Catalina 36 Weekend Cruiser — Lithium Conversion
sailboat · 12V system · San Diego, CA
36-foot sailboat retrofit from flooded lead-acid to 400Ah LiFePO4. Coastal cruising out of San Diego, weekend passages with 2-3 nights at anchor. Goal: eliminate the nightly engine run to recharge AGMs while keeping the chartplotter, reefer, and anchor light up until morning.
Daily load
1,747 Wh
Daily Ah
146 Ah
Battery
400 Ah LiFePO4
Solar
600 W
Load budget
| Load | Watts | Qty | Hrs/Day | Wh/Day |
|---|---|---|---|---|
| 12V Marine Fridge | 45 | 1 | 16 | 720 |
| Anchor LightCRITICAL | 10 | 1 | 10 | 100 |
| VHF Radio (Standby)CRITICAL | 5 | 1 | 24 | 120 |
| Chartplotter | 25 | 1 | 4 | 100 |
| Depth Sounder | 10 | 1 | 4 | 40 |
| AIS TransponderCRITICAL | 5 | 1 | 24 | 120 |
| LED Cabin Light | 5 | 4 | 4 | 80 |
| Freshwater Pump | 60 | 1 | 0.5 | 30 |
| Bilge PumpCRITICAL | 30 | 1 | 0.3 | 9 |
| Laptop | 60 | 1 | 3 | 180 |
| Phone Charger | 10 | 2 | 3 | 60 |
| Autopilot | 40 | 1 | 2 | 80 |
| Interior LED Strip | 12 | 1 | 4 | 48 |
| Hatch Fan | 10 | 1 | 6 | 60 |
Battery bank
2 × 200Ah in parallel
Your daily consumption is 146Ah. With 2 days of autonomy, you need 291Ah of usable capacity. LiFePO4 (Lithium Iron Phosphate) batteries should only be discharged to 80% depth of discharge, so you need 364Ah of total capacity. We recommend a 400Ah bank (2 × 200Ah in parallel), giving you 320Ah of usable capacity — enough for 2 days without any charging.
Solar array
3 × 200W panels · 63A charge controller
Your daily consumption is 1747Wh. With 5.5 peak sun hours, a 75% system efficiency factor, and LiFePO4 (Lithium Iron Phosphate) round-trip efficiency of 96%, you need 441W of solar panels. We recommend 3 × 200W panels (600W total). This array will produce approximately 206Ah per day at 12V. You'll need a charge controller rated for at least 63A. MPPT recommended — higher efficiency at this array size.
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