[1.20] Bulging and Engine rebuild isse/question

[nobody]

When you bulge a ship it usually says behind that "-2 knots +500 disp" (-3 kn if base ship speed is >24). If you replace the engines at the same time, this sometimes changes to "0 knots, +500 disp".

Why is that and what speed will the ship have after the rebuild? The following possibilities come to my mind:
1. It is a bug. Speed will be 10% lower anyway.
2. It's a feature. The ship will actually have the selected top speed. It's just a more extensive rebuild, which is why cost and rebuild time go up exponentially at the same time.



If this belongs somewhere else, feel free to move it there, but I couldn't find an FAQ folder or something similar.

[colprice]

Taking HMS Warspite as an example;
Bulging cost about 1.5 knots, subsequent rebuild & new engines/boilers restored the top speed and allowed for more armour.
See also the QE and Valiant refits.
Lightweight geared turbines and more efficient boilers saved a lot of weight as well as increasing power output.
Seems as if the simulation is reasonably accurate.

Colin

[oldpop2000]

Let me illustrate something to you. I have a ship that is 90 feet at the beam. Hull, fittings and equipment weighs about 13,639 tons or 41.4% of the total tonnage. I will now add about 10 feet of torpedo bulge to the ship. Hull, fittings and equipment have now increased to 16,638 tons or 45.5% of the total weight of ship. For the 30knots of maximum speed I need about 125,583 SHP. To gain that same 30 knots, I now need 135,660 SHP.

For a dose of reality, in 1933 as the British were designing what eventually became the Southampton cruisers, they reduced the waterline length from 600 feet to 584 feet without increasing the shaft horsepower. The ship went from 32Kts to 31.75. Doesn't seem like much, but you get the point. I don't know if this was theoretically, or during the speed trials. 

[nobody]

Colprice, Oldpop2000: That's all nice and valuable information, but has nothing to with my current problem whether I will get a 30kn (no bug) or 27kn (buggy display) ship.

[seawolf]

Its a bugged display

[oldpop2000]

Just some theory on this issue of the bulge. I have a design in Springsharp for the USS Boise which is very similar to the HMS Southampton cruisers. Engine power without a bulge was 100,350 SHP for a maximum speed of 33.734 knots. If I add a 10 foot wide torpedo bulge, which is what the Southampton's actually had, engine power necessary to maintain the same 33.734 knots was 111,678 SHP. I can't control SHP but I can reduce the speed until I get the original 100,350. I did this and arrived at the Maximum speed of 32.913 knots. So, with a torpedo bulge added, depending on its length and width, it will cause the requirements for engine power to rise or the speed to drop.

Now having shown this, it does not say that the game is wrong, its just the actual theory does work and that is what I am trying to illustrate. Some British cruisers had bulges of 5 ft. which was almost useless. Some US cruisers had bulges of 15 feet and so did the British. After WW1, I believe the naval engineers and officer realized the danger to their ships of the ever increasing lethality of the torpedoes and took appropriate steps.

[nobody]

Yea it's a game mechanic. On a capital ship a bulge is more likely to add 5000t (only partially usable of course) or more, with little loss in speed. And actually I would expect the speed loss to be lower for faster (big) ships. Putting a 500t bulge on the DD however, yea I can see that costing 3kn of top speed.

But that is not the point. The point was, that the rebuild-editor falsely(?) reports no loss in top speed.

[oldpop2000]

Jun 2, 2020 17:03:26 GMT -6 nobody said:

Yea it's a game mechanic. On a capital ship a bulge is more likely to add 5000t (only partially usable of course) or more, with little loss in speed. And actually I would expect the speed loss to be lower for faster (big) ships. Putting a 500t bulge on the DD however, yea I can see that costing 3kn of top speed.

But that is not the point. The point was, that the rebuild-editor falsely(?) reports no loss in top speed.

Well, I can't disagree, the facts show that a simple 10 ft. bulge will cause a lost of about 1.5 knots. It will also increase the tonnage. Something the team might examine.

[oldpop2000]

To the Team:

Could you examine the bulging function because I cannot and neither can others, confirm that it reduces speed. It does add weight remaining. Now, maybe it reduces the speed during actual combat operations, if so, could someone inform everyone of us. My figures above should help to show the actual losses in speed. Thanks for any help on this.

[oldpop2000]

I took the liberty of beginning a simple spreadsheet on the results of bulging in springsharp. I used the three typical bulge widths that I found in my books, but I am still researching. These were actual bulge widths for British and US Cruisers.

[oldpop2000]

I did some more reading and torpedo bulges can be included in the original design and placed inside the hull. This means they will not slow down the ship because its design length to beam is intact. However, when an older ship is rebuilt, its added outside, and this will slow down the ship and require more power. The Renown's were built in this manner. This cross section should provide some a picture of what I am talking about. 

[oldpop2000]

Just to let you know, the problem with the bulging has been fixed in 1.21 which should be out.

"Fixed a display bug with speed loss when both adding bulges and replacing machinery in a rebuild."

Attaboy to Nobody for bringing this up. I missed it, my bad.🙄

[oldpop2000]

I've just tested the new update, 1.21. When you are building a new ship, there is no bulged check box. When you are rebuilding and check the box, after replacing machinery, the horsepower figure shows up under the speed and now the horsepower will increase to maintain the same power. You must replace the machinery, THEN check the box to increase the power to get the same speed.