Monday, January 31, 2022

Re: [electricboats] Sizing batteries for a small boat

The below information was supplied by my motor vendor for my 2021 Marshall Sanderling (2200 lb. Cape Cod Cat sailboat). It's not quite what you're looking for but I think it'll put you in the ballpark.

I outfitted the boat with two Mastervolt MLI Ultra 24/5500 in parallel to a 2.5kW BLDC motor from QuietTorque. It is overkill for a daysailer but I have intentions of making a Cape Cod rounding one day in her, and I like the extra range/safety margin, so that's what I went with. I have not had the time/opportunity to verify these range numbers, my observations of hull speed to power draw are in line with the first table.  I looked into the generator option but my sailing needs have not made its purchase appealing to date. The system is mated to a Chargemaster Plus III 80/24V.

Speed & Power QT2.5 24v cooled Motor System (waterproof option available)
 
Kts Amps Watts (Calm Waters)
2.7 10 240
3.4 20 480
4.3 40 960 *This speed supported by portable 2kW generator
5.4 80 1920
2500 Max power of QT2.5 system
Hull speed 5.52
 
Range DOD to 80%
400ah 24v
Kts Hrs Nm
2.7 34.2 92
3.4 16.5 56
4.3 8.0 34
5.4 3.8 21
 
Range DOD to 80%
200ah 24v
Kts Hrs Nm
2.7 16.5 44
3.4 8.0 27
4.3 3.8 16
5.4 1.9 10



 

On Mon, Jan 31, 2022 at 8:50 AM Peter Ford <petersford@hotmail.com> wrote:
I am looking to repower a 22ft Norwegian wooden boat with an electric motor.  The boat weighs in the 2500-3000 lb range.  The 5kW thunderstruck kit would probably do, but their advice is to get a 10kW kit because the motor is air cooled and not sealed.  I am ok with that advice.  This is not a sailboat I am looking at continuous power draw for 4-5 hours.  On a sailboat I have used a Minn-Kota for getting in/out of the marina with good results.

The question comes to sizing the battery pack.   Does anyone have real world numbers for speed and amp draw for a small boat like this?   My goal is to be able to cruise 20nm, perhaps 30 in a stretch.   I am thinking somewhere in the 4 kt range.

Secondly, any real world experience using a regular 2000W generator to power the charger while the small boat is underway?

Any guidance or pointers appreciated.

Cheers, peter



--
Christopher Greenwald
14 Manitoba Rd.
Waban, MA 02468

Cell 617-699-9189
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