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Old 28-04-2018, 19:14   #1
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Diesel Tank Fittings and Plumbing

I started another thread for advice on diesel tanks, but the scope of my project has changed enough so I am starting another one. I am replacing the 1 tank in the bilge with 2 tanks under the after berths. This gives 2 isolated tanks and increases storage by ~50%. Since this is my first fuel system I would appreciate comments on the attached schematic and tank layout. The tank is on order, but I should have a week or so to change details of the design. I also included a picture of the tank mock-up I made out of cardboard, access to the top is very good and it fits through all the hatches. It will be made from 316L stainless, that is the only thing that is 100% fixed and I already know the pros and cons of that...
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Old 28-04-2018, 19:42   #2
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Re: Diesel Tank Fittings and Plumbing

Quote:
Originally Posted by SpaceRnglr View Post
I started another thread for advice on diesel tanks, but the scope of my project has changed enough so I am starting another one. I am replacing the 1 tank in the bilge with 2 tanks under the after berths. This gives 2 isolated tanks and increases storage by ~50%. Since this is my first fuel system I would appreciate comments on the attached schematic and tank layout. The tank is on order, but I should have a week or so to change details of the design. I also included a picture of the tank mock-up I made out of cardboard, access to the top is very good and it fits through all the hatches. It will be made from 316L stainless, that is the only thing that is 100% fixed and I already know the pros and cons of that...
Hi, the only comment I would make is that the tanks will have to be managed well as with any heel the pickup from one tank may pickup air if the tank is partially full wile the other tank will be fine. There is also the issue of relocation of the weight of the fuel further aft.
These are the reasons that the best place for the tankage is amidships, the keel or just above it being the perfect position.
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Old 28-04-2018, 20:03   #3
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Re: Diesel Tank Fittings and Plumbing

A suggestion... if at all possible add a sump and a low point drain. If you ever get water int he tanks you'll be very happy you did.

A couple serious concerns...

These are VERY shallow tanks. You will have a lot of trouble keeping the feed line submerged as the boat rolls with partially full tanks.

That is a LOT of free liquid surface. Have you done a stability calculation to be sure it is OK?

The tanks will be very noisy when partially full... under a sleeping berth they will be a nightmare.
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Old 28-04-2018, 20:35   #4
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Re: Diesel Tank Fittings and Plumbing

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Originally Posted by billknny View Post



These are VERY shallow tanks. You will have a lot of trouble keeping the feed line submerged as the boat rolls with partially full tanks.



That is a LOT of free liquid surface. Have you done a stability calculation to be sure it is OK?



The tanks will be very noisy when partially full... under a sleeping berth they will be a nightmare.

The drawing I included is not to scale... the fuel pickup area is 39 cm deep whereas the tank is ~90cm long and 15 cm tall on the outside edge. Actually the tank it is replacing was in the bilge straddling the keel (I am moving the holding tank there...) It was 1.4m long and only 24cm deep-this is one of the main reasons I am moving it... The new setup will be much better for heeling. There is no space for a specific sump, but there is a pump out line going to the very bottom of the tank so that is the next best thing...

I am worried about noise. Does anyone have experience with having tanks directly under the berth? I am hoping the baffle helps some. I don’t really have anywhere else on the boat I can put it and get reasonable volume so I hope it is not so bad...
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Old 29-04-2018, 08:43   #5
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Re: Diesel Tank Fittings and Plumbing

I can't clearly view your drawings even after download, but as I am just finishing up new tankage on a vessel, here are some ideas for you.

Bring all tank selection valving to a common point and mount them to a single easily accessed panel. Install plenty of baffels in your tank, limiting hole size, and assure your builder welds them 100pct on the perimeter, no tack welding nor 3 sided welding on the baffels - the tank must be built as a tube with the end plate last. (I'm replacing 5 year old tanks due to jackass welder advertised as a tank builder.)

One possible innovative idea we're doing is to build 3" high walls around the fuel pickup point so that fuel cant momentarily roll away from the pickup. It might also keep much debris away too. There's a small hole at the base of the wall to keep it replenished during low fuel situations.
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Old 29-04-2018, 08:44   #6
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Re: Diesel Tank Fittings and Plumbing

Schematic too small to see details.

Note: U. S. code requires a separate fuel fill on deck for each tank.

I recommend you valve return lines so you can return fuel from tank being used to either fuel tank, if you haven't done it already.

Multiple tanks make sense in case one get contaminated.
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Old 29-04-2018, 09:01   #7
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Re: Diesel Tank Fittings and Plumbing

The previous owner of a Paceship 29 I owned had replaced the fuel tank. The new tank was under the quarter berth. It was a good tank, but he hadn't taken into account the attached plumbing. The vent and fill lines came out the top with straight fittings that meant there was absolutely no way to put the locker lid back on...so the quarter berth could not be used at all. (this was just ONE of many reasons I was able to buy the boat VERY VERY cheap!!!). I was able to replace the hose connectors with 90 degree fittings and slightly re-position the tank so finally the locker lid could go back on and I reclaimed the quarter berth.

Anyway, I guess I'm saying don't just think about the tank...think about the hoses and connectors too.
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Old 29-04-2018, 11:27   #8
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Re: Diesel Tank Fittings and Plumbing

Its too bad you didn't post earlier asking for advice on the tank relocation plan. I'd second most of the comments here about desirability if the aft location. In addition, if you will be using the bilge area for storage, it will be inherently more damp than under the aft bunk.
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Old 29-04-2018, 14:07   #9
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Re: Diesel Tank Fittings and Plumbing

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Its too bad you didn't post earlier asking for advice on the tank relocation plan. I'd second most of the comments here about desirability if the aft location. In addition, if you will be using the bilge area for storage, it will be inherently more damp than under the aft bunk.
I did post in another thread about location--see link. http://www.cruisersforum.com/forums/...-s-199889.html

I have the original manufacturing drawing of the boat that show the tanks where I am putting them under the aftr berths, but they were crossed out as they were relocated in the bilge during manufacture. At some point, the original diesel tank was replaced by the one seen in the attached picture. It is 1.4m wide and only 26 cm deep. The bilge under the tank had a low spot that pooled liquid and the tank had not been installed with an air gap underneath it. No surprise it failed due to a few coin sized areas of severe corrosion. The tank was only 180l at best and due to its shallow design if the boat was heeling at all it effective volume was much reduced. I was also struggling to figure out how to get more tankage as 180l is less than ideal. All in all, I wasn't happy with the design so what started as a simple "lets have a look under the tank" has turned into something much bigger.

I am going fill the low spot in the bilge and put a fiberglass holding (sewage) tank where the old diesel tank was. It should be impervious to dampness and the plumbing is dead simple. The area under the aft births has always been bone dry so I am hoping the new tanks outlast the boat.

On a 44foot boat designed specifically to maximize accommodation (which is why we bought her) something is always going to be a compromise. Tanks are always a compromise and in my case I think they layout I am moving towards is the best option. No metal is cut so I can always change if anyone here has a great idea.
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Old 29-04-2018, 14:11   #10
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Re: Diesel Tank Fittings and Plumbing

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Originally Posted by Maka View Post
Schematic too small to see details.

Note: U. S. code requires a separate fuel fill on deck for each tank.

I recommend you valve return lines so you can return fuel from tank being used to either fuel tank, if you haven't done it already.

Multiple tanks make sense in case one get contaminated.
Lets see if I can upload a .pdf I think I covered all your points but I would love suggestions to simplify or improve the plumbing.
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Old 29-04-2018, 15:02   #11
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Re: Diesel Tank Fittings and Plumbing

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Originally Posted by hamburking View Post
I was able to replace the hose connectors with 90 degree fittings and slightly re-position the tank so finally the locker lid could go back on and I reclaimed the quarter berth.
How was the noise from the tank after you got everything back together? I am hoping 4 inches of memory foam provides a decent sound attenuation and the baffle helps keep the noise down...

The comments about connections are a good one. There is 6.5 cm between the top of the tank and the bottom of the locker lid. 1.5 inch hose has a 47mm outer diameter so clearly space is tight. Looking at this again I think I will specify a 90deg bend for the fill and vent lines to make sure it fits... The other connections are 1/2 inch threads so I can get 90deg bends that are very small--these are not a particular concern. The top connections are clearly an area I need to watch carefully for during manufacture...

I have updated the tank drawing to be closer to the scale of the actual tank. This shows how deep it actually is much better and hopefully solves some of the concerns regarding tank depth. Please note the drawing is still not completely to scale, especially regarding the pick up pipes.

Further comments are appreciated!
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Old 29-04-2018, 18:59   #12
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Re: Diesel Tank Fittings and Plumbing

As an alternative idea, we replaced our single black-iron diesel fuel tank with a 10mm close-linked polypropalyne tank. It is much lighter, has no corrosion issues, is quieter (its right under our (Mastr Ste) bed, and was cheaper! It's been in service now since 2013, with no issues.
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Old 29-04-2018, 19:14   #13
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Re: Diesel Tank Fittings and Plumbing

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As an alternative idea, we replaced our single black-iron diesel fuel tank with a 10mm close-linked polypropalyne tank.

I tried to use a plastic tank... problem is can’t get them locally, I couldn’t get a standard size that gave me decent tank volume (and I looked hours and hours and hours...), shipping to get them to Singapore is just incredibly expensive, and I would have to build the support structure under the tank. I got a quote from Tek Tanks as they had the closest standard size and shipping alone was over 500 GBP per tank! I also got quotes for aluminium and it was also very expensive here. I am going with 316L as it is the best value I could find, will be custom fit to give over 300 litres total tank volume, and will give me years of service in this very dry part of the boat...
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Old 29-04-2018, 22:30   #14
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Re: Diesel Tank Fittings and Plumbing

Just a straight question. Why are you using stainless steel? I have removed SS fuel and water tanks from boats but never a black steel fuel tank. The removed tanks all had spot corrosion holes. If a yard is fabricating the SS tanks I would be asking for a warranty for at least 5 years. There is no such thing as rustless steel irrespective of what the alloy is. My own mild steel fuel tanks (two at 350 L and one at 80 L) are now over 40 years old and still OK. They have oil based paints on the outside.
The wall thickness is 1/8 of an inch which allowed me to be successful with my very amateurish welding.
316 is not even a particularly rust resistant alloy. I think you may find its major property is that it is non magnetic (austenitic), so it is preferable around a compass. (304 and 316 alloys both contain the appropriate amount of nickel to confer this property.) I suspect corrosion resistance is also dependent on other factors such as surface treatment etc. Check it out as SS is not only much more expensive but may also be less reliable for your intended use. Very thin SS can also be prone to fatigue induced stress cracking which I understand is partly why SS rigging is periodically replaced.
Yes, it can be shiny .... but "all that glistens is not gold "...or even rust resistant.
Whatever you use I most strongly recommend that you have lowest point drains to remove any water or other rubbish that finds its way into the tanks. Very cheap insurance when building tanks.
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Old 10-05-2018, 00:45   #15
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Re: Diesel Tank Fittings and Plumbing

Thanks for the help so far. Tank is ordered. Next question is the vent. My original plan was to put the vent on the transom but that will require a 1m Long flat run of hose before I can go vertical. That makes me a little nervous about an air lock. The other option is putting the vent on the side of the hill about 2/3 of the way back. Plumbing would be very easy but I am scared about water getting in the vent when heeled. Any thoughts? Also, should I spec in a float valve in the vent line connection a the tank to prevent liquid from going up the vent hose? Perko seem to have some products that may work for both topics...
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