CTD Winches: Straight Pull VS Trailed

The CTD winch is a winch specially designed for the retraction and retraction operation of the CTD water harvester, using the armored machine cable. In the design direction of CTD winches, there are two types of straight pull and traction. This article will compare the advantages and disadvantages of straight-pull and traction in various aspects one by one.

1. Cable tension

The most important factor in the choice of straight-pull or trailed is to consider the response of the cable used to the tension of the storage cable. One of the great advantages of a traction winch is that the cable can be worked under high tension and stored under low tension. In contrast, straight-pull winches only allow the cable to be stored under high tension.

Initially, the operator found that the fiber optic cable suffered rapid damage after a period of time when using the fiber optic cable, and the service life was greatly reduced. After discussions and research with the cable manufacturer, it was found that the high tension storage cable was the cause of the damage to the fiber optic cable.

However, this is not the case for cables that do not contain optical fibers, such as steel cables, armored machine cables, etc. No historical study of these cable failures has ever been found to be caused by high tension storage or the absence of traction winches. Research and testing by cable manufacturers can also prove that the performance or life of cables such as steel cables, armored machine cables, etc. is not affected by the tension of the storage cable.

Therefore, the CTD rope does not require the use of a traction winch.

2. Simple structure

In terms of the simplicity of the structure, there is an intuitive and obvious difference between the straight-pull type and the traction type. The straight-pull winch is far more simple than the traction type winch.

The implications of this distinction are wide-ranging, with more complex traction winches meaning more equipment components, more routine maintenance tasks, more possible points of failure, more maintenance tasks, and more. Maintenance personnel spend more time and money keeping equipment up and running. In contrast, the straight-pull winch is more obviously simple and reliable.

3. Cable arrangement

At present, the primary reason why many domestic experts prefer towed winches is the concern about the cable arrangement effect of direct-pull winches. The main point of view is that arranging cables under low tension can achieve better cable arranging effects than arranging cables under high tension. But this is actually not a big difficulty for the winch designer. In other words, it is not the choice of straight-pull or traction that affects the effect of cable arrangement.

Markey has been supplying straight-pull CTD winches to American scientific research institutions for more than 60 years, and American scientific research institutions still choose straight-pull CTD winches. In the course of decades, Markey's straight-pull CTD winch has been repeatedly beaten and proved, and won the affirmation and recognition of American scientists, thus leaving an excellent reputation for Markey's brand.

The following table is the list of CTD direct pull winches above 10000m supplied by Markey in recent years.

4. Cable winding

As we all know, every time a cable is wound or bent in use, it will bring a certain degree of fatigue to the cable. Fatigue accumulation on the cable will affect the life of the cable. Usually the cables of scientific research winches are relatively long and very expensive. The length of service time of the cables will cause a very big difference in economic expenditure.

An important principle in the design of the winch is to reduce the bending of the cable as much as possible and prolong the service life of the cable. In this regard, the straight-pull winch has a natural advantage over the towed winch. In a traction winch, the cable is first wound around the traction head with 5 to 8 turns. If some manufacturers are equipped with a traditional slack compensator, the slack compensator will also add 270°~360° of winding before reaching the right-angle fairlead of the cable organizer. The total bending angle is very large, which is several times more than that of a straight-pull winch.

Figure: Comparison of cable winding of traction and straight-pull winches

5. Compatibility of AHC function

In recent years, more and more scientists want to add Active Wave Compensation (AHC) function to CTD winches, and AHC function has become a mainstream choice in the marine science community. The Active Wave Compensation (AHC) function is an advanced technology, but places very strict demands on the winch itself. Based on the current automatic control technology, the AHC function can only be realized on the straight-pull winch, and the application on the traction winch is still very immature. At present, no winch manufacturer in the world can come up with a reliable integration solution.

In AHC technology, the winch is required to respond very quickly to the undulating signal of the lifting point. If the response is not timely, it may even cause the opposite effect. This requires the winch to be able to make large adjustments to the rope speed within a very short time frame. Due to the simple structure of the straight-pull winch, the cable storage drum is used to directly retract and unwind the cable, so it is relatively easy to control the rapid adjustment speed of the drum on the straight-pull winch, and it is relatively easy to realize the AHC technology. However, for a traction winch, it involves multiple components such as traction head, cable storage winch, etc. It is a very difficult challenge to achieve rapid speed adjustment on multiple devices while maintaining the speed matching between the devices. Under the current frequency converter and automatic control technology, there is still a long way to go to overcome this challenge.

6. Cost

From an economical point of view, there is a huge gap between straight-pull and traction winches, which are mainly reflected in two aspects:

Procurement cost: Due to the increase in the complexity of the structure and components, the procurement cost of the traction winch is much higher than that of the straight pull winch, usually around 30% to 50%. This imposes a greater burden on the user's initial purchase investment.

Operation and maintenance costs: As mentioned earlier, more equipment parts, more routine maintenance tasks, more possible failure points, and more maintenance tasks, etc. Maintenance personnel spend more time and money keeping equipment up and running. According to the actual operation and maintenance experience of some shipowners, the operation and maintenance cost (manpower + material resources) of the traction winch is much higher than that of the straight-pull winch.

7. Dimensions and weight

Compared with other ships, scientific research ships are generally smaller in size, and the space and weight distribution on board are generally extremely tight, and the utilization of space resources on board often reaches a level of comparison. The size and weight of the traction winch are generally more than 40% higher than that of the straight pull winch. This brings great disadvantages to the layout design in the design process and the convenience in the use process.

Epilogue

By comparing the characteristics of the straight-pull and traction winches in various aspects, it can be seen that for the CTD winch, except for the same performance in a few aspects, the straight-pull winch has obvious advantages in other aspects. Markey has rich experience in both direct pull winches and traction winches, and has many famous cases in traction winches. But based on years of experience in the design of CTD winches, Markey strongly recommends that users choose a more suitable straight-pull winch.

Really hope this article can arouse users' interest in this topic, and all parties are welcome to discuss this topic in more depth with us.