Blood knot

What it connects

The blood knot joins two lengths of line end to end. It is the knot behind a hand-built tapered leader, where each section steps down in diameter from the one before, and it is the knot for adding a length of tippet or repairing a leader that has been cut back. Animated Knots describes it as primarily used to join two lines of similar size, such as sections of leader or tippet. NetKnots calls it a tried and true fishing knot and a favorite of fly fishermen, and says it works best with lines of approximately equal diameter.

It is a line-to-line knot only. It does not tie to a hook; for that see the Palomar. For the whole question of what goes in a leader and why, see leaders and tippet.

Basis: official on the descriptions (NetKnots, Animated Knots)

Compatible lines

• Monofilament to monofilament of nearly the same diameter: this is what every source below is describing. Orvis's page is written for monofilament.
• Fluorocarbon to monofilament of similar diameter: the Field and Stream test tied it (10 lb fluorocarbon to 10 lb mono) and measured it. See the tests below.
• Braid: Status pending. None of the pages we read describe a blood knot in braid, so we do not recommend it there. For braid to leader use the Alberto or the double uni.
• Lines of clearly different diameter: not what the knot is for. See the next section.

Basis: official on the pages named; the braid line is a gap in the record, not a finding

How much diameter difference it tolerates

The sources do not agree on one number, and none of them is a lab result. Read them as the rule of thumb each maker or writer works to.

• Orvis (its Learning Center blood knot page): the knot is for monofilament where sections do not vary more than .002 inch in diameter.
• Tom Rosenbauer, quoted in a Mid Current roundup: he ties a blood knot when diameters are within .001 inch, and a triple surgeon's otherwise or for fluorocarbon to mono.
• Orlando Outfitters (a fly shop's leader-building page, not a line maker): a blood knot can usually be tightened when the two materials differ by about .003 inch; if the diameters are widely different, double the lighter one.
• Lori-Ann Murphy, quoted in the same Mid Current piece, works to a "2-size grace rule" for blood knots and says the surgeon's is stronger when materials differ by more than that.
• Matt Supinski, a guide quoted there: with quite different diameters the blood knot may fail, and the surgeon's is very strong across differing sizes.
• Jim Vincent of Rio, in a 2007 Global Fly Fisher article by Steve Schweitzer: the blood knot for tippet diameters greater than .007 inch (4X), and the triple surgeon's for finer. The article gives no test data behind that.

So the spread runs from .001 to .003 inch across the sources, and the published figure from a line seller (Orvis) is .002. We use Orvis's .002 inch as the working limit, because it is the one stated on a page whose tying instructions we are following, and it sits inside the range of the others. Measure with a micrometer or read the diameters off the spools; "same pound test" from two brands is not "same diameter."

Basis: official on the Orvis figure; consensus and anecdote on the others; the choice of .002 inch is editorial

Turns per side

The sources give different numbers, and Orvis's depends on the line.

Status pending: the Orvis diameters, as printed, cannot all be right. Ordinary leader monofilament is not 0.17 inch thick, and the tiers are written inconsistently (0.17, then 0.15 to 0.10, then 0.009). We reproduce the page as printed and do not guess the intended decimals. What the page establishes is the direction: fewer turns on heavier line, more on finer. The count that NetKnots and Animated Knots both state is at least 5 and up to 7 per side. In the rest of this page we tie 5 turns for ordinary leader sections and go toward 7 on the finest tippet, which is editorial, and we check the Orvis page before settling on a number for any specific spool.

Orlando Outfitters says the normal number of wraps is 5, that you will need 4 or even 3 in very heavy materials, and that for a large diameter gap it can help to use 5 wraps in the thinner material and 4 in the thicker. We list that as one shop's advice, not a tested rule.

Basis: official on the quoted counts; the diameters are Status pending; the 5-to-7 working range is editorial

Strengths

• A smooth, slim, symmetrical joint that passes through guides well. Orvis's own instruction is that the barrels on both sides should form neat coils, and if not, cut the strands and start over (editorial reading: that makes a bad tie easy to see).
• It was built for tapered leaders. NetKnots describes the leader as a series of blood knots joining segments of about 24 inches in decreasing pound strength.
• In the one machine test of it we found, it kept 83% of the line's strength (below).

Basis: official (NetKnots, Orvis, Field and Stream)

Weaknesses

• It is slow. NetKnots calls the surgeon's the simpler alternative to the "more cumbersome to tie" blood knot, and Mid Current writers say the surgeon's is easier in poor light and cold hands.
• It tolerates little diameter difference (above).
• Tightening it alters the look of nylon, per Animated Knots, and the strand that starts inside ends up outside the wrap as it draws up.
• Guide Brant Oswald, quoted in Mid Current, says the double surgeon's may not draw up correctly for maximum strength. That is a point against the surgeon's, and it is one guide's observation, not a test.

Basis: consensus; official on the individual quotations

When the double surgeon's is the better choice

The double surgeon's is the better choice when:

• The two sections differ by more than the limits above. NetKnots describes the surgeon's knot as joining lines of equal or unequal diameters, and several sources in Mid Current say it handles a size gap that a blood knot does not.
• The materials differ: fluorocarbon to mono, per Tom Rosenbauer's stated preference for a triple surgeon's. (Our note: his is a triple, three passes, not a double.)
• You are tying in the dark, in cold, or fast on the water. NetKnots lists low light, cold hands and a hot bite.
• The tippet is fine. Jim Vincent of Rio, as reported by Schweitzer, recommends a triple surgeon's for tippet finer than .007 inch (4X).

The blood knot is the better choice when the sections match within about .002 inch, you have time to tie it, and you want the slim symmetrical joint, which is why Phil Monahan and Steve Hemkens, both quoted in Mid Current, say they still prefer it.

Basis: consensus; official on the quoted preferences; the summary is editorial

What the tests say

Almost nothing published settles blood versus surgeon's with a controlled test, and we found no side-by-side test of the blood knot and the double surgeon's with numbers. What we did find:

Read carefully: the Field and Stream pairing compared a 5-turn blood knot with a surgeon's knot of 3 turns, which is not the same count as either a double or a triple surgeon's as other sources name them. Treat 83% against 65% as one data point on one pair of lines, not a verdict that the blood knot beats the surgeon's. The honest summary is that the sources we could reach agree that both are strong when properly tied, disagree on which is stronger, and rest that disagreement on opinion.

Basis: official on the Field and Stream figures; consensus on the opinions; editorial on the summary

How to tie it

Steps follow Orvis's blood knot page, checked against NetKnots and Animated Knots. "Standing part" is the long line running away from the knot; the "tag end" is the free end you are working with.

1. Cross the two strands into an X, leaving 5 to 6 inches of tag end on each side (Orvis).
2. Wind one tag end around the other strand's standing part, working away from the X. Use the turns from the table above; 5 is the number NetKnots uses in its steps.
3. Pass the end you have just wound back through the loop at the X (Orvis). NetKnots and Animated Knots say the same: the tag end returns between the two lines.
4. Wind the other side the same number of turns in the opposite direction, then pass that tag end back through the same loop in the opposite direction from the first (Orvis).
5. Moisten the knot and pull both standing parts so the turns wrap and gather (Orvis says to pull quickly, NetKnots says slowly; the sources differ on speed). Orvis adds: don't pull on the tag ends while tightening. The barrels on both sides should form neat coils; if not, cut the strands and start over (Orvis).
6. Clip the tag ends close to the knot (NetKnots). We leave about 1/16 inch; that length is editorial.

Watch it tied. Animated Knots' blood knot page shows the sequence step by step, and Orvis' blood knot animation shows it for fly leader.

Animated Knots also gives a second method: overlap the two ends, twist them together for about ten to fourteen turns, make a hole at the center of the twists and pass both ends through it in the opposite direction. We have not tested it and the first method is the one we tie.

Basis: consensus (Orvis, NetKnots, Animated Knots); the tag-trim length is editorial

Building and repairing a leader

• Joining a new section: tie it in the order that suits you. Orlando Outfitters, a fly shop's page, says wrapping the thicker material before the thinner is easier; we list that as one shop's tip.
• A tapered leader: NetKnots' description is a series of blood knots joining segments of about 24 inches in decreasing pound strength. For where to taper and by how much, see leaders and tippet; this page does not give a taper recipe because none of the sources we read gave a recipe we could tie to a named maker.
• Large steps in size: double the lighter section per Orlando Outfitters, or use a double surgeon's or a uni.
• Check each knot before you fish it. Oswald's mantra in Mid Current, given for the surgeon's, is to test the knot before it is fished; we apply it here too. A firm pull on the standing parts after cinching is our editorial way of doing that.

Basis: consensus; official on the quotations; the pull test is editorial

What we don't know yet

• The intended diameters in Orvis's turns-by-diameter line. As printed, the numbers do not form a sensible sequence. Status pending until the page is corrected or a maker's own printed instruction is found.
• Any side-by-side machine test of a blood knot against a double surgeon's with the same line and the same turns. None found.
• Whether the blood knot has any published strength figure in fluorocarbon-to-fluorocarbon or in braid. The one number we have is mono to fluorocarbon.
• Rio's own leader-knot instruction. The 4X threshold above comes from a 2007 article quoting a Rio employee, not from a Rio page we read.
• How much hand-tied leader sections matter for the fish you are after. This guide does not address it.

Sources and how confident we are

Claim	Source	Confidence
Tying steps	Orvis, NetKnots, Animated Knots	Sourced
Orvis turns by diameter	Orvis blood knot page	Sourced, numbers Status pending
5 to 7 turns per side	NetKnots, Animated Knots	Sourced
.002 inch limit	Orvis	Sourced
.001, .003, 2-size and 4X rules	Mid Current, Orlando Outfitters, Global Fly Fisher	Reported opinion
83% blood knot, 65% 3-turn surgeon's	Field and Stream	Sourced, one test
Blood vs surgeon's verdict	none	Not established
5 turns as ordinary, 1/16 inch trim, pull test	us	Editorial

Sources

• Blood Knot — Orvis (How to Fly Fish) — the tying steps, the .002 inch limit, the turns by diameter as printed, and the neat-coils check.
• Blood Knot — NetKnots — five-turn steps; at least 5 and up to 7 wraps; approximately equal diameter; tapered leader of segments of about 24 inches.
• Surgeon's Knot — NetKnots — equal or unequal diameters; the more cumbersome blood knot; the triple pass.
• Blood Knot — Animated Knots by Grog — about six wraps; five to seven turns each side; similar size; the alternative twist method.
• The Strongest Fishing Knots for Each Type of Line, Tested — Field and Stream (John Merwin) — blood knot 83% and 3-turn surgeon's 65% on 10 lb fluorocarbon to 10 lb mono.
• Which Knot: Blood Knot or Surgeon's? — Mid Current (Phil Monahan) — the roundup of guides and writers, including the .001 inch and 2-size rules.
• Leader knots — Global Fly Fisher (Steve Schweitzer, 2007) — Jim Vincent of Rio on the blood knot and triple surgeon's; the 4X threshold.
• Blood Knot — Orlando Outfitters — the .003 inch note, varying turns, doubling the lighter line; the normal 5 wraps, 4 or even 3 in very heavy material, 5 in the thinner and 4 in the thicker for a large gap, and wrapping the thicker material first.

Related

Knots

• Double surgeon's
• Uni and double uni

Line

• Leaders and tippet