Why are keels fastened with studs and not bolts.

[BurnitBlue]

I am asking about threaded blind keels not through bolting with a nut on the bottom end. Is there a mechanical reason? The only reason I can think of is that a stud is "wound" into the keel with no tension, then a nut is wound on to the top of the stud then tensioned with a socket without rotating the stud.

In contrast a bolt is "wound" into the keel and tensioned with a socket. The threaded part turns with the bolt unlike the stud which stays as it was while only the nut turns. I am thinking that because of this a bolt may strip the thread in the keel while being tensioned whereas a stud will not.

I must change the keel bolts so I am considering 24mm bolts rather than studs. Easier to remove without the hassle of an extra lock-nut where the flanges do not line up

Thanks.

 

[rotrax]

Probably for assembly reasons when built.

If the hull/keel is fractionally out of line the bolts would be almost impossible to engage in the keel.

A keel which by its very nature is heavy and difficult to move fractional amounts. As is the hull.

 

[atol]

it is more of a practical issue,studs are easier to locate when lowering the boat onto the keel,and the large amount of sealant on the top of the keel is squeezed out at the joint evenly rather than into the stud holes which could create hydraulicking issues if bolts were used without removing any sealant that might have ended up in the holes

 

[Deleted member 36384]

In critical clamping applications it is to do with tensioning the fastener. Studs are easier to get to the correct tension with a nut, than it is with a bolt. The issue is with the extra length of thread engagement with a bolt, the associated friction may cause a torque, an indirect measure of tension, to be at the correct value without the bolt being fully engaged, thus giving a false positive. It is possible of course to prepare a threaded hole and bolt and have the checks in place to ensure correct clamping is carried out, but it is just easier with a stud and nut.

 

[Tranona]

With many modern keel shapes it would mean very long through bolts and casting in tunnels to take them. Through bolts are common on long flat keels such as on my old wooden boat. Usually inserted from the bottom with nuts inside rather than heads inside and nuts at the bottom. PITA to install as I know having done it twice!

Can see no advantage in through bolting - with studs the keel itself acts as the nut and usually with far longer threaded areas. Fail to see what you hope to gain changing from what is an almost universal and effective method.

 

[BurnitBlue]

Thanks a million for the replies. I will be replacinfg the existing studs with bolts.one at a time without removing or moving the keel so bolt heads will be an improvement in the bilge so will be an improvement. My concern of stripping the thread from the keel seems not be an issue.

My only objection to studs is the extra length of the stud above the nut which has chaffed the bilge pump hose. One of them also impedes the limber hole in the foor frame. Thanks again.

 

[BurnitBlue]

With many modern keel shapes it would mean very long through bolts and casting in tunnels to take them. Through bolts are common on long flat keels such as on my old wooden boat. Usually inserted from the bottom with nuts inside rather than heads inside and nuts at the bottom. PITA to install as I know having done it twice!

Can see no advantage in through bolting - with studs the keel itself acts as the nut and usually with far longer threaded areas. Fail to see what you hope to gain changing from what is an almost universal and effective method.

Sorry I did not ezplain very well. My keel is the usual big nut with a blind thread which in my case is about 8 cm deep. I was concerned because I can imajine a thread cast or tapped in cast-iron would be more prone to being stripped than a normal tapped steel nut. The advantage for me is a smoother bilge. Also removing a stud needs an extra lock nut which wiil invariably not line up with the flanges on the nut below it. My 35 mm ? socket will not fit. My plan is to keep the blind nut system but use a bolt rather than a stud.

 

[TernVI]

Cast Iron is (often) porous.
The stud-keel thread is 'outdoors' and subject to corrosion.
I'm not sure retro-fitting a bolt can be done as well as installing studs on a bare keel? Would it be nomal to use some flavour of loctite on the studs in the keel?
When you tighten a nut on a stud, you don't have the friction of turning the stud in the hole, so the torque is more directly going into tensioing the stud.

Some boats do use bolts, IIRC some of the UK Hunters have tapped holes in a flange around the top of the keel with two rows of bolts?

But it seems like a pretty serious thing to be messing with, just to lose some excess thread length in the bilge.
Why not just trim off the over-length studs?

I generally think any gasket or sealant based joint is likely to need completely re-making if you bugger about with it.

 

[BurnitBlue]

Cast Iron is (often) porous.
The stud-keel thread is 'outdoors' and subject to corrosion.
I'm not sure retro-fitting a bolt can be done as well as installing studs on a bare keel? Would it be nomal to use some flavour of loctite on the studs in the keel?
When you tighten a nut on a stud, you don't have the friction of turning the stud in the hole, so the torque is more directly going into tensioing the stud.

Some boats do use bolts, IIRC some of the UK Hunters have tapped holes in a flange around the top of the keel with two rows of bolts?

But it seems like a pretty serious thing to be messing with, just to lose some excess thread length in the bilge.
Why not just trim off the over-length studs?

I generally think any gasket or sealant based joint is likely to need completely re-making if you bugger about with it.

My keel bolts have a history. When I bought the boat Moody 34 in Greece the keel bolts had been replaced by a local engineer on the advice of an insurance surveyer. The boat had to moved halfway through because the local engineer refused to pay 20% to the boatyard. 24mm studding was not readily available so for speed, the engineer cut off the exposed rusty bits and welded a single nut to the smaller stud. When I discovered this i was very unhappy with a welded nut to a rusty stub. I sourced some 24mm studding (Made in China) and replaced the whole set of keel bolts but had to use the original paper thin rusty washers. A few days ago while at home in Sweden, I spied some 24 mm long Swedish made bolts and square washers and thought "what a good idea. Do the job properly" hence the question to this forum if there is a downside to using bolts in the blind hole rather than the original studs.

Regarding torque, I have been advised that i should use as much torque as possible because it would be immossible to exceed the rorque on a 24mm bolt in the close confines a a boat bilge.

 

[BobnLesley]

...My only objection to studs is the extra length of the stud above the nut which has chaffed the bilge pump hose. One of them also impedes the limber hole in the foor frame. Thanks again.

Those projecting bits of bolt aren't contributing anything, so after installation, why not get an angle grinder, or if space is tight a dremel type tool and cut them off?

 

[TernVI]

Potential problems include:
Getting the old studs out.
Threads stripping in the keel
The new bolts not having the right unthreaded length
Bolts bottoming in the holes
Tearing the sealant around the studs/bolts.

A proper job would include taking the keel off and re-making the joint.

Meantime, why not just change the washers under the nuts and trim the studs?

 

[Tranona]

Cast Iron is (often) porous.
The stud-keel thread is 'outdoors' and subject to corrosion.
I'm not sure retro-fitting a bolt can be done as well as installing studs on a bare keel? Would it be nomal to use some flavour of loctite on the studs in the keel?
When you tighten a nut on a stud, you don't have the friction of turning the stud in the hole, so the torque is more directly going into tensioing the stud.

Some boats do use bolts, IIRC some of the UK Hunters have tapped holes in a flange around the top of the keel with two rows of bolts?

But it seems like a pretty serious thing to be messing with, just to lose some excess thread length in the bilge.
Why not just trim off the over-length studs?

I generally think any gasket or sealant based joint is likely to need completely re-making if you bugger about with it.

The threads are not "outside" but sealed from the elements by the seal between the keel and the hull. If this seal is not broken then there is no reason why the studs should not last for the life of the boat.

The OP's problem starts from the duff advice from the surveyor that the studs needed replacing because of rust on the exposed nuts in the bilge caused by fresh water, followed by the "bodge". The boat is a Moody and the rust is a common issue because the boats have a habit of leaking but is mainly cosmetic. Solution is to remove the rusty nuts and plates - the threads will be fine - replace with new plates and nuts and then paint over them with something like Hammerite to minimise future rust (and find ways of stopping the freshwater leaks!). No problems cutting down the exposed excess thread, particularly if it is corroded.

Big challenge for the OP will be removing the studs from the keel. Personally if the existing bodge is secure I would clean them all up, cut down the excess if necessary, paint and stop worrying. The 24mm studs are way overspecced and if the nuts are tight no chance of ever coming loose.

 

[Caraway]

I agree with the last posters. You don't want to be disturbing the threads in the casting again. Ideally a stud should not be torqued down into a thread. Bottoming the insert (stud or bolt) will put extra stress on those threads, which are the only ones you don't know about. Studs only need to be finger tight into the hidden threads. Or wind them down and then back them off. But ideally, don't disturb them. If you are suspicious of the Chinese studding, replace them with a known quality of studding. One at a time.
If you use a thread locking compound, like Loctite don't use the permanent one (Red, in the case of Loctite) as they need local heat to remove.

Just use new nuts and machined washers, and as suggested, zip off the exposed threads.

 

[BurnitBlue]

Potential problems include:
Getting the old studs out.
Threads stripping in the keel
The new bolts not having the right unthreaded length
Bolts bottoming in the holes
Tearing the sealant around the studs/bolts.

A proper job would include taking the keel off and re-making the joint.

Meantime, why not just change the washers under the nuts and trim the studs?

I cannot remove the nuts because they have been welded by the engineer to the now short stud because there was no room for the locknut to remove the stud. That was the problem. To all purposes the welded nut changed the stud to a bolt.

I have not explaine it very well. When I bought the boat the keel bolts had already been changed by the engineer and the previous owner. I did not like the stste of the welded nuts on to the remains of the rusty bolt. So I pulled one out and as I suspected it was too short because the engineer cut the stud down to remove the rusty part then welded the nut to what was left of the stud. So I replaced them all with 24mm studs made in China but with the original washers. I have access now to long 24mm bolts and thick square washers made of Swedish steel. I do have to be very careful to have the bolt long enough for max effect but short enough to allow torque without bottoming out the bolt in the blind thread. Actually I have just thought that this may be the reason the boat builder uses studs. The stud can be threaded right to the bottom of the hole without the danger of bottoming out before full torque had been applied. I will enquire if his 24mm studding is made from Swedish steel.

 

[BurnitBlue]

I agree with the last posters. You don't want to be disturbing the threads in the casting again. Ideally a stud should not be torqued down into a thread. Bottoming the insert (stud or bolt) will put extra stress on those threads, which are the only ones you don't know about. Studs only need to be finger tight into the hidden threads. Or wind them down and then back them off. But ideally, don't disturb them. If you are suspicious of the Chinese studding, replace them with a known quality of studding. One at a time.
If you use a thread locking compound, like Loctite don't use the permanent one (Red, in the case of Loctite) as they need local heat to remove.

Just use new nuts and machined washers, and as suggested, zip off the exposed threads.

Our posts crossed. Yes the bottoming thing just occurred to me while writing it. Your post goes on to warn against torqueing the stud or bolt inside the csst iron keel. That answered my original question. So back to studs I will go finger tight and use the nut to torque the join together.and forget the bolt idea.. Thanks.

 

[penfold]

Surveyors are obsessed with keel bolts and a lot of money is wasted fiddling with entirely sound fastenings.