Talk:Turret deck ship

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A fact from Turret deck ship appeared on Wikipedia's Main Page in the Did you know? column on 15 November 2007.

[edit] relation to whaleback ships

It's hard to pin down definitively without some research to find solid references, but I keep seeing hints about the relationship. See for example: Sunderland Datapage 11 and in particular the 'Sagamore': Built Doxford in 1893. 2140 tons Hull 218 ... That ship may have been an evolutionary link. ++Lar: t/c 00:24, 9 November 2007 (UTC)

This reference: http://www.hhpl.on.ca/GreatLakes/Documents/Scanner/03/07/default.asp?ID=c011 may also be of some help. Pictures of these are hard to find. ++Lar: t/c 00:36, 9 November 2007 (UTC)

Sagamore was built by Doxford in 1893, but the first turret ship had been built the year before (and the year after Wetmore visited Liverpool). On the relationship between ship types, a drawing of cross-sections would be helpful. I have cross-sections for conventional, turret, and trunk deck ships; I do not have one for a whaleback. (The upper part is obvious, but the bottom does not show in the photos, and it would also be useful to know if there was a double bottom.) Kablammo 02:54, 14 November 2007 (UTC)

I think (but don't have a cite to prove it) that whalebacks had relatively flat squared off bottoms since they had to go through locks and into shallow draft ports. I don't know if they had double bottoms or not. Drawings are hard to come by, except that if we can figure out WHICH patent matters to the design, the many McDougall patents have drawings galore. (he patented a military landing craft that was roll-on/roll-off!!!) ++Lar: t/c 03:45, 14 November 2007 (UTC)

[edit] top importance

Is this really top importance in the ships article categorization scheme? ++Lar: t/c 13:54, 14 November 2007 (UTC)

I wouldn't think so, but Wikipedia:WikiProject Ships/Assessment suggests that it is. And as much of the content is new, the old assessment may not be valid anymore-- it's no longer a Start. But as I contributed that new content I won't assess it. Kablammo 14:04, 14 November 2007 (UTC)

Well I will. Wow. You added a lot, and it's well reffed too. Well done. Class B. I moved it to Mid but someone can change that I guess... to my way of thinking a design that resulted in less than 200 ships and that was more or less a dead end isn't "top" ... ++Lar: t/c 16:25, 14 November 2007 (UTC)

As per the assessment criteria established by the members of WP:SHIPS, articles on ship types are considered top importance. --Kralizec! (talk) 14:30, 15 November 2007 (UTC)

It may not be considered a type in the way that, for example, a tanker or aircraft carrier is, but rather a design. These vessels all appear to be general cargo vessels or bulk carriers. For whalebacks however there were bulk carriers, tankers, and even a passenger vessel. Kablammo 14:41, 15 November 2007 (UTC)

When we started our assessment drive, we decided to use a pretty liberal interpretation for type of ships. Check out Cat:Top-importance Ships articles for some examples. --Kralizec! (talk) 14:56, 15 November 2007 (UTC)

I just took a look at container ship (wrong project) and bulk carrier. There's some reassessment work to do! Kablammo 14:59, 15 November 2007 (UTC)

Thanks for catching these mistakes! In the course of just 54 days we assessed over 6300 articles that fell within the scope of the project ... and I fear that mistakes were bound to happen. --Kralizec! (talk) 15:49, 15 November 2007 (UTC)

[edit] Comments on Technical Details

1) I find it difficult to believe that the necking down of the strength deck (the uppermost continuous deck) could in any way improve the strength over a conventional arrangement. The improved strength of these ships is more correctly attributed to the introduction of the of the Inner Bottom or Double Bottom which also moved the Neutral Axis down to a point where the critical member was the strength deck. This was a good thing as any cracks caused by any over-stressing of the hull would now form on the deck where they could be monitored and repaired while underway (as opposed to the bottom of the ship). You may wish to research that point a bit further.

2) The statement "...loading heavy cargo too high, and failing to properly ballast the bottom tanks, increased the metacentric height and led to instability. " should read "... increased the KG and led to instability.". The metacentric height is dependent on form not weight distribution.

3) It may be useful to comment on the fact that the reduced beam at the weather deck resulted in a reduction in the range of positive stability similar to what happens on ships with a large tumblehome.

All in all an interesting article. A cross-section through a the hull would probably add much to the overall understanding of the unique geometry. Jmvolc (talk) 22:04, 27 November 2007 (UTC)

As always your insight is much appreciated. In partial response:

1) I will check my source for a quote. As I recall, the NMM book stated that both trunk and turret deck ships had strength advantages over conventional construction but did not say why. I have no sources other than those listed, which are not technical.

Followup comments interspersed

While it would make sense to me that the rounded corners of the turret deck would confer strength advantages, that does not apply to the trunk decks. The Craig book has a chapter on "Developments in the structure of cargo ships", which states that in trunk and turret deck construction "strength was maximized" and there was a "diminution in the amount of steel work necessary to constuct them". The book does not say why that is so, and I have no better sources readily available to me. The excerpt from the book reproduced at the dive web site may be of some help for turret decks, as it notes the stiffness conferred by the curved hull form. Maybe the best way to handle this is to keep the section about strength advantage in this article as that has a source which explains it, but remove it from Trunk deck ship.

Strength (like stability) is a term that is often mis-used, especially in older publications. The rounded corners on turret deck ships helps mitigate cracking but does not necessarily make the ship stronger (add strength). Interestingly, for an equivalent cross-sectional area and shell thickness, the circular section would have a section modulus 75% to 80% of a rectangular section and must therefore be inherently weaker.Jmvolc (talk) 13:23, 20 December 2007 (UTC)

(The later "refinements in the design of ships of more conventional hull form" mentioned in the article text were the "corrugated" ship of 1909, and the 1908 introduction by Joseph W. Isherwood of a system of longitudinal framing which saved as much as 10% in weight.) Kablammo (talk) 15:16, 9 December 2007 (UTC)

2) I will check this as well-- as I recall the book mentioned both metacentric height and center of gravity.

The books do not mention metacentre; I believe I got this from the Clan Line source, about 30% of the way down the page, which states: "care still had to be taken when loading the ship with a full cargo, to ensure that the center of gravity was kept low thus keeping the metercentre within acceptable limits". I will change the text to refer to center of gravity. Kablammo (talk) 16:24, 7 December 2007 (UTC)

The quote you refer to is correct but very dated. The 'metacentre' is now referred to as the GMt and is the vertical distance from the center of gravity to the transverse metacenter.Jmvolc (talk) 13:23, 20 December 2007 (UTC)

3) This is a good point and I will try to work it in, if I can properly source it.

Does this quote address the point? " The serious shortcoming of the “Turret” design was the stability at large angles of roll. The loss of buoyancy at the vessel’s side and deck gave them a decreased ability to withstand rolling force, although the full range of stability in degrees was as good as any other contemporary." Clan Line (immediately before the quote in 2 above). Kablammo (talk) 16:42, 7 December 2007 (UTC)

It is not possible that the vessel would have had the equivalent range of stability to a conventional ship. Assuming the the KG or vertical center of gravity of both ships is the same, range of stability is a function of how much area there is high and outboard above the waterline in cross-section. Obviously a round shape has less than a rectangular shape of the same cross-sectional area.Jmvolc (talk) 13:23, 20 December 2007 (UTC)

I have half-sections from which I can do a comparative schematic showing conventional, trunk, and turret ships. I would like to add a whaleback, but I am unfamiliar with their underwater form and did not want to speculate. Kablammo (talk) 02:30, 6 December 2007 (UTC)

Please have a look at http://www.mhsd.org/publications/glswr/ericsson.htm for some information you may or may not have on whaleback steamers.Jmvolc (talk) 13:23, 20 December 2007 (UTC)