Arbitrators Needed to Settle an Argument

Tighten the bottom line or loosen the top.

This is based only on gut feel and looking at the diagrams.

I agree with Lyn. Shorten the bottom line and loosen the top line.

If I understand the steering mechanism correctly you need to tighten the upper line to steer the net lower...

It seems to me there is a possibility that the board has been sanded down and that the balance has been altered, the center of gravity has risen higher...the board pitching upwards was addressed in the above video by adding weight to the base of the board thus lowering the center of gravity....but I'm just taking pot shots....but it seems to me that the length of the lines upper and lower are not that critical , it's the board rigging and design that guides the net....

Are the tops of the boards leaning one way or the other? Or are they always vertical? From my perspective it could be either...

But my gut says lower

Umm ... shorten the bottom line....or is this a riddle?

Lets try again. I added some more information that may help.

* The Chain bridles are tied up for shipping. when opened and in full array, they produce an angle of attack of 38º.*

These Trawl doors are referred to as Otter Doors. They are the most common used in the Research and Sampling field as they are extremely simplistic ( and in-expensive)

Their design dates back to 1500 France.

The nets attached to these Otter Doors produce 65% of the bollard pull of the entire gear.

Some of the doors shown on your answers are "V" doors which have a totally different High-Low pressure gradient than the older design Otter Door.

Midwater or Pelagic trawls tow entirely different also and have another more complicated design .

Also, these Otter doors, have 2 (two) bridle or leg lines...one TOP and one BOTTOM.

Can we look at it again. I can't give hints.

TOP line has more tension, than does the BOTTOM Line.

Line going to boat is at a steeper angle than the Top Line has rising due to the design and the floatation on the net.

When you mention tensions or pressure it makes me think that you need to even out the tensions on both lines.

This would mean to make the one longer that sees more tension in the hope that by the time it sees some pull the other one does as well.

The deal is this is an adjustment that you do on the boat where you have NO additional steel....you have only the two lines Top an Bottom of the Tie legs ( lines from the trawl to the Doors).

So, if I understand you correctly, you want to tighten the bottom line as a stopgap measure...? ....as opposed to redesigning the otter boards, or changing the rigging angles...or adding weights...?

Then by all means do so, if it works it works....

I say try it out. One experiment is better than a dozen theories...

Agreed. Otherwise, instead of attracting <...Arbitrators...> one will get opinionators.

This is a Stop Gap Measure used to fix a problem that comes up while onboard many research boats with no other means at hand.

In reality, when this happens,we generally re-gripp the entire net. That is, cut away the old, worn ropes and lines and re-tie the entire net to new lines and ropes.

There is seldom a need to adjust the doors except to replace the worn out steel shoe on the bottom or water logged planks every two years or so.

I wanted a definitive answer to corroborate my response to the Government Tech. This method has been in use since these Otter doors were first created.

It is ONLY used as an emergency fix, onboard, when there is no other recourse.

I've lost email contact with the Tech...so I suppose he gave up or didn't want to hear the answer corroborated by CR4...….

Clearly, from experience, you know the correct answer.

Although the intuitive answer seems to be the opposite, I think there is a simple way to explain it. When the rig is first set up the two lines are of equal length; during use the greater tension in the top line stretches it and the closely related portion of the net; to restore the status quo you need to shorten that line.

Late to another interesting discussion: if I'd responded to the original post I would definitely have voted to shorten the bottom line.

Me too. But being left handed, I usually have to do the wrong thing first, before i get anything right.

Thank you all as usual..... smartest bunch of guys on the internet!

I've never set nets before, but when setting a multi-furrow drawn plough behind a tractor there was a similar problem that would require consideration of a third option.

For the front of the board to be high implies that the pull vector from the boat is too steep. Thus the played out line is too short for the water depth OR the boat speed is too high causing the otter board to become a weight on the catenary created by the cable/ropes from the bollard on boat to the front of net. If you raise the connection onto the otter board (from the boat) [and maybe also shift that further back] that will provide more "front down" moment onto the board.

That is well thought out.

The scenario here is that the researcher has no tools on board or no skill in using said tools....he or she can ONLY use the Tie Legs ( bridles).

these types of Otter Doors are so very primitive, they are seldom used in large scale commercial operations.... researchers like them for the simplicity in setting and the low cost.....

Thank you again for your input.

OK, the pictures of the otter boards supplied by someone showed them with side chains and shackles that could provide that sort of adjustment. Surely on the boat they have a spanner??

If you can get the "pull" right, then the loading on all components is per design. If you fight it by other adjustments, then there is internal loading that is not per design.

I saw one guy with the wheels on a draw plough set to 45degrees with half a ton of ballast on the plough in an attempt to the plough to run straight when the discs were cutting. He wondered why wheel bearings were only lasting a few days and breaking axles occasionally. His tractor was also struggling to pull all that extra drag.

Took about an hour to reset the plough after we bought it from him. Wheel bearings lasted for years. We were able to gang that one behind another we were using.

If you know the original line lengths and you can measure how much they have stretched, then why not shorten the lines to their original length?

hA HA excellent.

Personally, I am an accumulator. I just sit and listen. ;-)

What is the reason that the 2 ropes between the otter board and the net attach at two separate locations on the otter board?

What would be the result if both ropes attached to a "spreader bar" that holds the ropes apart but attached at only one point to the otter board?

We do use that kind of attachment. I prefer this double line set up. That's all, just a matter of preference for these smaller nets...the larger nets we do go to a "Y" bridle.