Re: Would anybody be interested in an electric outboard like this?
Let me clarify a few points. I started Pure Watercraft, the company that the OP was studying. This project was for a UW entrepreneurship class, and the students came here to this forum to find out what the market thought. This was not posted by Pure Watercraft or anyone working on our behalf. Our system is in engineering prototype stage, not yet in production.
Some of the details they posted were right, and some were not. I want to make sure we leave this forum with the right info, directly from the source.
Our motor is rated at 20 kW continuous power. That translates directly to 26.8 HP; however, our prop is indeed more efficient than existing props, so it gets more propulsion than a gas motor of the same power. (Reasons: gas outboards run ~ 3000 RPM, while we run ~ 1500 RPM, with larger diameter prop, and we have full torque starting at 0 RPM, while gas motors have very narrow RPM zones in which they reach rated torque. Proof: we consistently outrun boats with 30 HP gas outboards, both from a dead stop and at top continuous speed. Gas motors would use more efficient props, too, if they would work well at both low and high speed, but they would not, because of the very low torque gas motors produce at low RPMs.)
We will market our outboard at different power levels, because there are distinct markets for them; however, it will be the same motor inside. So if you get the 9.9 HP version, you can run on lakes that limit power to < 10 HP and be legal, but get more propulsion than others with 9.9 HP gas outboards.
Our outboard does not go full throttle for 3 hours (without an inordinate volume of batteries). With a single battery pack it can go 27 minutes at 12 kW, and with two battery packs it can go 33 minutes at 20 kW.
If you use two battery packs, and go for 3 hours at constant power, using the full usable capacity, you'll be using about 3.7 kW, which is about 5 HP, and the propulsion would be equivalent to about 6-7 HP from a gas outboard. With a low-wake launch, we go about 10 mph at that power. So our range with that hull is about 30 miles with 2 battery packs running at 3.7 kW. Your speed at that power would depend on your hull, of course, and I'm sure nearly everyone on this forum knows exactly how fast they would go at that power.
Our motor works exclusively with our own battery packs. We focus exclusively on high performance systems; there is no sense in combining our very high power density motor with very low energy density batteries (especially because our voltage would drive an impractical setup of 12V batteries). Our packs can be combined for larger capacity. Using our own packs exclusively allows us to run more safely, as we can ensure affirmative communication between battery pack and motor in every case, and prevent running under adverse battery pack conditions.
Our battery packs have nominal capacity of 6 kWh and usable capacity of about 5.5 kWh. Voltage is 350V, which allows us to achieve much higher power density than other electric outboards (more than double that of the lower-voltage Torqeedos, for example). In prototype, our battery packs weigh 99 lbs, but we expect that the production version should weigh less (maybe 85 lbs?).
For those who compare our energy density to that of LiFePo4, ours is better, because Li-NMC is an inherently more energy dense chemistry. We include a thermal limiting material in our battery packs to ensure they keep at a healthy temperature.
We have two chargers: 120V 1 kW, and 240V 10 kW. The math on charging times is pretty straightforward; if you use 2/3 of a 12 kWh system (two battery packs), then using our 1 kW charger, it will take about 8 hours to nearly fully recharge (there is some additional time at the end to balance the cells). Our packs have a charging speed limit of 1/2 of their capacity per hour (to preserve battery health and cycle life), so even with our 10 kW charger, you could only charge at 6 kW if you were using two of our battery packs. The chargers can each charge multiple boats and battery packs at once.
It weighs 91.8 lbs in prototype, and should weigh about 15 lbs less in production. The motor is in-line with the 8:1 gear set and the prop, underwater, so the noise is very low. Its efficiency is very high, partly due to the high voltage, which leads to lower current and lower heat losses.
TOTAL SYSTEM WEIGHT
Our minimum total system weight in prototype is 190 lbs, and in production we expect it to be about 160 lbs. With two battery packs (which is the minimum configuration to get our total rated power of 20 kW), our system weight is 289 lbs in prototype, or expected weight of about 245 lbs in production.
For comparison, an equivalent power gas motor to our minimum configuration is 15 HP. The Honda 15 HP weighs 104 lbs. Add a 33 lb starter battery and filled 3 gallon gas tank (20 lbs) and you get a total system weight of about 157 lbs. So our production system is at virtual weight parity (albeit shorter range).
An equivalent gas motor to our 2-pack configuration is 30-40 HP. The Honda 30 HP weighs 160 lbs. Add a 33 lb starter battery and filled 6 gallon tank (40 lbs) and you get a total system weight of about 233 lbs. So our production system is about 12 lbs more (but again, lower range).
In each case, it's important to note that our weight comes mainly from the battery packs, so the transom weight is much less than with a gas outboard.
It's true that we use a low-wake, efficient hull for testing. Batteries are expensive, so investing in an efficient hull makes a lot of sense when it reduces the capital cost and weight of the power train. It's a realistic hull for many of our customers. We've also tested our system on a 15' rigid inflatable (RIB), and it worked very well.
It's a great motor for regular use, and for low to moderate range. As some pointed out, lakes are great, because there is a well-known limit to how far you'd need to go. This is not the best motor for going long distances infrequently (unless you place a very high premium on quiet operation or zero emissions, such as on bodies of water that prohibit internal combustion engines). For those who nearly always run at low to moderate range, but have to go a long distance once a year, it might be worth switching to a gas outboard for that one outing, and keeping the vast majority of outings quiet and clean.
Daily boaters who use outboards often experience hearing loss. Rowing coaches, for example, experience very high rates of hearing loss due to prolonged exposure to outboard motor noise over a number of years. Some tell us they've lost 20-50% of their hearing. They crave a system that will allow them to be on the water every day and focus on what they do, without losing their hearing in the process.
This is not for every application, but for some, it will be just right. As batteries improve (about 7% improvement per year in energy density and cost), the range of appropriate applications will grow.
We have not announced a price; however, we have said our battery packs should cost around $1/Wh (about the same cost per Wh as the Torqeedo battery pack), and that our outboard should cost a little more than a conventional gas outboard (which means more, but less than double). I'm sorry I can't be more precise at this time.
A few on this forum have remarked that they would not pre-order without knowing a final price. That's a valid point, and not everyone should pre-order. Like Tesla, we take pre-orders before we know the final cost of our production system. (Tesla took thousands of pre-orders for the Model S before announcing a price, and before having produced a volume car.) The deposits are fully refundable for any reason (or no reason). Pre-orders help us gauge volume, which is a key input into cost. We can get more conventional financing, and make more rational purchases of parts, when we have a good idea of volume. So with pre-orders, our costs are reduced, which allows us to sell a better product at a lower price.