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Re: CT-47 Keel Tank
Most similar designs from Taiwan yards, designed by Ladd/Perry/Garden, etc, etc. usually have their large bilge tanks removed by lifting/jacking*** 'straight up from the keel', then temporarily supported on the sole beams/framing, then if the companionway is dimensionally/geometrically compatible, the tank is simple brought (slid, etc) out using many strong backed helpers using blocks and tackles from the boom supported by the boom gallows, topping lift, etc. ... can be a PITA due to the tight clearances. Many such tanks were probably installed into the bilge before the deck/coachroof was connected to the hull and thus can't be removed through the companionway; and, have to be cut up before removal.
Usually in these Taiwanese built boats, the keel tanks are under the sole framing, usually with longitudinal framing with added and integral athwartships cross framing under the removable 'center' sole panels. Usually there are removable sections of the sole panels over the that that yield complete access to and removal of the tank; .... but, the cross beams between the transverse beams (parallel to the centerline) have to be cut. The cutting of the cross beams between the long parallel to long axis beams should be cut with suitable stubs - to which allows mechanical metal sister-plates + through-bolted for the 're-joining' (and epoxy re-gluing) of those under-sole cross beams after new/rebuilt tank installation.
Rob Ladd was the designer of this boat. I believe that his design bureau is located Annapolis Maryland ..... A simple and polite query to the Ladd Offices may be of help. I dont know if Robert Ladd is still alive.
These OEM tanks are/were very subject to weld corrosion, especially when acidic disinfection / sanitization compounds are used to keep microbial growth in check in those tanks. What probably happens is that chemical stress corrosion (hence leaks) occurs and propagates into the roughness, deeply into incomplete and non-full penetration welds, weld interstices/pin-holes of the UN-ground and UN-polished weld joints in the tank - 'nutherwords' these tanks will usually leak if sloppy welding was used to construct such tanks.
Suggested replacement (Stainless steel): Use a heavier gage metal, require the least amount of welding by minimizing the amount of welded seams - by utilizing as many 'large radiused' press-break bends as possible, minimized welds, and then all internal welds be ground flat and then polished/finished (quite expensive to do) to the approx. same mill surface finish/roughness as the as-supplied new base material. This will result in LESS chemical corrosion of the welds and their heat affected weld zones. Such a tank will be MUCH 'heavier' than whatever comes out of the bilge - you really dont want to do this job twice. Such a tank isn't going to be 'cheap', nor is the labor to remove the old one, nor install the new one - backbreaking.
Obviously these large tanks when filled add significant righting moment vs. heeling ... so you probably want of re-create an equivalent 'volume' when building a new tank.
*** I used 4X4" X ?" long yellow pine positioned though the opened portlights on the coachroof as beam supports for two 'come-alongs' to lift my big tank from the bilge onto 2X4's laid across the long-axis framing and before before 'sliding/lifting' it through the companionway --- using 4-6 adults and ~2-3 small boys to do the grunt work. Do consider to 'cover and protect' your solid Burmese teak to prevent gouges, blood and skin particles and tooth marks from your 'helpers', etc. Simple Luan Plywood works well as a 'protector' for the real expensive stuff.
Hope this helps. ;-)
Edit: I just noted that youre in the central Mediterranean. No-one, nowhere, does stainless steel work better and cheaper and faster than the Italians. Good Luck on your replacement; or, rebuild/repair.
Last edited by RichH; 12-05-2017 at 11:38 PM.