We are considering taking the ferry from Dover to Calais. Sea France offers a hydrofoil that makes the crossing in 1:49, and is not very expensive. Our only concern is that we are from the U.S., and we have doubts about driving a left-side drive car in a right-side drive country! Your comments, please.

You'll soon get used to it, after all, it's the same side you are used to.
Main difficulty is in seeing ahead when overtaking, you will have to hang back to give yourself a good view ahead, or trust your passenger implicitly !!
I've done it many times with no problem. Watch out for those gendarmes, they sieze any opportunity to nab tourists fresh off the ferry for speeding or other traffic offences.
If you have a hire car, check that you can take it abroad.

There are no hydrofoils running from Dover to Calais. SeaFrance runs large car ferries (www.seafrance.com), with a crossing time of 1 hour 15 minutes or 1 hour 30 minutes, depending on the ship.

Why do you need to take a hire? car across the Channel? It'll cost you for the ferry & for the "out of country" charges.

I seem to recall BTW a scheme operated by some of the hire companies that allows you to drop the car in the UK, cross the Channel as a passenger & pick up another car on the other side. Much cheaper & you don't have to worry about where the steering wheel is

Alan,
If a rental agency in the UK would allow us to drop the car at the ferry and pick up another one on the other side, that would solve all fo our problems! I am going to get started investigating this solution immediately. Thank you so much.

Whether you can swap the car or not is moot. Why not just return the car in UK and rent another one in France?

But why Dover - Calais? Unless you have a special reason for having a car in Calais area, much more sensible option is to drop off at Gatwick or Stansted, fly on a budget airline to a part of France you want to tour and pick up a rental car there. You can book a flight and a car through airlines' website, but check small print. Or go through Auto Europe.

Alec has a very good point. Look into flights or train/bus to the ferry and car rental on the "other side"