Dry or Waterless Measuring

[Lawrie Neish]

A suggested dry / waterless measuring jig has been posted on the Measurement sub Committee page. The item consists of text, photographs, drawings and a link to a short video.
I will appreciate any comments regarding it. These can be posted on the forum or sent to me direct at wlneish@shaw.ca

Thank you.

LawrieCAN202

[Antonio Espada]

Hi Lawrie:

Very good project and Video...

Are you the protagonist?

We send you a mail with the legal problems with the actual RuleBook... if you obtains a new text and general consense... ¡congratulations!.

Has you see the work of Roy Thompson 3-4 years ago?

Regards.

[Lawrie Neish]

Hi Antonio,

I found Roy's dry measuring work and postings sometime after the initial jig was constructed and used some of the information Roy presented to modify it to the present version. In fact the present jig has a close resemblance to a bulb and fin setting jig we have here in Western Canada.
Lawrie

[RoyL]

The effort and thought put into this project is appreciated. The problem that I believe is inherent in this and all other dry measurement systems that I have seen proposed to date is that it allows designers to fundamentally change the nature of IOM hulls. In the proposal it is acknowledged that hull forms that are presently not permitted would become legal with this dry measurement jig, but it is suggested that no advantage will be gained. Unfortunately, if an enterprising designer does find a significant advantage in the allowed change in hull forms, every existing IOM could be rendered less than competitive and perhaps obsolete. To me this is too large a risk to take for the convenience of a simpler measurement system. I have seen too many classes ruined by technical or measurement changes that were initiated with the best of intentions. The goal of waterless measurement is admirable and one that the IOM class should continue to seek, however, until it can replicate the current tank measurement system, I do not think it should be adopted.

[Bruce Andersen]

It might be interesting to bring the dry measurement system to the WC's and dual measure all the boats - of course the dry measurement system would have no bearing on the boats' legality, but it would allow for a direct comparison of the two methods over a wide range of hull forms.

[Lawrie Neish]

Hi Bruce,
The executive have agreed to sending an example of the jig (or an improved one) to the WC. I have had a brief email exchange with the MYA and I presently await a reply to a further email.

So far it has proved to correlate well with tank results. This is as it should be and could be expected from boats designed to fit the current rule and measurement method, but my hope in posting the information is that designers of "killer" boats will give me a clue as to how to take advantage of the jig.

[RoyL]

Given how quiet this board has become lately, it might be a good idea to send this information to various designers directly and solicit their comments and also to post this information on various NCA boards (Australia, US, GBR, etc.) to get some better feedback...roy

[Lawrie Neish]

Already being done and is ongoing.
Lawrie

[Hiljoball]

The dry measure looks very attractive as it is much faster and easier than the floatation tank. It is possible to conceive of hulls that could exploit the dry measure jig, eg a very narrow deep ‘U’ shaped hull that would measure in, but would float much lower end exceed the 60mm depth and max depth – but would such a boat be faster?

I think it is possible to take advantage of the jig without making any rule changes. In other words, use the jig at major events to quickly screen the boats and only refer to the tank, marginal boats or odd shaped hulls that will not fit easily into the jig.

With the upcoming Worlds, it would be good to put the fleet into the jig and also the tank, and compare the results. This would help validate the approach.

John

[Lawrie Neish]

Hi John,

Thank you for your comments.

I will comment on the second first as it is simpler. I personally think it is a case of one or the other but not both. I have a tank and it is well traveled. I would be happy to dispense with the fiddling with it to maintain accuracy - especially on cold days.

Regarding your first point. The jig, as it is at present, does make an attempt to curb attempts at producing hulls which sit high in the jig and then float lower in the water. At the stern, the datum point is split which does allow narrow hulls or skeg-like shapes to drop through to counter this attempt at getting increased bulb draught. I did consider doing something similar at the bow with a narrower slot. But this would produce the effect of extending the “waterline to the full 1,000mm and the aim in producing the jig was to arrive a compromise which would reflect existing successful designs. However, the possibility of adding a slot at the bow datum is not out of the question. I even considered adding a Plimsoll line to the hull at measurment!

I think that in attempting to produce “sinking” hulls they would suffer from increased wetted surface and loss of manoeuverability and form stability which I think would more than offset any gain in bulb and hull draught. Some of these effects can be attempted in tank measuring but it seems that designers are not inclined to try.

Lawrie

[Hiljoball]

Hi John,

Thank you for your comments.

I will comment on the second first as it is simpler. I personally think it is a case of one or the other but not both. I have a tank and it is well traveled. I would be happy to dispense with the fiddling with it to maintain accuracy - especially on cold days.

Lawrie

Hi Lawrie,

I agree that the ultimate goal is to have just one system, but before we can jump into a major change, we need to have a period of exposure and validation. If the validation and acceptance is high, then introducing a rule change to adopt dry measurement would have a better chance of voting approval.

John

[RoyL]

In thinking more about this issue, I believe the question of validity of a dry measurement system is two fold--first does a dry measurement system "accept" existing boats that measure in a tank? And second, what boats would a dry measurement system "permit" that a tank would not? Each would appear to be an equally valid concern.

I also believe that there might be a compromise here. One thought is to change initial measurement to include length, overall depth, and weight. Not the same as a tank, but simple to do with a jig and a scale and it would make those boats that have not yet been fully measured at an event at least closer to the class standard.

[Lawrie Neish]

In response to the two previous posts. If there is to be a change then I do not think this is going to happen overnight. Yes, a period of exposure would be very good, and I hope that present negotiations will ensure this happening. As noted in my post of 16th March, I hope to have a jig in the UK before summer. I am producing replicas at the moment. My present jig will make its way to events down the West Coast of North America during this year. I would like to see it also being tried in other countries - Australia comes to mind. I should note at this time that there are other jigs which can use the same datums to achieve the same end. It is not necessary to accept this particular version.

I had hoped that some public spirited members of the IOM community would produce replicas of the jig for trial purposes. It costs a lot less for material than freight charges and takes a little more than one hour to make with nothing other than square cuts!

At present I am working round known designers of IOMs in an effort to get their opinions on how the suggested jig would affect their present designs and I am also asking if they perceive ways to circumvent the fixed datum points.

The jig will pass any IOM which has a waterline in the region of 980 mm and replicate a tank almost exactly at this length . It really does not matter how the 980 is arranged. Naturally, if a boat has a longer waterline then the jig will lift the hull a small amount or if it has a short waterline then the hull will drop. The point is that these are, in the long waterline case, probably amounts to less than a millimetre at the bulb and for a short waterline it would depend on how short. One of the points I try to make is that all boats so far placed in the jig have passed as most the draught of most hulls is sufficiently above the limit not to be challenged by small variations. The same might be said about bulb draught and so far I have found that a lot of boats could be made more competitive as their bulbs are placed too high.

It goes without saying that hulls if they have passed tank flotation in the past or before an agreed date should be grand parented.. There is a catch in this - the hull draught is difficult to change modify in a competitive way, but the bulb is not. So, do we OK the hull and modify the fin / bulb draught? Or, dig out a tank?

Obviously the class rules and measurement forms would require some revision, but, because a dry jig of this type is much simpler to make, less bother and quicker to use it may lead to it being more readily available than tanks and lead to the inclusion of most of the MYA supplement form items in fundamental measurement. So a certificate would say that it is an IOM and not maybe an IOM. Yes, I know some items can be changed quite easily after measurement.

[Emilio Vidal]

Hello:
My name is Emilio Vidal Massanet and I’ve been designing, building and competing in IOM boats in Palma de Mallorca for 17 years.

After several years of triming and constructing my boats, I use an apparatus similar to the one you are proposing, but mine can fit the position of the boat in reference to the supposed water line. My experience is that the apparatus is amazing as long as the boat waterline is known. The ideal would be that boats had the waterline noticeable in prow and stern to place them in the apparatus correctly, wich supposes to make a change in the class rules, to force the boats to have flotation marks in the same way masts have measurement marks.

Once, in Palma de Mallorca, we made a dry measurement and we detected some problems because not all the boats did have the standard waterline: some of them had it but above or below from the standard, and as they were not noticeable in the hull, we needed to make later verifications with the tank for some of the boats.

As a designer I think that it is easy, if jig adopted, for some designs to take advantage of this defect. Right now it does not seem interesting but it could be in the future with the jig. It is also necessary thinking that some rare boats could not be measured with this jig, like the one appearing in the photo with a bulb in the prow.

Any way I think that measurement in dry is a very good idea; I have both systems and finally I use the tank only to mark waterline; for all the rest, I verify in dry.

[Lawrie Neish]

Hi Emilio,

Thank you for taking the time to comment. That is a mean looking paint job on the boat!

I appreciate what is being done in your method and there is a set up posted on our wcmya.ca site to achieve the same results although in a slightly different way.

However, I think it comes down to the choice of staying with the tank process or moving to dry measuring but not trying to mix both systems. No matter how hard we try there will never be a perfect match between the two methods. The question is how much difference can be accepted and how will it affect the class.

I am quite comfortable with tank measuring, but it is messy and unless you live in a compact country with a dense population of IOMs such as the UK then the tank has to be trucked around to each location. These are often far apart and sometimes less than convenient to set a tank up.

The great gain with a jig is the sheer speed of measuring and simple set up. The problem it is the fear generated that some designer will come up with a way to take advantage of the fixed datum points. It would be constructive for designers to show how they would go about doing this.to the class disadvantage.

So far in comparing tank measuring with the jig, the present jig has failed one boat which passed in the tank. The difference being 1 mm to long fin . The cause the hull was a little more than 1mm low at the stern. In this case the question would be how much would this boat suffer if the fin was shortened by 1 mm.

Personally, I think there is more of a problem in allowing underweight boats to place the correction weights at the keel.

Thank you,

Lawrie