You should be very careful about deducting any expenses if business is not the primary purpose of the travel. I'm going to assume, you are self employed in order to answer this question, as there are currently no allowed tax deductions for employees who travel for work for an employer.
If you travel for a vacation and do some work while you are on the trip, there is going to be very little you can deduct, as you are not going to the destination for a business purpose. Deductions for business travel can be available when someone must travel away from their tax home or main place of work for business reasons.
Unfortunately, trips that are primarily for personal reasons or vacations are completely nondeductible. However, if you do conduct any business while you are at your destination, only expenses that are 100% directly related to your business are deductible.
As long as you keep good records, you may be able to deduct some expenses that are entirely business related. If you are purchasing internet access on the ship entirely for business reasons, and will not be using it for any personal use, then you could deduct the cost of the internet access.
Thanks for participating in our event today @ateacton , its an interesting question.
