I worked on a Great Lakes bulk carrier. In the ballast tanks, she had 2 feet of sediment in most of her ballast tanks. One of the Mates estimated the extra weight at 1,700 tons. It took 2yrs to muck out all the ballast tanks. FYI-it was not a fun job :(
It is important to understand how little the center of gravity needs to shift. Many vessels only have a margin of 1-3 ft [0.3-1.0 m] between their current VCG location, and the maximum allowed VCG. This is why we need to monitor weight changes. Due to the massive weight of the ship, small changes in VCG can make a big difference in stability.
I went through this a bit when doing an aircraft annual on a small aircraft. One of the jobs we were to do was determine the center of gravity of the aircraft. There were specific points we had to measure. Me being a bit new I asked "why would we expect these dimensions to have changed from the measurements taken during the previous inspection" No one knew (one guy said "perhaps the spinner on the prop was replaced"). Nothing changed on the aircraft but we were still required to make the measurements for the new certification. The new measurements taken during the inspection we were currently doing were exactly the same as the measurements from the previous inspection. I asked if they ever found a plane that grew between inspections.
Thx Dan R. After a LOTT of look and asking on internet. So light airplanes is about 10(+) L/h op gas. So what is is on small bouts? Small aircrafts fly at 80-100km/h (55-60mph) and small boats? The new kind of boats "fly" on hydrofoils. ...
well, this raises a very interesting question, what is a "stability test" and if it is what it sounds like, is that something that can only be done on small yats/rowboats (ignoring the 796foot long fast support ships like the USS Camden AOE-2). do you just plunk knowen weights on the deck and measure the tilt of the ship or is there some NASA VAB sized rig to measure resistance to tilting of a ship? Oh, there is a vid, ok. B) "Stability Test Theory: The Math Behind the Measurements" ua-cam.com/video/Fn48RIXQPsw/v-deo.html
I'm only a recreational boater now, but I care strongly about this stuff. I wouldn't put a barbecue on the fly bridge without considering the weight change, for example. Thanks, great video :-) BTW, my boat (40 ft, 25 tons displacement, hard chine, wedge keel, unknown design provenance) has a worryingly long roll period at rest, but stiffens up when she gets tossed around. Should I read anything into this?
Probably no problem, but I can't be 100% certain. The main thing is to make sure the boat always returns to zero heel in calm conditions. Otherwise, you may have problems with an angle of loll. You can learn more about that here: ua-cam.com/video/k8H5M3jrqpY/v-deo.html
Big thanks for the reply. I already watched your angle of loll video (working my way through your channel), very interesting stuff. I find the way stability works on big boats both fascinating and unsettling. I have a friend who used to sail on a research ship that had a max heel angle of 25 degrees and a rumored PVS in the low thirties. How can you operatre on such tiny margins, let alone get to sleep on your off watch?! Anywho, I suspect that my boat's funky stability curve has something to do with the deeply submerged chine, as she's been built roughly 65% over her designed displacement. I plan on moving half a ton of ballast into the keel from the hull bottom over the screw, where it had been placed in a misguided attempt at silencing a 90 cm kort nozzle. Needless to say, I just cut the thing off; The vibrations were bad enough to crack windows while ice breaking :-D Working the kinks out of a badly designed boat is both time consuming and irrational in the traditional economic perspective, but also highly rewarding. Maybe why you shoudn't mess with poorly designed ships could be the subject of a future video? At any rate, your videos are a great help in getting the various aspects of boat design into perspective, and I'm really grateful that you share your wealth of knowlege like this!
The real problem lies with naval architects / engineering in continuing to design ships that are sensitive to roll-over. So long as they can roll over without harm and continue on their way via inverted power and control stations, etc., stability wouldn't be of much concern.
That has less to do with the engineering than with the cost. We have the science to design ships that can completely rollover and still keep going. US Coast Guard frequently requests this on their smaller boats. But it makes the ship much more expensive. That added cost is why we don't often add this feature.
@@DatawaveMarineSolutions I was joking, as I know of no way for containers and bulk-carry commodities to be just as safe on the bottom of a ship as sitting on deck or resting in the bottom of a hold instead of on the hatch covers, but yes, I am familiar with USCG applications of self-righting and other worst-case-scenario designs.
I worked on a Great Lakes bulk carrier. In the ballast tanks, she had 2 feet of sediment in most of her ballast tanks. One of the Mates estimated the extra weight at 1,700 tons. It took 2yrs to muck out all the ballast tanks. FYI-it was not a fun job :(
It is important to understand how little the center of gravity needs to shift. Many vessels only have a margin of 1-3 ft [0.3-1.0 m] between their current VCG location, and the maximum allowed VCG. This is why we need to monitor weight changes. Due to the massive weight of the ship, small changes in VCG can make a big difference in stability.
That obviously affects the meta-centre big time to right?
I went through this a bit when doing an aircraft annual on a small aircraft. One of the jobs we were to do was determine the center of gravity of the aircraft. There were specific points we had to measure. Me being a bit new I asked "why would we expect these dimensions to have changed from the measurements taken during the previous inspection" No one knew (one guy said "perhaps the spinner on the prop was replaced"). Nothing changed on the aircraft but we were still required to make the measurements for the new certification. The new measurements taken during the inspection we were currently doing were exactly the same as the measurements from the previous inspection. I asked if they ever found a plane that grew between inspections.
Thx Dan R. After a LOTT of look and asking on internet. So light airplanes is about 10(+) L/h op gas. So what is is on small bouts? Small aircrafts fly at 80-100km/h (55-60mph) and small boats? The new kind of boats "fly" on hydrofoils. ...
well, this raises a very interesting question, what is a "stability test" and if it is what it sounds like, is that something that can only be done on small yats/rowboats (ignoring the 796foot long fast support ships like the USS Camden AOE-2). do you just plunk knowen weights on the deck and measure the tilt of the ship or is there some NASA VAB sized rig to measure resistance to tilting of a ship?
Oh, there is a vid, ok. B)
"Stability Test Theory: The Math Behind the Measurements"
ua-cam.com/video/Fn48RIXQPsw/v-deo.html
I'm only a recreational boater now, but I care strongly about this stuff. I wouldn't put a barbecue on the fly bridge without considering the weight change, for example. Thanks, great video :-) BTW, my boat (40 ft, 25 tons displacement, hard chine, wedge keel, unknown design provenance) has a worryingly long roll period at rest, but stiffens up when she gets tossed around. Should I read anything into this?
Probably no problem, but I can't be 100% certain. The main thing is to make sure the boat always returns to zero heel in calm conditions. Otherwise, you may have problems with an angle of loll. You can learn more about that here: ua-cam.com/video/k8H5M3jrqpY/v-deo.html
Big thanks for the reply. I already watched your angle of loll video (working my way through your channel), very interesting stuff. I find the way stability works on big boats both fascinating and unsettling. I have a friend who used to sail on a research ship that had a max heel angle of 25 degrees and a rumored PVS in the low thirties. How can you operatre on such tiny margins, let alone get to sleep on your off watch?! Anywho, I suspect that my boat's funky stability curve has something to do with the deeply submerged chine, as she's been built roughly 65% over her designed displacement. I plan on moving half a ton of ballast into the keel from the hull bottom over the screw, where it had been placed in a misguided attempt at silencing a 90 cm kort nozzle. Needless to say, I just cut the thing off; The vibrations were bad enough to crack windows while ice breaking :-D Working the kinks out of a badly designed boat is both time consuming and irrational in the traditional economic perspective, but also highly rewarding. Maybe why you shoudn't mess with poorly designed ships could be the subject of a future video? At any rate, your videos are a great help in getting the various aspects of boat design into perspective, and I'm really grateful that you share your wealth of knowlege like this!
The real problem lies with naval architects / engineering in continuing to design ships that are sensitive to roll-over. So long as they can roll over without harm and continue on their way via inverted power and control stations, etc., stability wouldn't be of much concern.
That has less to do with the engineering than with the cost. We have the science to design ships that can completely rollover and still keep going. US Coast Guard frequently requests this on their smaller boats. But it makes the ship much more expensive. That added cost is why we don't often add this feature.
@@DatawaveMarineSolutions I was joking, as I know of no way for containers and bulk-carry commodities to be just as safe on the bottom of a ship as sitting on deck or resting in the bottom of a hold instead of on the hatch covers, but yes, I am familiar with USCG applications of self-righting and other worst-case-scenario designs.
miss pause 9:38 "contempt" OT; a queen 2&2x or 4x Rev 18:7 cap */=4.406 a word, revelation, command; ealy rain James 5:7 1x