let's build a ship

whswhs · 03-30-2023, 09:56 PM

As an application of the discussion of ship design using GURPS Vehicles in another thread, I'm going to do a version of the ship from a recent campaign of mine.

Dola's Fortune is a Bronze Age merchant ship sailing a sea that's narrower than the Atlantic Ocean, but larger than the Mediterranean Sea. It has a mixed crew of various races of different sizes. Its crew includes half a dozen sailors, standing watch two at a time. Going by Vehicles (p. 75), the sum of its mast heights is 64 feet. At TL1, it can only have one mast (p. 9), so that mast is 64 feet. This requires a body volume of at least 4096 cubic feet (p. 9). The mast's volume is 26 cubic feet (p. 17).

It has a flotation hull. Since it's design for exploration rather than carrying bulk cargo, it has Average hydrodynamic lines, probably at the low end of 5:1 length-to-beam ratio (p, 10).This requires an increase in its volume by a factor of 1.2 to 4915 cubic feet (p. 16). Multiplying this by 52 pounds per cubic foot (p. 11) gives it a flotation rating of 255,590 pounds.

The mast carries a square-rigged sail with an area of 1638 square feet (p. 30). This weighs 1638 pounds and costs $1638. Thrust is 3276 pounds for a fresh breeze.

The controls are primitive and require one watchstander (p. 73) who occupies a roomy exposed crew station on deck (p. 75) that weighs 40 pounds, occupies 20 cubic feet, and costs $100. The crew, the armed guard, and the owners aboard sleep in hammocks (p. 77). Ten of these are for SM -1, weigh a total of 500 pounds, occupy 500 cubic feet, and cost $100; five are for SM 0, weigh a total of 500 pounds, occupy 500 cubic feet, and cost $100; one is for SM +1, weighs 225 pounds, occupies 225 cubic feet, and costs $45. The ship is large enough to have a bilge pump for free (p. 66). The total volume these take up is 1245 cubic feet, which leaves 3670 cubic feet.

The area of the body is 2000 square feet (p. 18). The area of the mast is 60 square feet. We assume that the structure is light, typical of sailboats, and expensive; this gives the body a weight of 15,000 pounds and a cost of $10,000 (p. 19). The mast weighs 720 pounds and costs $600 (p. 20). The body has 1500 hit points, and the mast has 120 hit points.

Dola's Fortune has heavy compartmentalization, which weighs 1500 pounds and costs $1500.

The body is armored at DR 6 on all sides except the top, which is DR 2. The armor is expensive wood. That's 9000 pounds and $4500 for the hull, and 600 pounds and $300 for the top deck (pp. 21-23). The PD is 2 for the top deck and 3 for the other faces (p. 24). The area of the top deck is 333 square feet, divided by 2 to leave room for the mast, to give 166 square feet (p. 94). Waterproofing Dola's Fortune costs $4120.

Total empty weight is 28,223 pounds. Crew weight is 3361 pounds. When empty, Dola's Fortune has a draft of 2.53 feet or 30 inches (p. 132). That leaves unused flotation of 227,367 pounds. I'll assume loose cargo at 20 pounds/cubic foot (p. 26) and 90% of the unused volume filled with cargo, for 66,000 pounds of cargo, bringing loaded weight to 97,584 pounds; that takes draft to 3.68 feet or 44 inches.

Size modifier per Vehicles is +6. Price is $21,503, which implies a maintenance interval of 136 hours, or about 45 minutes per day; this can be covered by crew members with Carpentry skill (p. 146). HT is calculated at 8 (p. 26).

Now, let's guess at the actual dimensions of Dola's Fortune (this is what I was puzzling over on the other thread). For this I have to extrapolate from Vehicles.

We have the area of the top deck, which is 333 square feet before deduction for the mast. If we approximate its shape as an ellipse, we can estimate the area of the rectangle that encloses it by multiplying by 4/π to get 424 square feet. If we assume a 5:1 length:beam ratio, we get 46 feet long and 9 feet wide.

If we treat Dola’s fortune as a submersible, we multiply its volume by 62.5 to get a flotation rating of 307187.5 pounds. Taking this as its loaded weight, and assuming Submarine lines, gives us draft of 9 feet. Since its draft is 44 inches with a normal load, we get freeboard of 64 inches, for total height of 9 feet from keel to top deck. Alternatively, we could use the Average multiplier of 1.2 instead of the Submarine multiplier of 2, which would give us 65 inches, resulting in a freeboard of 21 inches. Would that be better for a 49-ton sailing ship? It seems more like the dimensions I’m used to seeing.

Unfortunately, 46 feet x 9 feet x 5.3 feet is 2194 cubic feet, which is less than half of 4915 cubic feet. There’s a major error factor here somewhere. Even using 9 feet as the height only gives us 3726 cubic feet. And that’s for a rectangular solid that includes a lot of space outside the hull. Something’s not right here, but I’m not sure what.

03-30-2023, 09:56 PM	#1
whswhs Join Date: Jun 2005 Location: Lawrence, KS	let's build a ship As an application of the discussion of ship design using GURPS Vehicles in another thread, I'm going to do a version of the ship from a recent campaign of mine. Dola's Fortune is a Bronze Age merchant ship sailing a sea that's narrower than the Atlantic Ocean, but larger than the Mediterranean Sea. It has a mixed crew of various races of different sizes. Its crew includes half a dozen sailors, standing watch two at a time. Going by Vehicles (p. 75), the sum of its mast heights is 64 feet. At TL1, it can only have one mast (p. 9), so that mast is 64 feet. This requires a body volume of at least 4096 cubic feet (p. 9). The mast's volume is 26 cubic feet (p. 17). It has a flotation hull. Since it's design for exploration rather than carrying bulk cargo, it has Average hydrodynamic lines, probably at the low end of 5:1 length-to-beam ratio (p, 10).This requires an increase in its volume by a factor of 1.2 to 4915 cubic feet (p. 16). Multiplying this by 52 pounds per cubic foot (p. 11) gives it a flotation rating of 255,590 pounds. The mast carries a square-rigged sail with an area of 1638 square feet (p. 30). This weighs 1638 pounds and costs $1638. Thrust is 3276 pounds for a fresh breeze. The controls are primitive and require one watchstander (p. 73) who occupies a roomy exposed crew station on deck (p. 75) that weighs 40 pounds, occupies 20 cubic feet, and costs $100. The crew, the armed guard, and the owners aboard sleep in hammocks (p. 77). Ten of these are for SM -1, weigh a total of 500 pounds, occupy 500 cubic feet, and cost $100; five are for SM 0, weigh a total of 500 pounds, occupy 500 cubic feet, and cost $100; one is for SM +1, weighs 225 pounds, occupies 225 cubic feet, and costs $45. The ship is large enough to have a bilge pump for free (p. 66). The total volume these take up is 1245 cubic feet, which leaves 3670 cubic feet. The area of the body is 2000 square feet (p. 18). The area of the mast is 60 square feet. We assume that the structure is light, typical of sailboats, and expensive; this gives the body a weight of 15,000 pounds and a cost of $10,000 (p. 19). The mast weighs 720 pounds and costs $600 (p. 20). The body has 1500 hit points, and the mast has 120 hit points. Dola's Fortune has heavy compartmentalization, which weighs 1500 pounds and costs $1500. The body is armored at DR 6 on all sides except the top, which is DR 2. The armor is expensive wood. That's 9000 pounds and $4500 for the hull, and 600 pounds and $300 for the top deck (pp. 21-23). The PD is 2 for the top deck and 3 for the other faces (p. 24). The area of the top deck is 333 square feet, divided by 2 to leave room for the mast, to give 166 square feet (p. 94). Waterproofing Dola's Fortune costs $4120. Total empty weight is 28,223 pounds. Crew weight is 3361 pounds. When empty, Dola's Fortune has a draft of 2.53 feet or 30 inches (p. 132). That leaves unused flotation of 227,367 pounds. I'll assume loose cargo at 20 pounds/cubic foot (p. 26) and 90% of the unused volume filled with cargo, for 66,000 pounds of cargo, bringing loaded weight to 97,584 pounds; that takes draft to 3.68 feet or 44 inches. Size modifier per Vehicles is +6. Price is $21,503, which implies a maintenance interval of 136 hours, or about 45 minutes per day; this can be covered by crew members with Carpentry skill (p. 146). HT is calculated at 8 (p. 26). Now, let's guess at the actual dimensions of Dola's Fortune (this is what I was puzzling over on the other thread). For this I have to extrapolate from Vehicles. We have the area of the top deck, which is 333 square feet before deduction for the mast. If we approximate its shape as an ellipse, we can estimate the area of the rectangle that encloses it by multiplying by 4/π to get 424 square feet. If we assume a 5:1 length:beam ratio, we get 46 feet long and 9 feet wide. If we treat Dola’s fortune as a submersible, we multiply its volume by 62.5 to get a flotation rating of 307187.5 pounds. Taking this as its loaded weight, and assuming Submarine lines, gives us draft of 9 feet. Since its draft is 44 inches with a normal load, we get freeboard of 64 inches, for total height of 9 feet from keel to top deck. Alternatively, we could use the Average multiplier of 1.2 instead of the Submarine multiplier of 2, which would give us 65 inches, resulting in a freeboard of 21 inches. Would that be better for a 49-ton sailing ship? It seems more like the dimensions I’m used to seeing. Unfortunately, 46 feet x 9 feet x 5.3 feet is 2194 cubic feet, which is less than half of 4915 cubic feet. There’s a major error factor here somewhere. Even using 9 feet as the height only gives us 3726 cubic feet. And that’s for a rectangular solid that includes a lot of space outside the hull. Something’s not right here, but I’m not sure what. __________________ Bill Stoddard I don't think we're in Oz any more.