Personally I would find a full carrick bend a bit of a hassle, its an old bend developed when the anchor warp was expected to pass around the capstan without causing riding turns.
I would use a bowline in each part , ie joined through the eyes.
A figure eight is quite a good knot, which does not weaken the rope excessively. Climbers use it in preference to a bowline for this reason. Tied on a bight it is even better, so would make quite a good means of joining warps.
Some while ago I got into a discussion on the merits of the inside and outside bowlines. Each of the protagonists suggested that his version was stronger. So having a tensile strength testing machine available to me, I tried them out.
I found that (as suggested above) that both bowlines, tied in poyester rope, weakened the rope by between 40 and 50%. Tied in nylon the strength loss was rather less (about 35%), tied in Kevlar it was considerably more (60-70%). The difference between the inside and outside versions was hardly detectable.
Since I had available a considerable amount of old Kevlar rope, I tried to find a knot which could be used without excessive loss of strength, and yet would hold despite the slippery casing on my rope. In the end I used a hard eye set in a hangman's noose; it held well yet only lost about 35% of the strength.
This sounds like an excellent magazine article - can you not sell the results to YM or PBO? Did you try a pair of figure eights, as in my previous posting? it would be interesting to know if the reports of this method are correct.
That's my question too, Vyv. Do you tie one in the end of one line, then use the other line to follow it round?
I agree with the carrick bend suggestion myself. (And now I think of it, it must be almost the same thing.)
I've come across the knots-weaken-the-rope-too-much argument about the high-modulus stuff before -- "don't knot kevlar (or whatever) because it weakens it by 70% (or whatever.)" But so what? It's nearly always overkill to use this high-modulus stuff in the first place, so what does it matter if it loses most of its strength through knotting? -- there's still plenty left. The real answer I think is that's it's usually just wasteful to use it in the first place. Using a more appropriate material, and knotting it in the traditional way, seems a much more sensible alternative to me.
Tie one on a bight (doubled back) in one end of the first rope. Tie a single figure eight near the end of the second rope, feed the short length through the loop created in the first, then take it back and feed the free end to follow the "8" previously created.
The beauty of this joint is that the minimum turn made by any rope is two rope diameters, whereas in the bowline it is only one diameter. Thus the strength of the rope is reduced less. The main disadvantage is that it tightens up and is not as easy to undo as a bowline. Look at http://www.massey.ac.nz/~sglasgow//nzss/knots.htm which is a caving site, but there are many climbing sites that give similar info.
NEVER .... the eyes would work and fray the meeting parts.
There is a knot based on the blood knot that would be better, or if you do use bowlines, then pass one eye through the other and bring the other rope through, so that the eyes form a type of 8 formation. This way the eyes will stay closed and not free to work against each other.
No, this was more than ten years ago, before I retired. But I agree that it would make a good magazine article.
Incidentally, the weakening is due to the fibres on the outside of the bend being under greater tension than those on the inside. With elastic ropes (such as nylon) the stretch allows a degree of load sharing, while in ropes such as Kevlar the lack of stretch means that the inner fibres are hardly loaded at all.
Note that is not the knot I am talking about. The climbing figure 8 is always tied in a bight of rope, forming a small loop at the end. Joining two ropes together requires one loop to be through the other, unless you add a carabiner in the middle, hence the second figure eight is a bit of a puzzle. Just found a good description, at http://www.climbing.ie/knots.html
I agree with peterb regarding reasons why a more elastic rope loses less strength than a low-elasticity one, but the knot itself is also a considerable stress raiser. The higher strength climbing knots, like the figure 8, have larger radii due to not rounding another single strand.