Kent chocks

[us5285]

My thoughts on the Kent style chocks. I`ve been racing D.N`s since the 2000-2001 season.I`ve had four types of chocks and have bellmouthed or bent all of them. What am I missing? It seems obvious to me that  the Kent chocks are at least stiffer than the standard chock. He`s basiclly made the outer flange of the chock thicker than normal.They have been running these chocks I believe for a couple of years now, has anybody heard of any reliability problems?
    As for cost, yes Jeff`s carbon bars are a bit pricey, but as the pictures that paul posted so beautifully illustrate, this chock modifacation is most certainly home buildable.I see about $15 worth of aluminum and nylon there. A saw a drill and a tap and your`e done. Not as sexy as Jeff`s but still quite effective. I`m machining a set out of 7075 aluminum bar stock and I still have only about $25 a set in them.
    We seem to be oddly selective in what we feel hurts the competivness of the class. Take for instance the new wide hounds many are now using. Effective ones are less home buildable than the Kent chocks are. They cost $85 and do nothing to increase the strength or durabilty of the boat. In fact a case could be made that they decrease the durability of the mast and the mast hound/tang specificly. There is certainly an increase of stress on the tang mast intersection when using the longer lever of the wide hound. On the most common mast/ hound / tang combination, the tang is butt welded to the fairly thin S.S. support inside the mast and there is no way to inspect the weld for fatigue or cracking. With the trend of pulling back very hard on the boom ( check out the twist in Matts mast in the runner tracks picture ) I`m surprised we have not seen a failure at that tang ( I`m not an engineer I`ve just seen alot of broken parts on racing stuff )
   Having said all that, does a piece of hardware that does not help the strength or durabiliity of the boat, and does help the performance of the boat , hurt the class? I don`t think it has. I don`t think the Kent chock modification would either.
   
   P.S. I don`t believe the two rules Paul has proposed would eliminate the use of the Kent stiffener.
 
   a) If you cut the outside flange of the chock down to 6.750 in. it would still leave you 1.125 in. on each end to run the bar.
   b) I`ve been running .5 in. hollow axel bolts in my front chock for two years now. E .RUNNERS 1f.

    CAN`T WAIT FOR ICE!!!!!!        Chris US5285

[John Davenport]

US5285’s comments are spot on.
Innovation is an integral part of this class and a big reason the class is so successful.  Think where we would be if development weren’t allowed.  There wouldn’t be near the interest if the boats hadn’t evolved into the cool rocket ships they are today.  I too find it odd that the Kent chock is being specifically singled out for the scrap heap after it has been found to be within the spec.  On the ballot the reason for the ELIMINATION of this class legal innovation is “Improper Introduction”, "cost" and "little benefit".
1.   Please, can someone from the Tech committee explain where the guidelines for “Proper Introduction” can be found?  If it is legal than there is nothing to introduce.  If it is Illegal, file a protest.
2.   If there is little benefit, than why is cost a consideration?  I don’t need Kent chocks to go fast.  If I want to spend a lot of money on things that look cool but don’t help my speed, then that’s my business.
His point that the wide hound rotator is correct too.  I bought one myself because I have had rotation trouble.  Here is an innovation that just might have been considered illegal and now there is a proposal from the Tech committee to specifically guarantee it’s legality.  I feel it is an improvement for sure, but there was no “Proper introduction”.
I know the tech committee is doing it’s best to serve the class, but I don’t find it proper to rule on a piece of hardware as legal and then introduce legislation to ban it.  What is the underlying reason for this?

Respectfully,

John Davenport
US4961

[Scott Brown]

I like the Kent chock.  It improves the boat without changing performance characteristics.    Nobody has to upgrade just to keep up. 

[Paul Goodwin - US 46]

Paul Goodwin - DN US46

First off, let me make one thing clear, the proposal that has been published under my name (to eliminate the Kent chock) has nothing to do with the Technical Committee. 

Personally, I like the Kent chock concept.  I think it has the potential to reduce some of the problems with the current chock design(s).  I don't think all of the bugs have been worked out, so I'm "waiting in the wings" to see how things progress before I make the change.  I have seen issues during the development of this chock, including during the last World Championship.

Now permit me to ramble ...

As far as the legality of the design - this was not an easy task for the Tech Committee.  The Committee was split on whether the chock is legal, and I still haven't published an Official Interpretation, simply because it is difficult to phrase without making it sound like "it's OK to use this illegal chock".

The legality of the Kent chock hinges in the reinforcing bar being a "runner stiffener".  As such, it must be attached to the runner (see Specs E.1.e, E.1.f, E.4, Interpretations E.Runner.11/14/89 and 7/1/92).  If it is not attached to the runner, then it is something other than a runner stiffener, and the legality becomes very questionable, or at least the bar must be within the runner cut.

So, back to my proposal.  I have heard numerous comments that the Kent chock was allowed only because it had been used for years without challenge.  Maybe there is some merit to this.  In any case, the Specification Management System (Article IX) states "Specifications, however complete, cannot anticipate every situation that may arise. If a point is not covered, a ruling must be obtained from the Continental Governing Group through the Technical Committee. The intended meaning and the basic principles of maintaining the DN as a one-design class shall be considered in interpreting any point not covered.  If a point is not clearly covered by the Plans and/or Specifications, it must be assumed to be illegal."

I think the Kent chock is clearly different than any chock design preceding it.  It certainly is different than the chock shown in the Plans, and has features that are hard to identify in the Specifications.  Because of this, I believe there was some obligation to request an Interpretation from the Technical Committee before using them.  This was never done, and there was never a challenge mounted, even though they were being used for years.

My proposal gives the general membership the chance to say "hey I don't like all these changes", and make the design illegal.  If the proposal doesn't pass (and I don't think it will) than we can say that it was fairly decided to allow this design.  If that is the case, than I plan on introducing another proposal(s) which would clearly allow the Kent chock design and introduce the "reinforcing bar" as a new piece of hardware and not require it to be a "runner stiffener".

As for the wide hound...
This was also discussed by the Technical Committee, and like the Kent chock, it was not unanimously endorsed.  However, there have been many variations on the rigging attachment to the mast over the years. and the common Sarns plate attachment is significantly different than the original DN design.  The Specifications make no mention of the size allowed for the hound, although it does make it illegal to use "a long fitting to connect the mast hound with the head stay" (Interpretation I.Fittings.11/23/87).  There was discussion in the Technical Committee about putting restrictions on the size of the hound hardware, however there is no mention of "hound size" anywhere in the Specifications, and the Technical Committee cannot make new specifications to suit it's desires.  The Tech Committee could have introduced a Proposal to put restrictions on the hound, but decided not to.

Personally I like innovation, and have witnessed many positive changes to the DN over the years. leading to a boat that is a joy to sail compared to the beast I first started with.  However, I also think there is an obligation to limit changes to the design, and proper procedures to follow when there is change.

[Paul Goodwin - US 46]

A couple more comments...

I mentioned that if the reinforcing bar was not a runner stiffener that it would have to be within the runner cut.  My bad ... If it isn't a runner stiffener, then it is most likely part of the chock or other plank hardware, and as such would be required to be within the maximum plank length (see Spec B.1).

Chris - The second part of my proposal requires the runner pivot bolt to contact the chock, and limits the size of any "washer" between the bolt and chock.  I was expecting this would make it clear that it would not be permissible to use the pivot bolt to provide pressure directly on the runner and bypassing the outside flange of the chock.

I was also asked to list some of the pros and cons of the Kent chock.  I thought I did this yesterday but so far it hasn't shown up on the posts.  Here goes attempt #2.  Keep in mind that I have never used a set of Kent chocks, so my opinion on them may not be worth much, a cup of spit perhaps.  I welcome any feedback from sailors that have actually been using these to enlighten us with their virtues.

PROS:

• Only the inside flange surface requires accurate machining.
• Only one width of slot is required (today European and North American runners/chocks have different thickness).
• US sailors can use European runners without modification (and vice versa).
• Chocks will be more robust since there is no outside flange to bend.
• Only one side of runner needs to be shimmed, cutting time to shim by more than 1/2.
• Existing chocks can be modified using simple tools, even previously bent chocks might be salvaged.
• Potential for reduced friction between runner and chock.
• Increased pressure between runner and inside flange of chock, providing better control over runner alignment.

CONS:

• More expensive than "standard" chocks, MUCH more expensive if high-modulus carbon bars are deemed necessary for performance.
• If many top sailors start using them, it will create "chock envy" and most racers will feel the need to make the change regardless of actual merit.
• The Kent chock design has more failure modes than the standard chock design.

[us5285]

   Hey Paul,
I don't want to get off on a tangent, but..... the hollow pivet bolt performs it's standard clamping function(however light that clamp might be). The bolt that helps attach the stiffener to the runner (E.Runners 1f.). Simply uses the axel bolt as a bushing. It would work but why bother, the Kent chock is so simple and good it would be a shame to screw with it. I like the pro/con list, although the chock envy sounds like a personal problem. I would also like to hear about the failures since I'm changing my chocks to the Kent system.
     See you at the Swap meet         Chris US5285

[Paul Goodwin - US 46]

If my proposal was to pass, then a hollow pivot bolt with a pass-through system allowing the clamping load between runner and chock to be applied via a "runner stiffener" would most likely be deemed illegal since the intent of the proposal is to not allow this.

One of the problems I've seen with the Kent chock has to do with the pivot bolt.  Since the stiffener must pivot with the runner, the bolt rotates relative to the chock when the runner pivots.  If the nut is stationary relative to the chock, then the bolt tightens and loosens slightly each time the runnner pivots.  This can lead to the pivot bolt loosening while your sailing.  One sailor had a bolt come completely out at last years Worlds, luckily the runner stayed in the chock until the end of the race, but a really nice carbon "stiffener" is somewhere on the bottom of Green Bay.

As for chock envy, note that Ron Sherry has never lost confidence in his chocks, and continues to use standard Sarns chocks with some success.

[us5285]

  good information, sounds like I need to either thru-bolt the axel bolt or set a bearing into the stiffener.
  I was just trying to make a joke about the " chock envy" you know "chock envy" ,I know it was bad....
  I personaly suffer from down wind light air envy and will pay almost any price for the solution.
       I'll be quiet now