Displacement???

[RainDog]

I think OP is asking how they come up with the displacement listed in the boat specs. From what I have gathered, there is not standardization on how this is done. Many builders list extremely optimistic numbers. They might list "designed" displacement, but that never really seems to be the actual as-built displacement.

So the answer is basically, in a lot of situations, the listed displacement does not really mean much.

[Coops]

Originally Posted by sabray

I think you just broke the be nice rule. Even if your right it still breaks the rule.

Was not aimed at you good sir, but any man asking for a ladies displacement, was a general insult not a specific one.

Coops.

[David M]

Originally Posted by Eumelia

Displacement = weight
Period

Thank gawd someone said it.

[St. Elsewhere]

If you want more details . . .

Displacement (ship) - Wikipedia, the free encyclopedia

[gjordan]

Displacement = weight____except when the Coast Guard is involved, and then it gets much more complicated. Registered tonnage is a measure of volume of the enclosed spaces of a vessel,less the spaces that are considered machinery spaces. This has lead to many ways to cheat on tonnage to get under rules that only apply to larger boats. I was told many years ago(I hope it is no longer true) that the SF bay ferries used to remove the rear doors on the lower decks at measurement time so that they were not considered enclosed spaces, and after the measurement was taken, put the doors back on. This allowed them to have less regulation (less safety) than if they were measured according to the law. As I said, I hope this is no longer true, but I saw some very large vessels being run by 100 ton masters and safety rules that applied to 100 ton and smaller vessels. Your CG tonnage on your documentations has little or nothing to do with the weight of your vessel. __Just something to think about.____Grant.

[markpierce]

Originally Posted by gjordan

... I was told many years ago(I hope it is no longer true) that the SF bay ferries used to remove the rear doors on the lower decks at measurement time so that they were not considered enclosed spaces, and after the measurement was taken, put the doors back on. This allowed them to have less regulation (less safety) than if they were measured according to the law. As I said, I hope this is no longer true
...

Don't worry. All San Francisco ferries are now purely passenger (not car or railroad) so there shouldn't be any question about doors.

[daddle]

Objects that are "floating" are "weightless", no? It is that simple. So we call it "displacement". Mostly to discriminate between our elite selves and the dockwalking riffraff.

[lateral]

Out of all my mates the only ones concerned with their displacement are skippers?
Odd.

[markpierce]

If you just "googled" it, you'd save us all the trouble.

Displacement (ship) | Ask.com Encyclopedia

[Lagoon4us]

Originally Posted by Coops

She would probably tell you that her "displacement" is being with you. She would much rather be elsewhere.

Coops.

Your absolutely correct some one will get "displaced"..... LMAO

Cheers

[nial]

Thanks for all the enlightening answers. I gather from them that there is no standard formula that builders adhere to when publishing the displacement weight of their boats. Thats really all I wanted to know. I kinda thought that most people would assume, since I was using a computer, that I was of normal intelligence and consequently would know all the elementary stuff, volume of water displaced=weight of displacing object, etc. Still, I did learn what I wanted to know. CF is a great resource.

[Richard_W]

Do you mean you've got more than you were hoping for?

CF is a great resource ... no doubt ... but like with everything on Internet, you need to know in order to know what you read ...

[Kettlewell]

That's what keeps this forum going--for most questions there is no single, correct answer. And, for those questions where there is a correct answer, there will always be someone who disagrees purely on principal.

[jeremiason]

Originally Posted by gjordan

Displacement = weight____except when the Coast Guard is involved, and then it gets much more complicated. Registered tonnage is a measure of volume of the enclosed spaces of a vessel,less the spaces that are considered machinery spaces. This has lead to many ways to cheat on tonnage to get under rules that only apply to larger boats. I was told many years ago(I hope it is no longer true) that the SF bay ferries used to remove the rear doors on the lower decks at measurement time so that they were not considered enclosed spaces, and after the measurement was taken, put the doors back on. This allowed them to have less regulation (less safety) than if they were measured according to the law. As I said, I hope this is no longer true, but I saw some very large vessels being run by 100 ton masters and safety rules that applied to 100 ton and smaller vessels. Your CG tonnage on your documentations has little or nothing to do with the weight of your vessel. __Just something to think about.____Grant.

You are now referring to Gross and Net Tonnages, which is very different from Displacement.

Gross Tonnage, the total internal volume and Net tonnage, the volume of the actual cargo space, basically refer to what the vesel can carry, at least theoretically. Yes, you can play with hose numbers by removing hatches or adding them.

You are correct, that a USCG Deck Officer's License is based on Gross Tonnage and that most SF Bay ferries are rated at 99 GT and I suspect that much of that has to do with costs associated with operation.

For example in my experiences, the USS Potomac is rated at 412 GT, which requires a Master with a license of a minimum of 500 tons and an addtional licesed crew of 4, but only carries 148 passengers. On the other hand the Red & White Ferry Fleet are all rated at 99 GT and only require a 100 ton Master and a crew of 3, but carry over 200 passengers. Go figure?

[St. Elsewhere]

Originally Posted by nial

I gather from them that there is no standard formula that builders adhere to when publishing the displacement weight of their boats. Thats really all I wanted to know.

If the boat is to be USGC Registered, the tonnage has to conform to the USCG measurement standards per their regulations. With that said, I also know that many vessels are USCG Registered with nonconforming tonnage reported.