Part I. Could Your Boat Sink? Even At The Dock?

This is the first installment of a two part series on preventing sinking and swamping by water intrusion. The first covers topside water integrity, scuppers and repowering with heavier outboards. The second will cover safe drains and through-hulls, including inspection and maintenance.

Owners blame sinkings on several factors:
1. The bilge pump failed
2. Rainwater could not drain out of the boat fast enough
3. Rainwater drained into the bilge
They could also blame a combination of these factors. The real reason that boats sink is because owners fail to keep the water on the outside of the boat. This may seem snarky, but it’s true, and fundamentally owners are placing too much reliance on bilge pumps to keep water outside the boat. Bilge pumps only remove nuisance water and help deal with minor leaks. They are not a “silver bullet” for preventing swamping or sinking. Let’s look at how water gets inside the boat, whether rain water or sea water.

Deck openings lacking watertight integrity

A common problem is hatch openings and access covers that are not tight or properly sealed. Some of these are in the deck, aft and forward of the outboard splash well, to provide access through the bilge to mounting bolts, pumps, wiring and hoses. Some times these access covers are in the splash well. If scuppers plug up or become overwhelmed, water can back up and drain into the bilge. Some storage compartments, cup holders, rod holders and live wells drain into or through the bilge. If the associated hoses and clamps are inaccessible their degradation cannot be inspected. The bilge pump cannot keep up with intrusion through these breaches, eventually the battery becomes discharged, and down she goes.

Backflow through scuppers

Note the well scuppers directly at the waterline. Note also the hatch mounted in the well that leaked, allowing water flow into the bilge, eventually sinking the boat.

Poor design and scupper location relative to the waterline is a cause of swamping and sinking. The American Boat & Yacht Council (ABYC) has recommended standards for the placement of scuppers, scupper sizes, and the minimum heights above the load waterline covering both while the boat is static and at maximum heel. Cockpit decks are supposed to be designed to be a minimum of four inches above the waterline but often are not, especially in types such as flats boats and some bay boats. Boats with these design limitations are risky to use offshore, to anchor in tidal waters, or to moor or dock while unattended. Rainwater back-ups in cockpits, on decks or in leaky storage compartments can contribute to overwhelming of the bilge pump capacity. On boats designed with little safety margin, storage or location of heavy gear in the stern can overcome the ability of the boat to keep heavy rainwater out of the bilge, and down goes the boat.

Float-ball or duckbill scuppers often seen in these boats, where outlets may be beneath the waterline during backtrolling, in tidal flows or when the boat is heavily loaded. While these designs prevent inflow, they also reduce outflow, which can be a problem during storms.

Repowering with a heavier engine

Repowering with heavier engines, even without increasing total horsepower, can cause water intrusion also. This often happens when converting from older two-stroke to four-stroke outboards, especially on an older hull designed during the two-stroke era. The weight difference can be 10 to 20 percent, which could amount to 200 pounds in a dual-engine installation. The added weight is right on the transom, directly above the scuppers. The effect is even worse if a bracket has been added to the stern and a splash well deleted to gain deck space. These modifications lower the load waterline, and openings that were above the waterline are no longer, putting the boat at further risk of sinking. In boats with foam or balsa cores, water intrusion and core saturation can easily add an additional 100 to 200 pounds of water.

Repowering this older boat with a heavier four-stroke engine brought the scuppers and the waterline too low for the boat to survive a deluge.

When repowering, it is wise to look up the typical weight of the maximum rated outboard engine for the boat. Then resist installing engine(s) that would exceed that transom weight, even if you have to de-rate your accustomed or desired horsepower. Another good step is to place upon the transom a quantity of weight equivalent to the weight of the repower, with the boat launched and fully loaded (gear and personnel), and check the waterline and scupper locations.

Adapted from When It Rains, Boats Sink, Story and Photos By Daniel Rutherford

Source: https://www.boatus.com/seaworthy/magazine/2016/april/when-it-rains-boats-sink.asp

Next time: safe drains and through-hulls, including inspection and maintenance.