But what kind of HP are they using? There are SHP, BHP and even IHP. (“Indicated” HP) The last used to be popular with the Bayou boys, as it sounded better on spec sheets. (bigger number)
When it became compulsory for tugs/OSVs to have BP certs. they came up with “Calculated” BP and S.Tons as unit of measurement for the same reason.
PS> The rest of the world has gone to use one measurement for power; Kilowatt
This to avoid confusion,
KW doesnt determine how its measured so there are as many kw ratings as there ever was in HP
PS choosing a 398, old as me
Ooops!! I didn’t look close enough before posting. Sorry!!
In this case the rating was given in SHP and KW, but in many cases the specifications are given as HP w/o specifying what type of HP,
Yes, there are many KW ratings for engines, but for different reasons than for engines rated in HP. Here is a guide to engine rating in KW:
PS> What is most confusing can be debated, of course.
This is why I just use bollard pull.
You, and anyone with any sense in the marine world.
Can’t think of the last time I thought about anything other than Bollard Pull
Oh yes I can .
Working Offshore North Sea, but then that was usually X bhp giving Y tonnes Bollard Pull
Ships ask me all the time what the horsepower of the tugs are. I have no idea. All I know is how much they can pull, and that’s all I really care about.
There is a lot of Liar’s HP out there, especially on the Gulf Coast.
A D398 is 900hp. A D399 is 1100ish hp.
A large prominent company has long claimed that it has a fleet of 9000hp tugs. They’ve told that lie for so long that everyone calls them 9000s. However, the pair of 20-645 EMDs that power those tugs tops out at 7200hp.
Yeah but did you add in the gens, tow cat, and Kitchenaid mixer in the galley? Gets you almost to 9.
Practically speaking what information is available and how much precision is required?
The engine type is usually readily available. Conversion between HP and kW is simple. A rule of thumb can be used to estimate bollard pull and in most cases is going to be good enough.
Bollard pull is not always known or available.
I once asked a pilot in a central American port what the hp was of a small, ancient looking tug, looked to have been converted from steam. He told me; I don’t know captain, when new 1800, now…maybe 900.
Not going to snap our lines, good enough.
Old joke, but hopefully no longer with any merits 
No it is NOT “good enough” A lot of factors decides how much pulling (or pushing) power you get from a given engine size.
The engine configuration, hull shape and most of all the type of propulsion (fixed pitch or CCP? Open or with nozzles?
The rule is therefore that a Bollard Pull certificate not more that 5 years old and based on a static pull test, carried out according to a sett of rules, (incl. min. water depth, max. wind force and cross current etc.) measured by a certified and calibrated loadcell and witnessed by a competent person from an approved organization (Class, MWS, Maritime Authorities)
Static BP is different from the pull force actually asserted on the towline during towing (Dynamic BP).
Modern towing vessels are equipped with load cell(s) on the towing winch.
This load can be watched in real time on the bridge and an alarm can be set to alert when the pull exceed predetermined parameter. This can be set based on SWL of the towing line, tow connection on the towed object, or whatever the MWS has set as the max, allowed in the CofA.
All you want to know about Bollard Pull:
PS> I have not proofread the entire article.
BP test carried out on a powerful AHT:
I was speaking of my own experience. In most cases. I only recall doing a calculation one time.
The general concept here, bounded rationality is broadly applicable in many situations in maritime and seamanship. For example when is good enough to eyeball, when to use instruments etc.
For example getting pushed onto a berth in good weather. Between 1800 and 900 hp is roughly in the same ballpark as the bowthruster (2000 hp) so it will be good enough.
How about reality of bollard pull when moving ( with current inrush) versus static bollard pull?
How much % drop do you use?
From Diesel Duck: Bollard Pull (Capt. P. Zahalka, Association of Hanseatic Marine Underwriters) (PDF)
I’m sure that the newer tractor tugs must have bollard pull certificates.
Most of the American coastwise and ocean tugs are old, in the 30-60 year old range. Bollard pull certificates are rare.
Class is not required for most US tugs.
A great many US tugs are not required to have a loadline.
Until recently, US tugs were not even USCG inspected vessels.
I’ve only sailed on one tug with a load cell on the winch. It’s not a regulatory requirement.
I can see the merit in having a bollard pull test and new certificate every five years.
But I have not heard of this being done on US tugs.
Worked ATB’s for that company that likes to lie about their 7’s and 9’s for horsepower ratings. We were actually doing bollard pull tests with the ATB tug. It must have been something regulatory because I don’t think anyone would do it otherwise. Don’t think it gives you any useful info on an ATB.
Now working ship assist and we have no load cell, no bollard pull cert. The pilots we work with know what the tugs can do, and there are no other tugs available, so it is what it is…
I can see that my statement below doesn’t apply to US tugs and OSVs
In the 1970 and early 80s I turned down a lot of US owned tugs/OSVs from use for ocean tow and rig moves. This was because of lack of BP certs, BP cert, based on calculated BP by some non-recognized entity, or BP Certs. not up to date.
This was the policy of the MWS companies I did the inspections for.
Eventually even TWD got the message that they had to comply, or have no jobs involving MWS approval.
PS> One time I met myself in the door:
On an AHTS they presented a BP Cert. that was way outdated.
On nearer scrutiny I found that it had my signature as the one to have witnessed the test for the issuing authority.
I agree, there’s going to be a progression from simple situations where estimates and rules of thumb will be adequate to more complicated jobs with higher loads, larger forces, more risk and costs where more formal practices will be required.
