Crotch-strap question

[jrtonkin]

Ok, I'm sure there's a good reason why things are done the way they are... Now I want to find out what it is. In most other applications I'm familiar with (rock-climbing, the trapeze-harness on a sailboat, flying-systems for theatrical use, fall-arrest systems) the crotch-strap has been replaced with a band around each thigh that is attached (usually with two seperate bands) to the waist belt.

These are applications which require use of the legs, and weight-support in the vertical direction, so those can't be reasons why BC's use the front-to-back strap. Additionally, the thigh-band is generally considered much more comfortable. (Especially in shock-load situations)

Another possible advantage to using a thigh-band (although this one is pretty negligible) is that it would give you a good place to attach the top of a pocket; out of the way of cannister lights or anything else you wanted on your hip. (This only matters to me since I'm still in the process of acquiring gear, and I don't think the LDS would appreciate me attaching pockets to the rental wetsuit).

So, why aren't things done this way? Just tradition? Convenience? A life-endangering reason I havn't thought of?

Thanks for any answers,

Jamie

 

[devjr]

The question you're asking harks back in time to when diving began. The early harness systems used a crotch strap to center the tank and prevent the large diameter double hose regulator from bumping the back of the head. Most divers didn't like this strap for several reasons. So, when the compact single hose and the backpac came along the manufacturers eliminated the strap although the pacs were still designed with a token slot to accept a strap. This was hailed as a needed simplification and a great advance.

Divers agreed, and from that time few used a crotch strap and was subsequently forgotten with the invention of the stab jacket. Due to the design, including snug fit with small arm holes and a wide, stiff belt, the extra strap was simply unnecessary as the tank was very stable without it. Elimination of the strap was not only more comfortable, quicker, but also functionally advantageous because it allowed the diver to don the weight belt before slinging on the tank, a great saving in convenience and effort.

The advent of wings and cave diving apparently generated a desire to design in more longitudinal stability. Hence, some genius reinvented the strap with much fanfare. Evidently, the one strap is considered sufficient for this purpose. Incidently, it has also contributed to the weight belt falling from favor, replaced by BC pocket weights and attached D rings. This is a continuation of the struggle to outfit the diver with more sophisticated and expensive gear while keeping the task load and complexity within acceptable limits.

 

[Wendy]

Although the previous post may have been accurate on the history of crotch straps ( I'm not a history kinda person) I can't agree with other parts of the post.

I first added a crotch strap to a Mares BC that I owned. It kept the bc from riding up, especially at the surface when it is inflated. It just helped keep the bc where it should be. For those that are thinking that I was wearing a BC that didn't fit, my BC did fit just fine, but I swim horizontal and never go vertical and in that (proper) position a BC tends to move around some.

Now I dive a b/p and wing set up. I have a crotch strap as part of the harness. I have seen the thigh things that the origianl poster referred to in climbing type activities, but I don't think that they would work well in diving. It doesn't seem that it would be easy to remove your gear in or out of the water with that set up. I still where a weight belt with my crotch strap. The weight belt is put on before I but on the rest of my gear. So the weight belt goes on under the harness. If the weight belt has to be removed in an emergency you just pull it out from under. If the weight belt buckle come un done during your dive you don't have to worry about accidently loosing the belt because it will be stopped by the crotch strap. I don't need to buy integrated weight pockets or anything else.

So to answer your question I think the back to front crotch strap is used because it offers stability, easy in gear removal, and simplicity (DIR).

 

[devjr]

Unfortunately, the BC designs which followed the patented SP stab do not always afford consistent positioning and stability. The crotch strap addresses these inadequacies. The wings harness is a retrograde copy of 1950's style gear.

One problem with the stab is that it is a one fit device. If it is stable over a wet suit then it will be too loose over a skin. The armhole is key to longitudinal stability. The old backpac was stable because the wide straps formed a continuous loop. Pulling on the waist belt would tighten the shoulder straps.

I have a Beuchat Masterlift which has the same problems as Wendy's Mares. It only works well with a crotch strap. I found a solution when a LDS persuaded me to try a Seaquest 3D(out of production). This one works, like the old backpac it has a continuous loop arrangement, but in this case it supports back inflation. Crotch strap not needed.

 

[Iguana Don]

The single crotch strap is all that is needed, since no shock load is needed. The single crotch strap keeps the BP/Wings down where they are supposed to be and also is used as an attachment point for your scooter. Also having straps around your thighs is mucking things up a bit. Keep things simple and in an emergency situation you will be thankful.

K.I.S.S.

ID

 

[Mverick]

ID is right.
On the subject of the crotch strap I usually wear a Dry suit or a Full suit. Even with my 3mm on I don't even notice the strap being there. I don't want 2 straps that I have to worry about if I want to take off or put on my BC underwater.
Also, the strap doesn't support much weight. I don't have to rest on it either. I use one on both my backplate and harness and my Transpac.

 

[Divesherpa]

I set up my sidemount harness by incorporating a climbing harness into it. Gives me a great place to clip off bottles

 

[Joe R.]

I do love this site! I too use my weights under the harness but also have the ABS+ system and use a tank weight. I like the idea of not having to drop all the weight at one time. One thing I do know is that if you 'drop the weight belt' from under your harness it will hang up (thats the way they fall) and its not easy weaving them through...especially when you "have" to drop them. So either you have to really practice this or divy your weights up...I think???:blahblah: :gunslinge

 

[Shadow]

Devjr,

I, too, have a Beuchat Master Lift BC, and it rides up terribly. How/where did you attach a crotch strap? Is this something you did yourself, or did you have to take it to a shop?

Also, I have trouble getting enough room on my torso for my weight belt and the cumberbun of my BC because I'm very short-waisted (and somewhat short - 5'4"). I end up having the cumberbun around my rib cage, above the weightbelt. Should it do up on top of the belt? Would a crotch strap pull the BC down too low so that I can't do it up (my belt is 28 pounds and the cumberbun isn't big enough to go over it). Thanks!

Anybody else have this problem?

 

[devjr]

Shadow, looking at my Masterlift Equalizer there is a small slot on the bottom of the plastic pac. It is almost unnoticable but it is there for attachment of a strap. You need a piece of one inch webbing about 3 feet long, and two small slides or buckles. These are common mil. surplus items or can be found at any marine store or dive shop.

You have too much weight on your belt. Your small size and short waist are not conducive to this arrangement. You probably should purchase a negatively buoyant tank such as the Scubapro "shorty" 72 cu ft 3000 psi tank made by Faber or a Faber 80 cu ft 3500 psi tank. These are -6 lbs. I can see reasons why you shouldn't let the cumberbun slip down too low. The cumberbun and crotch strap may hinder donning of the belt. However, you may wish to invest in a shot belt instead and not attach anything to it. Then put it on first and so under the strap. If the belt is still too fat you may, unless you are doing deco diving, be forced to reduce the belt weight further and accept some positive buoyancy. This is compensated as you go deeper anyway.

If you place the weight belt outside the strap you will have to put it on after you strap on the BC/tank and this seems problematical. However, a soft belt which is very smooth in contour should be safe under the strap, letting you put the belt on first, then the tank. Ditching the belt should be practiced at least once before doing a deep dive. Remember, the cumberbun may still ride over the belt but give it a go and see what happens.

Fit a crotch strap and see if the cumberbun is pulled too low for the outside belt. If it is, and if the belt is still too fat, something more creative may have to be found. It is an expensive proposition to buy a tank and belt and someone may ask "why not buy a different BC instead?". That is a legitimate question, and something in a back inflate with weight pockets may be the answer. I'm sorry for coming up with all the expensive solutions but the problem with your gear is pretty fundamental. The thickness of the weight belt is just too great in proportion to your waist.

If none of the above are appealing, you may wish to consult with a shop. They may have a line on some tank ballast weights, a "keel" weight or something similar. I don't think putting weights in the BC's pockets are the answer, kinda defeats the purpose. One more thing, in shopping around, ask the dealer if the Beuchat cumberbun can be extended. Don't forget that the waist strap length should also be looked at.