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Modern tanks do have a one-way valve, usually in the cap. I may be misremembering, but I think the current standards allow the tank to vent above 5psi. Better to vent some gas vapor than leak gasoline when the tank bursts. I'm surprised that your tank allows the fuel to reach the top of the tank. All of mine are marked to leave a noticeable gap between the fuel and the top of the tank.

Thank you everyone for the feedback and advice.

The existing tank was hooked up to a fuel breather vent that directly out the transom. Yes my old tank looks unusual but please don't beat me up too much, fuel grade tapes and sealants were used, and it was also never meant to be a permanent fix as I have always been planning on changing the tank. I just really wanted to find out where the fumes were leaking from so when I redid the system I would know how to ensure the best results.

Through process of elimination I suspect that the fumes may be coming from the primer ball, hose connections, or fuel indicator breather cap.
Yes - the cap breather valve has been closed tightly off to help ensure no fumes were exiting from there. But, despite thorough inspections without any obvious signs of any leakage from any of those locations I just haven't been able to determine the main problem location.

Before I had ever sailed the boat I did installed a blower to vent the lazaret, but excessive use of the blower fan drains my battery pretty quickly. (I always run it for a good while before starting and at random times as well. I also installed a couple of free air vents but they are underrated in my opinion.
I always pull the tank right out of the lazaret when sleeping or cooking in the boat for obvious safety reasons.

I will be changing the tank for sure.
Ideally, yes, I would like a hidden tank in the lazaret, but only if it can be done safely and right now I'm not totally sure how to best do that. I also haven't found a good place locally to buy a proper tank. (I live near Vancouver B.C. on the west coast)
Until I have a good and perfect lazaret tank solution, and even though it may be ugly and be inconvenient, I'm leaning towards hooking up a smaller 1 gallon tank somewhere externally and just refueling that as required. Every time I've been out so far one gallon has lasted me about two days.

I just haven't been able to find the tank and all the fittings to do a proper fuel tank installation in the lazaret area. I have found and purchased a vented marine fuel filling cap and proper fuel hose(1.5" ID), the hose in particular was quite expensive but would be worth it if I could source everything else.

Covid makes things tougher, but I've been thinking about crossing the board and shopping for boat tanks more around the Anacortes Area in Washington. What have others found to work best on the MAC S, maybe I should just totally forget the lazaret tank and stay with an external tank. If someone has this figured out, I'm all ears.

Again, I really appreciate all the pictures and advice everyone has provided, please keep them coming.

Hi Greg B

Here is an interesting fuel tank that you can externally mount.
We’ve been considering them for when we finally get to cruising the ICW.

They have a center mount hole and there is a companion bracket that it locks in with.
Designed for off readers so it mounts rather securely.

We would modify it so there would be a top double barb bulkhead fitting to siphon the fuel via a fuel selector valve rather than contending with attempting to pour fuel while enroute.

We are considering using the rear corner railings and or the aft stern wall.

Maybe this could be useful for your application and doubling you normal range?

Best Regards
Over Easy

My apologies in advance if any of this has been covered already...

When I bought my 26S the lazarette was a mess, with lots of petroleum-smelling gunk in the bottom. The owner had used it to store his gas tank, and had not installed any ventilation. After removing all storage and thoroughly cleaning the lazarette, I installed these, available from Blue Water Yachts:

https://shop.bwyachts.com/product-p/h001-1c0.htm

I went on to seal off the lazarette off from the cabin. In some areas it was as simple as applying tape. I used the 2.5" adhesive-backed foil tape, available at any Home Depot or Lowe's where I could. In other areas with larger gaps, I fashioned filler plates from Coroplast (ribbed plastic material used for temporary signs, available at your local sign company) taped in place with that same foil tape. A more dedicated owner might want to consider fiberglass or something more substantial. My solution was more expedient, and allows for flexing.

I check the seal from time to time and apply more tape as needed, and have found that it all but completely eliminates the gasoline odor.

While in a perfect world the fuel system would be leak free, accidents happen, and an enclosed area like the lazarette will end up smelling like gasoline eventually. Proper ventilation and sealing it off from other areas of the boat will help.

That said, any identifiable point of leakage should be sealed. If it is simply a matter of tanks or hoses being old, replace them.

Any new plastic tanks will be of the non-venting variety, and come with their own problems. After replacing my gas tank, I found that pressure build-up was causing flooding of my kicker's carburetor with subsequent starting problems. Installing one of these special valves in the fuel line alleviated that problem:

https://www.westmarine.com/west-marine- ... 54252.html

Unrelated, but helpful - I have installed a shut-off valve in the fuel line and run the kicker dry after each use. This gives me quick, trouble free starts consistently.

Hope this information proves helpful.

I think it would be cool to use one of those rotopax tanks (the big one) as my main gas tank and mount it to the stern with the nifty clamp. Then run a fuel line from it to the OB and not give up the space in the cockpit for a tank and not have to deal with placing in laz and venting.

All you would need is to put a fuel fitting on the tank yah? Maybe some sort of inline fuel filter to keep out any debris?

J

That larger tank is only 2 gallons, you must not be planning on going very far.

Two years ago we did a twelve day cruise of the Chesapeake. There were a couple fifty mile legs and a few legs of over thirty miles.

Years earlier - actually several years - I had read a post from a long time member of this board explaining that he uses two WWII Jerry cans for fuel storage, and he keeps them below deck. I did further research into this, and kept it in the back of my mind.

When we planned our trip, I decided that we needed more fuel than our two twelve gallon tanks supplied. I purchased two of these (5gal) tanks. https://wavianusa.com/collections/nato-fuel-cans

Cutting to the chase; we kept those cans below deck for the entire trip. At no time did we detect any smell of gasoline. The tanks did not ballon. I was amazed at how well built these tanks are. Other manufactures do not have the pedigree of Wavian tanks. I can only only attest for this company, no other Jerry cans.

I appreciate the tips.
I never thought of the overland fuel tank idea, I think I will run with that and buy myself something like the Rotopax tank.
I also really like the vent scoops and will adopt that idea for when I store gas tanks in the lazaret.

I will also seal of the area between the cabin and lazaret better. So far I have expanding foam sealing most of the gaps but it does not make a perfect gas tight seal.

Thanks again everyone who has posted and given advice, it is all greatly appreciated.

Just a suggestion….Some 1/2” thick closed cell foam board is easy to cut to fit. Some two part epoxy resin fiberglass overlay on both sides makes it very strong yet light weight and generally MUCH better than “great stuff” expanding foam which is open cell and entrains water (or any other liquid for that matter…..