This article is one in a series offering tips on boating skills and seamanship prepared for The Citizen by the U.S. Coast Guard Auxiliary.

Part of this column regarding the reasons why power boats sink was published last year. Today we are adding the reasons why sail boats sink.

With regard to power boats, the important information and the research was conducted by BoatU.S. and Seaworthy magazine. With regard to the reasons sail boats sink, BOATU.S reviewed the files of its Marine Insurance.

After publishing a recent study identifying the causes for accidental outboard powerboat sinkings, Seaworthy, recreational boating's damage avoidance magazine, has combed through the BoatU.S. insurance claim files to identify the reasons why inboard/outboard (I/O) powerboats sink. Interestingly, while outboard powerboats are similar in design to I/O's - and often made by the same manufacturer, the study found vastly different reasons why each accidentally sinks.

Outboard powerboats tend to sink at the dock due to poor cockpit designs that trap water, but an I/O's weakest link is the delicate connection between the inboard engine and the outdrive unit, called bellows.

“The use of bellows or boots pleated, flexible rubber membranes - that run between the inboard engine and partially submerged outdrive to seal the transom where cables and shafts pass through, have one weakness: a limited lifespan,” said Seaworthy Editor Bob Adriance.

He emphasized that bellows should be inspected annually - and more often in hot, sunny climates. “Any bellows that is over five years old, is living on borrowed time,” Adriance said.

He adds, “Many boats have more than one bellows (driveshaft, shift cable, exhaust, etc.) any one of which has the potential to sink the boat. And if one shows wear, they all should be replaced.”

Here are the top reasons why I/O's sink:

At the dock

1. (44 percent): Leaking bellows. A surprising number were attributed to the small shift cable bellows.

2. (23 percent): Failed below waterline fittings, hose clamps, and melted hoses as a result of overheating.

3. (15 percent): Failed above waterline fittings. Heavy rains overwhelm cockpit scuppers.

4. (11 percent): Poor docking arrangements: Boats or outdrives that snag on docks.

5. (6 percent): Uninstalled drainplug.

6. (1 percent): Miscellaneous such as a cracked engine block.

While underway

1. (36 percent): Struck a submerged object such as rock or logs.

2. (24 percent): Failed below waterline fittings.

3. (20 percent): Leaking bellows.

4. (12 percent): Swamping.

5. (8 percent): Miscellaneous.

Now to sailboats. A study of 100 sailboat sinkings from the BoatU.S. Insurance claims files could help prevent your sailboat from becoming a statistic. “The sinkings were found to be divided evenly into two broad categories - those that sank at the dock and those that sank while underway,” said BoatU.S. Marine Insurance Technical Director Bob Adriance.

“However, when it came to sinking underway, a sailboat's deep draft became the obvious factor,” Adriance continued. Striking a submerged object was found to cause 40 percent of the sinkings while underway.

Next on the underway list was a broken prop shaft or strut (16 percent) and damaged or deteriorated fittings below the waterline (16 percent).

“Prop shaft corrosion seems to be a bigger issue with sailboats than with powerboats as auxiliary sailboat engines are not run as often, allowing corrosion to set in,” Adriance added.

The most common cause of dockside sinkings were found to be the result of deteriorated, damaged or corroded fittings such as intakes, seacocks, and drains below the waterline. Stuffing box leaks were number two on the dockside list.

The complete study results are as follows:

Why boats sink

Sinking at the dock

Below waterline fitting 44 percent

Stuffing box leak 33 percent

Keel and centerboard 7 percent

Rain 7 percent

Head back-siphoning 3 percent

Above waterline fitting 3 percent

City Water hookup 3 percent

Sinking underway

Struck submerged object 40 percent

Prop shaft or strut 16 percent

Below waterline fitting 16 percent

Grounding 8 percent

Stuffing box leak 8 percent

Storm/knockdowns 8 percent

Above waterline fitting 4 percent

Five tips for prevent a sailboat sinking:

1. Any time your boat hits bottom, immediately inspect the bilge and keel bolts or centerboard pennant and hinge. To be safe, inspect again an hour later.

2. Routinely - twice a season - inspect all below the waterline fittings, hoses, and hardware. If the fitting is long enough, it's good practice to have two marine-rated stainless steel clamps on all hose ends. Any hoses showing signs of rot should be immediately replaced.

3. When at rest, stuffing boxes should never leak. If leaking persists after the packing gland nut has been tightened, the packing must be replaced.

4. Don't ignore through-hull fittings or hoses that are installed above the waterline. While they may appear to be “safely” above the water level, they can leak when heeled over in a seaway, or when snow or ice forces the boat under.

5. A winter haul out is the perfect time to inspect the prop shaft and cutless bearing.

John E. Keshishoglou is the IP flotilla commander of the Ithaca Flotilla 22. He can be reached at (607) 273-7175.