Hi All

I had intended to start this post over two weeks ago but forgot my pass word.

It is now very important for me to clarify these points

Is there a definitive Design and method for setting up and measuring a boat using a tank?

As I understand it the boat must be floated with each rig and be in its normal sailing attitude to measure

I have a copy of the MYA tank designed by Graham Bantock in 1990

Points to cover

The overall length of the boat must be within 1000mm There is no plus tolerance

The rudder must be within te length of the boat.

The maximum moulded depth must be within 60mm no plus tolerance

The maximum/minimum depth (draft) of the boat with each rig. From the waterline must be within 420mm/370mm again no plus or minus tolerance.

What have I missed out or miss interprited.

I need to make a Tank Help

Regards

JohnK

Guys

There has been a lot said over the last couple of days within the 'Southwestern District' over the measuring tank issue. Within this district there is only one measuring tank in existence and I believe it's located at the Poole club. Now it's not very practical if you live in Falmouth and you wish for your IOM to be measured.

If you take John Kiff's stance, it's creditable that he wants to make a measuring tank but should it come from his expense, the expense of skippers who want their yachts measured, or from the governing bodies who create and police the class legislation?

Is it not the responsibility of the IOMICA / MYA to provide the correct tools and equipment?

JT

Hi John

Thanks for your comment but the main reason for this thread is to find the best design for a tank and to formalize the method of using a tank.

Not the cost of a tank as compared to the money currently being spent on a new boat it is a small %.

Regards

JohnK

Hi John,

This does not answer your question but may be of interest and show the major features of a tank.

This video was made to show a comparison between wet and dry measuring. The dry method is not class legal and this was an exercise to test practicality.

Look at the tank. It has a wedge shape to reduce the volume of water. It has leveling screws on the base. It has two side windows with scribed lines for the 60mm max. It has a hole near the top that is exactly the water depth max. We use a small spacer block that is exactly 1m from the block to the other end of the tank. So the boat is rigged at at sailing weight and is floated. The spacer block is used to check for max loa. The window is used to check the hull depth from lwl. and the boat can be 'bounced' to test that it is not sitting on the bottom (ie fin too deep). The tank is filled from a hose and kept topped up after each boat. There is a drain in the bottom to help emptying at end of session.

http://www.wcmya.ca/wcmya_video/iom_dry_vs_wet.wmv

John

Additional comments. Lawrie Neish is the measurer in the movie and our local measurer (He is also on the IOMICA measurement committee). His scale has a platform with three levels: one for the fin, and above that a shelf for the hull, and above that two arms to hold a rig. Our normal procedure at a major regatta, is to weigh the fin, then the hull is added and each rig in turnis placed on top, checking for 4000 gms or more. Then the boat is rigged with its heaviest rig and then floated. Usually, we don't float the boat with each rig, just the heaviest.

The idea behind dry measure experiment is that it is so much faster and easier than floating - but the current class rules are just not compatible with the idea and so it was dropped. Main issue is that to do a dry measure means that you have to 'assume' a waterline location. Great experiment, but not implementable.

John

Hi John Ball

To many john's

Thanks very much I have a Jig but it has adjustable knife edges so the boat is set on the designed waterline. There is a platform 65mm below the knife edge and a 5mm spacer must pass under the hull. A second platform 425mm from the knifeedge to check the draught..

This set up has the added advantage that the owner can see the ballast/fin

But this method does not allow for variations in the water plain due to individual owners weight distribution.

So it looks like I must build a tank similar to yours. The only other design I have looked at is the Croatian 2007 worlds tank very high tec.

Regards

JohnK

Hi Barry,

See IOM Class rule C4 - boat floating in fresh water.

John

As well as this version where the measurements are defined by tank depth and strictly maintaining the water level I have also seen a version where a Jig is suspended on the tank top edge, with the boat floating in the water the jig height is adjusted to water level and then slid under the boat for pass/fail on hull and fin depth. Guess this method could simplify construction of the actual tank as the critical measurements are on the Jig. Tank still has to be levelled to keep the water line parallel to the top edge.

regards,

john

I would like to know when using a tank for wet measuring C.4:

a) does it have to have the rig in or

b) make up weights to bring to 4000 grms

I can see a problem with (a) if a boat weights more then 4000grms and (b) if the makeups are not in a location that represents the cog of the rig and alter the actual float trim.

I can't find any information/procedures to carry out a "wet measurment".

I look forward to your answers.

Edited August 25, 2025Aug 25 by SloopJohnB

The intent  for floating the boat is to establish that it does not exceed max hull depth below waterline, nor max draft. Also confirms min draft and LOA.

To do this the boat has to be race ready, fully rigged and its heaviest battery in position.

John

John Thanks for your reply, is this procedure laid out in the "Measurer's Guide" or some other document?

Part C is conducted under the control of the event organiser. How much of Part C that is actually checked is at the discretion of that committee, for example, at Word Championships, there is a team of measurers who check everything.

I found this document on the MYA web site some years ago-  there may be an updated version, but the parameters for Part C have not changed, so it should still provide guidance.

In Canada at championship events, we may weigh each rig and the boat batteries and establish heaviest and lightest. We weigh the fin/balast and rudder for min/max. Then we weigh the boat ready to race with lightest rig and batteries for at least 4000 gms. Then we float the boat with its heaviest rig and battery to check for depth compliance.

John

2014-05-23_ADVICE_FOR_MEASURING_INTERNATIONAL_ONE_METRE_BOATS.pdf

As a UK IOM measurer please note that the tank IS NOT needed for "Certification Control" - i.e. the process that you need to have completed to get a Certificate.

At important events the Race Committee may insist on boats undergoing Equipment Inspection and will provide information on what will be checked- for example at a ranking event last year I was asked to weigh every boat.  If you go to the IOMICA website and look for the Certification Control Form for hull and appendages you will see what will be measured. 

Thanks for the replies, I have been told that boats can be "wet measred" without the rig in and weights added to bring the hull up to 4000 grms, surely this method would make the LCG/LCB changes if the makeup weight does not match the LCG of the rig.

So if measuring with the rig in and the total weight of the hull & rig is greater than 4000 grms this will make the hull float low and may increase the draft greater than 420 mm, what happens in this case.

The immersion rate would vary greatly depending on the design take for example my Cockatoo and V10, at a guest the Coockatoo would have half the immersion rate of the V10.

At regattas here the boats are checked for overall weight, sometimes the all 3 rigs are weighed and the fin and buld are weight separately.

6 hours ago, SloopJohnB said:

 

So if measuring with the rig in and the total weight of the hull & rig is greater than 4000 grms this will make the hull float low and may increase the draft greater than 420 mm, what happens in this case.

 

I suggest that the boat would be non-compliant. The intro to Part C of the class rule says

The competitor and the boat shall comply with the rules in Part II when racing.
 

To me that means that with its heaviest rig and battery, the boat 'when racing' be a min of 4000gms and will not exceed the 420mm draft - and to show that it needs to be floated with that weight.

Other classes that use a waterline mark on the hull may be able to measure with surrogate weights , but not IOMs.

John

Thanks John, let me get this straight, if a boat weights 4025 grms (sitting lower in the water), it still has to meet the 420 mm max keeel draft and the 60 mm hull draft?

Yes.

John