To add to the multihull consideration, I think considering highly efficient hull forms and the larger than average sail plans makes sense for multiple reasons. I would like to add that I have worked with some of the prominent multihull designers, built several to my own design, have a patent in the field and have been a featured speaker at the Miami boatshow and published on this kind of consideration.
The points I would make are
1. Boats that sail well and fast don’t need propulsion nearly as much of their travel time, and so can afford lighter and smaller auxiliary drive systems.
2. Boats that sail well are not stranded with mechanical breakdowns to their engines in all but extraordinary conditions. I have done entire three month cruise on my 12 meter boats with only using a single 10 gallon gas consumption on a two stroke engine that could push the boat at 10 knots. I did have to motor around, but at a fraction of the throttle and for shorter distances because sailing was/is preferable. A better outboard with a larger prop would probably halve that amount consumed.
3. Regen on a small system does not create as much drag, supposedly , as a larger motoring capacity would require. This allows fortuitous advantages to life under sail.
4. Modern materials and design make the low boat weight very available, which allows the rig to be smaller and still have sterling performance. One has to escape the keelboat mentality of massive strength against the sea and go with the composite global loading technologies that produce terrific weight to drag to power combinations.
5. If we spend as much time as we would on the power side of boat design on becoming competent to built light hull forms, then performance and happiness under sail are a consequence.
6. The practice of weighting a sailing craft to keep it upright may be tradition in the European cultures, but it is laughable in many places in the pacific. We are still coming to grips, that ballast is a strange practice that has many negative consequences for the total system that a boat is. Perhaps it is time to escape the weight, embrace the multihull, and reap the benefits.
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Jace Hobbs
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From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of John Green
Sent: Thursday, October 11, 2012 2:23 AM
To: electricboats@yahoogroups.com
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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