To A New Paradigm With FPB

FPB 64 – Systems

The engineering concept we use today has its beginnings in the 1980s.

It was on the prototype sailing design Sundeer where we first used “traction” batteries, as the foundation upon which the rest of our approach to systems is built.

Since then, we have continually refined this approach. With the FPB 83 Wind Horse we have combined our tried and true DC side of the equation with the latest inverter technology for a highly efficient end result. The FPB 64 approach to systems is almost identical to the FPB 83, with a couple of refinements thrown in (for lots more details on how the FPB 83′s systems are designed see the sidebar, or click here.

The bottom line to this approach is robustness, reliability, and simplicity as a foundation. We then toss in a dose of redundancy – we do not want our cruising interrupted because of systems problems. What follows is based on these principles.

DC System Overview

As previously indicated, our DC systems are based on a huge bank of “traction” batteries.

They are charged while underway with specially built alternators running off the PTO on the main engine. At anchor the inverter/charger system can charge the batteries if the generator is running (or you are connected to shorepower).

This system allows long periods of quiet time without the frequent use of the generator, and eliminates the need to use the genset for air conditioning and most other AC loads when you are underway (resulting in a quieter, more fuel-efficient environment).


The main battery bank is made up of individual 2.2 volt “traction” battery cells designed for long life with deep discharge. The normal guarantee is for 1200 80% discharge cycles. What this means in our application is many times this number since full discharges are rare and the shallower the discharge the more cycles you get (for example, a 50% discharge rate typically increases available cycles to 3000 or more).

These batteries are typically used in electric trucks, and for emergency power supplies for utilities. They have a very low rate of self discharge, and if taken care of, will last 10 or more years (manufacturers claim double this).

There’s an important factor about traction battery capacity upon which we need to dwell. Think about how these compare to normal deep cycle batteries. Most experts suggest not taking your batteries deeper than a 50% discharge cycle, or their useful life is dramatically shortened. The top 15% of capacity is only going to be put back when you are on shore power, or motoring for long periods (that last little bit goes in very slowly). So in the average marine application, you have a useful capacity equal to at most 35% of the 20 amp hour rating.

Now compare this to our traction batteries. Their useful capacity is 80% fully charged, or 65% if you leave off the top 15%. That’s almost twice the useful capacity of conventional deep cycle batteries. Unfortunately, it is very difficult to retrofit this type of battery. They take room, are heavy, and need to be careful restrained. You have to design for their incorporation into your systems from the beginning.

Which is why we have been using this approach for almost two decades.

Based on our experience with the FPB 83, we know that electrical consumption has crept up compared to what we were used to just a few years ago with sail. Using home style big screen TV, lots of electrical appliances in the galley, often two computers (and one with a second monitor), and soft lighting, really eats the amp hours. Switching to mainly electric cooking in the galley, mostly done with inverter power, further adds to the amp hour burn rate. Which is why we specify a 1400 hour, 24-volt traction battery capacity (C20 rating). On the assumption that the genset was run every second day for a couple of hours while a major meal was prepared with lots of oven time (at the same the laundry is going), you could probably hang out for a week or two without using the genset specifically to charge the batteries, or heading somewhere new (whence the engine alternators would charge you back up). That short genset run every other day will give you back a third to half of the amps you have used (the inverters/chargers take all excess genset capacity and use it to charge the house bank).

These individual cells are big: 8.5″ x 10.9″ x 28″ (215 x 277 x 710mm) each. They each weigh 194 pounds (88kg). And there are 12 cells in the house bank. As big as they are, a couple of guys can get them into place where they can be lifted in/out through the salon hatch with a small crane. In the unlikely event of a cell failure, you replace the bad cell, not the entire bank. And this is an industry standard size, available in most of first world from a variety of manufacturers.

Bottom line: you cannot fit a better battery system to this boat.

For lots more details on this subject see the battery chapter in our Offshore Cruising Encyclopedia starting on page 858.


If you have a big battery bank, you need a powerful charging source to provide the necessary minimum charge rate. This means large alternators running at full output for many hours. Normal alternators become extremely hot in this type of application and quickly fail from overheating.

The alternators we have been using for the past two decades, made specifically for us by Electrodyne, are rated for full field output. The will deliver 150 amps/28V charging rate for hours, and stay relatively cool.

One of the secrets used is to remove the diodes from the alternator case. These are mounted in a remote, fan-cooled, rectifier assembly. That is what the center and right hand devices are in the photo above.

We have a pair of these on Wind Horse and they are running fine after more than 4500 hours of engine time.

AC System Overview

Our AC system is supported with inverters which draw from the big traction battery bank. The AC system is engineered so most AC loads are easily handled by the inverters. When there are extra heavy loads present, as during a wash cycle with the drier going, the genset will typically be on (but it is not essential – especially if you are under way).

Heavy loads are 230 volts, while a separate inverter provides 115VAC for small appliances if you are set up with US voltage appliances.

Inverter Chargers

The same Victron Energy inverter chargers that work so well on the FPB 83 are used for the FPB 64. There are three of these units in parallel, each with a 2500 watt rating and 70 amp DC charge capacity. That’s 7500 watts of AC and 200+ amps of DC charging.

These are “smart” inverters capable of supporting shore power or the genset, should either start to become overloaded. They also know when the genset or shorepower has excess capacity and will use the available extra AC power for charging the batteries.

This approach allows a smaller genset, sized for continuous AC requirements rather than peak demands, keeping the genset happily loaded all of the time (significantly enhancing genset life).


A 11.5 kW (9.5 at 50 Hz) genset is also in the system. This is enough capacity to do most combinations of power needs. From time to time the capacity may be exceeded, which is where the Victron generator support function comes online to help out.

The FPB 83 has basically the same system, except an 8kW/6.5 kW genset is in use. We have increased genset capacity with the FPB 64 to allow for upgrades in the galley.


The galley appliances represent a new systems direction for us. In the past, we have always used propane for cooking. We just never wanted to be at the mercy of a genset for our daily culinary needs.

Two things changed our minds. First, the efficiency of the traction battery/inverter/small genset package on the FPB 83 pleasantly surprised us, especially how well the generator support function works. Second, there is a new generation of highly efficient electric cooking appliances now in the mainstream, which are now cost effective in relation to the advantages they provide.

This starts with an “induction” cooktop. These use magnetic energy to create heat in steel or cast iron pots and pans. They are very controllable, fast, and about 40% more efficient than conventional electric stove tops. The cooktop itself does not get hot, a much safer system to use at sea.

The second item is the “speed oven”, a combination microwave, broiler, and convection oven that uses microwave energy for cooking and convection or infrared for browning and broiling – and makes the correct choices automatically (if desired).

Couple this efficiency with our DC/AC inverter package and these electric cooking appliances can be used, for the most part, without the genset.

Based on our own cooking habits, we find that we use the the inverter for breakfast and lunch (where the stove or oven was required) and then use the generator every second or third day for dinner, if a big meal is planned. Smaller dinners are done with inverter power.

The advantages of this approach are many. We get rid of propane from inside of the boat, and the requirement to find it in strange places (and match fittings), and we do not have to store the propane. We now have an oven with a reliable temperature control – something that seems to elude marine stove builders. The speed oven puts less heat into the interior, and the induction stove top heats faster and more evenly than propane.

The FPB 64 has a drawer-style dishwasher. The latest models take less water than washing by hand, and are more sanitary.

The final piece of the galley puzzle takes place outside. There is a locker integrated with the engine room air intake that has a sink and BarBQ. This is located in an area of calm air behind the house, extending the conditions in which it can be used.


The key to good refrigeration starts with the box design and insulation. We use isocyanurate foam, 3 inches (75mm) in the fridge and 6 inches (150mm) for the freezers. There is a heavy Mylar moisture barrier for longevity.

We are again using Frigoboat compressors and evaporator plates. These have proven themselves on the FPB 83. They are quiet and efficient. Note that the keel coolers, described below, significantly add to the efficiency of the fridge system.

There is a total of 28 cubic feet (792 liters) of volume between the three boxes. The basement unit can be used as fridge or freezer.

Air Conditioning.

There are four individual air conditioning units aboard. Two of these service the sleeping cabins, and the other two handle the salon. The air conditioning loads are light enough that you can run one of the sleeping cabin units via the inverters at night if required at anchor. And when underway, you can fully air condition the boat using the combination of powerful alternators on the main engine and inverters.

We have found with the FPB 83, that in the tropics – on those still and sticky nights when you want cool air for sleeping – running all of the air conditioning units for a couple of hours in the evening with the genset, cools and dries the boat to where the entire system can be shut down for the night. The hull insulation keeps us comfortable until morning.

Although there is a dedicated diesel heating system, the air conditioners will heat on reverse cycle. We have tested this in water as cool as 45F (7C) and are surprised to report that it works well.


A good heating system provides two important functions. One, it keeps the boat warm (and dry) and second, it heats domestic water for bathing and washing.

We are using the same system here as with the FPB 83, a Kabola diesel boiler, plumbed to heater coils in each room of the boat. The salon and each stateroom have their own thermostat controls for the individual heater coils.

As a back up, there is a heat exchanger on the engine, so waste heat can be used to heat the boat.

There is also a domestic hot water tank plumbed into this system. With the Kabola boiler turned on, there is sufficient capacity so you can take a long shower without running out of warm water. The engine will also heat this tank, and there are two electric elements (4000 Watts total) which can be run off shorepower or the genset.

Fresh Water

The fresh water system starts with the source. You can catch water off the decks or make it with a 800-gallon-per-day watermaker.

The integral hull tanks allow for a total capacity of 1800 US gallons (6800 liters). At sea, you would normally only carry enough fresh water to keep you at full load (for best powering efficiency). However, the last day or two of the passage you may want to fill the tanks, so you have the luxury of what in effect is unlimited fresh water, once you arrive at your anchorage.

There is a hot water “loop” with a valve at the forward end. Simply open the valve for a minute before starting your shower and you will have hot water (the cooler water in the loop returns to the tank).

There are two pressure pumps, one connected to each fresh water tank.

Miscellaneous Domestic Systems

The laundry room (located in the salon) is equipped with a matching pair of front-loading full-sized washer and drier. The washing machine consumes minimal water, and on high spin speed, dries the laundry so efficiently that the drier gets its job done quickly. That the wash cycle comes with a 360-degree view for the operator of this equipment is an added bonus.

No proper cruising boat would set off without an efficient vacuum system. The FPB has two. There is a dedicated central vacuum for the living spaces, along with a second, shop vac in the engine room.

One of the cruising problems we’ve all suffered with is trash. We have partially solved this on the FPB 83 with a trash compactor. It is such a blessing that the FPB 64 is also be equipped with a compactor. Compacted trash bags can be stored in one of the swim step lockers, or the forepeak.

Typical Cycle at Anchor

With 45,000 miles of cruising now behind us on the FPB 83, the systems usage has settled into a predictable cycle, which we expect to be the same with the FPB 64.

If the boat is sitting for long periods at anchor, washing-drying dictates how DC and AC power is managed. Washing and drying typically take place every second day, during which time we also run the genset. We have found this works best in the evening, typically starting during dinner preparation. While the wash cycle is progressing and dinner is being prepared, we often watch a movie (which is power hungry between the home style surround sound system and 42″ plasma TV). If fresh water is getting low, we will also turn on the water maker. Whatever AC power is left over with the genset is used to charge the batteries.

One riff on this approach, to which we have already alluded, is cooling the boat before we go to sleep. This has only been required when insects make it impractical to leave the hatches open. In this case we’ll run the genset for a couple of hours before turning in for the evening, after which the genset is shut down (as is the air conditioning). This drops humidity and lowers temperature so we get a good night’s sleep.

If we are not sitting for long periods – we do tend to move around a lot – the generator is rarely used. Rather, we wait on the washing/drying cycle until the boat is underway. All other AC loads are typically handled with the inverters.

For more information on the FPB 64 contact

Posted by Steve Dashew  (October 16, 2011)

12 Responses to “FPB 64 – Systems”

  1. Jon Says:
    Wandering through the website, learning a lot (I’ve never cruised but grew up with small boats always available for us to use). One thing that stood out on this page is the use of a plasma TV. Plasmas have wonderful picture quality, but have a few weaknesses: high electricity usage (compared to same sized LCD TV), heavy, subject to glare – all of which could be problematic in your environment. The newer LCD TVs have closed much of the picture quality gap, enough so that I would think on a boat the lighter weight and lower energy usage would make choosing one a no brainer! JB


    Steve Dashew Reply:

    Howdy Jon: All of the FPBs have been fitted with the LED TVs, and Wind Horse has been retrofitted with same. They are indeed marvelously light, thin, and consume a fraction of the heat of the older units.


  2. Bob Lemke Says:
    Steve, I have been following your recommendations for what makes a good cruising boat for close to 30 years when I purchased an old Cal 40, matched the purchase price in the refit with cruising goodies and headed off shore. Today in my 60′s, after a career in the Merchant Marine (CMA grad USCG Unlimited Tonnage Open Ocean license), I’m on the fence as to power or sail for my next cruising boat. A $15K suit of sails buys a lot of diesel, not to mention fickle winds. A good friend, Nick Vermeulen has been enjoying his Sundeer 64 S/V Jedi for the past 10 years. The only thing I would like to see in your FPB line is diesel-electric hybrid propulsion as an option. My current house bank of batteries are LiFePO4, and these lithium cells have exceeded all my expectations. No sag under heavy loads, flat voltage curve during 80% DOD, and very long cycle life. My distributor had a clearance sale, 700 a-hr 3.2 volt cells for $462. Now much cheaper than all other battery chemistry’s available. That, along with solar now dropping to $1 a watt, makes it feasible for diesel-electric propulsion. I’ve crunched some numbers, and for my needs, 2000 watts of panels would produce enough overage from powering house loads to allow 90 nm on batteries after 10 days on the hook. Still would have the speed and safety of the diesel propulsion, but for economy, the sun could cover all house loads and 90 nm per 10 days at a sedate 4.5 kt.


  3. Andy Says:
    Steve, thanks for great site. Clearly there has been great amount of thinking behind choice of systems and equipment. However, have you considered migrating DC-system to more modern Lifepo4-batteries? Great savings of space and weight for around similar price as traction cells, and with vastly better roundtrip efficiency plus similar life expectancy. And ability to accept full charge rather faster, especially towards reaching full battery charge. Have been using those for few years with great results so far – only problem is some difficulty in finding suitable chargers, Victron for example kind of support them, but I guess for their own batteries only. Inverters and all the rest of the equipment could not care less for where the electrons are coming from.


    Steve Dashew Reply:

    Hi Andy: We continue to watch the development of batteries with interest, and these seem to offer promise. However, the charging regime, is, as you have noted, still an issue. Compactness is not an advantage for us as we design from the begining for the large traction battery banks, and their weight is part of our ballast system.


    Andy Reply:

    Steve, the charging issue is indeed tricky, but there is always a choice of installing separate charger and inverter – not quite as convinient though. But I have to disagree in compactness issue. Surely it would be benefical for any boat to be able to install twice the capacity of batteries into same space and weight – especially considering added benefits of more optimal charge acceptance profile. I have yet to see a boat with too much battery capacity!


  4. Andy Says:
    Slight update on this. It seems Victron (among others) is now recognising growing need for lithium chemistry batteries, and they issued a application note ( on how to connect “foreign” lithium batteries into their chargers/inverters. I have not noticed this before. You will still need provide your own BMS (battery management system) to protect and balance the batteries, but this is definitelly progress. BMS-systems are readily available from same suppliers as the Lifepo-batteries, and already well matched and optimized to correct voltages etc of certain battery type.


  5. Andy Says:
    Just for a comparision and reference, a 24V 1000Ah Lifepo battery bank drawing with dimensions: 1040mmx560mm, 260kg


    Steve Dashew Reply:

    Andy: Do you have or know anyone with real world experience?


  6. Andy Says:
    Steve: I have limited experience running Lifepo-banks of various sizes for a couple of years, but not enough to feel like an expert. So far it looks very promising though. Here is one guy with plenty of experience and lots of insight online: Very interesting comparison test from link above: Flooded Lead-acid batteries (7yo) nominal 1260AH @24V, Latronics 3kW inverter Test Duration: 31days 1hr (Start and end SOC ~100%, but not measured precisely) Total DC output from charge controllers: 357.3kWh Total DC energy used by inverter: 272.3kWh (+3kW fan), at an average rate of power usage of: 369.53W AC energy used according to the digital kWh meter: 233.5kWh, Average = 7.5kWh/day Overall inverter efficiency: 86% Battery charging/discharging/float etc, efficiency: 77% Overall, about 66% of generated DC energy is available at the inverter output as 230VAC. CALB LiFePO4 cells 800AH @ 26V, Latronics 4kW inverter Test duration 14days 9hr 35mins (start and end @ the same State of Charge- 2.6kWh down from 100%) Total DC output from charge controllers: 126.75kWh Total DC energy used: 117.48kWh, at an average rate of power usage of: 339.94W (fan not logged) AC energy used according to the digital kWh meter: 101.36kWh, Average = 7.0kWh/day Overall inverter efficiency: 86% Battery charging/discharging/float etc, efficiency: 93% Overall, about 80% of generated DC energy is available at the inverter output as 230VAC Lithium batteries are far more efficient!


    Steve Dashew Reply:

    Fascinating data Andy. The charge efficiency is really interesting.


  7. Andy Says:
    Very interesting blog on all things lifepo and solar: (just the batteries: Especially interesting graph: 60% DOD gives you 5000 cycles. With large battery, that means practically forever. I will be glad to be a guinea pig to install a bank of these as ballast for my FPB!


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