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-   -   Quick displacement question... (http://www.sailnet.com/forums/general-discussion-sailing-related/18053-quick-displacement-question.html)

kclaybrook 07-09-2006 07:13 PM

Quick displacement question...
 
I have a quick question re: weight specs of boats. When finding the TOTAL weight of a boat, do you add the displacement and the ballast, or is the displacement the TOTAL weight? Might be a silly question, but I have no idea. I am looking at a '78 Ranger 22, and the displacement is 2189 with a ballast of 900. Went out on it today and loved it.

sailingdog 07-09-2006 08:28 PM

The displacement is the total weight of water displaced by the hull of the boat, and includes the ballast. This is generally quite different from the dry weight of a boat... which is what the boat actually weighs, not how much water it displaces.

My guess is the that the 2189 is the dry weight, including the ballast.

kclaybrook 07-09-2006 09:05 PM

That is what I thought, but the owner thinks that the dry weight (thanks for that term) is around 3000 lb. Are there any Ranger 22 owners that know that they know the dry weight of the boat? Thank you for any additional info.

Jeff_H 07-09-2006 09:15 PM

Unless they repealed Archimedes's law, a boat's displacement is equal to the boat's weight at some theoretical loading. (and that total displacment would include ballast). Since the designer usually gets to sellect the loading at which he calculates the displacement, the designer can chose to use a dead empty weight, or some partial loading or some maximum loading. Race boats are the exception to the designer chosing the loading at which displacement is calculated. Race rules define what can and what cannot be used in calculating the displacement. The Ranger 22 was an IOR mini-tonner and so had its displacement calculated as defined by the IOR rule of that era which would have included normal gear aboard.

If you can find one, a Ranger 23 is a far superior boat on all counts.

Jeff

Surfesq 07-09-2006 09:24 PM

Jeff: With all due respect, Archimedes' Law: Objects may displace fluids. If the mass of the displaced fluid is greater than the mass of the object, the object will float. If it is less, the object will sink. The density of an object is the mass of the object divided by its volume. Objects denser than the fluid they are in will sink, less dense objects will float.

kclaybrook 07-09-2006 09:36 PM

Thanks Jeff. I have been looking at boats for a while. I have just started learning to sail this year. I have been looking for something that my wife and I can handle ourselves and learn at our own pace. The sailing club we joined has a learners program, but it is hard to learn much in 2 hours a week sharing a boat with 5 or 6 other people. The other major factor is $. This Ranger is listed at $4000 with trailer. Nashville, TN is not a major market for used sailboats, so this is the first boat that meets all of our criteria. What do you guys think of the 22 as a first boat? (besides the 23 being a superior boat)

Jeff_H 07-09-2006 09:37 PM

Surfesq:

With all due respect, you are forgetting the relevant Archimedian law, which is an object that floats in a liquid will displace a volume of that liquid equal in weight to the object in question.

Jeff

Surfesq 07-09-2006 10:06 PM

No Jeff, you are describing the mathmatical equation that is derived from the principal that states that any object floating upon or submerged in a fluid is buoyed upward by a force equal to the weight of the displaced fluid. With all due respect. Now why don't you answer Clay's question.
Clay: The 22 is a nice boat and is perfect for a first boat. Enjoy!

Jeff_H 07-09-2006 10:21 PM

Surfesq:
I suggest that you bone up on Archimedes' law by following to this link http://www.walter-fendt.de/ph14e/buoyforce.htm where you will find Archimede's law stated as Follows:

Law of Archimedes:The buoyant force is equal to the weight of the replaced liquid or gas.

Or to this site http://www.phy.cmich.edu/people/osbo...Chapter8.htm#F where they also define Archimedes' law as follows:
A body partially or wholly immersed in a fluid is buoyed up by a force equal to the weight of the fluid it displaces.


Clay:
The Ranger 22 is a pretty nice little boat, albeit a little more squirely in higher winds (winds over about 12 knots) than non-IOR derived designs from the same era. They make a reasonably good first boat, but are not the easiest boats to sail in gusty conditions.

Jeff

Surfesq 07-09-2006 10:28 PM

Now Jeffy...go back read what I wrote. You simply repeated what I wrote. The first link is nonsense by the way. But if you makes you feel better you win okay? Now go to bed.


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