I've had a few boats (both sail and power) that I've towed with my 240 (years of experience) -- as well as bigger boats that need my GWagen), but since I also teach* this (as part of a state-required Boating course), let me make some suggestions that will apply to your V70....

~~~~~~~~~~~~~~~~~~~~
* I'm a nationally certified Boating Instructor and I teach their respective Boating courses of (and am also a member of) both the U.S. Coast Guard Auxiliary and also the U.S. Power Squadrons.
And I'm also a certified Vessel Safety Examiner of both those organizations, but that's another topic.
~~~~~~~~~~~~~~~~~~~~

1) first, you didn't say how big a boat you're getting. Remember to consider the weight of your trailer (and fuel, if a powerboat) in your calculations to keep within the 3,500 lb rating of your car. And don't plan to heavily load the car while towing, as exceeding this will not only leave you liable for a summons (if you're involved in an accident that catches the police's attention) but also will nullify your insurance coverage -- these weight capacities are not suggestions but are maximums that your insurance policy requires you to observe.
Also, as important as the total boat+trailer weight, also check your car's rating for "tongue weight", the weight of the trailer tongue that will press down on the rear of your car -- more on that below.

2) you didn't say what kind of boat you're thinking of getting. Remember that a sailboat will almost always (regardless of whether it has a retractable keel) require you to back further in the water to launch/retreive (even with a tilt-trailer made for sailboats) than a powerboat, because the former has a deeper hull than planing hulls of most of the latter.
And continuing this thought, a lot will depend on the slope of the ramp you'll use -- will you always use the same ramp, or are you going to be traveling around using a variety of ramps?
a) A shallow-sloped ramp will require you to back farther down into the water, possibly to a point where your exhaust is under water (think stall, or worse) before you're backed in the water far enough to retreive your boat (usually, you have to back farther in to retreive than to launch, especially if your trailer uses rollers; if it's bunks, then it's about the same). Also, if you're going into salt water, don't forget to hose off your car as well as your boat and trailer.
b) Whereas a steep-sloped ramp will let you launch/retreive easier (viz., while your car stays farther out of the water, preferrably with your exhaust clear). But it's not all good -- it's harder to pull up the ramp with your boat loaded on a steeper ramp, which leads us to the next consideration.

4) continuing the thought about pulling a heavy load up a steep ramp... in general, launch ramps are slippery (always wet at the end of the day, and often covered with algae making it slicker). And FWD cars are poorest trying to pull a boat/trailer up a slippery ramp. Reason is that the load of the trailer/boat on the rear of your car tends to weigh down the rear while 'pitching' your car so that the front lifts, taking the (usually heavier) weight off the front (drive) wheels -- result is that the unloaded front wheels are liable to spin on the low traction ramp surface. Only saving grace is that the higher area of the ramp is sometimes drier and less slippery -- it's a tossup which is more significant, and depends on your particular ramp.
So while FWD is the worst for pulling up a ramp with a heavy load, 4WD (in any variety) is the best (do you happen to have an XC? That would be good!), and RWD is in the middle.

And some closing thoughts -- be sure that your trailer is well designed so that the boat sits forward, to have 5-10% of the trailer/boats total weight as the tongue weight. This will ensure greater yaw stability (because the center of gravity, and therefore its mass, is farther forward), so that your trailer doesn't tend to sway and wag your car's rear end (ever hear of "jackknife"?).

Be sure to get Volvo towing equipment or the equivalent. I've seen really dangerous setups with 'bumper-mounted' hitches, etc. Get a frame mounted hitch, the heftier the better. I've got Volvo's older but heaviest "round-tube" style hitches, with a 2-inch receiver, on all my Volvos, but the "square-tube" styles that were sold later by Volvo is also acceptable, as well as some other recognized brands like Draw-Tite. Only keep in mind that Volvo's newer "square-tube" style hitches sometimes had a receiver with an odd size, not quite the U.S., small receiver standard dimensions, which means that you can only use the Volvo-only insert to mount your hitch ball.
When picking out the insert (assuming you've got a standard receiver), get one that will carry the ball at a height so that the trailer tows level (taking into consideration how much your car's rear will sag) -- get an insert with the necessary "rise".

And take a Boating course given by your local unit of either the U.S. Power Squadrons (www.usps.org) or U.S. Coast Guard Auxiliary (www.uscgboating.org).

Any other questions, I'd be delighted to help, on any subject of boating -- including different kinds of boats. I've owned a lot (except I've never owned a PWC), including powerboats: jetboats, inboards, I/Os, and outboards; and also a couple of sailboats. And all of them have been trailerable, so I'm in the size range that you're looking for.

Anyway, I hope this helped, at least to get you started.

Regards,