Why did the boat lose speed under the motor?

Unexpectedly @AlexMemfis suggested looking into the cooling system. He asked me to film the entire water route, from the inlet seacock to the outlet. Once I’d done it, he thought for about 15 minutes, then called with his observations.

The inlet valve is on the bottom of the boat, just behind the engine. A hose runs from it to the impeller. Water then goes to the siphon breaker above the waterline, which prevents reverse flow from the engine. From there, it enters the internal cooling circuit, mixes with exhaust gases, and passes through a hose into the waterlock/silencer — the green box in the video. Then it runs into the locker, up through a gooseneck bend, and overboard. The gooseneck prevents water entering backwards through the outlet when the boat heels or meets waves. The waterlock also has a second outlet for draining. The engine itself has an expansion tank containing antifreeze.

The inspection revealed two problems:
– water seeped from the anti-siphon valve while the engine ran
– no raw-water strainer to keep weed and other debris out of the system

I removed and cleaned the anti-siphon valve, refitted it, and adjusted its cap. I don’t know which bit helped, but the leak stopped.

I ordered a raw-water strainer on Amazon for €20.34. Fitting it was straightforward. After just a couple of outings, I found weed and a black piece of plastic inside. A satisfying result.

#maintenance

Trying to get to the bottom of the engine problem, I wrote in Telegram sailing chats, consulted @AlexMemfis, asked marina neighbours, found every authorised Nannidiesel service centre in Germany and emailed them all. Even Evgenia Lyubimova got in touch (@Liubimova_E).

The workshop at my marina checked the engine and said it was broadly fine. They tightened the alternator belt and adjusted the throttle linkage from the engine control. It made no difference to the revs.

Alexei and Evgenia suggested ruling out dirty diesel by running from a jerrycan. Modern biofuel made from organic waste can support microorganisms, which die and settle as sludge at the bottom of the tank. The circumstances fitted: the boat had sat still in the marina for nearly two months.

I shut off the diesel tank, disconnected the fuel supply and return lines, put both into a can of fresh diesel, and started the engine. After about 15 minutes at higher revs, I took measurements. They told me nothing new.

Whether anything I’d done helped, I don’t know, but the yacht’s speed in calm weather rose from 2.5 to 3.5 knots. A little better than nothing, I suppose.

#maintenance

@AlexMemfis and a couple of authorised service centres suggested lifting the yacht to clean off the growth. Fouling might have become so bad that the propeller was working like a mixer, churning the water in circles. I wasn’t convinced. But if that didn’t help, the next steps were compression tests, investigating the injection pump, and stripping down a relatively recent engine.

I arranged for a neighbouring marina to do the work for €300, took a day off, and came down the evening before. At seven, I picked up my toothbrush and toothpaste, put on my waterproofs, pocketed my phone, wallet and keys, and went into the cockpit. Every surface was wet with morning condensation. I carefully put one foot on the pier. As I brought the other across, I slipped and fell backwards into the water.

After hauling myself out by a mooring line and finishing what I needed to do, I cast off. Another yacht approached, her skipper eagerly drinking coffee. Wet through and freezing, I envied him.

White haze appeared from the exhaust. My spirits sank further. My faith in barnacles slowing us down dissolved in those little white clouds. It could, of course, have been steam: it was cold outside. I reduced the revs just in case.

The lift-out was straightforward. I released the backstay, topping lift and lazyjacks, attached the slings to the crane, and went ashore. The workers scraped off the barnacles with a flat shovel and used a scraper on the propeller and rudder. Then out came the pressure washer. About an hour later, Rassvet was afloat again. I secured the backstay, started the engine and cast off.

What followed is hard to put into words. The yacht didn’t so much move as glide. The engine’s rattle became a soft, even, harmonious purr. At low revs, we glided along at nearly three knots; more throttle gave us the full 5.5. The revs themselves had nothing to do with it: still 2,400rpm under load and 4,000 unloaded. Is that happiness or what?

#maintenance #notes