Shot.

Steve

Been doing a little thinking over the weekend and the topic of shot lines and shot weights came up. For those of you doing deep dives, 100m plus, how do you rig your shot line? Also what is the preferred shape of the shot itself? Obviously you want it to go straight down and not go off track, but what shape achieves this?



Lots of pictures would be great.



Thanks

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Bear

Hey Steve,

from the deeper stuff that I have been involved with I don't think there is much of a science involved or any real perfect solution. Most of the shots have relied on the target being big enough that divers should be able to find the big lump of rusty stuff or at worst the debris field IF the shot is close enough (within reason).

The weights on the shots themselves have ranged from a large "dog food" can with lead poured into it, multiple small boat sand anchors chained together, weightbelt webbing with combinations of 3lb, 6lb and 8lb normal weights, and combinations including having small reef anchors or grapnel hooks attached.

Some learnings though:

• The rate at which the vessel approaches the target influences how the shot travels through the water as the rope (especially 100+ m) does create significant drag through the water.
• Be mindful of your surface support crew IF you intend to recover the shot as pulling a large amount of weight back up can be a fair effort, not so much of a problem if you intend to cut/unclip the line (last man up).
• The size of the rope makes a significant difference in 1) comfort while divers hang off the line during deco, and 2) deck crew being able to grip the line during recovery and without damaging hands/fingers.

Least successful is the grapnel hook/reef hook combination (for the dives that I have been part of) as the grapnel/reef seems to unsettle the shot's deployment and can cause spirals which disrupts the descent onto the site resulting in unsuccessful deployment.

Something like the "Max Factor" is overkill and the Sydney Project's length of railway track is possibly similarly excessive.

Reef Anchor: http://www.boatshop.com.au/shop/media/100-106.jpg
Grapnel Hook: http://www.boatshop.com.au/shop/media/100-061.jpg

Cheers [edit to correct typo's and added some links]

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Steve

Thanks Bear. One other point I forgot to mention is tensioning arrangements. I have only ever used a top tensioning arrangement: i.e. the line runs freely through a ring on the buoy and is weighted at the top end by a small weight. I felt this worked well in keeping the length of the shot as short as possible and thus reducing the descent time. Has anyone here ever compared a top tensioning shot line with a bottom tensioning arrangement: i.e. the line runs freely through a ring on the weight and is lifted at the bottom end by a small buoy?



I feel like the top tensioning arrangement would drop better and be easier to deploy but this is just a guess.

Thoughts?

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wizbang

Bear covered it perfectly. I agree with it all.
The only thing I would add is that a loop at about 15-20m that the deco station can be clipped into via a V'd bridle makes setting it up and disconnecting much easier.

If using the BIG pink buoys then make sure there is the agreement that if it goes under that "the current is too strong" to dive. DOH

I could add a few more nice-eties but they are really for the station more than for the shot.

Edit: We did try the top tensioning system a couple of time with little and again with a bit of current. We dropped the idea, it was more hassle than it provided in benefits.

Bear

Hey Steve,
Might be worth trying to contact Rowan Stevens from www.vicshipwrecks.com as he made mention of a similar system that his "Red October" group uses during his presentation at the 2003 Oztek seminar.

Cheers

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Andy T

In my experience top tensioning is very easy to rig, but there is an issue you have to be careful with. You need a reasonable amount of counter weight for it to work, esspecially if you are using a thick shot line in a lumpy sea. This means that divers comeing up the line must be careful or they get a wack on the head. It can be a real pain when the counter weight is hanging at deco depth and the sea is choppy. In theory bottom tensioning would solve these problems - but I have never tried that so there might be other issues I am not aware of.

DaveB

My club uses bottom tensioning as standard, but not to the depths being discussed here - however I don't think that will make much difference to our system.

A suitable length of line (1 1/3 depth roughly) is wrapped arround a large buoy made from a 20 lt plastic barrel. The weight and small buoy being together at the end. When ready to drop the whole thing is chucked overboard. The large buoy then wizzes around merrily as the weight plumets, so speed of boat doesn't matter.

As the weight hits the bottom the wizzing reduces in tempo as the small buoy heads back up putting tension on the line.

We are going diving the weekend - I will try and take some pictures.

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David

Drmike

Dont often use weighted shots for deep dives as its too hit and miss in strong currents and hard work. Generally on the deeper stuff we tie the end of the line to the anchor and drop the anchor. Once GPS and sounder confirm position held and good a diver swims or more usually scooters down the anchor line to the wreck, unties the end of the line then swims it over to the wreck and ties it to the exact spot we want to be tied in (with a breaker).

One advantage of this is we often have 2 lines to the surface, the upline and in an emergency the anchor line. That has come in handy a few times

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wizbang

I like this system alot I just don't want to be the guy using his bottom time at 100m+ tieing in the line from the anchor.

Grassy

Don't worry Wiz, thats why we have Gav and Dave