Shipping firms spend 21 8billion fairly used vessels

I think there may be a small mistake in your statement. Shipping firms do not spend $21 billion on "fairly used vessels". Here's why:

1. "Fairly used vessels" is a contradictory phrase. Vessels are either new or used, not "fairly used". If a vessel is used, it's not "fairly used", it's just used.
2. $21 billion is a massive amount of money, and it's unlikely that shipping firms would spend that much on used vessels. While used vessels can be a cost-effective option, the cost of purchasing or leasing a vessel is typically in the millions, not billions.

It's possible that you meant to say that shipping firms spend $21 billion on new vessels, or on a specific type of vessel, such as tankers or container ships. Could you please clarify or provide more context about what you meant to say?