WEIGHT UP!

Though seem­ingly in­signif­i­cant, weights are an im­por­tant com­po­nent of a dive setup that should not be over­looked

Asian Diver (English) - - Research, Education & Medicine - By Marty McCaf­ferty, EMT-P, DMT, and Patty Seery, MHS, DMT

Early in dive train­ing, stu­dents learn that there are three el­e­ments in­volved in buoy­ancy con­trol: the buoy­ancy com­pen­sator (BC), weights and lung vol­ume. Although most divers are fa­mil­iar with the need to be prop­erly weighted, many do not un­der­stand all that it en­tails. Stu­dents and ex­pe­ri­enced divers alike make two com­mon er­rors when it comes to weight­ing: div­ing while over­weighted and fail­ing to ad­just the amount of weight used in re­sponse to changes in equip­ment and en­vi­ron­ment.

DON’T WORK TOO HARD

Im­proper weight­ing makes it harder to achieve neu­tral buoy­ancy. Many divers who wear too much weight do not even re­alise they are over­weighted. The ex­cess weight means that to achieve neu­tral buoy­ancy, the diver has to put more air into the BC blad­ders, which can cre­ate a more up­right pro­file in the wa­ter. The up­right po­si­tion in­creases drag when swim­ming, caus­ing the diver to ex­pend more ef­fort and con­sume more air. Un­der­weighted divers can also be­come sig­nif­i­cantly fa­tigued while try­ing to stay down. In ad­di­tion to in­creas­ing breath­ing-gas con­sump­tion, ex­tra ex­er­tion can el­e­vate de­com­pres­sion stress.

GET IT RIGHT

You may have heard a diver say, “This is how much weight I al­ways use.” While field test­ing and prior ex­pe­ri­ence can be use­ful, this state­ment shouldn’t be the end­point of a di­a­logue about weight­ing. Proper weight­ing re­quires thought and prac­tice, and the amount of weight worn is not fixed. Over the course of our lives, we ex­pe­ri­ence change in mus­cle mass, body fat and phys­i­cal fit­ness. Equip­ment, in­clud­ing wet­suits, wears out and gets re­placed. Dive en­vi­ron­ments dif­fer.

All these fac­tors af­fect buoy­ancy and re­quire ad­just­ments to the amount of weight used.

To de­ter­mine how much weight you need, con­sider your body weight, the ex­po­sure pro­tec­tion you will be wear­ing, the weight of your equip­ment and the en­vi­ron­ment in which you will be div­ing. Start with weight equiv­a­lent to 10 per­cent of your body weight, which is a good base­line for a 6mm full wet­suit. For a 3mm suit, use 5 per­cent of your body weight. Re­mem­ber that these per­cent­ages are sim­ply start­ing points.

Dry­suits and thick neo­prene ne­ces­si­tate more weight to counter the suits’ buoy­ancy than do thin neo­prene or dive skins. Body com­po­si­tion (mus­cle den­sity, for ex­am­ple) will in­flu­ence whether more or less weight is needed. Div­ing with an alu­minium tank also re­quires more weight than div­ing with a steel tank.

Salt­wa­ter is denser than fresh­wa­ter, thus in­creas­ing the buoy­ancy of im­mersed ob­jects and re­quir­ing more weight to de­scend. Dive train­ing typ­i­cally be­gins in fresh­wa­ter en­vi­ron­ments such as pools, quar­ries or lakes, so new divers should con­sider that even if they are wear­ing the same ex­po­sure pro­tec­tion they will need to add weight for ocean div­ing. The ex­act amount of ad­di­tional weight needed will vary from per­son to per­son. Per­form­ing a buoy­ancy check in each sit­u­a­tion will help de­ter­mine the cor­rect amount of weight to add.

SE­CURE IT

There are sev­eral op­tions avail­able for how and where to se­cure your weights. A weight belt is the most com­mon method of wear­ing weights; there are belts that ac­cept slide-on weights as well

as pocket belts that can ac­com­mo­date ei­ther solid weights or soft weights

(bags filled with lead shot). Weight belts are easy to ditch in an emer­gency as long as you keep other gear clear of the belt. A shoul­der har­ness is some­times used when the buoy­ancy of a ther­mal pro­tec­tive suit re­quires more weight than can com­fort­ably be worn around the waist.

In­te­grated weight pock­ets and har­ness sys­tems of­fer a cou­ple of ad­van­tages over belts: They can be con­sid­er­ably more com­fort­able, and they of­fer im­proved abil­ity to ad­just trim. But un­like belts, which have a sin­gle point of re­lease, har­nesses and in­te­grated sys­tems may have more than one re­lease point. This is cru­cial in­for­ma­tion for the diver and dive buddy to dis­cuss prior to div­ing – and to re­mem­ber in the event of an emer­gency. A down­side to us­ing weight pock­ets is that it may be more dif­fi­cult to add or re­move weights if ad­just­ments need to be made.

STAY TRIM

In ad­di­tion to wear­ing the right amount of weight, make sure it’s po­si­tioned to op­ti­mise un­der­wa­ter trim. Cre­at­ing a level pro­file in the wa­ter makes you more hy­dro­dy­namic. Dis­trib­ute the weights as equally as pos­si­ble from side to side; you should never feel as though you are list­ing to one side while div­ing. You should also con­sider the weight of your scuba tank and the style of your BC when plac­ing your weights. The tank can be moved up or down in the tank band to fa­cil­i­tate op­ti­mal body po­si­tion­ing in the wa­ter. Back-in­fla­tion BCs have a ten­dency to push the diver for­ward (face down) in the wa­ter, so plac­ing weights to­ward the back can help to counter some of this for­ward pitch, es­pe­cially at the sur­face. While weight pock­ets on the back of your BC can help with trim, they also present a hazard in an emer­gency be­cause buddy as­sis­tance is re­quired to re­move them if ditch­ing weight be­comes nec­es­sary.

Fins can be pos­i­tively, neu­trally or neg­a­tively buoyant, and each type may re­quire com­pen­sa­tion. An­kle weights

can help off­set a more buoyant lower body half, but they may be a chal­lenge to ditch, be­cause you have to reach to re­lease them. If your fins are neg­a­tive and cre­ate a down­ward pull on the lower half of your body, mov­ing weights higher on your body or shift­ing your tank higher in the band can move up your cen­tre of grav­ity to pro­mote a more level pro­file.

Re­view­ing where and how your buddy’s dive weights are placed is an es­sen­tial com­po­nent of ev­ery pre­dive check. Each buddy needs to know how to jet­ti­son the other buddy’s weights in an emer­gency.

Learn­ing to de­ter­mine proper weight­ing will en­hance your en­joy­ment of dives as well as your safety. Hav­ing a good un­der­stand­ing of your base­line weight­ing needs and the fac­tors in­flu­enc­ing your buoy­ancy will aid you in ad­just­ing to a va­ri­ety of en­vi­ron­ments and con­di­tions.

ABOVE A weight belt is the most com­mon method of wear­ing weights

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