My Bayfield 25 is listed at 3500# displacement but someone actually weighed one at over 5000#. What's the relationship between designed disp and actual weight?
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Pete
weight displacement/actual
Tom, displacement weight is the weight of the WATER that your(or any)boat displaces in the water.Actual weight is just that,the weight of the boat and any and all gear on the boat.(think of it as being on a scale)Actual weight and displacment weight and almost always the same (some exceptions) Manufactures almost always list weight with no water and fuel(or very little).Think about all the gear you have on your boat and 1500 pounds is not a surprising difference. There are people who have had to change the water line because of adding weight to the boat (think liveaboards) Hope this has been of some help !
Tom, displacement weight is the weight of the WATER that your(or any)boat displaces in the water.Actual weight is just that,the weight of the boat and any and all gear on the boat.(think of it as being on a scale)Actual weight and displacment weight and almost always the same (some exceptions) Manufactures almost always list weight with no water and fuel(or very little).Think about all the gear you have on your boat and 1500 pounds is not a surprising difference. There are people who have had to change the water line because of adding weight to the boat (think liveaboards) Hope this has been of some help !
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Bill
Pete's right
The exception is when the boat sinks when you put it in the water, i.e., fails to displace her weight in water. You can think of the boat being lowered into the water as being like a scales, with water as the counterbalance. The boat will be drawn downward by gravity just until the water pushed aside (and upwards, against gravity) matches the boat in weight. If the boat weighs more than the volume of water it displaces, it keeps going. I'm just now reading a great book "The Nature of Boats" (by naval architect Dave Gerr). In his chapter on Displacement, he says that quoted displacement is often the weight without crew, stores, sails, etc., which often add 50 percent to the weight, and therefore to the displacement.
The exception is when the boat sinks when you put it in the water, i.e., fails to displace her weight in water. You can think of the boat being lowered into the water as being like a scales, with water as the counterbalance. The boat will be drawn downward by gravity just until the water pushed aside (and upwards, against gravity) matches the boat in weight. If the boat weighs more than the volume of water it displaces, it keeps going. I'm just now reading a great book "The Nature of Boats" (by naval architect Dave Gerr). In his chapter on Displacement, he says that quoted displacement is often the weight without crew, stores, sails, etc., which often add 50 percent to the weight, and therefore to the displacement.
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RonD
Added confusion trivia
Internationally, boats are rated by Gross Registered Tonnage (GRT). That's something you'll see on your USCG Documentation certificate. GRT isn't a weight, either; it's a volume measure of the potential cargo capacity below decks. So, my C320 displaces 11,900lb (according to Catalina). Fully loaded with fuel, water, food, a crew of four, and gear I've barely noticed any change with regard to the waterline stripe. The GRT is 10 tons. I suppose that if I were ever to load it with anything close to 10 tons of cargo, the boat would sink, too.
Internationally, boats are rated by Gross Registered Tonnage (GRT). That's something you'll see on your USCG Documentation certificate. GRT isn't a weight, either; it's a volume measure of the potential cargo capacity below decks. So, my C320 displaces 11,900lb (according to Catalina). Fully loaded with fuel, water, food, a crew of four, and gear I've barely noticed any change with regard to the waterline stripe. The GRT is 10 tons. I suppose that if I were ever to load it with anything close to 10 tons of cargo, the boat would sink, too.
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Peggie Hall/Head Mistress
Ship's Tonnage has nothing to do with weight.
of the vessel, or its cargo, or displacement. It is a measure of how much wine a vessel can carry. The word "tun" was originally a size of a cask used to ship wine from Spain & Portugal to England. In 1347 a tax of 3 shillings per tun was imposed and this was called "tonnage." A ship's size became known by the number of casks it could carry, and the word tonnage started being used to describe a ship's size. It was found that if you took the length x the breadth x the depth of the hold under the deck and divided by 100 it was close to the number of casks. That is where we get the "Measurement ton" of 100 cubic feet per ton. There are several kinds of tonnage: The first two are used by the tax collector. The next two are used by designers. The fifth and sixth are used by freight salesmen and canal operators and the last one is used by the USCG for documenting boats. Gross Tonnage - is the internal volume in cubic feet of the vessel minus certain spaces above the main or "tonnage" deck, like stacks and ventilators, which are called "exemptions" . Net Registered Tonnage - is obtained by deducting from the gross tonnage the volume of space that can't be used for paying cargo or passengers, that is to say the space occupied by the engines, the crew's quarter, the stores, etc. Displacement Tonnage - is the actual weight of the water "displaced" by the ship and is usually quoted in long tons of 2240 lbs. Light Displacement Tonnage - is the weight with nothing in it. Loaded Displacement Tonnage - is the fully loaded weight to the maximum and is on her summer draft in salt water. Deadweight Tonnage - is the difference between Light and Loaded Displacement Tonnage....the actual carrying capacity of the vessel. Panama & Suez Canal Tonnages - these are different from the internationally accepted definitions. There used to be a lot of variations between countries and the canal owners thought they were being conned, so they came up with their own definitions. Simplified Measurement System - The USCG decided that all this was way too much for bureaucrats to deal with for yachts so they came up with their own formula: Take the horizontal distance between the outboard ends of the boat not including rudders and bow sprits. Multiply that by the maximum beam outside to outside. Multiply that by the distance from the sheer line not including bulwarks or cap rails to the outside bottom of the hull not including the keel. Add the volume of the deck house/cabin top. Multiply by .5 for sailboats and .67 for power boats. Divide by 100. This will give you the "Gross Tonnage". Net tonnage is 90% of gross for sailboats and 80% for power boats. It should be obvious to anyone who's managed to get this far that your boat's "tonnage" no longer has anything to do with anything real; it only exists in the mind of some government bureaucrat. Btw...Rummage was the manner in which the wine casks were stored in the hold of the ship and came to refer to the whole ship's cargo. After a voyage any unclaimed and damaged cargo was stacked on the dock beside the boat and offered for sale - a rummage sale. Another word of French maritime origin.
of the vessel, or its cargo, or displacement. It is a measure of how much wine a vessel can carry. The word "tun" was originally a size of a cask used to ship wine from Spain & Portugal to England. In 1347 a tax of 3 shillings per tun was imposed and this was called "tonnage." A ship's size became known by the number of casks it could carry, and the word tonnage started being used to describe a ship's size. It was found that if you took the length x the breadth x the depth of the hold under the deck and divided by 100 it was close to the number of casks. That is where we get the "Measurement ton" of 100 cubic feet per ton. There are several kinds of tonnage: The first two are used by the tax collector. The next two are used by designers. The fifth and sixth are used by freight salesmen and canal operators and the last one is used by the USCG for documenting boats. Gross Tonnage - is the internal volume in cubic feet of the vessel minus certain spaces above the main or "tonnage" deck, like stacks and ventilators, which are called "exemptions" . Net Registered Tonnage - is obtained by deducting from the gross tonnage the volume of space that can't be used for paying cargo or passengers, that is to say the space occupied by the engines, the crew's quarter, the stores, etc. Displacement Tonnage - is the actual weight of the water "displaced" by the ship and is usually quoted in long tons of 2240 lbs. Light Displacement Tonnage - is the weight with nothing in it. Loaded Displacement Tonnage - is the fully loaded weight to the maximum and is on her summer draft in salt water. Deadweight Tonnage - is the difference between Light and Loaded Displacement Tonnage....the actual carrying capacity of the vessel. Panama & Suez Canal Tonnages - these are different from the internationally accepted definitions. There used to be a lot of variations between countries and the canal owners thought they were being conned, so they came up with their own definitions. Simplified Measurement System - The USCG decided that all this was way too much for bureaucrats to deal with for yachts so they came up with their own formula: Take the horizontal distance between the outboard ends of the boat not including rudders and bow sprits. Multiply that by the maximum beam outside to outside. Multiply that by the distance from the sheer line not including bulwarks or cap rails to the outside bottom of the hull not including the keel. Add the volume of the deck house/cabin top. Multiply by .5 for sailboats and .67 for power boats. Divide by 100. This will give you the "Gross Tonnage". Net tonnage is 90% of gross for sailboats and 80% for power boats. It should be obvious to anyone who's managed to get this far that your boat's "tonnage" no longer has anything to do with anything real; it only exists in the mind of some government bureaucrat. Btw...Rummage was the manner in which the wine casks were stored in the hold of the ship and came to refer to the whole ship's cargo. After a voyage any unclaimed and damaged cargo was stacked on the dock beside the boat and offered for sale - a rummage sale. Another word of French maritime origin.
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