Towing Vessel Stability

[Guillermo]

At first sight it seems to be a narrow boat with big winches. Also the bollard pull seems only feasible if transverse thursters are not working. I would like very much to to have a look at the adopted stability criteria and the loading and working conditions studied.

Cheers.

[Guest-3-12-09-9-21]

They have a stability program for this vessel - I have no idea about the specifics. I am going to try and go over there at some point this fall to get some time on a DP 2 vessel. I will try to find out something then.

I agree with the narrow observation. I also am not too fond of the shallow hull and thrusters being so close to the surface when at a light draft.
--Chuck

[charmc]

Quick impressions from an "experienced layman":

" Continuous" bollard pull seems optimistic for the rated power output, even given nozzles, and thrusters off.

Based on dimensions, just wondering how stability will be affected significantly by loaded stores? If so, is working under extreme AH conditions to be recommended without the vessel carrying max stores?

HP seems light for an AHTS of that hull length. I note the emphasis on "eco friendly" design. Today that seems to mean sacrificing power for greeness. Does that create an oxymoron? The vessel seems built for less than extreme (medium duty) anchor handling, i.e. not for the depths the new rigs are working at. Is there a standard for determining vessel job assignments? This design has more power than a straight supply vessel, but significantly less than BD and others of similar length. Are there subcatagories within the AHTS type?

I don't know how valid any of these thoughts are. Those of you who have the design and operating experience in this field will know if there is merit in any of these questions/observations.

[Guillermo]

In my opinion 120 Mt bollard pull is about right for the 10.728 HP if applied to the main propellers in an efficient configuration (A rough number is BP =+/- 1% HP, being efficient systems slightly over that).

Narrow beam will not allow to carry the load of the 400 Mt winch much forward over the side in an emergency (Another candidate for a BD like accident?).

Cheers.

[charmc]

Just curious; is that formula for engine rated HP or net HP at the shafts?

[Guillermo]

This is just an statistical relationship between nominal HP and bollard pull for a series of tugs I've had the opportunity to appraise.

[Guillermo]

Interesting video:
http://www.splashvision.com/Video/14...overboard.html

Cheers.

[Nigel1]

Yep, should have fitted that gog rope.
Classic tug boat error

Nigel

[murdomack]

This is the specs for one of the newest AHTS being delivered...just wanted to get what the community here feels about the stability, etc. They are planning to install A-frames on the stern of a couple of these.

http://www.seacormarine.com/pdf/Flex...hn_Coghill.pdf

There is something about the specs that interests me. The weights, etc. are quoted in Lt and Mt when I know that US (short) tons are in common use over there. Coupled to this we have volumes in USG and BBLs and pumping rates in GPM which I know from conversion of the Metric figures is US gallons.
My question is; are Long tons the standard used in measuring US shipping weights?

Murdo

[Nigel1]

Hi Chuck, does seem a bit on the narrow side, for comparison, the specs for my new boat can be seen here

http://www.maersksupplyservice.com/v...=Newbuild(AHTS)

Nigel