Displacement weight versus actual weight

I've been looking at cradles and trailers to keep my sailboat on. The boat is an Alberg 30. The displacement is 9000lbs/4,082 kg. The boat is an early non liner boat. Everything is built into the hull so it should be lighter from my understanding. When I take into account everything in and on the boat, I come to a weight of around 6000lbs/2721kg. A member on another forum said his boat in cruising trim was 6600lbs/2993kg hanging in the slings. Why would I need a 12,000lbs/5443kg cradle or trailer to keep my boat on? That's double what the actual weight of the boat is and those heavy weight cradles and trailers are insanely expensive.

 

Displacement and weight are identical values. The first is the weight of the displaced water when the boat is floating. The other is the direct weight measurement of the boat. If the displacement is 9000 lbs, so is the weight. If it weights 6000 lbs, however you measured that, the displacement is 6000 lbs. How did you weigh the boat?

 

I haven't weighed mine. A member on another forum was told his weight (6600lbs) while the boat was hanging in the travel lift slings. I remembered the info but wish I had bookmarked the thread in the forum. I thought the manufacturer's stated displacement weight was the maximum weight a boat could have all in loaded to the max with gear, full tanks, persons, etc... My boat is very basic with empty tanks, no head, and no soft goods. No nothing except the furniture, drive line, and stuff built in the boat from the manufacturer. There's no way the boat weighs 9000lbs the way it sits.

 

There are two ways to find out the weight/displacement of the boat. Weigh the boat directly, is the easy one. You can calculate the immersed volume of the hull and multiply by the density of water and it will give you the weight. You can't reliably get a weight/displacement from rumors or hearsay.

 

Weighing in a Travelift is notoriously inaccurate unless it has been calibrated.
The displacement/weight the designer gives are with the boat floating on its "designed" water line.
That usually includes 1/2 the water and fuel capacity plus an allowance for some stores and personal gear.

SailboatData.com - ALBERG 30 Sailboat

 

It's hard to tell form sales literature what's what.