I wish there would come a day that all towing vessels use the bollard pull system, I think
that when you know this and even the dead-
weight of a vessel it’s much easier to use a
known vessel as a benchmark or reference
when doing a similar job with another vessel
if you know this, many vessels have a known
bollard pull listed on their vessel profile, a
lot of vessels do not. A true 2,400 HP vessel
to me would be a set of natural EMD 12 cylinder with open wheels or thereabouts ,
many vessels listed in the south predomitely
listed at 2,400 would be in big trouble if they
had the same oil barge making a transit
through Hells Gate with 20’ of draft, so to
me this has been a long time ignored issue
that has just become accepted in the world
of towing/work vessels, the ship pilots around the south know exactly what their
normal working tugs have for bollard pull
Very very few of the tugs that I’ve sailed on have Bollard Pull Certificates.
Bollard Pull Certificates should definitely be required under Subchapter M.
A re-test every five years would be a good idea too. Things can change. It’s an inexpensive test.
There is too much liar’s horsepower out there.
A big difference too between 15’ draft, 3000hp and two big wheels vs 6’ draft, 3000hp and four small wheels.
If a tug lacks a Bollard pull Certificate based on a test performed according to guidelines from a major Classification Society, approx. bollard pull can be calculated from the following guidelines:
Source: https://www.dieselduck.info/machine/02%20propulsion/2010%20GL%20on%20Bullard%20Pull.pdf
PS> Rough calculation of required Bollard Pull in case of ship-shaped tow in open waters can be found from page 8 of the same document.
Thank you for this helpful post.
Exactly, also a big difference between a heavy tug with 18’- 20’ draft loaded with
a pair of 16 645 turbo EMD’s rated at say
~ 4,800 HP or so with big wheels vs maybe
a Cummins powered triple screw rated at
the same HP, at least in the characteristics
anyway, the EMD vessel will crunch creosote
pilings just in clutch while the other has to
be turning a much higher rpm, and again
this is just characteristics and not how the
bollard pull number is obtained . Still lots
of towing vessels around that are under
100’ and even around 80-85’ that are
rated HP wise up there with larger EMD
& the 3516 Cats when actually they are
nowhere close in harbor work or ocean
towing and a little lite in the ass, the heavier
tug should always outperform a smaller
“inflated HP tug” in towing speed when
conditions are where you can still pull except
probably in fuel consumption.
There is also the concept of “power tonnage” a big, heavy, older, lower horsepower tug with fine entry, will outperform a boxy, lighter boat with higher horsepower going into a head sea.
Nothing will change so long as companies are happy to hire them…
Just like the dive vessels with 1 crew on the bridge.
Just like DP vessels with non classed approved DP systems.
What happens in the GOM stays in the GOM
There also is going to be a thrust deduction in the range of you calculation of -5-10% in most scenarios… I have seen vessels with the propellers well below baseline so there is no or very little thrust deduction because it is clean water in and clean water out of propeller vs most scenarios where the thruster is tight up against the hull and skeg and thus as you get the higher HP and more water requirements the efficiency of propeller is diminished a bit…
the other problem with bollard pull is its in static water flow.
Who has a tug with the water inrush curve to show you how the pull drops in current or when moving?
Could that be why it is called a “Static Bollard pull Test”?
Static because the test is carried out against a stationary Bollard.
The tug makes zero speed above ground when the measurement is recoded.
The “water flow” (i.e. current) and wind speed at the time has to be within set limits and direction to get a valid test result.
Dynamic Bollard Pull is the actual pull asserted on the towed object via the towline.
On modern tugs this is measured at the winch or tow hook in real time while in operation:
PS> For ocean towing operations the MWS may set a max allowed dynamic BP limit, based on the the mean break load of the bridle, or tow connections on the towed unit.
Here is some useful info re: bollard pull and capabilities of modern tugs:
I’m not really seeing the question here from the Original Post. “Bollard system?” What exactly is that? Then you mention using dead-weight of a vessel. So I’m going to guess you’re talking about the measurement units. I’ve seen bollard pulls listed in short tons, metric tons, KIPS, and pound-force.
Other than converting the units (I’m super lazy and have taken to chatgpt for this one!), the concept is solid I think. There are several variables that let a tug pull more or less on a static object, fluid dynamics of the hull being one of them. We mariners are practical people. Put a line on a bollard, pull like hell, and measure it.
It is also a sensible test, something that literally does come up in ship assist. When sailing a ship, everything is static, you get into your line and pull like hell.
The tonnage thing you mentioned is another fun barrel of monkeys. Gross Registered Tons, and the standard practice of “tonnage hatch” is asinine. But these are the rules we play by, design by, and pay our careers. There are a bunch of seemingly non-nonsensical rules!
Only Metric tonnes an Kilo Newton force are used as measurement of Bollard Pull internationally.
Likewise, GT is the international standard. GRT was discontinued in 1982, except in the US.
I was speaking just in practical terms, knowing the benefits of a heavier vessel,
and remember seeing all the vessel specifics
including deadweight in the Lloyds of London ship registry, being a tug guy most of
us know the capabilities of a vessel from
having worked on the vessel or one very similar , knowing the HP, the reduction gears
& ratio, the draft & what the main engines are, HP rating’s are so diluted these days
especially in the Gulf region, it’s why I wonder with all the Sub-M & everything else
we have to deal with why hasn’t a better
system of a tugboats true capabilities adopted other than HP, most of us know
just by longevity in the industry.Its usually
the lightweight tugs, built cheaper with a
lot less steel and smaller higher rpm engines
that have a high HP rating that tend to bite
off more than they can chew but are good
at finesse work, quick handling response
& overall good fuel consumption vs an old
stud tugboat.
A correctly performed static bollard pull test, certified by a competent organization (Class, MWS etc.) is the nearest you can get to assess tug capability.
That is what has been used worldwide for the last 40 years or more.
PS> I started approving towage operations as MWS in 1974. At that time few towing vessels had BP Certificate.
American tugs/OSVs specified their engine power in IHP, not BHP .
That gave a bigger number on the spec sheet, by didn’t help on their towing power.
Looking at multiple towing companies online
some list the vessels in a HP class that is
way off base of the actual combined engine
BHP and even in small print when listing the actual engine BHP at a said RPM than that
figure is bumped up a few hundred HP I
suppose due to the vessel having Kort
nozzles , which doesn’t raise the BHP, just
efficiency , some companies had the BP listed in short tons and a few cases of
the vessel deadweight was listed. It seems
only harbor assist tugs, rig moving vessels
& higher HP larger towing vessels that may
specifically be used on large heavy tows especially when insured for a large amount
and marine surveyors involved,lots of the
smaller stuff under a real 3,600 HP that
list no BP cert, some of the vessels may
be just load line anyway.
Like the salvage tugs of yesteryears. The John Ross.
Well know salvage tug Smit Amandla (ex John Ross) is sadly no more.
Broken up at Alang in 2023:
SA John Ross with her sister tug Wolraad Woltemade (aka WW, or; “Not John Ross but the other one with the difficult name”)
Seen here transferring towline at sea:
PS> The WW held the title as the world’s most powerful tug for several years.
Listed BP was 220 m.t., while John Ross were listed with a BP of 210 m.t.
I inspected both tugs several times and did a memorable tow as MWS on the Argentine J/U-rig “Rio Colorado 1” from Tierra del Fuego to Puerto Madry, Argentina with WW. (In 1985)
From Ship Nostalgia (require membership):
Impressive numbers for any era, did a tow transfer with this vessel last year.
I believe the world’s most powerful towing vessel is still the Island Victory:
Design: Kongsberg Maritime UT 797 CX.
Ship Builder: Vard Brevik/Vard Langsten
Delivery: February 2020
Certified Bollard Pull: 477 T
Vessel specification:
She took over the title from Normand Samson (ex Far Samson) Bollard Pull: 423 m.t.:
Photo: Neil C McBride
I completely agree about those “tonnages” being asinine. Using deadweight as a factor is also asinine. If only there was a way to discover the DISPLACEMENT! What a breakthrough that would be.