Here is an excerpt from some friends of mine who are cruising the coat in a Nordhaven 47. This might influence your decision on multiple selectable filtering:
"With weather forecasted to turn in our favor, rounding the peninsula to La Paz would take 23.5 hours. During the first leg (10 hours) seas were on our nose with 4-6 foot waves. The hobby horse ride did a good job of stirring up our 4 fuel tanks. During our trip south we typically transfer what fuel will be needed and then some (say 30% more) out of our storage tanks to a tank used as our primary operating fuel tank. The transfer of fuel to the operating tank allows for additional filtration of the fuel before it is pulled through a primary and secondary filter prior to use. For no good reason on this trip, we deviated from the norm and chose to take fuel from one of the storage tanks increasing our risk of failure. As fate would have it the primary fuel filter plugged. At 9 pm without warning the main motor, a John Deere/Lugger died. We were 2.5 miles off shore in pitching seas, 20+ knots of wind and an opposing current. Without hesitation the “wing engine” was started and used to hold our bow into the seas. At 2,500 rpm’s the little 30 horse power Yanmar, 3 cylinder motor with its folding prop pushed us along at 1.8 knots. We were safe so long as the wing motor continued running. Suspecting the problem was fuel related the thought of losing our wing motor was a real possibility. After switching over to the backup for the primary filter and bleeding the system of air the main motor was back up and purring. At 1475 rpms, given the sea conditions, the big Lugger was providing a 6.3 knot cruising speed. It would take several hours however, for our adrenaline to calm and one of us to get the required rest before a shift change at midnight
The prior month in Santa Barbara we took on 400 gallons of contaminated fuel. We were a bit peeved to find that we took on contaminated fuel in the US as we purposely took on the extra fuel so that we would not have to take fuel on in Mexico thinking that we would be avoiding the fuel contamination issue. Anyway, to kill the algae now growing in our fuel all of the fuel was treated with a biocide additive. The dead algae particles then settled to the bottom of our fuel storage tanks. That and any other contamination missed when we had theses tanks cleaned in British Columbia was now suspended throughout the fuel. So we took multiple days in La Paz opening up all the fuel tanks, scrubbing them out with a mop and polishing the fuel down to 2 microns into the clean tanks as we worked our way around cleaning all 4 fuel tanks.
We have unexpectedly come to rely on the little Yanmar “wing” engine twice during the last year. And, if ever asked “yes” we are sold on having an alternative propulsion system or wing/get home system as they are often referred to."
