Squat

Bill Davies
12th September 2009, 22:28
It would be interesting to hear from fellow Masters and Pilots on their thinking re title phenomena. Many academics have tried to pin this topic down but I believe it to be most elusive and subject to many influences.

Bill

makko
13th September 2009, 02:02
Bill,
Is this hydrostatic action on the hull?

I remember on Barber Priam (Panamax) being quite prone to this: The first time through the Panama Canal I was quite surprised by the "banging" when the hull was sucked into the lock wall and then onto the lock bottom due to very little water keeping the vessel afloat. A friend who was Mate with Canadian Steamship commented that they thought that they had lost a propellor blade going up a river in Venezuela (forget the name!). The reason was that the water level was low and that the river bed had the consistency of gelatine, resulting in the vessel being "sucked" onto the bottom continuously.B. Priam also suffered over the sand bar on the approach to Savannah (problems too for the pitot tube).

Hopefully I have understood the question, if not it was a good reason to "nostalgiacize"!!

Best regards Bill,
Dave

Nova Scotian
13th September 2009, 02:28
Captain Bruno Ortlepp was a fellow instructor at the Nova Scotia Nautical Institute who wrote several papers on squat. He even identified a formula which identified an increase of draft in shallow and confined waters. His interest resulted from his experiences with Irving Oil and Sanko Line. I must confess that I found his proofs and calculations a little mystifying and hard to follow. However, this was 1980 and there was little information on the subject at that time.

Bruno also published papers on Longitude Without Time, and developed tidal atlases for the Bay of Fundy area.

Captain Ortlepp passed away in 2003.

exsailor
13th September 2009, 11:51
The subject even has its own website - www.ship-squat.com/index.html

Bill Davies
13th September 2009, 12:35
The subject even has its own website - www.ship-squat.com/index.html

Exsailor,

Many thanks yours.

I was aware of that site and implied same in my opening. However, I was looking for peer input as 'Squat' is a subject close to me having commanded ships of a size where this phenomenon was more than academic.

Brgds

Bill

6283
13th September 2009, 13:01
Has anyone experienced the opposite of squat? Where the bow digs in, so-to-speak, and a laden vessel steaming ahead in a relatively shallow channel goes down by the head? And when she loses her forward movement, she resumes her normal even or nearly even keel condition? If anyone has felt this, is there a name for it?

John Briggs
13th September 2009, 14:11
Has anyone experienced the opposite of squat? Where the bow digs in, so-to-speak, and a laden vessel steaming ahead in a relatively shallow channel goes down by the head? And when she loses her forward movement, she resumes her normal even or nearly even keel condition? If anyone has felt this, is there a name for it?

Yes, it's called going aground!

6283
13th September 2009, 14:26
Very funny!

Billieboy
13th September 2009, 15:18
Squat and Hammer, deck department hydrostatic phenomena! Sometimes confused with removal of rust!

Derek Roger
13th September 2009, 15:19
On taking the CCGS Earl Grey out on sea trials from Pictou Nova Scotia just as we were crossing the bar we had the misfortune to experience of a severe squat which caused th stern roller to submerge and covered about half the after deck in water . Too much pitch applied in shallow water which sucked the stern under untill pitch was reduced . Pictou has a difficult narrows and sandbank which required power to be applied due to the incoming tide to ensure we did not end up on the bar .

Derek

callpor
13th September 2009, 16:19
It would be interesting to hear from fellow Masters and Pilots on their thinking re title phenomena. Many academics have tried to pin this topic down but I believe it to be most elusive and subject to many influences.

Bill

Bill,

Have always been interested in this phemonma having experienced the effects many times during my seagoing career, so your thread caused me to look further. It's not so elusive, from the 641000 references Googling the subject (which I am sure you have already done), I picked up the following which you may find of interest http://www.maritime-connector.com/Administration/_Upload/Documents/Squat-Interaction.pdf
.
I first experienced the Benoulli squat effects when attending Port Revel shiphandling centre near Grenoble in France in 1973 where we practiced manoeuvres in the models in both shallow water and passing or overtaking in a narrow channel. Gave me a lot of respect for the pilots in the MSC and St.Lawrence Seaway who continuously experience this very powerful phemomena.
Regards, Chris Allport

Bill Davies
13th September 2009, 18:04
Bill,

Have always been interested in this phemonma having experienced the effects many times during my seagoing career, so your thread caused me to look further. It's not so elusive, from the 641000 references Googling the subject (which I am sure you have already done), I picked up the following which you may find of interest http://www.maritime-connector.com/Administration/_Upload/Documents/Squat-Interaction.pdf
.
I first experienced the Benoulli squat effects when attending Port Revel shiphandling centre near Grenoble in France in 1973 where we practiced manoeuvres in the models in both shallow water and passing or overtaking in a narrow channel. Gave me a lot of respect for the pilots in the MSC and St.Lawrence Seaway who continuously experience this very powerful phemomena.
Regards, Chris Allport

Chris,
Whereas I never attended Grenoble I understand it was very informative.

I used the word elusive in that it was unpredicatble and modified by channel positiion/configuration. So often people use 'rule of thumb' 10% for squat. Example would be a North Sea pilot reporting your draft to Dover 60' for say 55' arrival at Redcar. Thats Cape size. On the Bantry class which were 26mtrs we would be looking for 30mtrs. Further, position in channel would modify/reduce squat by making use of the bank effect.
Larger ships than the Bantry class, +400K were not as bad.

PS I was hoping Pilots would be embracing this topic.

Bill

Billieboy
14th September 2009, 06:01
There has been lots of work on Squat in Holland, The deep draught ships, 20M+, is the basic reason for the study. Although for entering Rotterdam at high water with less than a meter under the keel (at times), the pilots are more worried about swell induced roll, as deep draught vessels, in order to be so large, sometimes have beams which; should they roll; just one degree, will add one meter to the total draught!

In the late sixties I can remember coming North through Suez, as #1 in the convoy, with a bit of extra ballast so that we could, "wash the bottom", for a lager tanker behind us. Our ship was Llanishen.

Klaatu83
14th September 2009, 14:29
The best ways to mitigate the effects of squat are to reduce speed and try to move in and out of port only during high water. The latter is not always possible, however. The ships I sailed on used to go into Port Newark, which involves a draft-restricted channel (Kill van Kull) combined with passage under a height-restricted bridge (the Bayonne Bridge). Some of the big containerships had masts so tall that, if they tried to pass at high water, they could strike the bridge. On the other hand, at low water they could run aground. Some ships solved the problem with retractable masts, while others simply timed their passages very carefully.

Bill Davies
14th September 2009, 19:52
Thanks for that Klaatu83. Squat is indeed related to speed. Their may be several passenger ship (fine hulled) can comment on the way those ships trim by the stern.