On Boston Whaler classic OUTRAGE hull boats with the optional sump pump, the pump is located in the deepest aft inboard corner of the sump. The pump is oriented so the discharge outlet points outboard and upward. The discharge hose is carried upward and passes through a notch in the corner of the wood cover, the fixed portion, not the moving hinged portion. The hose rises a few inches above the boat waterline and connects to a plastic through-hull fitting.
I think you want exact dimension where that hole in the hull side was located if made by Boston Whaler; I don't have that information. Let's hope an OUTRAGE 18 owner with the OEM pump comes by with it.
The thickness of the hull at the point where Boston Whaler put the discharge through-hull is several inches. I don't think putting in a two-inch or larger hole there is a great idea. Also you will need a fitting that has a lot of threaded length.
- Fig. 1. Through-hull discharge on 22-foot hull. The distance of the outlet above the waterline is likely to be the same on all hulls as that aspect of the pump installation should not vary with the hull length. Photo by the author.
- pumpOutletOUTRAGEhull.jpg (16.47 KiB) Viewed 6744 times
On sump pumps in generalThe general problem with the OEM Boston Whaler sump pump is its design: it is a centrifugal pump. These pumps exhibit reduced output flow as the head on their output increases, that is, the higher they have to lift output water the more the pump output flow decreases. This characteristic is probably why Boston Whaler put the through-hull so close to the waterline: to keep the head on the pump to a minimum so the pump would not become less effective.
There have been instances where the discharge hose from a sump pump has been routed to discharge into the engine splash well. This will be a workable arrangement until you really need the pump to get water out of the boat. If the boat is in a swamped condition, a pump lifting water from the sump to the splash well will never actually get the water out of the boat. The water will stay in the boat and just circulate. I have seen this happen in an actual incident with a Boston Whaler boat that had such an arrangement.
The same deficiency will be seen in a pump discharging overboard through the hull side just a few inches above the water line. It works fine until you really need it and that through-hull is underwater. Now the pump is trying to push against the seawater trying to flow in.
If you really want to pump water out of the boat, you need a pump that can lift the discharge water high enough to pump over the transom notch--at least--or better still lift water over the un-notched transom.
A typical centrifugal marine pump is the RULE brand (now made by Xylem). A
document from the manufacturer gives suggestions for installation and also shows flow rates as a function of the head on the pump. The pumps are rated at no-head flow. For example, RULE 2000 pump will discharge 2000-GPH if there is no lift involved. Note that the smaller pumps suffer more decrease with head than the larger models.
The installation diagrams show that the discharge from the pump should be 12-inches above the hull waterline when the hull is listing severely in the direction of the pump outlet. This is probably a reasonable location for the discharge hole to be made on an OUTRAGE 18 hull.