How to Measure your Boat

Posted by on Apr 26, 2012 in Boat Maintenance | Comments Off on How to Measure your Boat

When must a J24 be measured?

A J24 must be measured any time it’s competing in one design events (rule 2.5.3) and the certificate must be carried aboard (rule 2.5.6). Fleet 26 policy gives you a one year grace period from when you first begin racing with us, although your boat must be measured before you may compete in districts, regionals, nationals or continentals. All boats are measured at worlds.


How do I get a measurement certificate?

Certificates come from the national class. You can get one in one of two ways:

  • When you buy a boat that      already has a certificate, you file a change of ownership form with the class.      This needs to be signed by both the previous owner and the new owner, and      a processing fee paid. (currently $15). The class will check and update      its records, and print and mail a new certificate to you.
  • If you need to certificate for a boat that hasn’t been      measured, or for which the certificate has been lost or invalidated,      you’ll need to get the boat measured. This must be done by a certified measurer (rule 2.7). Once the measurement is      completed, the measurer will file the form with the class and give you a      photocopy. The class will send you a bill for processing, enter the data      from the form into their database, and print out and mail a form. The      processing fee (currently $15) is waived once per boat.

Here is a description of the full process from the class website http://www.j24class.org.


What parts of the boat do you measure?


What sort of things invalidate a measurement certificate?

Any change may invalidate the certificate. Usually if you replace a sheet or halyard, we’ll presume they’re close enough to the old ones that they don’t invalidate things. However, keel repairs, replacement of any part of the standing rigging, and a whole host of other changes do invalidate the certificate.

Change of Ownership invalidates measurement, but if the measurement is current, you may be able to transfer the certificate.

Occasionally, the International Technical Committee will make a rule change which requires all boats to be remeasured. These are fairly rare, and usually we don’t force everybody to update their certificates immediately. Instead, we’ll just check the new things as boats change hands. However, if you’re going to a big regatta, like Nationals or Continentals (e.g. North Americans), You should probably check with your measurer and get any such updates.

The technical committee is careful that any changes in rules or measurements is done in a way that will not require boats which remain “as built” to make any modifications. All such changes that I’m aware of were done to catch modifications which were done to get an unfair advantage.


If I’ve only made a small change to the boat, do I need to get a full measurement?

Probably not. If you’ve only made a minor change (for example, a new headstay or mast, or keel or hull repair), we should be able to remeasure just what you’ve changed and file an update. Sometimes, however, such a change may require something else to be measured too (most commonly re-weighing).

If you modify the keel or gelcoat in any way, you must get it checked out by a measurer. If the bottom of the boat has been damaged, please contact your measurer before beginning repairs. Some modifications require written documentation from a measurer. (rule 3.1.2)


How do you measure the keel and rudder?

The boat needs to be presented on a trailer or stand, so that we can easily access the keel. Ramp launching guides should be removed if present, as we need to access all parts of the keel, to put a series of templates around it to check its shape. we also check the draft and the thickness of the trailing edge. (rule 3.3)

we’ll mark the keel with a pencil or felt pen to help us place the templates correctly

We also weigh the rudder and measure the rudder’s draft and rake, and several aspects of its shape. the rudder needs to be off the boat for weighing it, and mounted on the transom for measuring draft and rake. (rule 3.4) The process takes 10-15 minutes.


How do you measure the weight?

The main weight we measure is called the “basic dry weight”. There is also an All up weight which is normally calculated.

The boat must be presented dry and empty of everything except the standing and running rigging. All sails, gear, required and optional safety eqipment, must be removed. The measurer will climb through the boat opening all compartments and removing anything that may be there, checking for wetness, and for existing corrector weights. (3.7.1)

Then the boat will be lifted with a crane and a load cell, and the weight recorded. The hoist is preferably done with a lifting strap attached to the keel bolts, although we can use a sling if it’s dry. It needs to be a windless day, or even better, indoors.

The boat needs to be dry, inside and out. water sticks to the skin of the boat and it will continue to drip for several hours. This makes a difference of several kilograms. Depending upon what needs to be removed, complications with the crane and so forth, the process may take as little as 5 minutes or as much as an hour. If the boat is underweight, corrector weights must be installed fore and aft. See the description in the rulebook (rule 3.7.2, and Plan A) for exactly where to put them. Your measurer will help you with this. The correctors must be sealed in place with fiberglass to prevent tampering. (a small source of confusion may be that there are two separate sets of correctors, one that may be supplied by the builder (rule 2.8.2), and one which is installed when the boat is measured. (3.7.2))


How do you measure the spars?

The Mast must be presented down, and on sawhorses or equivalent. We only measure a couple of things on the mast, but they are critical. The most important is the permanent mark, which is 7725 mm below the fixing point of the headstay, and is an indelible scratch or dimple made in the surface of the mast. the lower contrasting band is there to help measurers find it later. We also measure the upper contrasting band, the spreaders, and the spinnaker rings.

Once the rig is up, we measure the tip weight of the boom and the black band there, the position and height of the mast, and the length of the headstay. We use the permanent mark for all of these. Note that we detach the headstay from the bow as part of measuring it. (Rule 3.5)

We also check to make sure the running rigging is legal, the standard fittings are legal and in the right place, the height of the lifelines, etc.

Then we’ll go below and check whether the mast is properly secured and whether the sink’s drain is being collected properly.

Measuring the mast while down only takes a couple of minutes, but taking it down and putting it back up again often takes a long time. Doing the other rig measurements only takes 10-15 minutes.


What restrictions are there in the running rigging?

Rule Application Min Dia Max Power Ratio
3.5.4b Mainsail   halyard (wire) 3mm   (1/8″)
3.5.4b Mainsail   halyard (rope) 8mm   (5/16″)
3.5.4c Jib   halyard(s) (wire) 3mm   ( 1/8″)
3.5.4c Jib   halyard(s) (rope) 6mm   ( 1/4″)
3.2.5 Second   set of lifelines (wire) 3mm   ( 1/8″)
3.5.4d Boom   vang wire strop (305mm) 4mm   ( 5/32″)
3.5.4d Boom   vang / strop (rope) 8mm   ( 5/16″) 8:1
3.2.5 Upper   lifelines (wire) 4mm   (5/32″)
3.5.3a Backstay   and bridle (wire) 3.9mm
3.5.3a Shrouds   and forestay (wire) 4.7mm   (3/16″)
3.5.4a Spinnaker   halyard 6mm   (1/4″)
3.5.4h Backstay   adjuster (rope) 4:1
3.5.4n Spinnaker   boom uphaul (rope)
3.5.4e Spinnaker   boom downhaul (rope)
3.5.4k Spinnaker   sheets (rope) 8mm   (5/16″)
3.5.4f Mainsail   outhaul (rope/wire) no   minimum 6:1
3.5.4g Cunninghams   (rope/wire strop) 6:1
3.5.4i Mainsheet   traveler control (rope) 2:1
3.5.4m Reefing   lines
3.5.4j Mainsail   mainsheet (rope) 8mm   (5/16″) 6:1
3.5.4l Headsail   sheets (rope)

In addition, there are a number of prohibitions. Elastic cord is disallowed in the running or standing rigging (rule 7.1.19). This includes the backstay adjusters. However, you can use it (for example) to secure the throwable lifesaving device. Titanium is specifically prohibited (rule 7.1.18), as are other exotic materials, unless they’re available on the open market at competitive prices with non-exotics.


How do you measure the sails?

If we’re measuring a lot of sails, we’ll make a set of templates on the floor of a large room, using masking tape or mylar sheets. Measuring sails this way only takes a minute or so each for the genoa or jib, and about 5 minutes each for the main and spinnaker. The sails are held against these template to make sure that they are within specifications. If we’re only measuring one or two sails, it may be more convenient to just measure it directly. We also record the royalty tag number and check to make sure the materials tag is valid. Sails must be measured for any regatta that’s a worlds qualifier, so we tend to do a lot of them at that time. You can help speed up the process by presenting the main with the battens removed (as they are measured separately) and being there to help get sails rolled up and out of the way once they’re done being measured.


What is the Permanent Mark?

The Permanent Mark is a scratch or dimple in the front side of the mast that is exactly 7725 mm below the center of the fixing point of the headstay. (rule 3.5.2 (e). Placing it is a job for a measurer. a 20mm band that’s there to help future measurers find the mark is placed just above it. It’s used to measure the position of the mast in the boat, and to measure the forestay length.


what are the contrasting bands for?

The lower band is there to help measurers find the permanent mark. The other three (at mast head, gooseneck and outer end of boom) are the farthest extent that a sail can extend. No part of the sail can overlap any part of the contrasting band.

The bands are placed by measurers. Please don’t try to put them on your spars without the help of a certified measurer, although feel free to refresh them if for some reason they have been damaged. If you’re not sure, your measurer is here to help.

Class rules are that the contrasting band be at least 20 mm wide (rule 3.5.2(d). 3/4″ electrical tape is 19.1 mm wide. It’s unlikely anyone will protest you for having bands less than a millimeter under width though. If you’re concerned about this, ask your measurer to double up the bands.


For some reason, Sparloft (new zealand) masts come with the contrasting bands and permanent mark already installed. Nearly all of the sparloft-installed bands I have measured have been placed incorrectly. They use a material that’s quite hard to remove. I’ve tried to make them stop, but they keep doing it. I like their masts a lot, with this one exception.


What must I carry aboard while racing?

Part C of the measurement form is called “Inventory of Required and Optional Equipment“. It can be found here along with the rest of the measurement form.

According to rule 3.8 and 4, you must carry:.

  • A Bucket of not less than 9 liters (2.4 gallons)      with lanyard attached.
  • An Anchor and chain of not less than 6kg (13.25      lb) and at least 40 meters (131.25 ft) of anchor line, attached. Yes,      anchoring in Puget Sound or Lake Washington with a line that short will      probably not work, but that’s what the rule says.
  • One Outboard Motor that weighs at least 14kg (31      lbs), securely stowed under one of the main berths or aft of the sill of      the companionway, and 2 liters (.53 gal) of fuel.
  • At least one Compass. It must be capable of      instantaneous reading only, and not capable of displaying stored headings.      No GPS compasses, and GPS may not be used while racing.
  • A fire extinguisher.
  • At least one lifejacket for everybody aboard.
  • A throwable lifesaving device with a sea anchor      attached, on deck, ready for use.
  • Equipment capable of disconnecting and severing the      standing rigging. A hacksaw is sufficient.
  • A first aid kit and manual.
  • The measurement certificate
  • The completed inventory of required and optional      equipment.

Obviously the papers should be in a waterproof container. The Racing Rules of Sailing and the sailing instructions should probably be in there too. The outboard, anchor and battery (if carried) must be secured against movement in a capsize.

Recent Changes:

  • The outboard used to be required to be at least 3.5 hp.      There’s no longer a minimum. The 3.5 horse 2 strokes that many of us use      are now banned for retail sale in most countries, and 4 strokes are      heavier, so they took off the horsepower rule.
  • An 8kg battery and working running lights used to be      required. No more. For our evening races, I think it’s a good idea to have      them anyway. The battery may weigh no more than 25 kg.
  • a working flashlight is a really good idea, but is no      longer required. I recommend one of the new LED batteryless type.
  • a two way radio (e.g. a marine VHF) is a very good idea      but is no longer required.

All together, the boat, rigging and the gear listed on the inventory must weigh no less than 1345 kg (rule 3.7.3). This is called the All Up Weight. Sails are not included in this weight, nor is personal gear like foulies or lunch. In theory, your inventory could be checked on the way in after a race and if it doesn’t match (for example you’ve drunk some of the water listed on the form) you could be DSQed.


How does one become a measurer?

To become a measurer, you need to take a course given by the J24 class International Technical Committee. These classes are given every few years, usually at the world championships. Once you’ve taken the class, you need to measure a few boats under the supervision of an experienced measurer. The worlds are a good place to do this, because all boats must be measured before competing. It’s actually a pretty interesting job, and measuring at worlds, while a lot of work, is also a lot of fun.

Fleet 26 has three measurers:

In addition, Paul Bogataj and Jack Christiansen are certified measurers but they no longer have J24s and aren’t really current. For other fleet 26 contacts, click here


Why do you measure in metric?

The J/24 is an international class, and nearly all countries use the metric system. It’s much easier for an American measurer to use Metric than for a French, or Italian, or Japanese measurer to use the English system. However, the J/24 was designed in the US, so there are a number of measurements that are conspicuously odd in metric, but not if you understand the boat’s heritage.

Converting between English and metric tends to be the source of errors, so we don’t do it. We use metric tape measures and scales.


Where can I get forms, manuals and rulebooks?

All of these are from the J/24 class international web site http://www.j24class.org.

  • The measurement form is what we use to create a      certificate.
  • The Change of Ownership form is used to transfer      a certificate from one owner to the next when boats are bought and sold.
  • The Rule Book is the most important and      reliable. While there are a few errors in it, in most cases it should be      regarded as the final arbiter. If you’re a member of the class, they will      mail you a paper edition every two years.
  • The Measurement Manual is a guide for measurers.      It describes the jigs, templates and techniques we use. It’s unfortunately      full of typos, so if you’re not completely sure, contact your measurer      before modify your boat based on anything it says.

What is a Gin Pole and how does one use it?

A Gin Pole is a temporary mast set up next to (usually forward) of the main mast, to help you raise or lower the mast. It’s not a difficult procedure but if you’ve never done it before, I strongly recommend you get help from someone who has. All of our measurers have done it numerous times. The pole needs to be 20 feet long and stiff enough it can support at least 300 lbs. The mast doesn’t weigh that much, but you’ll be leaning on the butt of the mast during the process. a 2:1 or 3:1 block and tackle makes the job easier, and you’ll occcasionally find the need to cleat the tackle, so a horn cleat is a good idea.

Here’s a short list of bad things I personally have seen with gin poles. Don’t let them happen to you! :

  • the      pole moving on the deck while under load. this resulted in the mast      falling and being damaged.
  • the      pole itself being made of too-thin material and buckling.
  • one of      the shrouds coming uncleated. I’ve seen this several times, but it’s      always been caught early enough to avoid dropping the mast.
  • a      rachet block failing to let the mast come down once it’s been hoisted.      don’t use rachet blocks.