Drop/Clump Weight


#1

Hello,

After successful use of the platform to survey shallow water marina fish assemblages, we are moving on to hopefully look at some unsurveyed deepwater rock structures (~200fsw) near the cables running from Miami to the Bahamas on the Florida shelf.

I’m looking for any designs of a clump tether weight to eliminate a lot of the tether drag at those depths. There are a lot of topics on the forums however I can’t find any finalized designs. I know @Walt_Holm mentioned having a design he was happy with I’d be interested in seeing. I also saw the use of one on the gripper test video and it just looks like some dive lead strung on the tether with a beacon light. Is this the most effective method?

I guess what I’m asking is does anyone have a photo or materials list of a clump weight system they’re content with?
Also any tips for deepwater deployments appreciated, especially if the vessel can’t be anchored.


#2

Did you ever figure out a good clump weight set up? I will be getting a Trident soon and interested in some deep water exploring.

I was thinking of using a downrigger and cannonball weight and then fixing a carabiner for the tether with a short length of heavy fishing line to the breakaway clip. That way you could still free the tether if the weight snagged on something.


#3

I would also be interested to hear if anyone has experience of a good clump weight setup for a trident.

What depth am I likely to require a clump weight when using a Trident? I will be working in depths of about 60m?

Alaskasurf, have you tried the downrigger setup? This is exactly what I intend on trying once my Trident arrives.


#4

I didn’t yet. I think the downrigger is going to be overkill and it sounds like a 1-2 weight should be sufficient. Walt Holm has a good post in this thread 'Clump weight' system to reduce tether drag

I tried dropping a 4lb weight off a fishing rod with a carbiner clipped to the tether but encountered two problems: the fishing line somehow wrapped around the tether and I got a lot of drag from the tether, the Trident had trouble pulling tether through the small carabiner I was using. I could try with a larger carabiner or ring.

Using Walt’s suggestion of 1-2lbs, next time I’m going to try wrapping a 1lb length of lead rope fishing weight around the tether about 75-100’ above the ROV. This should be easily movable along the tether, relatively snag resistant, and unlikely to damage the tether, it also should be easy to reel onto the spool and not have to remove it every time. I will also try his strobe idea for a reference point while diving deep.


#5

I noticed increasing trouble with tether drag past about 150’/50m. Any current worsens it, anchoring the boat helped. If in currents, I will also try placing those weights every 50’ or so along the tether to help keep it straight down. Will report back, but a cold snap here will keep me out if the water for a bit.


#6

Hi @Tim-H:

For a 60m dive you should definitely use a weight of some kind. I use a weight even for a 30m dive- in calm conditions, you’ll note that the trim of the Trident is improved if you cancel out the buoyancy of the tether above the ROV. If there’s a current running, the weight will hold the tether in the current and keep you from being blown off of your target. I generally place the weight about 10m above the ROV.

Unless there’s a strong current running, the weight doesn’t have to be large. Many times I’ll just use something like a wrench, attached to the tether with a short piece of line using a prusik knot. You can use much heavier weights if you want, the tether is plenty strong- but that just is more weight that you have to haul up at the end of the dive.

If visibility is not that good, it’s handy to have a strobe light on your clump weight. That will help you keep oriented with the ROV.

Next time I’m out on a boat with a Trident, I’ll try to snap some photos of all of the above.

-W


#7

Thanks all - appreciate the advice - one of the many great things about Trident is the community.


#8

I’m thinking about a clump weight that can be attached to the tether and not make the tether any more prone to snagging. It is already tough enough to keep your tether from snagging!


I’d like to hear your thoughts or possible a source for purchasing something like this, perhaps a type of fishing tackle that will work.

Another piece of info that would be nice to know is how much buoyancy per foot of Trident tether in both fresh and saltwater. That would let you place the correct clump weight for the desired dive depth.


#9

I’m thinking about trying this set up next time I’m out.

1.5 oz Rubber Core sinkers, pried open to tether diameter (pounded a flat head screwdriver through opening). Spacing these out along the tether every 40-50’. If done right the tether fits snuggly but can be easily removed, they are small and very streamlined.

About 50-100’ from the tether I’m going to wrap a few spirals of solid lead rope, available as lead rope or pencil weights in fishing dept. It is very soft and easy to snug up. It could be wrapped loosely so the tether can easily be unwrapped or done tightly Once proof of concept is figured out, I will spray paint them with Plastidip so I don’t have to handle the raw lead. Both can be easily wrapped on to the thether reel.

I think a relatively heavy weight closest to the ROV will be necessary because you will want to feel a difference in the controls when you try to move it, otherwise as soon as you stop forward thrust, it will pull you backward as the weight sinks again.


#10

I think the idea of the clump weight is more to reduce drag than just minimize the tether bouyancy. If you are in 250’ of water and have 300’ of tether out and a clump weight at 225’ then the ROV will act like it only is dragging 75’ of tether instead of 300’.


#11

Hi @alaskasurf:

There are a number of different ways of thinking about how a clump weight changes the way the ROV drives. But I mainly think of it as isolating the ROV from all of the tether that is above the clump weight. So whatever current is pulling on that tether, whatever buoyancy is pulling on that tether, the ROV doesn’t see it. Small ROVs like Trident are extraordinarily sensitive to correct buoyancy and balance. If you have a pool, drop your Trident in and drive it to the bottom. Now pull straight up on the tether with just a small force, a couple of ounces. It will definitely change the pitch and the driving characteristics of the Trident.

There is another subtle benefit of having a clump weight- it improves your ability to navigate the ROV at deep depths. If you are in reasonably calm water and have a strobe light on your clump weight, then if you look around with the ROV and spot your clump weight strobe, this will let you know exactly where your boat is with respect to the ROV- it’s directly over the strobe light.

There is a downside of having a clump weight if you are doing large transects. In your example above, if the clump weight is 75’ above the ROV, then whenever you try to drive more than 75’ away from the clump weight you’ll start dragging the clump weight from its vertical position. You will definitely notice this change while driving.


#12

Tried the clump weight yesterday, placed about 1 lb of lead spiral wrapped around the tether 50-60’ above the Trident. Worked well, a little bulky but winds onto the tether reel nicely and is easily moveable.

I was suprised how hard it was to find the light I clipped to the weight, I assumed if I did a 360 I could locate it pretty easily, might need a brighter light, was using a small fishing light that clips to lures, probably depends greatly on visibility.


#13

I tried my Trident off a boat for the first time today, in about 15 meters of water, with a gentle current (1kt) and an unhelpful wind also drifting the boat.

I used a clump weight, in the form of a diving weight attached to the tether with a prusik, and also a small strobe.

I found the clump weight very helpful for negating the tether drag, but I did struggle with the fact the boat was blowing across the water which resulted in the tether very quickly becoming taught and making manoeuvring difficult. With practice and experience I am sure it will become easier.

I presume (hope) that without the wind, drifting on a tidal current shouldn’t be a problem because the whole column of water is moving?

Does anyone have experience of flying their Trident in a current, and do you have any advice?

Thank you


#14

I’ve had trouble with the boat drifting as well. Once that tether gets taught, I find it hard to turn around and get ahead of the tether drag. Anchoring definitely helps the most, especially if you see something you want to spend more time checking out, if you drift over it, it may be hard to find again. Also unless you are on a fairly flat bottom, you do have a risk of snagging your tether on something during the drift.

Regarding tidal drift, 15m may be fairly doable and uniform but the deeper you go, the more likely there will be a change in tidal current with water depth, but still better than the boat drifting with the wind.


#15

I’m curious if most everyone is using the Velcro strap to attach the tether to the aft end of Trident. I am wondering if not using this strap would result in better handling in currents and would let you pivot the ROV around when the tether becomes taught more easily. I almost always use the Velcro strap for ease of recovery purposes and since most of my dives have been off docks or the shore it has proven very helpful to have it.


#16

That’s a good thought, I think the tether definitely affects it more if velcro’d. But if lifting it out of the water I can see the tether giving up at the attachment over time. The first time I drove without the velcro, it it felt more responsive but I didn’t know how to drive it yet either. I’m thinking of trying without and fishing it out of the water with a landing net.


#17

Yesterday I had a few dives with the Trident off a boat in approx 45m of water using a 1kg clump weight tied about 15m above the Trident, with about a 1knot current and a f3 wind. Almost every time the tether went taught, and once that had happened I couldn’t turn the Trident around to try and drive back towards the cable. The best I could do was sit there and enjoy the view looking backwards as we drifted along.

There are a lot of currents where I live and only very brief slack waters, which means many of my dives will be drifts, so I need to try and solve this. :thinking:

In my (limited) experiences my boat has always been drifting faster than the Trident.
I would therefore like to try and rig the trident so the tether is attached forward on the vehicle, so that in the event of the tether pulling the Trident along it will be facing forward, and therefore much easier for me to drive it towards the cable and create some slack. Failing that I will at least be able to watch the drift facing forwards!

Does anyone here have any thoughts / suggestions about the best way to do this?

I’m thinking maybe loop the tether around the tail then run it forward and attach it with something to the cover of the vertical thruster? I’m mindful of keeping the point of balance somewhere relatively central to aid manoeuvrability, yet far enough forward to ensure it points in the correct direction when being towed.

Thank you


#18

I have thought of rigging up some sort of tow harness for the Trident. Perhaps you could “troll” the Trident off a downrigger or fishing rod, just screw a small attachment point to the threaded inserts. Then you could put your weight on the trolling line and just leave enough tether slack for manuverablity. If you use a good length of 200-400lb fishing leader material I think you would wouldn’t have to worry about fishing line getting sucked into the thrusters.