A Monel tank is a bad thing?

[LazyGuy]

Paper Moon is in the process of getting a new diesel. Yes.... pictures to follow. The mechanic tells me that I need to replace the Monel tank. While it is 40 years old, I was planning on removing the tank, cutting an access hole in the top, cleaning it out, installing the access plate, pressure testing it and putting it right back in. His claim is that Monel is no longer used because it does not crack it fractures and surveyors will no longer allow Monel. I always understood that Monel was the best and the only reason it is no longer used is cost.

The cost/time issue of replacing the tank is probably a wash. Especially when you consider I will need to add a diesel return line to the tank. For the existing tank, which was a switch from gas to diesel 20 years ago, they put a T in the vent line for the return. I scratched my head but it worked.

The tank is located under the cockpit sole/ above and a little behind the engine. It is supported by a fiberglass sling that is enabled by the rounded corners of the Monel tank. An Aluminum tank will have square corners that will require me to completely rethink the mounting of the tank (fiberglass does not do corners well).

Thanks for the opinions.

[Tim]

Monel is still an acceptable material for a diesel fuel tank, assuming the wall thickness is a minimum of 0.031" (according to ABYC H-33 Table IV and referenced by ABYC H-33.18.3.1). I think it's always prudent, when upgrading on-board systems and installations, to ensure that older materials, when reused, generally meet current standards.

Monel is an alloy of copper, nickel, and other elements, and is known to be extremely corrosion resistant and long-lasting. I don't know about its failure mechanism, or the potential thereunto, but assuming the tank is in good condition, meets current and applicable standards for tank wall thickness and testing, and has no obvious flaws I don't see why it'd be a problem to reuse it as you suggest.

That said, there's a strong argument to be made for replacing the tank at this juncture as well, but not for the reasons you've been told--at least not that I can determine in 5 minutes of research.

I'd be interested in hearing the chapter and verse being quoted by these surveyors who, according to your mechanic, are "not allowing" Monel.

[catamount]

I voted no, keep the tank.

[LazyGuy]

I'd be interested in hearing the chapter and verse being quoted by these surveyors who, according to your mechanic, are "not allowing" Monel.

Me too. He gave me a name and it is the surveyor I used last spring. I will post what he says. The mechanic I am using is very good but he is all gloom and doom when it comes to anything that is not exactly the way he thinks it should be. There is only one way to do it and if you don't do it that way, you may die.

It looks like we will be going with a Phasor diesel. It is another brand of marinized Kubota. They derate the the horsepower and use the next larger block than Beta. In other words, Beta 28 is the 1005 block at 3400 RPM while the Phasor 28 is the 1105 block at 2800 RPM. I had never heard of Phasor but they are built in Florida. I will be doing a bit more research before I pull the trigger.

[Tim]

Please continue to post details on your engine repower as you go along, including anything more you find out on this Monel issue (or non-issue, as the case may be...)

The Phasor diesels look interesting, so lots of pictures and details, please! This is all very relevant.

For comparison's sake as you look into the engines, check out the pricing on this site. I bought a Vetus diesel from these folks a few years ago and found their pricing on that particular engine to be far and away the most reasonable.

Link: Phasor Diesel Pricing from Marine Engines

[Arcadia]

I believe you you are talking about a Luders 33?

If that's the case, I have the same boat and went through the same exercise a few years ago. I ended building a tank that had a sloped shallow 'v' bottom for better fuel pickup (more usable fuel) and a location to pump potential water from the bottom sump area. The pick up and sump are nearly directly below the fill, which is strait into the tank. I can reach the sump with a small hose with a squeeze bulb type pump from an outboard fuel line. The tank may have a little less capacity, but I figure we would lose quite a few gallons of usable capacity just from having a flat bottomed tank.

Our tank was mounted the same as yours. I simply left the wooden spacer blocks glassed under the cockpit in place when I removed the tank. I had aluminum angle iron welded along the length of both sides of the top of the new tank. The tank was designed to be wide enough for the angle iron flange to slip up around the existing mounting blocks where it is through bolted in place.

If you'd like, I can post photos (if I can remember how), but unfortunately I am headed out of town for the next week or so and don't have time to get down to the boat before I go.

I'm also interested in your diesel choices as I will have to do either a rebuild of an old Yanmar 3GM or new engine in the near future as well.

[LazyGuy]

Arcadia,

Yes, I have questions:

Did you remove the old tank without destroying it? If yes... How? The tank has two bands of fiberglass holding it up and appears to be bedded in 5200. If the tank cannot come out in one piece, I will not loose sleep over it.

I certainly am interested not only in your replacement tank and how you set it up but who made it? Are there any other changes you would have made if you were to do it now?

Thanks

[Arcadia]

Dennis
In haste; I was able to simply grind the glass at the joint of the tank and wooden mounting spacers without any problem. I strapped the tank to the cockpit to support it while cutting.
I don't think our tank had ever been out, although it had a diesel in it at the time we bought it. (I was told most L-33s came with gas engines, especially the early ones.) I think our tank also had a 'T' into the vent for the return, which also argues for an earlier gas installation. From what I could see of the inside it was quite a mess. If yours is bedded in 5200(ours wasn't), you might have more of a problem, but I suspect you could cut it with a chisel. The bearing surface is not that great if I recall.
I will see if I can find my drawings for the tank, it was about ten years ago. If I can't find them I can get you the rough dimensions, you'll probably need to make some adjustment to fit your boat anyway. If I am remembering correctly the tank ended up being 26 gallons, it think the original was listed as 28, but as I mentioned before I think we probably have about the same amount of usable fuel anyway. I'll also have to check with my yard about who they used for the fabrication. I did the removal and installation but I just gave them the drawings and they sent them out. I think it was some place in R.I. but not sure. I'll get back to you on that.
In retrospect, I would put an inspection port in if I were to do it again. At the time I couldn't think of an easy and water tight way to open up enough of the cockpit floor to make effective access to a clean out. Without that access, there really seemed no reason to put in an inspection port; there would be no way to reach it without removing the tank. I was also concerned with possible leakage. Since I was bolting the tank in place, I figured it wouldn't be that much work to just remove it and send it out to be steam cleaned.( Of course I'm kind of kicking myself now, especially since we've all seen Tim's nice aluminum hatches)
I might also consider a true sump if it would fit. The sloping 'V' bottom that we have works fine, and there really wasn't much more room to go lower with the tank bottom, but it would be nice to know for sure that if any water got into the tank it would be in only one spot, and not potentially sloshing around the bottom of the tank. That said, I don't recall ever sucking up any water, and adding a true sump to the bottom would add to the cost somewhat, depending on how it was done.
Unfortunately, I probably will not be able to get any of these things to you before next week, but I'll get back to you.

Chris

[Zach]

The CG 83 footer I've been helping out with had 3 monel water tanks. They all leaked at the lower corner welds. Not sure what the service life is, but the boat is WWII vintage.

I pulled a few hunks out of the scrap pile, and the cracks were outlined by extremely fine red lines, the red goes through the thickness of the metal.

[Ceasar Choppy]

Sounds like the magnfluxed the metal to determine where the cracks were and decided not to repair.

I do know that with monel, seams are brazed-- not welded. It is a softer, weaker metal than stainless or aluminum, but you can't beat the corrosion resistence. A service life of 50+ years sounds pretty good to me.