Torquing bolts a pointless task.

[Sneaky Pete]

Boat is on the hard for winter maintenance. I have been cleaning some rust stains where the hull joins the cast iron and cast iron joins the lead on the keel. While boat is out would it be worthwhile to re-torque the keel bolts. There are eleven of them Ø35. Or is this a pointless task.
The boat is fourteen years young and I do not believe this has been done since new.

 

[elton]

It's never pointless to tighten bolts to the recommended specification. The required torque will stretch the bolt within its elastic limit, and retain a pull on the union. This will keep the fitting secure in future, and ensure the stresses are equalised across the union. Over-tightening can lead to failure of the fitting or the bolts; under-tightening can result in all sorts of problems. In any case it's easy enough to do, so why not?

 

[Topcat47]

+1. A couple of decent torque wrenches are vital components for any serious work.

 

[pvb]

Boat is on the hard for winter maintenance. I have been cleaning some rust stains where the hull joins the cast iron and cast iron joins the lead on the keel. While boat is out would it be worthwhile to re-torque the keel bolts. There are eleven of them Ø35. Or is this a pointless task.
The boat is fourteen years young and I do not believe this has been done since new.

Do you know what the torque should be?

 

[Sneaky Pete]

No. However I will phone boat manufacturer tomorrow for settings and if there is any kind of sequence when torquing.

 

[pvb]

No. However I will phone boat manufacturer tomorrow for settings and if there is any kind of sequence when torquing.

Not an Oyster, I hope!

 

[William_H]

Recommended torque for bolts is indeed to provide correct stretch to minimise damage from fatigue from cyclic loading as in engine head bolts. The torque is predicated on the structure being totally stiff ie not yielding to the torque. So all torque results in bolt stretch. However bolts through GRP into caste iron are possibly going to crush the GRP before stretching the bolts. likewise the bolt into lead may just damage the lead before stretching the bolts. So do not use a recommended torque for the bolts alone but rather consult the boat manufacturer as he well may have found that you cannot stretch the bolts to full torque in the substrate. If he can not tell you then just check tighten them to a reasonable but low torque.
It is a bit like my argument re stay tension. Wire manufacturer may recommend a tension for the wire to stretch it to minimise fatigue but that is predicated on a solid no stretch structure. (A caste iron hull might do it) but a GRP hull will often distort before you can stretch the wire.
olewill

 

[Daydream believer]

Yes, definitely torque to the manufacturer first :encouragement:

 

[Robert Wilson]

Yes, definitely torque to the manufacturer first :encouragement:

Problem is that Javelin30s don't have any detailed manufacture's advice any longer.
Anyone know of the torque settings for the Javelin30 would they please advise me.
Failing that, are there any rules of thumb for "general tightening"?

 

[vyv_cox]

This is some information I put together a year or so ago. Some of it is tabulated so I hope it will be readable. The document is in Word or .pdf, which I can send you if you e-mail me via the website.

Coincidentally, I was giving a talk on Saturday about mechanical problems that can lead to major problems at sea. One is undertightening of keel bolts, which will cause them to fail in fatigue. At least one well-known failure was caused by this .

Keel bolt torques.

This is some info I posted for a Sadler 34. In the event the owner was not present when the keel was rebedded 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, so here are some comparable figures for machinery. For M20 bolts in 4.6 material (which I think would be correct 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 150 – 200 lb.ft. would not be far off.’
There is some USA information in a table here https://j109.org/docs/keel-bolt-torque-table.pdf that agrees pretty well with my figures.

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.
Here’s another file:///C:/Users/vyvcox/Downloads/Keel%20Bolt%20Torque%20(1)%20(1)%20(1).pdf 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.
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 13 23 45 9 27 46 90 36 94 166 325 65 195 333 651
M20
M24
M30
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 M20 M24 5 16 28 11 32 55 36 116 203 80 231 398



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 M36 M42 19 33 52 38 65 104 137 239 376 275 470 752




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.

 

[jwilson]

I am not an engineer, but in general I am not a fan of messing about with keelbolts on GRP yachts unless there are signs of problems. I know surveyors who share this opinion.

The OP's description of "rust stains where the hull joins the cast iron and cast iron joins the lead on the keel" might or might not represent a problem. If there were clearly defined rust points matching bolt locations then I'd regard it as a problem, if not then probably just a normal situation with cast iron parts underwater. I assume from the OP's text the boat has a composite iron/lead keel.

 

[catmandoo]

I always visualise the torquing increases the bearing pressure on the hull / keel faces so that the bolts remain only in tension ( or shear ) and that bending moments on the keel due to water pressure when sailing is reacted by deflection of the relative GRP or Steel bearing surfaces spread over a much much wider area than the bolt cross-sections

every surface compresses or relaxes by an amount proportional to the load, its direction and the properties of the materials used

 

[Robert Wilson]

This is some information I put together a year or so ago. .

Thank you Vyv.
I'll print it off and take it to read in bed tonight (I'm part way through "The Death Zone" by Mat Dickinson, his account of the disastrous 1966 year on Everest), so I need a bit of light relief............

 

[Sneaky Pete]

Yes it has a iron/lead keel and it's not an oyster. The manufacturer recommends the following settings.
Bolt......................Torque (Nm) ISO 12215
M12..................................56
M15..................................58
M16..................................71
M20..................................99
M24..................................172
M27..................................254
M30..................................343
M36..................................603
M42..................................968
Looks like Vyv’s table was close. I’ll give it a go and see what happens going to torque from centre out in a circular rotation.