# How Much Power Is Needed for Large Sailboats?

#### August 16, 2022

Whether you like it or not, electric boats are gradually becoming a thing. As governments plan to incentivise electric boats, the need for electric motor boats will soon become as popular as their diesel- or gas-powered counterparts. This steady rise of electric boats is mainly due to necessity and practicality, among other things.

For this reason, some boat owners, especially those who own large sailboats, are planning on replacing their fossil fuel-guzzling engines with electric inboard motors. Having said that, some boaters wonder if a 100 kW electric inboard motor would suffice or if it is too much.

But before boaters even start replacing their engines, are there factors that they should be aware of or concerned about before getting an electric inboard motor? This article will clarify some concerns you might encounter or ponder if you are planning on switching from a combustion engine to an electric inboard boat motor.

## Calculating the Required HP for your Boat

When determining the power needed for your boat, you will need to find out its hull displacement in displacement lbs (displacement per pound). Technically, the boat's weight is the same as the amount of water it displaces when afloat.

### What is Hull Displacement?

Simply put, hull displacement refers to the amount of water the boat displaces or the weight of the boat itself. On the same note, if you calculate the boat's overall weight when loaded, you are determining its maximum hull displacement.

#### The formula for Boat Propulsion Power

No matter what type of boat you own, calculating how much power is required to propel your boat forward is based on this formula: HP (Horsepower) = displacement lbs / 550.

With this formula, you need 1 HP per 550 displacement lb. Therefore, if you have 2200 lbs, you need 4 HP. Since we are dealing with a large sailboat, which averages around 8800 lbs, your electric inboard boat motor should produce around 16 HP.

Below is a table of different sailboat weights and lengths and their corresponding HP requirement. You may use the list as a guide but be reminded that this is only a close approximation since the figures for the HP are rounded off. Apart from that, the weight and length of one boat vary significantly compared to another.

Boat Weight Average Boat Length Corresponding HP
1,000 lbs 18' 1-2 HP
2,000 lbs 20' 4 HP
3,000 lbs 22' 6 HP
4,000 lbs 24' 8 HP
5,000 lbs 26' 9 HP
6,000 lbs 26' 11 HP
7,000 lbs 27' 13 HP
8,000 lbs 28' 15 HP
10,000 lbs 30' 18 HP
12,000 lbs 32' 22 HP
15,000 lbs 36' 28 HP
18,000 lbs 40' 34 HP

Source: www.improvesailing.com

## Things to Consider Before Getting an Electric Inboard Motor

Changing your combustion engine to an electric motor is relatively safe. Some boat owners do this using DIY conversion kits. If you plan on doing the same, you should consider certain factors, especially if you fancy a high-powered engine, such as a 100 kW electric inboard motor.

### Max HP Capacity

Knowing the vessel's speed and power limit is crucial, whether you own a bluewater cruiser or a powerboat. For safety reasons, boat manufacturers indicate the amount of maximum HP required for your boat in the user manual.

Check your capacity plate, which indicates its max gross load, number of passengers aboard, etc. You can find the plate near the transom or steering area of the boat.

### Purpose and Usage

For obvious reasons, you would not get a 100 kW electric inboard boat motor if you plan on using your boat for cruising along the shore with family or friends. This type of electric inboard motor will be ideal for a large sailboat or sailing yacht that has a hull weight of, say, 30,000 lbs or thereabouts.

### State Regulations

Mounting a high-powered electric inboard motor in your boat is illegal because you could also endanger your life and others within the area. Make sure that your electric inboard motor does not exceed the amount provided in the capacity plate to avoid getting into trouble with law enforcement personnel.

## Features of an Electric Inboard Boat Motor

Since these newer, eco-friendly models are different from the combustion engine, performance-wise, it will be wise to consider some of the significant features of an electric inboard motor. Some of the factors that you should take into account to know more about electric inboard boat motors are as follows:

### Rated Power

Depending on the brand and model, electric inboard boat motors have a rated peak power that ranges from 75 kW to 330 kW. The higher the kW consumption, the faster your boat goes. So if you mount a 100kW electric inboard motor in an 8,000-lb sailboat with a length of 29 ft, your boat could cruise at over 200 knots. However, some factors can affect the overall speed, such as resistance, windage, and even the design of the hull.

### Torque

Electric inboard motors have high torque at low-end power because they have a maximum torque output ranging from 30 Nm (Newton-metres) to an impressive 3400 Nm. Again, the torque output of a particular electric inboard motor depends on the model or brand.

### DIY Conversion Kits

Some manufacturers offer electric inboard boat motors DIY conversion kits. Boaters prefer these kits because they are significantly more cost-efficient than purchasing a new electric boat. You can find some of these conversion kits on the market.

### Components and Other Features

Typically, an electric inboard boat motor would include the following parts and capabilities:

• Batteries have monitoring systems that display real-time range and capacity
• All system components are waterproof
• Hydro regeneration capability
• Onboard computer display with touchscreen capability
• Remote throttle control

## Conclusion

If you want an electric inboard motor for your large sailboat, you should first compute the required power to propel the vessel at preferred speeds. Before calculating how much power you need, you should first determine the weight of your boat, which is expressed in displacement lb, and divide that by 550. With this formula, you will get the total horsepower that your electric motor should produce.

Before installing a DIY electric motor conversion kit (if you plan on getting one), you should first determine the maximum capacity, state regulations, and how you will use the boat. Also, the specifications of electric inboard motors may vary from one another. Once you have found the proper electric motor that suits your boat's hull displacement and overall capacity, it will be smooth-sailing from here onwards.

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Carlos Diaz
I believe in making the impossible possible because there’s no fun in giving up. Travel, design, fashion and current trends in the field of industrial construction are topics that I enjoy writing about.
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