Propulsion Systems 

Comparing three types of propulsion on the same catamaran

The Three Propulsion Types

Diesel Engines

This is a typical catamaran, running two diesel engines 
This is the system that most boats use, it is tried and true.

What we like: 
Diesel engines are far cheaper than setting up a hybrid and come with the boat!  Secondly, diesel engines turning a prop are anywhere from 10% to 20% more efficient than a diesel generator supplying electric power to a motor turning a prop.  The percentage range is based on the number of conversions of energy.  If you go directly from a diesel generator, without going to the batteries first, you cut down on some of the conversions.  In that case, there is less of a penalty.  Finally, diesels have better horsepower.  Our boat will likely have two 55 hp diesel engines for a combined 110 hp! 

Why people will tell you Diesel boats are better:
At the root, the extra cost of a hybrid system, the percentage loss during conversion, and the overall extra horsepower are the main factors which most proponents of diesel power will use to argue against a hybrid system.  And, they are correct about these factors!  However, as you will see, this is not the whole story, there are many advantages for an electric propulsion system as well.

Diesel

Hybrid

Running two electric motors with a diesel generator.

The electric system obtains energy from several sources, diesel fuel (a generator), solar power, wind generators and, occasionally, a little from sailing regeneration.

What we like about a Hybrid:
They are quiet, they don't smell, they take less maintenance, and they don't burn diesel for 3-5 hours a day when running off batteries that were charged by solar panels.  In fact, on 90% of the days we are making a passage, we won't burn any diesel fuel at all if we have electric propulsion.  In most cases you have additional range (even with conversion losses) due to recharging via solar panels making up more than what you lose in conversion while using making electricity from diesel fuel.

Why people will tell you they are worse than a diesel boat:
They are underpowered; with only 30 hp per 20 kw electric motor, for a total of 60 hp.  The batteries will only take you a few hours of motoring off of electricity per day, and then you must turn on a generator.  Now you are back to the same noise, smell, maintenance (on the generator), and burning diesel fuel at a less efficient rate due to losses in conversion.

OceanVolt

Combo Electric and Diesel

Running two electric motors and/or two diesel engines.

Like the Hybrid, the electric system obtains energy from several sources, plus one more.  They can use solar power, wind generators, diesel fuel (from a generator) and, occasionally, a little from sailing regeneration.  In addition, by adding high capacity 48v alternators to the diesel engines, we can recharge while the diesel engines are powering the boat.


Diesel/Pod

What we like about a Combo Hybrid/ Diesel:
While motoring by electric pod they are quiet, they don't smell, and they don't burn diesel for 3-5 hours a day when running off batteries recharged by solar panels.  In fact, on 90% of the days we make a passage, we won't burn any diesel fuel at all if we have electric propulsion.  You also have more range than a diesel or hybrid boat, because you can motor off electric when you have the battery power, then switch to the more economic diesels (versus a generator), which gets rid of some of the conversion losses (see the fuel comparison below).  Finally, you have more horsepower available than either of the other options because you may choose to power the boat from both engines and pod motors, simultaneously.  This is excellent in a situation where power is needed for a short time where we may use up to 130 hp (110 hp from the diesels, 20 hp from the pods).



Helia 44

Why people will tell you this option is worse:
The two combined systems are heavier than either of the separate option above.  This is true, but a lot of that weight is in the batteries, and we plan to have a lot of battery power anyway, so the added weight is not as significant as you might imagine.  With extra battery power and the pods, they total about 300 extra pounds. 

People will also tell you that this system will require more maintenance, which is also true (but only over a Hybrid boat).  Yet, how much more?  Compared to the diesel boat, there would actually be less maintenance because the diesel engines will run so much less often, as will the sail drives, and the electric system is extremely low maintenance.  However, compared to the Hybrid system, the Combo boat will require more maintenance since there is an additional diesel engine to service, and two sail drives.  (The Hybrid has two generators while the Combo has 2 diesel engines, plus a generator, and two saildrives).



Helia 44







Fuel Use Comparison

Below is a fuel use comparison of all three propulsion types, on different types of passages. 

  1. Passage One - Short passage of less then 6 hours 36 miles)                                                         Jump to the data
  2. Passage Two - Single day passage during daylight, (60 miles)                                                     Jump to the data
  3. Passage Three - Single day passages during night, (60 miles)                                         Jump to the data
  4. Passage Four - Single day passages during daylight, (90 miles)                                        Jump to the Data
  5. Passage Five - Two day passages with two says of sunlight, (260 miles)                         Jump to the Data
  6. Passage Six- 21 day Atlantic ocean crossing in Trade Winds, (3,000 miles)                               Jump to the Data
  7. Passage Seven- 21 day Pacific ocean crossing across the equator, (3,000 miles)                   Jump to the Data
  8. Passage Seven- 21 day ocean crossing becalmed for 7 days, (3,000 miles)                    Jump to the Data
Route One

1) Short Passage Less than 6 hours  
(36 nautical miles or less trips)

This is a 6 hour trip, leaving at 8 am arriving at 2 pm.

Diesel:
Burning at .50 gallon an hour, and motoring for 50% of the trip, means 3 hours of diesel motoring, so it burns 1.5 gallons of diesel fuel.

Hybrid:
Motoring on battery power for the first 3 hours and sailing the other 3 hours means zero diesel used.

Combo Diesel/Hybrid:
Motoring on battery power for the first 3 hours and sailing the other 3 hours. This means zero diesel was used.

Winner: either the Hybrid or Combo by 1.5 gallons per passage.

RouteTwo

2) Single Day Passage During Daylight                 (60 nautical mile trip)

This is a 10 hour trip, leaving at 7 am arriving at 5 pm.

Diesel:
Burning at .50 gallon an hour, and motoring for 50% of the trip means 5 hours motoring, so 2.5 gallons were burned.

Hybrid:
Motoring on battery power for the first 3 hours and sailing for 5 hours followed by 2 hours of motoring off of solar recharged batteries.  This means zero diesel was used.

Combo Diesel/Hybrid:
Motoring on battery power for the first 3 hours and sailing for 5 hours followed by 2 hours of motoring off of solar recharged batteries.   This means zero diesel was used.

Winner: either the Hybrid or Combo by 1.5 gallons per passage.

Route Three

3) Single Day Passage During Night                        (60 nautical mile trip)

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

Diesel:
Burning at .50 gallon an hour, and motoring for 50% of the trip means 5 hours motoring, so 2.5 gallons were burned.

Hybrid:
Motoring on battery power for the first 3 hours and sailing for 5 hours followed by one hour of the 20 kw diesel generator running.  Calculating a 20% conversation loss, they send 15 kw to the motors while storing about 20 kWh in the batteries.  The boat can then motor on battery power for the last 30 minutes, leaving enough for house uses when they arrive.  They used 1.6 gallons of diesel.

Combo Diesel/Hybrid:
Motoring on battery power for the first 3 hours and sailing for 5 hours followed 2 hours motoring on a single diesel engine. This sends just 9 KWh back into the batteries (200 amps) for house uses and maneuvering when we arrive. We used 1 gallon of diesel.

Winner: Combo boat by 0.6 gallons per passage better than the Hybrid boat and 1.7 gallons better than the Diesel engine only boat.

Route Four

4) Single Day Passage During Daylight              (90 nautical mile trip)

This is a 15 hour trip, leaving at 4 am (dark) and arriving at 7 pm (sunset).

Diesel:
Burning a half gallon an hour and motoring for 50% of the trip means 7.5 hours motoring, so 3.75 gallons were burned.

Hybrid:
They motor for the first 3 hours on batteries and then sail during the day for 7.5 hours, recharging their batteries via solar.   Then they motor on electric for another 3 hours.  At the end of the trip, they fire up the generator for an hour while recharging the batteries about 10 kWh.  They motor on battery power for the last half hour.  They used 1.6 gallons of diesel.

Combo Diesel/Hybrid:
They motor for the first 3 hours on batteries and then sail during the day for 7.5 hours, recharging their batteries via solar.  Then they motor on electric for another 3 hours.   At the end of the trip, they fire up a diesel engine for 1.5 hours of motoring while recharging the batteries some for House needs.  They used 1.13 gallons of diesel.

Winner: Combo boat by 0.47 gallons per passage better than the Hybrid boat, and 2.62 gallons better than the Diesel engine only boat.

Route Five

5) Two Day Passage with 2 days of sunlight   (260 nautical mile trip)

This is a 43.5 hour trip, leaving at 11 am arriving on the second day at 5:30 am.

Diesel:
Burning at .50 gallon an hour, and motoring for 50% of the trip means 21.75 hours motoring, so 10.89 gallons were burned.

Hybrid:
They motor the first 3 hours on batteries, then regain 25 kWh via solar recharge each of the two days.  That is a total of 50 kWh which is about 6 hours of motoring time.  All total, they will motor off batteries for 9 hours on this voyage.  That still leaves about 12.75 hours out of the total 21.75 that they need to motor.  They run a diesel generator for 2.5 hours, sending 25 kw to the batteries then motor for 3 hours off the battery charge.  That leaves them with 7.25 hours motoring still required.   They run the generator for 2.5 hours and motor off batteries again for 3 hours.  Now they are 1 and 3/4 hours motoring from their destination.  They run the generator for one hour and motor off batteries for the final 3/4 hours.  All total, the generator ran for 6 hours, so they burned 9.6 gallons of diesel.


Combo Diesel/Hybrid:
They motor the first 3 hours on batteries, then regain 25 kWh via solar recharge each of the two days.  That is a total of 50 kWh which is about 6 hours of motoring time.  All total, they will motor off batteries for 9 hours.  That still leaves about 12.75 hours out of the total 21.75 that they need to motor.  They run a diesel engine for 6 hours, sending 27 kw to the batteries from the alternator.  They switch back to the pods and go for 3 hours on batteries.  They are still 3.75 hours short, so they motor for 3 hours, sending 13.5 kw to the batteries, then motor for the remaining 45 minutes (leaving some for House uses).  All total, they ran one diesel engine for a total of 9 hours, so they burned 6.75 gallons of diesel.

Winner: Combo boat by 2.85 gallons over the Hybrid and 4.14 gallons over the Diesel boat.

Route Six

6) 21 Day Atlantic Crossing                                     (3,000 miles)

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.

Diesel:
Burning at .50 gallon an hour, for 6 hours a day for 21 days equals 63 gallons of diesel.

Hybrid:
They motor the first 3 hours on batteries.  Then they charge up 25 kWh via solar power each day, allowing them to motor for another 3 hours per day.  This covers the motoring needed for the first day but they need an extra 3 hours each day thereafter.  They run their diesel generator for 2 hours each subsequent day, putting 15 kWh into the batteries.  They use 7.5 kWh to motor the final hour needed and the other 7.5 kWh for House needs.  They ran their diesel generator for 2 hours for 20 days, or 40 hours total.  At 1.60 gallons an hour that equals a total of 64 gallons burned.

Combo Diesel/Hybrid:
They motor the first 3 hours on batteries.   Then they charge up 25 kWh via solar power each day, allowing them to motor for another 3 hours per day.  This covers the motoring needed for the first day but they need an extra 3 hours each day thereafter.  They run one diesel engine for 2.5 hours each subsequent day, putting 11.25 kWh into the batteries.  They use 3.75 kw for the final half hour of motoring off electric, leaving the rest for house needs.  They use their diesel engine for a total 50 hours.  At .75 gallons an hour that equals a total of 37.5 gallons burned.

Winner: Combo boat by 26.5 gallons over the Hybrid and 25.5 gallons over the Diesel boat.

Route Seven

7) 21 Day Passage over the Equator            (3,000 mile trip).

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.  That, and this time, we will calculate in the crossing of the equator as 3 days of no wind.

Diesel:
Burning at .50 gallon an hour, for 6 hours a day out of 18 equals 54 gallons of diesel.  Then add three days of motoring 24 hours a day for 36 gallons additional diesel giving them a total burn of 90 gallons.

Hybrid:
They motor the first 3 hours on batteries. Then they charge up 25 kWh via solar power each day, allowing them to motor for another 3 hours per day. This covers the motoring needed for the first day but they need an extra 3 hours each day thereafter. They run their diesel generator for 2 hours each subsequent day, putting 15 kWh into the batteries. They use 7.5 kWh to motor the final hour needed and the other 7.5 kWh for House needs. All total, they ran their generator during those 17 days for 34 hours.

However, on three days they were becalmed in the doldrums. During those three days they must motor 24 hours a day instead of six.  They still regain 3 hours of motoring from solar each day, leaving 21 hours of remaining motoring still needed per day.  While running the generator, 7.5 kw goes to the motors to keep moving while 10 kWh gets stored in the battery bank per hour.   Recharging the batteries takes 2.5 hours.  So, each 2.50 hours they regain a full charge allowing 3 hours of motoring.  To motor that extra 21 hours requires about four such cycles per day, which also leaves them enough extra power for house uses.  So each day they motor for 10 hours with the generator running burning 16 gallons of fuel, for a total of 48 gallons.  They add that to the other 17 days where they only had to run the generator for 2 hours a day, which equals 34 hours and they get a total run time of 64 hours, or 102.4 gallons of fuel burned.


Combo Diesel/Hybrid:
They motor the first 3 hours on batteries.  Then they charge up 25 kWh via solar power each day, allowing them to motor for another 3 hours per day.  This covers the motoring needed for the first day but they need an extra 3 hours each day thereafter.  They run one diesel engine for 2.5 hours each subsequent day, putting 11.25 kWh into the batteries.  They use 3.75 kw for the final half hour of motoring off electric, leaving the rest for house needs.  They use their diesel engine for a total 42.5 hours.  At .75 gallons an hour that equals a total of 31.88 gallons burned during those 17 days.

However, on three days they were becalmed in the doldrums.  During those three days they must motor 24 hours a day instead of six.  They still regain 3 hours of electric motoring from solar each day, leaving 21 hours of remaining motoring still needed each day. While running one diesel engine, 4.2 kWh gets stored in the battery bank per hour.  Every two hours they gain 1 hour of electric motoring (with some left for house needs).  So, they run on the diesel engine for 14 hours and electric motor for 7 hours.  All total, they run the diesel engine for 42 hours during those three becalmed days.   At .75 gallons an hour, they burn 31.5 gallons.  Add that to the 31.88 gallons from the other 17 days and you get a total diesel usage of 63.38 gallons.

 
Winner: Combo by 39 gallons per trip over the Hybrid and 26.62 gallons over the Diesel boat.

Route Eight

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

21 Day Passage but they are becalmed for seven days.

Diesel:
Burning at .50 gallon an hour, for 6 hours a day out of 14 equals 42 gallons of diesel. Plus, seven days of motoring 24 hours a day when becalmed is 84 gallons for a total burn of 126 gallons.


Hybrid:
Everything is the same as the voyage above, but now they use their generator, burning 3.2 gallons a day for 13 days and 16 gallons a day for 7 becalmed days. That totals 153.6 gallons burned.

Combo Diesel/Hybrid:
Everything is the same as the voyage above, but now they run one diesel for 13 days for 2.5 gallons (32.5 gallons). Plus, for seven days, they have to run one diesel for 14 hours a day, using 73.5 gallons during the 7 days becalmed. That plus the other 32.5 from the 13 days is 106 gallons total.

Winner: Combo by 47.6 gallons per trip over both the Hybrid and 20 gallons less than the Diesel boat.

Fuel Consumption Winners

Passage Length Miles WinnerOver DieselOver Hybrid
Passage One35Hybrid or Combo1.5 gallonsEqual
Passage Two60Hybrid or Combo1.5 gallonsEqual
Passage Three60Combo1.7 gallons0.6 gallons
Passage Four90Combo2.62 gallons0.47 gallons
Passage Five260Combo4.14 gallons2.85 gallons
Passage Six3000Combo25.5 Gallons26.5 Gallons
Passage Seven3000 (3 days becalmed)Combo26.62 gallons39 gallons
Passage Eight3000 (7 days becalmed)Combo20 gallons47.6 gallons
Showing entries (filtered from total entries)

Fuel Comparison Conclusion

In the examples above, the Diesel boat saves fuel over the Hybrid in three cases (all the longer passages).  While the Hybrid beats the Diesel in all the shorter passages.  However, in all but the two short passages, where they tie, the Combo boat beats the Hybrid on fuel savings.  Against the Diesel boat the Combo always saves fuel over that boat, long or short passages.  Therefore, when it comes to fuel savings, the Combo boat wins, hands down. 

Cost Comparison

What about what it costs to add a Hybrid or Combo system to an exiting Diesel boat?  And, what are the fuel savings over time?

Initial Cost to add Hybrid system

Hybrid System Components:

Two Oceanvolt ServoProp Motors: $50,000
One 20 kw Generator: $20,000
Four 11 kWh of LifePO4 batteries: $10,000
Two 8,000 watt Inverters: $10,000
Ten 550w solar panels $2,000
Five MPPTs: $1,000

Other things of Note:
There will be additional costs for circuit breaker, wiring, etc., which could lead to another $3,000 approximately.

Total Price to upgrade: $96,000

Hybrid System

Initial Cost to add Combo system

Combo System Components:

Two SeaDrive 7.5 kw Pop Motors: $20,000
Two Hydraulic motors and arms: $2,000
Four 11 kWh of LifePO4 batteries: $10,000
Two 8,000 watt Inverters: $10,000
Ten 550w solar panels $2,000
Five MPPTs: $1,000

Other things of Note:
There will be additional costs for circuit breaker, wiring, etc., which could lead to another $3,000 approximately.

Total Price to upgrade: $48,000

Combo System

Cost Conclusion

After calculating all our passages on our sixteen year voyage around the world and the Ring of Fire, we come up with approximately $50,000 savings in diesel and propane fuel for the Combo and a little less for the Hybrid, about $48,000.  Figuring in less maintenance, we save about $37,000 with the Hybrid and $15,000 with the Combo (it still has diesels and saildrives, but they run far less hours than the diesel only boat).  Total savings (fuel and maintenance) equals $85,000 for the Hybrid and $65,000 for the Combo.

That means, after subtracting fuel and maintenance savings from the purchase costs of the two systems, we save about $17,000 going with the Combo over a Diesel boat while the Hybrid loses about $11,000 compared to the Diesel boat.

Therefore, the Combo saves us money, being half the cost of a Hybrid propulsion system.  Even though the Hybrid saves in maintenance, in the end, it still looses $11,000 compared to the Diesel boat due to the high initial cost to add the system.  When it comes to the Combo boat, it actually saves $17,000 over a Diesel boat, due to fuel and maintenance savings over the whole voyage.  Winner, Combo Boat Propulsion system as the least expensive option (in the long run).

Horsepower Comparison

What about how much horsepower we obtain with each system?

  1. Diesel Engines - there are two 55 hp diesels                                                                              Total: 110 hp
  2. Hybrid motors - There are two 20kw electric motors, which supply about 30 hp each.    Total: 60 hp
  3. Combo Engines & Motors - Two 7.5 kw motors (10 hp ea.).  Plus two 55 hp diesels.     Total: 130 hp

Power Conclusion

The Hybrid boat is woefully underpowered when in certain situations while the Combo boat beats the Diesel with 20 more total horsepower.  Horsepower is the category that eliminates the Hybrid from our consideration, since it does not have enough power in a dire or required situation so get us where we need to go, while the Combo boat is the best.  Yet, both the Hybrid and the Combo are better than the Diesel boat in all situations where you don't need all that horsepower, like maneuvering around in a marina where electric gives you full torque at any RPM, or when you are departing early from your anchorage and don't want to have to warm up the smelly, noisy, fuel wasting, diesel engines.  Winner, obviously, the Combo boat.

Final Conclusion



The Combo wins in every category we have listed, with only two negatives, weight (compared to the Diesel Boat) and maintenance (over the Hybrid).   The extra 300 lbs. can be mitigated by reducing weight in other places and the maintenance is less than a standard Diesel boat (though more than the Hybrid).

We get all the comforts of electric propulsion and far less times where we must obtain diesel fuel compared to either the Hybrid or Diesel boats.  We have no need for propane, eliminating those hassles and dangers.  We also get rid of the dangers and limitations of an underpowered Hybrid boat.  Therefore, the Combo boat propulsion system is our winner, by a long shot.  And though an initial $22,000 to install the pod motors is a hard pill to swallow, in the long run, it saves us $17,000 and adds a whole lot of comfort to the voyage.


Combo System

Help us out

Subscribe S/V Lynx Youtube

Please subscribe to our Youtube channel and earn a chance to win a cabin for a week on S/V Lynx!  To subscribe, click the Youtube link (left).

Created with Mobirise site template