Our first indication of a problem was the starboard tank doing strange things. It would pop and make other noises when we were taking fuel out of it. When we opened the deck fill, there would be "gassing". We suspected a plugged vent line, but a thorough check of that line from the tank connection outward was all OK. Meantime the noises continued anytime we took fuel from the tank. Finally we took the tank hose fitting off the flange and tried sticking a screw driver into the tank. Guess what. It wouldn't go into the tank. We finally figured out that there was a wooden plug in the tank from the original factory pressure testing, so the tank was completely unvented. No wonder it complained. We had to find a very small angle drill that could access the fitting and drilled out the vent port. Whether or not this contributed to our next set of problems is one of the unknowns, but probably not, although the flexing of the tank cannot have helped. Meantime we had been noticing a dribble of fuel on the hull at the engine room bulkhead.
We kept looking for this leak, but were not having any luck in finding a wet fitting or other indications. Of course very little of the tank is visible with the wood covers, so it is hard to really inspect it in a meaningful way. After this dribble became a definite leak at about 7 ounces of fuel a day we installed the diaper system to contain the fuel. Using the diaper system soon palled and we decided we had to find and fix the leak. The fuel was passing through the tank stringer at the forward end, running down the hull, passing through the engine stringer, and ending up in the bilge where the diaper was installed. Both tanks at this time were close to full.
Our first cut was a pressure check of the tank. From that we learned that pressure checks are not to be trusted unless you are willing to put more pressure on the tank than I chose to do. It takes at least 5 psi for a valid check, maybe more. That's a lot of pressure considering the area of an already compromised tank. We drained the starboard tank and installed the pressure tester in the fuel outlet port of the tank.
We brought the pressure to 2.8 psi and it held steady for more than thirty minutes. This generated a bit of head scratching as we were measuring a 7 ounce per day leak prior to the test. We finally concluded that maybe the leak was in the outlet fitting, though that wasn't one of the suspect areas we had in mind, and there was no evidence of leakage there.
So we reassembled the fuel lines and refilled the tank. It still leaked!! It was time for a break to consider where to go from here. We talked to a mathematician friend about the pressure test. He asked how tall was the tank and I watched him integrate the weight of a one inch column of fuel in his head. After about half a minute he said, "Not enough pressure. The fuel column is exerting about 4 psi at the bottom." The decision was made that the starboard tank had to be replaced. Our thoughts turned to the port tank that had shown no evidence of leakage.
The specs were roughly as follows:
Once these steps were complete removal of the old tanks began. The first step is to remove the engine, muffler, and anything else that will be in the way. While the engine is out is a good time to clean it up; touch up the paint, change the thermostat and fuel filters, reroute any plumbing, etc. It's also a good time to send the prop off to be trued, pull the shaft and check it and the cutlass bearing, repack the packing gland and do all the little things that are just too much trouble because you have to tear the boat apart to get at them. The generator didn't need to be moved. Tank removal is the next step.
The old tanks had to be cut in pieces for removal. This was accomplished with a Sawzall, cold chisels, etc. Lots of noise. Once the tanks are out, you'll find that the work area is a mess. So a little temporary cleaning was done. Wires temporarily stashed and area scrubbed.
We also learned some interesting things about the actual tank capacity. We found an area about 8 inches high at the forward end of the tank tapering to nothing a couple of feet from the aft end of the tank that had not been covered with fuel. The fills are aft of course, and our boat had sat stern heavy due to the location of the batteries. After we had added 400 ft of 3/8th chain to the chain locker she was nearer level and I suspected that she would hold a great deal more than the 700 gallons shown in the specs. I thought one time that I had about 740 aboard. Claus Menzel, prior owner of Krogen 42 Hull 150 "Till Eulenspiegel" confirmed that he had loaded more than 800 gallons in his tanks. A calculated capacity showed about 804 gallons and possibly as much as 810. Compound curves are not easy to calculate volumes under. The next step is to build an exact templet of the tanks fitted into place.
The maximum length for the port tank is the limiting factor. This is determined by the distance from the forward electrical ground box aft to the support post for the saloon floor mounted on the cross frame aft of the muffler. We determined to build the starboard tank the same length, then build secondary tanks about 23" long to fit aft of the main tanks. We elected to use these secondary tanks (capacity 65 gal each) for water as we had learned that the actual capacity of the main water tanks is about 280 gal. The added 130 gallons brought us to 410 gal of water total. If they are used for fuel they will bring the fuel capacity to about 780 gallons.
The maximum width of the tanks was determined by the width of the hatches in the saloon floor. Don't forget to include the extra inch for the angle braces on the inboard side of the tanks, although lowered at an angle with the outboard side leading they might clear at full width due to the shape of the tanks. About here I realized that the tanks were going to be one inch narrower than the originals, considerably reducing the capacity. So we increased the height of the tanks one inch to compensate. I didn't check the space available as there seemed to be plenty, but when the tanks went in the starboard tank rides right against the floor frames aft. so check before you increase the height of the tanks.
In the tank area, all wires were secured in bundles and fastened near the inboard side of the tanks where they are accessible. We installed a ventilation duct from the port fresh air intake directly to the inverter, and installed a new vent through hull for the secondary tanks. After the area was secured we began scrubbing again. We then glassed in 1/4" strips where each of the baffles would rest. On top of the glassed strips we contact cemented 1/8" hard rubber as shock absorbers for the tanks. The purpose of these strips is drainage and ventilation below the tanks to prevent corrosion. Jim Krogen told us that his specs called for such spacers, but none were installed on our boat. When this was done we painted the hull interior white using Pettit Easy-Poxy. We were now ready for the tanks.
When the tanks showed up the first thing we did was to stamp into them the serial number of the boat for identification purposes. We then applied three or four coats of polyamide epoxy as a sealer (West would do as well, as long as it's opaque to conceal the numbers). Now it's time to see if they really will go through the saloon hatches. One reason we chose aluminum was weight. Aluminum 3/16th thick is lighter than 1/8th black iron or stainless steel. Six men (three each side) could pretty easily lift the tanks using webbing straps and ease them down through the hatches. Only the three forward hatches needed to be removed. We had about 1/8th inch clearance on each side and a few inches fore and aft. The port tank went in first.
The forward end had to be lowered and then the tank eased forward to provide clearance for the aft end. Finally it rested on the engine stringers. The port tank required a bit of wrestling to move forward to the electrical locker, outboard into the tank cavity, then forward again to the forward bulkhead. A push here and a shove there and she was in place. Next comes the starboard tank.
This one was a piece of cake. The space is such that it could go in at an angle, then just rotate into position. The secondary tanks were now positioned temporarily to check positioning and fit. It was all pretty good. Now it was time to work out the anchorage system. You'll recall that we welded 1" X 1/4" angles to the inboard side of the tanks in way of the baffles. This is where they come in.
We first dropped a plumb line from the saloon floor beams to align with the inboard edge of the tank stringer and marked the positions. Onto this line went a 2 X 2 aluminum angle fastened to the floor beams with 1 X 1/4" lag bolts. The inboard side of the tanks was now aligned vertically. Fittings were custom fabricated for each position to match the angles on the tanks. The individual fabrication was necessary due to changing heights and changing angles of the tank stringer. The fitting was a rough "T" shaped piece of angle where the cross of the "T" will be fastened onto the top and outboard side of the tank stringer. The top of the fitting will be bolted to the angle installed on the floor beams. The lateral dimension of the fitting must be such as to almost reach the tank with a generous overlap with the angles welded to the tank. All angles are 1/4" thick. Width to match as noted.
The fitting is now fastened to the top of the tank stringer with 1 X 1/4" lag screws and a generous application of 3M 5200. They are positioned tightly against the tank angles before fastening top and bottom. Once the vertical angles are secured, holes are drilled through both the tank angles and the anchoring angles. These are fastened with 1 X 1/4 bolts and lock washers. This pretty much completes the tank installation.
The clean out covers were pre-drilled by the welder before welding the flanges to the tanks. Each was marked as to position. Even so we had to bend a special wrench to reach behind the flanges to tighten the nuts. Each bolt, I believe there are 18, has a lock washer. Real fun fitting with my fat fingers, especially considering that there were a total of 8 clean outs or 144 bolts. The bolts are again 1 X 1/4 with lock washers.
The secondary tank had to have a short section of the angle ground away to allow installing the inspection cover. Not a big problem. These tanks, in addition to the vertical angles, are secured by a foot long piece of 2 x 4 glassed in at the aft side of the tank. Since the main tanks are butted right up against the secondary tanks, these 2 X 4's also serve to lock them in place to prevent movement aft.
When we got all done, the welder working with us (he didn't make the tanks) took a look at the installation and said, "If those tanks ever move you have more to worry about than just a loose fuel tank!" I believe him and so will anyone else who looks at it.
The only things left to do now were to install the fill and vent lines, connect bonding wires and ground plane copper strips, and finally install some sort of covers for appearance. We decided not to fully cover the tanks so we could monitor the bottom corners. We did install 3/4" plywood panels over about half of the port tank and most of the starboard tank as mounting panels for water pumps and miscellaneous items. Oh, yes. Don't forget to reinstall the engine.
Capacity of the main tanks is a measured 325 gallons each with 3 gallons unusable. With half a dozen men in the cockpit to allow more fill aft, it would likely take 350 gallons. There is an estimated 15 to 20 gallons expansion space at the 325 gallon level. Capacity of the secondary tanks is a measured 65 gallons each.Total capacity of the tanks is 780 to maybe 830 gallons.
What caused these leaks in the first place? The weld on the inboard bottom of the tanks is covered with fiberglass reinforced plastic. This pulled loose in some areas and allowed water not only to penetrate to the weld, but forced it to sit there until it evaporated. Inside the welds looked sound, so we don't believe it was sedimentary water in the fuel. Perhaps exacerbating the problem was an engine room wash down hose that was used pretty regularly, both by us and the two previous owners. This regularly forced new water under the loose fiber glass and further enlarged the loosened areas. Would it have happened without the fiberglass? Probably it would have as the tanks were not elevated for drainage and ventilation, so any water in that channel along the stringer was going to wet the weld, and would sit if there was a low spot. It would have probably have taken longer for the leaks to occur without the fiberglass, however.
If you have any questions or need anything clarified leave a message
S. B. Hull