Background:
This question was asked and answered in the last FAQ but the question was misleading and the answer too short with multiple issues.
Existing FAQ
"Q: Ship Upgrades and the Shipyard: For ship upgrades such as Elven Sails that have a experience cost, is this experience cost paid by the entire party (similar to the Tamalir upgrades in Road to Legend) or does only the hero who purchased the upgrade pay the experience cost?
A: Upgrades are paid for by the party."
For the question, there is no connection with Tamalir upgrades at all and inserting the Tamalir upgrade is a misleading reference (which appears to have misled). The only remote similarity is the placement of the XP cost symbol on the card. Tamalir upgrades do not take up time (thematically they involve the whole party meeting the town elders for a single meeting) but merely require the party to end their game week in Tamalir. Ship upgrades require a specific hero take an entire training week action spent at the shipyards, while other heroes may train elsewhere at the same time.
It is a awkward answer for multiple reasons.
First, it doesn't clearly specify the XP, just generally says 'paid for'. The cash portion is always paid for by the party, so the answer isn't really all that useful. If taken literally it indicates that even, for example, trait upgrades should be paid for by the whole party. Even though we know that it doesn't intend this, trait upgrades have a cash cost, an XP cost, and take a specific hero an entire week training at a specific location. Exactly like ship upgrades!
Second, it goes directly contrary to everything we can find in the rules and doesn't say why, or acknowledge that this is a rule change. RtL has a type of upgrade and mechanism where the whole party pays an XP cost (Tamalir upgrades). SoB contains nothing like that anywhere.
There is no connection between RtL and SoB (even though there are some references to things they changed). SoB stands alone, with the base set (and can accommodate the other vanilla expansions and the RtL dungeon levels). RtL rules have no bearing on or relevance to SoB. So where is this new 'whole party pays XP for an upgrade' mechanism coming from? (Well, we can see it comes directly from the misleading question actually).
Third, this brings up the problem where a hero goes to train during his train week action and finds that another hero has spent *his* XP without his permission during the same week and he cannot complete his training. This didn't happen in RtL because Tamalir upgrades were bought collectively at the end of the week (so after training) - as opposed to singly during the week.
Please confirm the original answer in a clearer manner, or change it as a mistake due to the poorly worded question.
Modified Question:
Q: For ship upgrades such as Elven Sails that have a experience cost, who pays the XP cost?
A1: The hero who spent the training week at the shipyard pays the XP (and cash from the party treasury , if appropriate) for the upgrade he trained.
A2: The hero party pays for ship upgrades collectively, so *each* hero must pay the XP cost for a ship upgrade that any *one* of them trains even if that hero is busy training something else at the same time. Sorry we forgot to put this in the main rules!
A3: Something else we haven't thought of?