Do all ships need double-row airbags for launching?

No. Small and narrow ships with strong bottom structures can safely use a single row of airbags. Double rows are usually needed for heavier, wider, or flat-bottom ships.

At what ship weight should double-row airbags be used?

There is no strict rule. Around 1,000 tons, ship width and bottom structure should be carefully evaluated. For ships over 1,500 tons, double-row arrangements are commonly used to improve safety.

What are the advantages of double-row airbag launching?

Double-row airbag arrangements spread the ship’s weight more evenly, reduce pressure on the hull bottom, improve sideways stability, and increase overall safety during launching.

What risks can occur when using a single row of airbags?

For heavy or wide ships, a single row may cause airbags to approach their load limit, increase local stress on the hull bottom, and reduce sideways stability during rolling.

Is double-row airbag launching much more expensive?

Not significantly. Double rows mainly require additional airbags and slightly more setup time. Compared to the potential cost of structural damage or accidents, the extra investment is usually worthwhile.

Are double rows recommended for flat-bottom ships?

Yes. Flat-bottom ships benefit from double-row arrangements because the load is distributed across a wider area, reducing stress concentration along the centerline.

When Do You Need Double-Row Marine Airbags for Ship Launching?

Airbag launching is a common way to move a ship from land into the water. It is widely used because it is flexible, cost-effective, and does not need a large slipway.

But one important question often comes up:

Should we use a single row of airbags or double rows?

Some people think large ships must use double rows. Others try to save money and use only one row. In reality, there is no simple rule. The right choice depends on the ship’s size, structure, weight, and the condition of the ground.

In this article, we explain in simple terms when double-row airbags are a better choice.

1. What Is the Difference Between Single and Double Rows?

Single-Row Arrangement

In a single-row setup, the airbags are placed along the center line of the ship.

Features:

Simple layout
Lower cost
Weight is supported mainly in the middle
Less sideways stability

This works well for:

Small ships
Narrow hulls
Ships with strong keels (V-shaped bottoms)

Double-Row Arrangement

In a double-row setup, airbags are placed on both sides of the ship bottom.

Features:

Weight is spread out
Better sideways stability
Lower pressure on each airbag
Higher safety margin

This is often better for:

Heavy ships
Wide ships
Flat-bottom ships

2. When Should You Use Double Rows?

There is no single rule. You should look at several factors.

1) The Ship Is Heavy

As ship weight increases, each airbag must carry more load.

If you notice:

Airbags are close to their load limit
Too many airbags are needed in one line
Airbags deform too much

Then double rows may be safer.

General industry experience:

Below 500 tons: usually single row
Around 1,000 tons: depends on ship width
Above 1,500 tons: double rows are common

Heavier ships usually need more safety margin.

2) The Ship Is Wide or Flat-Bottomed

Ship width is very important.

If the ship is wide and airbags are only in the center:

The sides hang too far out
The bottom plate may bend
Stress becomes concentrated in the middle

Flat-bottom barges are especially sensitive to this problem.

If ship width is over 10–12 meters, double rows are often a better choice.

3) The Ship Has a High Center of Gravity

Some ships have heavy structures on top, such as:

Passenger ships
Workboats with upper decks
Ships with tall equipment

These ships are less stable sideways.

With only one row of airbags:

The ship may sway more
Tilting risk increases
Airbags may not share weight evenly

Double rows increase the support width and improve stability during rolling.

4) The Ship Bottom Is Not Very Strong

Some ships have thinner bottom plates or lighter structures.

If weight is supported only in the center:

Local dents may appear
Long-term structural damage may happen

Double rows spread the load and reduce pressure on any single area.

5) Ground Conditions Are Not Ideal

If the launch area has:

Soft soil
Uneven ground
Limited load-bearing capacity

A single row puts pressure in one narrow line.

Double rows spread the pressure over a wider area, reducing the risk of sinking or uneven movement.

3. A Simple Way to Decide

In real projects, not every team does complicated math. Many decisions are based on practical checks.

Ask these questions:

1. Are the airbags close to their load limit?

If yes, double rows are safer.

2. Is the ship bottom wide and flat?

If yes, spreading the support makes sense.

3. Does the ship look unstable during testing?

If the ship sways or tilts easily, double rows help improve balance.

4. Are you saving much money by using one row?

Often, the cost difference is only a few more airbags.

Compared to the risk of structural damage, using extra airbags is usually a smart investment.

Engineers often say:

It is better to use two extra airbags than to risk one serious accident.

4. Real Project Examples

Case 1: 800-Ton Flat Barge

Width: 9 meters
Strong structure
Low center of gravity

Single row was used successfully. No structural problems.

Conclusion: Medium-small ships with strong bottoms can use single rows safely.

Case 2: 1,800-Ton Cargo Ship

Width: 14 meters
Flat bottom
Heavy upper structure

Originally planned for single row, but changed to double rows after evaluation.

Result:

Smooth rolling
Even load distribution
No deformation

Conclusion: Large and wide ships are safer with double rows.

5. Important Tips for Double-Row Setup

If you decide to use double rows:

Keep both sides symmetrical
Use equal numbers of airbags on each side
Maintain equal air pressure
Keep spacing consistent
Monitor sideways movement during launching

Even with double rows, poor setup can cause uneven loading.

6. Cost vs. Safety (Short Discussion)

Yes, double rows cost more.

But the extra cost usually means:

A few more airbags
Slightly longer setup time

Compared to repair costs or accident risks, this is usually a small price for better safety.

In launching operations, safety margin is more important than saving a few airbags.

7. Final Thoughts

Using double-row airbags is not only about ship weight.

You should consider:

Ship weight
Ship width
Bottom structure
Center of gravity
Ground conditions
Safety margin

Double rows are strongly recommended when:

The ship is wide
The ship is flat-bottomed
The ship is over 1,000–1,500 tons
Airbags are near load limits
Stability is a concern

In ship launching, proper arrangement is more important than minimizing cost.

Safety should always come first.

FAQ

1. Do all ships need double-row airbags?

No. Small and narrow ships with strong bottoms can safely use a single row.

2. At what weight should double rows be used?

There is no strict rule. Around 1,000 tons, you should check ship width and structure. Above 1,500 tons, double rows are common.

3. What is the main advantage of double rows?

Better load distribution and better sideways stability.

4. Is double-row launching much more expensive?

Not usually. It mainly adds a few more airbags, which is often worth the extra safety.

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