Welcome, Guest
Username: Password: Remember me
If you don't like what you see click the Report button or...
Read More...
BARGES: All about barges and barging - building, buying, maintaining, equipment, handling on the water, etc.
  • Page:
  • 1

TOPIC: Hull Thickness 1902 Iron barge 20m in salt water

HULL THICKNESS 1902 IRON BARGE 20m IN SALT WATER 28 Apr 2020 13:14 #115592

  • Balliol Fowden
  • Balliol Fowden's Avatar
  • Online
  • Posts: 2564
HI Paul,

I was thinking of avoiding this very broad and potentially contentious issue, but perhaps not! The following is a slightly adapted precis (!) of an email I wrote when asked a similar question a few years ago.

There are a number of factors here.

1. You need to check with your insurer. Many UK insurers require periodic surveys, typically every five to seven years. ES-TRIN if applicable requires surveys every five to ten years, although 5 to 7 is the norm. The decision might not be yours to take!

2. Do you have a survey trail for this vessel? Can you see any pattern of diminution in successive surveys, or does the hull condition appear stable? Has the vessel been on salt water for a long time or is this a new habitat in say the last five years? Does a change in “home” conditions merit a condition update?

3. Has the vessel been the subject of very extensive repair or do significant areas remain original? If it has been re-plated or overplated (properly!) in recent years then there will be less of a risk of hidden or undiscovered gremlins, but more risk of, for example, electrolytic corrosion, although you would probably have seen that at the last anti-fouling. If the plating is largely original it must be born in mind that many old barges have plating which has fallen well below the permitted diminution levels allowed in merchant shipping and on that basis would have been scrapped long ago. Merchant shipping tends to be recycled once the incidence of excess plating diminution (usually a loss in excess of 20 or 25% of original plating thickness) reaches a certain level. We are preserving ships at nearer 50% permitted levels of diminution, thus much closer to risk of hull weaknesses and shell perforation, and much frailer. 4.5mm of soft or brittle iron is very little really! The continued existence of our older barges is due to a number of perfectly reasonable considerations (e.g. not carrying cargo any more, limited use, historic ships etc.), but we are talking about very old boats that in general need reasonably regular monitoring and ongoing repair.

4. Has the barge been converted for a long time? When was the interior of the shell last preserved? Is there active internal corrosion? This can very often be much more of an ongoing problem than external corrosion, and this corrosion will continue however often you anti-foul the exterior (and anti-foul is not a “protective” coating).

5. Do you have confidence in the last survey? At the last survey were the access conditions satisfactory? Was the hull plating grit blasted prior to the survey, or was it sufficiently clean? Did it carry large deposits of old paint and pitch which might have rendered the survey less effective? Were there significant caveats to the survey report beyond the standard ones? No survey will ever be 100% for all sorts of perfectly valid reasons, and there will almost always be something to find!

6. Was the inspection indeed ultrasonic only? Did the surveyor also go over the hull intimately with the right hammer, strake by strake, frame space by frame space, and “sound” it? Was it a random grid pattern ultrasonic assessment only, or a considered and analytical “fingertip” examination? It must be clear that ultrasonics in a 1902 barge can be highly unreliable, sometimes indeed absolutely meaningless, due to the non-homogeneous nature of the hull material (some form of iron), for which ultrasonic meters were not designed and in which they sometimes simply do not work. Unfortunately some surveyors tend to take the ultrasonic-only sampling course as applied to merchant shipping and just measure a “modelled” number of pretty random points. You mention that the hull was “tested ultrasonically.” Bear in mind that an ultrasonic meter, even in ideal conditions, is only measuring the metal literally at a POINT. Even if you said that the ultrasonic transducer was applied to an area of say 1 square centimetre then in actual effect the average 20 metre barge, with a wetted area of say 100 square metres, and with say one hundred measurements, would only actually be “tested” over 1/10,000th. of its wetted area Hammer soundings, properly carried out (and it is much more than just a matter of hitting the hull hard!) can be a much more effective and widespread means of detecting thinned plating, followed up by ultrasonics at specifically identified areas to confirm the point, if a reliable measurement can be obtained.

I could go on, but the simple answer to your very broad question is that your insurers may well want a survey shortly, for good reason, and that for your own peace of mind it might be a false economy not to have the hull inspected if it is coming out of the water anyway.
I am also making the point that no survey can ever be exhaustive or 100%, and can never make any guarantees, especially in very old boats which can require specialist experience, and where various areas will be inaccessible, so a regular survey routine is sensible in the hope of picking up problems that may not have been reasonably detectable or detected previously, however good the surveyor, quite apart from new deficiencies which may have developed.

Balliol.
The following user(s) said Thank You: Andy Soper, Bob Marsland, Lynn Woods, Tim Horchler, Sam Archer, Peter Johns

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 28 Apr 2020 12:39 #115591

  • Paul Gillieron
  • Paul Gillieron's Avatar Topic Author
  • Online
  • Posts: 6
Will do - soon.....
Paul

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 28 Apr 2020 12:37 #115590

You should be able to see when you have it out of the water if the anodes are working or not by the wastage on them.

Tam

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 28 Apr 2020 12:34 #115589

  • Paul Gillieron
  • Paul Gillieron's Avatar Topic Author
  • Online
  • Posts: 6
Thanks Tam - they were chosen by local experts.

Best

Paul

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 28 Apr 2020 12:30 #115588

I haven't got the figures to hand re anodes, but I assume they were sized correctly when they were fitted. I've always understood that if they are too large they will not do their job correctly. (Balliol will probably correct me if I'm wrong.)

Tam

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 28 Apr 2020 12:22 #115587

  • Paul Gillieron
  • Paul Gillieron's Avatar Topic Author
  • Online
  • Posts: 6
Dear Richard - many thanks for this. Pretty well my thoughts. Bilges in very good condition and protected.
Monster 6kG anodes (9). We'll be using a high performance AF.
Best,
Paul

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 28 Apr 2020 12:14 #115586

I always assumed that antifouling was just a coating to deter creatures and plants from living on the surface of the hull and not really designed to protect against corrosion but I'm happy to be corrected. I assume that the hull will be pressure washed and that should give you an idea of the pitting and general condition. Personally I would see if it looks OK and if it does I would do some research on underwater coatings, e.g. Jotun and others and then decide what to paint it with, If it looks OK on the outside and if you can check the inside too then I would not bother with the ultrasonic but I really don't have much experience with iron or saltwater. Hope this is at least some help.

Please Log in to join the conversation.

Hull Thickness 1902 Iron barge 20m in salt water 27 Apr 2020 18:03 #115577

  • Paul Gillieron
  • Paul Gillieron's Avatar Topic Author
  • Online
  • Posts: 6
Dear Bargers, 5 years ago, the hull was tested ultrasonically and repaired - after that all measurements above 4mm, Average 4.5 - 5mm.
Antifouled twice since then.
It's coming out mid May for antifoul - should I have it remeasured? New anodes on both lifts.

Paul

Please Log in to join the conversation.

  • Page:
  • 1
Moderators: Pete Milne
Time to create page: 0.249 seconds