It's all about the owner's use case. EVs with their very large battery banks typically have a useful operational range of about an hour followed by a recharge cycle that is close to 8 hours. That is why many people believe that electric cars are not a particularly viable solution.
I try to focus my evaluation of a planing v-hull project on the actual power used by the person that is considering the conversion. With the gas engines, how much fuel do you usually consume in a day? That should be your target. If we factor in that electric drives are 3 times as thermally effficient (1/3 the energy required to do the same work), then you only need 11kWh of usable battery capacity to replace 1 gallon of gas (gasoline = 33kWh/gallon).
So lets assume that you only use two gallons of gasoline for your typical outing. Assuming a 60% depth of discharge for flooded batteries, you'll need at least 37kWh of rated storage to replace the gasoline (actually a little more than that because of Peukert's Effect). Regular deep cycle batteries weigh about 75 lbs for each kWh of usable capacity, so your "two gallon" flooded cell battery pack will weigh about 1650 lbs.
Let's do the same for AGM. AGM can be regularly discharged down to 70% depth of discharge. This brings the total rated capacity requirement down to 32kWh of AGM batteries. Because of their improved depth of discharge and reduced influence from Peukert's Effect, AGM weigh about 70 lbs per kWh of usable capacity. This brings your "two gallon" AGM battery pack will weigh 1540 lbs.
Finally, let's look at Lithium batteries. LiFePO4 prismatic cells are generally used in electric boat conversions for their large format and reasonable(?) pricing. Lithium cells like this will take an 80% depth of discharge. Now you need only 28kWh of total rated capacity. Lithium cells weigh less than 32 lbs per kWh of usable capacity, so your "two gallon" LiFePO4 battery bank weighs only 700 lbs. On my 30' ketch, the "2/3 gallon" LiFePO4 battery bank takes about 4 hours to replace 1/2 gallons worth of energy with a 28A 48V charger.
By comparison, the two gallon of gas that you're replacing weighs less than 20 lbs including the gas tank itself. Like Denny said "it's not even close."
My friends with ski boats and fishing boats regulary use more than 10 gallons of gas in a day on the water. There is no way that today's batteries can meet that kind of demand.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "ams_ak@..." <ams_ak@...> wrote:
>
>
> Re: planing in a v-hull.. Tim ive replied to your mail but thought id respond here aswell. I am converting a glastron bayflite to electric drive. 26kWh of lithium, kostov 11" 250V motor and an evnetics soliton controller. I am taking out the same weight as is going in, peak mechanical power will be significantly higher, range shorter. Yes it is expensive but well worth it in my estimation. If you often cruise, but want to have the option of power, this could be just the thing. I believe we can show all other speedboats are 'broken' by comparrisson.. Noisy, smelly, and polluting the water and nature we are out to enjoy in the first place.
>
> Good luck on your project,
>
> AK
> --- In electricboats@yahoogroups.com, Tim Williams <tajw@> wrote:
> >
> >
> > Thanks a million. Great considerations.
> > My boat sounds similar to your example, it is a 19', 1990, bayliner, capri but with a Force L-Drive I/O (which makes it inviting to change engines to anything else). It is sequential lift hull, and your assumptions about lifting to plane are about spot on. Seems an obvious obstacle now - though one of the things we love doing is slowly(3-4 mph) cruising through our sloughs, bird watching. Never getting to plane, I suppose even this will be too much for an E solution? Back to the kayaks, I suppose.
> > ps, metro curb weight is 2100", good guess.
> >
> > To: electricboats@yahoogroups.com
> > From: dwolfe@
> > Date: Tue, 14 Jun 2011 10:15:18 -0400
> > Subject: Re: [Electric Boats] Re: conversion
> >
> > The second line of the story title should have said - 'not by a long
> > shot'.
> >
> > A modern ICE converts about 1/3 of the heat energy in burning
> > gasoline to mechanical energy. A good electrical setup is more like
> > 85 to 90%. So far so good, the MOTOR is a lot more efficient but
> > the batteries are still far, far heavier than a gas tank holding the
> > same amount of energy.
> >
> > Take your Geo Metro example: Assuming your 12v deep cycle batteries
> > weigh 60# apiece, you can go 35 mph for 42 miles with a 600# battery
> > bank. 600# (100 gallons) of gas would drive your standard ICE
> > Metro, what, 5000 miles? - more than a hundred times as far. (There
> > is your two orders of magnitude)
> >
> >
> >
> > "Speed" boats are very different from cars. At a steady speed, the
> > drag of a car is based on its aerodynamics only. Their powerful
> > engines are there for acceleration, not speed Adding weight affects
> > acceleration but not steady state speed so a car with much less
> > powerful electric motor and a heavy battery bank will be a slug on
> > acceleration but can still go pretty fast. A planing boat needs a
> > lot of power to raise the hull up out of the water and the more it
> > weighs, the more power needs to hold it up on plane. Planing boat
> > speed is closely related to the square root of power/weight.
> >
> >
> >
> > Your Geo (2500# ??) might need only 10 hp to maintain 35 mph. An
> > average deep V 2500# boat would need 105 hp to go 35 mph. The Geo
> > battery bank weighs as much as a 100 hp outboard and 25 gallons of
> > gas; assuming your 100 hp electric motor weighed nothing your
> > electric boat would run 35 mph for 9 minutes. Switch to LI
> > batteries (for many $$$) and your range would be around 25 minutes.
> > In the real world I'd bet an electric motor capable of 100 hp
> > continuous would weigh as much or more than a 100 hp outboard ICE.
> > Add 600# of batteries and the boat might not be able to get up on
> > plane at all. I used to have a 19' Bayliner with a 120 hp Volvo I/O
> > that would top out at 36 mph. Once we had 8 adults on board at the
> > top speed was about 8 mph as the boat did not have enough power to
> > get 'over the hump' and up onto plane.
> >
> >
> >
> > Edison Boats made a wood Chris Craft replica the would plane at
> > speeds in the low 20s for 5 - 10 minutes with lead batteries. A
> > fiberglass deep V would require much more power, due to weight and
> > hull shape, to plane.
> >
> >
> >
> > Electric works pretty well in displacement hulls like sail boats and
> > old timey power launches because the power requirements for
> > displacement speeds are so low. 4 hp will drive my 2000# launch 7
> > mph.
> >
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