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DISP@DWL What Does This Mean ?


ebenton009

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Displacement at designed water line. The total weight of boat, crew and gear for which the boat is designed will result in the boat floating at that waterline. It indicates what the designer thinks is a reasonable load for the boat as designed. Obviously this is a guide not an immutable law. Heavier loads (to some degree) would be OK especially in more protected waters. Lighter is always better for performance.

Of course sailors always want maximum speed while taking along the kitchen sink. :D

Cheers

Peter HK

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Welcome to the forum.

 

Displacement is the weight of the water that's pushed out of the way, when the boat is floating. This figure changes with crew, equipment, supplies, how many beers are consumed during the sail, etc. The DWL (Designed Waterline Length) is generally an ideal volume the boat will display, given a specified (often quite generally as well) load. The waterline length will change with loading, because the boat will have more or less volume pushing on the hull, when afloat.

 

More important information in regard to your question might be the PPI (Pounds Per inch of Immersion). For example, you might find a PPI for the BRS of say 250 pounds, which means if you add 250 pounds to the boat, it'll settle down one inch more. For specific maximum loading, Graham will be happy to offer some set figures, though I think you'll find it's pretty hard to max out the BRS or Core Sound series designs, as they're hearty and very capable. This said, any boat will progressively lose some level of ability and performance, once significantly over the DWL figure. Simply put, this means she'll be a bit more sluggish, not as fast, doesn't accelerate as quickly, etc., as loads increase, but this is true of any boat.

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One thing to remember is DWL is a somewhat arbitrary line used in the design process to figure out hydrostatics. Moving the DWL up or down a little bit changes this hydrostatics, usually not all that drastically. DWL doesn't mean maximum safe displacement. Overloading any boat is unsafe, but my experience with my CS17 is that it will haul quite a large load quite satisfactorily.

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  • 2 weeks later...

Displacement is the weight of the water that's pushed out of the way, when the boat is floating. This figure changes with crew, equipment, supplies, how many beers are consumed during the sail, etc. 

 

Hmmm. I always thought that mere consumption of beers didn't affect displacement as much as the rate of discharge over the side* after being "processed" by the crew?

 

My cooler-to-belly consumption merely increases righting moment since the cooler is on centerline and I'm on the gun'l; just shifting the ballast to where it is more useful, so to speak. This is how I explain the increase in speed, but more erratic wake as the afternoon goes on.  ;)

 

*12 miles off-shore, of course. 

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Hi Don

 

Not to stray too far off-topic or bore the others: I have an old 110 keel (as if there are "new ones" laying around, right)--the hull project was delayed by the arrival of kids, etc. but that or an EC22 are back on the burner...sent you a PM with the history of the 110 project. 

 

Cheers, Pat. 

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