Keel bolts torque

[TiggerToo]

Does anyone know if there are guidelines for what torque to apply on keelbolt nuts?

 

[coopec]

Surely it would depend on the design/construction?

 

[Tranona]

Yes. Ask the builder - see the thread just below on Beneteau keel bolts. Typical torque is around 200nm - will be much the same for most boats of that size as they tend to use the same size bolts or studs. Often quite difficult to get bolts done up accurately because of things like furniture being in the way limiting swinging room, so you need serious gear with a long extension.

 

[jonjo]

I have read on the internet, so it must be true, that excessive torque can compress GRP laminate and turn it into GRP crumble.

 

[PuffTheMagicDragon]

I have read on the internet, so it must be true, that excessive torque can compress GRP laminate and turn it into GRP crumble.

One more reason for the importance of having substantial backing plates to spread the load, especially when heeled, and not the wimpy 'large' washers that are so often seen. Unfortunately, many of today's boats seem to be built down to a price instead of up to a standard.

 

[Slowtack]

Foot on 600mm wheel brace, sitting on floor, back against bulkhead...................

 

[Tranona]

I have read on the internet, so it must be true, that excessive torque can compress GRP laminate and turn it into GRP crumble.

I doubt you could ever get enough force on a nut to compress GRP. suggest you read the ISO or the ABS standards on keel attachment then you will appreciate why this would not happen.

 

[coopec]

Foot on 600mm wheel brace, sitting on floor, back against bulkhead...................

Well I have ten 30mm tungsten carbide nuts and bolts securing my keel. I use a converted stay tensioner off a North Sea oil rig to tension up the nuts. Finally, after donning a loose shirt and my weight lifters belt, I nip them up by hand.

 

[thinwater]

?? Do the math.

A 5/8" bolt will have a clamping force of about 16,000 pounds. The area under the nut is about 0.35 in2, so the compression is about 45,000 PSI. Fiberglass typically has a compression strength of about 20,000 PSI, so you will easily tighten the nut right through the fiberglass. I have done this in testing, even with plain bolting washers, many times.

Of course, a thick (not bendable) washer or backing plate increases the area, and you need to stay below a safe working load (~ 3000 psi), so you need at least 16,000/3000=5.3in2 in this case, about 2.7" diameter, or about or at least 4 boat diameters. 5 diameters is conventional wisdom, since the loading will include shear.

 

[Birdseye]

?? Do the math.

A 5/8" bolt will have a clamping force of about 16,000 pounds. The area under the nut is about 0.35 in2, so the compression is about 45,000 PSI. Fiberglass typically has a compression strength of about 20,000 PSI, so you will easily tighten the nut right through the fiberglass. I have done this in testing, even with plain bolting washers, many times.

Of course, a thick (not bendable) washer or backing plate increases the area, and you need to stay below a safe working load (~ 3000 psi), so you need at least 16,000/3000=5.3in2 in this case, about 2.7" diameter, or about or at least 4 boat diameters. 5 diameters is conventional wisdom, since the loading will include shear.

Excellent - some real facts rather than speculation. All I need to do now is to convert into modern units

 

[coopec]

It would be good to know the design of the yacht and construction material. Also it would be good to know the designer's recommendation.
But presuming the boat construction is fiberglass then surely it would only be necessary to do the keel bolts up sufficiently to hold the keel in place and not the theoretical maximum torque. After all you wouldn't torque car wheel nuts up to the point where it was about to strip threads.

 

[Carl s]

I have always found the F T method works well.

 

[coopec]

I can’t remember precisely but I think I used to torque then to somewhere between 150 and 200 ft. lbs. using a torque wrench. The bolts on that boat used split ring lock washers under the nuts.
http://www.cruisingworld.com/dont-let-loose-keel-bolts-ruin-your-day

If you can get a 1" drive torque wrench and the 1 1/2" deep socket you can do it yourself. You'll also need an extension(s) long enough to clear the floor boards.
I've tightened mine both our of the water and in the water.
The information I got from Catalina calls for 235 lb-ft torque.

Nick Wigen
Ursa Minor #178 FK, 3-Cabin
Olympia, WA

http://catalina42discussionforum.yuku.com/topic/1658/Keel-Bolts#.Vy2-NOQgnx0

I have a 30' Sabre, and the manual states the keel bolts should be checked and torqued (to 90 foot pounds), as necessary.

From the manual:

"...Occasionally, water from the bilge may seep through this crack when boats are hauled. This would be due to a slight leak at a keel bolt, which can be readily be overcome by tightening the keel bolt nuts. As part of launching procedure, check all keel bolt nuts for tightness to 90 foot pounds before the boat is lifted out of the cradle."
http://www.sailnet.com/forums/gear-maintenance/65330-re-torquing-keel-bolts.html

Torquing Bolts
________________________________________
First start with the bolt size.. typically manufacturers use a bolt size appropriate to the load they will encounter with some safety margin. You would be amazed by how much linear force a thread will transmit because of the mechanical efficiency. 90 ft-lbs is a literally a boat load of force.

Using the simple calculator here

http://www.engineersedge.com/calcula...orque_calc.htm

a 1" bolt @ 90 ft-lbs transmits 960 lbs of linear force. If you have a half dozen, that is close to 3 Tons of clamp.

Torque with caution, & not all at once.

TD

On my C&C30 Mk 1 I believe there are 4 keel bolts (maybe 5). What I'm sure of is they are 1" diameter and are torqued to 350 ft lbs.
To actually torque them to specs, you'll need a deep well 1-1/2" socket (if the bolts are 1") and a torque multiplier or one heluva big torque wrench. I actually bought a torque multiplier and the deep well socket to allow use of my 1/2" torque wrench with 3/4" adapters to fit the socket and torque multiplier. It cost me about $175 for the tools.
If I had it to do over again, I'd let the yard do it, although I don't think they had the tools anyway.
They really needed it. They were just beyond hand tight and the C&C smile required yearly patching. Since torquing to specs, the smile has not reappeared.
http://www.sailnet.com/forums/gener...3927-1983-c-c-29-mk11-keel-bolt-question.html

 

[Bilgediver]

I have read on the internet, so it must be true, that excessive torque can compress GRP laminate and turn it into GRP crumble.

This is quite correct as some times people check engineering tables based on torque for different material nuts and bolts. These figures are derived and correct for engineering applications where the bolts are securing steel structures however they are much too excessive for use on keels where the bolt passes through fibre glass. ie a Westerly etc. If you use these tables then here there is a chance of crushing the fibre glass under the bolt washer inside the boat and I have seen on a Vulcan where the nuts and washers had almost been forced half way through the hull where the bolts had been repeatedly torqued up to dry and stop leaks.

Some modern yachts have a steel frame bonded into the hull to transfer keel loads and these may take higher torque figures than plain GRP.. Check the the owners group for your yacht for good advice or the builder if still in business.

 

[thinwater]

Coopec:

The basis for torque settings is to pre-tension the joint slightly in excess of any actual load the joint can see. Not the average working load, not the breaking load, but the maximum actual load. Any less, and the joint will move and open at peak load and the stretch of the bolt will vary, which are both very bad. Same on cars. Normally the torque is near the WLL and serves to prevent fatigue induced by motion. Thus, it should be well below the point of stripping threads. Lubing the nut also helps by reducing the torque requirement (there are typically lubed and unlubed values).

 

[macd]

"As part of launching procedure, check all keel bolt nuts for tightness to 90 foot pounds before the boat is lifted out of the cradle."

That's odd 'cos foot-pounds is not a unit of torque, but of work. Torque is measured in pound-feet (or Nm if you want to be more modern about it.)

 

[thinwater]

I can’t remember precisely but I think I used to torque then to somewhere between 150 and 200 ft. lbs. using a torque wrench. The bolts on that boat used split ring lock washers under the nuts.
http://www.cruisingworld.com/dont-let-loose-keel-bolts-ruin-your-day

If you can get a 1" drive torque wrench and the 1 1/2" deep socket you can do it yourself. You'll also need an extension(s) long enough to clear the floor boards.
I've tightened mine both our of the water and in the water.
The information I got from Catalina calls for 235 lb-ft torque.

Nick Wigen
Ursa Minor #178 FK, 3-Cabin
Olympia, WA

http://catalina42discussionforum.yuku.com/topic/1658/Keel-Bolts#.Vy2-NOQgnx0

I have a 30' Sabre, and the manual states the keel bolts should be checked and torqued (to 90 foot pounds), as necessary.

From the manual:

"...Occasionally, water from the bilge may seep through this crack when boats are hauled. This would be due to a slight leak at a keel bolt, which can be readily be overcome by tightening the keel bolt nuts. As part of launching procedure, check all keel bolt nuts for tightness to 90 foot pounds before the boat is lifted out of the cradle."
http://www.sailnet.com/forums/gear-maintenance/65330-re-torquing-keel-bolts.html

Torquing Bolts
________________________________________
First start with the bolt size.. typically manufacturers use a bolt size appropriate to the load they will encounter with some safety margin. You would be amazed by how much linear force a thread will transmit because of the mechanical efficiency. 90 ft-lbs is a literally a boat load of force.

Using the simple calculator here

http://www.engineersedge.com/calcula...orque_calc.htm

a 1" bolt @ 90 ft-lbs transmits 960 lbs of linear force. If you have a half dozen, that is close to 3 Tons of clamp.

Torque with caution, & not all at once.

TD

On my C&C30 Mk 1 I believe there are 4 keel bolts (maybe 5). What I'm sure of is they are 1" diameter and are torqued to 350 ft lbs.
To actually torque them to specs, you'll need a deep well 1-1/2" socket (if the bolts are 1") and a torque multiplier or one heluva big torque wrench. I actually bought a torque multiplier and the deep well socket to allow use of my 1/2" torque wrench with 3/4" adapters to fit the socket and torque multiplier. It cost me about $175 for the tools.
If I had it to do over again, I'd let the yard do it, although I don't think they had the tools anyway.
They really needed it. They were just beyond hand tight and the C&C smile required yearly patching. Since torquing to specs, the smile has not reappeared.
http://www.sailnet.com/forums/gener...3927-1983-c-c-29-mk11-keel-bolt-question.html

I think you made some error using the calculator. I get about 7000 pounds (depending on lube) per bolt at 90 ft-pounds. The total clamping force is much greater. This is only about 1/2 the ASME standard torque, but that is because it is GRP and because of the large corrosion allowance. But for only 960 pounds clamp force they would have used a 3/8-inch bolt.

 

[coopec]

Thinwater

My post was a series of quotes from other people to demonstrate the torque required varied tremendously according to the design the yacht.

I agree 100% with your previous post

"Coopec:

The basis for torque settings is to pre-tension the joint slightly...................................."