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 diesel engine on a 50' catamaran will use about 1 gallon per hour (GPH) at a boat speed of 5 knots.  For the Hybrid, a 20 kw generator uses 1.6 GPH (when needed).  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).  While acting as a generator, the 50 hp engine turning the 10 kw electric motor will add  extra drag and increase fuel burn to 1.25 gph.  Sometimes, we must run both diesels to get the additional generated power, but does send 7 kw to the battery while running at cruising speed.  The Combo boat's diesel will burn more like 1.5 gallons per hour when generating power since it has to turn a 25 kw motor, which causes 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.
Without Regen Summary With Regen Summary
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 1 gallon an hour, and motoring for 40% of the trip, means 1.8 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: Hybrid boats over the diesel by nearly 2 gallons

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:
Running the diesel for 40% of the trip means 3 hours motoring, so 3 gallons were burned.

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

Parallel Diesel/Electric:
Motoring on battery power for the first 1.3 hours.  They then sail for 4.5 hours, recharging the battery to full.  They motor for another 1.3 hours off of batteries then turn on one diesel engine for 20 minutes.  0.33 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 around three gallons of fuel.

Route Three

3) Single 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:
Running one diesel for 40% of the trip means 3 hours motoring, so 3 gallons were burned.

Hybrid:
Motoring on battery power for the first 2 hours.  They then sail for 4.5 hours.  They 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.  They then sail for 4.5 hours. Then turn on the diesel engines for 1 hour, charging back 10 kw.  They motor on electric for the last 40 minutes and burned 2.5 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 1.5 gallon of diesel.

Winner: Combo over the Parallel by 1 gallon, over the  Diesel and Hybrid by 2 gallons.

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:
Motoring for 40% of the trip means 5.6 hours motoring, so 5.6 gallons were burned.

Hybrid:
They 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 they motor on electric for another 2 hours.  Then turn on the generators and motor for 0.5 hours with 1.6 gallons of diesel burned.

Parallel Diesel/Electric:
They 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 they motor on electric for another 1.3 hours and turn on the diesels 1 hour, recharging 10 kw.  They motor for the remaining 50 minutes.  2.5 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. 1.5 gallons of diesel burned.
Winner: Combo over the  Parallel and Hybrid by a gallon,  better than the Diesel by four gallons 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:
They motor for 13 hours means they burn 13 gallons.
Hybrid:
They motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar.  As night falls, they motor for 2 hours on battery.  Then turn on the generators for 2 hours, regaining 28 kWh.  They motor again for 2 hours and then sail for 6 hours recharging 11 kWh.  They run the generators for 2 hours putting 28 kWh in the batteries.  Then sail for 3.5 hours, recharging an additional 11 kw from solar.  Then motor off batteries for 2 hours into the anchorage.  All total, the generators ran for 8 hours, so they burned 12.8 gallons of diesel.

Parallel Diesel/Electric:
They motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar.  As night falls, they motor for 2 hours on battery, and turn on the diesel engines for 2.5 hours, regaining 25 kw.  They motor again for 2 hours and then sail for 6 hours at night.  They 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 they burned 12.5 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 6.75 gallons of diesel.


Winner: Combo over Parallel, Hybrid and Diesel boats by about 6 gallons.

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:
They motor for 43 hours, which equals 43 gallons of diesel.
Hybrid:
The first day they motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, they run the motors for 2 hours using the batteries.  Then they kick on the diesel generator for 2 hours, recharging the batteries 28 kWh and the motor 2 more hours.   Each following day they run the diesel generators for 2.5 hours in the morning, then motor for 2 hours.  They sail until night, then run the generators again for 2.5 hours and motor for 2 hours.  They repeat that for two more days.  With solar, that also gives them enough power for House needs.  For the final half day they run the generators for 2 hours in the morning, then motor for 2 hours, then sail.  As they get near the destination, they 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 they motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, they 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, they run the diesels for 2.5 hours, charging 25 kWh and then motor 2 hours.  They recharge from solar during the day.  That night, they 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, they turn on the diesels for 2 hours, then motor for 1.5 hours, then sail for a few hours, then motor for 0.5 of an hour into the anchorage.  They ran the diesels for 37 hours and burned 46.25 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 27.75 gallons burned.

 
Winner: Combo by 18.5 gallons over the Parallel, 39  over the Hybrid and 15 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:
They run a diesel engine 6 hours a day for 15.5 days equals 93 gallons of diesel used.

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

Winner: Combo boat over the other three options by around 37 gallons.

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:
A diesel runs 6 hours a day out of 12.5 days equals 75 gallons of diesel.  Then add three days of motoring 24 hours a day for 72 gallons additional diesel giving them a total burn of 147 gallons.
Hybrid:
The first day they motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, they run the motors for 1.75 hours and then kick on the diesel generator for 1.25 hours.   Each following day they run the diesel generator for 1 hour in the morning, then motor for 2 hours.  They sail until night, then repeat that, using 1.25 hour of the diesel generator and 1.75 hours motoring.  That also gives them 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, they must motor 2 hours, followed by 3 hours of generator.  If you divide 5 hours into 24 you see that they must do this about 4.8 times during each of those three days.  Therefore, they  ran their 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 they motor the first 2 hours on batteries and then sail, recharging the batteries from solar.  Come nightfall, they run the motors for 2 hours and then kick on the diesels for 1.5 hour.  Each following day they run the diesels for 1 hour in the morning, then motor for 2 hours.  They sail until night, then repeat that, using 2 hours motoring and then 1.5 hour of the two diesels.  They did this for 11.5 days, burning 57.5 gallons.  That also gives them enough power for house needs.  For the three becalmed days, they must motor 2 hours, followed by 2.5 hours of two diesel engines.  If they divide 4.5 hours into 24 you see they must do this about 5.33 times on each of the three days. Therefore, they ran their diesel engines an additional 79.95 hours. Together, the total diesel run time is 142.45 hours burning 178 gallons of diesel.

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 103.1 gallons burned.

 
Winner: Combo by about 75 gallons per trip over the Parallel, 7  over the Hybrid and 44 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:
Running one diesel for 6 hours a day out of 8.5 days equals 51 gallons of diesel.   Then add seven days of motoring 24 hours a day for 168 gallons All total they burn all 158 gallons in the fuel tanks, plus 10 jerry cans for 50 gallons, leaving them becalmed and out of fuel until the wind comes up.  They needed 219 gallons to keep motoring the entire way.

Hybrid:
The first day they motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, they run the motors for 1.75 hours and then kick on the diesel generator for 1.25 hours. Each following day they run the diesel generator for 1 hour in the morning, then motor for 2 hours. They sail until night, then repeat that, using 1.25 hour of the diesel generator and 1.75 hours motoring. That also gives them 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, they must motor 2 hours, followed by 3 hours of generator. If you divide 5 hours into 24 you see that they must do this about 4.8 times during each of those seven days. Therefore, they ran their 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.  (They would have to carry Jerry Cans for extra fuel, about seven cans).

Parallel Diesel/Electric:
The first day they motor the first 2 hours on batteries and then sail, recharging the batteries from solar. Come nightfall, they run the motors for 2 hours and then kick on the diesels for 1.5 hour. Each following day they  run the diesels for 1 hour in the morning, then motor for 2 hours. They sail until night, then repeat that, using 2 hours motoring and then 1.5 hour of the two diesels.  The diesels run 5 hours a day and they do this for 7.5 days.  Adding the first day with that, they burned 50 gallons. That also gives them enough power for house needs.  They start the seven becalmed days with only 50 gallons of diesel left.  They must motor 2 hours, followed by 2.5 hours of two diesel engines. If you divide 4.5 hours into 24 you see that they must burn 5 gallons  about 5.33 times on each becalmed day.  That means they use up their 50 remaining gallons in two days.   At that point, they must switch to slow motoring at 2 knots and make it without stopping, just on recharge from solar.

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 burning 1 gallon an hour.  We do this for three days of the diesel running 24 hours a day for 72 gallons more diesel.  All total, we burned 92 gallons out of our 100.  At that point, we must switch to slow motoring at 2 knots and make it without stopping, just on recharge from solar.
Winner: Combo over the Parallel since they didn't have to slow down for another 24 hours, it also wins over the Hybrid by only burning 92 gallons vs 190.29 gallons, and over the diesel 108 gallons, and the diesel is becalmed and out of fuel.

Fuel Consumption Winners with no Regen

Passage Length Miles Combo Parallel Hybrid Diesel
Passage One360001.8
Passage Two60 (day)0.330.3303
Passage Three60 (night)1.52.53.23
Passage Four901.52.51.65.6
Passage Five2606.7512.512.813
Passage Six1,00027.7546.2567.243
Passage Seven300056.6394.494.493
Passage Eight3000 (becalmed 3 days)103.1142.45110.4147
Passage Nine3000 (becalmed 7 days)92100190.29219
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:
Running one diesel for 40% of the trip, means 1.8 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 hybrid boats win, while the diesel loses ,burning 1.8 gallons of fuel.

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:
Using one diesel for 40% of the trip means 3 hours motoring, so 3 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.  0.33 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 2.5 gallons 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:
Using one diesel for 40% of the trip means 3 hours motoring, so 3 gallons were burned.

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

Parallel Diesel/Electric:
Motoring on battery power for the first 1.3 hours.  They then sail for 4.5 hours and regenerate 4.5 kWh.  They must turn on their diesel engines for 1 hour, charging back 5 kWh.  They then motor on electric for the last 40 minutes.  They burned 2.5 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 1.5 gallons of diesel.

Winner:  Combo or Hybrid both beat the Parallel by 1 gallon and the Diesel by 1.5 gallons.

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:
Using one diesel for 40% of the trip means 5.625 hours motoring, so 5.6 gallons were burned.

Hybrid:
They 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 they motor on electric for another 2 hours.  Then, they turn the generators and motor for 0.5 hours.  1.6 gallons of diesels burned.

Parallel Diesel/Electric:
They  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 they motor on electric for another 1.3 hours.  They turn on the diesels 1 hour, recharging 10 kw.  They motor for the remaining 50 minutes.  2.5 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. 1.5 gallons of diesel burned.
Winner: Combo and Hybrid, which win over the Parallel by 1 gallon and the diesel by 4 gallons.

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:
Using one diesel for 13 hours we burn 13 gallons.
Hybrid:
They motor the first 2 hours on batteries and then sail for 10 hours, refilling the batteries via solar and some regeneration.  As night falls, they motor for 2 hours off their batteries.  Then they turn on the two generators for 2 hours as they continue to motor regaining 28 kWh in the batteries.  They motor again for 2 hours to morning and turn on the generators for 1 hour to gain House needs.  Then they sail for 6 hours recharging 11 kw from solar and regenerating 24 kWh.  Then they motor off batteries for 2 hours.  They sail for 3.5 hours, recharging an additional 11 kw from solar and 13.5 kWh from regeneration.  They then motor for 2 hours into the anchorage.  All total, the generator ran for 6 hours, so they burned 9.6 gallons of diesel.

Parallel Diesel/Electric:
They  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, they motor for 2 more hours on battery.  Then they turn on both diesel engines for 2.5 hours, regaining 25 kw.  They motor again for 2 hours and then sail for 6 hours until morning.  Then they turn on the diesel engines for 1 hour sending 10 kWh to the batteries.  Then they sail for 3.5 hours, recharging about 13 kw from solar and gain 3.5 kWh from regen.  They then motor for 2 hours.  They fire up the diesels for 2.5 hours and recharge 25 kWh.  They then motor for 2 hours into the anchorage.  All total, the engines ran for 12 hours, so they burned 15 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 5.25 gallons of diesel.

Winner: Combo over the Hybrid by 4.4 gallons, 10 gallons over the Parallel boat, and 4.5 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:
Running one diesel for 43 hours total equals 43 gallons of diesel.
Hybrid:
The first day they motor the first 2 hours on batteries and then sail, recharging the batteries from solar and regen.  Come nightfall, they 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, they kick on the diesel generators for 2 hours, recharging the batteries 28 kWh and the motor 2 hours.  They run the diesels again for 2 hours and motor for 1 more.  They sail during the day and motor off batteries come nightfall for 2 hours.  Finally, they run the diesels for 1 hour to charge the House bank. This is done for three days. With solar, that also gives them enough power for House needs.  For the final half day they run the generators for 2 hours in the morning, then motor for 2 hours, then sail.  As they get near the destination, they 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 they motor the first 2 hours on batteries and then sail, recharging the batteries from solar and regen.  Come nightfall, they 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, they run the diesels for 2.5 hours, charging 25 kWh and then motor 2 hours.  They recharge from solar and regen during the day.  That night, they 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, they turn on the diesels for 2 hours, then motor for 1.5 hours, then they sail for a few hours, then motor for 0.5 of an hour into the anchorage.  They ran the diesels for 40 hours and burned 50 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 which equals a total of 26.25 gallons burned.

 
Winner: Combo by roughly 24 gallons over the Parallel, 34  over the Hybrid and 17 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:
One diesel engine for 3 hours each day times 15.5 days.  They burn 46.5 gallons of diesel. 

Hybrid:
They 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 They motor for 2 hours on electric and then use the generators for 1 hour until the wind kicks in to charge House needs.  Then they start sailing for 21 hours.  They repeat this for 13.5 more days.  Therefore, they ran their diesel generator for 29 hours and burned 46.4 gallons of diesel. 

Parallel Diesel/Electric:
They 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, gives them 7 kWh.  Together, regen and solar add up to 25 kWh.  They use some of this for house needs, but still have 17 kWh for propulsion.  If they run both diesels for 1 hour the next day, they make an additional 10 kWh.  After that, for the next 14.5 days, each morning, when the wind drops, they must motor for 2 hours on electric and run the diesels for 1 hour.  Then they start sailing for 21 hours regenerating 21 kWh of energy.  They repeat this for 13.5 days. Therefore, they ran the diesels for 29 hours and burned 36.25 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 21.75 gallons of diesel. 



Winner: the Combo over  the Parallel by14.5 gallons,  24.65 gallons over the Hybrid, and 24.75 gallons better than 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:
Running a diesel for 1 hour a day for 12.5 days is 12.5 gallons.  Then 24 hours of motoring for the three days crossing the equator burns 72 gallons.  Total diesel used is 84.5 gallons.

Hybrid:
They 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 they hit the doldrums and have to motor for three days.  They use the SD15s for 2 hours, followed by 2.5 hours of the two generators to recharge 35 kWh.  They have motored for a total of 4.5 hours.  If you divide 4.5 hours into 24 you see that they must do this about 5.3 times during the three becalmed days. Therefore, they 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:
They 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 they hit the doldrums and have to motor for three days. They 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 you divide 4.5 hours into 24 you see that they must do this about 5.3 times during the three becalmed days.  Therefore, they ran their diesel engines for 79.5 hours using 99.38 gallons out of our 100 available. 

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 59.63 gallons of diesel.

Winner: Combo over the Parallel by 39.75 gallons,  67.57 over the Hybrid, and  24.87 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 124 gallons of diesel burned 

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

Parallel Diesel/Electric:
They 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.  They also charge up 22 kWh via solar power,  This means, as night falls, even having burned house needs they still have full batteries.  When the wind drops, they motor for 2 hours, on the battery bank. Then they turn on two diesel engines for 2.5 hours, putting 25 kWh back into the battery.  Then they motor for 1,5 hours on electric.  They start sailing again for 16 hours, sending 22 kWh to the batteries adding another 16 kWh through regeneration.  Solar handles the house needs and they end up with a full battery come nightfall.  This repeats for thirteen and half more days. All total, they used the diesel engines for 67.5 hours, burning 84.38 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 70.88  gallons.


Winner: Combo over the Parallel by 13.5 gallons, 115 gallons over the Hybrid and 53  gallons over the Diesel boat.

Fuel Consumption Winners with Regen

Passage Length Miles Combo Parallel Hybrid Diesel
Passage One360001.8
Passage Two60 (day)0.330.3303
Passage Three60 (night)1.52.51.63
Passage Four901.52.51.65.6
Passage Five2605.25159.613
Passage Six1,000 (overcast)26.255060.843
Passage Seven3000 (overcast)21.7536.2546.446.5
Passage Eight3000 (3 days becalmed)6099127.284.5
Passage Nine3000 (no wind at night)70.8884.38185.6124
Showing entries (filtered from total entries)

Passage totals over our double circumnavigation

Short DaylightOvernightTwo DayMid LengthMajor 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 LengthMajor CrossingTotal gallons burnedCost at $5/gallonHours Diesel ran
Diesel (2 55 hp engines)2584.801482
102715482450.59092.3$45,461.509092.30
Hybrid (2 20 kw electric motors plus 2 diesel generators)0790.4379.22,188.83,688.87426.40$37,132.004,641.50
Parallel (2 45 hp diesels with 10 kw elec. motors)07417111,0801,729.274,261.27$21,306.353,629.216
Combo (A 80hp Diesel w/ 25 kw elec. motor + a 20 kw elec. motor)0494276.56301152.752,553.25$12,766.251,977.68
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.

 entries (filtered from total entries)

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, the Combo boat wins in every case except the first two short passages, where it ties the other Hybrid options, but does better than the diesel.  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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