You're right, it's big, bloody big in fact at 4.5 kg it's overkill on your tiny boat. Are you sure that the lead isn't just for the 24 volt DC light?
Information is very scarce on the net for this brand even though they are still very much in business. you could try an email to the company and hope that someone understands English and will respond to your request.
For what it's worth here's the company site
www.783.to/ email to here
[email protected]Good luck