Windsurf carbon boom wear
Updated: Jan 11, 2021
Let's leave the grip out of the discussion. The nuisances of boom grip may plague aluminum and carbon booms alike and its caprices depend largely on the owner.
Instead let's focus on what's under the grip. Let's examine the types of wear that originate from flaws in the design and construction of booms and their ancillaries. Such wear may escalate to the point that a boom is rendered unable or unsafe to serve its purpose.
Spots where wear is most likely to commence are:
the clamp area,
the tail tubes - pin holes
the tube arms - harness area
the tube arms - pin holes
For those who rig their windsurfing gear on grassy or carpeted grounds non of the following applies. For most though, windsurfing is synonymous to sandy beaches and rigging is performed under circumstances that cannot guarantee proper gear hygiene.
Inevitably, sand enters the interface between the boom clamp and the boom neck. As the boom articulates within the clamp seat, sand works its way into the composite structure. The firmness of the binding deteriorates and wobbling commences despite the repeated tightening of the clamp screws. The boom is taken apart, at this point, to detect wear in excess of 0.5 mm of the carbon wall thickness at the neck. Mind you this is vital carbon fiber missing from its task of carrying torsional and axial loads. This material deficit jeopardizes the boom's reliability and unless booms are made with the provision for carbon to be wasted in such a fashion one has every reason to start worrying.
Handy men have been known to rectify such situations by laminating layers of fiber reinforcement over the damaged area for as many times as are needed to maintain a boom to life. Alternatively and only with the use of a mold, the boom's neck may be refurbished with a mineral formulated epoxy compound in order to maintain the original dimensions and attain a perfect finish (see pic). Quite often such interventions are combined with an upgrade of the clamp fitting, to one that is more robust and suits a bigger diameter than the OEM's. All this adds up cost and weight to an already expensive item that is usually marketed as ultra light and able to withstand the most demanding of environments.
Reason says that if sand has no chance to ingress, wear will not develop. This is true and possible. For sand not to ingress there must be no space in the interface between the boom's surface and the clamp seat. The best condition for this is a true tight fit between a smoothly finished clamp seat and an equally smooth boom neck, the two being in full contact along the entire circumference. Both elements must be perfectly round and free of surface imperfections. Like a shaft and a bushing. These characteristics are easy to detect on a boom after removing the clamp fitting. Again, they are: smoothness and roundness.
With clamp fittings it is a little bit less obvious and the following brief presentation of the various makes aims at providing some insight and sense for a proper evaluation. Clamps with rubbery insert seats all around the circumference are fit for the job. So do clamps that hug the boom neck with two sections that form a continuous seat surface with just two tiny seams along the parting lines. As the screws are tightened the two sections are brought snugly together and the seams become smaller. Sand has no chance with these:
Other types of clamps that boast material cut outs for decreased weight or cosmetic accommodations and two section clamps with a step between the sections fail to meet the condition of continuity along the circumference. Sand may enter and accumulate in crevices and finally enter the sliding interfaces. These types of clamps are suspects for accelerated wear to a bigger or lesser degree:
TAIL TUBES - PIN HOLES - TAIL HOLES
With use, all booms with internally fitting tail tubes exhibit ring-like wear at the extension location to which the boom is most frequently adjusted. The wear appears as a ring scar and may, sooner or later, evolve to an annular ditch all around the tube. There is no remedy to this besides the replacement of the worn tail.
Yet, not all booms are equal candidates for the race to the point of no return. Booms that exhibit excessive clearance between the clip pins and the pin holes on the boom tubes or the pin wells/holes on the tail tubes are the 'winners'. The pins' duty is to secure the tail at a desired boom length and any clearance between the pins and their seats allows the tail to slide in and out of the boom tubes, ever so slightly. The booms' flex and recovery action, while windsurfing, causes the axial reciprocation of the tail tubes in and out of the boom tube bores that house them. The travel is as large as the clearance between the clip pins and their collaborating holes allows. Any clearance is bad! Anything that allows carbon to rub against carbon or against the hard thermoplastic housing of the boom clip leads to wear. Add some sand in the sliding interface and things become worse.
Unfortunately, the aforementioned clearance is absolutely necessary to facilitate the easy operation of the boom clips. The holes on the boom and tail tubes are customarily drilled or molded for a free running fit with the pins so that the latter don't get stuck as corrosion adds abrasive deposits around them. Nevertheless, some booms boast smaller pin-to-hole tolerances than others and opt for a longer life.
So grab a boom, lock the clips to a position and try to push n pull the tail in n out. If you feel motion the boom is signed up for wear. If it doesn't budge, don't rest assured as it may do so later, after a few rough sessions which will dilate the phenomenally snug holes. You need to investigate further for the design factors that will prevent the enlargement of the holes. Check this list:
Ample wall thickness where the boom is drilled for the pins (3-4mm wall),
Molded or machined pin wells on the tail tubes !
Proper tolerances for the drilled holes.
Perfect and alignment/coaxiality of the holes bores
The above four factors define the quality of service that one is to expect of a carbon boom's rear end. It is worth explaining a little bit more about it, despite the somewhat technical approach needed. If a windsurf boom maker wants to maintain a comfortable clearance fit so that the clips snap in and out without effort, serious compensations have to be made in order to make sure that the pins are true stabilizing elements of the sliding group: boom+tail. It is a bad strategy to rely on the integrity and strength of the boom clip to hold the tail fixed. Testimony to this are the events of clips popping open, pins being yanked out of their plastic encasing, pins breaking whether plastic or metal.
The best way to establish easy clip operation is to make sure that the pins have a long land to slide on in both the boom tubes and the tail tubes. This means beefy tubes ends - >3mm wall thickness, and twice as deep solid walled wells in the tail. These two factors guarantee that the pin is laterally anchored in its seat and is not allowed to wobble and transfer breaking loads to its root or the clip that carries it. It is obvious that the pins have to be long to accommodate such a setup.
The length of the pins you can measure easily and the wall thickness you can eyeball once you remove the clips. The detection of the pin wells is pretty straightforward as well. The tolerance of the holes to the pins calls for more exotic measuring instrumentation - caliper. In the absence of such you may refrain to the am yanking test.
So to summarize, if the pins are long, the tail tubes feature wells instead of holes, if the boom's tube ends are beefy and if the assembled tail doesn't badge during the yanking test, then the boom is a go for ! One should still, always check on the integrity of all these components in the course of time to detect issues like hole dilation, pin clip cracking, pins missing and cracking on carbon.
BOOM TUBE WEAR at the harness lines
If wear is detected on the boom grip at the location of the harness line straps, take action before the sand enhanced nylon webbing of the straps starts gnawing at the boom's carbon tubes. Remember, carbon booms are lightweight tools and they need every fraction of their material to function properly and safely. Nearly 1mm of carbon wall is missing from the boom tube in the pic and what makes it even worse is that the wear is shaped like a notch, hungry for failure initiation. If it is only the grip that is worn, you may enhance the durability of the area by doing one more thing past putting new grip. You may install heat-shrinkable cable tubing, just for these 20 to 30 cm where the harness straps noose around. This stuff is readily available in hardware stores, get the plain version and not the one with the adhesive. If you don't have a dedicated heat gun, a strong hair drier will be just fine to make a nice snug fit.
The good thing with heat shrinkable tubing is that it is replaceable and cheaper than grip.
Crafty windsurfers may choose to replace the grip with a short length of Paracord braiding. The trade takes some time to master and the end result is bombproof.