We have observed Waterway and Bahama sail cruisers operate their boats in very close parallel to the way trawlers operate, and we spend a lot of time among both. A primary topic of conversation is fuel quality — getting it and maintaining it. We have yet to meet one who did not have switchable filters at a minimum and most have in-line fuel polishing which can be run underway or when power is available. Most of these pumps draw around 2 amps.
Since form follows function and so many of us end up motoring for far more of our trips than we might like and are dependent (want to be or not) on power to get us in and out of places and situations where sails just don’t work, it seems the discussion has to end up on what kind of fuel quality systems, not, can one get by without them?
We have been cruising for 40+ years seasonal and full time. We have had 20, 120 and 200 gallon fuel capacities over those years. We have had no less than a Racor 500 2 micron on the diesel boats. We have dual Racor H-leg bypass fuel polishing on the current boat.
Fuel polishing will help with dirty and wet fuel. Polishing won’t help with bad or stale fuel — these are physical vs chemical issues. We know of a bad fuel incident in Maryland when gasoline was pumped into a (kinda iffy) marina’s diesel supply tank and it was noticed six wrecked engines later. The watermen involved were NOT happy.
Unless the fuel is unburnable for some chemical contamination reason, e.g., gasoline mixed in (not a rare thing on a boat-by-boat basis either), too much additive (not a rare occurrence), etc, burning the fuel through the engine GENERALLY will not be a problem as much as it will be an performance irritant. Also, local pollution ordinances need to be considered. We know of boats stopped for emitting too much smoke. If you don’t want to or can’t burn it through, you will want the services of someone licensed to dispose of it. If an unlicensed service provider breaks the law in disposal, you may well get to share the fine and/or whatever else goes with the penalty. Some locales offer bounties on illegal disposers (much as with refrigerant). We are aware of a spill from this process that ended up being charged to the owner’s pollution liability coverage because of license issues with the disposer, even though the spill was not near the boat.
Wet fuel comes primarily from bad supply, water inflow and condensation. One boat on our last trip south was alongside for several days as they dealt with the results of a water hose being put in the diesel fill — by the owner. If water has made it into the tank, an easily reachable sump (we’ve seen maybe 10 in 40 years) from which it can be slurped is great. We used an engine oil change pump for this. If a sump is not built in then it’s empty the tank and add a filter-separator. Or a polishing system.
If the fuel is getting wet from sucking in humid air into the tank which first condenses on the fuel surface and tank walls there are a few remedies. A chemical air dryer in the vent line can help, but it adds complexity and if it gets wet from liquid water or fuel the vent will cease to be one. A good strategy here is to reduce the volume available for damp air to occupy — by keeping the fuel level topped off. However, this is not necessarily a great idea if the fuel is bad/stale. Table on this below.
Dirty fuel can be from bad supply or crud accumulations in the tank. I won’t get sucked into the debate as to the degree this is the result of flora or fauna. Suffice it to say, filter, filter, filter. That same pump for water will handle the crud that ends up in a sump. However, vacuum style pumps that use small tubing will choke almost instantly.* Beyond that would be a separate post on tank cleaning and off-board fuel polishing. [covered very well here] Even if we did not have on-board fuel polishing, we would have two selectable filters. One of our boats under a later owner ended up adrift in the Delaware Bay ship channel because one filter was completely compromised with crud, and there was no second filter.
So what about in-line, on-board polishing?
We’ve been using it for our main engine and genset for 10 years now. The issue hasn’t been power for polishing — it runs when either engine runs and is powered by the main alternator or the genset via ac/dc converter or solar. We run it independently of the engines when we have been forced to buy less than desirable fuel or if the boat is left to sit for an extended period. We have 200 gallon fuel capacity between two tanks. In 10 years we have removed* around a pint of water from the separators and removed about a tablespoon of dirt.
Key is fuel turn-over. Turn-over at the dock and turn-over aboard. At the dock, we look for fuel suppliers to sport-fishermen and commercial vessels that have additional smaller nozzles and appropriate flow rates for us. “How often do you refill your main supply tank,” is our first question after, “do you have fuel?” If the supplier is really moving the fuel, it is rare to get wet or dirty fuel, but one such place we bought fuel, we found the nozzle stowed in a bucket half full of rainwater. If it’s an out of the way source, expect water, dirt and crud to get in your tank [Yes, a Baja funnel can help here, but they slow flow rate and extend the amount of time one ties up the fuel dock. If using deck fuel containers. consider a Baja or filter funnel a must even with polishing.]
Turn-over on the boat is a two-edge sword. Here frequent topping off to keep range at the maximum and water vapor condensation at the minimum works against clean fuel. Lets say you started from empty and filled the tank with, you guessed it, fuel too bad to be good but not bad enough to remove and start over. The table below shows how many top offs by tank percentage fill it takes to really get rid of that fuel. Ten 10% top-offs will add another 100% of the fuel, but 34% of the bad fuel will still be there. It will take 29 ten% top-offs to get the remaining bad fuel below 5%.
Bottom line. To us, fuel polishing is like good ground tackle. It’s a form of insurance and cheaper than the paper kind.
Top Off Table