Ship’s motions at sea

A vessel under sea has two types of movements:

• Desired, to move the ship from one point to another and get she achieves the objectives for which  was built
•  Unwanted, occurring mainly as a result of the waves and wind on the ship and causing trouble, inconvenience and danger to the vessel, persons and cargo, so they try to minimize them.

In this post I will only refer to the second type of movements, motions, relating to ships sailing on the surface.

The ship motion in a 3D space is made up, like any other solid, of the motion of its center of gravity and the movement or rotation around that point. The six possible motions, summarised in the following table, consist of three translations and three rotations, which refer respectively to the trajectory of the center of gravity and the rotations  around the main axes through it. Names are given in Spanish and English languages​​.

Reference axis	Translations	Turns r/ ref. axis
Longitudinal x	surge (avance)	roll (balance ó rolido)
Transversal y	sway (deriva)	pitch (cabeceo)
Vertical z	heave (arfada)	yaw (guiñada)

In the following drawing the three axes are shown, for which the movements of translation and rotation relate.

Coaster ship Project "Gijón"

Comparative analysis with GetxoNaval program

The September 2013 issue of Ingeniería Naval journal has published an article from Aurelio Gutiérrez, Dr. Naval Architect, with the description of a desing coastal vessel prototype called "Gijón", for the short sea shipping trafic.

This article described in some detail the vessel specifications and published some interesting particulars from the point of view of naval architect, which are not very common in the journals, what suggested me the interest of comparing the published particulars with those obtained with my program "GetxoNaval" focused to ship preliminary dimensioning, that can be freely used on-line
by clicking here.

In this link you can look at the mentioned comparison that shows a good agreement between the results obtained with GetxoNaval and project characteristics published by Ingeniería Naval.

Holtrop & Mennen's ship powering method

Ship designers are familiar with the Holtrop & Mennen' method (H & M) to calculate the relationship between power and ship speed, used for years in the technical offices of shipyards and engineering sites. Due its great interest I programmed this method and have included it in GetxoNaval website as part of the calculation procedures used to perform preliminary design of a merchant ship.
The H&M method was developed by J.Holtrop & G.G.J.Mennen from MARIN "Maritime Research Institute" in Wageningen (Netherlands), based on the results of hundreds of tests with ship models and correlations with the data recorded in actual sea trials.
This method affords results considered satisfactory in 95% of cases, in the preliminary design stage, provided that the range of the variables is within the limits given in Ref.1, summarized in these figures:

Ship type	No. Froude máx.	Cp min-max	L/B min-max	B/T min-max
Tanker, Bulkcarrier	0,24	0,73-0,85	5,1-7,1	2,4-3,2
Coaster, Tug	0,38	0.55-0.65	3.9-6.3	2.1-3.0
Container C.	0.45	0.55-0.67	6.0-9.5	3.0-4.0
Carguero	0.30	0.56-0.75	5.3-8.0	2.4-4.0
Ro-ro	0.35	0.55-0.67	5.3-8.0	3.2-4.0

At this link to Getxo Naval site you access the main page and can choose between the Spanish and English versions of the H&M method. In addition to presenting the power-speed results in tabular form, a graph is displayed with delivered power curves in service and trial concitions, as shown herein.

Ref.1 An approximate power prediction method. J.Holtrop & G.G.J.Mennen - International shipbuilding Progress 1978 -

Container vessels Capacity and Stability

Using GetxoNaval program

In my post of October 12, 2012 I enclosed a reference to an aproximate calculation of capacity of container vessels that now I have included in a larger program, called GetxoNaval, made-up of a set of calculations relating to main aspects to be considered during the preliminary design of a merchant ship, i.e. the dimensioning stage. But the revised module corresponding to container vessels is far more complete than the one displayed in said blog post. It now includes stability calculation, static and dynamic, with corresponding curves.

Clicking on next link you will enter in GetxoNaval program, that at this moment includes following modules:

GETXONAVAL

1. Tonnage
2. Cruising ships
3. Stability cargo ship
4. Stability deck barge
5. Stability container carrier
6. Hull forms (coefficients)
7. Freeboard
8. Maneouverability
9. Lightship weight
10. Predimensioning
11. Powering
12. Cargo & tanks capacities
13. Help

Additional modules are expected to be added and all will be subject to continuous revision.

Dimensioning a merchant ship

 With the program GetxoNaval

GetxoNaval program  objective is to  allow making  quick, approximate calculations necessary to define the dimensions of a merchant ship. This program can be used basically in two different ways:

• To make an estimation of the main ship dimensions based on  its size, defined, for example, by deadweight, number of containers, volume  of cargo spaces etc.
• To make a calculation of different particulars (deadweight, speed etc.) of a ship whose  main dimensions are known, either  because they have been defined in the previous point, or for being a known ship but one or several of her capacities are unknown.

Clicking  following link you can access to the program GetxoNaval  hosted  in Google-Sites.

GetxoNaval

Preliminary dimensioning

Cargo ships

In my post of April 9, 2010, I presented a form to get a preliminary dimensioning of cargo ships once the user defined her type and a goal particular, deadweight, cargo volume or containers number, depending on the selected type. I have revised the form to be used and I present now its second edition.

To use this procedure click on following 

                                                   "CALCULATE"

Stability of deck barges and pontoons

In a previous post I included an approximate procedure to estimate the stability of cargo ships in the preliminary design stage, but a blog reader pointed out to me that it was not good enough for the special case of   deck barges and pontoons , which are artefacts carrying all load above the deck. Due to this so special condition these floaters (they are not conventional ships) have received a different stability consideration in the IMO  regulations and I have been preparing a specific procedure for estimation of their stability.

In the form that opens by clicking the following link, GetxoNaval ship dimensioning program is open and selecting the deck barges stability tag, the user is requested to input a few data of the barge / pontoon and he gets a suitable information about its stability in the specified loading condition. After the form a user guide is shown and a results interpretation.

Begin calculation

Container vessels capacity

In the form that follows the cellular container vessel dimensions are input and her 20 ft TEUS capacity is estimated
This 2nd. edition fixing some errors and adding drawing of Containers in holds

Click to begin calculation

(updated on 21 Feb 2012)

"La Naval" shipyard of Sestao(Spain) launches the "Joseph Platou"

 "Fall-Pipe" type vessel for Jan de Nul

On August 3, 2012 "La Naval" shipyard, in Sestao (Spain), of the CNN group (Construcciones Navales del Norte =  Northen Shipbuilding) proceeded to launch this vessel for the Belgian shipowner Jan de Nul, a regular customer of this shipyard which has already delivered a twinship, "Simon Stevin", and several suction dredges, including the two largest in the world, in its class, "Cristobal Colón" and "Leiv Eiriksson". About these ships I already included posts  stressing their notability and the "La Naval" capacity to build such a high technology ships and competing worldwide with major shipbuilders .

The shipyard invited me to attend this launching, that I thanked especially in these times of shipbuilding drought , as evidenced by the absence of a keel laying after this launch, as was to be the norm in old good times when shipyards laid the keel of following ship waiting her turn in the queue of orders. I have news, unconfirmed, that "La Naval" will finish the construction of two medium-sized vessels begun in the late Seville shipyard, what will lead to an easing of shipyard situation in the absence of "serious" contracts, matched to its proven category and capacity. I hope that the "tax lease" system  resolves soon, after many months of stand-by, without which the shipyards in this country would have many difficulties to survive.

In this post about the "Simon Stevin", first ship of this series, I summarized the main features of this vessel whose dimensions are

Overall length (m)	191,50
Breadth (m)	40,00
Depth (m)	13,20
Draught loaded (m)	8,50
Deadweight (tonnes)	32.500
Speed (knots)	15,50
Crew	70
Propulsion
Azimuthal propellers	4 x 4.500 Kw
Retractable propellers	2 x 2.000 Kw
Electric generators	5 x 3.300 Kw

Delivery of "Joseph Platou" is scheduled for early next year.

I wish I had taken pictures and video of the launching from the other side of the river, but as I saw it from the guests platform visibility was very poor and I include here some photos of the event only as a recollection, nothing to be with quality.

Ship launching seen from the visitors platform

Which sails quicker the rowing boat "trainera" or "trainerilla" ?

The great mathematics magazine + Plus Magazine, in its May 2012 issue published an article entitled "Outer space: Canoeing and kayaking", authored by John D. Barrow, which raises the question of whether these boats run more or less when they double the crew, which we do not know in advance because if the propulsive power is doubled so does the displacement and therefore the hydrodynamic resistance.

+ Plus presents simple and reasonable equations to estimate the variation of this resistance and determine from it the necessary power increase, which compares with the increased power provided by the additional rowers. He gets a theoretical conclusion that  a double crew boat increases its speed by 8 to 10%, what matches well with the actual data recorded in kayacs and canoes races. This conclusion appears consistent with the intuitive impression we have that larger similar boats are faster than smaller ones. 

A new website about Naval Architecture

In the February issue of the Spanish journal Ingeniería Naval (Naval Architecture) they report the creation of a new website entitled "Revista del Sector Marítimo. Ingeniería Naval" (Journal of the Maritime Sector. Naval Architecture), whose stated aims are to "... encourage news update daily and flexibly, enabling readers to easily find news of interest through tags that allow you to select all news related to a topic."

This website is in this URL "Ingeniería Naval"

The journal editorial keeps saying they have tried that the new website be accessible from the largest possible number of devices in addition to PCs, such as tablets, already in operation, and smartphones, which will be soon.

Index of sections of the website is this

• Home
• Information
• Maritime news
• Maritime energies
• Magazines
• Subscription
• Reports
• Ships
• Applications
• Sitemap

The preceeding items are subdivided, in some cases, into lower levels and in particular, subscribers have access to the full contents of the journal "Ingeniería Naval" (Naval Architecture), on all its numbers since 2004 when the digital version was created, that is also handed over annually on a CD.

The inclusion of RSS allows you to add news to feeds readers and share them on social networks like Facebook and Twitter and to connect to the video channel of Naval Architects at Youtube.

I think that this site is very well presented with large and handy information and although it is currently a complement to "Ingeniería Naval" paper magazine edition, I think, is my opinion, that it will not be long until they retire the latter from the market, because, contrary to the opinion of some friends of mine, I think that although currently books and publications coexist in digital and paper formats, the very next generations will know the latter only in museums.

My congratulations to the AINE President, José Esteban Pérez Garcia and to the Journal Director, Belén García de Pablos, together with all their team, for the creation and promotion of this new publishing media, which I hope will help to reactivate the decayed shipbuilding situation in our country.

Should cruise ships have a double hull ?

Considerations on the Costa Concordia accident

The recent accident involving the cruise ship Costa Concordia on the Italian coast of the Giglio Island is producing the usual questions that arise after any disaster affecting human lives. It is the question of whether the safety of the facility in question is sufficient, be it either a ship, aircraft, train, skyscraper etc. Clearly there is not a complete safety in any order of life, but it is also clear that any current safety level can be improved and the issue is deciding when and where the laws and regulations governing safety are to be changed to get better expectations.

History teaches us that mankind is learning the hard way. When we suffer a great accident is when we consider that perhaps safety provisions are not adequate and should be analyzed in detail and realism to decide whether they should be improved.

Ship lightweight Calculation

(In cargo ships preliminary design)

Introduction

The calculation of the ship lightweight and her center of gravity is one of the basic tasks to be performed in the ship initial design stage, where it is advisable to be able to perform quick, approximate calculations, allowing to quickly analyze many alternative dimensionings. In this blog I present a form to enter the main dimensions of a cargo ship from which the program computes, approximately, the ship lightweight and center of gravity height broken down in Steel, Equipment and Machinery. Results are limited to ships up to 320 m. length between perpendiculars and aspect ratios should be normal.

Ship's hull form coefficients

(At preliminary merchant ship design)

Introduction

HELLO!

Herein I present a form to get basic hull form coefficients of merchant ships, following the formulae and concepts explained in Refs. 1 and 2, in order to serve as a guidance in the preliminary stage of a ship's design.

The main goal of this form is to get reasonable values of block (CB), midship section (CM) and loadline (CW) coefficients to be used in the different modules presented in the program Arqnaval, enclosed to the book Ref.2, and the program Getxonaval, being under construcion, to be used on-line via any browser, both intended to offer approximate and quick calculation methods in the preliminary stage of a ship design.

Some additional coefficients are also calculated and displayed in the enclosed form, of a lesser interest but that can also be of some utility.

Stability Calculation

(At preliminary stage of cargo ships design)

Introduction

Calculation of the stability is one of the basic and primary tasks that are to be done at the initial ship design stage, where it is not absolutely necessary to be quite exact, but where a quick calculation is very advisable, even if being approximate, allowing to analyze many alternative dimensionings in a short time. In this blog post I enclose a form where main cargo ship dimensions are to be input by the user and from them the program makes an approximate calculation and stability results are displayed for transverse metacentric height GM and righting levers GZ at several heeling angles.

Freeboard calculation

(At the ship design stage)

Introduction

Calculation of the freeboard is one of the basic and primaries that are to be done at the initial ship design stage, where it is not absolutely necesary to be quite exact. An approximate and quick calculation is therefore very suitable. After a brief concepts reminder I enclose a form where main ship dimensions are to be input by the user and freeboard results are displayed.