T-Pain Is On A Boat: Re: [Electric Boats] regen again again

Monday, June 15, 2009

Re: [Electric Boats] regen again again

Thanks Phil for posting that file, I read it several years ago when I started experimenting with the possibilities of generating power from the main propeller shaft. In part 3 of his (Gorlov) conclusion the theoretical limit for efficiency for an open propeller is 30.1% and an average for an open, unducted propeller type turbine is only 10/20 percent. The best efficiency for turbines is the Helical turbine, which he (Gorlov) holds the patent and has developed, pretty nice unit...Unfortunately one of these turbines cannot propel anything, just develop power in wind or water to maximum efficiency of about 35 percent.... I will continue to experiment on ducted propellers as time permits. I'm not trying to start
urinating contest over this, it is a very good article with a lot of great information....

Dave K

--- On Mon, 6/15/09, Phil Sweet <phil317@sunflower.com> wrote:

From: Phil Sweet <phil317@sunflower.com>
Subject: [Electric Boats] regen again
To: electricboats@yahoogroups.com
Date: Monday, June 15, 2009, 5:41 PM

I see regen is being revisited again. I've uploaded a file on turbine efficiency entitled "Gorlov". Regarding some of the numbers being bandied around regarding potential to recapture energy via the electric propulsion hardware, I would would suggest a good goal for round trip efficiency might be 1%. Suppose you're sailing at 5 knots. Engage regen; sail 100 miles; point into wind; lower sails; and power 1 mile into
wind at 5 knots on captured energy. Don't know of any vessel capable of doing this yet.

Since a prop is matched to a hull in such a way as to provide maximum thrust with minimum hp; it will produce minimum power with maximum drag when used in regen. It is the worst device imaginable for generating electricity on a moving boat. A wind generator will always be better if you compare comparable boat performance. Solar is usually more reliable than (the most common) wind gens by a factor of 5-10; and will usually produce the cheapest cost/watt over its lifetime of the green alternatives.

Getting the energy into the batteries is by far the biggest technical challenge for most sailboat conversions. It will most likely drive your choice of battery tech and BMS. You may also be obliged to size your battery bank based on its ability to absorb charge, rather than its ability to discharge. This is particularly so if
a genset is involved.

There has been a lot of discussion here and on other forums about using "excess" energy when already sailing at hull speed. The idea being to use regen when the boat is over-canvassed; and that way you won't be slowed down much. This is bad economics. Good economics is to use a smaller (and cheaper) rig, and use the savings to purchase a bit more fuel as you go. To put this in perspective, a naval archetect who designs blue water cruisers reports that his boats can motor 6.5 times around the world for the price of a sailing rig for his boats.

PS. I know there are good, durable wind gens out there. They are not common, and the ones I know of start at around 5000 USD for a little one.

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