Boat weight?
- Thread starter marchem
- Start date
Jim, I agree that the angle of the straps has nothing to do with the actual weight of the boatHold the horses...
Almost all big weighing scales, fork lifts, cranes, etc. use "strain cells" and are good to maybe 3 digits of precision.
So to make a lift safely, all crane lift points have a strain cell and are SUMMED for Total Weight.
If that is NOT true, stop using that lift. UNSAFE!!!
If that lift has not recently calibrated their strain cells [by license and law they must]
Lookout boat!
ANGLE of the straps has ZERO to do with total weight. However the Angle of lift, of a single boom crane, is key to prevent "tipping".
If those strains cell said 16,000 lbs and they were calibrated correct, then your boat weight is 16k ±1k precision.
. If there is only a single lift point then the weight of the boats is the same as the load measured at the strain cell. However, in this case there are 4 strain cells (2 lifting straps), and because the straps come in at an angle (maybe 10-20 degrees from vertical) the load measured by the strain cells is greater than the weight of the boat. The front strap/cells read 8000 and the aft strap/cells read 8000 for a total load of 16,000 lbs with a boat weight of 14-15,000 lbs.See this description: https://www.ropebook.com/information/vector-forces/
I asked the guy running the travel lift if he ever got complacent. He said: "If you're not puckered you're not paying enough attention"!!
Sorry guys, nice try...
Boat Displacement "dead" weight is Floating weight [water weight of the Volume of the " hole" in fresh water that the boat makes floating] at Designer boat load conditions. This is normally without "live loads".
Cargo incremental displacement weights are added weights and rough [very imprecise additional cargo load]
Strain Cells will be actual lift loads [if cells are calibrated]. Angle effects = Zero
A static floating boat fresh water weight = ZERO
Jim...
PS: I did read your links. I don't mean to argue in a forum.
Boat Displacement "dead" weight is Floating weight [water weight of the Volume of the " hole" in fresh water that the boat makes floating] at Designer boat load conditions. This is normally without "live loads".
Cargo incremental displacement weights are added weights and rough [very imprecise additional cargo load]
Strain Cells will be actual lift loads [if cells are calibrated]. Angle effects = Zero
A static floating boat fresh water weight = ZERO
Jim...
PS: I did read your links. I don't mean to argue in a forum.
When a designer designs a boat, they will use whatever tools they have available to estimate the boats 'light displacement'; the displacement of the hull, sails, lines.
When in this 'light' mode, the boat will sit inches above her lines.
When loaded down with the anticipated gear and tankage compatible for her design brief, she will sit on her LW (Load Waterline), which is where the LWL measurement comes from. That gear can weigh several thousand pounds.
N.B. - Builders never 'weigh' boats to get displacement, they use the designer's numbers. And this can be WAY off, due to both errors in the calculations, and also in variances of hundreds of pounds in the build process. Often boats in the same model can weigh hundreds of pound different based on how much resin was used in construction.
When in this 'light' mode, the boat will sit inches above her lines.
When loaded down with the anticipated gear and tankage compatible for her design brief, she will sit on her LW (Load Waterline), which is where the LWL measurement comes from. That gear can weigh several thousand pounds.
N.B. - Builders never 'weigh' boats to get displacement, they use the designer's numbers. And this can be WAY off, due to both errors in the calculations, and also in variances of hundreds of pounds in the build process. Often boats in the same model can weigh hundreds of pound different based on how much resin was used in construction.
And sanded, and painted, and buffed/polished/waxed, and replacing the cutlass bearing....
I agree with everything you are saying: the strain cells will see the actual lift load. However, if there is an angle in the straps then that lift load will be greater than the weight of the boat (as it comes out of the water!).Sorry guys, nice try...
Boat Displacement "dead" weight is Floating weight [water weight of the Volume of the " hole" in fresh water that the boat makes floating] at Designer boat load conditions. This is normally without "live loads".
Cargo incremental displacement weights are added weights and rough [very imprecise additional cargo load]
Strain Cells will be actual lift loads [if cells are calibrated]. Angle effects = Zero
A static floating boat fresh water weight = ZERO
Jim...
PS: I did read your links. I don't mean to argue in a forum.
Technically it doesn't matter if it's fresh water, salt water, or hypersaline. The weight of the volume of liquid displaced is the displacement weight. That's the gist of Archimedes' "Eureka" principle.
Not an argument, just a healthy discussion.
All crane weights are approximate not legal weights.
My first "real job" was working at a boat yard with a very large travel lift on the west coast. Not the dinky things I seen in the midwest for winter haulouts. I often talked with the operator about boat weights and lift readings and he had to zero the scale to get an "official" weight. This means that the lift needed to read zero with all straps, pins, etc rigged and wet. Depending on the size of the boat sometimes it was 2 large straps, other times 4 large straps or more. this would give him a boat weight. However if it was not zeroed (and not done unless requested beforehand as time is $$) then you also get the weight of the straps, blocks, etc... for whatever the last setup was when it was zeroed. Often the crane scale was set to read heavy to keep the operator safe. The travel lift tires are foam filled so they cannot blow out but the frame if overloaded can fold if the crane is over taxed and trust me then the bells go off as a multi million dollar yacht comes out of the water you will see the operator sweat big time!
Fast forward a number of years and I worked for a wind turbine company still playing with large cranes. In Fact at the time to lift a new large MW turbine into the air it took a specialised crain of which there were 3 in the USA. It took 27 semis along with 2 smaller cranes to deliver and assemble onsite (cost over $100K just to get it there). I called the crane as the operator works in the blind over the radio and the scales on thoes cranes are the same way. The operator had to zero and set the crain. Often times the operator would forget and things would get exciting. Every time you switch from a cable on a single block to a multi block set up the scale needed to be reset. Even then though the shipping weight of a gear box (25 ton) or a nacelle (50 ton+) was never the same as the pick weight. The crane was almost always heavier by a few thousand pounds or more. This is why you will see large loads lifted a few inches and then left for a min or 2 to make sure everything is right before proceeding. You need time for the crane to be stopped for the scale to read well and then this weight becomes your working weight for the lift.
Vector forces of straps at angles do change and the addition of blocks, straps, etc... can allow a crane to pick more weight than is safe but none of those things will be able to "reduce" the weight of the item being lifted. Only how it is read on a scale and require the scale to be reset. If you want as accurate weight of the boat as possible tell the operator and he can check the scale. Then get the empty weight before the lift, the weight with the boat in the slings, and lastly the weight after the pick. These 3 numbers will allow you to get the best and most accurate weight outside of a legal scale.
Just remember the most important thing is does the boat float with all the accessories on board. If so then stop worrying about your weight and get that things out to exercise. Any sailor is bound to drop a few things overboard each season and thus sailing is your weight loss plan for both the boat and yourself!
Good discussion though.
My first "real job" was working at a boat yard with a very large travel lift on the west coast. Not the dinky things I seen in the midwest for winter haulouts. I often talked with the operator about boat weights and lift readings and he had to zero the scale to get an "official" weight. This means that the lift needed to read zero with all straps, pins, etc rigged and wet. Depending on the size of the boat sometimes it was 2 large straps, other times 4 large straps or more. this would give him a boat weight. However if it was not zeroed (and not done unless requested beforehand as time is $$) then you also get the weight of the straps, blocks, etc... for whatever the last setup was when it was zeroed. Often the crane scale was set to read heavy to keep the operator safe. The travel lift tires are foam filled so they cannot blow out but the frame if overloaded can fold if the crane is over taxed and trust me then the bells go off as a multi million dollar yacht comes out of the water you will see the operator sweat big time!
Fast forward a number of years and I worked for a wind turbine company still playing with large cranes. In Fact at the time to lift a new large MW turbine into the air it took a specialised crain of which there were 3 in the USA. It took 27 semis along with 2 smaller cranes to deliver and assemble onsite (cost over $100K just to get it there). I called the crane as the operator works in the blind over the radio and the scales on thoes cranes are the same way. The operator had to zero and set the crain. Often times the operator would forget and things would get exciting. Every time you switch from a cable on a single block to a multi block set up the scale needed to be reset. Even then though the shipping weight of a gear box (25 ton) or a nacelle (50 ton+) was never the same as the pick weight. The crane was almost always heavier by a few thousand pounds or more. This is why you will see large loads lifted a few inches and then left for a min or 2 to make sure everything is right before proceeding. You need time for the crane to be stopped for the scale to read well and then this weight becomes your working weight for the lift.
Vector forces of straps at angles do change and the addition of blocks, straps, etc... can allow a crane to pick more weight than is safe but none of those things will be able to "reduce" the weight of the item being lifted. Only how it is read on a scale and require the scale to be reset. If you want as accurate weight of the boat as possible tell the operator and he can check the scale. Then get the empty weight before the lift, the weight with the boat in the slings, and lastly the weight after the pick. These 3 numbers will allow you to get the best and most accurate weight outside of a legal scale.
Just remember the most important thing is does the boat float with all the accessories on board. If so then stop worrying about your weight and get that things out to exercise. Any sailor is bound to drop a few things overboard each season and thus sailing is your weight loss plan for both the boat and yourself!
Good discussion though.
I don't think the clevis pin from the furler would impact the scale very much.Any sailor is bound to drop a few things overboard each season and thus sailing is your weight loss plan for both the boat and yourself!
Wasn't there a famous backpacker who used to say "Watch the ounces and the pounds will watch themselves"? Those clevis pins can make a difference-if not in the weight then certainly in the rig tuning!!I don't think the clevis pin from the furler would impact the scale very much.
This all started because I was wondering what other Catalina 310s weighed. The one response I got from a C310 owner pretty much agreed with what we saw.Just remember the most important thing is does the boat float with all the accessories on board. If so then stop worrying about your weight and get that things out to exercise. Any sailor is bound to drop a few things overboard each season and thus sailing is your weight loss plan for both the boat and yourself!
Good discussion though.
The diversion about lifting angles has been interesting. Imagine a 10,000 lb boat so wide that it just barely fits between the sides of the travel lift; two sets of straps, perfectly centered, lifting straight up. Each strap is picking up 2,500 lbs and has a load on it of 2,500 lbs. Now imagine that same amount of weight (10,000 lb) in a round steel bar, 12" in diameter (the length ends up being about 26'), but the straps are at a 45 degree angle to vertical (not very realistic, but I hope it makes my point). Each strap is still picking up the same 2,500 lbs. but the actual load on each strap will be 40% more, because of the angle of lift. If you kept lifting up the bar and the angle from vertical kept increasing, the load would also increase.
In fact, if the load cell has enough resolution I should be able to see a difference in load from when the boat is at maximum height, and just before it touches the water, as the angle of the straps changes. I'll see if the operator will humor me and check that when we launch; hopefully Friday.
Hey with the batten I lost this year and all the sweat I lost over how I was going to explain how I need more $$ for boat parts it was good for at least a pound or 2.I don't think the clevis pin from the furler would impact the scale very much.
Get the accountant good and plastered before you explain how pretty these carbon parts are and how they'll make her look good.Hey with the batten I lost this year and all the sweat I lost over how I was going to explain how I need more $$ for boat parts it was good for at least a pound or 2.
It sounds like you got it! Here is a link on how we figure it when rigging to lift heavy machinery and what the Vector forces or "load Factor" on each strap is. The shallower the angle from 90 deg the higher the forces.
A boat in a travel lift is simply a double crane setup where your pulling on the spreader bar from each side and up on the singular pic point. I don't know if the load cell on the travel lift will notice the weight change though. Still report back when you find out. Most operators are good guys and a good operator is worth their weight in gold!
To indulge this a bit further if you really want to boggle your mind think about how this applies to a Zip line where the endpoints on the line see more than double the weight of what is sliding down it. That's why zip lines always bow in the middle. If they were drum tight they would snap or be to big to have fun with and why a tight rope walker needs such heavy cable to support his weight!
OMG
Make a note to self....
"Don't make a strong case on SBO without 2 cups of coffee"
Boat Displacement Weight is NOT Total weight of the boat!
Displacement weight = Weight of Water Displaced when the boat is....
Floating!!
Whew! Boat lift is probably safe.
Jim...
PS: Fat floats.
Um, what do you think the boat is floating upon??? The weight of the displaced water is equal to the weight of the boat floating in the water. If the boat weighed more than the displaced water, it would become a submarine (i.e. sink).
Google: "Archimedes Eureka"
Exactly!!!It sounds like you got it! Here is a link on how we figure it when rigging to lift heavy machinery and what the Vector forces or "load Factor" on each strap is. The shallower the angle from 90 deg the higher the forces.
A boat in a travel lift is simply a double crane setup where your pulling on the spreader bar from each side and up on the singular pic point. I don't know if the load cell on the travel lift will notice the weight change though. Still report back when you find out. Most operators are good guys and a good operator is worth their weight in gold!
To indulge this a bit further if you really want to boggle your mind think about how this applies to a Zip line where the endpoints on the line see more than double the weight of what is sliding down it. That's why zip lines always bow in the middle. If they were drum tight they would snap or be to big to have fun with and why a tight rope walker needs such heavy cable to support his weight!
I am still laughing at this thread...
You all should read it from start to finish.
You are arguing with me, but I said exactly the same thing.
and again with a bit of "tongue in cheek"...
@Jackdaw got it right about Displacement by Designers.
"Dead Load" is the Designer calculations. "Live Load" is all the other stuff and extras.
The Lift, I said was 16k lbs, it is not precise or it is rough. crude, etc.
_______
Just to keep it rolling. My boat floats higher in the fresh water river, but sinks a bit when I hit the Gulf.
Quiz: What is the Displacement weight in the river?
I can't wait for the answer.
Quiz: When I stand on my electronic bathroom scale and then lean over about 20° angle, did I lose weight?
This one is really tricky.
Quiz: If a truck full of sand pulls up on a public scale and it reads 43,100 lbs, a small pick up pulls up and 2 guys
get out and shovels 4 more shovels of sand on the big truck. New reading 43,000 lbs.
Did the truck steal some sand?
Go for it!
Jim...
You all should read it from start to finish.
You are arguing with me, but I said exactly the same thing.
and...
_______
and again with a bit of "tongue in cheek"...
_________A static floating boat fresh water weight = ZERO
@Jackdaw got it right about Displacement by Designers.
"Dead Load" is the Designer calculations. "Live Load" is all the other stuff and extras.
The Lift, I said was 16k lbs, it is not precise or it is rough. crude, etc.
_______
Just to keep it rolling. My boat floats higher in the fresh water river, but sinks a bit when I hit the Gulf.
Quiz: What is the Displacement weight in the river?
I can't wait for the answer.
Quiz: When I stand on my electronic bathroom scale and then lean over about 20° angle, did I lose weight?
This one is really tricky.
Quiz: If a truck full of sand pulls up on a public scale and it reads 43,100 lbs, a small pick up pulls up and 2 guys
get out and shovels 4 more shovels of sand on the big truck. New reading 43,000 lbs.
Did the truck steal some sand?
Go for it!
Jim...