HOT TOPICS
Topics of interest to boat builders, repairers and owners. Subjects discussed by boating groups and forums.
On this page are issues that cause a lot of discussion pro and con in the boating community. These are my opinions. As with most things, there are two sides to every issue. I hope that these will give you food for thought and maybe contribute to a better understanding of the issues involved.
I will also post links to other online discussions or information on the subject. These will be included in the article or immediately below the article.
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Electric Propulsion and Lithium Batteries
The hottest topic in todays boating world is electric propulsion. Everyday someone, somewhere, introduces a new boat powered by electricity. Some are inboards, some outboards, some jets, some have hydrofoils. Every kind of imaginable watercraft, from stand up, one person hydrofoil jet boards to big yachts. It's all the rage. But you can't talk about electric propulsion, no matter how big or small, without talking about the source of the electricity, lithium batteries.
A system using Lithium batteries needs to be designed from the ground up, to maximize the power and range, and to prevent over loading, overheating and fires, and to provide the shortest possible recharge times.
ABYC has developed standards for Lithium Batteries and electric propulsion systems. For more Information Contact ABYC at abycinc.org and purchase a copy of E-13 Lithium Batteries and E-30 Electric Propulsion Systems. In addition to the ABYC E-13 and E-30 Standards there are Underwriters Laboratories (UL) Standards, IEC Standards and SAE standards for Lithium batteries and installations. All of these are referenced in the ABYC standard.
The U.S. Coast Guard has published a policy letter regarding standards for Flotation, Safe Loading and Maximum Horsepower ratings on boats with electric propulsion. Essentially the policy letter says that manufacturers of electric propulsion recreational boats should comply with the same standards for Safe Loading, Flotation, and Safe horsepower as gasoline powered recreational boats and refers to ABYC Standard E-30 for Boats with Electric Propulsion. The policy letter can be seen at the Coast Guard's website at https://safeafloat.com/wp-content/uploads/2022/08/BSX-23-Electric-Propulsion-Policy-FINAL.pdf
There are electric outboards on the market ranging from trolling motors which are less than 1 horsepower, to much more powerful outboards such as Axopar 25 with the Evoy Storm Electric outboard, rated 300 Horsepower. 11,000 Watts is about 15 horsepower. 300 HP is in the range of 220KW. So it takes a lot of watts to generate horsepower. Electric drives have also entered the sailing world. Yanmar has a drop-in saildrive rated at 15KW, replacement for their engines.
As with gasoline powered engines, how your engine performs is dependent on the size and weight of the boat, and the type of boat. Here is a link to a converter from Watts to horsepower. https://www.unitconverters.net/power/watts-to-hp.htm
The more powerful the motor is, the more batteries you need to power it. The other consideration is weight. If you use 12V marine lead acid batteries, which can weigh up to fifty pounds (22.7 KG), the weight can be considerable. If you use 12V lithium batteries, which weigh about half as much, the weight is reduced considerably. But lithium electrical systems are more complex than lead acid systems. See Batteries.
There are two categories to consider: inboard electric motors and electric outboards,.
Inboard Electric propulsion:
Electric propulsion boats have been around a long time. ELCO has been in business for 130 years (https://www.elcomotoryachts.com/) so inboard electric propulsion is nothing new. Even large commercial and naval vessels have used electric propulsion. It was called diesel electric. That is, generators were driven by diesel engines. The resulting electricity was used to drive large electric motors which drove the propellers. Probably the most common use of this was submarines. Today we call this a hybrid system. But electric recreational boats have almost always used batteries. Until the advent of lithium batteries, this has almost always been lead acid batteries. This required long charging hours and added a lot of weight to the boat. This resulted in restricted use of the boat, and slow speeds. The features of lithium batteries, light weight and longer amp-hours, along with better design of small electric motors, has made it possible to power boats for much longer times and achieve much higher speeds. In the last twenty years or so the boating market has seen higher power outboards being introduced, such as Torqeedo and lately the Evoy Spirit, featured by Axopar. This has resulted in planing boats being able to achieve speeds comparable to gas outboards.
Power Sources: (battery banks) Battery banks are multiple batteries hooked up together in series and parallel to provide the voltage and watts, and the amp-hours to power the motor. Battery banks are two or more batteries connected in series or parallel, to increase the amount of power available, or make it last longer. See https://newboatbuilders.com/pages/electricity3.html and https://newboatbuilders.com/pages/electricity4.html to explain battery types and series/parallel circuits.
When planning for electric propulsion you need to determine the size of your battery bank, and how long power will last. To learn how to size your battery bank go to my page on Electric Propulsion
Critical Decisions to be made in selecting how to power your boats:
Safety: Safety is paramount. Having a safe electrical system and batteries is all important. This involves selecting the right type of batteries and selecting a low voltage system. Currently, 48 Volts appears to be the system of choice. The voltage is low enough to reduce the danger of shock and fires, but high enough to deliver the performance and reliability needed. There a many types of Lithium batteries but at the time of this writing LiFePO4 are the batteries of choice for boats as they present the least danger of thermal runaway, yet are reliable and able to deliver the needed perfomance. The Battery Management System is very critical to the battery's performance. You can chose an internal BMS built into the battery, or an external BMS. Both can do the job.
When I speak of performance I am not talking about speed alone. Reliability, longer Watt Hours, as well as speed are important. As I have said before, this is not a time to cut corners. Spending more will result in a longer lasting, safer, and better performing system.
Other Standards: Standards for Electric Propulsion boats, for Flotation, Safe Loading and Maximum Horsepower Ratings.
Links to Other Pages having information for Electric Propulsion Boat Manufacturers
Other standards that may be applicable to boats with electric propulsion.
References:
Lithium Ion Batteries on Wikipedia. https://en.wikipedia.org/wiki/Lithium-ion_battery
List of Battery Types; Containing a list of Lithium Battery Types. https://en.wikipedia.org/wiki/List_of_battery_types
Battery University; List of Lithium Battery Types and their uses. https://batteryuniversity.com/article/bu-205-types-of-lithium-ion
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