Power consumption of electric drives in Catamaran

[valhalla360]

Originally Posted by Ifitsworthdoing

Hi Saltifinch - we are planning the same thing as you: We are commissioning a non-sailing version of the Broadblue 346 (34ft, 5 ton lightship) catamaran with plenty of solar electric on board.

Primary propulsion is going to be 2 x 9kW rim driven thruster pod motors with possibly a NeanderShark 50hp diesel outboard (installed in the centreline cockpit floor lazarette) as secondary/back-up propulsion and a small/portable 3.2kW diesel gen set in the aft cockpit floor storage space (where the gas bottles would normally live except we will do without LPG).

OceanVolt kindly ran the boat's design numbers through their proprietary software and came up with the following performance figures:

Speed (kn) / Shaft power delivery (kW) / Battery power draw (kW)
2.4 / 0.3 / 0.4
3.4 / 0.8 / 0.9
4.3 / 1.7 / 1.9
5.3 / 3.6 / 3.9
6.3 / 5.3 / 5.7
7.2 / 11.3 / 12.3

So 6.6kn is roughly the unity point for speed vs. power draw. I trust this helps somewhat.
Best wishes with your enterprise!
Kai (IfItsWorthDoing)

If the shaft power delivery is per motor, that fits well with my experience for a similar size catamaran.

So it comes back around to how do you supply 10kw to get a 6kt cruise for a long enough period of time to make 30-50 miles per day and then replace it for the next day.

I also appreciate they are using a realistic twin 9kw motors (24.5HP), that aligns well with the recommended HP for a 34ft 5 ton cat.

[Adelie]

Azura Marine has a 40’ cat with 58m2 of panel charging a 60kWH battery bank.

That would be 14-15kW of panels.

Twin 10kW motors can push it 10kt. It can go 24hr a day at 4kt.

https://asia-pacificboating.com/sing...lar-catamaran/

[Montanan]

This insolation chart shows the average daily hours of solar insolation for the United States which can be used for exemplary purposes, if you know where you will be voyaging you can access similar charts for those regions. Charts or maps such as the one below accurately predict the annual insolation of an area and can be used to determine the needed size of a solar energy system or to calculate future energy production.

Note that the 29.5% efficiency of Oxford is at the lab tested conversion of the cell and is not the entire system efficiency which involves power conversion charging and discharging of the batteries and of course the discharging to the inverters and the loads. The actual system efficiency will be very much less.

Reference as to insolation: Solar Insolation Chart, Solar Insolation Data | Average USA Sunlight | Solar Energy Radiation Map

Reference as to system efficiency.

https://solaranalytics.zendesk.com/h...f...%20More%20

[PeteDale]

Hi Guys

If you search/google Electra (its a Catalac) on Youtube, he does 5kts on around 1100 watts per motor. The boat is approx 10,000lbs displacement.

Obviously, to go 6kts is a lot more (I cannot remember offhand how much exactly) I know he suffers cavitation if he uses too much power, so he sticks to his 5kts or less mainly.

Anyhow, he cruises mostly at 5 kts around the Med, he has 3200 watts (8x400w panels) and usually only uses around 2200 watts for his motors, the rest to run his watermaker lights etc.. I know he did not even bother to erect his sails because he did not deem them necessary in the beginning.

If you install a small 3kw generator (maybe Champion multifuel) you can effectively power through the night at 5 kts if you use propane instead of petrol, especially if you only run 1 motor.

On a sunny day his battery is full by 11 am..however, he mainly does not need the batteries due to his solar setup, where he says he would cut back on batteries and install more solar if he did it again.

Anyhow, these are my plans (dual 11 kw 72v elec motors) on a 11,5m Malcolm Tennant extended Shilo..approx 4000watts solar for me. (8x500watts). 2 x Champion 3kw gennies running on propane..

Hope this helps.

Go well.

[PeteDale]

(Also 2x 72v 150ah batteries too..)

[barnakiel]

While thinking about the solar panels part of equation, it is good to recall that in most cases the panels will deliver well below the full output. How much less will depend on sun angle, clouds, and how clean the panels are.


I found many owners overestimate their actual solar harvest capacity - despite the fact that this data is easily calculable and plenty of info is available from solar farm installers/managers.


b.

[CaptainRivet]

Originally Posted by Saltifinch

I think the formula is roughly 1kw per square meter. If the vessel is 10.5m x 4.5m, then to generate 25kw of power should only require approximately half the approximate space of the vessel. We picked a plan specifically that has a very large cabin specifically for this.

Waterlength is the key here. Give it 14m length with slim hulls and your 35ft accommodations and you have a very good base. Basically a sailing performance cat hulls, take off the mast and put a roof and David’s that consists of bifacial solar panels.
Waterlength runs means you need less energy to reach 6kn which should be your travel speed calculated and everything optimized for that.