Dolphin Mooring/Berthing Design

A photo on a recent front-page article inspired some questions I’ve had regarding the below mooring design versus a traditional pier (be it parallel, perpendicular, or other in relation to shore). Mostly just idle, non-political, maritime curiosity…:

  • Why, for starters?
    • Is this more cost effective?
    • Is it better/easier to install based on water depth, currents, etc?
    • Aren’t you a bit limited by only being able to ever moor a single vessel?
  • What is the reason for the skewed offset (breasting?) dolphins?
    • Does this offset give a better line angle for holding tension / adjusting while loading/discharging?
    • Why are the ones fwd of center slightly different than those aft of center?
    • Can you fit a tug in the pocket?
  • How does this arrangement compare to a traditional pier from the approaching Master/Mate/Pilot’s perspective?
    • Is this a more cautious approach?
    • Is there concern with hull damage from lower surface area potential impact points?
    • Is it more of a pain to get messenger lines out to the farther dolphins?
    • Are you more limited in any sort of springing to pull in / ease away in wind?
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That would be my guess, especially as the distance from shore increases.

How about the design makes it possible for tugs to push the vessel away?
I think all of your other questions have merit. Given enough equipment, almost all of the build sites could be active at the same time.

Are tugs more effective pushing rather than pulling?

A cynical part of my mind says this beautiful image is the design of someone with more imagination than seagoing knowledge. It looks cool, as magazine articles are meant to do. Is it a serious design? I’m not an expert at oil terminal moorings, so someone else can comment on that.

When I see an asymmetrical design like this I think bottom topography is the cause. Bottom topography might drive the overall design. As was the case with the old breakbulk finger piers in places like Seattle. The piers were constructed at an angle to shore to keep them in shallow enough water to use wooden pilings. In this design maybe the isolated piers are built on rock outcroppings, at the outer limit of a shallow shelf.

A symmetrical design would be less costly to build. Look at all the angles for the fitters to make. But far more costly is the labor after the dock is built. Most of the mooring lines need to be transferred from ship to the dock by boat. Why waste the time and effort?

While the vessels are of vastly different scales, I do have experience with tying up vessels on dock faces shorter than the vessel itself. There are a few dodges a short dock gives you in clearing the dock with a very strong onshore wind and no tugs, but these maneuvers wouldn’t be used with a vessel of the size shown, where tugs and thrusters are always used. Pivoting on the corners of a dock puts enormous strain on the dock, and not a little on the hull.

Having the tugs place themselves “inshore" of the ship to push her away from the berth gives no advantage whatsoever, since the mooring lines are in the way, and tugs like to make themselves fast before castling lines away.

My two cents anyway…

All else being equal, yes. On a conventional tug, the ahead bollard pull is much stronger than the astern. Same is true (to a lesser extent) on an ASD. Other advantages are that the wash doesn’t interact with ships’ hull and line angle and bollard pulls limited by bitt/chock SWL are not a factor.

Working a line does however allow for easier variance of the ahead/astern angle if needed, although most tugs can push at angles off of 90 just fine to a certain degree.

The tug doesn’t work the inside until the lines are taken in. Generally, you pin the ship with the tug using no line then move inshore of the ship once the mooring lines are clear of the water. Of course having no line up means you better have enough sea room on the other side of the ship since the push is a one way move…

Good example here:

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The vessel’s picture is strongly distorted:

On my computer screen, the beam near the bridge measures 26 mm, behind the bow only 23 mm.
The bridge is inclined 78° relative to my screen’s bottom, while near the bow the beam is at 54°.
Hence, the bow bollards are distorted too, the installation is probably symmetric.

The bow bollards are on top of tubular pillars; the stern ones are on quadratic concrete platforms, for their part probably on top of straddled tubular legs.
This may be due to the water depth or the quality of the bottom.

The design does allow for optimum fleet angles and leads on bow and stern, breast, and spring lines. Your average marginal wharf or flat pier face makes breast line leads nearly vertical and thus useless.


It’s a serious and common design pushed out by OCIMF guidelines and you can zoom in on the Valdez Terminal to prove that (berth four and five below). Putting a low profile structure and pushing the mooring out from shore opens up draft ranges, simplifies the current impacts by removing nearshore or structural effects, and also allows for full encircling with containment boom.

Doesn’t work so good if you want to do multiple berths, here’s Buckeye in Grand Bahama

I was trying to find a ‘free’ copy of the OCIMF mooring design guide but this paper gives an idea and is free

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Don’t have much experience on tankers but my understanding is that working ships with this much displacement it’s more on the science and less on the art end of the seamanship spectrum.

From what I’ve seen ships of this size get pushed in flat, or as flat as possible by tugs and then held there while the crew run the lines. I’d assume that a max lateral landing speed is used and monitored by Doppler.

As far messenger lines, some car ship docks have similar layout. The heaving line can be laid across anywhere that can be reached by the linehandlers and they walk it out to the ends.

Here is Terminal 5 car dock in Vancouver Wa. It lacks walkways so one of the tugs transfers the mooring lines to the dolphins.


The ramp is landed on what is actually a converted barge. Getting tied up is a pia but once all fast it does have the advantage of not having to watch the tide heights. Worse thing for the tug crews is having to climb up on the dolphins to handle lines in winter after an ice storm or with snow.

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That’s a pretty standard oil terminal berthing arrangement. Even older terminals have added similar style fendering in the midbody area and offset hooks as much as possible or added an offset dolphin. No need for a full faced pier with all the business done at the manifold.

Offset dolphins provide longer leads at optimal angles for much greater holding power. Lines are typically run by messenger to a capstan on the dolphin, 2 guys on the dock on each end to run the capstan and place eyes on the hooks. It’s a pretty simple operation, 30min from first line to all fast.

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Awesome, I think that answers most of my questions…I knew I came the right place!