Hi Joern,
The deficiencies you identify may or may not be a real concern. but added together may not be cheap to rectify.
Starting with the easiest, the rusty keel. Sanding will help you get a coat of antifoul on for a season, but won't get rid of all the rust or, more importantly, all the salt in the pores of the cast iron. A fuller cure will be to grit blast the keel, then pressure wash it with fresh water before grit blasting lightly once more to get rid of the gingering caused by the washing. Without that, the salt in the cast iron pores will cause more rusting. However, this cure won't be cheap and would only be justified if you planned to Coppercoat her. Sanding and wire brushing tend to drag iron over the pores leaving salt and iron trapped inside so is not helpful. Grit blasting and needle gunnimg are more effective at getting rust off cast iron. I would guess that more than half the 30 year old boats with iron keels are in a worse state than your photos show, so it is certainly not a walk away issue.
If the antifoul is coming off, that's what it's meant to do.
The rudder patch may be something and may be nothing - it's quite possible the rudder is half full of water. Again, many 30yearold grp yachts are sailing around with water in their rudders and the owners not even aware, further investigation is needed to see whether a repair is needed. Perhaps a matter for your surveyor.
The damp spots around the chainplates may be a concern. Where the chainplates penetrate the side decks, there are little stainless steel plates fixed to the deck around the chainplates to keep them watertight. The sealant used for these plates tends to dry out over the years and crack. Owners who know about this rebed the little sealing plares every few years. If this has not been done on this boat, the sealant will be about 30 years old. The chainplates themselves are bolted to a marine ply part bulkhead behind the cabinetry and these part bulkheads are tabbed to the hull down to a level well below the bunk, If the penetration leaks over the years the part bulkhead gets damp and starts to rot. In extremis, the timber can get so rotten that the bolts tear through he timber and he rig loads push the deck up - it can lead to loss of the rig, but I've never heard of a case that got that far. A good check to make is to use a straight edge around the chainplates on the deck to look for any bulges - a bulge here is a serious issue. However, the damp showing may be from another source, so you really need to inspect the part bulkhead where the chainplate is bolted on to it to see whether it is damp or dry. This isn't easy as it's all hidden behind cabinetry. We have installed inspection hatches for this purpose others have used an endoscope with much smaller holes. This is certainly an issue you should ask your surveyor to look into. If any of the part bulkheads are soggy or rotten, the cabinetry will have to come out to replace the part bulkheads. If the sealing plates have been leaking for along time, there may also be a problem with water in the balsa deck core around the chainplates, Some models of Moody don't core much of the side decks and others had quite a lot of coring there. I don't know how much coring wasused on the M336.
Even in the worst case, thee is an argument not to walk away, but to determine the extent of the problem and get an estimate for the cost of repair. You can then make an offer reduced by the repair cost or ask the vendor to get the repair done prior to sale.
Hope this heps,
Peter.
