Whatever happened to AVS?

Tranona

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Old news!. As a specific measure it has lost much of its relevance because stability is much more complex than one single measure and neither is it a particularly good indicator (on its own) of a boats capability. It came about because of a spate of designs coming on the market with low AVS and being used in conditions where ultimate stability was potentially an issue. New boat buyers now seem to be concerned about different aspects of design and assume (mostly correctly) that designers have done a good job, including meeting appropriate AVS figures for the category.
 
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Old news!. As a specific measure it has lost much of its relevance because stability is much more complex than one single measure and neither is it a particularly good indicator (on its own) of a boats capability. It came about because of a spate of designs coming on the market with low AVS and being used in conditions where ultimate stability was potentially an issue. New boat buyers now seem to be concerned about different aspects of design and assume (mostly correctly) that designers have done a good job, including meeting appropriate AVS figures for the category.

I suppose you could say that the RCD fixed it...
I believe it has requirements for this (directly or indirectly) and any large boat will be expected to meet cat A.

Now that's going to be unpopular, what did the EU every do for us? eh! ;)
 

Birdseye

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The answer Nicho is that AVS vanished.:D

I suspect that in the chase for increasing cost reduction by the BeJenBav builders et al, there is a bit of a conspiracy of silence about AVS or ballast ratios. Put more ballast into a boat to increase AVS and you have to have a heavier hull at greater cost, then a bigger rig to move it and so on. Can you charge more? Certainly Beneteau were for a long time very difficult about publishing stability data whether AVS or Stix.

There is some truth in what Tranona says. The average buyer wouldnt understand what AVS meant and what its significance was. To him it would just be a number and like the length of his willie, the bigger the number the better. But reality isnt like that. Capsize is an issue of energy transfer from the waves so not only is AVS relevant but so it height of topsides, cross section of keel, depth of keel, weight and many other factors. Hence the derivation of Stix
 
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nicho

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The answer Nicho is that AVS vanished.:D

I suspect that in the chase for increasing cost reduction by the BeJenBav builders et al, there is a bit of a conspiracy of silence about AVS or ballast ratios. Put more ballast into a boat to increase AVS and you have to have a heavier hull at greater cost, then a bigger rig to move it and so on. Can you charge more? Certainly Beneteau were for a long time very difficult about publishing stability data whether AVS or Stix.

There is some truth in what Tranona says. The average buyer wouldnt understand what AVS meant and what its significance was. To him it would just be a number and like the length of his willie, the bigger the number the better. But reality isnt like that. Capsize is an issue of energy transfer from the waves so not only is AVS relevant but so it height of topsides, cross section of keel, depth of keel, weight and many other factors. Hence the derivation of Stix

Mmmm, interesting, thanks.
 

Tranona

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The answer Nicho is that AVS vanished.:D

I suspect that in the chase for increasing cost reduction by the BeJenBav builders et al, there is a bit of a conspiracy of silence about AVS or ballast ratios. Put more ballast into a boat to increase AVS and you have to have a heavier hull at greater cost, then a bigger rig to move it and so on. Can you charge more? Certainly Beneteau were for a long time very difficult about publishing stability data whether AVS or Stix.

There is some truth in what Tranona says. The average buyer wouldnt understand what AVS meant and what its significance was. To him it would just be a number and like the length of his willie, the bigger the number the better. But reality isnt like that. Capsize is an issue of energy transfer from the waves so not only is AVS relevant but so it height of topsides, cross section of keel, depth of keel, weight and many other factors. Hence the derivation of Stix

A little bit misleading in the first paragraph. High ballast does not necessarily lead to high AVS, neither does displacement on its own. High ballast ratios were common when hulls were narrow and bilges slack - that is when there is little form stability, but also when the ballast is not low down as in some IOR type designs where the rule penalised stability and keels were of the shape where the ballast was not at the bottom of the keel.

Over the years, ballast ratios have fallen and there are few boats with ratios of over 40% and many nearer 30%, but with wider flatter hulls, high topsides and deep bulbed keels AVS is often higher than the heavily ballasted boats of the past. Draught is almost universally greater these days than in the past with 1.9-2m common on mid 30' boats. My new boat is a shallow draft version but with a draft of 1.5m which is greater than similar sized Moodys and Westerlys for example. The standard draft is 1.95, but the shallow draft has the same stability by having a longer and bigger bulb on the bottom.

Your second para gets nearer the point. Designers have a target AVS (and STIX) determined by the category they are aiming at. With almost all boats over 32' this will be Cat A and achieving that in the smaller sizes, particularly STIX is a real challenge, but achieved by deep bulbed keels, wide beam, flat bilges, high topsides and buoyant superstructures. Whether this makes them more capable boats in adverse conditions is of course open to question. Many boats from the past with far lower stability have proven themselves in such conditions even though they would not stand a chance of getting into Cat A if they were built today.

Like many regulations and standards, these have little relevance to the average buyer who will probably never get anywhere near the limits of the boat's capability. He is more likely to judge a boat on its overall merit and suitability for the intended use. Interestingly that is the trend in magazine boat tests (more properly reviews rather than tests) as they tend now to spend less time on the technical aspects of design and more on trying to assess how well the boat meets the perceived needs of potential buyers.
 
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JumbleDuck

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Interestingly that is the trend in magazine boat tests (more properly reviews rather than tests) as they tend now to spend less time on the technical aspects of design and more on trying to assess how well the boat meets the perceived needs of potential buyers.

On that related note. YM's "100 point boat test" didn't last long, did it? Perhaps they realised that a score which weighted "chart table" as highly as "seaworthiness" was a bit silly ... and that anyway the perceived needs of different potential buyer groups vary enormously.
 

Tranona

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On that related note. YM's "100 point boat test" didn't last long, did it? Perhaps they realised that a score which weighted "chart table" as highly as "seaworthiness" was a bit silly ... and that anyway the perceived needs of different potential buyer groups vary enormously.

The latest 5 category, 5 star system based on type of usage seems to work better - even though Snooks has had a bit of stick here with his star ratings certain categories on one or two boats!

Certainly found the reviews of the three boats on my short list very useful, particularly the videos that went with 2 of them plus an Australian video of the third. No longer doing videos since the staff cull! Generally I agreed with their assessments on all three except for the actual sailing bit as I have not sailed any of them yet! However the differences (which are minor) are relatively easy to see from the designs and layouts. Boat is being built now and leaves the factory next Friday so not long to find out if I got it all horribly wrong.
 
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