Displacement vs loaded weight

Sailcy, I am not really sure what your question is any longer....as you mention lagoon i'll respond in words suitable to pleasure craft.
"light" displacement i guess is what the boat weighs when it is equipped according to the manufacturers spec. but empty, no fuel, water, equipment etc unless they are included in the spec description. but you will be able to read what it consists of precisely in the document you have located.
max loaded displacement is what the boat weighs when it is loaded with whatever, people, fluids, equipment, cans of beer...whatever... to it's maximum draft. means the boat is as deep in the water as it is allowed to be per it's design & rating, (class, flag, ec etc whatever is being applied)
as gonzo said in post 2. displacement = weight....archimedes explained it a long time ago. as the boat is floating it is "displacing" a volume of (in our case) water whose weight is equal to the weight of the boat. little boats you pick up on a crane and weigh them. big ships can't be picked up so you "weigh" them by measuring the volume of water displaced...this is the origin of the term, it is applied to boats large & small. hope this helps

 

Yes, sorry, probably I should specify more correctly my question at the beginning. It is not about the theory of displaced water by boat. What, I asked actually is about the general definitions of "displacement" and "loaded weight" in other words, from what point all the thinks that you add to the boat are considered as "loaded weight". My question arises as I could not find any regulation mentioned "empty displacement" which many small boat designers referred to. For example- does the CLEAT belong to the bare hull or not?

 

Now, you're trying to classify the weights of different items found on a boat into separate groups, like what is structure, what is mooring equipment, etc.

In most circumstances, you won't find any regulations or laws which define the various groupings of weights in a vessel, because they're irrelevant for the most part. It's one person's opinion of which group this item should be included versus the opinion of someone else.

For the light weight of a vessel, this generally includes all the structure, equipment, machinery, and outfit which comprise the vessel. It's things like cleats, bitts, plates, screws, bolts, engines, etc. which allow the boat to float and be used as a boat.

For example, some people keep spare parts aboard so that minor items can be fixed while the boat is away from the dock. Should these spares be considered part of the light weight, or should they be part of the deadweight? You can arguably make a case for either.

For small boats, it's relatively easy to inspect the vessel and its contents and decide on the spot if this should be included in the light weight or the deadweight. When vessels get larger, this is not an eminently practical way to do things, as it would take many people many days to go through all the items which can accumulate on a vessel. The deadweight then becomes primarily the variable weights, like the fuel, the fresh water, the number of crew and passengers, their effects, food and provisions, etc. The weights of these items are usually easy to quantify.

The EU took some grief over trying to regulate the size, shape, and color of what a banana should be. Writing regulations to govern the minutiae of what is found on a more complex and varied object like a boat would bring the bureaucracy to a complete halt.

 

sailcy, we need to explain another term, as used above, sorry that you are struggling with the terms used but they are what is used in the industry and you will have to get used to them ! as in everything, communication requires an understanding of the "language".
"deadweight" is everything that is on board which is not included in the "lightweight".
"lightweight" is the weight of the fully built (but empty) ship equipped with everything included in the specification and everything that is required by the governing regulations. I have given you this in the term you used "light displacement" in post #16.
So, if the spec says the boat has an engine for example, the complete engine, equipped as per the specifications is included in the lightweight, if there is an option.... for a racor fuel filter (for example) and you choose to have this fitted it's weight will not have been included in the lightweight in the brochure and it will be eating into your deadweight.
using cleats for an example...the boat fitted with the cleats mentioned in the standard spec will be included in the lightweight, if extra cleats are offered as an option the weight of the extra cleats will be eating into your deadweight.
you used the term "loaded weight", i would understand this to be the weight (or displacement as previous...) of a boat that was loaded with something...it isn't the weight that was "loaded" on to it....that is "deadweight".

i guess this can be confusing ..... as the racor filter and the extra cleats are bolted in so why are they not in the lightweight??? the answer is that they are in the lightweight of your boat in its delivered condition...but they are not in the lightweight of the boat which is specified in the brochure...which is what gonzo was alluding to earlier. this results in your delivered boat having a reduced deadweight capacity

i didn't invent the terms...just trying to explaining how they are applied...hope this helps

 

Ok , guys I really appreciate your effort trying to explain things to me, but my question still remains unanswered. First of all, let's define we are talking about small crafts up to 24m known as pleasure crafts, to which I believe this forum mostly belong to. Not about the ships where everything of cause become more complicated.

 

I see your confusion is similar to mine, as again explanation continues about "LIGHT displacement"- which I fully understand and gave examples earlier that even EU regulation precisely describe what should be included into "LIGHT displacement" definition.
What still remains unanswered is the meaning of an "EMPTY displacement"))))

 

sailcy, i give up.....last response from me. I am using terminology that has been in use for a considerable time within my explanations, perhaps EU or whomever is seeking to apply new terms, I am confident the definitions will be the same and it should be obvious what each term is.

"your confusion is similar to mine"....i have no confusion on the subject of hydrodynamics, only some difficulty trying to understand what you are seeking to clarify.

"empty displacement" is not a term i am familiar with, you might ask whoever used it ??? however it seems self evident that it would be the same as "lightweight" as I have previously defined.

 

Hello all, i am so glad i found this site. I have two very similar inflatable boats. So also two CE reports. Report 1 states the max loaded displacement is higher than the max load and report 2 states the opposite. Must be something wrong. I think report 1 is correct. Am i correct?

 

@Walterkooy63 I think you are.

The max loaded displacement of the inflatable = Lightship mass + maximum weight (mass) of the cargo (people?) that can be (safely) carried.