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Old 06-09-2012, 22:14   #1
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Your Power to Weight Ratio ( Sail area to displacement in kilos )

please post your displacement and sail. for everybody's interest.


there is a lot of talk on here of speeds, and miles sailed per day.


be nice to have some context with that. your specs and your opinion.

Are your sails too big or too small?

What is your Cruising Displacement and how much sail do you have?

Are you happy?

If you were in charge of the sail plan for the very next model of the same boat you have now; would you have more sail? or less sail? would you do anything differently?



Power to Weight Ratio

(or more correctly, Kilograms per meter of sail)

1 meter squared of sail (power) to Kg's of weight.

i've always wanted a metric version, as you can see the relationships instantly. so i did it.


Click image for larger version

Name:	Power.jpg
Views:	663
Size:	225.4 KB
ID:	46119

i found these on dif peeps pages on the web. if you can change any dodgy data, then yes please.
be nice if this list kept growing.


really nice if you posted your boat.

that way we can see where your miles sailed per day fits in.

i'll redo the jpeg every so often if dif peeps add their own boat specs.

i'd also find it real interesting to see live aboard cruisers weights on the scales versus the marketing blurb weights.




Caveat.
Though engineers do it as meters of sail per ton, i did it this way because 85 Kg per meter of sail is a far more meaningful and comprehensible number to a human.

People can instantly relate to the quantities involved as they have experience physically manipulating, manhandling, and dealing with these quantities. One persons weight per meter of sail. This is the most relevant, human and appreciable scale.

(it's impossible to get this forum software to format perfectly).
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Old 06-09-2012, 22:34   #2
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

power to weight ratios in *.txt
http://www.filedropper.com/power


in open doc *.odt
http://www.filedropper.com/powertoweightratios
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Old 07-09-2012, 10:02   #3
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

Appreciate your efforts but I believe Multihull Dynamics has all this already:

Multihull Dynamics, Inc. - Home

free to download individual boats' data, he is selling his 'reviews'
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Old 07-09-2012, 19:10   #4
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

Apparently my Seawind 24 is about 30 KG per M2. Jeff.
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Old 07-09-2012, 20:01   #5
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

The Egan 1240(theoretical-in build) is about 75KG per M2 loaded with gear/stores etc or passenger loads & about 55-57 light.Jeff.
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Old 07-09-2012, 20:16   #6
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

The Beach Marine PC 10M I had was about 58 light & 74Kg per M2 Loaded.Jeff.
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Old 08-09-2012, 11:33   #7
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

Quote:
Originally Posted by tamif27 View Post
Appreciate your efforts but I believe Multihull Dynamics has all this already:

Multihull Dynamics, Inc. - Home

free to download individual boats' data, he is selling his 'reviews'
MY OBSERVATION WHEN VISITING MULTIHULL DYNAMICS TO TEST THE DATA WAS AS FOLLOWS:-

Catana 381:
Multihull Dynamics data;
Weight: 4.4T actual 5.5T
Sail area: 888 ft2 actual 900 ft2

Conser 47:
Multihull Dynamics data;
Weight: 4.5T actual 6T
Sail area: 1024 ft2 actual 1065 ft2

In both cases above the data at MD differs from published data of each boat, therefore making the power to weight ratio (Bruce number) published by MD less than convincing.

Slander comes to mind with you guys in America so I watch my words but read my lips w _ _ _ g.

Multihull Consultant
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Old 08-09-2012, 12:18   #8
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

Weights on cats are always an issue, first the cat is weigthed when it hits the water with out rig , sails cruising gear etc.
Once these items are added the final weight is still not there , one has to add water diesel, a RIB outboard etc etc
In the list in the first post I noticed the Fastcat 435 twice, once as a bare Basalt fibre version 6500 kilo and another one loaded with all possible at 9000 kilo huge difference
A fair comparison would be a bare ready to sail boat plus 250 kilo for each person on board including water diesel etc.
That might give a better way to compare cats.
I noticed on Multihull dynamics the Gunboat 60 ( very nice ) 14996 kilo in Lt condition
on the Guboat websire 16200 in LT condition a difference of 8 % and both in light ship condition.
One or the other changes the SA/ D Ration substantially !!!

It would be nice to start a spread sheet with bare but ready to sail cats and have the possibility to add weight / options etc to show how all changes.
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Old 08-09-2012, 16:04   #9
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

Hallo Bazcatana, I do not know if Multihull Dynamics is to light or if the data from Gunboast themselves are acccurate ? or both.
I know one thing what we boatbuilders aim for and what at the end of the build is accomplished always differs , most of the time boats ( cats ) are heavier than predicted by the designers but sometimes it is the other way around.
It would be great if , once a boat is ready to sail it is lifted out of the water with a accurate load cell to see what the actual weight is. We did that with our hull number 2 and it was 6955 kilo with water and diesel in the tanks ( 50 % )
Many boat builders are not very accurate in the weights given in brochures maybe not even intentionally , they might give the designers estimate of what the boat should weight once finished, if howver the person spraying the gellcoat in to the mould has an off day , the weight obn a 50 ft cat can come out 200 kilos heavier , and that is only one item. the same with bonding paste , resin and other variables in the build process.
all these items together plus any extra,s/options can make a cat a lot heavier than one might expect. In our case I have seen as much as 2500 kilo of extras added to a 44 ft cat. Multihull Dynamics works with data provided by builders and or designers , and that is all they can work with.

Kind regards and thanks for your explanation.
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Old 08-09-2012, 18:30   #10
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

I think the op question is irrelevant. Or is more pertinent to a Hobie Cat forum. Horsepower to weight ratios are only used in handicapping races and not one single cruising catamaran owner I've met could answer this question. I know I can't.

It's always the armchair guys who worry about such things. My advice is for the OP to buy a boat and learn about what's important. Forums are a great introductory, but can only go so far...
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Old 08-09-2012, 19:35   #11
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

Quote:
Originally Posted by PooBeetle View Post
please post your displacement and sail. for everybody's interest.


there is a lot of talk on here of speeds, and miles sailed per day.


be nice to have some context with that. your specs and your opinion.

Are your sails too big or too small?

What is your Cruising Displacement and how much sail do you have?

Are you happy?

If you were in charge of the sail plan for the very next model of the same boat you have now; would you have more sail? or less sail? would you do anything differently?



Power to Weight Ratio

(or more correctly, Kilograms per meter of sail)

1 meter squared of sail (power) to Kg's of weight.

i've always wanted a metric version, as you can see the relationships instantly. so i did it.


Attachment 46119

i found these on dif peeps pages on the web. if you can change any dodgy data, then yes please.
be nice if this list kept growing.


really nice if you posted your boat.

that way we can see where your miles sailed per day fits in.

i'll redo the jpeg every so often if dif peeps add their own boat specs.

i'd also find it real interesting to see live aboard cruisers weights on the scales versus the marketing blurb weights.




Caveat.
Though engineers do it as meters of sail per ton, i did it this way because 85 Kg per meter of sail is a far more meaningful and comprehensible number to a human.

People can instantly relate to the quantities involved as they have experience physically manipulating, manhandling, and dealing with these quantities. One persons weight per meter of sail. This is the most relevant, human and appreciable scale.

(it's impossible to get this forum software to format perfectly).
Well, I don't WORRY about any of it either, I prefer to be sailing , but forums are good when we are hove to , at anchor , or at home due to bad weather , eh? So i'm happy to submit my data here! So . . .
Bristol sloop, 1974 vintage, but better than new condition today. Displaces: 3 tonnes, LOA=8 metres, LML= 7.8 metres, Breadth = 2.5 metres, Draft: 1.2 metres, Wt. of ballast = 2400kg, lead ,encapsulated, Capsize factor 1.7, Sails reg. used; I=9.75m x J 3.2m, P:=8.2m x E:= 3.6 m,SA (fore)15.6m2 , SA(main)14.75m2, total SA=30.35m2
Forestay len. 10.3m, SA to Displacement ratio= 16.45:1, D:L ratio =255:1 so med. cruz for now, We'll go back to the cutter rig next year when I 've replaced the bow sprit and boomkin which are now being rebuild in stanless steel. Hell they gave 40 years service , time to replace them with modern metal components , eh ?
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Old 08-09-2012, 21:11   #12
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

My goal in life is to cut out all the garbage talked about Cat design, it's plain to see what the designers think is important and what is good design and what is second best.

Lets take an example: Catalac design - Zero, Sail area, 10' of Mast cut off all Cats in production (we can Reef guys, so lets have a a Mast to be proud of) Self tacking Jibs, OK if you have good mast height to put the sail area back in the rig. Skeggs are second best to dagger-boards. Fat hulls -Drag. Low Bridge-deck clearance, 2'6'' is the minimum the designers say is required, see Multihull Dynamics. Over weight, this is tied up in the 'Power to weight ratio' but heavy is slow.

If you all concentrate on the 6 important SAILING requirements and then sprinkle some comfort ingredients into the mix and now you have a Catamaran worth it's name CATAMARAN, not Oil Drum.

As you can tell, I am not an Armchair sailor, I'm one of the quick guys who has a day off now and again and enjoys Cruising.

I know - have a day off.

Over and out.

bazcatana
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Old 08-09-2012, 22:17   #13
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

And yet there are a lot of proud and happy catalac owners
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Old 09-09-2012, 01:41   #14
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

A shepherd was herding his flock in a remote pasture when suddenly a brand-new BMW advanced out of the dust cloud towards him. The driver, a young man in a Broni suit, Gucci shoes, Ray Ban sunglasses and YSL tie, leaned out the window and asked the shepherd... "If I tell you exactly how many sheep you have in your flock, will you give me one?" The shepherd looked at the man, obviously a yuppie, then looked at his peacefully grazing flock and calmly answered "sure".
The yuppie parked his car, whipped out his IBM ThinkPad and connected it to a cell phone, then he surfed to a NASA page on the internet where he called up a GPS satellite navigation system, scanned the area, and then opened up a database and an Excel spreadsheet with complex formulas. He sent an email on his Blackberry and, after a few minutes, received a response. Finally, he prints out a 130-page report on his miniaturized printer then turns to the shepherd and says, "You have exactly 1586 sheep. "That is correct; take one of the sheep." said the shepherd. He watches the young man select one of the animals and bundle it into his car.
Then the shepherd says: "If I can tell you exactly what your business is, will you give me back my animal?", "OK, why not." answered the young man. "Clearly, you are a consultant." said the shepherd. "That's correct." says the yuppie, "but how did you guess that?" "No guessing required." answers the shepherd.
"You turned up here although nobody called you. You want to get paid for an answer I already knew, to a question I never asked, and you don't know crap about my business...... Now give me back my dog!"
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Old 09-09-2012, 15:36   #15
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Re: Your Power to Weight Ratio ( Sail area to displacement in kilos )

I have removed a number of commercial posts and others that do nothing but attack members.

This thread is about cat SA/D. Stay on topic.
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