Water Tanks

My current boat ( 28 Carver Mariner) has a whopping 25 gallon water tank and Im amazed at how long we can make that 25 gallons last. On the current boat we use water primarily for washing dishes and an occasional quick shower. The head on the Carver is raw water flushed so we dont tap into that precious 25 gallon supply.

The water tanks on the trawler ( I guess Im going to have to name her soon so I stop calling her the " trawler ") are constructed out of stainless steel. I went with stainless steel vs plastic for a few reasons. Stainless is considered top of the line in regard to potable water tanks. Due to where Im placing the tanks it made more sense for me to fabricate the tanks vs having them fabricated out of plastic. I used 14 gauge 316L for fabricating the tanks. All the associated fittings for the tanks are 3/4 NPT stainless ( fill, vent, supply) couplers welded in place. All the tanks have one center baffle running across the width of the tank. The tanks fit between the frames of the forward area so the tanks have to fit into a 30" wide space. Because of the 2" flange I welded on to the frames I had to make the tanks 27" in width to give me a little room for the install. I might be kicking myself in the ass years down the road, but I decided to not install inspection covers in the tanks. I have a total of 8 tanks giving me approximately 350 gallons of water.

The tanks are held in place with a flange welded on to the front and back of each tank. The forward mounting system consists of a bracket welded to the hull with 3/8 studs welded to that bracket. The forward tank flange fits over those 4 studs and is bolted down. The rear mounting system consists of a similar bracket only I welded nuts to that bracket and used four 3/8 bolts through the tank flange to mount the rear part of each tank. I used studs on the forward mounting system because the bracket is so deep it was easier to get a nut started vs getting a bolt started. It was also easier installing the tank by dropping the tank over the studs then having a little wiggle room to get the bolts started in rear of the tank. For 3/8 studs and bolts I drilled the corresponding mounting flange to 1/2 " and used thick washers for the mount. I made a gasket out of flexible PVC to help isolate the tank bottom from the mounting brackets ( no metal to metal contact other than the mounting hardware). I allowed myself 4" of clearance between the front of the tank and the center longitudinal frame ( center spine). 4" of clearance was barely enough room, as it is a tight fit to get my arm in there. All the tank mounting hardware is stainless steel

To supply water to the pump I welded a 3/4 stainless coupler in the the bottom of each tank. Having given this a little more thought I now wish I had used a pick up tube entering the top of the tank and going to the bottom. Too late for the pick up tube method now, but again I wish I had gone that route. So each tank has a coupler welded in for supply, followed by a gate valve for each tank,followed by a "T" for each tank, all of this terminates into a common supply line leading to the pump. I went with this set up so I could isolate each tank vs all eight tanks having a shared liquid level. If I ever have a catastrophic failure of a tank, I can take that tank off line and not loose all my water. I also have the choice of just filling a couple of tanks if I want. Since I am able to isolate the supply side of the tanks, I also have to be able to isolate the vent side of the tanks. All the vents will terminate at a manifold that can be valved before venting at the wheel house deck above the fill point. The tanks will fill from two points on the wheel house deck via port or starboard fill pipes. Because of the large cabin and wheel house roof areas Im making provisions to be able catch water off the roof to fill the tanks.

I air tested each tank to 6 psi as this will be more than the static head the tanks will see once the vent tube fills to the deck level. After I fabricated the tanks I installed them to check fit and make sure all my brackets would work so I could start the interior painting. If I had been a little more careful with my measuring and fabricating I could have squeezed another 50 gallons of storage in my system, but all in all Im happy with 350 gallons.

Read More..

Fuel tanks

I have four fuel tanks on board of my trawler. Given this first sentence seems to sum things up I could be getting off easy in regard to this post and leave it at that. But since Im a little on the long winded side of this world, and the fact that Im totally into all things steel boats, I feel as if I should elaborate a little on my fuel tanks.

The four fuel tanks on board are integral tanks meaning they are now part of the hull. The tanks are on the outboard sides of the hull in the engine room between station 9 @ 14. I am using the term station as this is how the prints describe frame locations, and these two locations are actually steel bulkheads. I framed the tanks using 1/4" plate. All the tanks have a baffle located @ 30" on center witch is also what the frame spacing is. The baffles have the corners clipped off of them and also have 2" holes in the center to let fuel flow freely between them. The baffles are welded on all four sides of the tank walls and by using the slug welding method I was able to weld the baffle to the tank top. All four tanks have a drain valve at the lowest point in the tank in case I ever have to empty the tanks completely.

I could not in good conscience build these four tanks without providing a way to get back inside of them if I ever have to. I added an inspection port between each baffle for future maintenance. The inspection covers are made of 3/8 plate and are attached to the tank by a 3/8 stud that is welded to the inside of the tank wall. The inspection ports are 12" in diameter and are in the front wall of the tank. Because of the size of the tanks, putting the inspection ports on the top of the tanks made no sense as it would serve little use due to the depth of the tank. Getting the inspection covers to pass the air test proved to be the most difficult part of building these tanks. Using fuel rated gasket material I cut a gasket for each cover and punched holes for the studs. I then used a fuel rated gasket sealant applied to the gasket to improve the seal of the gasket. Because I did not want to stretch my mounting studs I used a torque wrench to tighten the nuts to the correct torque for a 3/8 bolt. My first air test showed each stud to leak! Next I tried using a heavy thread sealant on the studs. My next air test showed the studs to leak! The problem was the weld holding the stud to the tank was not air tight and my 7 psi air test was leaking past this weld and then past the mounting nut. My solution to making the covers air tight was to mill a counter sink in each tank cover to accept an "O" ring for each stud. I milled the counter sink in the covers to a precise depth so that the washer under the nut would compress the fuel rated "O" ring and provide a seal once the nuts were torqued down. My next air test proved all the studs passed the 7 psi test. I spent another day or so finding pinhole leaks in the tanks and making weld repairs. The final air test was to have the tanks hold 7 psi for 24 hours.

My two forward tanks ( port and starboard) hold 200 gallons each. The two aft tanks ( port and starboard) hold 500 gallons each. I intend to use one of the forward 200 gallon tanks for running the main engine and generator and the other three tanks will be used for storage. Ill have to transfer fuel from the various tanks via an electric fuel transfer pump. Ill probably use this same pump to polish my fuel from time to time to keep it clean and keep the condensation water out of the fuel. The total fuel capacity on board will be around 14oo gallons. This 1400 gallons is more than what the boat was designed for so I contacted the architect who designed the boat and reviewed this with him. Hal Wittacre ( the naval architect) did some stability calculations and recommended adding more ballast to the boat.

Each tank has a pick up tube for fuel supply and return. These pick up tubes go to within 1" of the tank bottoms. There is a fill point for both port and starboard on the aft deck of the boat. A two inch steel pipe will be used as the fill tube, with a vent that leads back to the fill port. The fill ports on the tanks just dump into the the top of the tank but I want to change that and add a tube that goes to the tank bottom. Bringing the fill tube to the tank bottom is a better design element for fuel tanks and I will make this change.

The fuel management system is fairly complex and really needs its own post to get into the details. Once I start work on this part of the fuel system Ill add a fuel management post.

The tanks are shown in these pictures with a plywood cover. I did this so that I could protect them during construction. Plywood will also be the final cover as there are many things that will be attached to this plywood.

Conall

Read More..

Water tanks installation

I have eight water tanks for my potable water supply located under the forward sole of my boat. The first tank I built I measured for cubic footage, then filled it with water, and by using a shut off valve and a five gallon bucket I was able to measure the amount of water in the tank. My method of measuring cubic footage and measuring with the five gallon bucket gave me about the same volume of water within two gallons, so Ill stick with measuring for cubic footage vs filling each tank to get volume. I have 325 + gallons worth of water tanks.

After the boat is insulated and Im assembling components of supply, vent, and filling of the tanks, Ill post more regarding the system as a whole.

Im mounting the water tanks using a flange welded to the tank ends and a corresponding bracket welded to the hull of the boat. Where the bracket is deeper in the hull ( by the center line of the boat), I used studs welded to the hull bracket that the tank flange will drop over. On the less deep end of the tank ( outboard ends), I used nuts welded to the hull brackets that the tank flange will bolt to. I used 30 mill pvc pond liner I had laying around the shop to act as a gasket to go between each tank flange and hull bracket.

I had installed the tanks prior to final painting to make sure all the brackets would work and also that the tanks would finish out below the sole framing. I also needed to verify that the valves I was using on the supply end of the tanks would clear all the steel framing. I ended up having to adjust the access holes in the frames for the tank fill lines ( I guess I screwed up on the cut twice measure once thing). 4 3/8" clearance between the front of the tank and the center longitudinal frame of the boat is barely enough ( it fit) room to get a close nipple, valve, close nipple then a "T" for the tank supply. I dont think the Governator would be able to get his arm down in that space to operate this gate valve, but Im able to so Im happy with the final fit. Because I had installed the tanks prior to painting the tank install went fairly smooth. My 13 year old son helped me as the tanks are to large for one person to handle. The only real issue we had was that the amount of paint on the hull brackets caused me to use a tap or a die to clean up the threads on the respective hull bracket. The tanks are a tight fit between the frames so we used as much care as possible lowering each tank into its "bay" so we would not damage the paint. It would take a hard hit to get through all the coats of paint in the bilge area, but I still was very carefull.

I held off installing the tanks as long as possible to try to keep the trash generated from bolting the firing lumber to the frames from getting under the tanks.

Conall

Read More..