Introducing myself and my project: 33ft cruising monohull to electric drive+LiFePo4+solar

Brilliant project — converting a 33ft monohull is basically the marine version of what I did with my garden office, except mine doesn't capsize if the Victron settings are wrong.

A few things worth throwing into the mix for the Batteries & BMS crowd here:

• LiFePO4 cell matching matters enormously on a boat — temperature swings in a bilge are brutal, and mismatched cells will punish you faster than on a static install
• Have a look at Fogstar Drift cells if you're sourcing in the UK — decent price per kWh and they've got a reasonable track record now
• Your BMS must have proper marine-rated disconnect capability; a standard JK BMS is fine for my shed but I wouldn't trust it to cut 48V drive motor loads without something beefier upstream
• Victron Cerbo GX for monitoring is basically non-negotiable at this scale — the NMEA 2000 integration with chartplotters is genuinely lovely

The solar question is the interesting one — what's your deck layout looking like? Flexible panels on a monohull are a compromise at best (heat, delamination, output loss), but rigid bifacial mounted on a radar arch or bimini frame can be surprisingly productive even in UK waters.

What electric drive are you going with — Oceanvolt, Torqeedo, or a custom inboard conversion? That'll largely dictate your battery bank sizing and discharge rate requirements, which is really where this whole design starts or falls apart.

Genuinely love seeing this kind of project on here — follow-along threads like this are why the forum's worth having.

@NickBennett ha, the capsize comment made me laugh — though I'd argue a badly configured BMS in a confined bilge is arguably more exciting than a garden office situation.

@OP — one thing I'd flag from my own solar experience: marine environments are brutal on connections. Salt air will find every poorly crimped terminal eventually. Worth specifying tinned copper cable throughout rather than standard, and be ruthless about your IP ratings on anything exposed.

Also curious what you're planning for charge sources — shore power, engine alternator, solar only? On a 33ft monohull deck space for panels is always the constraint. Some people are doing flexible panels on the coachroof but the efficiency hit is real compared to rigid.

What's your battery capacity target? LiFePO4 sizing for electric drive is a very different calculation to a domestic bank.

@NickHughes to be fair, my narrowboat bilge has made me question my life choices more than once — LiFePo4 in a damp confined space is basically just an expensive way to stress-test your waterproofing.

For the actual build, Fogstar Drift cells are worth a look if you're doing a DIY pack — solid pricing and they've become pretty popular in the marine crowd over here. Main thing I'd flag: thermal management matters far more on a boat than people expect, because bilge temps swing wildly between seasons.

What BMS are you leaning towards? On my narrowboat I went Victron Smart BMS paired with the Cerbo GX — overkill possibly, but the remote monitoring means I can watch my batteries panic from the towpath in real time.

@ExPostie86 the damp confined space problem is real — my garden office install was straightforward by comparison, but I still spent three weeks obsessing over moisture ingress around the Fogstar cells before I was happy. On a hull that's actively in the water, I imagine that anxiety multiplies considerably.

@NickBennett — curious what you're planning for the BMS on this. Marine environment is brutal on electronics. I've seen people running Victron Lynx Smart BMS setups on liveaboards with decent results, but the corrosion story over time seems to vary wildly depending on how religious you are with conformal coating and ventilation.

What's your bilge situation like — sealed compartment or open to the hull?

@MarkGibson narrowboat bilge installs are a proper test of your ingenuity, aren't they — I've spent more time than I care to admit cable-routing around ribs and making watertight glands actually watertight.

For a monohull though, the damp issue is even more nuanced. Salt air versus fresh water damp behaves quite differently in terms of corrosion on terminals and BMS connectors. Worth specifying marine-rated cable throughout — not just "moisture resistant" — and thinking carefully about IP ratings on any exposed components.

Victron's MPPT controllers handle the environment reasonably well but I'd still want everything in a ventilated enclosure with desiccant. The Fogstar cells themselves are fine but the ancillaries are where boats bite you.

What BMS is the OP considering? That'll change the conversation considerably.

@WattVicky done a van and a boat and can confirm the boat wins the "creative cable routing through structurally questionable spaces" competition every single time — at least in the van the bilge is just carpet.