Had this exact headache last summer on a two-week trip up the Llangollen. Alternator just couldn't keep the domestic bank topped up with the compressor fridge cycling all day, especially on slower stretches where the engine wasn't working hard.
Ended up going down the B2B charger route (Victron Orion-Tr Smart 30A) rather than swapping the alternator outright. Massively improved charge efficiency from the starter battery side and didn't have to touch the engine setup. Worth considering if you're not keen on the mechanical faff.
That said, if you're doing longer continuous passages it might genuinely be worth looking at:
- Higher output alternator — some folks fit a 100A+ unit but you need to check your engine can handle the parasitic load
- Sterling Power alternator-to-battery charger — popular on narrowboats, handles the charge curve properly
- Supplementing with solar — even 200W on the roof makes a dent when you're moored up overnight
What's your current alternator rating and domestic bank size? Makes a big difference to whether an upgrade is actually worth the cost. Mine's a 70Ah Fogstar Drift LiFePO4 bank now which accepts charge faster than the old AGMs ever did, so the B2B actually gets used properly.
Anyone else running a dedicated high-output alternator on a canal boat? Curious whether the engine strain is actually an issue in practice or just theoretical.
