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.  Depending on the size, Cen-Tex doors can handle approximately 30 psi in a closing direction, and approximately 2-4 psi in an opening direction.  These are rough estimates and do not take into account your door size.  For smaller door openings, Cen-Tex may be able to make doors to handle a higher internal pressure, but this needs to be evaluated on a case-by-case basis.  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:

Thursday, February 8, 2018

Chalk Testing a Gasket on a Watertight Door or Hatch

What is a chalk test, and why do you need to do one?  A chalk test is a way of verifying that the gasket in a watertight door is evenly contacting the frame, which ensures a watertight seal.

Chalk testing is one of the key elements in quality testing at the manufacturing plant.  All doors and hatches are chalk tested to make sure the dogs are adjusted properly, and the frame was not warped in the manufacturing process.  Once the door has been installed, it is critical to chalk-test the door again to make sure that the frame was not warped during the installation process, which could create low points of contact and possible leaks.

A solid chalk mark means that the gasket is contacting the knife edge of the door frame.  A light or absent chalk mark means that the gasket is NOT contacting the knife edge of the door frame, and shows where a potential leak path exists. We have created a three-minute video that demonstrates how to perform a chalk test on an individually-dogged door, and how to adjust the dogs if there is an uneven chalk mark.  This procedure also works for individually-dogged hatches.

For doors and hatches with dog arms operated by quick-acting mechanisms, we have created a separate video showing how to perform a chalk test on a quick-acting door, and adjust the dog arms.

If you're interested in watertight products, you can use these links for more information on individually-dogged doors, or quick-acting doors.

Thursday, January 25, 2018

Sorting out Left-Hand and Right-Hand in Doors

One of the key pieces of information we need when building a door is the hinge placement, or "handing" of the door.  This one question gets so confusing that we have even made a one-minute video to show the difference between a left-hand door, and a right-hand door.  People often think that "handing" refers to which hand you use to open the door.  That is NOT correct.  "Handing" refers to where the hinges are located on the door, NOT the hand you use to open it.

The easiest way to visualize door handing is to imagine standing in front of your refrigerator.  When you open the fridge, where are the hinges on the door?

Cen-Tex water-tight doors are designed to work best when the water is on the outside of the door, pushing the door closed.  They are most commonly used on the decks of commercial boats that sail in rough weather.  The doors are designed to seal water-tight and withstand the heavy waves washing across the deck.  However, if you have water pressure inside a compartment or tank, depending on the amount of pressure that needs to be contained, a Cen-Tex door may still be your most cost-effective solution.  We would then recommend that you install the water-tight door so that the frame is on the inside of the compartment wall, and the water pressure inside the compartment would still be pushing the door closed.

To see a selection of Cen-Tex water-tight door designs, click here.

Monday, January 8, 2018

Unusual work always welcome!

We frequently get calls from our regular customers who have an unusual situation and need a custom water-tight solution.  A perfect example of this is the Cen-Tex #225 Flush Quick-Acting Water-Tight hatch with a fold-down lever.  Our customer was tired of a competitor's hatch where the quick acting mechanism is operated with a t-handle that drops down through a central hole in the cover.  The seals have a tendency to fail, which causes the hatch to leak.  They wanted a flush hatch with a handle topside that folded down into a pocket to eliminate the possibility of the hatch leaking.  We took on the project and designed a new quick-acting mechanism.  The hatch can be opened with the fold-down lever from above or a wheel from below.  The innovative part of the design is that when the handle is folded down into the recessed pocket, it is disengaged from the dogging mechanism, so the wheel can operate below, independently of the handle above.

When we had a sample of this hatch on display at the Pacific Marine Expo, another customer saw the dogging mechanism and realized it would be the perfect solution for a problem they were having with a wheel-operated quick-acting door on their catcher/processor.  The door was located on the main deck, and the nets were snagging on the exterior wheel of the door as they were being hauled in.  They asked if we could modify this fold-down flush handle for their quick-acting door.  We took on the project, and created a custom quick-acting door with a fold-down flush handle.  (See photos.)

So, if you don't see what you need in the catalog of Cen-Tex products, call us or email us and let us know what you need. 

Quick-acting water-tight door
Cen-Tex QA Water-tight door with fold-down flush handle