Have a friend who wants to keep a Hunter 34 on a lift. Needs to know how big of a lift to buy. How much does a 34 weigh? Is it the displacement number which I looked up?
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Do they make a lift for a sailboat?
Jim: Do they actually make a lift for a sailboat? With a powerboat you can just drive into your slip and start pumping the tanks with air. The boat is basically floating. The floats are connected together underwater. With a sailboat how are you going to get the keel past the area where the tanks are connected on the aft of the system. When you consider the weight of the boat remember that the published weight is probably very understated and it does not even consider the gear that most sailors would or may have aboard. I do believe that this takes into consideration water and fuel. I would bet that you would need a 14k-16k lbs unit.
Jim: Do they actually make a lift for a sailboat? With a powerboat you can just drive into your slip and start pumping the tanks with air. The boat is basically floating. The floats are connected together underwater. With a sailboat how are you going to get the keel past the area where the tanks are connected on the aft of the system. When you consider the weight of the boat remember that the published weight is probably very understated and it does not even consider the gear that most sailors would or may have aboard. I do believe that this takes into consideration water and fuel. I would bet that you would need a 14k-16k lbs unit.
Thanks Steve
Steve, My friend (I have never considered putting a sailboat on lift) has slip available for free that has enough water at high tide but not enough at low and has decided on a lift solution. He tells me that they make lifts at least as high as 15,000lbs. I looked up in spec section a Hunter 34's displacement - 11.000 and something. I know that does not include water, fuel, gear but is it even the weight. I am a lawyer - if I understood mathor physics I would be a doctor - does displacement weight equal lift weight putting aside for a moment the extra weight issue?
Steve, My friend (I have never considered putting a sailboat on lift) has slip available for free that has enough water at high tide but not enough at low and has decided on a lift solution. He tells me that they make lifts at least as high as 15,000lbs. I looked up in spec section a Hunter 34's displacement - 11.000 and something. I know that does not include water, fuel, gear but is it even the weight. I am a lawyer - if I understood mathor physics I would be a doctor - does displacement weight equal lift weight putting aside for a moment the extra weight issue?
One pound of boat displaces one pound of water
So, displacement is the weight of the boat. That what you are looking for?
So, displacement is the weight of the boat. That what you are looking for?
Isn't the Displacement and Weight Different Things
I always understood that what made a boat float was that it displaces more water (by weight) than what it weighs.
I always understood that what made a boat float was that it displaces more water (by weight) than what it weighs.
Rick, hope this helps
The reason a boat floats is that it displaces its own weight in water. A 10,000 pound object whose proportions (volume) are such that it displaces less than 10,000 pounds of water will sink. An object whose proportions are such that if held under water displaced more than it's say 10,000 punds of weight, will float with some freebaord above the water line when let go. It has to do with gravity. I find it convenient to think of Archimedes coming to the realization that in sinking into the tub, he made an amount of water equal to his weight rise as his body pushed is aside (displaced it). The concepts are a bit tricky I know. Found them that way myself.
The reason a boat floats is that it displaces its own weight in water. A 10,000 pound object whose proportions (volume) are such that it displaces less than 10,000 pounds of water will sink. An object whose proportions are such that if held under water displaced more than it's say 10,000 punds of weight, will float with some freebaord above the water line when let go. It has to do with gravity. I find it convenient to think of Archimedes coming to the realization that in sinking into the tub, he made an amount of water equal to his weight rise as his body pushed is aside (displaced it). The concepts are a bit tricky I know. Found them that way myself.
goodness!
Displacement is the THEORETICAL designed weight of the boat plus everything in it such as tankage, gear, passengers, et cetera. Displacement is always greater than actual boat weight, or else the boat would sink, as per Archimedes, who said that an object is buoyed up by a force equal to the weight of the liquid displaced.
Displacement is the THEORETICAL designed weight of the boat plus everything in it such as tankage, gear, passengers, et cetera. Displacement is always greater than actual boat weight, or else the boat would sink, as per Archimedes, who said that an object is buoyed up by a force equal to the weight of the liquid displaced.
Thanks to all for remedial science
Thanks. I am visiting my parents this weekend and will mention that perhaps they should seek a rebate on their property taxes as I somehow missed the whole Archimedes/bathtub thing.
Thanks. I am visiting my parents this weekend and will mention that perhaps they should seek a rebate on their property taxes as I somehow missed the whole Archimedes/bathtub thing.
Eureka?
Sound like we all understand the principle but we are not expressing it well. Maybe there is a grade school science teacher out there who can give us a more understandable explanation. Seems like it was explained to me by three examples. 1. a rock - the weight of the water it displaces is less than the weight of the rock, it sinks 2. - a submarine can adjust it's weight whereby it weighs the same as the water it displaces, it is neutrally buoyant and does not sink or float 3.- a boat displaces a greater weight of water than it weighs itself, it floats Perhaps hunter could provide the shipping weight for a 34 that would be a closer number than the displacement I would think. None of this helps helps Jim figure out how big a lift his friend is going to need but it sure beats working on a Friday. Come to think of it I am leaving now and going sailing.
Sound like we all understand the principle but we are not expressing it well. Maybe there is a grade school science teacher out there who can give us a more understandable explanation. Seems like it was explained to me by three examples. 1. a rock - the weight of the water it displaces is less than the weight of the rock, it sinks 2. - a submarine can adjust it's weight whereby it weighs the same as the water it displaces, it is neutrally buoyant and does not sink or float 3.- a boat displaces a greater weight of water than it weighs itself, it floats Perhaps hunter could provide the shipping weight for a 34 that would be a closer number than the displacement I would think. None of this helps helps Jim figure out how big a lift his friend is going to need but it sure beats working on a Friday. Come to think of it I am leaving now and going sailing.
Weight and displacement are NOT the same
The general misconception is that the boat is measured in weight, i.e., pounds as if it were on a scale. While this can easily be discerned from the advertised 'displacement' of the boat --i.e., that a 15,000-lb boat weighs 15,000 lbs when you load it onto a trailer-- this is NOT how displacement is determined. Displacement is NOT the weight of the water displaced (as in the analogy of a 1-lb rock displacing one lb of water) but the VOLUME. One cubic foot of boat displaces one cubic foot of water. We can easily attribute weights in averdupois to that, but-- give me a minute here. The designer goes through excrutiating mathematical calculations to determine the volume of the underbody of the boat-- it is NOT as simple as hanging the thing from a scale and taking a reading in pounds. In fact he doesn't care about pounds. Once the displacement figure is published it falls to the shop to ensure that their work will produce a boat which not only weighs in correctly but also that it's not out of trim anywhere. A poor design job can have catastrophic results (I knew an owner-designer once whose boat would not float level at all, due to design, not being loaded out of trim. It was scrapped for parts in the marina). How much the boat then weighs whilst in the water depends on the weight of the WATER, not the weight of the boat, which is constant all round the earth (forget lunar pull for this argument). Salt water weighs 62 lbs per cubic foot. Fresh water weighs 64. So you will see that regardless of the weight of the boat, a given hull will 'displace'-- push aside-- less water (and therefore less weight of it) in salt than in fresh water. For obvious reasons all responsible designers design for fresh water and let the thing be more buoyant in salt water (and who could calculate for brackish??). As far as the trailer goes, use the displacement figure for the boat's weight out of water-- just don't confuse the two when the boat is IN the water, because they are NOT necessarily the same even if the resulting figures may suggest they are. As I've said before I did a lot of work for my dad-- he was injured when I was 16 and one of my jobs then was to calculate the displacement of the original Hunter 30 (10002 lbs). This was in the days before calculators and CAD software and was done with a plinometer and a slide rule. I imagine there may even be commercial designers out there today who do not know how to calculate displacement without the aid of computers... but more's to pity them for they cannot shed light on an issue like this if all they do is double-click on a window and publish what the idiot box tells them to say. J Cherubini II Cherubini Art
The general misconception is that the boat is measured in weight, i.e., pounds as if it were on a scale. While this can easily be discerned from the advertised 'displacement' of the boat --i.e., that a 15,000-lb boat weighs 15,000 lbs when you load it onto a trailer-- this is NOT how displacement is determined. Displacement is NOT the weight of the water displaced (as in the analogy of a 1-lb rock displacing one lb of water) but the VOLUME. One cubic foot of boat displaces one cubic foot of water. We can easily attribute weights in averdupois to that, but-- give me a minute here. The designer goes through excrutiating mathematical calculations to determine the volume of the underbody of the boat-- it is NOT as simple as hanging the thing from a scale and taking a reading in pounds. In fact he doesn't care about pounds. Once the displacement figure is published it falls to the shop to ensure that their work will produce a boat which not only weighs in correctly but also that it's not out of trim anywhere. A poor design job can have catastrophic results (I knew an owner-designer once whose boat would not float level at all, due to design, not being loaded out of trim. It was scrapped for parts in the marina). How much the boat then weighs whilst in the water depends on the weight of the WATER, not the weight of the boat, which is constant all round the earth (forget lunar pull for this argument). Salt water weighs 62 lbs per cubic foot. Fresh water weighs 64. So you will see that regardless of the weight of the boat, a given hull will 'displace'-- push aside-- less water (and therefore less weight of it) in salt than in fresh water. For obvious reasons all responsible designers design for fresh water and let the thing be more buoyant in salt water (and who could calculate for brackish??). As far as the trailer goes, use the displacement figure for the boat's weight out of water-- just don't confuse the two when the boat is IN the water, because they are NOT necessarily the same even if the resulting figures may suggest they are. As I've said before I did a lot of work for my dad-- he was injured when I was 16 and one of my jobs then was to calculate the displacement of the original Hunter 30 (10002 lbs). This was in the days before calculators and CAD software and was done with a plinometer and a slide rule. I imagine there may even be commercial designers out there today who do not know how to calculate displacement without the aid of computers... but more's to pity them for they cannot shed light on an issue like this if all they do is double-click on a window and publish what the idiot box tells them to say. J Cherubini II Cherubini Art
But........
Many thanks for the great explanation, JCII, but surely there is a typo..? Isn't the salt water 64 lbs, not the fresh?
Many thanks for the great explanation, JCII, but surely there is a typo..? Isn't the salt water 64 lbs, not the fresh?
Weight of my 85 34 when shipped
When my boat(85 H34 #686 shoal draft) was hauled(dried out)and put on the trailer for shipping it weighed in at a whopping 14,287lbs( weight of trailer has been removed). This was on a certified scale(DOT demands that they are). This included sails(3 sets), instruments, and about 300lbs of spare parts. Sails weighed in at about 225lbs.
When my boat(85 H34 #686 shoal draft) was hauled(dried out)and put on the trailer for shipping it weighed in at a whopping 14,287lbs( weight of trailer has been removed). This was on a certified scale(DOT demands that they are). This included sails(3 sets), instruments, and about 300lbs of spare parts. Sails weighed in at about 225lbs.
Big difference from the published weight!
Gene: That's about 20% heavier than the published spec's.
Gene: That's about 20% heavier than the published spec's.
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