Unblock Seawater Intake: Dinghy Pump Hose Hack

It was another spectacular summer day as we released the dock lines and once again escaped life ashore, the trusty diesel humming beneath our feet. The weather forecast promised sunshine and moderate winds. My wife and I were away uncharacteristically late, something that seldom occurred on our boat. Friends were in a beautiful anchorage ten miles away, cocktails and dinner awaiting our arrival. We wanted to be there! Light wind rippled the clear blue water as we passed the breakwater, a plethora of boats skittering about like water bugs on a lake. A busy afternoon at the marina with a promise of another relaxing weekend on the water.

UNUSUAL ALARM

Suddenly an alarm shattered the idyllic scene, one that I had not heard before! A quick scan of the engine panel showed a bright red warning light for engine temperature, the accompanying gauge showing well above normal and rising rapidly! Not good. I quickly shut down the diesel and scrambled to roll out the genoa to maintain steerage in the crowded channel. Fortunately, the breeze was just forward of the beam and we could maintain course on a tight reach.

HOT ENGINE

Carey took the helm as I dove below to open the engine compartment. A wave of heat billowed into my face as I removed the companionway stairs. The trusty diesel seemed somewhat forlorn, apologetic for causing such a problem. The heat exchanger was too hot to touch, I wasn’t going to open the coolant cap to check fluid levels. The raw water strainer’s clear plastic top showed no debris, and empty of water as well. Strange! I’m somewhat fanatical about engine maintenance and knew the raw water pump was almost new and probably not the cause.

ASSESSING THE PROBLEM

I instructed Carey to momentarily start the engine. No seawater flooded into the strainer. Not good! The strainer was mounted so that the top lip of the bowl was at seawater level. I knew that if I took the screw top off the strainer water should quickly flood to the top of the plastic bowl. I did, and it didn’t! Damn! A quick check of the hose between the raw water intake and strainer showed no points of collapse. Something was plugging the intake. I wasn’t going to be able to fix that right away and so climbed back into the cockpit to assess our predicament.

We were about a mile from the safety of our berth at the marina, it was mid afternoon on the first day of a four-day jaunt into the Canadian Gulf Islands, and friends were awaiting our arrival. The breeze was steady and from the right direction. It was a very short discussion. We’re on a sailboat, lets go sailing! The main was hoisted and joined the genoa as we heeled into the breeze. The afternoon quickly vanished in a glorious three-hour reach to Bedwell Harbour. Although the wind went very light for a while, we managed to sail to a vacant mooring buoy and secure the boat. Diagnosis and repair could wait, cocktails, dinner and good company under a setting sun took precedent.

The next morning, I re-assessed the problem. Aboard Natasha, our 1978 Islander Bahama 30, we had a Beta 20 diesel mounted on a sail drive, a system I had installed nine years before and was very familiar with. This reliable combination allowed for quiet, nearly vibration-free motoring when we lacked wind. The raw water intake was through the sail-drive leg protruding under the hull, much like the water intake of an outboard motor. What could have plugged the intakes on both sides of the leg? I had no intention of going for a swim in the 10 C water if I could help it. I started the Beta momentarily and put the prop in reverse, hoping the wash would force the obstruction away from the inlet ports. No luck.

UNBLOCKING A SEACOCK INLET

In past years we had the old Volvo MD7A diesel with a shaft and fixed prop. When we faced a water flow blockage, I would close the through-hull seacock and remove the intake hose. With a metal probe (usually a long icepick) I would carefully open the seacock and start poking at the obstruction, usually kelp, as water started to geyser in. Always an exciting and wet experience! But I couldn’t do that with the sail-drive leg. The openings for water intake were just too far down the leg from the seacock mounted on the upper part of the leg inside the boat. No way to push the obstruction out. I needed something else to remove the obstruction from the leg, but what would work? I needed to put my thinking cap on!

CREATIVE USE OF DINGHY PUMP HOSE

On Natasha we’ve always had an inflatable dinghy for going ashore. The dinghy came with a foot pump for inflation. Although not identical in diameter, the hose of the pump lined up reasonably well with the raw water hose I had removed from the intake port of the raw water strainer. I taped the two hoses together using plenty of “rescue” tape (something every boater should carry).

Starting carefully, I pressurized the raw water intake hose leading into the leg. Nothing happened other than to pressurize the hoses, no sound of bubbles under the hull. Careful pressure eventually led to stomping on the pump. Suddenly the pump went slack and I could hear air bubbles escaping under the hull! Success! I quickly shut the seacock at the leg before seawater flood up into the foot pump. The two hoses were separated and the raw water hose reconnected to the raw water strainer. Opening the seacock quickly filled the bowl with seawater. Starting the engine showed excellent water flow. We were back in business. I never did see what it was that had plugged the intakes.

NYLON ADAPTER FOR FUTURE BLOCKAGE TROUBLESHOOTING

With this new successful solution, I now carry a nylon adaptor to connect the raw water intake hose to the dinghy air pump hose. Two properly sized hose clamps are included in the “emergency kit,” should this occur in the future. No need for the rescue tape. I’m ready! This set up would also work well for the standard engine through-hull intake hose. No need to get wet as water pours into the boat.

ADDING AN ADDITIONAL SEACOCK AND WATERFLOW SENSOR

As is typical of this type of boating issue, they always seem to occur at critical times, not when you have the luxury of time to come up with a solution. At next haul out I installed a second raw water through-hull near the engine, with proper seacock. A “T” connected the new through-hull to the seawater strainer hose. Should this problem crop up again, particularly around marinas and other tight places, I can simply open the seacock on the back-up intake to keep the engine happy until I can sort out the blockage.

I have also installed an Aqualarm waterflow sensor with alarm indicator on the engine control panel. If the intake is blocked in future the alarm will sound long before a blocked water intake becomes an issue at the engine, allowing ample opportunity to shut down before overheating occurs. The diesel is too valuable, both as a reliable friend, as well as a financial expense, should we not catch such a failure in time.