Michael. Jim Brown, primary designer of Searunners, with John Marples, is an outside the box type thinker. I am sure your answer is not to take one of these designs and simply widen it. You perhaps do not know about" tripping", a common problem with poorly designed ama placement. I don't think your massive sailplan needs to be anything more than modestly bigger, because the boat will sail so much better that your motoring needs will diminish. Jace
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Jace Hobbs
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From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Michael Mccomb
Sent: Friday, October 12, 2012 2:35 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: [Elec B] Re: (to John) regen, displacement, sail plan, hull form....
Hi John,
Thanks for the input.
My goal is to completely dump the need for diesel BUT have it handy as a backup for unusual circumstances. At least I will TRY to keep the need for it unusual.
For me any type of regen would be preferable to using diesel. I'd use shore power when it was rarely available as well as wind and solar to recharge the LiFePO4 bank. Unfortunately compared to the power required to move a boat the wind/solar won't actually contribute that much. I suppose I should say that the criteria for the word "much" has to do with the time required to produce the power consumed while on a typical motor run so figure about 1200 watts as a sort of typical low consumption to get away from a mooring. 1200 watts of solar/wind is a lot when you throw in the inefficiencies involved.
I like your idea for a multi-blade prop. I have always thought in terms of three blades but even that was an old rule of thumb based on minimizing vibration when a two-blade comes into line with a keel. Of course the tri has no keel (although there still might be a pressure dif directly in line with a hull, more research for me) so the two might work.
As you add blades you decrease efficiency BUT also reduce the diameter of the prop. While two blades is THE most efficient the tip speed and diameter comes into play and causes a lot of stress to the system. I will have to study carefully the possible advantages to be had by going to multiple blades (three, four or five) as even though there is a slight penalty the reduced diameter might be a great advantage.
I need to find an engineering group associated with off grid electricity to clue me in a bit more on what exactly is needed in a configuration like i am contemplating.
So far I am thinking of the following...
Alten Duke 4850 or 48100 dc gen.... very light weight and highly reliable continuous use 48v 50/100amp respectively bat chgr
LiFePO4 batteries, 48v 100ah array
ME0913 motor
reverse mounted prop of diameter and blade count yet to be determined but theoretically sized to give about 500watts???
the Alten Duke item has add on components that make it very desirable such as enhanced mufflers, oil sump and fuel lines... it utilizes a Hatz engine and these are proven reliable in military service... these engines are "right" engineered in that they do exactly what they do well with no excess materials dragging down their efficiency
the Duke units are built for battery charging BUT i would assume that would be lead acid batteries and not LeFePO4s that require or at least should have a battery management system (BMS) attached to properly charge them... the BMSs are designed to use grid plugged battery charges and function by being able to cycle the actual battery charger off and on as the Li batteries are topped off.... this won't work very well with a diesel dc battery charger as the starting and stopping would be very inefficient and harder on the unit.... and SO i am wondering about the alternative of slowing the engine way down AND dumping the little electricity generated to a water heater or some such.... one question would be, could you slow the engine and dump the little elec to an AGM and then let the BMS cycle a small grid charger connected to the AGM.... in this way the diesel could recharge the AGM and nearly charge the Li batteries before shutting down and allowing the AGM/charger to top the Li batteries off......
much to consider and i need some expert advice that i am hoping the off-grid people can provide
the ultimate idea is to load a tri with 20 or 30 gal of diesel and then sail for a few years before needing to replace the diesel for the fact that it is just too old and stale
1200 watt consumption for an hour and a 5 or even 2 hundred watt regen would just about do that for me
if i were on the ICW or inland passage and simply could not sail then the diesel could directly power the motor reliably but i tend to stay away from places that i cannot sail... in the Caribbean trades and a lot of other venues one would simply never need diesel
one concern is the tri probably does not currently exist.... in order to carry a larger than normal sail plan the tri would have to have a beam that would be considered oversize in relation to current tris...... not much extra speed would be had from such a boat and the misuse of the larger sail plan COULD cause catastrophe if the person didn't understand the situation.... in the regen mode, to slow the boat down while trading for power generation the full plan could be used but while sailing without regen one would have to reduce sail in all but the slightest of wind conditions.... it's just a matter of thinking about dual use for the sail plan, propulsion AND regen rather than thinking of the sail plan as being fully about propulsion and getting a small amount of regen as an after thought
to date, tris have not been designed with this in mind and i am wondering what it would take to modify a current tri for such use.... more beam and a larger mast for certain..... need an experienced designer to think outside his normal box
also thinking in terms of modifying something like an old Searunner.... how does one successfully move the amas out???
Michael
From: John Green <v_2jgree@operamail.com>
To: electricboats@yahoogroups.com
Sent: Thursday, October 11, 2012 7:24 AM
Subject: [Electric Boats] Re: (to Jace) regen, displacement, sail plan, hull form....
Hi, Mike, I agree, Jace has good points.Here's a thought.......Why don't you, instead of initially investing time/money etc in regen, get your trimaran setup, use minimal batteries, to save costs, and re-evaluate what you need?The key to success might be the low weight, rather than the regen. Especially seeing as you intend to carry a diesel as well. But it is an interesting subject, seeing as with a tri, you will/might get away from the powerhogging as hull speed is reached. Also, with a tri, you have lots of potential area for solar panels. You might find that regen is not worth the resources to set it up.Final thought - you might find that a multi-bladed prop, as in, maybe at least 5 or 6 blades, might give the best results, as it would/should generate more torque at lower revs. And cause more drag, of course, so it might be good to have it retractable. John 1e. Re: (to Jace) regen, displacement, sail plan, hull form.... Posted by: "Michael Mccomb" mccomb.michael@yahoo.com mccomb.michael Date: Wed Oct 10, 2012 3:51 pm ((PDT)) I completely agree with what you are saying here. I like to sail, not motor. To the extent that I can do completely without a motor I am much happier. The trimaran format allows one to go from point A to B more quickly and therefore more reliably. I quite like the idea of the Fisher boats and the 37 especially BUT the darned things are doomed to be motorsailers (lousy sailers) pretty much no matter what you do to them. For my purposes much better to have a trimaran that can move right along under normal circumstance AND one with a larger sail plan so that a significant amount of power can be consumed by the larger prop of a maximally efficient REGEN/propulsion system. A larger prop works better for regen because it has the ability to convert more of the power that is ultimately provided by the sail system. If one wishes to sail without penalty of regen one simply turns the prop over at a speed that neutralizes the large props drag. Adding even more power than the required neutralizing revs provides propulsion and adding less power than the neutralizing revs to the prop provides regeneration. I need propulsion on the boat but the efficiency of the prop in propulsion is not nearly as important as the efficiency it has during regeneration. So for instance I'd rather have a propulsion to regeneration efficiency ratio of 40/60 than 60/40. Propulsion is only for getting away from the mooring, handling tides when necessary and emergency situations such as storm or dead calm conditions. I want a serial hybrid with a highly efficient diesel dc generator used mainly to drive an electric motor when the batteries run too low on juice to do so. Trimarans should be as easily driven by electric motors as they are by wind and therefor I would expect a decent turn of speed on good sized trimarans for even motors considered to be smallish (such as the ME0913). All of the above says MAINLY that the propulsion system is a backup that I wish to use a little as possible because, i wish to sail not motor. kind of an aside to the above but one fellow suggested that a normal prop mounted backwards would produce the best regeneration.... intuitively this seems correct to me.... it would be less efficient in propulsion mode but probably maximally efficient for regen..... you seem a knowledgeable fellow and I wonder if you would you have any thoughts on this???
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