires some careful resource management, and some folks might consider the info I'm providing as kind of like meta-gaming, so stop reading now if you want to keep dragging your battered boat from port to port, desperately scrounging every coin you can find.

Step 1: You need the merchant ship with its 120 units of cargo space. Your profit is maximized by the amount of cargo available. Scrimp and save until you have enough for it and a decent engine. Don't be afraid to sell Treasures in Khan's Shadow to help finance the purchase.

Step 2: In London buy 12 Fuel and 6 Supplies, and fill the rest of your cargo space with Mushroom Wine.

Step 3: Chart a path to Port Carnelian on the Southern Continent, hitting as many ports as you can on the way. (Shepherd's isle is a good stop to get you Zee-Stories, which you can trade at the Fathomking's Hold if it's en route to get benefits from the king.) Take note of exactly how much Fuel and Supplies it took to reach Port Carnelian to calculate future trips accordingly. Every free cargo space generates more profit, but you need to have some extra fuel/supplies to deal with emergencies.

Step 4: Sell all your Mushroom Wine. Hey, 165 echoes profit or so will help defray refueling costs. Purchase enough Fuel to get to at least 13 and enough supplies to reach 7. Pan for Sapphires. Then fill your hold with as much Darkdrop Coffee Beans as it can hold.

Step 5: Chart a path to Khan's Shadow or (even better!) Khan's Heart, if you can trade there. Keep track of how much fuel and supplies you used and note it for future travel. Purchase enough Fuel to get to 12 and Supplies to get to 6, then if you're at Khan's Heart and can trade in the Nephrite Quarter top up your hold with as much Darkdrop Coffee as you can.

Step 6: Chart a path for Irem, hitting as many ports as possible on the way. If Polythreme is on your route, don't bother transporting Clay Men to London. You'll make more from the same space with coffee. Do sell your Sapphies there (if any), unless your route includes the Chelonate.

Step 7: Use one coffee to rest in Irem, get your terror down. Then sell all your remaining Coffee, replacing it with Parabolla-Linen. You paid 38 echoes for each Coffee, but the Linen sells for 60 back in London. That's a nice profit margin right there. Purchase enough Fuel to get to 8 and Supplies to 4, and then head for Mount Palmerston.

Step 8: This is the tricky part. If Mount Palmerston is far away from the west coast, you will have to play around with what amount of Parabolla-Linen is safe to carry, considering you'll need more space for Fuel/Supplies. Also you'll have to dodge some nasty creatures if you head back through the north sea... sometimes Mount Nomad! Avoid all of these enemies at all costs. Fighting uses fuel and cuts into your precious, precious profits. Refuel in Mount Palmerston (or Venderbright if you have to) and then chart a path for home.

Step 9: Sell all your Sapphires (if any) and Parabolla-Linen back in London and cash in your Port Reports, and you will find yourself several thousand echoes richer.

Then rinse and repeat as needed. Keep in mind you'll have to play around a bit to get the right mix of Fuel/Supplies to carry you around the map, but prioritize restocking at Port Carnellian, Khan's Shadow, Khan's Heart and Mount Palmerston. It is also very possible on this route to mine stat increases as well, giving you between 5 and 10 stat increases with each circuit. But that's a post for another day.

Good trading!

AegerHant: Ha, I didn't know you could convert wine in the Empire of Hands. I always avoid helping them on the blimp, being a loyal little British citizen. That would make for an even better payoff.
I tend to avoid doubling back to the Elder Continent if I'm visiting Irem, because that doubles you back through ports you have already visited, and travelling without fresh Port Reports on your path is much less profitable... although... assuming you can fill up 95 hold slots and sell them all at Adam's Way, you make a difference of +3 echoes for each, and that's 285 more echoes. That might actually make it worthwhile, and you could just run coffee/linen back and forth between Irem and Adam's Way. Do you know if you have to have Recent News to visit the shops in Adam's Way? If so then that's a stumbling block.
I really dislike the Republic of Iron as a regular port. The Port Reports there are really random and can drain your stats (or sometimes increase them) and add to terror. I usually skip it entirely.