Criteria for best electric drive system for sailboats
In our first blog on electric sailboat conversion we described our initial criteria for an electrical drive system. First of all we want to reduce the drag. In addition we want to use the propeller for regeneration of the batteries. Regeneration of electricity under sail is the Holy Grail of electrical propulsion. However the problem is that the propeller must be small to minimize drag, and large for regenerating the batteries. Because it takes a lot force to make the electric motor rotate. Expensive three blade folding propellers alleviate this partially the regeneration performance of folding propellers is under debate.
Boat speed and autonomy are a function of the efficiency of the electrical BLDC motor (3W-7kW) and the battery package (Lithium Ion Phosphate LiFePO4). We set our minimum specifications for the electric motor and the batteries in a prior blog post.
Especially relevant is the fact that BarcelonaSail is a commercial sailboat tour operator. Therefor it is important to have easy access to the entire electrical drive system. Consequently we focus on an electric drive system for sailboats that allows access to all parts of the system. Furthermore we want the electric BLDC motor inside the boat, in other words, an inboard motor system.
In conclusion we believe that the best electric drive system for sailboats is an inboard motor system that eliminates hydrodynamic drag under sail, therefor solves drag versus regeneration and is easily accessible for maintenance. In addition we believe that the installation of electric BLDC motor should be possible without the need to create more holes in the boat and have a specialist involved.
Best electric drive system for sailboats
Our solution can be best described as an electric propulsion system for sailboats with the reliability of an inboard motor, but the flexibility of an outboard motor. That means easy access for maintenance, flexibility, no additional drag and most noteworthy low costs. Let’s look how we designed it.
Drag vs Regeneration
Best electric drive system for sailboats solves the paradox between drag and regeneration problem, our solution does this via the rotation of the propeller section out of the water when regeneration is not required.
Easy access and no more holes in the boat
Best electric drive system for sailboats uses the existing transom exhaust opening, offering an easy low cost installation without making additional holes in the hull.
Existing transom exhaust opening is used to connect the inboard electrical motor with the carbon propeller shaft. Regenerating when under sail.
Very efficient simple electric drive system
Sail-drive, pod-drive, shaft-drives and outboard-drive propulsion systems loose mechanical efficiency with the use of traditional gearboxes, universal joints and bevel gears.
Best electric drive system for sailboats uses a direct drive with an elegant first-principles system of gearing to minimize mechanical losses in the transfer of power to the propeller.
How the electric drive system works
The design team uses the exhaust opening to connect the carbon propeller arm with the electric BLDC motor. Especially relevant is the fact that this specific design is under investigation for an IP. Rotating the carbon shaft 90 degrees to reduce drag is easy. The carbon shaft is very light and hollow. The inside space is used for gear reduction to increase the torque at the propeller.
This green and simple solution exists basically of two components: one, the propeller with the propeller arm outside, and two, the electric BLDC motor system inside. An IKEA ready package for boats between 7 and 13 meter will be available late 2017 according to the designers.
Remove propeller out of the water to minimize drag.
Benefits of this system
- No additional openings required in the hull.
- Simple rotating connection between the transom and the propeller arm using the existing exhaust outlet.
- In board motor with the ability to eliminate hydrodynamic drag that the electric sail-drive, pod-drive and shaft-drive propulsion systems cannot.
- No motor shaft issues.
- Minimal mechanical efficiency losses with direct gearing.
- Fast, easy and cheap maintenance.
- Easy and low cost installation.
- Flexible design fits all boats between 7 and 13 meters.
We believe that with this solution we can make the world of electric propulsion for sailboats more accessible to a wider range of boat owners.
