It could look something like this:
1) Building a Shipyard in the town would cost more gold but fewer resources; additionally, hiring ships would happen at half price;
2) It would be great if the Shipyard itself could be upgraded (similar to market-warehouse) into a City Lighthouse. Then all heroes traveling by ship would immediately receive a +3 bonus to sea travel, or there would be an opportunity to reduce the penalty when embarking/disembarking from a ship)
3) The Warehouse in Haven, besides the mandatory resource each week, could additionally bring in a random amount of wood ("washed up by the tide")
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