I have an aluminum hulled Bolger Oldshoe sailboat. Also a sharpie hull. 5 foot beam. 11.5 feet long. Fixed full length keel (about a foot "high") in the center. I suspect the bottom of my hull is more curved than yours.. And the keel (7 inches wide) probably adds some drag as well.
250 lbs ballast. say another 50 for masts and rigging. 200 to 300 for hull. 2 people another 300. Gear another 50. Anchor and tools another 50. Ice chest and some more junk another 50. So all up 950 to 1050 lbs.
I used a trolling motor for a bit. 50 lb thrust. Controller was dead so I ran it full out with motor connected directly to the battery. In very calm conditions...with a very modest headwind (and sails tightly furled)...that motor would push the boat along at 3.6 mph give or take.
So there are some real world numbers to work with.
However, with some rough conditions and some decent headwind...that 50 would barely move the boat...in those conditions it was more like 1 mph. Thats when the 2.5 hp outboard got bought. Though cruising with the trolling motor sure was sweet....may still rig that up again and only use the outboard when really needed.
IIRC (somebody needs to check me on this )....the 50 lb thrust trolling motor drew something like 50 amps at full power. So, for 4 hours you are going to need 200 amp hours (at least.....you really don't want to regularly draw your batteries all the way down...not good for them at all....you need to leave the last 25 percent or so in the batteries...and only use that rarely for emergencies.
Again, IIRC your typical Walmart/autostore deep cycle battery has about 100 amp hour capacity....so that is 2 batteries per day....4 batteries for 2 days....something like 60 lbs per battery....so 240 lbs worth of battery.
Again...rough numbers...will need to look up the specifics...but these are fairly close ballpark number.
If your hull is a bit "faster" than mine and you can stand to go a bit slower....under calm conditions you might get by with a 25 to 35 amp draw.
Hope that helps....did a lot of battery research earlier in the year...later today I'll dig up what I found...
take care
Buddy
On Monday, May 21, 2018, 9:31:35 PM PDT, yahoomail@curtisteam.org [electricboats] <electricboats@yahoogroups.com> wrote:
Hello All. I have a microtrawler I'd like to electrify. The boat is basically a sharpie hull, 42 inch beam, 15.5 feet in length, 7" draft. She needs a total about 800 to 900 lbs to get her to her lines.
My goal would be two consecutive 4 hours days at 4 kts without a charge. I'm hoping a 50lb trolling motor and four T105 (220HA, 6V) batteries would possibly be enough. If not I could go with 6 or 8 T105's.
I'm just looking for any "rules of thumb" that I could possibly use for sizing batteries, etc,
Chris Curtis
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Posted by: Fish Canoe <fishcanoe@yahoo.com>
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