A while ago, I showcased a few sterndrive installations of varying quality, and pointed out some of the engine access problems that result when these units are shoehorned into too-tight spaces. Here's an example of one that's done relatively well. The boat is a 19-foot Doral runabout, built in Midland, Ontario in 2007.
(Registration number Photoshopped out for privacy.)
The aft deck and seat back hinges up, the entire width of the boat, for engine access. Some manufacturers use electric actuators for hatches like this; Doral uses the same gas-lift struts found on the cargo doors of vans and station wagons. These are simpler, cheaper and much less likely to fail than power actuators, which really aren't necessary on well-designed pleasure craft.
As with most Volvos, the critical tanks, filters and check points are brought high up and forward. The alternator is mounted where it will be clear of any spray coming in the vents, or any bilge water that gets flung around lower in the boat. This battery box would likely not be enough for an offshore boat, but is well secured and quite adequate for this lake cruiser.
The spiral-wound duct in this photo is for the bilge blower, which clears gasoline fumes from the engine bay before you start the motor. Gasoline is heavier than air, so this duct is lead as low in the bilge as it can go without sucking up bilge water. Also note the easily reachable spin-on fuel filter, with fire-rated USCG type A1 fuel hose. A longer-term cruiser would likely want a pair of Racor filters with valves for hot changeover, but that would be overkill on a boat like this. Note the absence of any structural members between the mechanic and the engine- the lip of the deck above the engine is reinforced to be stiff enough without a centre brace. (The stainless steel posts help support the weight of people on the swim platform, and provide the mechanic with something to grab onto while she's working.)
Runabouts this size often have the engine mounts lag bolted directly to the stringer tops- a less than ideal solution, as the mounts can then let water into the stringers and trap it there. This boat has a better system, with a beefy L-angle through-bolted to the side of the stringer, and the engine mount bolted to the L-angle. This leaves more clearance for a mechanic, and should be less prone to water damage. Even down here in the bilge, there is enough room to swing a socket wrench, once you remove the black baffle that keeps loose gear out of the engine. You can catch a glimpse of the bilge pump in this photo- undersized and hard to reach, a fault that virtually all boats of this style share.
Note the chafe protection sleeving on all the wiring bundles here. This isn't a perfect installation (it could be considerably neater) but the wiring is reasonably well protected. Many boats this size have loose-tied harnesses similar to what you'd find coming out of a computer power supply, or under the dash of a car. You can see the negative bus bar at the top of the photo, mounted on the underside of the deck- it looks a bit strange, but it'll keep it dry and easy to reach. The exhaust installation here, is, I think, relatively clean and well done; the coupling boot is well above the waterline and the hose clamps are of good quality (but their screws should be pointing outboard on the coupling boot so they can be reached for inspection or repair).
One giant serpentine belt runs the alternator, water pump and power steering pump on this engine. The clearance to the bench seat is a bit tight, but it's better than most cars and represents enough room to swing a wrench and replace any of these components without dismantling anything. The fuel feed, fill and vent hoses, in the background, are routed well clear of the engine, and (although it's hard to tell from this photo) are fairly well secured.
It's not a perfect installation; I've never seen a production boat that is. The engine setup in this Doral, though, is considerably better than most of what I see at the boat shows, and should have a good shot at living a long, well-maintained life. If you make critical parts easy to reach, inspect and repair, they will be inspected regularly and repaired when needed. And you'll save some skinned knuckles, considerable cursing and a horrific labour bill when the boat does end up in the shop.