Basically all of it! The motors are wired for 24V, the glow plug and all the electronics. It is possible to run it by feeding the whole thing from a 12-24V DC/DC converter, though.
Years ago I bought a 24V eber from ebay. They are cheap compared to the 12V versions. In the end I decided that it was just too much hassle trying to run a 24V one on a 12V boat so resold it on ebay.
Depends on how big your boat is. I would just buy 2 X 12 Volt Batteries, wire them up so they give 24V and you have the answer. (Is it called Series or Parallel) Also you have another 2 Back Up Batteries.
That is an ancient model £175 is very expensive for 24 v.
I have used DC converters on several 24 ebers and they have worked well. You would need a powerfull converter for that model though, probably £100 plus
I bought a 24v Webasto off ebay and also got a 12v>=24v 10 amp converter. Runs absolutely fine, just plumb in the converter prior to the heater unit and a 12v supply to converter and Bob's your auntie as they say!
Summers coming.Panic buying of diesel heaters starts to fade.
Bought my 12v d3 off ebay for £100.00 came with a few bits.Bought minitimer for £35.00.
Hotair trunking from caravan shop at about £8.00 a meter.
Entire install in 36ft boat about £250 ish including buying diesel pipe feed and stainless exhaustpipe from cheapo oufit in Turkey.
Made up exhaust skin fittng from old bronze boat skin fitting and van outlet for nothing