Essential Guide to Marine Sea Strainers for Engine Cooling Systems

An Introduction to Marine Hardware Sea Strainers

If you own a boat with an engine or generator, a marine sea strainer is an essential piece of marine hardware that you need. A sea strainer is a specialized type of faucet and plumbing fitting that is installed inline on the seawater intake system and its main function is to filter out solid debris from the seawater before it enters the engine's cooling system or generator.

What is a Sea Strainer and How Does it Work?

A sea strainer works by pulling in seawater through an intake scoop at the hull's bottom. The water then passes through a screening element inside the strainer which filters and removes debris like seaweed, sand, silt, barnacles and any solid particles. The filtered seawater then exits the strainer through an outlet and continues on to circulate through the engine's cooling system before being discharged back into the ocean. This protects the cooling system from damage or clogging.

Key Components and Design

Marine sea strainers have a simple two-piece component design:

• A removable lid or top section
• A bowl or bottom section

The bowl has threaded ports for intake and outlet plumbing connections. Inside it has a screened basket that traps debris and is accessible for cleaning when you remove the lid. Common screen types are perforated stainless steel sheets or wire mesh screens. The intake port has a scoop outside the hull to face oncoming seawater flow.

Materials Used

Most sea strainers intended for marine engines are made from durable and corrosion-resistant materials that can withstand saltwater exposure, such as:

• Bronze
• Plastic reinforced with fiberglass
• Stainless steel 316 grade

The sealing gasket material is usually rubber or nylon.

Where are Sea Strainers Installed Onboard?

Sea strainers are installed in the seawater supply line somewhere along the route between the intake scoop at the hull and before the water circulates into the engine itself. Most are found secured along the inside of the boat hull near the engine.

Plumbing Connections

Proper installation requires threaded fittings, hoses and clamps rated for marine use. The intake line's low point should have the sea strainer mounted above it to encourage priming. Installing a sea cock shutoff valve before the strainer lets you service it safely. An air bleed petcock goes on top to vent trapped air.

Parallel Strainer Setup

It is smart practice to install strainers in a parallel layout, where seawater first passes through a primary strainer, then through a secondary backup strainer before entering the engine. This adds redundancy in case one strainer clogs up and needs cleaning.

Maintenance and Cleaning Sea Strainers

Check and clean your boat's sea strainer regularly as part of routine engine maintenance. Clogged strainers can restrict water flow and lead to overheating or damage. When sailing in muddy or debris-filled water, check more frequently.

Cleaning Procedure

Cleaning steps are straightforward:

1. Close the inlet seacock valve
2. Open the strainer's bleed valve to release pressure
3. Disassemble the two halves of the strainer housing
4. Lift out the screen basket and rinse it off with fresh water, removing all debris
5. Scrub and rinse the inside of the strainer bowl
6. Reassemble the strainer and reopen the seacock

Let some water flow through to check for leaks before restarting the engine.

When to Replace

Over time, the strainer screen mesh holes can get enlarged by repeated cleanings. The scoop at the hull inlet can also erode or take damage. Inspect your strainers periodically and replace them if the screen or hull scoop shows significant wear or damage.

Strainer Failure Consequences

If the sea strainer completely fails and allows debris into the cooling system, it can clog and ruptures hoses, corrode the engine, or lead to overheating damage. A blocked strainer can sink or disable a boat, so they perform a vital role.

Selecting a Sea Strainer

Sizing and Flow Rate

Sea strainer sizing depends on three key factors:

1. Engine/Generator Cooling Needs - Select a strainer rated for your engine's cooling system flow rate (gallons per minute). Marine engines average 1-3 gallons per minute per 100 horsepower, but check your engine specs to get the right flow rate.
2. Boat Speed - Faster boats need more strainer capacity to filter heavier debris loads in the seawater.
3. Screen Surface Area - More/larger filter baskets provide greater screening surface area.

Other Features

Look for these useful extras when sea strainer shopping:

• Clear bowl - Visually inspect for debris buildup.
• Metal guards - Protect glass bowls from damage.
• Vents and drains - Smooth water flow, self-draining helps avoid marine growth clogs.
• End connections - Match to your existing hose barbs or pipe threading.

Maintaining Optimal Engine Cooling

Along with strainers, optimal engine cooling requires:

• Antifreeze coolant designed for marine engines
• High-quality hoses and clamps rated for wet exhaust systems
• Properly de-aired cooling lines with a fill neck and bleed petcock at the high point
• Clear seawater intake scoops and checked impellers on raw water pumps
• Regular flushing of the engine cooling system

Consult your boat or engine owner's manual for all the manufacturer-recommended installation and maintenance specifics for your model.

FAQs

How often should I check and clean the sea strainer?

Check and clean the sea strainer regularly, at least a few times per season or every 25-50 engine hours. Check more frequently if sailing in debris-filled or muddy water. A clogged strainer restricts cooling water flow.

What happens if the strainer screen fails and debris gets into the engine?

Strainer failure can allow debris into the cooling system, potentially clogging and rupturing hoses, corroding the engine interior, or causing overheating damage. A blocked sea strainer can disable propulsion and leave a boat stranded offshore.

Where is the best place to install a sea strainer?

Install sea strainers somewhere along the seawater supply line running from the hull inlet to the engine's cooling system intake. Secure it to the inside of the hull near the engine.

Should sea strainers be installed vertically or horizontally?

Vertical installations are best to promote self-draining and avoid marine fouling organism accumulation inside the strainer housing. Mounting it horizontally can trap water and increase chances of clogging.