Holes in a steel hull...what to do?

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cmorganobrien

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Can anybody advise us, please? We bought a 1991 steel hull motor cruiser last summer and had a fabulous summer afloat. We cruised her from the South Coast all the way to Padstow and then home to Kilmore Quay, Ireland. During winter works, three holes were found in the hull, under the engine room. We have been in touch with our surveyor and, hopefully, all will be well. But....how big a job is this? We've had different suggestions from different engineers. Surely a steel hull can be repaired without having to replace it entirely???? PLease help! This is our first boat.
 
How were the holes found? For example, were they found by bashing with a chipping hammer, and the hammer went through the hull in three places?

Has your surveyor carried out thickness determinations (eg by ultrasound) of the plating in the area where the holes are?

If the plating in this area is 'thin', then the only recourse is to cut it out, and weld in new plates. This is not a terribly difficult job. However I would be concerned about the shell thickness elsewhere in the hull bottom as well, not just where these holes were found. I hope that your surveyor will check / has checked the whole bottom of the hull.
 
Don't panic firstly. Keeping the engine room dry if you can is good, as is an oil-proof paint. For repair, I had the bottom of my steely over-plated, they just puddle-welded through the old plating directly onto the frames. Worked a treat. Downside of that cheapest option is that any water getting into the engine room and lying on the inner skin can get into any gap between the two skins via holes. However, the unprotected face of the new skin shouldn't suffer much as no oxygen can get in.

As with any welding, first make sure NOTHING can be set alight inside the boat whilst welding from the outside!
 
Thanks so much for your reply. The holes were found while painting on the anti-foul. We saw a powdery residue and the brush went right through. The pre-purchase survey did not find any problems with the hull and we have the orifginal ultrasound readings. We've since had our Irish surveyor take new reading s and he says our only problem is in the three areas he has highlighted. One engineer has told us to get our money back....that the boat is a dud, but we think that's a bit drastic. Another engineer has said to replace the entire hull, which sounds prohibitively expensive- it is a 1991 boat, after all.
Had a wonerful honeymoon in Barbados 10 years ago.....so beautiful!
Thanks again for your reply.
 
Thank you very much for your reply. I agree- we've been told it's come from the inside out and that it is primarily in the engine room. You think replacing the entire hull is ridiculous? That's one of the options we've been given by the engineer.....sounds drastic to me!
 
This foum is fantastic...all this advice is very reassuring. We have had weeks of panic, as we are not sure how keen our original surveyor will be to assist. Thank you for your really helpful reply. Have you confidence in your repair? Because we're new boat-owners, we don't want to be misled by companies telling us to replace the entire hull. Mant thanks again for your advice.
 
If the enginner says replace the hull, replace the engineer! The beauty of a steel hull is that is can be repaired with simple tools - a hammer, angle grinder and a welder. The trick is knowing where to apply the tools!

Check the hull thickness in all areas below the water line and patch away where its thin

Keep the anodes and paint in good condition and that should be that.

PS a useful tip: dont let engineers know your new to boating
 
Having had steel boats for over 25yrs I would ask how has the water got in the engine room.You should have no water anywhere inside the hull.Have you got a water tank thats using the outer skin?or is it just engine room.If you get the right people its not a prob.
 
Well, If the paint brush found the hole and went through, 'd probably faint.

The original surveyer wants sueing and I'd want alot of proof about the rest of the hull being sound. Infact I doubt if I'd ever trust it.
 
Thank you to everyone for your advice. We were whacked by a basking shark in Dartmouth.....our six year old had stitches in Truro, after we berthed in Falmouth. We think that's when we sustained damage to the drive shaft, which we replaced. This is when we let in the water. It was a very eventful summer......think we might be lucky to be alive. Definitely one for the "You'll never believe what happened to us" pages in MBM! We are having "talks" with our original surveyor!
 
I am surprised that nobody noticed how thin the hull shell was when she was surveyed - I presume last summer?
I guess it is possible that if only a few random ultrasound readings were taken in different areas of the hull it could be possible to miss these areas.
Have large are the three areas of concern? And where in the engine room are they? As noted above, are they in way of a fuel or water tank, or are they 'out in the open', perhaps under the engine(s)? Can you now see any areas of heavy rust exfoliation on the inside of the hull in way of the holed areas?

Although Clive has mentioned above that it is possible to repair the holes by welding a patch over them, it would be much better practice to cut out the wasted areas of steel, preferably with each cut out being a nice simple square or rectangle, and then welding in new plates to fit the areas cut out.
If these areas are under the engine(s), then access from the inside will be difficult. You would then probably have to take the engine(s) out, because you should ideally continuously weld the joint on the inside as well as on the outside.

I think it would be prudent to carry out a very thorough survey of the hull bottom now, as there is a very good possibility that there are other areas of excessive corrosion, if three areas were literally paper thin. This could be done initially by hammer testing, followed up by ultrasound testing if more suspect areas become apparent.

If you beat 7 bells out of the hull bottom with a big hammer, and nothing happens, and the steel does not deflect at all, then the odds are the steel thickness is still adequate.
(BTW, what is the hull shell bottom thickness supposed to be?)
And if the hammer 'goes through', well, you have found another area in need of attention.....
Pay particular attention to the areas in way of tanks, shower sumps, and any areas where water can collect.
And in future, endeavour to ensure that you only ever see dry dust in your bilges...... that is how steel boat bilges should be!
 
The original survey took 30 readings. The only recommendations the survey made were to replace the horn and the u-bend in the galley! We had checked out the surveyors credentials etc before purchase, so we were happy to accept his survey. The holes are under the engines. If we were to take out the engines, that would be a huge job...but needs be. The hull should be 4mm and Irish surveyor we employed when all this mess became apparent took 60 readings. These readings show that the hull has an average of 3.7 - 4 mm, except where the holes appear. This Irish surveyor checked the hull depth against the plans and the original shipbuilder.
Would you like to see a photo of these holes?
 
30 or even 60 readings seems kind of low to get anything other than a general indication of hull thickness - but perhaps that's all that was intended?

We have a steel hulled boat, and observation strongly suggests that it'd take ages to rust from the outside in. but much much less time from inside out..
 
Yes please re photos, if you can post some - that would be most interesting!

How big a boat is she? And what type of hull form, and how much power are the engines? Just asking for background reference.
4 mm bottom plate is about the rock bottom minimum one would use, even for a 'small' motor cruiser or sailing boat, as rust does not discriminate - steel will rust as fast on a small boat as on a big boat, given similar conditions.
But that is good that the minimum thicknesses found elsewhere are still 3.7 mm, especially as the hull is 15 years old now.

How much clearance have you got between the hull shell and the engine above, in way of where the holes are?
It might be possible to cut out the plate from the outside, edge prepare the cut out with a bevel and weld in a new 4 mm thick bevelled plate. The bevels are needed so that the first weld run is effectively on the inside of the plate, as you most probably will not be able to get a welding torch in under the engine to run a fillet weld on the inside. But if you can, good!

You will have hassles though, if the areas to be cut away are in way of any stiffening, eg the longitudinal engine beds, or any transverse framing between the longitudinals. If this is the case, you might have to consider taking the engine(s) out.

Whichever method is employed, ensure that the new plate is well prepared, primed and painted to reduce the rate of future corrosion. If the plate is welded in from the outside only it would be a good idea to prepare (by grinding, although blasting would be better) and coat the inner face of the plate with steel primer before welding the plate in. The primer will be burnt off in way of the welds, but these can then hopefully be cleaned up and then re-painted (fi there is enough access under the engines).
 
4mm is pretty much the norm for a steel hull on a small to medium sized motor cruiser as they are not likely to suffer the abuse that a commercial boat suffers. unless it's a canal boat where 25mm bottoms are not unusual. It's also not unusual for a hull to rust through under the engines, mostly because that's where all the activity re: servicing takes place and spillages of anti-freeze goes (during winter layup). You mentioned a white powder, that is either due to battery acid leakage or anti-freeze, both highly corrosive. However, cheer up because most hulls are built with an oil tight bulkhead either side of the engine bay to contain such spillages so the likely area of repair is almost certainly confined to the hull under the engines. My steely (4mm) had rust in the bottom where persistant topsides leaks over the years had not been rectified by the previous owners.

Patching up was fairly easy, like the man says, don't be afraid to wack it all over because if you can damage it it needs repairing. In suspect places I used a club hammer and chisel to abuse it to ensure I got all the areas needed checked. I know that you should ideally weld from both sides, but frankly I think you might be better served by over-plating with a good lap and fillet welding rather than on 4mm letting a yard loose butt welding, especially if to do so means removing engines. Costs are going to go through the roof and lets face it, the bit you repair is out of sight under water so does not have to be too pretty, just sound and workmanlike.

My steely was a Dutch built ex North Sea boat (commercial fishing) 40 years old, so don't think your 15yr old could have had the abuse that one had in it's life. I'll repeat, don't worry, get it lifted out and check it your self or with friends and get someone to weld some 4mm over the bad bits. Good luck!
 
Cmorganobrien has kindly emailed me some photos of their boat, and of the holes, which I shall post below.
The vessel is a Waverunner 38 'stretched' to 43', designed by Bruce Roberts and built by Budge Marine. She has twin Cummins 300 hp inboard diesel engines.

[image]
Caitriona1.jpg
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Here is a view of a couple of holes in the hull :

Caitriona3.jpg


While here is a close up on one of the holes :

Caitriona2.jpg
 
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