Ship Weight

[Cardea]

Has anyone come up with weight for any of the ships found in Stormwrack? Specifically, the Pinnace.

[Ashtagon]

Has anyone come up with weight for any of the ships found in Stormwrack? Specifically, the Pinnace.

A ship's weight is equal to the weight of the volume of water it displaces. That pinnace is 30' long, 10' wide, and has a 5' draft. That describes a box of 1500 cubic feet, or 42.475 cubic metres. Sea water has a density of 1.025 t/m3, so that's a theoretical maximum weight of 43.537 tonnes. Of course, the ship's displacement is actually a "hull" shape (for want of a better word), not a box. It's probably closer to 1/8 that amount, or about 5.442 tonnes.

Of course, the game designers probably had no idea about all this. They just pulled numbers out of a hat.

[Lord Vukodlak]

Has anyone come up with weight for any of the ships found in Stormwrack? Specifically, the Pinnace.
If its for some spell effect etc, the answer is to heavy.

[Cardea]

A ship's weight is equal to the weight of the volume of water it displaces. That pinnace is 30' long, 10' wide, and has a 5' draft. That describes a box of 1500 cubic feet, or 42.475 cubic metres. Sea water has a density of 1.025 t/m3, so that's a theoretical maximum weight of 43.537 tonnes. Of course, the ship's displacement is actually a "hull" shape (for want of a better word), not a box. It's probably closer to 1/8 that amount, or about 5.442 tonnes.

Of course, the game designers probably had no idea about all this. They just pulled numbers out of a hat.
That's very well explained. Thank you.

If its for some spell effect etc, the answer is to heavy.
Not so. Ironwood affects wood based on weight and CL. Just means I meet multiple Schemas of the thing.

[nedz]

Weight = Displacement, i.e. the amount of water displaced: Source: Archimedes.

There is a Rule of Thumb formulae:
Length x Breadth x Draft x Coefficient of Finesse

The Coefficient of Finesse is depends upon the hull shape: this is normally about 0.65, though barges are about 0.85.

It's easiest to do this with SI units which yield metric tonnes; because otherwise you need to factor in several conversion coefficients to cope with the Imperial/American units — which, of course, are the units the rules use.

From Ashtagon metrics, assuming a Coefficient of Finesse of about 0.62 for a Pinnace (they are very fine) we get about 27 tonnes. This is 27,000 Kilogrammes or about 56,510 (avoirdupois) pounds.

[Elkad]

A ship's weight is equal to the weight of the volume of water it displaces. That pinnace is 30' long, 10' wide, and has a 5' draft. That describes a box of 1500 cubic feet, or 42.475 cubic metres. Sea water has a density of 1.025 t/m3, so that's a theoretical maximum weight of 43.537 tonnes. Of course, the ship's displacement is actually a "hull" shape (for want of a better word), not a box. It's probably closer to 1/8 that amount, or about 5.442 tonnes.

Of course, the game designers probably had no idea about all this. They just pulled numbers out of a hat.

Looks pretty close to me. Most modern 30' sailboats are in the 5-7 ton range, including a couple tons of ballast, which you could swap for cargo if needed.

[Lord Vukodlak]

That's very well explained. Thank you.

Not so. Ironwood affects wood based on weight and CL. Just means I meet multiple Schemas of the thing.

Well one, you can't partially ironwood an object but that aside it makes it as heavy as steel which is ALOT heavier then wood. Your pinnacle would be too heavy to move under its old sail power.

Thirdly given the weight is around 7 tons, you'd need over a hundred schemas. So again to heavy for spell effects. You'd be better off investing that gold in a flying castle.

[hamishspence]

Well one, you can't partially ironwood an object but that aside it makes it as heavy as steel which is ALOT heavier then wood. Your pinnacle would be too heavy to move under its old sail power.

Solution - get more sails.

Steel sailing boats could be pretty fast:

http://en.wikipedia.org/wiki/Windjammer

[Knaight]

Well one, you can't partially ironwood an object but that aside it makes it as heavy as steel which is ALOT heavier then wood. Your pinnacle would be too heavy to move under its old sail power.

Steel is roughly 10 times the density of wood, specifically, though that depends on the steel alloy and particular wood. It can also work with a much thinner hull than wood can, which makes this ironwood plan somewhat functional. The boat would need to be slimmed out in the hull to about 1/10 thickness, which brings the mass down significantly for the ironwood spell. Multiple castings will obviously still be necessary, but that's not necessarily an issue - "object" is a bit of an odd term, and if different parts can be treated as distinct objects all's well.

I've also looked into some contemporary sail-boats of comparable length - 4 tons is more common than 7. The pinnacles actual design would need to be looked at, as the cross-section as viewed from above likely involves much greater proportional width for about the first half of the boat, so 5 tons is a pretty good estimate. Once thinned out, this is a mere 1,000 pounds of wood, which is 10 castings at max CL.

That said, the ironwood boat plan likely works best if you make a brand new boat with the explicit design of a metal craft, using a very low density wood. Balsa, for instance. Things would also be much more convenient if aluminumwood was a thing, but as far as I know there's no way to produce that.

[Cardea]

Well one, you can't partially ironwood an object but that aside it makes it as heavy as steel which is ALOT heavier then wood. Your pinnacle would be too heavy to move under its old sail power.

Thirdly given the weight is around 7 tons, you'd need over a hundred schemas. So again to heavy for spell effects. You'd be better off investing that gold in a flying castle.


Steel is roughly 10 times the density of wood, specifically, though that depends on the steel alloy and particular wood. It can also work with a much thinner hull than wood can, which makes this ironwood plan somewhat functional. The boat would need to be slimmed out in the hull to about 1/10 thickness, which brings the mass down significantly for the ironwood spell. Multiple castings will obviously still be necessary, but that's not necessarily an issue - "object" is a bit of an odd term, and if different parts can be treated as distinct objects all's well.

I've also looked into some contemporary sail-boats of comparable length - 4 tons is more common than 7. The pinnacles actual design would need to be looked at, as the cross-section as viewed from above likely involves much greater proportional width for about the first half of the boat, so 5 tons is a pretty good estimate. Once thinned out, this is a mere 1,000 pounds of wood, which is 10 castings at max CL.

That said, the ironwood boat plan likely works best if you make a brand new boat with the explicit design of a metal craft, using a very low density wood. Balsa, for instance. Things would also be much more convenient if aluminumwood was a thing, but as far as I know there's no way to produce that.
While its not relevant to how many times I need to be using Ironwood and asking for DM fiat on this new issue (thank you, Vukodlak), I'd like to point out that I'm only looking into Ironwood'ing the ship in the first place for the hardness increase: the thing is flying via magic, not sailing via physics.

[Knaight]

While its not relevant to how many times I need to be using Ironwood and asking for DM fiat on this new issue (thank you, Vukodlak), I'd like to point out that I'm only looking into Ironwood'ing the ship in the first place for the hardness increase: the thing is flying via magic, not sailing via physics.

Does the magic scale? Because if you're magically getting lift within a certain range, the thing is going to have issues even getting airborne.

[Lord Vukodlak]

That said, the ironwood boat plan likely works best if you make a brand new boat with the explicit design of a metal craft, using a very low density wood. Balsa, for instance. Things would also be much more convenient if aluminumwood was a thing, but as far as I know there's no way to produce that.

Exactly, he's not trying to build a ship out of ironwood. he's trying to turn an existing ship into iron wood which of course has that pesky duration problem.


I've also looked into some contemporary sail-boats of comparable length - 4 tons is more common than 7. The pinnacles actual design would need to be looked at, as the cross-section as viewed from above likely involves much greater proportional width for about the first half of the boat, so 5 tons is a pretty good estimate. Once thinned out, this is a mere 1,000 pounds of wood, which is 10 castings at max CL
I'm getting very different numbers, a 40ft Pinnace called the "Sparrow Hawk" had a displacement of 30 tons, which means the ship weighed 30 tons. Now the one in the book is only 30ft long so it would be lighter but not by much.


Solution - get more sails.

Steel sailing boats could be pretty fast:

http://en.wikipedia.org/wiki/Windjammer
When they were designed that way and had a **** load of sails. He's trying to convert a boat to metal. In what world is that a pinnacle? None.


While its not relevant to how many times I need to be using Ironwood and asking for DM fiat on this new issue (thank you, Vukodlak), I'd like to point out that I'm only looking into Ironwood'ing the ship in the first place for the hardness increase: the thing is flying via magic, not sailing via physics.
That would depend on the method of flight, and propulsion. Does your ship still suffer reduced speed if its full of cargo? Does it still require sails and wind to move forward not just stay in the air?

Perhaps you should consider the hardening spell aside from being permanent its based on volume and not by weight which is much easier to figure out.

[Lightlawbliss]

I'm getting very different numbers, a 40ft Pinnace called the "Sparrow Hawk" had a displacement of 30 tons, which means the ship weighed 30 tons. Now the one in the book is only 30ft long so it would be lighter but not by much.

Link please? I think your looking at max displacement or standard load displacement.

[Cardea]

Does the magic scale? Because if you're magically getting lift within a certain range, the thing is going to have issues even getting airborne.
Has not been addressed. Using the Airship from Eberron but resized to being made from a Pinnace. I'd hope that the weight difference wouldn't matter too much, given the size difference.

Really, just trying for one problem at a time.

[Lord Vukodlak]

Has not been addressed. Using the Airship from Eberron but resized to being made from a Pinnace. I'd hope that the weight difference wouldn't matter too much, given the size difference.

Really, just trying for one problem at a time.

Ah well such ships move more slowly when carrying a full load of cargo thus increasing the weight of the hull would also slow the ship down. Furthermore Lyrandar airships are made from soar-wood which is half the weight of normal wood. Increasing it to the weight of steel... sounds like a very bad idea to me.

As I said above you're better off using the hardening spell its permanent and effects 10 cu. ft./level. Much easier to figure out.



Link please? I think your looking at max displacement or standard load displacement.
http://en.wikipedia.org/wiki/Sparrow_Hawk_pinnace

[Knaight]

I'm getting very different numbers, a 40ft Pinnace called the "Sparrow Hawk" had a displacement of 30 tons, which means the ship weighed 30 tons. Now the one in the book is only 30ft long so it would be lighter but not by much.

It would be significantly longer. If the dimensional shrinkage is consistent across all 3 dimensions, it would be 42% of the displacement. That figure would include the hull being 3/4 thinner, but even if surface area is used 56% would be expected. That gets 13-17 tons, both of which involved rounding up. If I assume that the length-width ratio is also lower, 20 is plausible.

Also, what length are you using? Both length of the water line and length overall see use, and if you're using length of the water line while the book is using overall length, it throws things off. It also throws things off if the mass used includes any sort of load, whether cargo or ballast.

The 5 was based off a different boat design entirely though, so it could easily be too low. The Pinnace does have a substantially higher draft than the typical sailboat, and that's with the width being proportionally greater for the front half. I could easily see 15 tons.

[Lord Vukodlak]

Also, what length are you using? Both length of the water line and length overall see use, and if you're using length of the water line while the book is using overall length, it throws things off. It also throws things off if the mass used includes any sort of load, whether cargo or ballast.


The waterline or Beam as it was also called is 12.83ft. What I don't know is did the length include the mast that sticks out form the bow. If it does then it may be the same size as the one in the book.

[Cardea]

Ah well such ships move more slowly when carrying a full load of cargo thus increasing the weight of the hull would also slow the ship down. Furthermore Lyrandar airships are made from soar-wood which is half the weight of normal wood. Increasing it to the weight of steel... sounds like a very bad idea to me.

As I said above you're better off using the hardening spell its permanent and effects 10 cu. ft./level. Much easier to figure out.

That does. Huh. Thanks for the pointer.

[ericgrau]

You could also do ship surface area x thickness x ~40 lbs. per cubic foot and remember to include the internal wooden beams, in case you think the 5 foot draft is a rough number.

The problem with decreasing thickness to save weight for an ironwood spell is that the ship may end up being weaker than a wooden one overall. 1/10th as thick means 1/1000th as rigid, so the extra strength of steel will not make up for that and you will be in a rather flexible boat that may easily crumple. In game terms iron or steel also have 30 hp per inch, while wood has 10 hp per inch, so you end up with 1/3 the hp too. I think even in the real world the reason we switched to metal & fiberglass ships is because they don't rot, hold a more consistent shape, and repel bullets better in the case of warships. Not because of any strength to weight advantage. Plus extra weight in the ocean isn't a big deal, especially on huge ships. It only means more draft which slows you down, but it won't make you 10 times slower for 10 times the weight. It's more like a little under half speed in that case.

[Elkad]

https://upload.wikimedia.org/math/b/1/8/b1842285c9f3d627b92a768aae4011af.png

30' length, 12' beam gives 13.8 tons.
30' length, 8' beam is only 7.5 tons

I'd call the pinnace in Stormwrack about 28x8, or 6.8 tons

[Lord Vukodlak]

https://upload.wikimedia.org/math/b/1/8/b1842285c9f3d627b92a768aae4011af.png

30' length, 12' beam gives 13.8 tons.
30' length, 8' beam is only 7.5 tons

I'd call the pinnace in Stormwrack about 28x8, or 6.8 tons

And those numbers are relevant how? They were created in the mid 1850's for recreational ships, not cargo vessels from two centuries prior. Also it was also for tonnage, aka cargo capacity. NOT the weight/displacement of the ship.

All of which is moot though, as I already pointed out that its the hardening spell is a more efficient way of toughening up the ship.

[Knaight]

I think even in the real world the reason we switched to metal & fiberglass ships is because they don't rot, hold a more consistent shape, and repel bullets better in the case of warships.
The more consistent shape and bullet repelling are functions of strength. Early metal warships were nearly impervious to contemporary cannon, the shape holding allows for drastically larger ships on the high end (there is no way a modern cargo ship could even be made out of wood), etc. That did come at the cost of more weight, so narrowing the ship out to 1/10 probably would be overkill, but that doesn't mean narrowing it wouldn't work. There's also the matter of hardness - steel is substantially harder than wood, and that helps with puncture resistance, which is very much an issue here, as the ship in question is almost certainly going to see combat use.

[Ashtagon]

Weight = Displacement, i.e. the amount of water displaced: Source: Archimedes.

There is a Rule of Thumb formulae:
Length x Breadth x Draft x Coefficient of Finesse

The Coefficient of Finesse is depends upon the hull shape: this is normally about 0.65, though barges are about 0.85.

It's easiest to do this with SI units which yield metric tonnes; because otherwise you need to factor in several conversion coefficients to cope with the Imperial/American units — which, of course, are the units the rules use.

From Ashtagon metrics, assuming a Coefficient of Finesse of about 0.62 for a Pinnace (they are very fine) we get about 27 tonnes. This is 27,000 Kilogrammes or about 56,510 (avoirdupois) pounds.

nedz speaks much wisdom.

The best information I can find for block coefficient suggests that typical sailing ships will have a value of about 0.4 (lower for high-speed "sleek" military vessels, higher for barges and freighters). That gives a final figure of about 16.5 tonnes.

Yes, these numbers are possibly a bit higher than modern construction. Modern construction tends to have a considerably shallower draft that these for equivalent main deck area, thanks to more advanced lightweight materials and modern engineering techniques. Additionally, they tend to use much smaller crews (Renaissance through to early modern vessels were shockingly overcrowded by modern naval standards).

https://en.wikipedia.org/wiki/Block_coefficient
http://www.seleneannapolis.com/tech-tips/18-hydrostatic-data-.html
http://www.sponbergyachtdesign.com/THE%20DESIGN%20RATIOS.pdf
http://www.boatdesign.net/forums/stability/hull-displacement-calculation-14705.html

[ericgrau]

The more consistent shape and bullet repelling are functions of strength.
More like warping and hardness rather than strength. Wood has a pretty good strength to weight and rigidity. Wooden planes were built alongside aluminum ones for quite a while and performed well, until everyone decided more and more that it was impractical to make them. This strength to weight is less important for boats though where you can make them 5 or 10 times heavier and it's still not a big deal. Or in other words cast the ironwood and add more sails. Keep it heavy. Don't make the boat much thinner or it will crumple far more easily than wood.

You need to distinguish between rigidity, bending strength, surface hardness, formability, resistance to deterioration, etc.

[sleepyphoenixx]

If all you want is the hardness you could just cast Augment Object (SBG). It can affect 200 cubic ft./level, doubles hardness and hitpoints, lasts 1day/level, allows the object to make saves as if attended (at 2+1/2CL) and is a 3rd level spell for wizards, sorcerers, clerics, druids and spellthiefs.

[Lord Vukodlak]

More like warping and hardness rather than strength. Wood has a pretty good strength to weight and rigidity. Wooden planes were built alongside aluminum ones for quite a while and performed well, until everyone decided more and more that it was impractical to make them. This strength to weight is less important for boats though where you can make them 5 or 10 times heavier and it's still not a big deal. Or in other words cast the ironwood and add more sails. Keep it heavy. Don't make the boat much thinner or it will crumple far more easily than wood.

You need to distinguish between rigidity, bending strength, surface hardness, formability, resistance to deterioration, etc.

Reminder, this is a Eberron style flying ship, the kind that use soarwood which is half the weight of normal wood. Its simply the size of a pinnacle.

[nedz]

Reminder, this is a Eberron style flying ship, the kind that use soarwood which is half the weight of normal wood. Its simply the size of a pinnacle.

Reminder: Weight = Displacement, i.e. the amount of water displaced; Source: Archimedes.

If you are right then the draft should be less; probably a bit less than 2 foot instead of 5.

[Knaight]

Reminder: Weight = Displacement, i.e. the amount of water displaced; Source: Archimedes.

If you are right then the draft should be less; probably a bit less than 2 foot instead of 5.

I assume the draft figures are for a normal wooden ship, and that the wooden parts are half weight. Which probably leaves about a 3-4 foot draft still, as a pinnacle has a pretty strongly tapering keel, and the volume from 3-4 feet to 5 feet could easily be the same as the volume from 0 feet to 3-4 feet. Were it a barge, it would be pretty close to 2.5 feet.

[ericgrau]

Reminder, this is a Eberron style flying ship, the kind that use soarwood which is half the weight of normal wood. Its simply the size of a pinnacle.
I missed that part. Ok, in that case iron/steel is a pretty poor material choice compared to wood. A downgrade in fact. Maybe if there was a spell called mithralwood. But ya apparently there are plenty of spells to make a material stronger without adding weight, so go with that.

[nedz]

I assume the draft figures are for a normal wooden ship, and that the wooden parts are half weight. Which probably leaves about a 3-4 foot draft still, as a pinnacle has a pretty strongly tapering keel, and the volume from 3-4 feet to 5 feet could easily be the same as the volume from 0 feet to 3-4 feet. Were it a barge, it would be pretty close to 2.5 feet.

Yes — I made a sign error on my subtraction :smallredface: :smallsmile:

[Knaight]

Yes — I made a sign error on my subtraction :smallredface: :smallsmile:

It looked like something like that had happened (or that you figured that the top 2 feet were equivalent to the bottom 3, then accidentally used the wrong number).