same here with regard to thinking rather than any true engineering training.....
it just seems to me that the energy generation is related to the sail area.... the speed of the boat is sort of miss thinking in my mind.... an aircraft carrier moving at a speed sufficient to turn any prop at all would produce tremendous regen but a small hydro foil boat with a potentially very high speed could not get up onto the hydro foils if the regen resistance were added to the normal hull drag and would surely bring the boat speed way down if the resistance were added back in even once the boat were on the foils...
a trimaran is good in terms of getting from point A to point B faster than other hull forms but that speed will be sacrificed tremendously if one attempts to take a great deal of regen from it... it would seem that the only thing that can counteract "regen speed reduction" is sufficient sail plan to overcome the resistance of the regen prop dragging in the water.... the best possible regen prop is desired but the energy is generated by turning of the regen prop which is necessarily related to additional drag that the sail must overcome to generate speed.... in a way you could think of it as being 500 watts of regen at an imagined 100% efficiency MUST amount to 500watts of drag on the boat
yes?? maybe???
From: John Green <v_2jgree@operamail.com>
To: electricboats@yahoogroups.com
Sent: Wednesday, October 10, 2012 8:23 AM
Subject: [Electric Boats] regen, displacement, sail plan, hull form....
Hi, Mike, Your trimaran choice might be right on the money, provided you keep the weight down. I don't know if it is for certain that you would need to increase the sail area. Seems to me that the top, say, 20% to 30% of speed is a power hog, whether the power be from sail or motor. By tolerating a slightly slower speed at the top end, the regen power gained is worthwhile. From Eric's power consumption figures, from very rough memory, he uses about 4500 plus watts at hull speed, and 20% of that at about 50 or 60% speed. Presumably, assuming enough wind, the reverse is true, and there would be potentially 3500 w or so of regen available if he could accept the slower speed and yet still carry the sail needed to go at hull speed. You might find that you would have to add a massive amount of extra sail, just to gain a few knots that represent a small percentage of your speed? But bear in mind that I am just a thinker, not yet a sailor. John 2b. regen, displacement, sail plan, hull form.... Posted by: "Michael Mccomb" mccomb.michael@yahoo.com mccomb.michael Date: Tue Oct 9, 2012 10:25 am ((PDT)) Wanted to see what responses I would get to the following thoughts. I've been going back and forth on which type boat is best converted to a regenerating sail plan and have now pretty much settled on a trimaran with a larger than average sail plan balanced out by whatever increased beam is necessary. It seems to me that the only variable that comes into play concerning regen IF one can reach say 6 knots is the amount of power that the sail plan can generate. Displacement has mostly to do with acceleration and the only consideration to the reduction of regen capability with concern to displacement is that for a given same hull form a boat of increased displacement has an increased whetted surface area. Even the 1.3 hull speed rule for figuring cruise doesn't seem too relevant when compared to sail plan size. A very fast hull will, during regen, be penalized at a higher percentage of that hull speed during when in regen mode. A trimaran which can be very fast due to very low resistance will give up a much higher percentage of it's speed if a prop is being used for regen than would a more normal mono-hull. IF the above is more or less all correct then it would seem that the primary consideration when trying to develop good regen would be to make certain that one has the optimal sail plan in terms of power generation and that would necessarily point one at a taller sloop or perhaps cutter rig. Multiple masts carry more sail but with reduced efficiency so that the same boat with a commensurately larger single mast rig will be faster due to it's producing more power. A taller rig then requires more keel to keep it where it belongs and the most efficient keel is the deeper blade type which adversely affects draft. And so even though the trimaran would give up a greater percentage of speed during regen it would seem that in order to get rid of the deeper draft required to offset a larger sail rig the trimaran would be the ideal regen platform as it may offset the larger sail plan with beam rather than, as must be done with a mono, draft. am i missing something obvious???
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