I am surprised no one has mentioned the possible legal
issues. Are you an American citizen? Is the boat a US documented vessel? If either is true, you should do a lot more research
before deciding you can leave Miami
and just pull into Havana to refuel. US citizens are prohibited from visiting Cuba
(there are exceptions none of which will apply to you). Purchasing fuel
will be an additional violation of the "Trading With the Enemy Act." While there is a probability you may not be stopped or bothered, the downside if you are is very expensive and may cost your delivery
customer his boat. Leaving Miami
and heading straight to Havana at 24 knots is a very good way to attract a lot of unwanted attention. You might want to chart an alternative course.