there are some commercial solutions, like
Products | GreenStar Marine
Their largest engine has been used on boats up to 40 ft.
Major drawback of electrical engines is the difficulty and limitation of energy storage. This leads to a limited range, and to a somewhat lower power compared to diesels. In itself this is not any show stopper as long as one is aware of it - you state you only wnat to use the engine when mooring etc - should work fine then.
Hi, My name is Oscar Théen and I work at GreenStar Marine. I found our company name on this forum and I thought that a short comment would be in place.
When you come to choosing between a traditional diesel solution and an electric solution you must ask yourself what you actually want of your motor/engine. A diesel solution is for some the best choice and the electric one is better for others.
The electric solution is best for those who prioritize high torque, maneuverability, availability, low maintenance, simplicity, quietness etc. The diesel is best for those who prioritize long transportations at high speed.
Pure plugin boats with our systems usually have a calm weather range at 4 knots of around 30 NM. Full speed is usually around 6 knots. Range at full speed and AGM lead batteries is usually around 6 NM.
We have never installed a system in an Islander 36 but we have installed systems in several boats of similar size and weight. For an Islander 36 I would recommend something like:
Greenstar system: GS18
Battery bank: 8 * GS12-100 Deep Cycle AGM lead batteries
Estimated economy speed: 3 ½ knots in 9 ¾ hours
Estimated full speed: 6 knots in 80 minutes
Note 1. Economy speed for the Islander 36 is probably a bit lower than for the average boat. Economy speed can be increased by changing propeller but that will cost thrust. If a bigger propeller, both in terms of pitch and diameter were to be used there is a risk of overheating the motor at full speed.
Note 2. Runtimes in the Islander example are with batteries that are run absolutely flat which is not recommended. This can be done in case of ”emergency” but usually you should not use more than 50 % of this.