IOMICA Forum

I am building a float tank for our fleet. Does anyone have drawings or photographs of float tanks they can post - I'm not interested in re-inventing the wheel! Thanks

I have emailed Bruce the six pictures I have of the tank that was used at the worlds in Vancouver 2003.

Sails ETC also sells a plan.

If we ever do a spec update, we should consider changing one of our rules.

Sei up the rules so that the keel/ballast does not extend beyond 360 mm below the bottom of the hull. This plus the 60 mm hull max equals teh 420 mm max right now. With a slightly shallower hull, the overall depth might be 5 mm or so smaller, hardly a major change.

This would eliminate a major hassle by eliminating the float tank.

Ralph

Tank free measurement has been discussed at length in the exec and especially the measurement sub-committee. Everyone has considered it very important that current IOMs remain class legal when the class rule or the measurement procedure is changed.
There is no easy solution.

A measurement gauge that would measure the real draught without a tank seems to be quite hard to construct...

If anyone has any bright ideas I am sure that the measurement and techincal committees would like to hear about them !

Anders:

I don't see the problem others apparently see.

Take my suggestion below and have it applicable at a selected date, say 1/1/2006.

Have all current IOM owners measure their boats/keels to see if the keels are longer than the new 360 mm value, and if so, have them get them certified by their measurer and then grandfathered.

All new craft meet the simple draft control measurement value of 360 mm max.. All new keels are to meet the 360 mm value, even when fitted to existing hulls.

Seems simple to me.

Ralph

The difference with gauge measurement is not a problem to check but that different hull forms will permit different actual hull and boat draught. A gauge rule will thereby drive design development.

Measurement from waterplane and measurement with a gauge are not compatible methods and only class owners can decide which one is in the best interest of the class.


Regards

Ralph
Under your scheme woudn't you still need to float the boat to check that the hull doesn't exceed the 60mm?

Alan:

Perhaps you are correct. Of the craft I have seen, none exceed the 60 mm value and some are quite shy of this hull depth, but I suspect that you have more knowledge of this than I (since you are in a hot bed of hull design and developement).

Back when we had to record this data on the initial measurement for certification, and when we did not have a tank, we simply put the boat in the water (fully rigged and ready to sail with batteries) and noted where the waterline was located on the hull. Then we set up the hull alone on a table and aligned the hull to match this waterline, and with the height (off the table) at the bow and stern the same, noted the dimension. It was never over 60 mm.

This seems to work OK, for none of the craft that we measured this way was ever rejected by a tank test. Admittedly, our sample getting both the table top and tank test was small, but then the "commercially available" hulls always passed both tests.

As for Jan's comments on hull design development, it seems to me that this IOM class is a hybrid of a development and one-design where the one-design aspects deal with the rigs and the development aspects deal with the hull and fins. So if any slight rule modification like I suggested to simplify measurement at regatas results in some tweaking of the hull design, is this not what is the core philosophy of the class -- work on development of hull and fin shapes?

I guess that if the designer thought that, say up to maybe 5 mm or so extra draft of the ballast was very important, they would design a hull with a full 60 mm of hull draft. On the other hand, they might think that a hull shape that was not forced into a specific draft value would have better performance, and they would then not restrict themselves to a maximum draft value. That is the nature of a development class.

We see a wide variety of hull designs competing in this class and in good skippers hands all seem to do quite well. Based on this I would not expect to see any major design changes wherein the front running skippers feel the need to change their boats. But then I am not one who has to have the latest "fad" boat.

I will bow out of this discussion now since it is unlikely that this concept will get class management support.

ralph kelley wrote: ... if any slight rule modification like I suggested to simplify measurement at regatas results in some tweaking of the hull design, is this not what is the core philosophy of the class -- work on development of hull and fin shapes?

When we formulated the rules we were very well aware that a draught restriction measured from waterplane makes checking more difficult. The intention however was to produce a class with clean line hulls that would appeal to sailors and spectators.

If a guage is used to control draught the contact points/lines at the hull get very interesting and bumping of different forms will likely appear. Would this be something good or bad? That is for the class owners to decide.


Regards

We here in Vancouver are lucky to have a few enthusiastic sailors who didn't mind the time and effort to design and build a tank. Once built they are simple to use and who can argue with the measurer?
From a design point of view I for one am in favour of the tank rule and would not like to see "measurement bumps" apearing to maximise an advantage, real or percieved. And there is allways the possibility that the change of rules may produce a hull form that is genuinly faster than present crop of boats?

ralph kelley wrote:Alan:

Perhaps you are correct. Of the craft I have seen, none exceed the 60 mm value and some are quite shy of this hull depth, but I suspect that you have more knowledge of this than I (since you are in a hot bed of hull design and developement).

Speaking for the German NCA I can say that we have got some designs over here pushing very close to the 60mm. For example, Michael Scharmers boat sailed at the Euros in Arcos. http://el-servo.physics.helsinki.fi/per ... ct2876.jpg

With some European designs tending to have less beam obviously we are seeing increasing hull depths requiring greater attention when measured.

I am greatlly in favour of a rule that allows for a measurement gauge instead of a tank, but I have no real idea how to acomplish this keeping in mind that we do not want to creat a "second generation IOM" with a design advantage over the current fleet.

I have home built a couple of bantock designed 'Kite' IOMs, (plans commercially available) and the hull depth is very, very close to the 60mm max!!!!!!!!!!!!

Nigel said:

And there is allways the possibility that the change of rules may produce a hull form that is genuinly faster than present crop of boats?

You can rest assured that as far as IOMICA Vice Chairman Measurements is concerned, the number one prioity for any new 'gauge' for measuring hull/total depth, is that the current IOM designs are not prejudiced by a change in the way we measure.