Marine Surveys by Acker Marine Survey Co., Dewey Acker SAMS® AMS®, Marathon, Florida, USA Acker Marine Survey Co.
Thirty Years Of Integrity
Marathon Florida
Serving The Florida Keys
From Key West to Key Largo

Anthony Acker, SAMS® SA
ABYC Standards Certified Technician

Principal Marine Surveyor
Dewey Acker, SAMS® AMS® - RET,
Senior Marine Consultant

Holes In Your Boat.
This article was published in the Florida Keys Keynoter on Wednesday, July 24, 1996
Nobody wants a hole in their boat. Some boats naturally have holes below the waterline and more boats sink from holes that were designed into the vessel than from accidents that create a hole in the hull.

For instance the average 35-foot sport fishing machine will have a ¾-inch hole and a 1 ¼-inch hole below the waterline for the marine toilet, two 1 ½-inch holes for the propulsion engine inlets, a 1 ½-inch hole for the depth sounder transducer, a 1 ½-inch hole for the speed log paddle wheel and several other holes below the waterline for air conditioning, seawater washdowns, live wells, etc. Add a water maker and other applications using seawater and the number of holes continues to grow.

A sailboat is likely to have as many, if not more, below the waterline through-hull fittings as a sport fisherman. Even an average trailerable 25-foot sailboat with an outboard auxiliary engine may have one or more holes near or below the waterline. The more holes in your hull the greater chance of you finding your boat sunk at the dock some day.

sinking boat A hole in the hull as small as ½-inch at only a foot below the waterline will allow about five gallons per minute to enter the hull. Make that a one-inch hole at four feet below the waterline and you can expect seawater ingress at a rate of nearly 40 gallons per minute.

Fortunately most recreational vessels will have sufficient automatic bilge pumps to keep up with quite a bit of seawater ingress. If, that is, your batteries remain fully charged, all the automatic switches operate properly and you remembered to leave all your bilge pumps with their switches on automatic. Bilge pumps should be energized from their three-way switches directly from a storage battery and should bypass all battery selector switches.

Most boaters do not take into consideration that, if a bilge pump is rated at 2,000 gallons-per-hour, you cannot expect to get that much water actually moved. The dewatering output of the pump is measured at the pump's outlet spigot, not allowing for any head, which is the vertical distance from the pump's outlet to the through-hull outlet. This is generally two to three feet above the pump, which significantly lowers the bilge pump's output. Its functional output can often be less than half the pump's rating.

Unfortunately, it seems only the most knowledgeable of boat owners are aware of the need for regular attention to the seacocks, scuppers, through-hull fittings, bilge pump outlets, inboard/outboard boots and other holes in the hull that are near or below the waterline.

Sseacock A seacock is your first line of defense. Any through-hull fitting at or below the waterline must have a seacock. Avoid gate vales and stick to seacocks that have positive stops in both the "open" and "closed" positions, such as ball valves or tapered plug valves. You must be able to tell if a seacock is open or closed just by looking at the valve. A gate valve used as a seacock will sooner or later corrode and seize up. When it does, you will not know if it is open or closed. Use seacocks made only of bronze or reinforced nylon (Marelon). A plastic or nylon through-hull fitting or seacock is just waiting for someone to accidental kick it or drop something heavy on it and break it off, opening up a hole in your boat.

The second line of defense is the hoses attached to the seacocks and their securing clamps. Be certain you use hose that is designed for the application, whether suction or discharge. Water and heater hose should be labeled as to their intended use. Avoid that thin-walled corrugated plastic hose in black or white that is sold as bilge pump hose. The only proper function of that type hose is for use as chafe protection for real hoses. Be sure you use two non-corrosive hose clamps at each end (if possible). Make sure both clamps are impinging on the nipple or spud and not just solely on the hose. Think of it this way: You may have your hose double-clamped at the seacock, but only single-clamped at the sink or sea strainer. If a clamp at the strainer or sink fails, the hose can fall away and the open end will be below the waterline.

It is a good idea to take a magnet with you when shopping for marine hose clamps. Some of the imported hardware seen recently may have good stainless bands, but the screw will sometimes be another alloy, which may not inhibit corrosion. If the clamp shows any magnetism, move on.

bilge Inspect your through-hull fittings and seacocks regularly. Exercise the valves back and forth occasionally to keep them loose. You may want to routinely check the seacocks when you check your engine oil or cooling fluid. You may even want to take the ultimate precaution and leave all your seacocks closed when you leave the boat. If you're like me, you will want to leave yourself a written note to remind you to open the seacocks before using the boat. The last thing you need is a fried engine or generator.

Holes in the boat. Most of us don't want them, but most of us have them. Once we begin to routinely pay more attention to them, the less chance our boat will become the subject of an insurance claim.

Dewey Acker, SAMS® AMS® - RET

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