Depends on how many times a day he needs to check in and what he needs to do. If simple texts or emails are all he needs and only needs to check in once or twice a day, you can get wifi at just about every anchorage that has a bar/restaurant.

If it's anything more than that, I'd suggest hitting the Digicel store in Road Town when you arrive and pick up a mobile mifi device. You should expect to pay around $50 for the device and another ~$30 for access with adequate data to send/receive plenty of photos and documents. It probably won't cost you much more than renting one and you keep the mifi device to use for future trips.

What company are you chartering with? TMM and some others offer free wifi on their boats. You might check with your charter company first before you go any further.