ABS scantling rules

[MikeJohns]

The rules are not infallible and have underestimated both the dynamic loads and the fatigue failure of hulls and fittings in the past. This has happened to vessels across the design spectrum.

Yacht keels are of particular concern since their failure is so catastrophic to life and vessel. ABS have erred in the past particularly with GRP.

The 1986 revision of the ABS OSRY does not properly account for the keel attachment shear loads. Hulls built to the minimum FOS under that rule will have inadequate hull shell thickness in way of the keel attachment. This was remedied in the 1994 edition after some catastrophic failures.

GRP boats built to this 1986 rule with a minimum FOS need their scantlings beefing up with extra laminate.

Adopting a higher FOS allows for errors in both design and construction.

[Guillermo]

Have a look a this interesting paper from Finot web pages:
http://finot.com/nouvelles/actucours...rche/csys4.pdf

From there:
"Several authors have contributed with theoretical and experimental investigations on this subject. Joubert (1982), Brown, Joubert and Yan Ping (1996) and Brown, Wraith and Joubert (1999) have carried out an extensive analysis of local pressure loads on hull plating and the associated structural response. They concluded in most instances that the rules in the American Bureau of Shipping “Guide for building and classing Offshore Racing Yachts” might lead to inadequate scantlings.

Reichard (1984) and Hentinen and Holm (1994), carried out some full-scale measurements by instrumenting sailing boats with pressure transducers. The latter also deduced that actual pressures are higher than the ones recommended by the ABS guide and that the unaccounted nonlinear mechanical behaviour of the hull panels combined with design safety-factors would explain the relative absence of damage on most sailing vessels. Their conclusion then was that “there is a lot to learn about slamming loads, and the mechanisms of the structures are yet by no means fully understood”.

Indeed the question about the correct definition of design pressures for modern sailing yachts remains an open problem. Brown et al. (1999) suggest that, because every impact produces a different impact pressure, what is needed is an estimate of worst case loading. This would certainly be valuable information for design purposes, but it would not be sufficient. In fact if slamming loads are to produce a structural failure, it is more likely to happen because of fatigue rather than because of maximum stress exceedance. For example, this was probably the case with the numerous sandwich core failures observed at the end of leg 5 of the 1993-94 Whitbread race: as Bowler commented (Jeffrey, 1998) failures only started to appear on yachts after they had sailed 20000 miles and most of them had already survived conditions similar to or heavier than those encountered during leg 5 without damage. Hence, ideally materials and scantling definition should also take into account non-maximum slamming loads and their frequency of occurrence."

Cheers.

[mgpedersen]

Originally Posted by Robert Gainer

Of course the underlying problem is that a light boat is a fast boat and there is no incentive for a builder to add structure (weight) when that adds expense and impairs performance. Does the scantling rule need to include limits for ballast/displacement ratios and minimum hull weights for boats? If it was required to carry around the weight in the hull instead of in the keel it would go into improving the strength of the hull girder.
All the best,
Robert Gainer

The ABS rule does specify a minimum skin weight, which varies depending on the material chosen. Interestingly it also includes some requirements for grounding loads, and requires the boat to be able to sit on the keel without any problems.

ABS doesn't care about ballast/displacement ratio, it looks at 1) hull material properties, 2) weight and CG of the keel, and 3) the geometry of the attachment (spacing of bolts, height and spacing of frames, etc.).

If you enjoy reading the standard, it is available at www.eagle.org It's the 1994 rule for classing offshore racing yachts IIRC.

[Tanton]

All building methods are covered in the "Ambush", ABS. program by Tanton Yacht Design. As are calculations for Keel bolt diameter, rudder stock diameter and rudder bearing sizes. All minimum limits on plating thickness are automatically applied.

[waterman]

So I have to admit, I haven't read all of the replies in the thread, so I am trying to answer the original question.
ABS doesn't class Yachts to the sailing yacht rules anymore. (At least not by ABS Americas). That being said, they still publish the rules/guide.
The sailing rules/guide was developed to fill a market demand for a sailboat standard. Essentially, the rules had a couple of problems, lawyers were involved and ABS no longer classes sailing boats.
However, in the absence of some standard it is used to show that at least due diligence has been done (this topic has been covered by other threads).
There are other sailing yachts sets out there though. BV has one. The ISO has been working on one for a while the final version is still being vetted and hasn't been released to the world yet.
Having seen a copy, I would say (at least for powerboats) it is more convoluted than the ABS motor yacht rules, and like any rule set there is always questions to be asked.

[Willallison]

Yves - is Ambush a program you are making commercially available? If so, does it also cover the ABS powerboat rules, and can you provide a link to your appropriate web page please?