Polyethylene diesel tanks

[Andy G]

We have come to the inevitable situation of having to replace our mild steel tanks. Victims of historical leaking decks, their time is up.

There seems to be three main choices of material for the new tanks, Stainless Steel, Aluminium or Polyethlene. I have been reviewing some terrific threads on the forum and have some questions for any who have been down this path.

In particular is it possible to have baffels in the 'plastic' tanks and additionally can they incorporate inspection hatches given the way they are made.For me inspection hatches are important.

I am waiting on prices from two shipwrights to replace the tanks, one who likes the polyethylene tanks and one who prefers stainless steel/aluminium.

Any advice gratefully received.

Andy

 

[Comodave]

Plastic tanks don’t usually have baffles. They are usually rotocast so they can’t do baffles. There are a few places that do welded plastic tanks but not sure if they are approved or not. Personally I would not so S/S because when you weld it you can take some of the stainless out. I would go with aluminum. Make sure the grade is correct, 5052 I think but check to be sure. Then I would have the tanks made out of thicker aluminum than required. That will buy you a longer life at an incremental cost increase. Definitely have inspection ports put in each baffle section.

 

[Lepke]

If you go with metal tanks, coat the inside and the baffles with a good tank coating made for diesel and the tanks will last just about forever.

 

[tiltrider1]

I have know of a few projects that attempted to use welded plastic tanks. In both cases the end product did not pass a pressure test. In both cases the supplier did not make things right.

Now, if a stock rotocast tank fits your needs I would feel comfortable with that as long as you can meet the manufacture's support requirements.

All my tanks have been Aluminum. I use strips of starboard that are glued to the tank with 5200. This keeps the tank a 1/2" off the floor allowing any water to run down the tank and drip off.

 

[CharlieO.]

I replaced with plastic tanks. I didn't get custom made ones, I just ordered ones that would fit where I needed them. Most plastic tanks don't have baffles but some get creative with their molding to try to slow the sloshing effect. As for as access holes, I would only feel comfortable with them on the top of the plastic tank. My tanks do have the sending unit and the fuel and vent lines on top that are mounted onto plates that I can unscrew to see inside the tank. I haven't done it yet, but I plan to cut holes in my floor above those access points to be able to get to them. Luckily the new access points will be under the salon bench and under the cabinet.

When I received my tanks, I actually sent one back for replacement because I wasn't happy with the fit and finish.

I like that I can see my fuel level at quick glance at the tanks. Haven't gotten around to getting the gauges yet.

All the above is based on my experience and opinion.

 

[boomerang]

Being able to see the exact level of product in a (opaque) poly tank is a great asset for me. I also understand that poly doesn't allow for condensation to form in the tanks as readily as metal tanks ,which seems like it would be a plus ,too, if that is true.
Something I've wondered about is poly allowing light in and promoting algae growth ,which is a mariners worst nightmare in a fuel tank. (Knock on wood), our poly tanks have remained squeaky clean.

 

[psneeld]

Boomerang's poly tanks also have baffles in them. They are way smaller than the original tanks but for ACIW cruising, they were fine.

The baffles in rotomolded tanks are often just a what appears to be a large hole though the tank (top to bottom) that forces the fuel to flow around it and cuts the volume allowed to slosh back and forth.

 

[Andy G]

Interesting meeting today with the shipwright who is looking at our tank replacement.

Apparently the 'plastic' tanks have baffels and inspection ports. This was something I was not aware of.

The tanks are welded. A box is made up then the baffels are welded in before the top is also welded on. There is an inspection port on the top of the tank. A side inspection port is probably prefereable but not a deal breaker.

They have fitted quite a few tanks this way with no issues. This boat shed deals with a lot of the classic Halvorsen boats as well as Island Gypsy's. The old tanks will be cut up in situ after removing the Gen Set, motors stay in place, no idea on price yet.

 

[alormaria]

My info is pretty old (1995) but I had the tanks replaced with exact duplicates made of aluminum by a reputable tank maker here in NJ. The engine was pulled, the leaking tanks removed intact and sent to the tank maker to duplicate them in aluminum. It's thick aluminum, I don't know how thick, and painted. They were placed in the original mounts and the engine replaced.

The boatyard took care of everything. I just signed checks. With a few additions the bill came to a little over $8,000.00. Took most of the summer. Launched the next spring with no problems.



Hope yours is as painless.

 

[DDW]

If you are having custom aluminum tanks made, consider specifying two things which will improve and lengthen life: first, put a small sump or definite low point right under the pickup, and a 1 1/4 port directly above. This allows the gunk and water to collect, and a means of extracting it easily with a suction pump. Second, have them weld the seams on the side first (of course, you can only do that on the bottom 5 sides before the top goes on). This makes the inside corners much cleaner than if welded only from the outside, which leaves the welding 'sugar' on the inside seam. Cleaner corners trap less gunk and water, often it is the seam that fails first.

 

[HeadMistress]

Fwiw, PE fuel tanks must be made from a different type of PE than water or waste tanks and must meet USCG criteria.


Water and waste tanks are made using LINEAR PE...fuel will saturate it. Fuel tanks must be made using CROSS LINKED PE...among the things the USCG requires are "all fittings must be on the top of the tank" and "cannot have any surface on which liquid can pool." There are few more things that I've never learned because I've never had anything to do with fuel tanks.


--Peggie

 

[rslifkin]

Fwiw, PE fuel tanks must be made from a different type of PE than water or waste tanks and must meet USCG criteria.


Water and waste tanks are made using LINEAR PE...fuel will saturate it. Fuel tanks must be made using CROSS LINKED PE...among the things the USCG requires are "all fittings must be on the top of the tank" and "cannot have any surface on which liquid can pool." There are few more things that I've never learned because I've never had anything to do with fuel tanks.


--Peggie

The fittings only on the top requirement is only for gasoline tanks. Diesel tanks are allowed to have fittings elsewhere on the tank (for a sump drain, bottom outlet, or sight tubes).

 

[Southern Boater]

……….This boat shed deals with a lot of the classic Halvorsen boats as well as Island Gypsy's.

Bobbin Head or Cottage Point spring to mind?!

 

[Andy G]

Bobbin Head or Cottage Point spring to mind?!

Yep, Cottage Point.

 

[slowgoesit]

The fittings only on the top requirement is only for gasoline tanks. Diesel tanks are allowed to have fittings elsewhere on the tank (for a sump drain, bottom outlet, or sight tubes).

I was under the impression that ABYC recently changed their recommendations to allow only top openings for new diesel tanks as well. Am I mistaken?!?

 

[Comodave]

I didn’t see anything like that. I did see where it talked about sight tubes having shutoff valves. So the fittings for that would not be just on the top.

 

[rslifkin]

I was under the impression that ABYC recently changed their recommendations to allow only top openings for new diesel tanks as well. Am I mistaken?!?

It's possible they have, but if so, I haven't seen a mention of it. For gas tanks, as far as I know it's a USCG requirement, but not for diesel.

 

[stephenbandi]

I replaced both of my 200 gallon tanks with 4 50 gallon polypropylene tanks. Easy to get in without removing engines, no need for baffles and I did add inspection access to each.

 

[fdw]

Source for polypropylene diesel tanks

stephenbandi: Would you please share your source and/or link for the polypropylene diesel thanks. Thanks. FDW

 

[oguidry]

My Sabre 38 has polyethylene fuel tanks manufactured by Moeller. The label says that they are made of "Crosslink Poly" and recommended for diesel.

 

[Comodave]

We had a Triumph center console that was completely rotocast HDPE. It was a neat boat. Indestructible. I have hit it with a sledge hammer and it just bounced off. It had a plastic fuel tank. It never leaked but you could smell a faint whiff of gas if you opened the compartment where the gas tank was located. Don’t know exactly what plastic the tank was made out of though. But diesel has different requirements.

 

[Sailor of Fortune]

Definitely not stainless steel for fuel tank... Mild steel, Aluminum etc.. Fiberglass fuel tanks work well too..

 

[Parry]

Talk to Shane Douglas at Douglas Marine.
I believe he has done several of these.
He suggested it for my GB42 when/if the fuel tanks need replacing.

https://www.douglasmarine.com.au/

 

[stephenbandi]

Moelerhttps://www.westmarine.com/moeller-50-gallon-permanent-below-deck-fuel-tank-45inchl-x-12.5inchw-x-22inchh-8978538.html?&utm_medium=cpc&utm_source=google&utm_campaign=PMax:%20GSC%3eSmart_Shopping%3eEngine%20SystemsEngineSystemsBreakout1_Test&gclid=Cj0KCQjw0vWnBhC6ARIsAJpJM6dqYEbMsCAm9lTASlHviMh4O0-kMKjhAi1BJU7mOhlGE0_K3zw_5SMaAjgjEALw_wcB

 

[Andy G]

Talk to Shane Douglas at Douglas Marine.
I believe he has done several of these.
He suggested it for my GB42 when/if the fuel tanks need replacing.

https://www.douglasmarine.com.au/

Thanks, I will contact him.

 

[BruceK]

Yep, Cottage Point.

High standard of work gives rise to Andrew`s well deserved popularity but, it can mean months in a queue to have your job done.

 

[kapnd]

If you do decide to go with metal tanks of any material, get the sides folded on a brake, and eliminate much of the welding.
Canting the tops can help prevent further damage from leaky decks, and a sump drain can save lots of headaches later on.

 

[Almad]

I replaced steel tanks with fibreglass. 2x1000.
Then at a later date topped up with 4x390 litre baffled pe tanks from vetus for extended cruising.
All work really well, except that there is a small leak on filling one tank from the top mounted inspection hatch that has me beat atm.
Interesting as noted before to not allow fuel to pool, as over the 6 years they’ve been installed, the tops have subsided 2cm(?) ish, so makes mopping up any spills easy. But maybe doesn’t hold the 390 litres any more?