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Old 26-04-2008, 14:44   #91
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This thread started as Catana question but in now one of the most informative ever!

Thanks to you smart guys.
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Old 26-04-2008, 15:01   #92
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Are polars generated by computer or are they based on actual real world sailing? I would think if they are computer generated then they are worthless.

That was why I asked Catabroker to answer my question regarding this.

I very much doubt that all the polars are verifed, the ones posted so far mostly carry the designers logo, and I doubt that at best more than one of the curves is verifed. You need to find a day with steady wind and sea state and do several timed runs, maintaining AWA, optimising trim etc. Then afterwards do it at several different boat loads.

Fastcats carry the Lavranos logo, he hasn't got the 455 into the water yet. The polars for the 435 are for a boat that is heavier than what he claims for the newer boats...

The Leopard polars have the Morelli & Melvin logo.

My educated (sceptical??) guess is that they are all generated by the VPP used by the designer. As the parameters in these VPP's are closely guarded secrets, and not open to scrutiny, I suggest that they all be viewed with a healthy dose of scepticism, just like the weights specified in most sales material for cats. (The manufacturer reserves the right to change the specification without notice - is a standard Cover my A*** clause)only way you can get anywhere close to the truth on performance, without actually testing the boat is going down the route Mamo is going, but he needs to get more information, like max. hull beam, waterline length, wetted surface area, Cp, beam centreline, etc. and this is seldom made available by manufacturers.

We have started a project in the Danish Multihull Assosiation, to attempt to collect as many of these figures as possible from standard production boats, including real weights, but there are only 5 or 6 different boats in current production on the list at present, and all data is not yet available.

Maybe there is a club/organisation in the US that could look at this?

Regards

Alan
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Old 26-04-2008, 15:06   #93
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Are polars generated by computer or are they based on actual real world sailing? I would think if they are computer generated then they are worthless.
Both. In general you start with a design polar and develop it through sailing trials.
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Old 26-04-2008, 15:15   #94
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Both. In general you start with a design polar and develop it through sailing trials.

Yes for race boats. You know how much time it takes to generate a full set of polars for a racer, as you fiddle with the trim to optimise along the way.

I doubt that this has been done on all the polars published on this thread.

The 3 or 4 sets we have seen here, are all for boats that have undergone a number of changes over the span of the production run, some have no weight specification, so basically they are nearly useless. One is for a boat that isn't on the water yet.

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Old 26-04-2008, 15:18   #95
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Yes, I know what it takes to develop polars. But ya gatta start somewhere right?

And I would tend to believe the polars developed by Angelo Lavranos, good desinger..........

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Originally Posted by Nordic cat View Post
Yes for race boats. You know how much time it takes to generate a full set of polars for a racer, as you fiddle with the trim to optimise along the way.

I doubt that this has been done on all the polars published on this thread.

The 3 or 4 sets we have seen here, are all for boats that have undergone a number of changes over the span of the production run, some have no weight specification, so basically they are nearly useless. One is for a boat that isn't on the water yet.

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Old 26-04-2008, 15:26   #96
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Yes, I know what it takes to develop polars. But ya gatta start somewhere right?

And I would tend to believe the polars developed by Angelo Lavranos, good desinger..........
Absolutely a good designer - they are probably not far off the mark. But, the question was if they were computer generated or actually verified, and my suggestion was that they probably aren't all verified.

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Old 26-04-2008, 19:09   #97
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Good work Mamo.My suggestions:
Fuel 250 kgs
Water 250 kgs
Options added to the basic boat, like extra anchors and rodes, biminis, electronics, tender, outboard, extra sails, watermaker, tools and spareparts, charts, books, extra batteries, cooking utensils etc.
Say 500 kgs.
Provisions for 4 crew for 30 days @ 3 kg/person/day = 360 kgs
4 crew including luggage = 440 kg

Total say 1800 kgs. This is in my opinion a conservative figure for a 45-50 ft cruiser.
many thanks Alan.. that was what I ve been looking for.. I will upgrade table ass soon as possible with 2 ton payload and it will be more meaningful..

could you all help me about completing the missing number on the table?
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Old 27-04-2008, 00:46   #98
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Great Thread

Yes I agree with others , this is turning into a great thread. I suppose the published polars must be taken with a grain of salt, after all the manufacturers are operating in a competitive and at times unethical world.

I have just dug up some long straight line race results, in fresh reaching conditions, for the schionning 15m performance cruiser. I would suspect that there isn't too many faster 50' performance cruising cats around . In the 2007 Darwin Ambon Race with minimum weight, spinnakers , down wind in 15 to 25 knots it averaged only 9.7 Knots.
In the 2008 Brisbane Gladstone the average was 10.7 knots.

Well below what we are seeing on polars published here With what I assume is just working sails. Also upwind at 17 with tws 25 and hence 40 over the deck..... I'd like to see that.
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Old 27-04-2008, 01:57   #99
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many thanks Alan.. that was what I ve been looking for.. I will upgrade table ass soon as possible with 2 ton payload and it will be more meaningful..

could you all help me about completing the missing number on the table?
Mamo

There are 2 other figures that give an idea of performance.

Bruce Number: Square root of Actual sail area (in square ft) / cube
root of actual displacement (lbs)

Performance Index: 0,5 x SQRT((Lwl x SA/(Displ x2240))
Lwl and SA in ft/ft2, Displ in tons

Performance Index is an estimate of the relative boat speed to wind speed on a reach, i.e., a figure of 0.6 says a boat will do 6 knots in a 10 knot wind.

I like to use PI as it easier for me to relate to

Regards

Alan
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Old 27-04-2008, 02:34   #100
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Hallo Mamo
I unfortunately have to much work to do to join the ARC however just ask cutomers of mine that have or have purchased a FastCat for the verified results.
If you incude the Fastcat at least put in the correct weights and dimensions see below
Greetings Just a few corrections for the FastCat 435 that is now the 455

The light weight displacement is 5.5 tons including 250 liters of water and 250 liters of diesel, the sail area for the jib is 39,5 meters and for the main 79 meters squire.
The waterline lenght is 12.99 meters

Have a good sunday

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Old 27-04-2008, 06:20   #101
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In the 2008 Brisbane Gladstone the average was 10.7 knots. .
I am not sure which boat you refer to in terms of the Bris gladston average being 10.7 knots. So here are a few finish times.

2008 Brisbane to Gladstone which was predominantly reaching with 5-10 knots early then 10 - 15 late first afternoon and then settling into 15-20 most of the rest.

MONO
Ichi ban - first mono 23.34 (hrs Mins) (volvo 70 canting keel - and I think that any boat that has to run a motor non stop shouldnt be allowed in a sail boat race, but that is a whole other story)

Southern Cross Yachting Sydney 41 - pretty reasonable all round racer cruiser, and sailed by Michael Job - a pretty good sailor - 36 hrs 56 mins

Oscars ride - a sun odessy - a pretty much straight out cruiser 40 hrs 05


MULTI
Raw to the core - 23.16 (outright race boat - a lot like ichi ban cept it cost about 1/10the the money - if that)

The two schionnings (I am not sure which desgn you were referring to as performance cruiser - I think Jeff would suggest that all his boats were performance cruisers - were 28.34 and 31.48 respectively and of course the ability of both these boats is heavily influenced by sail quality sailor quality etc - like most boats

Wilparina was 25 hrs (its a trailerable tri Farrier f9)

All the results are available on the respective club web sites (MYCQ for multis and CYCQ for half boats)
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Old 27-04-2008, 09:21   #102
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This is my new table comparing catamarans.. I added 1800 kg payload colomn and some more cats.. I need your comments, corrections and help for missing numbers..



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Old 27-04-2008, 09:46   #103
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Gideon or mamo,
Could you please explain what the ARC requirements are, what this means and why FastCats do not qualify? Which boats do qualify? What does this mean with regards to safety?
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Old 27-04-2008, 09:48   #104
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Mamo,

I found these specs for the Gunboat 48 from Cruisingworld:

Gunboat 48 Specs

LOA: 48' 4" (14.74 m.)
LWL: 45' 11" (14.00 m.)
Beam: 24' 3" (7.39 m.)
Draft (boards up/down): 1' 1"/7' 5" (0.33/2.26 m.)
Sail Area: 1,106 sq. ft. (102.7 sq. m.)
Displacement: 20,100 lb. (9,117 kg.)
Water: 120 gal. (454 l.)
Fuel: 120 gal. (454 l.)
Engines: Twin Westerbeke 35-hp. diesels
Designer: Morrelli & Melvin
Sailaway Price: $1,680,000


Regards

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Old 27-04-2008, 10:24   #105
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Quote:
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This is my new table comparing catamarans.. I added 1800 kg payload colomn and some more cats.. I need your comments, corrections and help for missing numbers..



hallo Mamo I have given you corrected numbers but you are not using them.
waterline length 12.99
weight includng the 1800 kilo load is 6800
sail area jib 39.5 m2
sail area main 79 m2
total sail area 118.5 m2

greetings
Gideon Goudsmit
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