When to Splice

There's a lot of snobbery surrounding splices and knots, as though knots are only used by hacks that can't splice. The thing is, I know perfectly well how to splice most materials--I've published several articles on testing of splices and knots--but I only splice when it is the logical answer. In fact, I find it embarrassing to have splices where a knot is the better choice.

It comes down to four differences:

1. knots are easier to redo
2. splices are stronger
3. splices are lower profile but longer
4. knots are more abrasion resistant in double braid

The Marlow Splicing Fid is my long-time favorite for 3-strand. You push it through to open a spot, insert the strand, no matter how frayed, and it pulls it back through. Very fast.

When to Splice.

High Strength

• Docklines
• Snubbers
• Rope to Chain (no other method will pass through the windlass)
• Safety Tethers 
• Jacklines

Won't Hold a Knot. This means Dyneema/Spectra in most cases. Fortunately, a bury splice is dead simple and a brummel not much more difficult.

No Room. Rubbing with tackle. Sometimes a knot will get in the way, though often this can be avoided by trying a different knot or rotating it 180 degrees.

Snagging. Splices are generally smoother to run, though flipping a knot over can help.

• Genoa Sheets
• Safety Tethers. 

Can't be Constructed Any Other Way

• Soft Shackles
• Adjustable Stropes

Adjustable strope. From "Keeping a Cruising Boat on Peanuts."

The Brian Toss Wand is my favorite for double braid. I use a cut-off hollow knitting needle for single braid.

When Not to Splice

Must be Re-Made at Some Frequency.

• Halyards. First, I like to cut a few inches off every few years to move any chafe spots. Second, halyards are sized for stretch, not strength, and as a result are massively over strength. 
• Most tackles. Should they twist-up or a component fail, knots are easier to re-do.

Splice Will Jam. A splice makes the rope fatter. Sometimes this causes a jam in a block. It also keeps tackles farther apart than a knot.

• Halyards
• Traveler
• Davit tackles 

Abrasion. A double braid splice caries nearly all of the load on the cover on one side, and it is vulnerable near the throat. A knot breaks inside and is thus generally unaffected by wear and UV.


Old Double Braid

Even if a splice would be nice, old double braid rope is impossible to splice, IMHO. The solution is either a knot (obvious) or a sewn splice. These can be just as strong as a conventional splice, although they do required protection from UV and chafe. When don properly, they'll last as long as the rope. Much industrial
splicing is sewn.

My genoa sheets, made from a salvaged big boat halyard.  The cover is 2-inch tubular webbing. This splice is 5 years old. From "Keeping a Cruising Boat on Peanuts."

Dynamic Rope

The tight cover makes a splice nearly impossible. Additionally because it is dependent on both the core and the cover the splice is complex.  Most industrial tethers are sewn.

This is my deck tether. 8 mm ice climbing rope.

a. Yes, those are screw lock carabiners. I keep them well-greased, and because of the boat design, they generally stay on the jacklines.
b. The rope is sewn. Do NOT try this unless you have done a lot of sewn joint testing.
c. One leg is 2', the other 10'. This is for a cat with narrow side decks and a wide fore deck. On my try I use conventional tethers. 

But note that I have a storage spot for the spare tether.