What size inverter?

a 1500W load will draw nearer 150 Amps given the efficiency of most inverters; also you'd probably want to not discharge the batt's below say 50% to keep the life reasonable ( unless you buy something very flash/expensive... and they are as good as claimed- hmm) .

a leccy blanket, sure; I've used mine to heat the water via an immersion before now ( yes, about 1500W ) so an hour tops still leaves plenty for the things you really bought an inverter for ( I've got abt 700AH total service capacity ).

Overall, I tend to agree with many others, not to rely on it for actual heating, likely you'll spend more on speccing it sufficiently for that than you would getting a better or secondary heating system.

Victron or mastervolt in a sinewave inverter/charger'd be my choice if speccing from scratch; note that inverter manufacturers vary somewhat in their description of say a 3KW output- some'll run this power even at typical ambient eng room temps, many won't - some will run start-up loads of perhaps 5KW+ & well over 3KW for quite some time....again, others won't. The makers I mentioned aren't as I recall especially generous in their specs, I just like their gear. pointing really to ensure that you buy gig.carefully enough to operate what you want it to.

Get cheap superflex or regular high current cable/lugs from Furneaux riddall if you're diy'ing, cheaper still from http://www.beal.org.uk/ . I've a giant crimp tool if you need it, or they're abt £100+. if you're running big loads, don't waste power in cables.


ahh, and shop around for prices as always, Victron & mastervolt vary widely in the uk, from full-retail to 30+% off last time I looked.
 
An inverter supplying a 500W appliance will draw approx 50 AH, so will completely drain a 140 AH battery in three hours... but as you do not get 100% of a battery at all levels of charge, in reality you will drain it much quicker... even when battery bank is multiplied by three, or even four.

A much better choice would be to have a genny supplying your 220V needs and have a small inverter running for your laptop needs.... or even a small £30 inverter from Maplin to supply your laptop requirement fro 12 to abot 19V
 
Spent a lot of time looking for a suitable genny. At the end of the day it really depends on your usage; I reckon the "right" genset would have set me back 4-5 grand(!!), and in reality I will generally use the boat for evenings and weekends, with the very occasional longer cruise. I am lucky enough to moor her at the foot of the garden, so shore power is not an issue. I think the "pukka" genny would be overkill for my usage, but agree, essential to spend longer periods on board.
 
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