Literally a weighty topic! Heh. After figuring a scale model weight of 5'ish pounds for the 260 ton Le Requin (which sounds light based on the ship's wide 8" beam), I started rechecking figures and doing some research on ship weights. An interesting fact came to light. Today's practice of measuring a ship using displacement weight actually started circa the late 1800s when iron/steel hulled ships started making appearances in place of wooden hulled ships. Before that, ships were generally measured by actual tonnage. Going back and researching the Le Requin weight online revealed some inconsistancies with how the weight was listed. Some sources said 260 tons, others said 260 tons displacement. It didn't clear anything up, much less make it any easier trying to compare actual weight to displaced weight (apples to oranges). So I grabbed the little 1:144 Verite for a side by side hull volume comparision. The Verite is 5" longer and 1.5" less beam than the Le Requin. Also the hull shapes are different. But it gave a flawed yet somewhat good idea of how much hull volume the Le Requin has compared to the 13 pound Verite. If I had to guess, the Le Requin weight should actually come out around 8 - 10 pounds. I think Clark mentioned that the Minerva he is building may weigh as much as 50 - 60 pounds. So here is the questions for discussion: Has anyone figured out the model weight of thier ship? What full size weight was it based on? Does the calculated weight instinctively feel right (highly subjective)?
Hull shape has a huge effect on displacement. To give you an idea, my current models of USS Constitution (1:96 scale) and HMS Victory (1:100 scale) are virtually identical in hull length, beam, and draft. However, HMS Victory carries nearly 5lbs of ballast in her extended keel, while USS Constitution carries only 1.5lbs of lead in her extended keel. The difference is almost entirely in hull shape. When you start going towards smaller ships, their displacement shrinks much faster than their sail area does. That's why I'm going for a frigate, rather than a brig or corvette. Le Requin is probably going to be a real featherweight, relatively speaking. Alas I have no real feel yet for estimating weight for sailing ships.
My Brig Somers. also a low sleek hull ship with a burthen of 259t and at nearly the same scale at 1:51 came out displacing 2kg or 4,4lbs to float at her design waterline. of this 1kg or 2,2lb is ballast. Out of the water she is a bit heavier, as her external ballast keel (without the leadshot in it) is also weights 650g while displacing 600g (i.e. teh ballast keel without teh lead only adds 50g to the total displacement of the hull) That displacment is absolutely spot on by a scale reduction of the displaced tonnage: Original displacement in kg 259000 --------------------------------- = ---------------------- = scale displacement of 1,95kg scale ^3 51^3 Same example for Constitution in 1/96 scale: 1576t (as per Howard I.Chappele ------------------------------------------ = 1,78kg displacement or 3,9lb (sounds about right kotori ? ) 96^3
That is where we have to be careful. Displaced tonnage and actual tonnage are not the same. Ships built before the late 1800s were usually measured in actual tons, not displaced tons.
I don't see the difference. A floating ship will displace an amount of water equal in weight to the weight of the ship. So whether you call it weight or displacement, it's the same thing for floating ships. Unless you're talking about tons burthen or similar. I know they often used other methods for rating a ship's size, often by cargo capacity, or by various rules of thumb based on statistics like length between perpendiculars, beam, etc. and called it "tons" of some sort or another. If you tried to scale one of those "tons", it would give inaccurate results because those are measures of cargo capacity or something else, not displacement.
Displacement is tons of water displaced, which is NOT the same as amount of water displaced. Splitting hairs as we don't battle in saltwater, but that's important for your naval knowledge young padawan
I don`t think my self an expert i only have 1 year and 5 boats of ship building under my belt so i can only fall back on that limited and purely empirical experience. when i started with Somers i had the same problem, no experience coming from airplanes and needing more data to see if it was possible with the weight, so when i modeled the hull in delftship i found out that the 259tons given by chapelle in his lines plan fits very close to the delftship displacement calculation when scaled to full size. So i just made my delftship model smaller and tried again and found that i could get a pretty accurate displacement like that. On the next few scratchbuilts that i made i found that everytime i estimated the target weight of my boats this way (tons burthen *1000 / scale^3) i arrived at +-10% of the displacement needed to float them at the intended waterline. That is US Somers which is comparable size and scale about 2kg displacement, 2 very small carved hull Square riggers ST. Helena 1/85 scale and HMAV Bounty 1/110 scale at 350g respectively, The Schooner America of 1851 at 1/85 scale at 250g and 1/64 HMS Snake (ship rigged Cruizer class) at 1,5kg I still think it`s possible to build and sail the La Requin even if she displaces only 2,5kg or 5lbs, AS mike is doing an awesome job building a super lightweight hull there, i just think that maybe the armament will have to be slightly lighter tan intended (maybe only 1 bow chaser ?) and the pumping capacity next to zero... but then i think that`s quite realistic as these where frail craft not designed to slug it out broad side to broadside with their opponents but rather dash in and snap up a merchantman. Even if no armament is possible due to weight constraints this can be a fun addition to AoS combat as a commerce raider by allowing "boarding" of merchantman and capture by staying alongside for say longer than 30seconds. With the speed and agility of the Xebec you`d drive the escorts nuts without firing at them at all
Interesting.... But the pumps are quite light, and with a lightweight aircraft battery, it should be easy easy to get 1/2 gallon per minute under 1/2 pound.
On the subject of displacement, the confusion often results from the different meaning given to the term. Ships built to washington treaty for example use the term displacement and it means the weight of the water displaced when the ship is fully loaded for battle, but without fuel or water. When you see displacement listed on a set of ships plans, it generaly means the weight fully loaded. Hull shape has nothing to do with displacement, only draft. So when we're looking at plans for our wooden warships we have to find out how the term was defined at the time it was built. I do understand about salt water floating a ship slightly higher, but the mass of the displaced water is the same, only the volume changes slightly. Hope this helps.
Sorry for my lubberliness, but I built the hull, painted the scale waterline on by eyeballing, and then stacked lead inside until it sat right. Now I'm moving that lead to an extended keel - full hull length. As long as she performs, and sits pretty . . . .
Agreed. A ship should sit right no matter the weight needed to get there. In the case of the Requin, I was trying to figure out how much weight I could put into the ship and how heavy a keel weight I could get away with and still have the ship float at the waterline indicated on the plans. Having a good estimate of the model's weight (not displaced weight) let me subtract internal equipment and hull weight form the estimated total weight and whatever was left over would be keel weight. With the previous guess of 8 - 10 pounds, that ended up somewhere around 1.5 - 2.5 pounds of keel weight. After the ship was built and float tested with enough weight to bring it down to the waterline on the plans, the model weight ended up to be 8.5 - 9 pounds ... right there in my estimated weight range.
To add to the confusion: At one time, ships were measured by the number of "tuns" they could stuff in the hold. Tuns were big wooden barrels used for shipping wine. I expect they were the closest thing shippers had to a "standard". So, by this measure, a ship would look small (Can't jam a big barrel in a triangular space, ie bow, stern). Also, the tuns method would miss all the air space between barrels, unless the calculation were mathematical, rather than practical. Thus, the old measure was one of volume, but a volume not really indicative of the weight of water displaced (and thus the buoyancy). For designing models, ie. for figuring out how much rc gear/guns/ ballast etc. the ship will manage, we need to know the weight of water displaced. If your published data is based on the tuns method, then the real ship' displacement, and thus your model's estimate, would be low. Of course that would be nice because a model never comes out weighting less than intended . I've had good luck just estimating the volume below waterline by mathematically slicing the hull into chunks. The chunks are chosen to make the math easier: rectangles for parts of the hull that are mostly rectangular, triangles (prisms) for the rest. Vol rectangle=length x width x depth; vol triangular prism = 1/2 x base x height x length. If measured in cm, then the cm^3 of the volumes = grams of water displaced. Small models of insufficient displacement: For freshwater sailing, you could put your big battery (for pump, etc.) at the bottom end of the finkeel, using it as ballast. I regularly get my batteries wet when flying float planes, and they don't have a problem. If you run the battery wires up from the finkeel in an airfoil shape brass tube (K&S), then there would be little drag penalty. Considering the primitive way I attach my PVC ballast tubes (lashed to the finkeel with strong string), drag is not much of a hinderance....all my models sail 3-5x as fast as the real ship, considered as hull lengths/sec.
As many of us are motorized naval combat battlers, we have a LOT of experience in getting our batteries wet. Interesting thought about putting the battery down in the bulb.
Very interesting subject. For what it's worth, I actually have no idea how much any of my ships weigh : they have the waterline in the scale location, and are ballasted to float at it. Perhaps I should break out the scales, and do some measurment. I do know my Rodney has been gaining weight in her old age...
