Dirona Fuel Manifold

Nordhavn delivers an unusually complete fuel manifold with far more flexibility than most production boats. In fact, the manifold is sufficiently complex that some new owners can find it difficult. More than once, I’ve heard of an owner accidentally closing the return path for the main engine or generator, leading to fuel leaks or, worse, engine fuel pump failure.

Even with the unusual flexibility offered by the Nordhavn fuel manifold, we found it didn’t do some of the things we wanted it to be able to do so we made fairly substantial fuel manifold modifications on Dirona. Some of these modification were driven by us extending some of the applications of the manifold and some were driven by us operating the fuel systems a bit differently from some. Let’s start first with how the standard manifold works, look at the most common operating modes, and then at the manifold changes we made and why.

Most Nordhavns come delivered with a separate day tank to feed just the get-home (also called wing) engine. One of the most common causes of diesel engine fault is dirty fuel, so having a separate fuel tank where no fuel is even placed there unless first proven to be good via use for days in the main engine adds considerable security. The wing engine has a separate, known clean fuel in addition to its own mechanical control system, transmission, prop shaft, and prop. It shares almost nothing with the main engine, reducing the likelihood of a correlated main and wing failure.

In addition to the day tank feeding the wing engine, there is a supply tank which feeds all other engines on the boat. The supply tank is always the fuel source for the engine(s) and generator(s). There are also multiple bulk storage tanks. On Dirona, we have two side tanks of 835 gallons each, a supply tank of 65 gallons, and a day tank of 15 gallons. The day tank feeds only the wing engine, and the supply tank feeds all others engines and generators. The bulk tank contents are moved into the wing or supply tanks prior to using the fuel.

The picture above shows the fuel transfer manifold on Dirona when it was delivered in early 2010. It’s similar in functionality and design to the manifold delivered on most Nordhavns, although many have more tanks, engines, and generators. The lower manifold is the transfer manifold and the upper is the return manifold. All engines, except the wing, draw fuel from the supply tank and return it to the return manifold. The fuel transfer pump sources from the transfer manifold (the lower one). This transfer manifold selects which tank the transfer pumps draws from. The return manifold gets the output of the transfer pump and the return from all engines except the wing. It’s this manifold that sets which tank the return goes into. Understanding how the systems are laid out, let’s look at how they are typically used and why some of our usage models are different and the design extensions we implemented to support these other operating modes.

The most common operating mode for Nordhavns is to choose one of the bulk fuel tanks to draw fuel from and to open the valve at the bottom of that tank to gravity feed into the supply tank. The return manifold is set to send return fuel back to the supply tank. Since the supply tank bottom is below the bulk tank bottoms, the supply tank won’t run out in this mode. As the fuel draws down, the selected bulk tank gets lighter and the boat will eventually start to list away from it. At that point, the gravity feed from the first selected bulk tank is closed and another is opened on the other side. This keeps the supply tank full and keeps the boat relatively well trimmed.

To further improve the trim, some owners chose to have all the bulk tank gravity lines open. This has the advantage of pulling them all down equally but there are two downsides: 1) you might want to more more fuel on one side to correct a list (perhaps the dinghy is down) and 2) having tanks on both sides of the boat connected allows fuel to move side-to-side which isn’t ideal from a stability perspective. Consequently, I don’t recommend running with more than one of the gravity feed lines open at a time.

Another variant of the single-gravity-feed-at-a-time model is to return fuel to the bulk tank that is currently gravity feeding into the supply tank. The tanks will all run at the same levels in this mode of operation, and it can allow cooler operation. Here’s why. The bulk of the fuel the engine draws from the supply tank is not consumed, but is used to cool the injectors and other fuel parts and the warmer fuel is returned. If just the supply tank fuel load is in circulation, that fuel will heat up. Whereas, if the entire bulk tank and supply tank fuel load is in circulation, there is much more fuel and much more fuel tank surface area to cool and the fuel will run cooler. Modern engines measure fuel temperature and take into account changes in temperature when computing the amount to inject, and cooler fuel does allow just slightly more power. This mostly is irrelevant but just barely useful enough that, if you do chose to gravity feed as most do, I recommend transferring back to the bulk tank that is currently gravity feeding rather than directly back to the supply.

We chose to not gravity feed to the supply tank even though, as described above, this is an easy to manage and reliable way to operate the fuel system, and it would keep the fuel cooler. Instead we chose to explicitly pump fuel from the appropriate bulk tank to the supply tank every four hours rather than gravity feed. This is a slightly more manual operating mode but has some advantages that we really like. The first advantage is if there is a leak on the engine, at the filters, or in any of the fuel lines, you can’t possible loose more than the volume of the supply tank. If you are gravity feeding, you could lose the entire bulk fuel load and could end up out of fuel and risking environmental damage via a large fuel spill. Avoiding this is important any time but even more important when doing long ocean crossings sometimes more than 1,000nm from the closest shore. Having no fuel when days from shore could really be a disappointment.

The second advantage of the explicit fuel transfer system is all fuel has to pass through the transfer filter before it gets to the supply tank. Given the uncertainty of fuel quality world-wide, we really like a layer of filtering prior to the fuel even getting to the supply tank. The combination of keeping the bulk fuel locked up and safe from leaks and the additional layer of filtering makes this operating mode important to us. It is a bit more manual work but it feels worth it. This is the source of the first fuel system modification we made. The standard fuel pump, a Walbro 6802, is incredibly slow at 43 gallons per hour. In fact, so slow that this way of operating the boat can be frustrating. So we replaced it with a Jabsco VR050-1122 pump capable of 660 gallons per hour.

Like many modifications, when you make one change, it can drive others. To accommodate the transfer rate of this pump, we needed to go with a much larger transfer filter. We went with Racor FBO 10, pictured below, which is commonly used in bulk transfer commercial fuel management applications. This filter has the advantage of supporting large transfer rates but it also has large filtration area so few filter changes are needed.

One of our goals is to be able draw fuel from the supply tank and return it to the supply tank while polishing one of the bulk tanks. The standard manifold design doesn’t support this. The engine return goes to whatever tank the transfer pump is returning into. Unless you are gravity-feeding, polishing one of the bulk tanks while underway has the downside of the supply tank being completely pumped out every 30 to 60 minutes and runs the risk of running the main engine out of fuel. So we made manifold changes to support what we wanted.

Dirona‘s manifold pictured at the top of this post supports many extension from standard. The first to address the issue we just brought up. If you look closely you’ll see that we can polish fuel from a bulk tank back to the same bulk tank but still direct the main engine fuel return to the supply tank. There is a bypass that runs between the engine return and the supply tank fill that allow the main engine to return fuel to the supply tank while still being able to polish fuel in any other tank. This bypass hose can be seen running through a valve on the right side of the manifold.

Another addition we made to the manifold is provision to drain pump out of the supply tank. We have added a hose from the bottom of the supply tank into the transfer manifold allow the supply tank to be polished if a fuel problem is encountered. It also allows the supply tank to be pumped out if there is a need to service it or some of the fuel lines in that area. Because we can pump out the supply tank, and the supply tank is below the wing tank, we can actually pump out the wing tank as well by first pumping the supply tank level to below the bottom of the wing tank and then opening the wing and supply return manifold valves and allowing the wing tank to drain down into the supply tank. We think it is super important to be able to pump out, service, or re-filter the fuel in any tank and especially the wing and supply tanks. These changes allow the supply tank to be directly polished underway and supports draining the wing and supply tanks if needed.

The next extension is to allow Dirona to carry more fuel in those rare times when greater range or higher speed over long distances are needed. Dirona as delivered is capable of around a 2,400nm range and this is more than enough for 99% of all she will ever do. However, there are times when very long crossings are planned or when we want to run faster on a passage that is within range. The nicest solution is to put more tankage on Dirona but it’s impractical to install more and it’s probably not worth the space compromise that has to be paid every day for the entire life of the boat just to get more range or speed on a long crossing. You may only need this greater range every few years and yet more tankage take up more space all the time. Our solution is to run on-deck fuel tanks when we do want to run more or ran faster. This is more of a hassle but, since the extra fuel is rarely needed, it feels like a better answer on a small boat than giving up more space inside the boat. Our longest run has been 2,600nm , and having more fuel made this much more practical. But, in five years, we have only needed this additional capacity once and only used it twice. On-deck fuel bladders are a good compromise when you don’t want to give up more space and very rarely need more fuel.

To make the bladders easier to manage, we have a bulkhead fuel fitting in the cockpit plumbed into the fuel manifold at bottom left (and pictured above). When we install the bladders, we install a short length of fuel hose between the bladders and the bulkhead fitting using cam lock snap fittings. This allows us to drain the bladders without going on deck and without having the fuel intakes open to potential water ingress. When we are ready to draw them down, we just turn on the fuel transfer pump, select the tank we want to pump into, and the transfer pump quickly does the work. This has the added advantage of putting all bladder fuel through a filtration phase before bringing it into the fuel tanks.

We’ve mostly gotten good fuel, but there have been a couple of times over the last fifteen years when we’ve bought some expensive water, or picked up some fuel with lots of foreign matter. We buy fuel all over the world and the good news is that bad few is fairly rare. But it does happen. Our defense against it is mass filtration with lots of spare filters. The way we use the boat, fuel will be filtered at least four times before reaching the engine injection pump: 1) through the transfer filter to the supply tanks, 2) through the primary filters to the main engine, 3) through the first on-engine filter, and 4) through the final on-engine filter. We have a lot of filter spares on board, with more than 40 of our primary filters stored away. If we get bad fuel, we probably have the filtration to be able to manage the problem.

The final issue is complexity and human error. Nordhavns have very flexible fuel transfer systems but with flexibility comes some complexity. On Dirona, we have extended the design but, with those extensions comes some additional complexity. It’s hard to avoid. And where there is complexity and potential tired boat operators, mistakes can happen. The most common mistake is to close an engine return valve or close the return manifold tank connection. This causes the running engines to not be able to return, which will very quickly lead to leak or pump failures. You can disable an engine quickly this way. Another mistake is to accidentally pump fuel overboard.

We battle complexity and potential error every way we can think of, including posting the fuel transfer diagram at the manifold and having all valves brightly and clearly labeled. We have also calibrated the sight gauges in our all our tanks and installed redundant digital tank level monitors. We have installed a digital fuel transfer timer and both calibrated it and labeled it for the number of gallons transferred per minute. So, if you are moving 17 gallons, you can see exactly how many minutes of transfer time is needed, substantially driving down the risk of mistake. But it is still possible. To catch mistakes in either direction, we also have digital level indicators on all tanks, a high-level alarm on the supply tank, and low level alarms on the wing and supply tanks.

Finally we label all fuel transfer valves as normally off or normally on to make it clear where they should be in normal operating mode. But, even this isn’t enough. In a storm with only two people on the boat, there is a risk of getting tired. And, if there is a fault at the same time, mistakes get harder to avoid. So, we tie-tag all valves open that need to be open to avoid the blocked return problem described above. The only way to close a valve that could hurt an engine is to go and get wire cutters and cut the tie tag off.

All these design changes give Dirona a flexible system that can polish fuel while operating at sea, can’t lose all the fuel in a fault, supports easy service, and helps manage human error while still offering a fairly flexible system.

If your comment doesn't show up right away, send us email and we'll dredge it out of the spam filter.

13 comments on “Dirona Fuel Manifold
  1. Frida says:

    I want to say Honda XR250, as the cam cover and rocker caps, clcuth arm and clcuth casing would match, but not sure about the shaped trim cover over the oil filter.

  2. George, asked what Micron rating our the filters used in Dirona. Well, like so many things in boating, this is an area of hot debate. Generally, the industry recommendation is to have stepped filtration on the way to the injectors where each level of filtration is finer than the last. This allows early filters to do bulk filtration of the big stuff and last well and distributes the filtration job over all filters. Putting very fine filtration on the primary filter is loved by many but frowned upon by most of the pros. The concerns are legit and focus around:1) fine first-level-filtration won’t last long (they plug up fast), and 2) if not watched incredibly carefully can lead to fuel pressure problems on engine due to unnoticed blockage.

    On our system we have 4 levels of filtration between the fuel fill and the main engine fuel injection system. The first design we went with was the industry recommended stepped filtration approach. Between the main tank and the supply tank we had 25 micron (not available in greater than 25micron). Between the supply tank and the engine we had 30 Micron and, on engine, we have 10 micron followed by 2 micron.

    Because our engine is a high pressure common rail system with fuel pressures frequently near 20,000 PSI, the fuel quality is super important and that why the manufacturer puts 10 micron followed by 2 micron on the main engine. The downside of this approach is 2 micron filters can plug up quickly, the on-engine filter pair is US$140, and the on-engine filters can only be changed with the engine off.

    Since most fuel delivered at the dock has never been filtered at anywhere close to the 2 micron, there is often a lot of small particles in the fuel. This isn’t an issue in that they get filtered out but it means filters need to get changed frequently. Often in the 200 to 500 hour range. This isn’t really an issue except I really, really don’t like to shut the engine off when at sea.

    With all these factors in mind, we went to a 2 micron primary filter. This filter can be changed without stopping the engine which solves that problem. It costs US$13 rather than US$140 which solves the cost problem. We have fuel pressure readings on the dash, alarms on low pressure, and fuel pressure gages in the engine room that get checked every 4 hours. That generally solves the risk of not noticing they are plugged problem which is what brings manufacturers stress with this non-stepped filtration design. The final concern is that you can use a lot of them when you get bad fuel. We solve that problem in two ways: 1) we have a very large Radio FBO-10 at 25 microns in front of everything to get the big stuff, and 2) we have more than 40 of the 2 micron primary filters on the boat so we can afford to go through multiple a day and still not run out.

    The end design has four levels of filtration: 1) Razor FB0-10 with 25 micron elements, 2) Razor 900 with 2 micron elements, 3) John Deere first level filter at 10 micron, and 4) John Deer second level filter at 2 micron. We mitigate the faults with this non-stepped design by having many filters and lots of monitoring and alarms.

    You also asked about solar and wondering if I felt solar was more practical now that we had passed through the South Pacific. I love solar and didn’t mean to imply it doesn’t work. It can work very well when the boats energy consumption is low enough and the available surface area is high enough. Many folks get very good results from solar.

    But, on Dirona, it’s our home and we have lots of electronics and generally don’t live a power constrained life style. We have both 120V and 240V inverters to power the boat and the system is anchored in 1020Ahr of battery. For us to be drawing as high as 150A at 24V is not uncommon and we will likely average 30A at 24V. That means we draw between 1 and 4 Kw and average in the 1Kw range. If you assume that the solar system is only delivering 1/3 to 1/4 of the day, than means we would need a system that delivers 3 to 4kw when producing. If using 300W panels, that would be 10 to 14 pannels. Placing 10 to 14 panels on Dixon a would be tough.

    How about using Solar as an assist rather than as a primary power sournce? Yes, absolutely we could do this but it didn’t seem easy to place enough panels to make a noticeable difference. And, when looking at a small panel count installation, I didn’t feel like stepping up to the engineering hassle and maintenance with the surface area we have available not likely to make a substantial contribution to overall load.

    Thanks for the question George.

  3. george banker says:


    Could you share what filter size (micron) you use for the various filters in your system?

    On another subject I remember reading an older blog wherein you thought that solar panels were not practical. I am wondering if you have had second thoughts having cruised through the South Pacific.

  4. That’s a good point Jeff. We calibrated all tanks early on. On the main tanks, we added 25 gallons at a time and marked them from 0 up to the top. We did the same thing on the wing tank marking every gallon and the supply tank was done every 5 gallons.

    It great always knowing exactly how much fuel is on board without question or ambiguity. And, most important, most boats carry considerably different fuel loads than estimated by the manufacturer. For longer runs especially when crossing oceans, knowing the full fuel load exactly can be important.

    In addition to the sight guages, we also have Maretron tank level sensors on each tank so we can see the tank levels from the pilot house. We also have alarms so that if the supply or wing tank gets low, we are alerted. Or, if a mistakes is made during a fuel transfer and the supply is over-filled, we alarm there as well minimizing the chance of problem.

  5. Jeff Merrill says:

    James: Great summary and very clearly stated. I remember when Dirona was new you and Jennifer went to a lot of effort to calibrate the sight glasses for accuracy. I think that people reading this blog would love to see photos and your narrative of the approach you took to measure the volume of fuel you have available. If I recall correctly you used a small file to "notch" the edges of the sight glass housings, anyway, I think it would be a nice follow up to this great report. Merry Christmas down under! Cheers, Jeff

  6. Yes, correct. I’m refering to the fuel transfer pump.

  7. Jacques Vuye says:

    Got It!
    When you say "the pump" , you mean the big(ger) Jabsco, right?

  8. Hi Jacques.The pressure guage shows the the amount of pressure at the transfer pump outlet. The pump is capable of overdriving the capacity of the piping into the supply tank. When it builds up more than around 15 PSI of head pressure, it’ll pop the breaker so I set it to no more than 10 PSI of head pressure.

  9. Jacques Vuye says:

    Excellent description and definitely something to ponder and implement on (the future) Chelonia.
    Just a quick question: what is the purpose of the little pressure gauge on the pump return line to the return manifold?Thanks

  10. Got it. Sure, that would work fine and be easy to execute upon. Good idea Alex.

    Dirona also came with suspect fuel from the yard as well. We ended up collecting a fair amount of water from that load but haven’t seen any since.


  11. Alex says:

    James: Sorry I was suggesting just polishing the tank as it loads, not filtering the loading fuel directly. By polishing the filling tank, and returning to the filling tank, the polisher is getting a "sample" of the loading fuel. If filthy, and if you could detect it, you could prevent loading a lot bad fuel that would continue to clog polishing filters. The only example I can think of was the fuel in our new boat when delivered from China. There was only 50 gallons or so but it was waxy and clogged several filters before cleaned and was obvious on the polisher gauge. If you ever do get some bad fuel, please blog about it. Thanks. Alex

  12. Good quesiton Alex. Filtering while filling is a great idea but fairly tough to implement at even medium fill rates. We fill at over 900 gallons per hour and its super hard to design a filtering systems that feeds at that rate. Some hoses allow camlocks but most just are nozzle ends so you have pull fuel at the rate the nozzle is producing since there is no posive connection at the nozzle. It’s pretty hard to do at reasonale fill rates so we take the fuel from what look to be volume suppliers with a good reputation and then deal with it once we have it on board.

  13. Alex says:

    Great ideas about keeping the fuel clean once aboard. Have you considering polishing the fuel tank as it loads? And, if the fuel is really dirty I would think it would show up on the polisher gauge pressure. If dirty, you could stop loading and find a different supplier. Of course maybe where the fuel is filthy, there aren’t any other suppliers! Just a thought. Alex, Wild Blue

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.