Model Boat Mayhem

Mess Deck: General Section => Chit-Chat => Topic started by: Bunkerbarge on June 10, 2007, 10:00:18 AM

Title: Riveted Repairs
Post by: Bunkerbarge on June 10, 2007, 10:00:18 AM
Sorry for the delay in my reply to the question regarding riveted and welded repairs but I was waiting to have a conversation with a Lloyds surveyor who we have had on board doing a survey for the past week.

I was always under the impression that you could not effect repairs to a riveted hull with welding and basically until recently this has been the case.  We are only talking about repairs that cover a joint as plate cropping and patching with a deep weld prep that does not go over a joint has always been acceptable.

Nowadays though, as has been suggested, there are so few yards that can do riveted repairs that an alternative had to be sourced for the few ships out there that still have such a construction.  In fact the Lloyds surveyor knows of one yard only in Canada that is able to do such repairs at this moment in time.  The big problem is the completely different amounts that the two different construction techniques flex under deformation forces.  A riveted joint will deform considerably more than a welded joint so if a welded joint is introduced into a riveted construction then the greater flexing of the riveted surrounding area will induce very high stresses into the welded joint. 

For such ships a technique has been devised where welding is used to simulate a riveted construction.  What they do is to remove the rivets by cropping off the heads and punching them out then a new plate with a matching rivet hole pattern is placed in position and the plate is welded into position by welding inside the rivet holes and at intervals along the edge only.  This allows a similar degree of flexing of the repair and minimizes the stress induced into the repair metal.

Unfortunately of course now that there is an acceptable technique for such repairs the requirement for a yard that can offer riveted repairs has now gone completely so this will unfortunately be another area of technical expertise that will completely die out.

I hope that this makes some sort of sense.  I must say the Lloyds surveyor did look a  bit puzzled at the question until I explained where it came from!
Title: Re: Riveted Repairs
Post by: Colin Bishop on June 10, 2007, 05:08:30 PM
Thanks for the comprehensive and interesting reply Bunkerbarge. Like so many things, the problems with stresses are obvious when somebody explains them but it's not something I would have thought of myself. I would also suspect that the plate thickness of older riveted vessels is probably rather thicker than on modern construction too.
Title: Re: Riveted Repairs
Post by: Bunkerbarge on June 10, 2007, 06:17:21 PM
Quite right Colin, steel has become thinner over the years in hull construction and strength has been impaired to the structure by more complex frame designs. 

Unfortunately this makes it considerably less resistant to penetration damage so the whole picture of the internal watertight integrity also plays a part.
Title: Re: Riveted Repairs
Post by: Colin Bishop on June 10, 2007, 07:13:38 PM
I see, so to the tune of "Yellow Submarine":

We all float in a fragile steel balloon.... :D
Title: Re: Riveted Repairs
Post by: Bunkerbarge on June 10, 2007, 10:42:38 PM
Twice in my career I have had my finger through a hole in a ships hull.  Both times I was inside a cramped internal double bottom void and both times I was waiting for the hole to open up and end it all prematurely!

Not pleasant!