OK Dinghy Weight Concentration
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I have posted this on the UK site, but my intention is to communicate with the class at large.
On the pages of the UK Forum and on Facebook there has been much discussion, angst, accusation and general misinformation as a result of the disqualification of Jorgen Svendsen from a race which he won at the recent World Championships at Black Rock.
As I wasn’t there I can’t comment on that specific case, but as someone with 30 years. experience in the class many of which were spent as Vice Chair of the OKDIA technical committee I am very familiar with the class rules, so I feel qualified to share my perspective on the subject of weight concentration. I have no affiliation with any of the class builders.
The first thing I would like to point out is Rule 8.3 which states: Construction of the hull, with the exception of stringers, shall be of approximately even thickness (within 10%) and density longitudinally and no attempt shall be made to concentrate weight near mid-length, or at any other point. If it is suspected that this rule is being broken a NA may order test holes to be drilled in the skin or structure.
Seems pretty clear to me:- ‘No Attempt shall be made to concentrate weight near mid-length’.
With the rules as they are written today my interpretation is that a boat does not comply with the rules if:
1. The Bulkhead at Station 2 is made from thicker material than that of the transom and/or Station 1 bulkhead.
2. The Bulkhead at Station 2 is made from more dense material than that of the transom or Station 1 bulkhead.
3. The Hull material in the mid-section of the floor is more than 10% thicker than at the ends.
4. The Hull material in the mid-section of the floor is more dense than at the ends.
5. A material not listed in the allowable construction materials (for example Lead, Steel or carbon at the ends) is hidden within the hull skin.
6. Excessively heavy fittings are used in the mid-section of the boat. Specific areas of concern are toe strap supports, mainsheet block mounts and traveller supports.
7. Excessively thick or dense centreboard case.
8. Excessively heavy Non-slip materials on Cockpit floor.
There seems to be some general confusion over where responsibilities lie with regard to rules compliance, so I have attempted to identify the basic responsibilities of the sailors, builders, measurers and event officials.
• The OKDIA Technical Committee is responsible for monitoring trends in the class and making judgements on new materials or technologies which may affect performance. Any fundamental rule change will be voted on at the OKDIA AGM.
• The Boat builder should be fully aware of the rules and not make any attempt to construct a boat which does not comply with the class rules
• Every boat must go through primary measurement carried out by a qualified national measurer. It is the measurer’s responsibility to ensure that the boat complies to the class rules. This is the point at which any mistakes by the builder should be picked up.
• Event measurement checks are overseen by the Chief Measurer, they do not replace primary measurement and are designed to enable the TC to monitor class developments and help the Chief Measurer ensure boats are compliant. It remains the responsibility of the competing sailor to ensure their equipment is class legal.
• Any competitor, race official or member of the measurement team can lodge a protest if they believe a competing boat does not comply with the class rules.
Personally I think the rules are clear and the appropriate measurement systems to ensure compliance with the rules are in place. The reason we are beginning to see issues at major events is because there is a breakdown at Primary measurement. Rule interpretations seem to differ between nations and there is no direct connection between national measurers and OKDIA. If something needs fixing that would be a good place to start.
Best Wishes to all my OK Dinghy Friends
Regards Terry CurtisHi Terry,
I was hoping someone else might post a reply, they’re obviously all keeping their heads down! There’s obviously a lot of scar tissue out there, and anything you can do to repair things based on moderation and knowledge can only be welcome.
I think the only thing myself and Finn disagreed in our banter was where the concentration on policing should be. I think you’re right when you say that the measurers may need some help and guidance on what to look for and stop the problem at source. At the same time maybe we ask too much of them if rules are based upon opinion.
I’d be interested to hear your opinion if the rules need modifying or not to assist. Item number 6 for example needs an opinion and as we already know they can vary! It was interesting that the protest notes highlighted the difference in specification of toestrap backing supports between the bulkheads. Maybe that needs ‘firming up’. Whatever you have in the front you have to have in the back. That way it takes opinion out of the equation.
Regards, Woodsy.I haven’t read any of the comments on this subject except on this forum but would like to offer a simple practical solution to what I’ve always thought was a virtually impossible rule to police and interpret. The Cadets use this system which is a simplified Lambole test like the Finns and Europes use.
The hull is placed on a round bar at an agreed mid point and the bow must swing downwards to touch the ground. If not weight has to be fixed to the boat until it does. Very basic I concede but at least everyone will feel a little more on a level playing field which is important in all measurement matters.
i have no problem with the 10% rule which is more about structural soundness than weight concentration but the statement that no attempt to concentrate weight at mid point or any other point is too vague. Define mid point, indeed define point. Primary measurers of which there are fewer and fewer in all classes need to be miracle men and women with x ray vision to be able to assess build materials and make decisions or recommendations regarding possible weight concentration. we need to accept that weight has gradually become more concentrated in boats over a long period of time as new building methods have been adopted. Builders are caught between the devil and the deep blue sea. Build a boat which is slow in the eyes of customers or oneself or one that is on the pace and the same as others that might not quite be to the letter of the rules but perhaps in the spirit of a modern forward thinking class. Most development in classes is made in this way. Remember we are not sailing round in boats built exactly to the original plan and if we had to there wouldn’t be a Class.
As Jesper has already reportedly bravely stated, the horse has already bolted and I would hope the practical solution outlined above might help reign it back in to most people’s satisfaction.
Interestingly the Solos have never had a weight concentration rule and gradually over time the Class has accepted that with modern construction methods more weight has been concentrated in the middle area and lower down and that making a fuss about it is counter productive. Ironically its actually made the boats stronger and longer lasting.
Tony Thresher
Interestingly, I think that my mid-1980s OK Dinghy might fall foul of that suggested rule 1…and i’m not sure that it’s really contravening the spirit of the rule.
The transom is, I think, lighter material than the bulkheads at either end of the cockpit. But doesn’t that make sense? Lower loads, lighter material? Of course, I’d have to check if it’s really thinner, but that is my impression.
H
I have not been studying the case referred to but I feel I should comment as arep to the Technical Committee currently. I would like to hear comments about this and basic construction rules.
There has been discussion at length recently about construction of wood boats and framing/stringers/floor stiffening etc..My own feelings are that we have become too bogged down in construction methods and details at the risk of making boats less well constructed and more expensive.
There have always been issues with weight in lieu of correctors in the bottom of boats etc. and weight concentration is an issue that is greatly discussed.My opinion is that trying to control the construction in minute detail is counterproductive and confusing and if we want to control the c of g of the boats we have to have a way to measure it. There have been various offerings as above or as per the cadet class or a swing test. This has been tried before but apparently unsuccessfully.
As far as special materials are concerned (carbon etc.) – I am in the “if it is not on the list you can’t have it” camp. You may disagree with me – I am always open to other opuinions.
Rule alterations should be done to make it easier for measurers and owners – not more complex.
Terry’s summing up is sound and made with good experience.
I will listen to this with interest and put my comments to the Tech committee accordingly. The members of the committee do read this site and your views will be seen. They do try to do the best for the class and there is no interest in doing otherwise.
Bill
Hi..
This weight issue is of course being discussed on other websites and discussion forums as well. Your views here are very interesting, and they would be worth sharing on the new forum on Facebook. OK dinghy European discussion forum.
Brgds
LaugeTerry said:
It is the measurer’s responsibility to ensure that the boat complies to the class rules.
but rule 4.5 says it’s the owner’s responsibility to ensure that the boat complies to the class rules.
It’s no good expecting measurers to find unequal construction or any other deliberate attempts to centralise the weight: you’ll notice that it’s the National Authority who can drill holes to determine the natureof the structure, not the measurer, probably explains why it happens so rarely!
I think Tony Thresher’s on the right track: what’s required is something that measurers can measure. If finns, europes and cadets can do it, I can’t imagine its impossible for oks.Dave Cooper
Hi,
Yup, a swing test would do it, but it would have to be a ‘full on’ test like the Finns if it’s to work, otherwise all that would happen is the ‘centralisation’ of weight would move further forward a bit to get a ‘bow down’ attitude in a simple suspension test.
Er, 2kg centreboard bolt washers anyone?Bob
Dave,
I don’t disagree with you, i am not saying that i think the rules don’t have room for improvement i have just provided my interpretation of what they say.
If someone really wants to cheat it is easy enough to build the cheat into the construction of the boat that is very difficult for a measurer to find, but it is still the responsibility of a measurer to ‘try’ and identify these things.
The issue in Black Rock was far more simple. I am pretty sure that you as a UK measurer would not have issued a certificate to a boat that had 5kg of backing plates attached to the back of the toe straps. Yet the boat in question presumably had been measured in Denmark, so there is clearly an inconsistency in terms of measurement from country to country. I think the Chief Measurer has a role to play here.
Swing and Tip tests have been discussed and discarded several times. No harm in revisiting them, but i recall tests in the past proved unsatisfactory.
To Tony Woods point i think there will always be an element of judgement needed by measurers.
I would think about it like this: What does the fitting do and how strong does it need to be?
A toe strap backing plate does a similar job to a backing plate on the towing eye of your boat (in fact it probably takes less load). If you wouldn’t use the same backing plate on your towing eye that you used on your toe straps then you are probably concentrating weight.
I am sure the debate will rumble on, but i hope we don’t see anymore of the character assassination i have read on facebook over the last couple of days.
Cheers TerryHa, yes, the stuff on facebook is a bit unrestrained, isn’t it?
First chance, I think I’ll have a go at a swing test, see what results. Fortunately I have a ready supply of boats that I’m pretty confident are of reasonably uniform construction.
If it pans out I’ll report back on here.
DaveDavid Carrol posted something on facebook to suggest we just remove the root cause and drop the min weight by 5kgs.
Maybe it is time to do that. It would certainly deal with the problem – at least for a while.Hi Folks,
Well said Terry
My 2p worth from Finn experience is that a c of g swing test only takes a few minutes and is accurate
It would remove any debate and controversy which does the class no favours
DC makes a good point on hull weight reduction. That decision shouldn’t be taken lightly as a change would lower the ideal helm weight and potentially change the ideal hull shape and rig set-upPerhaps a 1kg weight reduction effective from say 2017 would be a nudge in the right direction and give people time to transition. Burt should have saved up for a new boat by then!
Anyway it looked like some great sailing in Melbourne – what a close finish!
Hopefully see lots of you at Northampton later this month
Cheers
NickI’d go for getting rid of weight concentration rule rather than dropping weight. Gradual change is what is required and as the weight concentration rule has been pushed a little for many years it is perhaps time to finally get rid. Losing 5kgs won’t get rid of the issues we are talking about here if they are not enforced effectively. I’m sure other builders will confirm that an OK hull could be built perfectly strong enough, weighing 67kgs with max correctors and a high % of the weight near the mid point using modern construction methods and without the use of carbonfibre! Whats the point? You’d change the boat completely and out date a large proportion of the fleet very quickly.
Tony
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