Performance graphs that I have seen indicate that power catamarans operating at "displacement" speeds, i.e., 7.5 to 8 knots, also make efficient use of energy. Confess that I lack data to support that, but it has been my anecdotal experience.
Hi TwistedTree. I found your quote below on another thread.
Yes, I agree. This is an excellent analysis. The best I have ever seen. And this is why electric is not the future for trawlers. However, one thing has changed since you wrote this, the cost of LiFePO4 batteries.
The sixteen 280Ah cells I purchased cost me $1720 including shipping and customs from china. Add another $1000 for a bms, fuse, contactors, bus bars and extra thermal sensors. And that is for the good stuff (Orion and Blue Seas). This comes to $2720 for 14.5 KWh (I used 52 volts average instead of 48 volts nominal) or $187.50 per KWh instead of the $500 per kWhr as you calculated.
So if you are willing to DIY, (which I think results in a better battery with better components and an expanded knowledge of what happened when things go wrong), you can do it for 1/3 the price.
Still expensive though (and it doesn't change the weight, room, range and fill up time factors, all important points as you mentioned above), but cheap enough to get it to fit within my budget.
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It is hard to for me to wrap my mind around the amount of energy stored in a 1000 gallon diesel tank. I imagine with the right type of boat you could travel between Seattle and Juneau without stopping once. I am trying to make that trip on 120KWh, stopping at every power pedestal along the way.
So a 1000 gal of diesel is about 100 of your battery banks. I imagine that's a good bit bigger than the entire boat.
How are yo going to outrun the weather with your limited battery capacity?
Well I am not, unless the leg was a very short one and I had lots of energy to spare. That would not be often though. This is why I am reconsidering. I am looking into using a displacement hull and going 6 knots instead of 7. So, I have started asking questions about FD hulls.
That is a cute little tug, but probably a SD hull. And it may be just as heavy as a TT35 but with less room for solar panels. At low speeds power required is mostly related to hull type and displacement so it will probably take just as much power to push it to a given speed as the TT35.
Scott needs a light, long, full displacement boat. Not many of those out there.
David
For the foreseeable future, may I suggest the boat should have a generator onboard to charge the batteries as a safety measure.
If there is a lengthy solar powered race, the generator can be sealed in someway, reserved for emergencies.
For the recreational boater, nothing will mess with the the enjoyment than flat batteries.
Scott needs a light, long, full displacement boat. Not many of those out there.
David
I have been thinking about a solar trawler that would use a towed solar array of panels that would be deployed in good weather and stowed on the boat in bad weather. Seems like you could have a lot more solar panels that way.
How are yo going to outrun the weather with your limited battery capacity? You base your electric consumption on a speed to length ratio of about 1, but to outrun any weather you probably need to get up to 2 or more. That probably triples electricity consumption per mile.
David
....I continue to consider it because of the hope that it may obtain 7 knots using only 7 KW of power. I would need to test this out before giving it further consideration though.
7 kW is barely 9 HP. I know of no boat that size capable of 7 Kt with only 9 HP.Hi Miz Trom,
I like your boat. Where did you get that fly bridge?
I was first attracted to the TT35 because of its large flat roof that could hold a lot of solar panels. As I did more research into the trip I realized that the size of the battery bank and the efficiency of the boat would be the most important factors. Even though I have recently learned that the TT35 does not have the best hull for the PNW, I continue to consider it because of the hope that it may obtain 7 knots using only 7 KW of power. I would need to test this out before giving it further consideration though.
How is the efficiency of your boat?