T-Pain Is On A Boat: Re: [Electric Boats] regen, displacement, sail plan, hull form....

Wednesday, October 10, 2012

Re: [Electric Boats] regen, displacement, sail plan, hull form....

My bunion tells me that a longer, deeper-hulled monohull with a powerful rig (ie, oriented toward power rather than speed -- and probably split rather than sloop/cutter) is the best fit with the regen objective.

Conventional multi-hulls are relatively fast because they can often exceed hull speed due to their relative lightness and relatively low wetted surface compared with conventional keelboats. And working in their favor is that the faster you go, the more wind is generated (except when running), and therefore the faster you go -- etc etc. But adding significant battery weight (effectively, ballast) will increase wetted surface and decrease ability to break out of displacement mode. Adding regen drag will also hinder it. Also, tris have less center-hull volume than an "equivalent" monohull, so finding a good home for the batteries is more of an issue. And adding beam to the tri means more structure, etc, meaning yet more speed-robbing weight.

On the other hand, batteries can make decent ballast in a deep hull-form monohull, enabling it to carry a more powerful rig. Other things equal, a monohull will be longer than a tri -- and therefore have a higher hull speed, which is perhaps the effective max speed for any regen candidate. And a rig that's perhaps less efficient (to weather) but able to carry more total canvas over a range of conditions, points of sail, etc, due to lower CG and CE and more sailplan flexibility and user-friendliness seems likely to be less compromised by more drag, and better suited to the brief.

Put another way, which is better for dragging a wagon: Arabian, or Belgian? Only my bunion's 2c worth.

-Per

-----Original Message-----
From: Michael Mccomb <mccomb.michael@yahoo.com>
To: electricboats <electricboats@yahoogroups.com>
Sent: Wed, Oct 10, 2012 11:27 am
Subject: Re: [Electric Boats] regen, displacement, sail plan, hull form....

i have to believe that the resistance to forward motion is in direct proportion to the size of the prop and the amount of energy/regen being created... the more regen, the more drag

From: Steve Dolan <sdolan@scannersllc.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Wednesday, October 10, 2012 5:20 AM
Subject: RE: [Electric Boats] regen, displacement, sail plan, hull form....

Michael,

Something I don't think has been discussed about regen is how much resistance the electric motor actually creates versus a sail drive or one of the bolt-ons. I now I start to here the prop spinning as low as 3 knots. I have a brushless motor with straight shaft so the resistance would be low and restricted to the packing gland and the motor itself.

Steve in Solomons MD

Lagoon 410 SE

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???