I agree with your scupper comment, except if there is standing water in the boat. If there is standing water, the ski locker will fill (doubtful about the extent of the fuel cavity since there is a rubber seal under your floor). If your ski locker port is open, water will drain into the bilge, bypassing the scupper. In that scenario, instead of having the both bilge and scupper draining your boat of water, you are forcing more water to the bilge pump.
If your ski locker plug is open or closed all the water that gets into the ski locker is bypassing the scupper. In every scenario that water gets into the ski locker, you'll need the bilge pump to get it out.. (or some other bailing method)
END OF RESPONSE
A few notes to the owners of 2015-2016 AR240/242 boats.
Previously I always had my boat on the trailer from day to day and not exposed to rain, but the first time I left it in the water (uncovered) the ski locker was 1/2 full of water overnight. This was just prior to heading to Bimini - and it rained really hard that night. Water getting into these boats does not escape if that ski locker plug is left in. What's worse is that all the rain that enters the boat pools up front and heads into the ski locker. It will fill the ski locker by overflowing the front edge of the hatch. I had to remove that plug and once on plane the water could reach the bilge pump and get pumped out. If I hadn't noticed and left all that extra weight in the ski locker the trip to Bimini could have ended in a swamping. So ALWAYS in or ALWAYS out just doesn't really work. Depending on your model, you may have to adapt to nonsense like this.
While we were at Bimini it rained a few times pretty hard, even after that hard rain the ski locker would be 99.5% empty but you could see water sloshing just under the plug hole, and sometimes wet just into the locker. That would all be dry at the end of the day's use if we were on plane for a while. These boats sit nose down and the water collects in the front and can't be bilge pumped out when sitting. My two girls and I stood on the back of the swim deck each morning and that was enough to get most of the water to flow aft to be pumped out. But by seeing that there wouldn't be any standing water in the ski locker with the plug out - it tells us that it mostly is eventually reaching the bilge pump and not weighting the nose down past a certain point.
Tell me that yamaha with all their engineers planned for this to occur ? Nope, the boat should sit at least slightly nose up and all the water coming in should go around the ski locker and fuel tank compartments in their channels and end up at the scupper but it doesn't work that way in reality. So in reality - I leave out the ski locker plug at all times, but I know that if there were a hull breach, I WOULD and SHOULD plug that hull and use that ski locker for additional buoyancy. Those of you whom don't own this model might think yamaha engineers are smarter than that and my boat must be heavily loaded in the nose.. but that's not the case.
In an atypical scenario such as the Bimini crossing where this is a big deal... - If a wave washed in over the nose, most of that water will head toward the scupper (especially if you keep a nose up attitude), but some of it will seep through the ski locker hatch and either be trapped in the ski locker making your boat more and more nose heavy, or will go through the drain plug and get bilge pumped out. (depending on if you've got it plugged or not)
If you leave your boat in the water exposed to rain water will collect in the ski locker.
Anyhow, there are too many scenarios to count, so I've boiled my practice to this for anyone interested:
When out of the water, all the plugs are out so any water can eventually run down hill to bilge drain. (I'll admit on rivers and lakes there's never any water in the fuel compartment or on the plug forward of the engines so I don't normally touch those). lets face it - it's not going to sink out of the water so pretty much anything you do is fine.
When in the water,
1. ski locker plug is out for normal use so normal water taken on board that isn't scuppered can get pumped out
2. fuel compartment plug in so it can remain an air chamber (I've never had water come out of that compartment, so I think it's fine to keep it sealed )
3. bilge drain forward of engine is out so if water were to get into that little cavity it will drain down to the bilge pump. That plug appears to be useless anyways.
A friend of mine has a 2007 ar210 and his bilge pump appears to be mounted on the inner hull in the engine compartment, and out of reach of any bilge water - on my boat there is a hole cut in the inner hull, and the bilge pump in the engine compartment sits on the actual bilge. I believe that these design differences if not taken into account add up to some pointless arguments in this thread. I've owned many boats before but the bilge arrangment on this boat has baffled me - I hope that what I've learned may help some folks.. Keep an eye on the ski locker, it's a design flaw that allows it to fill with water.
Stay safe everyone.
