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Is your (boat) bottom clean? A clean hull = peak performance

Hull

Is your (boat) bottom clean? A clean hull = peak performance

This hot summer, we’ve noticed that the cruising performance of Calypso II has steadily declined over time. We needed to figure out what was going on.

Calypso was at peak cruising performance 2 months ago, and here’s why

Before we left Grasonville, Maryland in May, we had the boat pulled out of the water and power-washed. The boat had been in the water since March, when we performed a sea trial prior to our purchase. At the time of the sea trial, Calypso II’s 350 hp Caterpillar 3126 engines turned up to specification which is 2,800 rpms. At that rate, the boat made 26 knots with less than half fuel and water and four people onboard.

Calypso had received fresh ablative bottom paint in 2019 but was not repainted in 2020. While she was being short hauled, we also had the running gear spray painted with zinc paint to provide some protection. Also, during the winter of 2020, both propellers were removed and reconditioned to specification. Knowing this baseline information is key to assessing the cause of changes in your boat’s performance over time. 

So, it’s no surprise that when we departed Maryland, Calypso II (with her cleaned up bottom) had no trouble cruising at 21-22 knots at 2,400 rpms. That performance continued for the remainder of our trip back home to Marion, MA.

Last weekend, our boat wouldn’t exceed 16 knots and the engines would not exceed 2,500 rpm

All instruments indicated that the engines are operating normally except for their inability to achieve full revs and speed. I inspected the bottom of the boat (without the benefit of scuba equipment) and observed that there is a lot of barnacle growth on the bottom of the swim platform, the trim tabs, the underwater exhaust and a general coating along the underside of the hull. The area around the waterline is relatively clean.

Sippican Harbor, our home port, is relatively shallow and well protected. As a result, on most days there is little water current moving around the boat, and the Summer, the water is warm, often in the high 70s. These conditions, I am told, are perfect for marine growth like barnacles. Ugh.

It’s the barnacles!

Therefore, I’ve concluded that marine growth, potentially due to the fact that the bottom paint is not fresh, is the cause of our cruising performance degradation. In the past, we painted the bottom of Calypso I, our 2000 310 DA Sundancer, every year. While we did get some marine growth, we never saw the decrease in performance that we are experiencing now.  

Solution: hire a diver to clean the bottom

While I’ve not taken this step in the past, the cost of a diver is less than the cost of a short-haul and power wash in our area. I am optimistic that when we next use the boat, her performance will be restored.  Having never had the bottom cleaned by a diver, but having had the boat power washed, We hope the results will be similar.  In Marion, where Calypso II is moored, we have access to a boatyard to power wash and dive services.  In other areas, access to services may decide which route to go.

What is the cost difference between a diver and power wash?

The cost of short hauling a boat at the local boatyard is $12-$13/foot. A diver can range in cost from $3-$8/foot depending on how long it has been since the last cleaning which will dictate how long it will take to complete the job.

For those of you experiencing similar performance issues, don’t overlook a dirty bottom before thinking about more complicated problems. If you can rule that out as a source of performance issues, it will make diagnosis that much easier. And after all, keeping your hull clean and growth free is important maintenance for boaters to ensure you get the desired performance out of your vessel. 

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