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@dropsheet.com
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.
On 6/14/2011 2:53 AM, Tim Williams wrote:
You might find the following article of interest: http://www.sciencedirect.com/science/article/pii/S0301421509001323
It posits the question: "Batteries: Higher energy density than gasoline?"
In part due to these assumptions: "The energy density of batteries is two orders of magnitude below that of liquid fuels. However, this information alone cannot be used to compare batteries to liquid fuels for automobile energy storage media. Because electric motors have a higher energy conversion efficiency and lower mass than combustion engines, they can provide a higher deliverable mechanical energy density than internal combustion for most transportation applications."
So again my question, except for the lack of regeneration (which helps support the above statement) what is the difference between a boat conversion vs. an automobile conversion? What I was asking is: what are the practical differences, HP conversions, prop changes, battery storage locations/movement, etc. and except for the lack of regeneration, what is the downside that seems to keep any "speed boat" conversion from coming to fruition?
Clearly energy storage is a constraint. However my keel storage could easily contain 10 deep cycle 12v marine batteries, storage fore and aft could accommodate at least 8 more - that's some pretty deep cycle. 4.5 factor for a 48 volt system.
A Geo Metro automobile conversion, using an 18hp continuous, 49hp peak, 144v motor, with 10 - Deep cycle, flooded acid, 6v.s can do 65mph, and at 35mph has a 42 mile range.
My boat, with existing lower end I/O at a 2:1 gearing w/ reverse and a 120hp ICE, is a similar scenario - if I went with the same system (but more batteries) as the Geo, what might the consequences be? What else might I do? Prop changes for instance.
Any insights of that nature will be much appreciated.
Tim
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