Seagoing Vessel Design

[Timerover51]

This is derived from another thread.

Special Supplements were generally for stuff that has too much content for just an article -- they typically ate up the bulk of one issue. Missiles, for example, were a special supplement. Sometimes they can function as teasers to gauge interest in expanded rules.

Seagoing Vessel Design would be a potential Special Supplement that I'd like to see.

After having spent a month looking at how it might be done, a realistic seagoing vessel design system similar to the system used in MegaTraveller for vehicle and starship design or the system that appeared in Challenge magazine is not possible. Naval ship design simply does not work that way. Warships are built to one standard, merchant ships to another, except for a period in the late Medieval when Northern European merchant ships made for acceptable warships.

Ptolemy IV built what was apparently a twin-hulled galley about 425 feet long in a stone dry dock. Aside from the size of the dry dock, that is about the limit of length for any wooden ship. By the way, the galley was pretty much immobile.

The Romans had at least one merchant ship of about 1200 tons capacity, which would equate to a displacement of about 2400 tons, with a single mast and single large sail, along with a small bowsprit sail. The ship made one round trip per year carrying grain from Egypt to Rome. Comparable sized ships to this were not built in Northern Europe until the 16th and 17th centuries. The Chinese did build some extremely large wooden ships in the 14th century.

Speed for a sailing ship has so many variables that stating that a vessel has this speed as a top speed is effectively meaningless.

Trying to work from the MegaTraveller ship design sequence is not really doable, as the ship hulls are dimensioned assuming a displacement ton of approximately 14 cubic meters, which equates to about 14 displacement tons wet measure. A 100 ton hull gives you a ship about the size of the frigate USS Constitution, and a 200 ton hull something about the size of HMS Victory. A 1,000 ton hull equates to a full-sized Pre-Dreadnought battleship or a WW2 Liberty Ship. A 5,000 ton hull gets you the IJN Yamato. The Nina and the Pinta, on the other hand, would go about 5 tons MegaTraveller displacment. However, a design system would have to accommodate ships ranging in size from WW2 small landing craft, Greek pentaconters, the Nina and Pinta to the IJN Yamato, current aircraft carriers, the 150,000 ton plus cruise ships and the massive bulk carriers and oil tankers. The size range scale is on the order of 10,000 from smallest to largest.

Probably the best that could be done is something like Traders and Gunboats on a larger scale, with one for oared and sailing ships, and another for metal-hulled steam ships.

 

[Fritz_Brown]

Have you looked at Striker vehicle rules? I would initially limit design to "modern" vessels, then see if it could expand down into other types.

 

[McPerth]

Trying to work from the MegaTraveller ship design sequence is not really doable, as the ship hulls are dimensioned assuming a displacement ton of approximately 14 cubic meters, which equates to about 14 displacement tons wet measure. A 100 ton hull gives you a ship about the size of the frigate USS Constitution, and a 200 ton hull something about the size of HMS Victory. A 1,000 ton hull equates to a full-sized Pre-Dreadnought battleship or a WW2 Liberty Ship. A 5,000 ton hull gets you the IJN Yamato. The Nina and the Pinta, on the other hand, would go about 5 tons MegaTraveller displacment. However, a design system would have to accommodate ships ranging in size from WW2 small landing craft, Greek pentaconters, the Nina and Pinta to the IJN Yamato, current aircraft carriers, the 150,000 ton plus cruise ships and the massive bulk carriers and oil tankers. The size range scale is on the order of 10,000 from smallest to largest.

Just one point here. A 1000 dton ship will represent a ship with a total of 14000 (13500 in MT) kl, included the parts underwatr and over flotation line.

I'm not sure what perecentage of volume is underwater in a ship, but only this one should be counted (at 1 ton/kl*, as you did) for the wet ship tonnage, while the part over the flotation line shuld not (submarines excluded).

NOTE: *In fact, being salt water, it would be closer to 1.025 to 1.03 (on earth, on other planets could vary, as we're dealing with Traveller), but IMHO this error is acceptable as to lower the difficulty.

 

[Fritz_Brown]

I think that might make the problem worse, the way timerover is looking at it, McPerth. He's saying that something like the lowly scout is as big as an old wooden frigate. If you remind that say, only half of that is below the waterline and actually displacing water, then the wooden ship to which he's comparing is only 50dTons. (Unless, of course, I have read you totally wrong, and you mean something else.)

That is one of the problems with using the ship rules to build ... ships. The spaceship rules are based entirely on volume, while a maritime vessel requires volume and mass (weight). I know the Striker rules incorporate mass, but I don't know if they will work for ships. (Some have said they don't really work for tanks and things, either.)

 

[McPerth]

I'm afraid it's just the opposite.

A 1400 tons sea ship means that it desplaces 1400 kl under water. If the underwater part is 50%, as you say, the whole volume of the ship would be 2800 kl, making it a 200 dton in Traveller.

 

[Enoki]

Some general notes you can follow on ship design:

Warships will have a length to beam ratio of about 6 to1 to 10 to 1 with faster ones having the higher ratio.

Propulsion is roughly a cube function and for larger ships 30 to 40 knots is about the max on a conventional hull if you want to have any other stuff on the ship. You might get faster with more powerful plant technology than is currently available however.

There are two basic "schools" on systems design: Weight critical and volume critical. Weight critical ships are those with guns and armor as you might find from sailing ships to about WW 2. Volume critical ships use missiles and electronics. In both the weight of the actual ship determines how much water is displaced. Draft is an indication of volume. That is, if the ship is weight critical it sits low in the water and has a deep draft. A volume critical ship has a shallower draft and lots of volume above water. The enclosed volume is determined by weight so it isn't a clean move from starship design where weight is not critical but rather volume. Here weight is critical and determines volume. You have to deal with the ship floating on water and the gravity present rather than being able to almost entirely ignore such considerations in spaceship design.

Right now there is a movement to new hull designs like catamarans, SWATH, etc. These follow the displacement rules but have different propulsion properties.

Merchant ships on the other hand are all about efficency. They use the most fuel efficent engines, hulls that allow for the most cargo, and are generally as large as possible for efficency. Speed is definitely not a top priority.

I'd say however, that you are probably fairly well off with something close to what is used in RL on Earth however. There is a "best" way to do things and naval architechs generally are on that curve.
Now, materials would make a difference. A metals poor planet might have to resort to something like ferro concrete (or a ceramic) for hulls (heavier than steel) while steel and aluminum would be better choices on worlds having access to metals in abundance. Wood would definitely not be the first choice if other materials were available but could be used to build a large ship. Pykrete (a frozen ice sawdust mixture) might be a good choice on a colder world as an alternative to metal or wood (building an 'iceburg' ship).

Well, there's some ideas.

 

[PFVA63]

Hi

I suspect that the relationship between internal volume for a sea going vessel and its overall "weight" or tons of slat water displaced in terms of metric tons of hydrostatic displacement is going to depend a bit on the type of vessel in question.

For example, a while ago I plotted up this graph relating the internal volume of some various fairly modern warships vs their nominal hydrostatic displacement. I converted it to Traveller Terms by putting internal volume into dTons (where one dTon equals 14 cubic meters) and left hydrostatic displacement in metric tons (which equal 2204.6 lbs of water displaced @ 15degC - if I am remembering everything correctly).

Anyway, the graph shows data for the following type vessels:

MCM - small mine warfare craft (such as mine hunters and mine sweepers, and other Mine Counter Measures vessels)
SC - modern surface combatants such as corvettes, frigates, destroyers, and cruisers
Des - design studies for SC's not actually built
SS - submarines
LSD - Amphibious vessels (such as Landing Ship - Dock vessels)
WWI - a very rough estimate of a couple WWI era Battleships, for comparison

From the plot, you can kind of see that the MCMs, SC, & Des points all fall fairly near a line where internal volume in dTons is just about 1/4 of the ship's hydrostatic displacement in metric tons. As such, for typical modern combatant type warships (as opposed to carriers or amphibious ships) you could more or less divide its hydrostatic volume by 4 to get a pretty good approximation of how big it would be in Traveller terms, or conversely, you could take a Traveller ship and multiply its size by 4 and compare that number to modern ocean going warships to give you a feeling for how big the Traveller ship would be compared to a modern warship.

For example, a 2000 dton Traveller warship would be roughly equivalent in overall size/internal enclosed volume to an 8000 metric ton modern destroyer (similar to the US Navy's DDG51 class ships).

For the SS curve you see that the relationship is 1 metric ton hydrostatic displacement is equivalent to 0.0732 dtons, or conversely 1 dton of volume equals about 13.66 metric tons of hydrostatic displacement (where 13.66 times the density of salt water @ 15 deg C [1.025] equals 14.0).

For the Amphibious ships, you can see that they have a bit more internal volume per ton hydrostatic displacement than the Surface combatants, while the rough estimate of the WWI battleships appear to have a little less internal volume per ton hydrostatic displacement. This is likely due to the fact that older WWI type battleships carried heavier armament, armor and machinery than modern vessels while ships like the amphibious vessels have a need for large internal volumes to house the vehicles and small craft that they carry.

PS. sorry for the size of the plot, its the only copy I currently have available, and since I just migrated to Windows 8, the current machine that I'm on does not yet have the tools for posting a new smaller version.

 

[Timerover51]

I'm afraid it's just the opposite.

A 1400 tons sea ship means that it desplaces 1400 kl under water. If the underwater part is 50%, as you say, the whole volume of the ship would be 2800 kl, making it a 200 dton in Traveller.

It is far worse than that. The cruise ship, Freedom of the Seas, of which I was on the maiden voyage, has a gross tonnage of 154,407, which would equate to a hull size of about 11,500 in MegaTraveller displacement tons. A quick and dirty estimate of mass is 85,000 tons displacement tons. The ship has a draft of 28 feet. It has 18 decks, most of which are above the water line. About 1/6 of the ship is below the waterline, the rest is above it. Total capacity of the ship is 5,014, passengers and crew.

By MegaTraveller rules of 4 tons volume per state room, if the entire ship is staterooms, the capacity is 2,875. Note, there is a LOT of space onboard the Freedom that is NOT staterooms. The crew quarters, except for officers, are primarily below the water line, as is crew messing and recreation, engine rooms, fuel tanks, fresh and gray water storage, and supplies. I was on the bridge, which it is not that big compared to the size of the ship, and a large part of the volume is occupied by the bridge wings, which extend beyond the waterline beam by a fair bit to allow for docking control. The Traveller Book calls for a bridge size of 2% of the hull size. The bridge on the Freedom did not occupy 230 MegaTraveller displacement tons. Think about that for a while, as that is large than your standard Free Trader displacement.

While the Freedom has most of her volume above the waterline, as does also an aircraft carrier, your bulk cargo ships and oil tankers when loaded have between 1/2 to 2/3 of their volume below the water line, and the load line is based on the worst ocean conditions that they will encounter, Winter/North Atlantic being the worst, and requiring the lightest load.

(To be Continued.)

 

[robject]

Potentially, the details could sink under a few general rules, with a resulting set of tables which paints ship design by period (unpowered, powered, and gravitic). The result would be a system which builds ships that are playable out of the box.

Before TL4 we have a general set of ship types and some universal design rules.

From TL4 to TL7 we have narrower ship mission types, which can define preset assumptions about construction. Some additional tweaks can modify these presets.

After TL7 we can only extrapolate, in which case it is most convenient to extrapolate in ways that are convenient to a design system, or (perhaps) interesting from a tactical point of view.

 

[Carlobrand]

I'm afraid it's just the opposite.

A 1400 tons sea ship means that it desplaces 1400 kl under water. If the underwater part is 50%, as you say, the whole volume of the ship would be 2800 kl, making it a 200 dton in Traveller.

I'm not an engineer, but if half the mass of a ship is underwater, and half above, then the center of mass is about at the water line, and ... doesn't that make it susceptible to rolling over in high seas?

 

[Enoki]

I'm not an engineer, but if half the mass of a ship is underwater, and half above, then the center of mass is about at the water line, and ... doesn't that make it susceptible to rolling over in high seas?

You have to determine the metracentric height of the ship. This is a point determined by the center of bouyancy or flotation and the center of gravity of the ship. One is pushing up the other down. The higher the metacenter the less stable the ship is the lower and the easier it is to sink it.

 

[Dragoner]

You have to determine the metracentric height of the ship. This is a point determined by the center of bouyancy or flotation and the center of gravity of the ship. One is pushing up the other down. The higher the metacenter the less stable the ship is the lower and the easier it is to sink it.

Agreed. The ocean isn't ever really that calm, plus it can change from simple white caps to 10m swells very quickly, on smaller ships freeboard is important; though the dton is a measure of volume, not mass.

 

[BytePro]

It is far worse than that. The cruise ship, Freedom of the Seas, of which I was on the maiden voyage, has a gross tonnage of 154,407, which would equate to a hull size of about 11,500 in MegaTraveller displacement tons. A quick and dirty estimate of mass is 85,000 tons displacement tons. ...

Is this the same as CT dTons (4 dTon stateroom is same spec)?

[From http://science.howstuffworks.com/engineering/structural/floating-city1.htm: 'Freedom Ship will be built on top of 520 airtight steel cells that will be bolted together to form a sturdy base. Each cell will be 80 feet (24 meters) tall, between 50 and 100 feet (15 and 30 m) wide and between 50 and 120 feet (15 and 37 m) long.'

So, minimum of 520 x 24m x 15m x 15m => ~ 2.8 million cubic meters. In CT terms of 14 m3 per dTon that's around 200,000 dTons.
(From ship dimensions of 1,317m x 221 m x 104 m not inc. draft and assuming about 120 m of width is those wings - near 1,000,000 dTons.)]

 

[Timerover51]

Is this the same as CT dTons (4 dTon stateroom is same spec)?

[From http://science.howstuffworks.com/engineering/structural/floating-city1.htm: 'Freedom Ship will be built on top of 520 airtight steel cells that will be bolted together to form a sturdy base. Each cell will be 80 feet (24 meters) tall, between 50 and 100 feet (15 and 30 m) wide and between 50 and 120 feet (15 and 37 m) long.'

So, minimum of 520 x 24m x 15m x 15m => ~ 2.8 million cubic meters. In CT terms of 14 m3 per dTon that's around 200,000 dTons.
(From ship dimensions of 1,317m x 221 m x 104 m not inc. draft and assuming about 120 m of width is those wings - near 1,000,000 dTons.)]

You are mixing up two totally different ships. The "Freedom of the Seas" is operated by Royal Caribbean Cruise Lines. Your "Freedom Ship" is still a hypothetical design.

 

[BytePro]

Oops - yeah, that would be closing on like a mile long ship...

So trying that again... roughly from http://en.wikipedia.org/wiki/MS_Freedom_of_the_Seas - 338.94m x 38.60m x 63.70m / (14 m3 / dTon) => ~ 60,000 dTons .

I'd call it 45 to 50 thousand dTons accounting for shape, 18 decks and draft region.

It has 1,817 staterooms (double capable) and assuming 680 doubles for crew... that still comes to less than 10,000 dTons for Traveller style staterooms.

 

[Timerover51]

Continued from earlier post.

With respect to ship construction materials, the primary ones are wood, wrought iron, mild steel, and high tensile strength steel. You can use animal hides for small, like up to about 50 foot vessels, and fiberglass (over some form of frame for larger ships) for up to say about 150 feet or so.

Not all wood is suitable for ship construction, and some woods are preferred for certain parts of the ship. Ideally, the wood should be seasoned for 2 to 3 years prior to using it. Building a ship out of green, unseasoned wood means a very short useful life of 3 to 5 years. Wrought iron was used during the 1800s, being replaced by mild steel starting about 1880. High-tensile strength steel is normally used for warships.

Crew size on cargo ships pretty much remains the same regardless of ship size, and for the US, is set by Coast Guard manning standards. The US Coast Guard also set manning standards for passenger ships. Bridge size does not vary much regardless of the size of the ship either.

With respect to projecting commercial ship design, take what is in use today and that is what is going to be used for a long time into the future. The St. Mary's Challenger, sailing on the Great Lakes, was launched in 1906 and is still in full use. Short of some drastic change in propulsion, such as fusion plants directly converting the fusion reaction into electricity, I cannot foresee any significant change in power plants.

Sailing ship rigs are widely varied, and for steam ships, any engine plant is going to have to include boilers, with the size of the plant being heavily influenced by the operating conditions of the boiler, and how efficiently the steam power produced is processed. When it comes to Diesel power plants, you have straight Diesel, reduction-geared Diesel, and Diesel-electric plants, with civilian ships being much more interested in having a highly reliable power plant than one that is extremely lightweight or compact.

For those interested in seeing the development of ships from earliest times to just about the present, I would recommend Bjorn Landstrom's book, The Ship.

 

[Timerover51]

Oops - yeah, that would be closing on like a mile long ship...

So trying that again... roughly from http://en.wikipedia.org/wiki/MS_Freedom_of_the_Seas - 338.94m x 38.60m x 63.70m / (14 m3 / dTon) => ~ 60,000 dTons .

I'd call it 45 to 50 thousand dTons accounting for shape, 18 decks and draft region.

It has 1,817 staterooms (double capable) and assuming 680 doubles for crew... that still comes to less than 10,000 dTons for Traveller style staterooms.

I am not going to get into an argument with you.

 

[Timerover51]

Potentially, the details could sink under a few general rules, with a resulting set of tables which paints ship design by period (unpowered, powered, and gravitic). The result would be a system which builds ships that are playable out of the box.

Before TL4 we have a general set of ship types and some universal design rules.

MegaTraveller defines Tech Level 4 as approximately 1900, characterized by the internal combustion engine.

The Traveller Book defines Tech Level 4 as approximately 1860 to 1900, again characterized by the internal combustion engine.

MegaTraveller is about correct for the internal combustion engine, the Traveller Book is about 40 years too early.

In either case, precisely where does the steam engine power plant fit in all of this? Iron shipbuilding began in the 1830s and became a major factor in ship construction, with mild steel appearing about 1880. You go from wooden hulls to the steel hulls of far larger ships in a span of 100 years from 1800 to 1900. All of that occurs prior to Tech Level 4 in the case of MegaTraveller.

Your general list of ship types goes from Bronze Age Egyptian and Greek vessels to the Great Eastern and Pre-Dreadnought battleships. Then you also have the first military submarine in David Bushnell's "Turtle" of 1776, and Fulton's "Nautilus". For warships, I am not even bothering to cover the various types of armor or the changes in armament.

From TL4 to TL7 we have narrower ship mission types, which can define preset assumptions about construction. Some additional tweaks can modify these presets.

In MegaTraveller, Tech Level 7 is listed at starting about 1970 and running to 1990. In the Traveller Book, Tech Level 7 is listed at running from 1970 to 1979.

From 1900 to 1970, the range of warship types expanded significantly, along with cargo ship types. For propulsion systems, the range is sail, steam (reciprocating engines, turbine, and turbo-electric systems), Diesel (direct drive, reduction geared, and Diesel-electric), gasoline internal combustion, gas turbine, and nuclear power. You are going from ships with virtually no electronics to ships where electronics are a major factor in power consumption. Then there is the aircraft carrier, which should have aircraft on it and all of your various types of amphibious ships. And lastly, you do have some "minor" changes in armament in there.

After TL7 we can only extrapolate, in which case it is most convenient to extrapolate in ways that are convenient to a design system, or (perhaps) interesting from a tactical point of view.

We are now almost in 2013. Are we still in Tech Level 7, and if so, what is any higher Tech level supposed to be? With respect to the "interesting from a tactical point of view", does that mean a primary focus on warships?

 

[PFVA63]

Hi,

I'm a bit confused by the Freedom of the Seas example. Looking at Wikipedia it lists a size of 154407 GT for this ship, and the definition of GT in Wikipedia is given as;

GT = K * V

where

V is the ship's total volume in cubic meters and
K is a multiplier based on V where K = 0.2 + 0.02 * Log (V)

Working this all out then it appears that a ship with a GT of 154407 GT would have an enclosed volume of about 492,000 cubic meters or about 35,142 dtons (if I did the math right)

Next, the ship is listed as having a passenger capacity of 3634 with an additional crew of 1360.

If we assume that each passenger and crew require 4 dtons (for berthing and life support, passages, and other common spaces) then that appears to be a requirement for about 14,536 dtons for the passengers and between 2720 to 5440 dtons for the crew (depending on if you assume 2 dtons or 4 dtons for each crew member).

Based on this it looks like the passenger and crew spaces would take up between about 49 to 57% of the ship's total interior volume.

I suppose that you could assume double occupancy for the passengers, but you'd still have to account for other stuff like passages and common spaces, which I've always kind of assumed would be part of the 4dtons allocated to each passenger in Traveller.

 

[Timerover51]

Hi,

I'm a bit confused by the Freedom of the Seas example. Looking at Wikipedia it lists a size of 154407 GT for this ship, and the definition of GT in Wikipedia is given as;

GT = K * V

where

V is the ship's total volume in cubic meters and
K is a multiplier based on V where K = 0.2 + 0.02 * Log (V)

Working this all out then it appears that a ship with a GT of 154407 GT would have an enclosed volume of about 492,000 cubic meters or about 35,142 dtons (if I did the math right)

Next, the ship is listed as having a passenger capacity of 3634 with an additional crew of 1360.

If we assume that each passenger and crew require 4 dtons (for berthing and life support, passages, and other common spaces) then that appears to be a requirement for about 14,536 dtons for the passengers and between 2720 to 5440 dtons for the crew (depending on if you assume 2 dtons or 4 dtons for each crew member).

Based on this it looks like the passenger and crew spaces would take up between about 49 to 57% of the ship's total interior volume.

I suppose that you could assume double occupancy for the passengers, but you'd still have to account for other stuff like passages and common spaces, which I've always kind of assumed would be part of the 4dtons allocated to each passenger in Traveller.

Then you do have the dining rooms, which do extend through 3 decks,the Grand Promenade, the Theater, the Casino, the Ice Rink, several restaurants, the shops, not sure how the swimming pools and swimming pool area is handled under that, the fact that some suites are far larger than the standard Traveller accommodations, children's area, various ship offices, and a lot of elevators and stairwells. Most of the cabins can handle 4 people, not just 2.

I did make one error in my original calculations, as 1 Traveller displacement ton is equal to 13.5 cubic meters, which is about 500 cubic feet or 5 measurement or gross tons. I should have divided by 5 rather than 14 as the Freedom is a high volume ship, so goes about 31,000 Traveller displacement tons.

The crew quarters are pretty spartan, and the crew pulls 3 months on, then 3 months off. Voyages are for one week, and the ship carries supplies for 2 weeks in case of things like hurricanes.