Blogpost by Founder Joe Grez, November 7, 2023
Manufacturers characterize their outboards with a dizzying array of ratings.
These include horsepower, equivalent horsepower, propulsive watts, input watts, shaft kW, motor
efficiency, propulsive efficiency, lb thrust, battery Ah, battery Wh, and so-on. Though these
ratings exist to compare outboards, each is only useful when comparing similar technologies.
No standard rating proposed to date can predict the performance on a specific boat in terms of
speed and run-time for all outboards. (see our paper on
Instead of using ratings that don't work, EP Carry offers an online speed
and range calculator that does. Just input your hull-type (see description), length and total
loaded weight, and the calculator gives you full throttle and half throttle speeds and ranges.
Results are usually within 5% but we guarantee that the results are accurate within 10%.
We realize that our unique approach on performance can complicate comparisons
to motors that use ratings instead. This report is intended to offer some insight into the
comparative performance of EP Carry vs. the increasing array of pod motors. This work was not
independently done. But it is an honest assessment within the stated scope and methods used.
The smallest electric outboards from Torqeedo, ePropulsion, Mercury, Newport etc.
all share the same "pod architecture". And according to their performance statements, and
according to independent reviews, they all appear to all have a quite similar propulsive effect vs
input power. The Torqeedo Travel 1003 is the most common portable electric so that's what we chose to
represent pod outboards in general. Speeds vs electrical input powers were measured when used on a
typical dinghy. Since we know the battery capacity for each model tested, input power also gives us
ranges at those speeds.
The closest competitor to EP Carry, in terms of propulsive power, cost and weight,
is the Torqeedo 603C. This motor's max-stated input power is 600W. Here's the result for that motor
vs EP Carry with its boosted power option.
EP Carry vs Torqeedo on a 9ft, 400lb Minto rowboat
Torqeedo 603C has a max input power rating of 600W. Speed and input power
results shown come from measuring the performance of a model 1003 at 600W, and ranges were calculated
using input power and battery capacity. If you want to know more about how to do this math, see our
paper on electrical concepts
is using its boosted power option in this example.
You might have been surprised to see that EP Carry provides similar top speeds and
ranges vs the Torqeedo while using significantly less input power and a much smaller battery. This
difference is a big part of why EP Carry is lighter and less expensive even though it is built in the
USA. So why does EP Carry need less input power?
Manufacturers who rely on ratings instead of speeds/ranges need to keep input power
high (the logic is: higher input power → higher rating → more sales). But EP Carry was designed to
provide optimal propulsive efficiency, which is the functional opposite of a high input power rating.
Following is a detailed test report that presents the measured relative
performance of three motors on a typical 9ft rowboat; an elevated architecture motor (EP Carry),
a high efficiency pod architecture motor (Torqeedo) and a trolling motor.
Summary of tests
that EP Carry is under the protection of issued US patents for our elevated motor design for small
electric outboards, our water lubricated gear case/ high aspect ratio boat propeller, and other
claims relevant to robustness and usability, and has patent pending on its closed-loop control
Summary of tests:
In this test, we measured the electrical input power needed to push a dinghy
(a 9' Minto rowboat) to various speeds for each of the three test motors; a Torqeedo 1003, a Minn
Kota Endura 30, and an EP Carry. Below is a graph of the results. Following the 4-knot line,
you can see that EP Carry uses 230W, and the Torqeedo uses 470W. The trolling motor can only
reach 3 knots at full-throttle. Instantly you can see that the Torqeedo is a significant
improvement on the trolling motor, as you would expect. But at 4 knots, EP Carry uses ½
the input power vs the Torqeedo.
This graph shows speed vs input
electrical power for each motor when used
on a small boat. Curves are best-fit lines from raw data. Correlation coefficients for these
best-fit lines are 0.99.
Relative Power Consumption:
If all three motors were paired with EP Carry's battery (288Wh of usable stored
energy), the EP Carry would provide ˜ 2x the range of the Torqeedo at 4 knots.
Ranges; Torqeedo 1003, Endura 30, EP Carry, all with a
Ranges of EP Carry (EPC),
Torqeedo 1003 (Torq) and the Endura 30 (Trolling) with a common battery capacity.
But the Torqeedo 603C comes with a much larger 500Wh battery.
As you can see, both the Torqeedo with its 500Wh battery and EP Carry with its 288Wh battery
provide a similar range at each speed.
Torqeedo 603C vs. EP Carry ranges with their standard
Ranges of EP Carry (EPC) with its 288Wh
battery and Torqeedo with its 500Wh battery.
It is interesting to note that a Torqeedo 1003 at 3.7x the
input power provides only ˜0.5 knots of additional speed vs EP Carry. This reflects an
efficiency difference between the two test motors in part, but it also illustrates that once a
boat's natural maximum speed range is reached; even multiples of additional input-power produce
little additional speed.
Top speeds and input powers for each motor.
|@ 254W input
|EP Carry, std pwr*
|@ 220W input
|EP Carry, high pwr*
|@ 270W input
|@ 1,000W input
* EP Carry
comes with a standard
220W input power limit. You can install a higher power limit of 270W using your smart phone–
See our firmware update
for more details. Our standard battery provides 70 minutes of run time using standard power
firmware, and 50 minutes using the high power firmware.
You may be aware that Torqeedo claims a peak propulsive efficiency of 48%
for the model 1003 tested. EP Carry's relative efficiency of 2x does not mean that EP Carry's
efficiency is 96%. It does mean that when used on a rowboat, Torqeedo's efficiency is
lower than its advertised peak propulsive efficiency. In other words; Torqeedo provides 48%
propulsive efficiency on some kind of boat, but not on small boats like the one tested. This is
one of the problems with efficiency ratings– read more in our ratings paper.
- The test boat was a 9ft rowboat (Minto) with one person aboard. Estimated bare boat weight:
120lb empty. Person weighs 210 lb. The Minto is shaped similarly to the Trinka,
Gig Harbor-Captains Gig, CLC's Tenderly, Portland Pudgy, Fatty knees, Dyer Dhow, Walker Bay, etc.
- EP Carry and its standard 288Wh battery: 14lb + 6.4lb = 20.4lb.
- Torqeedo 1013 long shaft with its 532Wh battery: 32.4lb.
- Minn Kota Endura 30 powered by a 12V, 245Wh K2 Energy Lithium battery. Measured weight 22.4 lb.
- Power was measured for EP Carry and the trolling motor using a Watt's–Up power meter.
Torqeedo measurements were taken from its integrated power meter.
- Speeds were measured using a Garmin hand held GPS, model GPS 12 with 0.1 knot resolution.
- Additional equipment aboard included a paddle, PFD and a dry-bag with
required safety equipment, wind meter, pen and notebook.
- Rattlesnake Lake in King County, WA, USA was used for all tests.
- The same boat and person were used for all tests.
- The Torqeedo battery had recently returned from a scheduled factory inspection. All motors
were inspected at the EP Carry factory to ensure correct operation before each test.
All batteries received a full-charge before each test.
- GPS had fresh batteries and the power meter was checked with a benchtop power supply.
- Gear and captain were positioned to ensure that trim was level at rest before each test.
- Torqeedo testing was done with both the Torqeedo setup and EP Carry setup aboard. Estimated
- Trolling motor testing was done with both the trolling motor setup and EP Carry setup
aboard. Estimated displacement: 378lb.
- All tests were done in light (barely perceptible) wind conditions from the East
(no reading on a wind-speed meter when at rest).
- No test data was taken while changing course.
- For each test, speed and power data was taken for each throttle setting.
- EP Carry and Torqeedo have continuously adjustable throttles; test point throttle
settings were roughly distributed throughout each motor's power range. The trolling motor
that has 5 discrete forward power settings.
- For each throttle setting, data was only recorded after boat speed and input power readings
remained steady for 15 seconds. Power and speed results were then recorded.
- An equal number of data points were taken traveling E to W, as for W to E.
Graph of individual data points collected for all motors tested. The EP Carry data set includes
points from two separate day's tests; one when it was compared to the trolling motor and one when
compared to Torqeedo. Consistent performance of the EP Carry on these two days indicates that a
comparison between Torqeedo and trolling motor performance is also valid.
Clearly, in these tests, EP Carry has proven more efficient than other motors tested, at least
for a 9ft. rowboat at just under 400 lb displacement. While we conducted this particular test on
only one boat, EP Carry has proven similarly efficient on everything from a 7.5ft CLC Eastport
pram kit, to a custom 1000lb 14ft solar boat.
In this discussion section, we explain how such a large efficiency gap is
possible. We'll start with resistance differences.
The Endura 30 motor (rated by 30 "lb thrust") could only drive
our 9' Minto rowboat to 3 knots. The total boat resistance at that speed is 7 lbf. Small-boats
are easier to drive than boaters have been led to believe.
Resistance vs. speed; Minto
Graph of total boat resistance vs. speed for a 9 ft Minto
rowboat at 400 lb displacement.
Interesting information in itself, but when total boat resistance is so
low, things like the drag forces from an outboard's lower-unit are more relevant than one may
Torqeedo and the trolling motor locate their electric motors in a
relatively large sealed underwater pod. So how much propulsive thrust is lost due to a pod design's
When the Endura 30 (propeller removed) pod and stanchion is pulled through
the water at 4 knots, the measured drag force is 4 lbf, which increases the total (boat + motor)
resistance by 29%. This must be overcome by additional propulsive power. Pod motors like
Torqeedo, Mercury, and others have a fairing to reduce stanchion drag. However, we did not measure
their resistances at 4 knots.
EP Carry's lower unit has a drag force of 0.8 lbf at 4 knots, which
calculates to 7W of lost propulsive power, or a 6% increase in resistance of boat + lower unit,
much lower than the resistance of the trolling motor pod.
If EP Carry produced a motor with its same propeller force output at 4
knots, but with a trolling motor pod design, than EP Carry would need 297W instead of 220 Watts to
drive this boat to 4 knots. This would reduce run time from 70 minutes to 52 minutes.
Pod motors require a shaft seal with friction losses. We have measured
20-100W of input power needed to overcome friction in pod motor shaft seals.
EP Carry has an elevated motor architecture like a typical gas outboard
but instead of an oil-filled gear case with seals, EP Carry uses the surrounding water so there
is no underwater seal at all. EP Carry's motor does have a seal in the motor head that draws 3
Watts of input electrical power at full-RPM operation.
A trolling motor propeller, like a gas outboard's propeller, is primarily
designed to allow the motor to reach its specified RPM under a range of conditions to keep the motor
from burning out. And what's good for maintaining high RPMs is not good for propulsive efficiency.
Compared to a gas motor propeller (Honda BF2.3) the EP Carry propeller
is more than twice as efficient at converting shaft power to propulsive power.
Typical "high efficiency" electrics use an efficient propeller
design when driving larger boats, but these designs also create higher propulsive power losses in
easier to drive applications like small boats when compared to EP Carry's high aspect ratio with a
larger disk area. Note that EP Carry's high aspect ratio propeller and water lubricated gear case are
With the trolling motor tested, partial throttle settings operate switches
that engage different coils submerged in the motor pod. This reduces speed at the expense of propulsive
efficiency. More expensive trolling motors are available with PWM controllers that are more efficient
at partial throttle settings but PWM attenuation does not influence the full-throttle trolling motor
performance as measured in this test. Some trolling motors are available with brushless pod designs
like the other electric outboards referenced in this article. While these increase efficiency
throughout the power range, they are not more efficient than the pod motors tested, and come at a
similarly high price.
High end electrics like the Torqeedo also use a PWM control approach.
But variable loads create variable power absorption levels that can cause an electric motor to
operate outside of its peak efficiency region. For example- during the test, I noticed that the
Torqeedo absorbed more power when accelerating than when at a constant speed.
EP Carry's closed-loop motor controller (pat pending) maintains the
requested input power level regardless of battery voltage or loading, which maintains motor efficiency
over a wider range of load variance and assures the same run-time at a fixed throttle setting regardless
of the load.
To conclude, differences in propeller, control methods, seals, underwater
resistance, and choice of power vs speed characteristics explain the performance differences measured
in this test.
Minto Dinghy: Weight:120 lb,
LOA: 9 ft.
EP Carry is installed in this image, with the trolling motor aboard awaiting its turn.
Minto dinghy with a Torqeedo 1003
installed. When raised, the
Torqeedo twists backwards like this due to battery weight. The EP Carry is barely visible in the bilge.
Minto dinghy with the trolling motor installed and EP Carry at the ready.
Watt's Up power meter (no longer available, unfortunately).
Garmin GPS 12 is the most accurate hand-held
GPS we have found. It produces 0.1 knot resolution.
Cutaway of EP Carry's motor-head
showing an all-aluminum motor housing, controller heat sink above, and cooling fan (under motor),
upper sealed shaft bearings, and electronics encapsulated in clear epoxy. The plastic housing
guides cooling air over the individually sealed motor and electronics. All connections in the motor
head are soldered and then potted in epoxy for robust waterproof service.
EP Carry on a CLC Eastport Pram, Port Townsend bay near Rat
Ferrying gear to the mothership before a winter drizzle-cruise. You can see that as loads increase,
EP Carry keeps things moving. Fisherman's bay, Lopez Island, WA
Two solar cruising boats in
Olympia WA. Electric Philosophy is a solar powered Sam Devlin cruising catamaran collaboratively
built with the owners Ed and Eileen Pauley. This boat has clocked thousands of solar-powered
nautical miles In the Salish Sea and along the inside passage and can recharge faster from its
giant array than from dockside power.
EP Carry on a Takacat
at the Anacortes Boat Show, WA
Sunnyside is a 14' home-built
camp cruiser for two. Cruise displacement is 1,000lb. Sunnyside was built to conduct long
distance reliability testing (its hard work, but someone has to do it). Sunnyside's EP Carry-powered
top speed is 4.2 knots, but she has traveled up to 38 nm in a day using her roof-mounted 300W solar
array. Even on week-long cruises, she has never needed to recharge from dockside power.
Evening at anchor along the
Salish 100 cruise route.
Sunnyside's EP Carry has rope steering and a remote throttle setup, which is available as a
Throttle with forward and reverse, emergency key, steering and motor tilt all work remotely.
Swe'Pea is a 14 ft solar-powered
runabout based on a 1960s hot-molded International 14 hull using the same motor now used on Sunnyside.
This picture of Swe'Pea was taken by John Kohnen during the 2019 Salish 100 cruise. Sunnyside was
captured here in a small trough, heading north against a waning southward tide and with
following winds, just north of Kingston WA. At this point, the motor was using only 70W of
input power from two 100W solar panels in overcast conditions, yet she was traveling 2.8 knots
against the tide.
This particular EP Carry, made spring 2018, has clocked over 600nm driving these two boats
that each represent the largest and heaviest recommended for an EP Carry outboard. Most travel
has been in the Salish Sea, through calms, sun, rain, rips, winds, tides and powerboat wakes, and
this motor has even towed several disabled boats (up to 6,000lb displacement) to safety.
We know of other EP Carry units with high mileage, also powered using onboard solar. Smaller boats
are easier to power with solar vs larger boats due to a square-cube law relating resistance to solar
area. Sunnyside and Swe'Pea are able to cruise 10hrs a day at 80% of hull-speed using relatively small
200W or 300W arrays. This is possible because when compared to other "high-efficiency" electrics,
EP Carry needs only a fraction of the solar collector area for a given speed.
Sunnyside gets the royal
treatment in Anacortes WA.