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Old Nov 28, 2011, 08:03 AM
A posse ad esse
United States, FL, Tampa
Joined Feb 2011
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Is There a Way to Calculate Keel Weight?

I recently acquired a model sailing yacht plan, but it's annotations are written in Russian. Shown on the plans is a keel weight cast from lead (I presume) but I am curious how to calculate the amount of actual weight that will be required for the keel. Is there a formula for this?
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Old Nov 28, 2011, 08:56 AM
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Keel Weight

From the drawings, the boat appears to be a model of an International Star class boat. One might look at that classes rules (find them on the web), then develop a ratio of model length/prototype length. Use that ratio cubed, (multiplied by itself 3 times) to find the ratio of volumes between the two. Then multiply the prototype keel weight by the ratio cubed to find the weight of the scaled model.

Check with the AMYA Star 45 class rules to see what they are using for a keel weight, and perform the same exercise. The result will be a different calculated weight for your model, but you'll at least have a couple points of reference.

Remember to use the same length units for all the calculations.

rodcarr@carrsails.com
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Old Nov 28, 2011, 09:46 AM
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disabled's Avatar
Vienna/Austria
Joined Jan 2009
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Hull length?

From the proportions I see I would say 90cm.

Maybe in the range of 2.5 to 3.0 kg therefore.
but thats just an estimate for now.
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Old Nov 28, 2011, 09:51 AM
A posse ad esse
United States, FL, Tampa
Joined Feb 2011
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Originally Posted by disabled View Post
From the proportions I see I would say 90cm.

Maybe in the range of 2.5 to 3.0 kg therefore.
but thats just an estimate for now.
Wow. I would have never guessed that much weight. In the past, have built many static scale model ships, but never an RC sailing ship. As a matter of fact, don't even know how to sail an RC ship. Maybe I should start with an RC proven design or a kit. At least then I could read the instructions/annotations.

Cheers
Craig
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Old Nov 28, 2011, 11:23 AM
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Canada, BC, Maple Ridge
Joined Jul 2011
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If you are interested in the look of the Star and want to build one, there is an excellent class already called the Star 45. There is a class web site

http://groups.yahoo.com/group/Star45/

Join the group.

Then you will find links to get the plans and also to get the frames already laser cut to assist the building process.

John
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Old Nov 28, 2011, 12:25 PM
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Auckland New Zealand
Joined Sep 2010
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The plan shows length 750mm beam 185mm mast height 980. with the short keel depth I would estimate the bulb weight to be about 2Kg. The plan is a similar size to a Victoria.
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Old Nov 28, 2011, 12:39 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
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KIWINB, coming from NZ, I'd have expected you to suggest the Racing Sparrow http://www.racingsparrow.co.nz/ which is much better documented for a beginner as well as being quite nifty according to what I have heard.
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Old Nov 28, 2011, 01:03 PM
A posse ad esse
United States, FL, Tampa
Joined Feb 2011
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Originally Posted by martin richards View Post
KIWINB, coming from NZ, I'd have expected you to suggest the Racing Sparrow http://www.racingsparrow.co.nz/ which is much better documented for a beginner as well as being quite nifty according to what I have heard.
Now, that's what I need. Don't think I will have any trouble building a ship model, but something that takes me through the learning curve for RC sailing will be extremely helpful to begin with.

Are there any designs that incorporate a motor and screw to go along with sail? I promised a good friend I would build him a model ship as a gift to sail while he sits at the dock in his back yard on the river. There is tidal current as well as normal flow, so something with a motor may be more useful for him as I am not sure a sailing vessel would be appropriate on a river. I live at a lake, so a sailing vessel is fine for my own model.

Thanks to everyone who has replied. You have all given me very helpful information.

Craig
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Old Nov 28, 2011, 02:29 PM
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Asturias, Spain
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http://www.cornwallmodelboats.co.uk/...pner_1175.html is afaik the only motor specifically made for model sailing boats. I'm not sure who handles Graupner products in the USA.
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Old Dec 14, 2011, 08:49 AM
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Hi daddyrabbit 1954 you want to find what you require for keel weight.I use this method for getting an idea.once the hull is waterproof I use plastic bottles all but one his full of water.the last bottle is to trim the hull to its water line in a test tank.when it is correct weigh the bottles of water in their containers. All this gives you is how much weight is left available to add to your hull,from this point weigh all that is applicable,radio batteries.mast sails and fittings etc., before you fit to the hull till the only thing left is the keel weight required.Don't forget that if you have to paint it that must be added by approximation.
Hope this helps and good luck Tricat
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