Fuel Comparison 

Comparing fuel usage of four types of propulsion

Below you will find our fuel use comparison examples and data using all four propulsion types we considered.  The passage examples use some different lengths and situations. 

For these examples we wanted to use a mix of motoring and sailing.  It is accepted by most cat sailors that a typical production 'comfort' cats has a 50% motoring vs sailing ratio, though this is on the shorter passages.  However, we are planning to build a performance cat which means we can sail in lighter winds.  Therefore, our ratio will be figured at 40% motoring and 60% sailing for most passages.  For a Trade Wind passage while we cross an ocean, things may be different.  We figure we will only motor a maximum two 3 hours stints a day, but may become becalmed at times as well.  There are some examples of these in our calculations. 

About regeneration while sailing: additional power would come from regen and will make the Hybrid, Parallel, or Combo systems even more fuel efficient.  The first eight examples will be without regeneration, but I will go over eight more passage examples using regeneration. 

The Hybrid will be far more efficient at regeneration if using the SD15 servoprops. We will figure them at 2 kw per prop sailing at 9 knots.  The shaft drives with auto adjusting ECO*Star props on the 20 kw motors of the Combo system will be only half as efficient at 1 kw per prop at 9 knots.  Finally, the 10 kw motors of the Parallel system will be closer to 500 watts per motor at that boat speed.

Note: these trips figure in the need to make power for House uses of at about 10kw per 24 hour period. 

How we calculated: Based on other boat data, a single engine on the Diesel boat will use about 0.5 gallons an hour at a boat speed of 5 knots.  For the Hybrid, a 20 kw generator uses 1.6 galleons an hour.  For maximum efficiency, an electric motor should be run at 75% of max rating.  Therefore, we will figure 15kw, minus the conversion rate of 20% means we actually get 12 kw when motoring for long stints.  5 kw is needed to keep cruising speed of 5 knots.  Our parallel diesel engines (2 x 50 hp) will burn around .75 gallons, each, per hour to maintain cruising speed (5 knots).  Sometimes, we would run both to get the additional generated power.  This fuel usage is slightly worse than just a diesel because of the extra drag from the 10 kw motor, but does send 7 kw to the battery while running at cruising speed.  The Combo boat's diesel will burn more like 1 gallon per hour when generating power since it has a 20 kw motor to turn, which is even more drag.

Finally, the hybrid boat would have a slightly larger permanent battery bank at 33 kw.  The Parallel and Combo systems will have 22 kw of main battery and shorter passages, but add the tender/auxiliary battery for longer passages, increasing to 33 kw.  That equates to 1.3 hours on 22kw or 2 hours motoring on 33kw, both at 5 knots.

One last note: Any savings of less than 1 gallon is within my margin of error, so we should just throw out that difference and figure that when the numbers come out that close, those boats are tied for that passage.

Or jump to the summaries...

If you want to skip the details and get right to the conclusions, here are two buttons, one for the 'non-regeneration' passage summary and one for the with regeneration summary.  Or, just keep reading to see the full passage details below.
Route One

1) Short Passage: 4 hours and 30 min.  
    36 nautical miles trip
    (1:48 motoring, 2:42 sailing )

This is a 4.5 hour trip, leaving at 11 am arriving at 3:30 pm.

Diesel:
Burning at .50 gallon an hour, and motoring for 40% of the trip, means 0.83 gallons of diesel fuel used.

Hybrid:
Motoring on battery power for 1.5 hours and then sailing 2.42 hours, while recharging 9kw from solar,  Followed by 18 minutes of motoring means zero diesel used.

Combo or Parallel Diesel/Electric:
Motoring on battery power for 1.3 hours and then sailing 2.42 hours, while recharging 9kw from solar, Followed by 28 minutes of motoring means zero diesel used.

Winner: All boats are less than a gallon apart, so tied within my margin of error.

RouteTwo

2) 1 Day Passage, Daytime: 7 hours and 30 min. 
     60 nautical mile trip:
    (3 hours motoring and 4.5 hours sailing)

This is a 7.5 hour trip, leaving at 9 am arriving at 4:30 pm.

Diesel:
Burning at .50 gallon an hour, and motoring for 40% of the trip means 3 hours motoring, so 1.5 gallons were burned.

Hybrid:
Motoring on battery power for the first 2 hours.  We then sail for 4.5 hours, recharging the batteries from solar.  We motor the last hour off of batteries.  Zero fuel used.

Parallel Diesel/Electric:
Motoring on battery power for the first 1.3 hours.  We then sail for 4.5 hours, recharging the battery to full.  We motor for another 1.3 hours off of batteries then turn on one diesel engine for 20 minutes.  0.25 of a gallon fuel used.

Combo Diesel/Electric:
Motoring on battery power for the first 1.3 hours. We then sail for 4.5 hours, recharging the battery to full. We motor for another 1.3 hours off of batteries then turn on the diesel engine for 20 minutes. 0.33 of a gallon fuel used.

Winner: Combo, Parallel, and Hybrid boats are too close to call, but all are better than the Diesel by at least a gallon of fuel.

Route Three

3) Single Day Passage Nighttime, 4.5 hours                  60 nautical mile trip
     (3 hours motoring and 4.5 hours sailing)

This is a 7.5 hour trip, leaving at 10 pm arriving at 8 am.

Diesel:
Burning at .50 gallon an hour, and motoring for 40% of the trip means 3 hours motoring, so 1.5 gallons were burned.

Hybrid:
Motoring on battery power for the first 2 hours.  We then sail for 4.5 hours.  We must then use the diesel generators for 1 hour.  3.2 gallons used.

Parallel Diesel/Electric:
Motoring on battery power for the first 1.3 hours. We then sail for 4.5 hours. We must turn on the diesel engines for 1 hour, charging back 10 kw.  We motor on electric for the last 40 minutes.  We burned 1.5 gallons of diesel.

Combo Diesel/Electric:
Motoring on battery power for the first 1.3 hours. We then sail for 4.5 hours. We must turn on the diesel engine for 1 hour, charging back 10 kw. We motor on electric for the last 40 minutes.  We burned 1 gallon of diesel.

Winner: All boats are less than a gallon apart, so tied within my margin of error.

Route Four

4) Single Day Passage, Daytime, 11.25 hours             90 nautical mile trip
     (4.5 hours motoring and 6.75 hours sailing)

This is a 11.25 hour trip, leaving at 6 am and arriving at 5.25 pm (sunset).

Diesel:
Burning a half gallon an hour and motoring for 40% of the trip means 5.625 hours motoring, so 2.25 gallons were burned.

Hybrid:
We motor for the first 2 hours on batteries and then sail during the day for 6.75 hours, recharging the batteries via solar to full.   Then we motor on electric for another 2 hours.  Then, we turn on the generators and motor for 0.5 hours.  1.6 gallons of diesels burned.

Parallel Diesel/Electric:
We motor for the first 1.3 hours on batteries and then sail during the day for 6:75 hours, recharging their batteries to full.   Then we motor on electric for another 1.3 hours.  We turn on the diesels 1 hour, recharging 10 kw.  We motor for the remaining 50 minutes.  1.5 gallons of diesel burned.

Combo or Parallel Diesel/Electric:
We motor for the first 1.3 hours on batteries and then sail during the day for 6:75 hours, recharging their batteries to full. Then we motor on electric for another 1.3 hours. We turn on the diesel 1 hour, recharging 10 kw. We motor for the remaining 50 minutes. 1 gallon of diesel burned.

Winner: Combo, Parallel, and Hybrid boats are too close to call, but all are better than the Diesel by at least a gallon of fuel.

Route Five

5) Day Passage with, 32.5 hour voyage                         260 nautical mile trip
    (13 hours motoring, 19.5 hours sailing) 

This is a 32.5 hour trip, leaving at 6 am arriving on the second day at 2:30 pm.  The Parallel and Combo would engage their auxiliary battery for this length or longer passages.

Diesel:
Burning at .50 gallon an hour for 13 hours means we burn 6.5 gallons.

Hybrid:
We motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar.  As night falls, we motor for 2 hours on battery.  Then we turn on the generators for 2 hours, regaining 28 kWh.  We motor again for 2 hours and then sail for 6 hours recharging 11 kWh.  We run the generators for 2 hours putting 28 kWh in the batteries.  We sail for 3.5 hours, recharging an additional 11 kw from solar.  We then motor off batteries for 2 hours into the anchorage.  All total, the generators ran for 8 hours, so we burned 12.8 gallons of diesel.

Parallel Diesel/Electric:
We motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar.  As night falls, we motor for 2 hours on battery, we turn on the diesel engines for 2.5 hours, regaining 25 kw.  We motor again for 2 hours and then sail for 6 hours at night.  We turn on the diesel engines for 2.5 hours, sending 25 kw to the batteries then motor for an 2 hours into the anchorage. 
 All total, the engines ran for 10 hours, so we burned 7.5 gallons of diesel.

Combo Diesel/Electric:
We motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar.  As night falls, we motor for 2 hours on battery and then turn on the diesel engine for 2.5 hours, regaining 25 kWh.  We motor again for 2 hours and then sail for 6 hours at night.  We turn on the diesel engine for 1 hour, sending 10 kWh to the batteries.  Then we sail for 3.5 hours, recharging about 13 kw from solar.  We then motor for 2 hours.  We fire up the diesel for 1 hour, regaining 10 kwh.  Then we motor for 30 minutes into the anchorage. All total, the engine ran for 4.5 hours, so we burned 4.5 gallons of diesel.


Winner: Combo over Parallel boat by 3 gallons, 3.5 gallons over the Hybrid, and 2 gallons over the Diesel boat.

Route Seven

6) Mid-Length Passage 
    1,000 mile trip: 4.5 days
   (43 hours motoring, 65 hours sailing) 

This is a four night trip, leaving at around 5 am and arriving at around 6 pm.

Diesel:
Burning at .50 gallon an hour motoring for 43 hours total equals 21.5 gallons of diesel.

Hybrid:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 2 hours using the batteries.  Then we kick on the diesel generator for 2 hours, recharging the batteries 28 kWh and the motor 2 more hours.   Each following day we run the diesel generators for 2.5 hours in the morning, then motor for 2 hours.  We sail until night, then run the generators again for 2.5 hours and motor for 2 hours.  We repeat that for two more days.  With solar, that also gives us enough power for House needs.  For the final half day we run the generators for 2 hours in the morning, then motor for 2 hours, then sail.  As we get near the destination, we motor for 2 hours, turn on the diesels for 2 hours, then motor into the anchorage. Together, the generators ran 42 hours.   At 1.6 gallons an hour that equals a total of 67.2 gallons burned.

Parallel Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 2 hours and then kick on the diesels for 2.5 hours, recharging 25 kWh, followed by 2 hours motoring and ten 0.5 of an hour to build up the House bank.  Come morning, we run the diesels for 2.5 hours, charging 25 kWh and then motor 2 hours.  We recharge from solar during the day.  That night, we motor for 2 hours, then use the diesels for 2.5 hours to recharge the House bank and motor 1 hour.  On the last day, we turn on the diesels for 2 hours, then motor for 1.5 hours, then we sail for a few hours, then motor for 0.5 of an hour into the anchorage.  We ran the diesels for 37 hours and burned 27.75 gallons of fuel.

Combo Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, we motor for 2 hours and then kick on the diesel again for 2.5 hours to recharge 25 kWh, then motor for 2 hours.  Each following day we run the diesel for 2.5 hours in the morning, then motor for 2 hours.  We sail until night, motor for 2 hours, and run the diesel for 1.5 hours followed by motoring for 1 hours motoring.  We repeat that for three days. On the last half day we run the diesel for 3 hours and then motor for 2.  We sail, then turn on the diesel for 1 hour and motor for 1.5 hours.  Therefore, we ran our diesel engine 18.5 hours.  At 1 gallon an hour that equals a total of 18.5 gallons burned.

 
Winner: Combo by 9.25 gallons over the Parallel, 47.7  over the Hybrid and 3 gallons over the Diesel boat.

Route Six

7) Day Atlantic Crossing, 15.5 days                                     3,000 miles: 15.5 days
    (6 hours motoring, 18 hours sailing, per day)

Being typical a Atlantic crossing, we can figure that they will only have to motor for two 3 hour stints per day, like early morning or during the night.  The trip lasts 15.5 days. 

Diesel:
Burning at .50 gallon an hour, for 6 hours a day for 15.5 days equals 46.5 gallons of diesel.

Hybrid:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 2 hours and then kick on the diesel generators for 1 hour.  Each following day we run the motor for 1 hour, then turn on the diesel generator for 1 hour, then motor for one hour.  We sail until night, then motor for 2 hours and turn on the diesel generator for 1 hour.  That also gives us enough power for house needs. That means 59 hours of diesel generator time which burns 94.4 gallons.
  
Parallel Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 2 hours and then kick on the diesels for 1.5 hour.  Each following day we run the diesels for 1 hour in the morning, then motor for 2 hours.  We sail until night, then repeat that, using 2 hours motoring and then 1.5 hour of the two diesels.  That also gives us enough power for house needs.  That means 75.5 hours of diesel engine time which burns 56.63 gallons.  

Parallel Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 1.5 hours and then kick on the diesel for 1.5 hours.  Each following day we run the diesel for 1 hour in the morning, then motor for 2 hours.  We sail until night, then repeat that, using 1.5 hours of the diesel engine and 1.5 hours motoring.  That also gives us enough power for house needs.   That means 37.75 hours of diesel engine time which burns 37.75 gallons.  

Winner: Combo boat over the Parallel boat by 18.88 gallons, 16.45 gallons over the Hybrid, and 8.75 gallons over the Diesel boat.

Route Seven

8) Ocean Passage becalmed 3 days            (3,000 mile trip: 15.5 days).

This is a bit of a different trip. With the Trade Winds, you only need some minor motoring.  For sake of argument, we will still figure in motoring for the occasional 3 hour stints, like early morning and at night.  That, and this time, we will calculate in the crossing of the equator as 3 days of no wind. The trip lasts 15.5 days.

Diesel:
Burning at .50 gallon an hour, for 6 hours a day out of 12.5 days equals 37.5 gallons of diesel.  Then add three days of motoring 24 hours a day for 36 gallons additional diesel giving them a total burn of 73.5 gallons.

Hybrid:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 1.75 hours and then kick on the diesel generator for 1.25 hours.   Each following day we run the diesel generator for 1 hour in the morning, then motor for 2 hours.  We sail until night, then repeat that, using 1.25 hour of the diesel generator and 1.75 hours motoring.  That also gives us enough power for house needs.  That is 11.5 days of this pattern.  Therefore, the generator ran a total of 25.89 hours during those days.  For the three becalmed days, we must motor 2 hours, followed by 3 hours of generator.  If we divide 5 hours into 24 we see we must do this about 4.8 times during each of those three days.  Therefore, we ran our diesel generator an additional 43.2 hours.  Together, the total generator 69 hours.   At 1.6 gallons an hour that equals a total of 110.4 gallons burned.

Parallel Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, we run the motors for 2 hours and then kick on the diesels for 1.5 hour.  Each following day we run the diesels for 1 hour in the morning, then motor for 2 hours. We sail until night, then repeat that, using 2 hours motoring and then 1.5 hour of the two diesels.  We did this for 11.5 days, burning 57.5 gallons.  That also gives us enough power for house needs.  For the three becalmed days, we must motor 2 hours, followed by 2.5 hours of two diesel engines.  If we divide 4.5 hours into 24 we see we must do this about 5.33 times on each of the three days. Therefore, we ran our diesel engines an additional 79.95 hours. Together, the total diesel run time is 1397.45 hours.  At .75 gallons an hour that equals a total of 103.09 gallons burned.

Combo Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, we run the motors for 1.5 hours and then kick on the diesel for 1.5 hours. Each following day we run the diesel for 1 hour in the morning, then motor for 2 hours. We sail until night, then repeat that, using 1.5 hours of the diesel engine and 1.5 hours motoring. That also gives us enough power for house needs.  Therefore, the diesel ran a total of 28.75 hours during those days.  For the three becalmed days, we must motor 2 hours, followed by 2.5 hours of the diesel engine. If we divide 4.5 hours into 24 we see we must do this about 5.33 times on three days. Therefore, we ran our diesel engine an additional 39.98 hours. Together, the total diesel run time is 68.73 hours. At 1 gallon an hour that equals a total of 68.73 gallons burned.

 
Winner: Combo by 34.36 gallons per trip over the Parallel, 41.67  over the Hybrid and 4.77 gallons over the Diesel boat.

Route Eight

9) Same as above, but becalmed for 7 days (3,000 mile trip: 15.5 days).

This is a bit of a different trip. With the Trade Winds, you only need some minor motoring. For sake of argument, we will still figure in motoring for the occasional 3 hour stints, like early morning or at night. That, and this time, we will calculate in the crossing of the equator as 7 days of no wind.  The trip lasts 15.5 days.

Diesel:
Burning at .50 gallon an hour, for 6 hours a day out of 8.5 days equals 25.5 gallons of diesel.   Then add seven days of motoring 24 hours a day for 84 gallons additional diesel giving them a total burn of 109.5 gallons.

Hybrid:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, we run the motors for 1.75 hours and then kick on the diesel generator for 1.25 hours. Each following day we run the diesel generator for 1 hour in the morning, then motor for 2 hours. We sail until night, then repeat that, using 1.25 hour of the diesel generator and 1.75 hours motoring. That also gives us enough power for house needs. That is 7.5 days of this pattern. Therefore, the generator ran a total of 16.88 hours during those days. For the seven becalmed days, we must motor 2 hours, followed by 3 hours of generator. If we divide 5 hours into 24 we see we must do this about 4.8 times during each of those seven days. Therefore, we ran our diesel generator an additional 100.8 hours. Together, the total generator 118.93 hours.  At 1.6 gallons an hour that equals a total of 190.29 gallons burned.  (We would have to carry Jerry Cans for extra fuel, about seven cans).

Parallel Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, we run the motors for 2 hours and then kick on the diesels for 1.5 hour. Each following day we run the diesels for 1 hour in the morning, then motor for 2 hours. We sail until night, then repeat that, using 2 hours motoring and then 1.5 hour of the two diesels. We did this for 7.5 days, burning 18.75 gallons. That also gives us enough power for house needs. For the seven becalmed days, we must motor 2 hours, followed by 2.5 hours of two diesel engines. If we divide 4.5 hours into 24 we see we must do this about 5.33 times on each of the seven. Therefore, we ran our diesel engines an additional 186.55 hours. Together, the total diesel run time is 206.8 hours. At .75 gallons an hour that equals a total of 155.10 gallons burned. 

Combo Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, we run the motors for 2 hours and then kick on the diesel for 1.5 hours.  Each following day we run the diesel for 1 hour in the morning, then motor for 2 hours. We sail until night, then repeat that, using 1.5 hours of the diesel engine and 1.5 hours motoring. That also gives us enough power for house needs. Therefore, the diesel ran a total of 18.75 hours during those days.  Then we run on the diesel, without using the generator function, thus getting 0.5 gallons an hour.  We do this for seven days of the diesel running 24 hours a day for 84 gallons additional diesel.  Solar recharges our House needs.  All total, we burn 102.75 gallons of diesel

Winner: Combo over the Parallel by 104.05 gallons, over the Hybrid by 87.54 gallons, and over the Diesel by 6.45 gallons.

Fuel Consumption Winners no Regen

Passage Length MilesComboParallel Hybrid Diesel
Passage One350000.83
Passage Two600.330.2501.5
Passage Three6011.51.61.5
Passage Four9011.50.82.25
Passage Five2604.57.512.86.5
Passage Six100018.527.7567.221.5
Passage Seven300037.7556.6394.446.5
Passage Eight3000 (3 days becalmed)68.73103.09110.473.5
Passage Nine3000 (7 days becalmed)102.75155.10190.29109.5
Showing entries (filtered from total entries)

Fuel Comparison with Regen

Now let's compare some passages using regeneration.  We are figuring 9 knots of boat speed for this performance catamaran.  At that speed, the Hybrid, using Oceanvolt SD15 servoprops, will have the highest amount of regeneration at 2 kw per motor.  The Parallel is the least, since it has 10 kw motors without servoprops, so it only gets 500 watts per motor.  The Combo is in the middle, with 20 kw motors, getting 1 kw per motor.  Let's see how they all do!

Route One

1) Short Passage: 4 hours and 30 min.  
    36 nautical miles trip
    (1:48 motoring, 2:42 sailing )

This is a 4.5 hour trip, leaving at 11 am arriving at 3:30 pm.

Diesel:
Burning at .50 gallon an hour, and motoring for 40% of the trip, means 0.83 gallons of diesel fuel used.

Hybrid:
Motoring on battery power for 1.5 hours and then sailing 2.42 hours, while recharging 9kw from solar,  Followed by 18 minutes of motoring means zero diesel used.

Combo or Parallel Diesel/Electric:
Motoring on battery power for 1.3 hours and then sailing 2.42 hours, while recharging 9kw from solar, Followed by 28 minutes of motoring means zero diesel used.

Winner: All the boats are less than a gallon apart, so this is too close to call.

RouteTwo

2) 1 Day Passage, Daytime: 7.5 hours 
     60 nautical mile trip:
    (3 hours motoring and 4.5 hours sailing)

This is a 7.5 hour trip, leaving at 9 am arriving at 4:30 pm.

Diesel:
Burning at .50 gallon an hour, and motoring for 40% of the trip means 3 hours motoring, so 1.5 gallons were burned.

Hybrid:
Motoring on battery power for the first 2 hours.  We then sail for 4.5 hours, recharging the batteries from solar and regen.  We motor the last hour off of batteries.  Zero fuel used.

Parallel Diesel/Electric:
Motoring on battery power for the first 1.3 hours.  We then sail for 4.5 hours, recharging the battery from solar and regen to full.  We motor for another 1.3 hours off of batteries then turn on one diesel engine for 20 minutes.  0.25 of a gallon fuel used.

Combo Diesel/Electric:
Motoring on battery power for the first 1.3 hours. We then sail for 4.5 hours, recharging the battery from solar and regen to full.  We motor for another 1.3 hours off of batteries then turn on the diesel engine for 20 minutes. 0.33 of a gallon fuel used.

Winner: Combo, Hybrid, and Parallel are too close to call, but all are at least a gallon or more better than the  Diesel boat. 

Route Three

3) Single Day Passage Nighttime, 7.5 hours                  60 nautical mile trip
     (3 hours motoring and 4.5 hours sailing)

This is a 7.5 hour trip, leaving at 10 pm arriving at 8 am.

Diesel:
Burning at .50 gallon an hour, and motoring for 40% of the trip means 3 hours motoring, so 1.5 gallons were burned.

Hybrid:
Motoring on battery power for the first 2 hours.  We then sail for 4.5 hours recharging 18 kWh from regen.  We motor for 2 hours off battery, then turn on the generators for 30 minutes, using 1.6 gallons of diesel.

Parallel Diesel/Electric:
Motoring on battery power for the first 1.3 hours.  We then sail for 4.5 hours and regenerate 4.5 kWh.  We must turn on the diesel engines for 1 hour, charging back 5 kWh.  We motor on electric for the last 40 minutes.  We burned 1.5 gallons of diesel.

Combo Diesel/Electric:
Motoring on battery power for the first 1.3 hours. We then sail for 4.5 hours and regenerate 9kWh.  We must turn on the diesel engine for 1 hour, charging back 10 kw. We motor on electric for the last 40 minutes.  We burned 1 gallon of diesel.

Winner: All boats are less than a gallon apart, so too close to call.

Route Four

4) Single Day Passage, Daytime, 11.25 hours             90 nautical mile trip
     (4.5 hours motoring and 6.75 hours sailing)

This is a 11.25 hour trip, leaving at 6 am and arriving at 5.25 pm (sunset).

Diesel:
Burning a half gallon an hour and motoring for 40% of the trip means 5.625 hours motoring, so 2.25 gallons were burned.

Hybrid:
We motor for the first 2 hours on batteries and then sail during the day for 6.75 hours, recharging the batteries via solar and regen to full.   Then we motor on electric for another 2 hours.  Then, we turn the generators and motor for 0.5 hours.  1.6 gallons of diesels burned.

Parallel Diesel/Electric:
We motor for the first 1.3 hours on batteries and then sail during the day for 6:75 hours, recharging from solar and regen until the batteries are full.   Then we motor on electric for another 1.3 hours.  We turn on the diesels 1 hour, recharging 10 kw.  We motor for the remaining 50 minutes.  1.5 gallons of diesel burned.

Combo or Parallel Diesel/Electric:
We motor for the first 1.3 hours on batteries and then sail during the day for 6:75 hours, recharging the batteries with solar and regen to full. Then we motor on electric for another 1.3 hours.  We turn on the diesel 1 hour, recharging 10 kw. We motor for the remaining 50 minutes. 1 gallon of diesel burned.

Winner: Combo, Hybrid, and Parallel are too close to call, but all three are over the Diesel by at least 1 gallon per passage.

Route Five

5) Day Passage with, 32.5 hour voyage                         260 nautical mile trip
    (13 hours motoring, 19.5 sailing) 

This is a 32.5 hour trip, leaving at 6 am arriving on the second day at 2:30 pm.  Note that the Parallel and Combo boats are using the auxiliary battery to increase to 33 kWh.

Diesel:
Burning at .50 gallon an hour and motoring for 13 hours we burn 6.5 gallons.

Hybrid:
We motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar and some regeneration.  As night falls, we motor for 2 hours off our batteries.  Then we turn on the two generators for 2 hours as we continue to motor regaining 28 kWh in the batteries.  We motor again for 2 hours to morning and turn on the generators for 1 hour to gain House needs.  Then we sail for 6 hours recharging 11 kw from solar and regenerating 24 kWh.  Then we motor off batteries for 2 hours.  We sail for 3.5 hours, recharging an additional 11 kw from solar and 13.5 kWh from regeneration.  We then motor for 2 hours into the anchorage.  All total, the generator ran for 6 hours, so we burned 9.6 gallons of diesel.

Parallel Diesel/Electric:
We motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via 22 kWh of solar and 5 kWh from regen.  As night falls, we motor for 2 more hours on battery.  Then we turn on both diesel engines for 2.5 hours, regaining 25 kw.  We motor again for 2 hours and then sail for 6 hours until morning.  Then we turn on the diesel engines for 1 hour sending 10 kWh to the batteries.  Then we sail for 3.5 hours, recharging about 13 kw from solar and gain 3.5 kWh from regen.  We then motor for 2 hours.  We fire up the diesels for 2.5 hours and recharge 25 kWh.  We then motor for 2 hours into the anchorage.  All total, the engines ran for 12 hours, so we burned 9 gallons of diesel.

Combo Diesel/Electric:
We motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar and regeneration. As night falls, we motor for 2 hours on battery and then turn on the diesel engine for 2.5 hours, regaining 25 kw. We motor again for 2 hours and then sail for 6 hours until morning, regenerating 12 kWh. We turn on the diesel for 1 hour and then motor for 2 hours.  We sail for 3.5 hours, recharging about 13 kWh from solar and 7kWh from regeneration.  We motor for 1.5 hours into the anchorage.  All total, the engine ran for 3.5 hours, so we burned 3.5 gallons of diesel.

Winner: Combo over the Hybrid by 1.3 of a gallons, 5.5 gallons over the Parallel boat, and 3 gallons over the Diesel boat.

Route Seven

6) Mid-Length Passage 
    1,000 mile trip: 4.5 days
   (43 hours motoring, 65 hours sailing) 

This is a four night trip, leaving at around 5 am and arriving at around 6 pm.

Diesel:
Burning at .50 gallon an hour motoring for 43 hours total equals 21.5 gallons of diesel.

Hybrid:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar and regen.  Come nightfall, we run the motors for 2 hours using the batteries then use the diesel 2 hours and then motor for 1 hour, leaving the rest for House needs. The next morning, we kick on the diesel generators for 2 hours, recharging the batteries 28 kWh and the motor 2 hours.  We run the diesels again for 2 hours and motor for 1 more.  We sail during the day and motor off batteries come nightfall for 2 hours.  Finally, we run the diesels for 1 hour to charge the House bank. This is done for three days. With solar, that also gives us enough power for House needs.  For the final half day we run the generators for 2 hours in the morning, then motor for 2 hours, then sail.  As we get near the destination, we motor for 2 hours into the anchorage. Together, the generators ran 38 hours.   At 1.6 gallons an hour that equals a total of 60.8 gallons burned.

Parallel Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar and regen.  Come nightfall, we run the motors for 2 hours and then kick on the diesels for 2.5 hours, recharging 25 kWh, followed by 2 hours motoring and then run the diesels just 0.5 of an hour to add some to the House bank.  Come morning, we run the diesels for 2.5 hours, charging 25 kWh and then motor 2 hours.  We recharge from solar and regen during the day.  That night, we motor for 2 hours, then use the diesels for 2.5 hours to recharge the House bank and motor 1 hour.  This pattern holds for three days.  On the last day, we turn on the diesels for 2 hours, then motor for 1.5 hours, then we sail for a few hours, then motor for 0.5 of an hour into the anchorage.  We ran the diesels for 40 hours and burned 30 gallons of fuel.

Combo Diesel/Electric:
The first day we motor the first 2 hours on batteries and then sail, recharging the batteries from solar and regen. Come nightfall, we motor for 2 hours and then kick on the diesel again for 2.5 hours to recharge 25 kWh, then motor for 1.5 hours.  Each following day we run the diesel for 2.5 hours in the morning, then motor for 1.5 hours.  We sail until night, motor for 2 hours, and run the diesel for 2 hours followed by motoring for 2 hours motoring.  We repeat that for three days. On the last half day we run the diesel for 1.5 hours and then motor for 1.5.  We sail gaining solar and regen, then motor for 2 hours.  Therefore, we ran our diesel engine 17.5 hours.  At 1 gallon an hour that equals a total of 17.5 gallons burned.

 
Winner: Combo by 9.25 gallons over the Parallel, 47.7  over the Hybrid and 3 gallons over the Diesel boat.

Route Eight

7) Ocean Crossing, overcast, with steady wind, with regen    
(3,000 mile trip: 15.5 days).

This is a third example, and an odd one.  This assumes that the entire ocean crossing is overcast and we will figure in regeneration.  You would think that the Hybrid, using Oceanvolt SD15 servoprops, should do the best in this situation due to regen, but let's see what happens.  With this Trade Winds crossing, we will figure in steady winds and minimal motoring for three hours a day, all while the skies are overcast.

Diesel:
Burning at .50 gallon an hour for 3 hours each day.  We burn 23.25 gallons of diesel. 

Hybrid:
We motor the first 2 hours on batteries and then start sailing for 18 hours.  The SD15s send 4 kw per hour to the batteries through regeneration, plenty to cover house needs and fully charge the battery each day.  Come morning we motor for 2 hours on electric and then use the generators for 1 hour until the wind kicks in to charge House needs.  Then we start sailing for 21 hours.  We repeat this for 13.5 more days.  Therefore, we ran our diesel generator for 29 hours and burned 46.4 gallons of diesel. 

Parallel Diesel/Electric:
We motor the first 2 hours on batteries then start sailing for 18 hours. The electric motors send 1 kw per hour to the batteries through regeneration, for 18 kWh.  Solar, though much reduced due to overcast skies, gave us 7 kWh.  Together, regen and solar add up to 25 kWh.  We use some of this for house needs, but still have 17 kWh for propulsion.  If we run both diesels for 1 hour the next day, we make an additional 10 kWh.  After that, for the next 14.5 days, each morning, when the wind drops, we motor for 2 hours on electric and run the diesels for 1 hour.  Then we start sailing for 21 hours regeneration 21 kWh of energy.  We repeat this for 13.5 days. Therefore, we ran the diesels for 29 hours and burned 17.42 gallons of fuel. 

Combo Diesel/Electric:
The first day we motor for 2 hours on batteries then start sailing for 18 hours. Sailing at 9 knots, the electric motors send 2 kw per hour to the batteries through regeneration, for 36 kWh.  Solar, though much reduced due to overcast skies, still gives us 7 kWh a day.  Together, regen and solar add up to 43 kWh.  This easily covers House needs and leaves us with a full battery.  Come morning we motor for 2 hours on electric and then fire up the diesel for 1 hour.  Then, when the wind kicks in, we start sailing for 21 hours regenerating 42 kWh of energy.  We repeat this for 13.5 more days. Therefore, we burned 14.5 gallons of diesel. 



Winner: the Combo over  the Parallel by 2.92 gallons,  8.7 gallons over the Hybrid, and 8.75 gallons over the Diesel boat.

Route Eight

8) Ocean Crossing, 3 days becalmed
    (3,000 mile trip: 15.5 days).

This is a second example, but this time, I will figure in regeneration.  The Hybrid, using Oceanvolt SD15 servoprops, will do the best in regen, but let's see what that does for the comparisons.  With this Trade Winds crossing, we will figure in steady winds and virtually no motoring  except for three days crossing the equator where we are becalmed.

Diesel:
Burning 1 hour a day of diesel to keep up with House needs for at .50 gallon for 12.5 days is 6.25 gallons.  Then 24 hours of motoring for the three days crossing the equator burns 36 gallons.  Total diesel used is 42.25 gallons.

Hybrid:
We motor the first 2 hours on batteries then start sailing for the next seven days using regeneration as needed to keep the battery full.  Then we hit the doldrums and have to motor for three days.  We use the SD15s for 2 hours, followed by 2.5 hours of the two generators to recharge 35 kWh.  We have motored for a total of 4.5 hours.  If we divide 4.5 hours into 24 we see we must do this about 5.3 times during the three becalmed days. Therefore, we ran our diesel generators for 79.5 hours. Burning 1.6 gallons an hour that equals a total of 127.2 gallons burned. 

Parallel Diesel/Electric:
We motor the first 2 hours on batteries then start sailing for the next seven days using regeneration as needed to keep the battery full. Then we hit the doldrums and have to motor for three days. We use the electric motors for 2 hours, followed by 2.5 hours of both diesel engines, generating 25 kWh to the batteries,   This is a total of 4.5 hours motoring.  If we divide 4.5 hours into 24 we see we must do this about 5.3 times during the three becalmed days.  Therefore, we ran our diesel engines for 79.5 hours. Burning .75 gallons an hour that equals a total of 59.63 gallons burned. 

Combo Diesel/Electric:
We motor the first 2 hours on batteries then start sailing for the next seven days using regeneration as needed to keep the battery full. Then we hit the doldrums and have to motor for three days.  We use the electric motors for 2 hours, followed by 2.5 hours of the diesel engine to generate 25 kWH to the batteries,  This is a total of 4.5 hours motoring. If we divide 4.5 hours into 24 we see we must do this about 5.3 times during the three becalmed days.  Therefore, we ran our diesel engines for 39.75 hours. Burning 1 gallon an hour that equals a total of 39.75 gallons burned.

Winner: Combo over the Parallel by 19.88 gallons,  23.85 over the Hybrid, and  2.5 gallons over the Diesel boat.

Route Eight

9) Ocean Crossing, no wind at night with regen     
(3,000 mile trip - 15.5 days).

With a Trade Winds crossing, we would only need some minor motoring.  For his example, we will figure in motoring at night for 8 hours when the wind drops.

Diesel:
Running one engine for 8 hours each night for 15.5 days equals 62 gallons of diesel. 

Hybrid:
We motor the first 2 hours on batteries then start sailing for 10 hours.  We regenerate enough power to shut that off after 5 hours to sail faster.  We also charge up 22 kWh via solar,  As night falls, even having burned House needs we still have full batteries.  When the wind drops, we motor for 2 hours, completely using the battery bank.  Then we turn on the two generators for 2 hours to power the servoprop motors which also sends 28  kWh to the batteries so we can then motor 2 more hours.  We turn the generator on for 2 hours and then motor for 1 hour until the wind kicks in.  Then we start sailing again for 15 hours refilling the batteries again from solar and regeneration.  This repeats for thirteen and half more days.  All total, we used the generator for 116 hours, burning 185.6 gallons.

Parallel Diesel/Electric:
We motor the first 2 hours on batteries then start sailing for ten hours. Each hour, together, the parallel electric motors regenerate 1 kw of energy when sailing at 9 knots.  That totals 10 kWh into the battery.  We also charge up 22 kWh via solar power,  This means, as night falls, even having burned house needs we still have full batteries.  When the wind drops, we motor for 2 hours, on the battery bank. Then we turn on two diesel engines for 2.5 hours, putting 25 kWh back into the battery.  Then we motor for 1,5 hours on electric.  We start sailing again for 16 hours, sending 22 kWh to the batteries adding another 16 kWh through regeneration.  Solar handles the house needs and we end up with a full battery come nightfall.  This repeats for thirteen and half more days. All total, we used the diesel engines for 67.5 hours, burning 50.63 gallons.

Combo Diesel/Electric:
We motor the first 2 hours on batteries then start sailing for ten hours. The parallel electric motor regenerate 1 kw of energy, each, when sailing at 9 knots.  That totals 2 kWh x 10 hours into the battery.  Therefore, we charge up 20 kWh.  We also charge up 22 kWh via solar power each day,  This is more power than we need so we won't have to regen the entire sailing time.  This means, as night falls, even having burned house needs, we still have full batteries.   When the wind drops, we motor for 2 hours, on the battery bank.  Then we turn on the diesel engine for 2.5 hours, putting 25 kWh back to the battery.  Then we motor for 2 hours on electric.   We have to run the diesel for 1 more hour and then motor for 30 minutes until the wind kicks in.  Then we start sailing again for 16 hours, sending 22 kWh to the batteries by solar while adding another 32 kWh through regeneration, which means we won't have to regen the entire sailing time. This repeats for thirteen and half more days.  All total, we used the diesel engine for 47.25 hours, burning 47.25  gallons.


Winner: Combo over the Parallel by 3.38 gallons, 17.55 gallons over the Hybrid and 14.75  gallons over the Diesel boat.

Fuel Consumption Winners with Regen

Passage Length MilesComboParallelHybridDiesel
Passage One36 miles0000.83
Passage Two60 miles (by day)0.330.2501.5
Passage Three60 miles (at night)11.50.81.5
Passage Four90 miles11.50.82.25
Passage Five260 miles3.599.66.5
Passage Six1000 overcast17.5
3060.821.5
Passage Seven3000 miles (Overcast)14.517.4246.423.25
Passage Eight3000 miles (3 days becalmed)39.7559.63127.242.25
Passage Nine3000 miles (No wind at night)47.2550.63185.662
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Passage totals over our double circumnavigation

Short DaylightOvernightTwo DayMid LengthOcean Crossings
1436494793629
As you can see, the vast majority of our passages are in daylight hours of one day.  After that, there are about one third less of overnight passages.  Two day, Mid length, and major crossings are much less and decreasing in numbers.

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Gallons used per passage by propulsion type

Propulsion TypeShort DaylightOver- nightTwo DayMid LengthOcean CrossingTotal gallons burnedCost at $5/gallonHours Diesel ran
Diesel (2 55 hp engines)1191.881111.5513.52,2321225.256274.13$31,370.658,536.25
Hybrid (2 20 kw electric motors plus 2 diesel generators)0395.2379.22,332.83,688.86,320.8$31,604.004,641.50
Parallel (2 45 hp diesels with 10 kw elec. motors)07427111,822.681,729.275003.95$25,019.755,681.50
Combo (A 110hp Diesel w/ 20 kw elec. motor + a 20 kw elec. motor)0494276.51,7011152.753,624.25$18,121.252,553.25

For these calculations, we used the regen numbers, and for the ocean crossings we used a typical trade wind crossing with 3 days in the doldrums.

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Fuel Comparison Conclusion

One thing to note, we are maintaining 5 knots of speed throughout these calculations.  Were we to slow down to 3 or 4 knots, the Hybrid would suddenly do far better since it would not need the generators anywhere near as much.  However, for our comparison, we wanted to keep up a typical cruising boat speed.

In all the examples, with or without regen, surprisingly, the Combo boat wins in every case but one, and that example is too close to call since the Hybrid, Parallel, and Combo boats are all within 33 cents of diesel for that passage.  Therefore, when it comes to fuel savings, the Combo boats win, hands down, nearly always coming out on top or equal to the other three boats. 

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