Bulbous Bows

[Dan K]

A couple of notes here:

"Junyo and Hiyo's bulbous bow and 4 bladed props may simply be a hold over from their original express passenger liner origins. Bulbous bows were universal on fast passenger liners of the era."

The 4 bladed props might be, but not the bulbous bows, at least on Japanese ships. Prior to the design that became Hiyo and Junyo, the newest, largest class of Japanese liners were the Kasuga, Nitta & Yawata Maru (the sisters that were converted to the the CVEs Taiyo, Chuyo and Unyo). All were completed in 1939-1940 with 4 bladed props and no bulbous bows. In fact, there are no bulbous bows on any Japanese liner prior to the Idzumo Maru (Hiyo) class.

" Even Shokaku's sister Zuikaku didn't have a bulbous bow."

Absolutely false. Perpetuated by conjecture in either Watts or Chesneau. Both ships had them, confirmed by Shizuo Fukui.

Cross pollination: Well, the Yamato design was finalized by R. Admiral Keiji Fukuda, who had succeeded R. Admiral Fujimoto as head of the Naval Technical Bureau upon Fujimoto's resignation in the wake of the Tomozuru debacle, and then passed away the following year in 1935. Fujimoto, if you recall, was the talented naval architect who built upon Hiraga's work while bending to the demands of the Naval General Staff. He modified the Myokos, and was primarily responsible for the Takaos, Mogamis, Fubuki's and others, none with bulbous bows.

Fukuda appears to be the champion of the bulbous bow for the IJN. Aside from the Yamatos and the Shokakus, other large warships freshly designed on his watch with (non protruding) bulbous bows include Taiho, Oyodo, and the 4 Agano class CLs (Agano, Noshiro, Yahagi, & Sakawa). It is entirely likely that his influence extended to the design of the Idzumo Maru class as well.

[chuck]

I was thinking about Bremen, Normandie, Rex, etc. Those all had non-protruding bulbs. I admit I don't know specifically about Japanese liners prior to Hiyo.

[Guest]

The difference between the two types of bulbs appears to be largely evolutionary. The type of bulb that swells out laterally but does not project forward seems to have made its first appearance around 1918. The non-protruding bulb was very common on WWII era warship in the US and German navies. The Japanese appears to have introduced the first protuberant bulb aboard the Yamato, but this type of protruding bulb did not seem to gain widespread acceptance until about 1955-1960. The non-protruding type of bulb now seems to be very rare. The protruding bulb seems to be very dominant, and the degree of protrusion seems to be increasing consistently since 1960, resulting in the almost obscene protuberances on the bow of some of the most modern ships, mostly cruise liners.

The athwartships bulge in the forefoot of a ship from 1918 up until the 1970's is called a "flared forefoot." As was discussed in posts above, the sole purpose of this bulge was to add buoyancy forward and support the longitudinal strength of the vessel. The fine entries of warships, especially, (and fast liners like the S.S. United States) created a bending stress on the length of the ship. The condition is known as hogging. Deck area on the bow of a BB, for example, is far larger than the area of her waterplane at the same point. The weight above is not adequately supported by the buoyancy of the hull without the extra submerged volume created by the flare in the forefoot.

The Japanese Yamato is the first true bulbous bow, as we define them today. It was designed for the express purpose of getting a respectable speed out of her with the given powerplant.

[richter111]

I just thought it was the return of the battering ram....



Ric

[ar]

The difference between the two types of bulbs appears to be largely evolutionary. The type of bulb that swells out laterally but does not project forward seems to have made its first appearance around 1918. The non-protruding bulb was very common on WWII era warship in the US and German navies. The Japanese appears to have introduced the first protuberant bulb aboard the Yamato, but this type of protruding bulb did not seem to gain widespread acceptance until about 1955-1960. The non-protruding type of bulb now seems to be very rare. The protruding bulb seems to be very dominant, and the degree of protrusion seems to be increasing consistently since 1960, resulting in the almost obscene protuberances on the bow of some of the most modern ships, mostly cruise liners.

The athwartships bulge in the forefoot of a ship from 1918 up until the 1970's is called a "flared forefoot." As was discussed in posts above, the sole purpose of this bulge was to add buoyancy forward and support the longitudinal strength of the vessel. The fine entries of warships, especially, (and fast liners like the S.S. United States) created a bending stress on the length of the ship. The condition is known as hogging. Deck area on the bow of a BB, for example, is far larger than the area of her waterplane at the same point. The weight above is not adequately supported by the buoyancy of the hull without the extra submerged volume created by the flare in the forefoot.

The Japanese Yamato is the first true bulbous bow, as we define them today. It was designed for the express purpose of getting a respectable speed out of her with the given powerplant.

If what you state is correct, then why did not the RN use such a device?
In the 1920s, the RN looked at constructing cruisers with a bulbous bow, of the type that you describe as a "flared forefoot". It was not adopted as the inceased speed attained at high speed was MORE than offset by a decrease in endurance at CRUISING speed.
I discussed this matter with the DNC in the late 1970s, who told me that it was NOT a matter of strain/stress on the hull at any point.
The RN NEVER used any form of bulb/flared forefoot before the 1950s and NEVER had problems.
You mention waterplane area. Which particular one do you mean? There are so many.

[chuck]

Actually, the Hood looks very much like she had a very modest bulb. If you look at the frame shapes near the forefoot, you would find her hull sides near extreme stem bulges slightly out for no other apparent reason. She most certainly had no ram whatsoever, vestigial or otherwise. It is very subtle and easy to miss in a photograph. But it is apparent in drawings of the frame shapes.

Also, the last generation of battleships with ram bows below and forward leaning flare above, such as the Repulse and Pennsylvania, are those really still true rams reinforced to withstand collisions? Or is there some element of a bulbous forefoot effect that encouraged the retention of a underwater protrusion forward?

[Werner]

Nevada and Pennsylvania most certainly did not have "ram bows". The documentation describes them as modified plough bows intended to improve wavemaking resistance.

Ram bows on ships from 1860 through the predreadnought era are the result of romanticization of the experiences at the Battle of Lissa in 1866.

[chuck]

Which documentation? The exaggerated clipper bow and true bulbous forefoot on the subsequent New Mexico class was an reaction to the large bow waves of Pennsylvania and Nevada.

[chuck]

Ram bows on ships from 1860 through the predreadnought era are the result of romanticization of the experiences at the Battle of Lissa in 1866.

It is not romantic fantasy to imagine ramming can be important when ships of 1870-1880s were impervious to all but the largest caliber guns at any range, the largest ships carried only a handful of the largest guns, and these guns takes 5 minutes - enough time for an 14 knot ironclad to completely cover normal battle range - to reload.

[chuck]

If what you state is correct, then why did not the RN use such a device?
In the 1920s, the RN looked at constructing cruisers with a bulbous bow, of the type that you describe as a "flared forefoot". It was not adopted as the inceased speed attained at high speed was MORE than offset by a decrease in endurance at CRUISING speed.

This is unexpected. The USN and German navies, for the lack of oversea bases, emphasize cruising endurance more than the RN. Yet neither accepted the same trade off decision adopted by the RN.

I think RN emphasize behavior of ships in heavy seas more than others. I wonder if there was concern that flared forefoot would experience more pounding problems in extremely heavy weather in the North Sea. I believe even now the RN resists for the same reason the bulbous sonar bow domes commonly used elsewhere , and prefers under keel sonar domes seldom used by anyone else.

[ar]

I went and looked at the body plans for;
KGV
County class cruisers
Fiji class cruisers
Battle class destroyers

Atlanta class cruisres
Cleveland class cruisers
Alaska c;lass cruisres
South Dakota class battleships
Liner SS United States

NONE of the RN ships have ANY flare at the forefoot.

ALL of the USN ships DO HAVE a pronounced flare at the forefoot.

The stem line of the SS United States is identical to that of the County and Fiji class cruisers.

GUest mentioned waterplane area as playing a part.
Would he please reply to my earlier question on this point.

[ar]

I looked at the plans for the US Sumner class destroyers and found NO flare at the forefoot.

[Dan K]

I wouldn't think that any WWII era destroyer would have a flare at the forefoot.

[Werner]

For what it's worth, this is what Wikipedia says about the development of the bulbous bow:

The first bulbous bows appeared in the USA being fitted to the USS Delaware which entered service in 1910 and the design is credited to David Watson Taylor, naval architect and Chief Constructor of the Navy [USA]. In the 1920s other nations experimented with bulbous bows with the introduction of the Bremen and Europa, two German North Atlantic ocean liners. Bremen, which appeared in 1929, was able to win the coveted Blue Riband of the Atlantic with a speed of 27.9 knots.

Smaller passenger liners such as the American President Hoover and President Coolidge of 1931 began to appear with bulbous bows although they were still viewed by many ship owners and builders as experimental.

In 1935 the French superliner Normandie coupled a bulbous bow with a radically redesigned hull shape and was able to achieve speeds in excess of 30 knots. At the time Normandie was famous for (among other things) her clean entry into the water and her greatly reduced bow wave. Normandie's great rival, the British liner Queen Mary achieved equivalent speeds with a non-bulbous traditional stem and hull design. However, the crucial difference lay in the fact that Normandie achieved these speeds with approximately thirty percent less engine horsepower than Queen Mary�and with a corresponding reduction in fuel use.

Bulbous bows were further developed and used by the Japanese. Some World War II-era Japanese battleships such as the Yamato were fitted with bulbous bows. However, Japanese research into this area did not spread to the western world, and much of the advances were lost post-war.

It is unclear when bulbous bows were conclusively first examined by western researchers, but scientific papers on the subject were first published in the 1950s. Engineers began experimenting with bulbous bows after discovering that ships fitted with a ram bow were exhibiting substantially lower drag characteristics than predicted, and eventually found that they could reduce drag by about 5%. Experimentation and refinement slowly improved the geometry of bulbous bows, but they were not widely exploited until computer modelling techniques enabled researchers at the University of British Columbia to increase their performance to a practical level in the 1980s.

[ar]

If anybody thinks that a 80,000ton, 1000 foot long ship can be driven at 30knots using ONLY 140,000shp, then THEY ARE NUTS. Who wrote this rubbish?

[Werner]

Normandie was rated 160,000 HP with 200,000 as an overboost maximum.

[gerinc]

This is "guest," I've now become a member. I will address the questions about my post as best I can a little later, but I've been busy with work, so hopefully later today I will have a few moments do it properly.


Cheers

[ar]

Normandie was rated 160,000 HP with 200,000 as an overboost maximum.

Does not compute.
At 160,000 shp you get about 27 knots, that,s it.
To achieve 30 knots you will need about 200,000 shp, and one needs a sustained/continuous 30 knots to sometimes maintain the timetable. EG leaving harbour several hours late.
The figures you give show a 25% overload. Do that on a regular basis, and after a while the engines will suffer.
Mary is rated at 212,000 shp for 30 knots, without overload. This is about right.
With the bulbous bow and her more efficient underwater hull form from bow to stern. Normandie could probably make 30 kots on 200,000 shp as opposed to 212,000 for the Mary.
Sorry to be argumentative.

[Werner]

Well, they are French....

As an aside, it's impressive what a difference a decade made in the length and weight of a 212,000 hp plant (RMS Queen Mary vs USS Iowa).

If they ever perfected the turbopressure boilers, I wonder what that would have looked like. I think it was 60-80,000 hp in the space of 35,000.

[Jean-Paul Binot]

Normandie was rated 160,000 HP with 200,000 as an overboost maximum.

Does not compute.
At 160,000 shp you get about 27 knots, that,s it.
To achieve 30 knots you will need about 200,000 shp, and one needs a sustained/continuous 30 knots to sometimes maintain the timetable. EG leaving harbour several hours late.
The figures you give show a 25% overload. Do that on a regular basis, and after a while the engines will suffer.
Mary is rated at 212,000 shp for 30 knots, without overload. This is about right.
With the bulbous bow and her more efficient underwater hull form from bow to stern. Normandie could probably make 30 kots on 200,000 shp as opposed to 212,000 for the Mary.
Sorry to be argumentative.

There is a long analysis of that paradox in the latest French book on Normandie, including a debate about teh turbo-electric drive and its many merits. I do not remember the specifics right now but I will have a look over the weekend and report if I find anything relevant.