After many years away from sailing, I am restoring a used Windrose 5.5, and am considering going with an electric trolling motor for my auxiliary, with a pair of 100ah lithium batteries. The motor hanging off the stern will weigh about 55 pounds, the batteries roughly 50 to 70 pounds.
From a wight distribution standpoint, the logical place is beneath the quarter berths, roughly amidships at the deeper area of the hull. However, that puts them between the only viable cabin exit and anyone in the cabin, something that makes me very uncomfortable.
The only other place is the lazarette at the aft end of the cockpit. I'm a big guy, about 240 pounds. The question is, how much of an effect will this weight concentration have on this 1500 pound boat's trim?
Après Vous II, I had a similar hull, a Windrose 18 for 48 years and used a trolling motor on it for 3 years with a FLA (Flooded Lead Acid) 100 A/Hr marine battery. It weighed a little over 70 lb. and with the battery behind the cabin entrance bulkhead, the anchors in the lazarette and my (also!) 240 lb in the cockpit, we were well down by the stern. Another issue with the 18 foot hull form from Laguna is the dramatic forefoot sweep which impedes pointing to windward.
My solution was to move the battery all the way forward, to an unused locker. My FLA was about 70 lb, and going from stern to bow (-70 lb in the stern to +70 lb in the bow) gave me a CG weight differential of 140 lb and got the nose back down and it pointed to windward much better.
It came with its own issues, in the form of humongous wire gauges, to go that much distance from bow to stern.
I am currently building a SCAMP sailboat and intend to use 2) 100A/Hr Lithium Iron Phosphate (LiFePO4) now abbreviated in the industry to LFP batteries, to power my trolling motor.
Here's a link:
https://www.wattcycle.com/products/wattcycle-12v-100ah-group-24-lifepo4-battery?variant=49287192248616
You can see the Group 24 is 23 lb and the Group 31 is 26 lb so for 2 batteries, you have a combined weight of 46 - 52 lbs. Still around a 100 lb weight differential to move them forward.
All the way forward, addresses one of your fire safety cabin exit concerns.
Here is a cable chart that shows wire gauges for a given current draw and distance, at 12 volts.
Cable_Chart.jpg
And one from MinnKota:
https://minnkota.johnsonoutdoors.com/us/support/trolling-motor-installation-guides/trolling-motor-wiring-and-battery-guide?srsltid=AfmBOorjjD5hTZipu-hc9IDJBZKPdoPsZCWVeHnHJ1dcemq1SBvSUnSV
And a wiring guide from MinnKota:
https://minnkota-help.johnsonoutdoors.com/hc/en-us/articles/24943541720471-Trolling-Motor-Amp-Draw-Circuit-Breakers-Fuses-and-Extending-the-Battery-Leads
Here is a link about ABYC wiring standards from a battery manufacturer:
https://battlebornbatteries.com/what-are-the-abyce-13-standards-for-lithium-on-boats/#:~:text=The%20newest%20guidelines%20from%20the%20American%20Boat%20and%20Yacht
And a general article on lithium batteries in a marine environment:
https://www.boatus.com/expert-advice/expert-advice-archive/2023/february/the-latest-on-lithium-batteries#:~:text=ABYC%20Standard%20A-31,%20E-10,%20and%20E-11%20address%20all%20battery%20and
On my Windrose 18, there was an access hatch all the way forward that was used to store foam flotation. (You can see the outline, just ahead of the table.) I scooped out enough to install a battery box and then ran the wire from there to the port side forward locker (lower left of pic) aft through the forward cabin bulkhead, then aft along the port berth and then to a bulkhead plug for the trolling motor on the stern. My hull came with a motor mount on the port side, so that 's why I ran wiring down the port side. If you don't have a motor mount, or yours is on a different side, then the wiring side choice is arbitrary.
If your hull is different you may not have side berth access for running the wiring.
Another alternative would be to run the wiring up on the sides, utilizing the hull/deck joint hardware.
The hull/deck joint is covered up inside, with a 6" strip of carpet glued to the sides as this picture shows.
DCP_0030.JPG
The hull/deck joint is fastened with 10-32 screws on 6" centers, under the vinyl rub rail. You could pull off the carpet (it glues back on with ordinary contact cement) and change out one of the screws every 12" or so with a longer 10-32 screw, that would allow you to attach the original nut, a screw-hole Ty-Rap to hold the wires and an extra nut on the screw.
https://www.amazon.com/MasiStranth-Mountable-Straps-Multipurpose-Mounting/dp/B0D9GKNZ3H/ref=sr_1_1_sspa?dib=eyJ2IjoiMSJ9.2IoBL5fcwhJBIh5IlMMYxsljVji5UWv7gmUqxwlt5LioKQ09ot60Qt8BloKQO3IO5n6Y3JmLI22QpDUfi3hxRNtYMzJqkR7ZoZhXTzma-eQjHa2oeaTC1h-9znVg6Xx2YD-ly25Gfov_hI_Bv1XUzSe_yCY0tmRjGjpGXgVQX7zcJocGaMAIKEm8WAe1ttQlGuYVZ6626I--YQH3FyqnuI1NaQOCTv2uSAMqw9WDaOg.wJsRR6sOTOasy4upXKgcWvk85QCytkRiZF-M8_Dvd4Q&dib_tag=se&hvadid=688963868091&hvdev=c&hvexpln=0&hvlocphy=1015134&hvnetw=g&hvocijid=1536080900331694676--&hvqmt=e&hvrand=1536080900331694676&hvtargid=kwd-806782602624&hydadcr=60_1014985623&keywords=cable%2Bties%2Bwith%2Beye&mcid=06ed9c7a355d3268bfd46295c8707470&qid=1757763637&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1
After the cabling is run, you simply glue the carpet strips back over the wiring and the cabin sides with contact cement.
If you have not selected a trolling motor yet, one way you could significantly reduce your wiring size (since you're getting 2) 12 volt LFP batteries) is to wire them in series for 24 volts and get a 24 volt trolling motor. This would allow much smaller wire gauge sizes.
Then run a pair of wires from your trolling motor bulkhead wiring, back to the electrical panel in the main cabin bulkhead.
A common temptation, is to run a third wire and center tap the two series connected 12 volt batteries to power the 12 volt devices already in the boat.
Big Mistake.
One battery will run down at a faster rate than the other battery and most LFP chargers assume relatively equal charges for re-charging the batteries with a 24 volt charger. Lithium batteries are sensitive in this regard. You'd have to disconnect the two batteries, charge them one at a time with a 12 volt charger, then re-connect them; clearly, a major hassle.
Instead, add this gadget:
https://bluemarine.com/products/victron-orion-tr?variant=45448078131496&country=US¤cy=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gad_source=1&gad_campaignid=20511573037&gclid=Cj0KCQjwrJTGBhCbARIsANFBfgu-xpgfc0HugV8AEDrveWdoDCE0KFiGZs2TfJuuHb2-jAIZZDEsAhoaAr7_EALw_wcB
It gets from 24 volts down to 12 volts for the rest of your 12 volt lighting and 12 volt accessory plugs on the boat. This particular model is only 60 watts, but this is not an issue for LED Nav and cabin lighting. If you have extraordinary power requirements (like a Bazillion candle-power spot light!) you can up-size to a higher wattage, voltage down-converter (at a correspondingly higher price).
Another advantage of a bulkhead trolling connector, is that you could attach your battery charger at home, right into the hull connector and not have to climb inside the boat, all the time.
Hope this helps,
Charles Brennan