Splicing a Y in 12 strand?
 

What sort of splice would be best to splice a length of 9mm Dyneema 12 strand into the standing part of some 12mm? The primary load will be on the 12mm and the 9mm serves as a position control. I am thinking maybe a double Brummel but the load may vary between the legs and I am not sure how the splice will react if one side goes slack.

Hmmm
 

Hello,
Two problems: the smaller diameter might not hold as well as needed, even with a longer bury; and a Brummel might create unacceptable distortions in the primary line's standing part as well as the smaller line's end.
What is the application? How much of an angle will there be?
Fair leads,
Brion Toss

Not about boats unfortunately.
 

We are lowering and retrieving a 1,000 kg package of geophysical instruments into a cave. Total hoist is about 30 M. We have rigged a block on an A frame out over the top ledge but there is a shelf about half way down that we have to get around. I rigged a line to a block on the opposite wall for a control line but there is a second shelf further down that fouls the control line if it is attached at the load. The current procedure is to lower it about half way to the shelf then tie on the control line but we have to retrieve the package every 10 days and climbing out on the A frame to put on an icicle hitch on the way down and again to remove it on the way up gets a bit harry. I was hoping for a splice that could pass over the block.

We are using the Dyneema because of the low stretch. The package hangs a few inches off the mud bottom so we need to know exactly how much line we have out.

Option?
 

Hi again,
I think I understand. It sounds like the control line takes a relatively trivial load, so a sufficiently secure splice probably isn't an issue. But it also sounds like you are talking about a long, annoyingly tangle-prone line. So how about a sliding control line? The simplest thing would be a round sail thimble, with the primary line running through it. The control line would be spliced around the thimble. You'd tend the control line from the wall opposite that first shelf. A snatch block might be required if there's too much friction on a thimble, which could drag the control line down. The control line would be cast off as the load came up, and would be resting on the load when the load was all the way up.
Would this work?
Fair leads,
Brion Toss

The round thimble worked great.
 

I was probably over thinking the problem. Spliced a ring on the control line and it solved the problem. Now I can get back to work on the boat. :-)