Fuel tanks for wooden hulls

I’m studying for my 3rds. I’m preparing by drafting answers to questions which people have reported seeing on their exams. At least twice in recent experience the following has been seen on the Transport Canada 3rd Class Engineering Knowledge General Exam.

DESCRIBE how a fuel oil tank is fitted in a wooden vessel, giving details of construction of the tank and fittings on the tank. What is the purpose of wire gauge diaphragms?

I have a lot of old books in PDF, but I haven’t seen any mention of this topic. Anyone can’t point me in the right way?

I’ve got a wooden boat and the tank is stuck on a platform mounted to the frames.
The attached is fairly straightforward but note the details about corrosion.


According to that, the answer to the first part of the question is plastic and glue. Which, for all I know, is a perfectly good modern method. My sense is that this question is a fossil from a bygone age, and its therefore likely that the correct answer will be of a similar vintage.

Are they talking about a strain guage connected to a diaphragm capsule? Wire gauge meaning one of the earliest pressure sensor types designed for remote reading and suited for tank level indicators. The modern version is a strain gauge mounted on a diaphragm with signal processing that delivers an output in current or voltage.



I think that’s a winner. Thank you!

I think that’s actually an old term with a possible typo for ‘wire gauze diaphragm’. I was confused at the phrase considering the topic—wood boats and fuel tanks. Mandatory fuel sensor tech when you could get away with a sight glass or sounding rod? But considering the phrase ‘wire gauze diaphragm’ appears in a couple Brit-related codes I’ve identified specific to fuel tank venting — believe they mean it as ‘gauze’ which is a archaic way of saying it’s a flame screen/arrestor.

“ Vent pipes from tank spaces and fuel tanks shall comply with the relevant requirements of Part C Section 2: Watertight and Weathertight Integrity of the NSCV. They shall be separate and non-communicating, and shall be fitted with spark arresters (e.g. wire gauze diaphragms).”

For the rest of the question, I’d advise the Transport Canada regs for wood passenger vessels. It’s a simple matter, what materials, how thick, baffles, venting (vent outside the machinery space), access hatches, location (Outside machinery space), fill pipe, gauging, and on a wood boat, if metal tank, electrically bonded to the main engine or main grounding point etc…

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That’s kinda what I was thinking. Or maybe, someone somewhere, long ago made a no-go “gauge” to make sure the holes in the flame arrester weren’t deformed and too big. I’m looking at you, Sir Humphry.

welcome back emrobu, can’t believe it’s been a year!, we’re all surprised sometimes by some archaic thing in the question pool, i’m sure canada has a few of them too but gauze is gauze and most certainly used in a flame screen.
I’d think that after apollo 13 and that airline incident (unless it was a missile) the industry tries to avoid putting electricity into a fuel tank. sonar, sight tubes, mechanical bs etc. etc. is what i’ve seen more of.

Thanks, @jimrr.

I’ve been searching for a regulation as @Jamesbrown suggested. Everything I’m finding is about fire resistant coatings, insulation, and fire fighting systems. It looks like

UL 1102-1992, Non integral Marine Fuel Tanks

might have the information, but its behind an $800 paywall, and it might be referring to gasoline, in which case my exam answer will be:


Try this link, review the fuel oil section (section 8) for requirements for tanks in terms of construction and variable properties. See also page 68 (of the document not pdf) for location of fuel tanks on wooden vessels.

It is reasonable to assume this reflects a ‘general engineering’ standard for a wooden vessel—which would tend to be of this kind of service since most higher levels of service, require steel or equivalent hulls. It’s not dissimilar to US rules for small passenger vessels. Class rules (the standard for good engineering) for wood boats would be another place to look. But, by seeing what the regulations require, an idea of ‘general engineering’ comes through, how big, what material, where situated, what fittings, should there be an access hatch for inspection and cleaning, etc… since it is a reg, and an older set of regs, it will be a minimum standard, which authorities hope is within the bounds of ‘good’ engineering.

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You are a scholar and a gentleman, sir! Warmest tanks! I mean, ‘thanks.’

Also this, to your point about the typo:

The outlet of this vent is always external to the machinery space and the end fitted with a wire gauze diaphragm serving as a flame trap.

The Running and Maintenance of Marine Machinery, 6th ed. 1992 published by IMarE, on page 167 in the chapter by R. F. Thomas.

Case closed by @Jamesbrown


I live on the Ohio river near the southern tip of the state of Ohio. About 30 miles up river is Gallipolis, Ohio which had a large Chris Craft Yacht factory when I was a kid. They made wooden haul boats there then as this area had fine quality wood available. Now across the river in West Virginia is a “Special Alloys” factory that the locals call “The Nickle Plant”.

As I understand Chris Craft bought and used a lot of “Monel” metal from them to make large fuel tanks for those Yachts… (it don’t rust or corrode and the metal can resist heat at very high temperatures).

I can’t tell you how they were fastened to the wooden frames but I’d imagine it was with bolts made of the same material. In the day the tanks may have been 300 gallons capacity in twin V8 engine boats like this one below.

Monel is too dear to make tanks from, I’d’ve thought. Especially for a fresh water application. But as long as money’s no object and dreams are free, we could gold-plate the inside, too.

Remember, a lot of these 40 & 50+ ft boats ran both fresh & salt water.
And it was in the 50’s when a US Gallon of Gasoline was less than .20 cent a gallon in those days. In some cases as little as .12 cent.

Large Corporations used to own these to wine & dine customers where in the USA they (and their operating cost) were largely tax write offs. But that’s the business side of things.

It used to be quite common. Many of the Navy small craft used monel tanks because of the corrosion resistance.

I had no idea. The only place I think I’ve seen monel is the demister in the FWG.

Pearson Vanguards (class of ~400 ~10 meter GRP sloops (and a few yawls) built in Bristol Rhode Island in the mid '60s) had 20 (US) gallon Monel fuel and 45 gallon Monel water tanks.

Here are the ~75 gallon carbon-fiber tanks custom built for a friend’s 1947 wooden schooner. The starboard side is installed and the port side is just about to go in. You can see the support bunks underneath on the starboard side; there’s no visible strapping though something might have been added as the refit progressed.

The top welds on the old (stainless?) tanks had rusted through/failed so we’d leak diesel into the bilge when the tanks were full in any kind of seaway. They considered standard plastic tanks but the shipwright convinced the owner that carbon tanks would (a) fit better, (b) hold more fuel, © last longer, and (d) “wouldn’t cost that much more at the end of the day.”

I have a feeling answering “carbon fiber” won’t get top marks on the exam.

Unless they cost less than around $500 they weren’t cheaper than a custom made plastic tank that wouldn’t have the potential corrosion (no pun intended) of carbon fiber/metal/salt water.

They might have saved about 10 pounds and gained about one gallon though.

Just as an aside, the USA’s coastal limit used to be 3 miles. I believe POTUS Reagan increased it to 10 miles during his presidency. But in the day when corporations wined and dined customers on big Yachts, 3 miles out put the good time fun & games into international waters and beyond “legal issues” for those involved… (what happens at sea stays at sea…as a lot of politicians were entertained/lobbied in this way too)

So…you’d want a Yacht equipped for fresh, brackish, or salt water operation.

Some here may remember a late 50’s TV Show…“Mr. Lucky” who operated a Large Yacht casino/restaurant in the heydays of this kind of “soldier of fortune” stuff