Thursday, April 23, 2020

Watertight Doors and ABS - Part 3

In our previous post, we outlined the different types of watertight doors described by ABS.  We are continuing to examine the types of doors in more depth, and this post will be focusing on "Doors Used While at Sea".

Sliding watertight door for flood-control

These doors are the most expensive watertight door on the market because of what they need to do for the vessel.  Often referred to as "flood-control doors", they need to be able to contain a flooding situation in the compartment they are closing off,.  This means that the door has to:

  1. Close quickly in case of emergency
  2. Be able to be closed remotely (i.e. from the Pilot House) if no one is nearby to close the door in a flooding situation.
  3. Withstand enough pressure so that if the compartment fills completely, the door will not deform or leak.
  4. If there is a fire in the compartment, the door has to withstand temperatures over 500 degrees Fahrenheit, to prevent the spread of the fire to other compartments.
Flood control between compartments was addressed after the sinking of the Titanic in 1914.  These doors would not have been able to prevent what happened to the Titanic, since six of her compartments were ruptured by the iceberg.  However, there has been a huge effort to put safety measures, such as flood-control watertight doors in place, to prevent future tragedies.

We can work with you to help you determine the door that you need, and get you the door that best fits your needs.  Contact us for your watertight door needs.

More information on ABS:


Monday, April 13, 2020

Watertight Doors and ABS - Part 2

In our previous post, we outlined the different types of watertight doors described by ABS.  In our next few posts, we are going to take a look at each type of door in more depth.  We will start with the category, "Other Openings Closed at Sea", which is the most common type of watertight door found on most vessels.

Watertight door installed, photo credit Pixabay
Watertight door installed
photo credit Public Domain Pictures at Pixabay
Cen-Tex #110 lever-operated
quick-acting door
These doors are the least expensive of the door types, and are the easiest to install and maintain.  A simple individually-dogged door will meet the ABS requirements for these opening.  If there will be lots of traffic through the door, then a quick-acting door is recommended.

For the individually-dogged door, there are the fewest moving parts that can fail.

The quick-acting doors have additional moving parts to allow all the dogs to operate simultaneously.  Quick-acting doors either use dog arms operated from a central hub, or use dogs on the perimeter of the door activated via a series of linkages.  These additional parts add to the maintenance, but knowing that the door is secured EVERY time you use it is worth it.

The wheel operation can be replaced with a lever to exert more leverage on the dog arms and make sure that they seal properly.

Close up of lever operated door dogs
Lever-operated doors with dogs on the frame are operated by linkages between each dog.  This requires more labor to assemble the dogging mechanisms, however, this mechanism creates a better seal than the wheel operated door with dog arms.  The dog rotating onto the panel provides more pressure at the edge of the door, more firmly compressing the gasket in the door panel onto the knife edge of the door frame.

These closures do not require remote indicators that the door is open or closed, and do not need to be able to be operated from a remote location (such as the pilot house), which greatly simplifies the installation and maintenance of the doors.

We can work with you to help you determine the door that you need, and get you the door that best fits your needs.  Contact us for your watertight door needs.

More information on ABS:

Wednesday, March 18, 2020

Watertight Doors and ABS - Part 1

There are several types of watertight doors that are classified and approved by the American Bureau of Shipping (ABS).  The different types are:

  • Doors Used While at Sea: sliding doors capable of being closed remotely from the bridge, as well as able to be operated at the door's location on each side of the bulkhead.
  • Access Doors Normally Closed at Sea: heavy-duty bulkhead style quick-acting doors with dogs spaced to ensure that the opening gets closed and seals watertight. These doors must have a way of indicating on the bridge an open or closed condition.  They must also have a notice on the door to indicate that it is not to be left open.
  • Doors or Ramps Dividing Large Cargo Spaces: These watertight doors can be rolling, hinged, or sliding, and do not need to be remotely controlled.  They must be kept closed while the vessel is underway.  The time that the door is opened and closed in port must be documented in a logbook.
  • Other Openings Closed at Sea: These are doors, hatches, manholes, portlights, scuttles ... basically anything that is to be kept permanently closed while at sea, to ensure the watertight integrity of the vessel.  These do not need to be fitted with a device to operate them remotely, or indicate if they are closed, however, they do need to have a notice posted that the closure must remain closed while underway.  Manholes are exempt from this rule.
These different classifications for watertight doors will help you decide which type you need for your situation.  We can work with you to help you determine the door that you need, and get you the door that best fits your needs.  Contact us for your watertight door needs.

More information on ABS:

Friday, August 10, 2018

Adjusting Spring Tension on a Hatch

Performing maintenance on a hatch with a spring-assist hinge can feel like playing with a loaded gun.  The spring that helps you lift the cover when you're underneath it and trying to shove it open stores plenty of energy that needs to be handled carefully when it comes time for maintenance or repair.  Cen-Tex hatches use stainless steel springs to provide the maximum service life possible, however, the springs do wear out over time and need to be replaced.

Since tensioning a spring can lead to injuries if not done correctly, we have created a video to show the proper procedure.  A spring-assist hinge can be installed on steel hatches as large as a 48" x 48" clear opening, and on aluminum hatches as large as a 60" x 60" clear opening.  The hatch cover can weigh up to several hundred pounds.  As a result, the following safety precautions should be followed:

  • Spring tensioning should always be performed by two people.
  • EXTREME DANGER WARNING - Failure to hold hatch cover open securely prior to adjusting spring tension may result in severe bodily injury, loss of limbs, or death. Always be sure that hands, feet, and toes are clear of closing hatch covers.
  • The hatch cover must be opened and held open to approximately 90 degrees in the open position before attempting to apply tension to the spring.
  • NEVER position yourself or others so that you cannot get completely out of the way of a falling hatch cover if required to do so quickly.
  • NEVER try to catch or stop the hatch cover from closing by placing fingers on the edge of the hatch cover. Always use lift handles on hatch. (You might be strong, but you will not catch and stop--plus or minus--200 pounds accelerated by gravity with your fingertips. It will win, and take your fingertips with it.)
  • USE CAUTION around open holes and hatches. Properly restrain hatches if required.

Spring-assist hinge hatches play a vital part in the every-day operation of a vessel. For example, putting a spring-assist hinge on an escape hatch located at the top of a ladder in a crew berthing area could make THE difference for the survival of the crew by making it easier to open the hatch when seconds count. Also, a spring-assist hatch can significantly increase the ease of access to a space, especially for a hatch that is used frequently, saving time and increasing productivity.

So, with these instructions in mind, we want you to stay safe while maintaining your hatches, so they will be ready for use when you need them.

Friday, July 20, 2018

Under Pressure

A common question regarding our watertight doors and hatches is how much pressure can they handle?  For the sake of simplicity (so we don't have to write out "door or hatch" constantly), we will discuss this using a watertight door as an example.  All of these questions apply to watertight hatches as well.  There are several variables to consider when answering the question about pressure:
  1. Will the pressure be pushing the door open (unseating/internal pressure), or will it be pushing the door closed (seating/external pressure)?
  2. What size is the clear opening for the door?
  3. How much pressure?
  4. Will this be "in case of emergency" or protection for the "once in 100 years flood", or will the water pressure be constant (for example, on the side of a tank that is normally full)?

Will the pressure be pushing the door open or closed?

If the pressure is closing the door, then more pressure can be applied without causing leaks, since the pressure is working to help seal the door.  If the pressure is opening the door, then it requires relatively small amounts of pressure to unseal the door panel and cause a leak.  How much pressure?   Well ...

How large is the door?

A smaller door can handle more pressure than a larger door.  We determine if our product can meet the specified requirements based on the number of pounds per square inch (psi) of pressure applied to the clear opening surface of the door panel.  For pressures in a closing direction, we are limited by the material strength of the steel or aluminum used for the panels.  If it is a large door panel, a large pressure load (greater than 30 - 40 psi) can eventually cause the panel to warp and fail.  For example, if you had 30 pounds per square inch pushing against a door with a 36" x 80" clear opening, that would equal 86,400 pounds or 39.27 TONS pushing against the door panel.  Cen-Tex products cannot handle that kind of pressure, however, MCS does consult with engineering firms that have built doors to handle higher-pressure loads on larger doors like this.

How much pressure?

A Cen-Tex door may be the perfect fit for you, provided your pressure requirement and door size are within limits we know the products can handle.  2019 UPDATE: Due to increased liability issues, Cen-Tex will build doors to handle a maximum of 7 psi in a closing direction and 2 psi in an opening direction.  For pressure requirements beyond these specifications, we can consult with manufacturers that specialize in high-pressure closures.

Will this door be used in emergency situations only?

A door that will be used once to make sure that an electrical vault in a building located in a floodplain stays dry can be built differently than a door located on the side wall of a tank that will be kept full all the time.  If you don't care if the door "takes one for the team", may get a little bent in the process, may not close the same way once the pressure is removed, but still holds and does its job, then you can go with a door that is not over-engineered for the job.  These questions are always a balancing act between what it costs to design a door to meet any contingency, versus the likelihood of these incidents to occur.  Basically, you're trying to balance being prepared without going overboard and spending too much money to be prepared for a situation that may happen in 500 years, if ever.

In summary, these are general guidelines for items that need to be evaluated on a case-by-case basis.  The consequences of throwing more water pressure at a door than it is designed to handle are potentially life-threatening.  Our extensive product knowledge and experience will help guide you to the product that meets your needs, while helping you find a product that doesn't exceed your needs (and as a result, exceed your budget).


Friday, June 8, 2018

Can Steel and Aluminum Work Together?

The doors, hatches, and manholes we sell are made out of three materials: carbon steel, aluminum, and stainless steel.  Anyone who has spent any time around ships knows that rust is one of the biggest maintenance headaches.  Hours are spent chipping paint, chipping off rust, patching areas, and repainting every exposed metal surface.

The problem only gets bigger if you start mixing metals.  Galvanic corrosion is what happens when you put two different metals together in an electrolyte solution, and seawater is a perfect electrolyte solution.  The salt dissolved in water forms an electrical circuit between the two metals, with the current flowing from the anode (the more electronegative metal) to the cathode (the more electropositive), which will cause the anode to corrode.  The metals that are in common use have been ranked based on how electronegative (anodic) or electropositive (cathodic) they are.  The further apart the metals are in this ranking, the more likely that the anode will corrode.

So, do you need to have an all steel or an all aluminum boat, or can you use aluminum and steel in the same boat?  Yes, you can use them together if you take the proper precautions.  Steel and aluminum are right next to each other on the rankings of electronegativity, so they don't have as large of a voltage difference between them when immersed in seawater.  A good paint system will prevent this galvanic corrosion from occurring by isolating the two metals.  Better yet, if you invest in a primer that has zinc incorporated into the primer, the zinc will act as a sacrificial metal (the zinc in the primer will oxidize before the item covered by the primer will oxidize), and provide increased protection from galvanic corrosion.

Our customers have successfully used doors and hatches with aluminum covers or door panels, and steel coamings.  The aluminum door panels and covers are much easier to lift and operate, yet the steel coaming or frame allows you to weld it into the steel structures of the ship.  As long as the metal is painted, you don't have to worry about accelerated corrosion.

If you are interested in reading more about galvanic corrosion, or would like to check out the research done for this post, check out the link to this article:

Also, here is a fun article about instances in history where we learned about galvanic corrosion the hard way:

Friday, April 27, 2018

Delivery Times and Amazon

I have noticed in recent years how Amazon Prime seems to be shaping people's expectations of delivery times.  As the number of Amazon Prime subscribers increases, people are beginning to think that free one or two-day shipping is "normal".  What they forget is that it takes the scale that comes from the largest company in the United States to be able to offer these shipping discounts.  Other companies cannot afford to offer free shipping.  In many cases, they would be negating their markup, or even wind up losing money to offer to absorb the shipping costs.

The one or two-day shipping also seems to be skewing people's perception of how long delivery for an item should take, and as a result, it is changing their planning process.  Even a few years ago, people would plan further ahead when ordering an item, knowing that it could take upwards of one to two weeks to receive it.  Now that people are beginning to see one and two-day shipping as "normal", they have stopped planning ahead for purchases like they used to.

This shift in delivery expectations creates some challenges when your product can measure five or six feet on a side, and weigh half a ton or more.  Our LTL (Less than Truck-Load) shipping tries their best to haul heavy freight as quickly as possible, but they just can't make the delivery times that people are starting to expect everywhere.  Is there a cheap and easy solution?  Do we start using air-freight to deal with customer's new expectations?

Perhaps the best lesson to learn is that Amazon has become a force unto itself.  We cannot all be Amazon, and we have to remember that when ordering from other companies, we need to remember that realistic shipping times -- and costs -- are part of the purchasing process.  We need to plan accordingly, and not be surprised by either factor -- time or cost.

I'm not the only one writing about this phenomenon.  If you're curious about this topic, I did a quick search for Amazon influencing shipping expectations, and found an interesting article on the subject: