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JohannDW · 19-06-2017, 08:51

Hi,
This has come up before but I cannot find the solution to my particular issue in the existing threads. I have a catamaran, with new engines that die (airlocks) when motoring in rough weather. There are no leaks in the system, and the air seems quite definitely to come from the tank, when it moves violently. The same does not happen in flat water. The tank was at least 60% full.

I would prefer to not have to cut out the tank to fit slosh plates, but was thinking of a smaller header tank between the engines and the main tank, with an in-line pump between those two again.

There are issues that arise from this: Will the in-line pump not just draw air and block anyway? It also means that the header tank will be pressurised- not ideal, I would think. Any experience and advice please.

zeehag · 19-06-2017, 08:55

engine dies in rough seas---polish your fuel, install baffles into tank if not already installed, and make sure no air or dirt is getting into your fuel pumps.
btdt in many boats, including my own.

JstaRebel · 19-06-2017, 09:20

I had this same issue. Installed an auxiliary tank as you describe and fitted it with an electric fuel pump. Solved my issues. Not a cat but same problem.

MV Wanderlust · 19-06-2017, 10:09

We had a similar problem right after we bought our diesel powered boat. Turned out the previous owner hadn't kept the tanks filled and algae got into the fuel. The rough seas caused the algae to stir up and get sucked up into the fuel pick up, clogging the filters. I second zeehag's suggestion to have your fuel polished.

stillbuilding · 19-06-2017, 10:54

How big is the fuel tank?
If very large and the fuel is not dirty/contaminated then maybe occasionally drawing a bit of air.

Instead of baffles i think there are some balloon- like structures which you can place in the rank.

In my case, drawing from a 1500 litre tank, all issues solved by installing a gravity- fed day tank of 200l. Easy to ensure fuel is clean, no air bubbles and placed so air not an issue if kept over 1/4 full.

Nicholson58 · 19-06-2017, 11:12

The polishing loop (FRANZ filter or Pacific coast filter) feeding your RACOR filter will probably solve the problem and will prevent injector and high pressure pump failure. Alternatively, if you can surround your suction pickup dip tube with a larger diameter pipe the result will be to reduce the sloshing turbulence.

JohannDW · 19-06-2017, 11:19

Thanks for the advice. The fuel is clean and the filters show nothing after a rough outing. The tanks were emptied and cleaned thoroughly eight months ago.All lines are new. But will check again and revert.

**GordMay** · 20-06-2017, 05:15

Greetings and welcome aboard the CF, Johann.

MV Wanderlust · 20-06-2017, 05:54

Quote:

Originally Posted by JohannDW

Thanks for the advice. The fuel is clean and the filters show nothing after a rough outing. The tanks were emptied and cleaned thoroughly eight months ago.All lines are new. But will check again and revert.

Then it definitely sounds like it's sucking up air somewhere. Considering it only does it in rough seas, you (and the others) are probably right about the fuel sloshing in the tank. Does this happen only when the tank is partially full or will it happen when the tank is fully topped up? If it doesn't happen when the tank is fully topped up, that would lend further credibility to your theory. Nicholson has an interesting idea about a pipe around fuel pick up tube. Perforated, perhaps. Like adding baffles to a tank without changing the tank. Please let us know what you find. This is interesting.