* All recent Yanbu crude loadings conducted without AIS

signals

* Dark voyages create wide discrepancies in Saudi export

estimates

* Saudi crude loadings from Egypt's Sidi Kerir hit record:

Vortexa

By Ahmad Ghaddar and Jonathan Saul

LONDON, Aug 12 (Reuters) - Saudi crude exports from the Red

Sea are increasingly vanishing from view as tankers switch off

tracking signals to avoid attacks by Yemen's Iran-aligned

Houthis, with analysts saying all recent Yanbu loadings have

been conducted "dark".

The Houthis declared a maritime embargo against Saudi Arabia on

July 20, opening a new front against the United States and its

allies in the Iran war.

Since then, they have claimed attacks on Saudi-linked tankers,

Yanbu oil facilities and, most recently, the Jazan refinery on

the Red Sea coast, prompting more vessels to operate without

publicly visible tracking data.

The growing use of so-called dark voyages is clouding

visibility into Saudi oil exports, making it harder to assess

the degree to which the Houthi threats may be disrupting crude

flows.

Ship-tracking firms have produced widely differing export

estimates - data which is used by the International Energy

Agency, OPEC and traders to assess global oil supply and

forecast market trends.

In the week beginning August 3, data analytics firm Vortexa

estimated Yanbu loadings fell to 2.38 million barrels per day

from 2.71 million the previous week, while Kpler estimated a

sharper drop to 1.78 million bpd from 4.04 million, and

AXSMarine calculated a rise to 640,000 bpd from about 420,000

bpd.

Saudi Aramco did not respond to a request for comment.

CONDUCTED DARK

Those trying to monitor shipments rely on a vessel

re-appearing on tracking systems once it has left the high-risk

area, using satellite data to cross-check movements and try to

fill in the gaps.

"Last week Yanbu liftings were all conducted dark. We're not

seeing any loadings with Automatic Identification System (AIS)

on at the moment," Vortexa analyst George Morris said.

Kpler analyst Nhway Khin Soe said about 70% of Saudi west

coast loadings over the past few weeks were dark, adding that

all Yanbu cargoes loaded since July 23 involved vessels without

continuous AIS coverage.

Shipping traffic through the Bab al-Mandeb Strait at the

southern tip of the Red Sea had already been affected by two

years of sporadic Houthi attacks on commercial shipping. An

average of 32 vessels a day transited the waterway last week,

according to Kpler data, down from about 50 a day before the

group announced its latest blockade.

Ship-tracking data shows that Saudi Arabia has been sending

more oil north through the Red Sea, either via the Suez Canal or

Egypt's SUMED pipeline, which links Ain Sokhna on the Red Sea to

Sidi Kerir on the Mediterranean coast.

Crude and condensate loadings at Sidi Kerir averaged a

record 2.17 million bpd last week, around 50% higher than the

previous week, with about 90% of the total volumes Saudi crude,

Vortexa's Morris said.

The cost of war risk insurance has jumped in recent days and

tanker companies are also shifting their sailing strategies.

Major tanker operator DHT previously exited the Red Sea via

Bab al-Mandeb when lifting oil.

"That has become a bit more challenging as of late," DHT CEO

Svein Moxnes Harfjeld said on an earnings call last week. "It's

fair to say most of the VLCC (supertanker) loadings, not just

ours, have been directed north, northwest now."

​

(Editing by Kirsten Donovan)