Moored Sterndrives: Understanding the Maintenance Reality for an Informed Boat Purchase

Moored Sterndrives: Understanding the Maintenance Reality for an Informed Boat Purchase

For aspiring boat owners, the appeal of a permanently moored vessel is undeniable. You get instant access to the water, avoiding the hassles of trailers or dry-stacks. The convenience of just setting off with minimal preparation is a significant draw. However, owning a sterndrive-powered boat that’s always moored has hidden costs. Specifically, it demands increased maintenance. Unlike trailered or dry-stacked boats, sterndrives submerged continuously face unique challenges in the marine environment.

The Constant Battle: Marine Growth and Corrosion

A major concern for moored sterndrives is marine growth. Creatures like barnacles and mussels attach to the drive unit. They create drag and can harm the gear case and rubber components. Over time, corrosion or electrolysis can set in due to depleted anodes. This can lead to expensive repairs or total failure.

sterndrive growth
A pair of Mercruiser sterndrives with heavy barnacle and shell growth

The Crucial Ritual: Annual Haul-out and Inspection

An annual haul-out for inspection and servicing is essential. This involves more than a simple wash. It includes removing the sterndrive for a complete inspection. Mechanics check the shield, bonding, gimbal bearing, uni-joints, and bellows. They also replace seals, oil, and anodes. Cleaning water passages and re-fitting with a new outdrive gasket kit is also part of the process. Preventative maintenance and early detection of issues are crucial. They prevent small problems from escalating into costly repairs.

Special Maintenance in High Growth Areas

In high-growth marine areas, especially for boats that are rarely used, mid-year lifts for water blasts and sterndrive removal may be key to ensuring reliable usage and trouble-free boating. In these regions, marine growth can accumulate rapidly, sometimes in as little as six months, necessitating shorter time periods between haul-outs. This rapid accumulation is particularly challenging for boats with little use, as barnacle growth can restrict water flow and cause engine overheating. 

Blocked sterndrive intake
This sterndrive water intake was blocked with an oyster, causing the engine to overheat
 

Exploring Alternative Cooling Options: Hull Water Pickups and Sea Strainers

In addressing the challenges with sterndrive cooling passages, some boat owners have adopted the practice of installing separate water pickups through the hull’s bottom. This modification is aimed at drawing cooling water directly into the system, bypassing the sterndrive’s traditional water intakes, thereby reducing the build-up of marine growth within the cooling passages.

Alongside this modification, it is considered good practice to integrate a sea strainer into the system. The primary function of a sea strainer is to filter out debris and marine growth, which is a common challenge in the marine environment. The significant benefit of this addition lies in its practicality – sea strainers can be cleaned out from inside the boat. This feature not only simplifies maintenance but also enhances the overall efficiency of the cooling system.

Using a Diver

If you’re having problems with excessive growth, using a diver at suitable intervals can be a good option. For example, I had a client who was having to antifoul every 6 months. By using a diver at 3 month intervals, he was able to push the time between antifouling up to 9 month intervals.

Prop Speed Coatings on Sterndrives

Another alternative to try in a high growth area can be coating the lower half of your sterndrive with prop speed. These coatings work best when they have water flow past them, so don’t worry about doing the top of your sterndrive. Only the lower section is useful, where the water intakes are and water flows past when underway.

Proactive Protection: Gear Oil Checks and Bellow Protectors

If doing a mid-year lift for a water blast,  a sterndrive check is always advisable. It helps catch minor issues early. A gear oil check and bellows inspection can reveal early signs of water ingress or bellow failure. This reduces the risk of internal damage. Simple measures like these can save thousands in repairs and extend your sterndrive’s life. In areas with aggressive marine growth, bellows protectors are a beneficial option to consider. These protect the uni-bellow from barnacle growth, reducing failure risk.

Informed Choice: Weighing Up the Cost of Convenience

Understanding the maintenance needs of moored sterndrives is crucial for prospective buyers. While in-water berths are convenient, they require regular inspections and maintenance. This often leads to higher costs. Comparing this with the benefits of dry-stored boats helps in making an informed decision. It allows you to balance lifestyle preferences against maintenance budgets.

Final Word: Knowledge is Power, Maintenance is Key

Regardless of your choice, understanding preventative maintenance for moored sterndrives is essential. Being proactive in scheduled servicing reduces the likelihood of breakdowns. It ensures reliability for enjoyable weekends on the water.

About the Author


Brendan is a dual certified Marine Surveyor & Engineer, who completed his trade at well respected marine engineering company based on the Hawkesbury River. After relocating his family to the Gold Coast, he joined the BoatBuy team. Brendan is an expert in his field, and completes over 200 inspections per year. Liked this article? Feel free to email me with any boating related questions you might have here. You can also contact the team at BoatBuy here.

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