Many owners ask about the torques required for keel bolts (studs with nuts). This page has been assembled over several years and is posted here .
The following is some info I posted for a Sadler 34. In the event the owner was not present when the keel was re-bedded and the yard told him they just tightened them as hard as they could!
‘I have seen quoted figures of 150 – 200 lb.ft. (200 – 275 Nm). I don’t know the material grade and am not certain of the diameter for these values, so here are some comparable figures for machinery.
For M20 bolts in 4.6 material (which I think would be similar for 316 studs) 185 Nm and
in 8.8 material (heat treated carbon steel) 476 Nm.
For M24 bolts in 4.6 material 320 Nm, in 8.8 material 822 Nm.
It looks from these values that 200 – 275 Nm would not be far off.’
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From another source, torques for keel bolts on Jeanneau SO37 are:-
M22 – 350 N.m maximum, 171 N.m minimum, 258 lb.ft maximum, 126 lb.ft minimum
M16 – 130 N.m maximum, 66 N.m minimum, 95 lb.ft maximum, 48 lb.ft. minimum.
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Here’s another file. Again, not a lot of difference from the others. It is important not to overdo the tightening as it is possible to crush the GRP, so I suggest you do not aim for the maximum figures. Beware – the metric figures are M.Kg, not N.m.
Keel bolt Torque Specifications. TABLE 6.5.2
DACROMATISED STEEL BOLTS TYPE 8-8.
| DIAMETER | TORQUE in M.Kg minimum | TORQUE in M.Kg – maximum | TORQUE in ft.lb – minimum | TORQUE in ft.lb – maximum |
| M14 | 5 | 9 | 36 | 65 |
| M20 | 13 | 27 | 94 | 195 |
| M24 | 23 | 46 | 166 | 333 |
| M30 | 45 | 90 | 325 | 651 |
STAINLESS STEEL BOLTS TYPE A4-70 and A4-80
| DIAMETER | TORQUE in M.Kg – minimum | TORQUE in M.Kg – maximum | TORQUE in ft.lb – minimum | TORQUE in ft.lb – maximum |
| M14 | 5 | 11 | 36 | 80 |
| M20 | 16 | 32 | 116 | 231 |
| M24 | 28 | 55 | 203 | 398 |
TABLE 6.5.3 STAINLESS STEEL BOLTS TYPE A4-55
| DIAMETER | TORQUE in M.Kg – minimum | TORQUE in M.Kg – maximum | TORQUE in ft.lb – minimum | TORQUE in ft.lb – maximum |
| M30 | 19 | 38 | 137 | 275
|
| M36 | 33 | 65 | 239 | 470 |
| M42 | 52 | 104 | 376 | 752 |
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There is some USA information on J109 yachts in a table here https://j109.org/docs/keel-bolt-torque-table.pdf that agrees pretty well with my figures. J109 keel bolts are 1 inch diameter.
Keel Bolt Torque Table
| Bolt Diameter | Torque Nm | Torque Ft/Lb |
| 1/2″ | 26.0 | 19.2 |
| 5/8″ | 66.0 | 48.7 |
| 3/4″ | 130.0 | 95.9 |
| 7/8″ | 190.0 | 140.1 |
| 1″ | 224.0 | 165.2 |
| 1-1/8″ | 420.0 | 309.8 |
| 1-1/4″ | 460.0 | 339.3 |
| 1-1/2″ | 795.0 | 586.4 |
This Table is derived from information in Table A7 from ISO/DIS 12215‐9.2. These values are for well-greased threads. Friction in the screw and under the bolt head makes up approximately 90% of the tightening torque and approximately 10% contributes to prestressing of the bolt. The user is cautioned to use good judgement in applying these values.
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Another one, ISO 12215
Bolt………………….Torque (Nm)
M12…………………………….56
M15…………………………….58
M16…………………………….71
M20…………………………….99
M24…………………………….172
M27…………………………….254
M30…………………………….343
M36…………………………….603
M42…………………………….968