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Thread: Yamato Bulbous Bow - Effect on speed of Iowa hull form?

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    Yamato Bulbous Bow - Effect on speed of Iowa hull form?

    I came across this section of video discussing how the bulbous bow increased the speeds attainable by Yamato.

    http://worldwarwings.com/crafty-desi...ttleship-fast/

    Question: Is it possible to estimate how much (if at all) a bulbous-shaped bow would have increased top-speed on the Iowas?

    I've seen various rumors that the Iowas were able to exceed their stated top-speed of 33 knots (35-37). Could such a bow have made it possible for them to hit 40+ knots?

    Are their any back-of-the-napkin sorts of engineering calculations for drag-reduction that would make it possible to compute a rough estimate of the effect a bulbous bow on their designed speed?

    Thanks.

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    Defense Professional RustyBattleship's Avatar
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    Quote Originally Posted by tmasi View Post
    I came across this section of video discussing how the bulbous bow increased the speeds attainable by Yamato.

    http://worldwarwings.com/crafty-desi...ttleship-fast/

    Question: Is it possible to estimate how much (if at all) a bulbous-shaped bow would have increased top-speed on the Iowas?

    I've seen various rumors that the Iowas were able to exceed their stated top-speed of 33 knots (35-37). Could such a bow have made it possible for them to hit 40+ knots?

    Are their any back-of-the-napkin sorts of engineering calculations for drag-reduction that would make it possible to compute a rough estimate of the effect a bulbous bow on their designed speed?

    Thanks.
    In another thread we discussed the pros & cons of bulbous bows. The Yamato, Musashi, Shinano & hull no. 111 were all built with bulbous bows following (copying) David Taylor's studies of such a bow in his speed tests with model ship hulls in his test tanks.

    It was found that the bulbous bow carried the water surge along WITH the ship rather than just pushing it to the sides. That's why Dolphins can travel alongside a ship because the ship is providing them with the bow wave that they can travel in. Sort of like guys hanging onto the sides of a San Francisco cable car.

    I'm sure that somewhere are publications of the studies done, records of the experiments & calculations of how much speed a ship can increase depending upon the size and shape of the bulbous bow and the size of the ship that it's attached to. Where they are I do not know nor do I really care to find out. I'll let you young whipper snappers do that kind of work.
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    Thanks, Rusty, for responding & pointing out the earlier thread --- I'll search the site for additional info. I suppose behind this question is the thought "If there was a known way to get more speed, what made the designers turn away from it?"

    There had to be some cost / benefit calculation to make them think it wasn't worth the effort... perhaps budget? Or added manufacturing time given I'm sure they wanted these ships at sea as soon as possible. Maybe it's only a one knot increase.

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    The last 2 Nimitzes have bulbous bows, but so far none of their older sisters have been retrofitted with them, and one would think that RCOH would be the perfect time to do it.

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    Quote Originally Posted by tmasi View Post
    Thanks, Rusty, for responding & pointing out the earlier thread --- I'll search the site for additional info. I suppose behind this question is the thought "If there was a known way to get more speed, what made the designers turn away from it?"

    There had to be some cost / benefit calculation to make them think it wasn't worth the effort... perhaps budget? Or added manufacturing time given I'm sure they wanted these ships at sea as soon as possible. Maybe it's only a one knot increase.
    The research and proof of a bulbous bow's benefits wasn't known until the first half of the 20th century (when ice breaker bows were showing speed/fuel savings when not breaking up ice). Also there was the mind set of some designers and builders that a clean cutting bow will do just fine ever since iron clads came into service.

    But sometimes a bulbous bow isn't all that beneficial if it was too WIDE. This head scracther came up when we first started adding bow mounted SONAR domes on Destroyers. LBNSY built the first one but all out of steel (page 280 of my book). It wasn't until a reinforced rubber dome was developed (with the density of the sea water both inside and outside the hull - Page 143) that an exact shape for most efficiency was designed.
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    Very interesting. I was looking at a picture taken of Ford's bow before she was launched and to the untrained eye, it looked less like the graceful bulb that you see, curving forward from Yamato's stem and much more like a rather fat torpedo had been just attached to Ford at the base of the bow. I suppose it acts like a ram, just moving all that water out of the path of the ship. but as you mention, it didn't look particularly wide at all.

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    Quote Originally Posted by tmasi View Post
    Very interesting. I was looking at a picture taken of Ford's bow before she was launched and to the untrained eye, it looked less like the graceful bulb that you see, curving forward from Yamato's stem and much more like a rather fat torpedo had been just attached to Ford at the base of the bow. I suppose it acts like a ram, just moving all that water out of the path of the ship. but as you mention, it didn't look particularly wide at all.
    In the bottom drawer of the file cabinet to my right I think I still have a blueprint of a RAM stem for a certain class of Destroyer. I'm not going to dig it out right now, but it is interesting that on some ships we did add on a sword like blade of steel just for ramming. But I don't think it was for ramming enemy ships but to act as an ice breaker. That is if the ice is less than four feet thick.
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    Quote Originally Posted by GrayGhost1975 View Post
    The last 2 Nimitzes have bulbous bows, but so far none of their older sisters have been retrofitted with them, and one would think that RCOH would be the perfect time to do it.
    U.S.S. George H. W. Bush (CVN 77)

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    .
    .
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    While it's not as pronounced as the bow on the Bush/Reagan, I'd call the Iowa's bow bulbous.. it's definitely not a straight edge bow.


    what is surprising, is that the Tarawa class LHA's don't have any type of bulbous bow at all.



    and the Wasp class LHD (America class LHA) have quite pronounced bows.


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    Quote Originally Posted by dundonrl View Post
    While it's not as pronounced as the bow on the Bush/Reagan, I'd call the Iowa's bow bulbous.. it's definitely not a straight edge bow.


    what is surprising, is that the Tarawa class LHA's don't have any type of bulbous bow at all.



    and the Wasp class LHD (America class LHA) have quite pronounced bows.

    You are correct on the Iowa class bow. The photo shows the Missouri in Dry Dock, probably in Pearl Harbor after having the forepeak tank repaired (those are not the kind of portal cranes we had at LBNSY at Dry Dock 1).

    The only interference is that darn forefoot skeg at the bottom for fairleading the paravane for mine sweeping. I had that totally removed on the New Jersey as it was extraordinarily receptive to corrosion and kept flooding the forepeak tank. I would like to have extended the "bulb" on out a bit further but funding, time and the engineering calculations would have taken too much time and busted the budget. See pages 204 & 205 of my book. Also read page 203 where I describe the removal of the paravane eye and about a week later I get a call from the Mine Warefare Group in Panama City to ask if the Battleships still carried the facilities to deploy Paravanes.

    Oh (expletive). Well, three of them can. But not the New Jersey. I just had the eye and chain piping removed because of excessive corrosion problems.

    You win some and you lose some. Let's see now, I think I bought a fresh bottle of Vodka just the other day.
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    Thanks for the info and pictures, everyone. I came across this picture of a destroyer (modified Fletcher?) where the straight bow is plain and the difference to the to Iowa's very apparent.


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    Knife edge .....

    Quote Originally Posted by tmasi View Post
    Thanks for the info and pictures, everyone. I came across this picture of a destroyer (modified Fletcher?) where the straight bow is plain and the difference to the to Iowa's very apparent.


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    Not just a "straight bow" but a Fletcher Class _ DD "cutting edge" bow ....
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    It does look razor-sharp!

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    Quote Originally Posted by blidgepump View Post
    Not just a "straight bow" but a Fletcher Class _ DD "cutting edge" bow ....
    YUP! That's the RAM STEM shown on the plan I have. The Buships plan number is H.S. S1101 - 550695. It does not indicate what class of ship it was designed for. But it doesn't take a genius to look at the elevation view and know it's a Destroyer type of bow. It was drawn at U.S. NAVAL DRY DOCKS TERMINAL ISLAND SAN PEDRO, CALIF. (the ORIGINAL Long Beach Naval Shipyard) and first issued on October 19, 1943. It was issued 7 more times with the last being on April 8, 1944. Reproducible copies were also issued to other shipyards.

    Oh, one interesting item is the material record of weights. The whole thing (including the reinforcing 1/2" thick shell doublers on both sides as well as the 1" thick Ram Stem) is/was 45,952 lbs.

    PS: That looks like a pretty modern photo of a Destroyer that has been rescued as a memorial/museum ship. If it is, I will be glad to donate the Ram Stem plan to the association that owns the ship.
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    Senior Contributor blidgepump's Avatar
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    All 3 DD's have the Ram Stem ...

    Quote Originally Posted by RustyBattleship View Post
    YUP! That's the RAM STEM shown on the plan I have. The Buships plan number is H.S. S1101 - 550695. It does not indicate what class of ship it was designed for. But it doesn't take a genius to look at the elevation view and know it's a Destroyer type of bow. It was drawn at U.S. NAVAL DRY DOCKS TERMINAL ISLAND SAN PEDRO, CALIF. (the ORIGINAL Long Beach Naval Shipyard) and first issued on October 19, 1943. It was issued 7 more times with the last being on April 8, 1944. Reproducible copies were also issued to other shipyards.

    Oh, one interesting item is the material record of weights. The whole thing (including the reinforcing 1/2" thick shell doublers on both sides as well as the 1" thick Ram Stem) is/was 45,952 lbs.

    PS: That looks like a pretty modern photo of a Destroyer that has been rescued as a memorial/museum ship. If it is, I will be glad to donate the Ram Stem plan to the association that owns the ship.

    Mr. L, DD-537, DD-661, DD-793 all have the Ram Stem. ( I just reviewed the photos to make sure )\Impressive numbers as to Weight === 23- Tons
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