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Old 21-07-2008, 10:19   #31
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It will be very hard to get your boat over the hull speed no matter if the motors are electric or diesel , in any case the torque will always be better with the electric motors given the same power .
At low speeds the electric motors will always be at an advantage.
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Old 21-07-2008, 10:21   #32
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We have been using the Valence batterys for well over 2 years and are very happy with these , Just ordered 80 units of the U 27 for the Green Motion Propulsion system

Greetings

Gideon
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Old 21-07-2008, 10:24   #33
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I think it all hinges on what the use the original poster has in mind for the boat. Stories 'out of school' about the Lagoon setup is that it has not performed as expected and they now offer the 420 with twin diesels. The original idea was diesel-electric only. I'm sure that one day, probably in the not too distant future, there'll be viable alternative fuels/power sources, but not just yet.
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Old 21-07-2008, 14:29   #34
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Electric Propulsion vs Mechanical Propulsion

Quote:
Originally Posted by decktapper View Post
OK, help me out here, I have been told by competent people that for a 40 to 42 foot cat not to accept less than 2 30 HP diesels because anything less is insufficient, and unsafe. that is 60 HP*746 watts per HP = 44760 watts or approximately 45KW. The last I checked none of the boats were coming with a 45 KW generator to power the motors, and the batteries would not handle a 2 hour trip up river much less all day against the wind and current. I have heard the story about being more efficient, but my yanmar book shows that the prop and the engine are perfectly matched at full horsepower, I do not buy that the electrical system outperforms the mechanical system at full power. So which is it? are the diesels way oversized? or is the electic way undersized?
Decktapper

Speaking from experience (there's not much of that about when it comes to hybrids), our Lagoon 420 Hybrid has performed well over the last year during which we covered about 10,000 miles fully laden (4 tonnes of equipment and supplies). The Lagoon 420 Hybrid features two 10kW electric motors. These have been adequate to keep us from harm and push us fully-laden through the water at an average speed of about 5 knots, with no headwind and moderate seas without relying on battery power (or sails). The 17.5kVA Onan generator driven by a 28hp Kubota diesel engine has produced enough power to drive us through the water for an hour or so at up to 8 knots when lightly laden and the batteries are fully charged, with no headwind and moderate seas.

We have motored fully-laden into a twenty knot wind in big seas, with a single operational motor (a line from a fishing pot was round the prop of the other) at about 1.5 knots. I was glad we were not on a lee shore, but the 420 points pretty well, so we could have sailed off had we been. Some people would say this is underpowered, but we have always felt safe.

The performance of the 420 hybrid powered by its single 28hp diesel generator is not far short of the performance of the conventionally powered 420 with twin 40hp diesels (there may be one knot in it at full power), so I deduce that electric motors must be more efficient at converting power into thrust.

Chris
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Isle of Arran, Scotland
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Old 21-07-2008, 14:37   #35
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I think with 50 knots on the nose one should still be able to move forward with 2 knots as a minimum
That way at least the boat is still steerable and that is our aim for Green Motion .

Greetings
Hi Gideon

2 knots progress against a 50 knot headwind! Phew, you are ambitious! How often does a prudent sailor encounter a situation where they have to make 2 knots progress against a 50 knot headwind?

Chris
P.S.
I admire your approach to hybrid propulsion
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Old 21-07-2008, 16:39   #36
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Upwind in 50 knots on a lee shore?

Almost all sailboats are auxilliary sailors, their motor is not their main propusion. (I used to be able to spell, I call it spell-timers) Any boat that is stuck against a lee shore in 50 knots is in big trouble. Seamanship is a study of how NOT getting in such situations.

Lets not condemn (sic) electric motors for what most diesels can't do. Hey listen, I should know! I put my boat in just such a situation, and silly me, I was engineless. Damn fool, I know! But I surived some how, and carried on to complete the circumnavigation.

What to know more? What to laugh at one man's folly?

education.of.a.falcon - **** ** Education of a Falcon var gaJsHost = (("https:" == document.location.protocol) ? "https://s

Cap't Mike
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Old 22-07-2008, 04:46   #37
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Gideon
"t will be very hard to get your boat over the hull speed no matter if the motors are electric or diesel ,"

I am puzzled.
If sail power can push a boat well over hull speed why cannot engine power?
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Old 22-07-2008, 05:07   #38
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Quote:
Originally Posted by Gludy View Post
Gideon
"t will be very hard to get your boat over the hull speed no matter if the motors are electric or diesel ,"

I am puzzled.
If sail power can push a boat well over hull speed why cannot engine power?
Hallo Paul
this has to do with the power your sail is able to give you.For instance, 2 x 20 HP will get the FastCat 455 to hull speed of lets say 8.8 knots as we have seen last sunday.
When we started sailing with around 20 knots of wind apparent at 30 degrees app. we moved along at 8.4 knots or just a touch below hull speed
when we started reaching with the wind of around 24 knots we have seen a top of 15.4 .
Sail power is a lot more that the engine power and it is always possible to go over hull speed but in order to do that with engine power you need a lot of it./
Just compare it with your last Powerboat. going 8.5 knots was easy and as fuel efficient as possible while your boat had a top speed of 25 or 26 knots if I remember well.
That is considerable higher than hull speed but it does take a lot of power , 2 x 720 HP ?
Your sail area can create a lot more power than the normally installed motors and thus your or in this case our cat will go over hull speed given the right conditions.
It is possible to make a cat go over hull speed but for the FastCat 455 to do so and give it 16 knots we need 2 x 150 hp motors.
I hope I have made it clear to you
Greetings

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Old 22-07-2008, 05:11   #39
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Quote:
Originally Posted by Octopus View Post
Hi Gideon

2 knots progress against a 50 knot headwind! Phew, you are ambitious! How often does a prudent sailor encounter a situation where they have to make 2 knots progress against a 50 knot headwind?

Chris
P.S.
I admire your approach to hybrid propulsion
Hallo Chris

it does not happen very often but can be very usefull just to get into a safe haven , or a good anchoring position and yes I am ambitious , the only way to go.
This is why late this year I will have a cat in the water that will almost use no Fossil Fuels at all. ( just for emergency have we put a Diesel and Biodiesel generator on board.)

Warm Greetings and congratulations with your great ( Green ) cat.
Gideon
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Old 22-07-2008, 05:14   #40
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Yes that is clear - its simply that the sails can provide a lot more power than any reasonable sized motors.

What sort of power would a fastcat need to motor at say 12 knots? My guess is that it would still be a lot.

Ok .... understood, I guessed it but needed it confirmed.

I have other questions but I will start a new thread as they are not really connected with electric motors.
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Old 22-07-2008, 05:18   #41
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Quote:
Originally Posted by Gludy View Post
Yes that is clear - its simply that the sails can provide a lot more power than any reasonable sized motors.

What sort of power would a fastcat need to motor at say 12 knots? My guess is that it would still be a lot.

Ok .... understood, I guessed it but needed it confirmed.

I have other questions but I will start a new thread as they are not really connected with electric motors.
2 x 75 hp diesel will give the FastCat a speed of 12 knots plus.
The most recently launched FastCat 455 has 2 x 40 hp and this will touch 10 knots at full speed.
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Old 22-07-2008, 05:30   #42
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Ok .. then say you are wanting to go as close to the wind as possible and use the 75 hp engines with a mainsail up say sailing at 25 degrees of wind and motor sailing at say 10 knots - what sort of fuel usage would you expect?

I am just watching a DVD where they motor sail like that at ten knots in a 65 foot mono and achieve an extra 25 per cent or so range because of the mainsail.
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Old 22-07-2008, 06:32   #43
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There is a lot of guess work in this but I estimate that when the true wind is 10 knots at an app. angle of 30 degrees , the maximum angle to sail at and using one engine at 2400 rpm the fuel consumption would be around 2 liters per hour. and the speed gained would be around 3 knots
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Old 22-07-2008, 06:47   #44
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Thanks Gideon - I understand that has to be just a best guess but that best guess by you is a liot better than a best guess by me!!
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Old 22-07-2008, 06:51   #45
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Quote:
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Thanks Gideon - I understand that has to be just a best guess but that best guess by you is a liot better than a best guess by me!!
With electric retractable motors even if the generator is running the fuel consumption will be lower and the speed gains higher since one motor is lifted from the water and the generator is a modular type and will run at a very low rpm setting .

Greetings
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