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Old 06-03-2012, 21:03   #1
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Economic Propulsion

There is a lot of talk about electric propulsion and a whole lot of talk about fosil proplusion and i am wondering if anyone has determined a workable formulation to determine:-

1. What torque is required to move your Cat on a windless day say flat
seas and say cruising at 5 knots?

2 What torque is required to move your Cat in vicious seas say at the
same speed of 5 knots?

Sailing in my opinion goes about being prepared and hopefully in control of situations done conomically yet effectively. Should one not use these perameters when planing propulsion?

The electric propulsion seems to have ecellent solutions for many circumstances but has any EP Cat been exposed to real vicious seas and did they have enough omph to try to steer their boat? Diesel has a history of bad smells and what not, but it has proved itself over and over for dependability and effectiveness perhaps not ecomic but so what, when you need it its there!

The Austrians has a combo on offer EP and Diesel propulsion which does make a whole lot of sense based on what we know and what we have experienced.

I have a drawing layout of this combo if anyone wants to have a closer look just mail me at gdmarais@gmail.com and i will send a copy.
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Old 06-03-2012, 21:21   #2
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Re: Economic propulsion

In a cat I would prefer the redundancy of diesel-electric. That old leeward side scenario, one diesel only propulsion, clogged filter, water or air in the line....oops.

Typical diesel electric on cat (2) electric propulsion motors, that can be run off of batteries, DC gen-set. The large pitch props an electric motor can swing even at two digit rpm makes tight maneuvering child's play. Efficiency of running the diesel at constant load and rpm saves fuel.

The ability to have a 10~20 minute high peak rating double continuous rating can come in handy against currents coming around the breakwater.

This SMG 50 Plus is a good example of forward thinking in sail plan, ULDH, and hybrid propulsion.

SMG 50plus - innovative catamaran with A-frame-rig
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Old 07-03-2012, 00:03   #3
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Re: Economic propulsion

Wow. Fascinating boat, the SMG. The A-Frame rig is really interesting.
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Old 07-03-2012, 00:17   #4
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Re: Economic propulsion

Yeah, all sails furling, the new Parasailor™, it has lift in two vectors when sailing downwind, keeping the bows up, so no worry of burying a bow.

And running 19.3 kt out of the box by an inexperienced owner speaks well for that design, doesn't it?

Beachable, no dagger boards, and only 2' 8" draft makes you wonder what are the drawbacks of ULDHs? 16,000 lbs for a 50 footer is damn light though.
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Old 07-03-2012, 16:08   #5
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Re: Economic Propulsion

Quote:
Originally Posted by niel12 View Post
There is a lot of talk about electric propulsion and a whole lot of talk about fosil proplusion and i am wondering if anyone has determined a workable formulation to determine:-

1. What torque is required to move your Cat on a windless day say flat
seas and say cruising at 5 knots?

2 What torque is required to move your Cat in vicious seas say at the
same speed of 5 knots?
I don't think torque will actually move your boat. It takes power to move it.

On a windless day we probably need about 10 hp to motor at 5 knots.

In "vicious" seas, who knows? Pushing into 30 kts and moderate seas at 5 knots probably took about 20-25 hp. (Really just estimating from throttle position and RPM)

Our old boat had an 80hp diesel, and at about 2/3 throttle, motoring into around 35kts and short steep waves (shallow water, wind against tide) a rapid succession of waves would pretty much stop us dead for a few moments.

At some stage regardless of how much power you have, ultimately the wind and sea will stop you.
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Old 07-03-2012, 18:07   #6
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Re: Economic Propulsion

niel12, My boat is 36X22' approx 5t & has 2X 7.5hp diesels that would only get about 2hp at 2 blade 12" folding props. Cruise power 7kts burns >3ltrs/hr. Plainly 2X 5hp electric motors would be better. The diesel electric (LPG electric?) on a new boat would be the way to go with limited time (30mins?) from the LIFEPO4 type installation to cover any failure of the generator for docking. I would be looking at proven industrial electrical gear & controllers.

Thats the way I would (may) be going.
Regards Bill
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