MASSIVE SPOILER about next book hardware

Real life considerations dictate redundancy if one is in the middle of the ocean. Boilers, being mechanical devices, suffer from what the engineers and manufacturers used to euphemistically refer to as casualties or mechanical disarray in their incident reports. That could be anything from a fuel explosion to a massive tube rupture to a turbine rolling out the side of the building. When a water wall tube ruptures in an operating boiler, especially in the furnace portion of the boiler and very especially in a coal fired boiler because one cannot quickly extinguish the fire as one can in an oil or gas fired boiler, very bad things such as the furnace door being blown open and the burning coals being ejected into the fueling area can happen very quickly. In any case, the boiler must be shut down and made cool enough so that people can enter both the steam drum and the mud drum and plug the ruptured tube or tubes. Even in a small boiler it still takes a day to cool down and another day to plug the tube(s) and bring the boiler back on line. In the meantime, adequate quantities of steam must be available for propulsion and the auxiliaries such as the evaporator, the feedwater pumps and a fair number of other steam driven devices.

kbus888 wrote:I agree.

In fact this will not be the first "what has gone wrong now" meeting the Group of Four has had.

It's a firm tradition.

Hi PeterZ,

I've always thought the navy's middle name was redundancy.

OTOH, a number of penny pinching secretaries of Defense or the navy have thought they could get away with one engine, one shaft, one propeller, one rudder among other things like weapons on a small warship; only to discover why the navy insists on redundancy as much as possible.

IIRC, the DE-1052 class had seven major failures in the above critical 'systems' in the first six month's of class operations that required them being towed back to port.

Thank you Robert Strange McNamara.

I thought I had sent this hours ago, but better late than never. :-)

L

PeterZ wrote:I got that from your initial post, redundancy, I mean. Its just that you write such imaginative stories that such plain vanilla bits of speculation seems unworthy. So even though redundancy was why it was designed the way it was, I have to add some color and what little je ne sais quoi that I might possess.

runsforcelery wrote:
I would simply point out that the reason their powerplants were doubled had absolutely nothing to do with towing power or the need to provide additional power at all. Hint: think redundancy here, then think 5,000-mile-plus voyage across blue water by a vessel not rigged for sail at speeds no escorting galleon could equal.

Just saying.

This ship seems too heavy for it's stated dimensions. Can someone tell me where I am going wrong here?

I am trying to convert the dimensions RFC supplied for the ship into it's liquid displacement and I am comming up significantly short of the required displacement tonage.

We know the following:
Dimensions: 140'x40'x6' (normal draft); with a tonnage of 1,200 tons

Assuming a perfect cubic hull form this is a displacement volume of 33600 cubic feet of water. According to Google 33 600 (cubic feet) = 951 446.045 litres or 951 metric tons assuming that the hull form is a perfect box shape. Any boat will loose a certain % of the cubic hull displacement due to the hull not being rectangular so we should multiply this by about 80% to get the actual boat displacement. This gives anactual displacement tonnage of 760 metric tons. Given the stated length and bredth we would need to increase the draft of the ship by 1200/760 * 6 to give us a draft of nearly 9'6" to displace the stated mass.

Is google giving me an incorrect conversion from cubic feet to litres or have I made an error someplace else in the calculations?

I also have concern about the weight of the designed 6'BL armourment.

Given that we have a listed armourment of 26 ports if we go with the 6” BL w/hydro-pneumatic recoil which has to be in the same ballpark weight as the British 6' BL (7.5 tons) http://en.wikipedia.org/wiki/BL_6_inch_Mk_VII_naval_gun that would be 195 tons just in guns and mountings exclusive of shells and crew, armour etc. I am assuming that when changed to 6' BL with recoil absorbtion the armourment will be reduced to 6-8 6' BL in line with what was mounted on WW1 light cruisers of 3-4 times the displacement.

First stupid thought. You are using metric on Safehold! <Huge grin>

"Langhorne! What are you thinking?"

Enjoy,
T2M

Couldn't help myself. Personal failing.

Interesting the real Royal navy are producing a "river class" patrol vessel.

I wonder if DW used the name as a parallel. if he does the real navy are producing just a 3-4 of them so that may just be the number he uses in safehold. (that of course is just a guess)

Silverwall wrote:This ship seems too heavy for it's stated dimensions. Can someone tell me where I am going wrong here?

I am trying to convert the dimensions RFC supplied for the ship into it's liquid displacement and I am comming up significantly short of the required displacement tonage.

We know the following:
Dimensions: 140'x40'x6' (normal draft); with a tonnage of 1,200 tons

Assuming a perfect cubic hull form this is a displacement volume of 33600 cubic feet of water. According to Google 33 600 (cubic feet) = 951 446.045 litres or 951 metric tons assuming that the hull form is a perfect box shape. Any boat will loose a certain % of the cubic hull displacement due to the hull not being rectangular so we should multiply this by about 80% to get the actual boat displacement. This gives anactual displacement tonnage of 760 metric tons. Given the stated length and bredth we would need to increase the draft of the ship by 1200/760 * 6 to give us a draft of nearly 9'6" to displace the stated mass.

Is google giving me an incorrect conversion from cubic feet to litres or have I made an error someplace else in the calculations?

I also have concern about the weight of the designed 6'BL armourment.

Given that we have a listed armourment of 26 ports if we go with the 6” BL w/hydro-pneumatic recoil which has to be in the same ballpark weight as the British 6' BL (7.5 tons) http://en.wikipedia.org/wiki/BL_6_inch_Mk_VII_naval_gun that would be 195 tons just in guns and mountings exclusive of shells and crew, armour etc. I am assuming that when changed to 6' BL with recoil absorbtion the armourment will be reduced to 6-8 6' BL in line with what was mounted on WW1 light cruisers of 3-4 times the displacement.

Couple of points. Well, three points, actually. [G]

First, the hull is very nearly rectangular. This is a converted canal/river barge, not an oceanic hull, which is the main reason such an absurdly overpowered hull isn’t capable of more than 17-18 mph in calm water.

Secondly, 951 metric tons is 1,048.3 short tons, which are the only tons available on Safehold, courtesy of Eric Langhorne, and it was short tons I was citing, so the difference in tonnage from my figures to your “rectangular hull” is only 151 tons, or roughly 7.5%, which very probably occurred in my original rounding and is close enough for me to feel perfectly happy using.

Third, the 6” BL gun you cite is a heck of a lot bigger than the gun I am citing. Your gun was a 6”/44 — that is, it was 44 calibers long, making the tube right on 22’ long; the 6” for the river class are black powder weapons, and longer tubes don’t give black powder cannon the same velocity advantage they give with nitro cellulose propellants because of the difference in burn time. A black powder weapon gives all of its acceleration almost instantly; after that point, friction with the barrel liner becomes a factor (especially in rifled guns, with their reduced windage) which actually reduces muzzle velocity in a longer tube. The 6” BL for the River class is a 6”/18, with a 9’ tube, just over 40% the length of your weapon, and a muzzle velocity of roughly 1,350 fps compared to the 2,700+ fps of the 6” you cite. Total weight of the gun on a wooden truck carriage is only about 2.5 tons and the new mount is based on the Marsilly carriage with a very simple hydro-pneumatic recoil system, so total weight per piece is only going to be in the 4-ton range. I also gave you 2 too many gun ports per broadside in my original notes (I forgot I’d shifted 4 broadside guns to bow and stern positions when I went with a homogenous 30-pounder/6” armament on a 140’ hull rather than having a single 8” fore and aft on a 160’ hull as in my original rough design), so the actual total armament is 22 guns, not 26, giving a weight of around 104 tons, not 195.

Armor (I’m shooting from memory here, rather than going back and hunting up my exact calculations) works out at about 280 tons, hull structure works out at around 250 tons, guns come in at about 100, and machinery (with all liquids aboard) is about 250 tons, for a total of 880 tons, or 1,360 with 480 tons of coal on board. I allowed myself the extra 160 tons as a wiggle-room number, given that all of the figures are approximations. (Besides, I thoght “twelve hundred tons” sounded better than “thirteen hundred and sixty tons,” so I exercised a little authorial license. [G])

If the weight of the machinery seems low, I would point out that the triple-expansion machinery of USS Maine (6,650 long tons [7,448 short tons]; 1895; fire tube boilers; 135 psi steam; trial speed 17.45 Old Earth knots [20.08 Safeholdian knots]) weighed about 700 short tons, whereas these ships have double expansion machinery, small water tube boilers, and 290 psi steam, so the 250 tons number is actually probably high. The third cylinder — the one these ships don’t have — is usually around 3 times the diameter of the first cylinder, so the weight of the engines themselves is cut approximately in half, while Maine had 8 boilers, all of which were bigger and heavier than any of these ships’ 4 boilers.

As another indicator of the difference between water tube and fire tube boilers, the weight of HMS Invincible's machinery (1907) was about 20% of her total displacement, or around 3,925 short tons, and developed 41,000 shaft horsepower. HMS Hood (designed 1917) devoted only 13% of her much greater displacement to machinery (around 6,800 short tons) but developed 144,000 SHP. This means that the earlier ship (with 31 fire tube boilers) developed 10.44 SHP per ton of machinery, whereas Hood (with only 24 water tube boilers and higher pressures) generated 21.22 SHP per ton of machinery, better than twice the efficiency. Both of these ships used turbines rather than reciprocating machinery (as in the River class or the Maine), but the decrease in weight per SHP (which was really pretty astonishing in only a decade) was due to the greater efficiency of the water tube boilers. That same efficiency curve, only greater, would be in play in comparing Maine's machinery weights to the River class'.

For anyone interested in real esoterica, USS Iowa's machinery weight in 1943 was 4,423.8 long tons (dry) and 4,815.8 long tons (with liquids) and generated 212,000 SHP. That comes to 39.3 SHP per short ton weight of machinery, which explains why a ship with a standard displacement 116% that of Hood was 10% faster than Hood's highest attained speed and 16% faster than her best speed in 1941. I don't know what Hood's steam conditions were, but Iowa's plant operated at 600 psi, which was 210% of the 280 psi of the Colorado class, the last USN BBs built before the Washington Naval Disarmament Treaty.

Returning to Safehold, one recurrent problem people seem to be having when they look at Safeholdian technology is an effort to pick a period of Old Earth technology and then use it as a yardstick for Safehold. The difficulty is that they appear to be picking the wrong periods rather than looking at the numbers I’m actually giving them, as when it was assumed in another post that Empress of Charis was basically a 16th century galleon with all guns on a single deck instead of, effectively, a 19th century double-banked frigate design. In this instance, for example, you were selecting guns which are much more advanced than (and more than twice as heavy as) the ones actually being mounted, while I suspect most people are looking at machinery weights in terms of around 1850-70 tech when they are actually far more comparable to those of around 1915 (USN service) in terms of steam pressures and weights and hence efficiency.

Wow I love the info dumps

I love infodumps too, they give you the inside view of the universe that I miss from other authors in other series.

So thanks RFC for everything and if we can help in any way please tell us (apart from buying the books of course).

At least they had failures that involved their retaining positive buoyancy, as opposed to reducing hull plate welding and fastening until something large falls off, as happened to another ship of another class.

We have not seen much of the RMN making any *bad* design decisions, other than the weapon of the accursed.

lyonheart wrote:Hi PeterZ,

I've always thought the navy's middle name was redundancy.

OTOH, a number of penny pinching secretaries of Defense or the navy have thought they could get away with one engine, one shaft, one propeller, one rudder among other things like weapons on a small warship; only to discover why the navy insists on redundancy as much as possible.

IIRC, the DE-1052 class had seven major failures in the above critical 'systems' in the first six month's of class operations that required them being towed back to port.

Thank you Robert Strange McNamara.

I thought I had sent this hours ago, but better late than never. :-)

L

PeterZ wrote:I got that from your initial post, redundancy, I mean. Its just that you write such imaginative stories that such plain vanilla bits of speculation seems unworthy. So even though redundancy was why it was designed the way it was, I have to add some color and what little je ne sais quoi that I might possess.

runsforcelery wrote:
I would simply point out that the reason their powerplants were doubled had absolutely nothing to do with towing power or the need to provide additional power at all. Hint: think redundancy here, then think 5,000-mile-plus voyage across blue water by a vessel not rigged for sail at speeds no escorting galleon could equal.

Just saying.