Fuel Tank Fastening System Retrospective

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Vance's Revenge
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Fuel Tank Fastening System Retrospective

Postby Vance's Revenge » Tue Jul 05, 2022 4:24 pm

FUEL TANK FASTENING SYSTEM

I wanted something incredibly strong to hold in place the new fuel tank I was installing on my REVENGE 22 because I was not going to foam-in-place the new fuel tank. I didn't have a way to weld aluminum so I needed to utilize stainless screws, nuts, and bolts to construct the aluminum hold down structure for the fuel tank.

After the fuel tank was installed, I ran the boat for one season, purposely beating the heck out of it on rough water to test the strength of the fuel tank fastening system. At the end of the season I pulled the floor and found everything was still solid with zero movement.

DETAILS OF FUEL TANK FASTENING SYSTEM

Whaler Pic fuel tank support bracket.jpg
Fig. 1. Fuel tank fastening system bracket.
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Fig2.jpeg
Fig. 2. Fuel tank fastening system.
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Fig3.jpeg
Fig. 3. Fuel tank fastening system.
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NOTES

DETAILS

The fuel tank cavity is incredibly thin fiberglass so to add strength for the lag screws I ground through the gel coat and reinforced the area with West Systems epoxy resin and fiberglass. The tube structure was 1 x 2 x 1/8-inch aluminum square tubing. All of the aluminum angle is 1/4 x 1-inch.

There number of screws to get this done was crazy, but the structure is solid.

I can't remember the hard rubber material I used both to cushion the bottom of the tank to the hull and on the aluminum tie down system.

Each leg of the structure Is held by 2 x 2 x 1/4-inch aluminum angle through-bolted in place. You can see four bolts and nuts in the Figure 1 below where the leg at the top is attached.

The structure came out incredibly solid.

On each end there is 1/4 x 1-inch aluminum angle bolted. The bolt head can be seenin the picture below. The angle is bolted to the underside tight to the tank to prevent it from moving sideways or front to back.

Every contact point is cushioned with rubber.

Each end has two pieces of aluminum angle; one on each side of the square tubing. The angle has a lag bolt on each side bottom to the hull, the top is a countersunk screw so there is clearance to get a bolt over the screw head and through the square tubing in both angle sections.

FINAL THOUGHTS

I'm going to say that if I had to do a fuel tank replacement again, I would not go this route. I would foam in the tank.

I would cover the tank and foam with a thin layer of fiberglass to prevent water from accessing the foam and tank. It is incredibly hard to prevent water from accessing the tank area. If you don't foam-in the tank in you really need a way to inspect and drain the tank cavity.

This is easily done with by installing a 1-inch-ID drain tube at the bottom between the fuel tank cavity and the factory rear under deck fish box. Utilize a 1-inch drain plug at the fish box end to prevent water from entering the tube. Pull the plug to inspect the tank area and drain it if necessary.

mikegcny
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Re: Fuel Tank Fastening System Retrospective

Postby mikegcny » Wed Jul 06, 2022 11:18 am

Thank you for posting this information.

ASIDE: I plan to replace my tank in Winter 2022-2023

I am still not sure if I should use foam or not. I am of the mindset that no matter what I do, water will always get to both the fuel cavity and under deck maze of tunnels. I like the approach of being able to drain it to a pickup, so that it can be pumped.

jimh
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Re: Fuel Tank Fastening System Retrospective

Postby jimh » Thu Jul 07, 2022 9:25 am

VANCE--thank you for the honesty expressed in your final thoughts. The Boston Whaler foam-in-place method is probably the simplest and easiest for mass production. If water can be kept out of the fuel tank cavity, the foam and tank can have a long service life.

dtmackey
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Re: Fuel Tank Fastening System Retrospective

Postby dtmackey » Thu Jul 07, 2022 1:48 pm

When I've replaced tanks, I always foam them in. Foam locks the tank in place and also support the bottom and sides, foam also removes any space where gas vapors can collect. Water will eventually get into a tank cavity (cavity where the tank is placed). However, on the Whaler outrage models, the design where the hoses to run from the tank to the gunwale is a poor design for keeping water out and sealed over time.

One good tip is to coat the tank with coal tar epoxy so any water that gets into the cavity cannot come in contact with the tank. Many tank builders offer this coating.

I noticed you mentioned rubber in the tank install. Is this rubber in contact with the tank? Rubber is a big no-no for aluminum tank installations. Rubber contains carbon, which is cathodic to aluminum and will cause galvanic corrosion

D-

mikegcny
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Re: Fuel Tank Fastening System Retrospective

Postby mikegcny » Thu Jul 07, 2022 6:45 pm

I was just doing some research on foam, and came across this site - http://www.uscomposites.com/foam.html

"Once fully cured this foam can be laminated over with any type of polyester, epoxy or vinyl ester resin without melting."

I wonder if instead of trying to glass over the tank and foam, it could be topped of with a flexible epoxy or coating?

Vance's Revenge
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Re: Fuel Tank Fastening System Retrospective

Postby Vance's Revenge » Thu Jul 07, 2022 9:17 pm

dtmackey wrote:When I've replaced tanks, I always foam them in. Foam locks the tank in place and also support the bottom and sides, foam also removes any space where gas vapors can collect. Water will eventually get into a tank cavity (cavity where the tank is placed). However, on the Whaler outrage models, the design where the hoses to run from the tank to the gunwale is a poor design for keeping water out and sealed over time.

One good tip is to coat the tank with coal tar epoxy so any water that gets into the cavity cannot come in contact with the tank. Many tank builders offer this coating.

I noticed you mentioned rubber in the tank install. Is this rubber in contact with the tank? Rubber is a big no-no for aluminum tank installations. Rubber contains carbon, which is cathodic to aluminum and will cause galvanic corrosion

D-


I had heard that about rubber and aluminum before. My old tank was corroded horribly everywhere but was corroded the least where it was protected by rubber. Apparently the rubber wasn't as corrosive as the salt water.

Myself, on my install under the tank I used a solid coat of 3M5200 adhesive between the aluminum tank and the rubber.

What do you suggest to protect the tank from the fiberglass and aluminum with other than rubber?

I believe the factory used rubber under their three aluminum brackets that hold down the tank.

mikegcny
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Re: Fuel Tank Fastening System Retrospective

Postby mikegcny » Fri Jul 08, 2022 8:59 am

Vance's Revenge wrote:What do you suggest to protect the tank from the fiberglass and aluminum with other than rubber?
Some people use [KING StarBoard] strips about two-inches wide that run athwart to the tank. They cut them about two-inches-short so that there is a small channel under the center of the tank for water to flow.

These KING Starboard strips are adhered to the tank with 3M5200, and then adhered to the fiberglass with 3M4200.

To use rubber, the rubber must be rated to be in contact with gasoline.

dtmackey
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Re: Fuel Tank Fastening System Retrospective

Postby dtmackey » Fri Jul 08, 2022 10:05 am

Vance's Revenge wrote:I had heard that about rubber and aluminum before. My old tank was corroded horribly everywhere but was corroded the least where it was protected by rubber. Apparently the rubber wasn't as corrosive as the salt water.

Myself, on my install under the tank I used a solid coat of 3M5200 adhesive between the aluminum tank and the rubber.

What do you suggest to protect the tank from the fiberglass and aluminum with other than rubber?

I believe the factory used rubber under their three aluminum brackets that hold down the tank.


I like the idea of using 3M5200 adhesive-sealant to separate the rubber from the alumimum tank. I see that as a benefit when rubber is used.

I believe there is guidance out there on rubber with ABYC and the USCG on fuel tank installation. I know Dave Pasco publishes survey notes on this on yachtsurvey.com.

To protect against the fiberglass and aluminum, I'd use KING StarBoard or similar material, but first coat the tank with coal tar.

rcapriola
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Re: Fuel Tank Fastening System Retrospective

Postby rcapriola » Mon Jan 30, 2023 11:43 pm

The main cause of crevice corrosion in aluminum fuel tanks is due to contact between the aluminum tank and any other surface where there is water in between the two surfaces.

The only way to prevent aluminum fuel tank crevice corrosion [in a Boston Whaler boat when a new fuel tank is about to be installed] is to remove all foam in the tank cavity, clean the surface of the fuel tank [cavity], and glue neoprene rubber pads to the new aluminum fuel tank with 3M5200 where the fuel tank may be in contact with the [fuel tank cavity] or straps holding down the fuel tank under the laminated cockpit deck plate cover above the fuel tank. This technique will prevent any water from [being retained] between the tank and any other pressure points. This method also will allow all water around the to drain [out of the fuel tank cavity if a new system of drains is also installed, as described below]..

I learned about this method from replacing the tank in my Grady-White 195 (on the Great Grady owners forum) and with my REVENGE 22. Both boats suffered from crevice corrosion leaks in 20-year old fuel tanks caused by poor installation methods.

In the case of the Grady-White 195 boat, the aluminum tank was set into the compartment on neoprene straps, but the aluminum tank was not glued to the neoprene straps; pinhole corrosion points developed under the straps.

In the REVENGE 22 boat, the fuel tank corroded around the outside where it was in contact with water-soaked foam. The laminated cockpit deck cover was not designed to prevent water from entering the fuel tank cavity. I now have modified the fuel tank cavity so that water in the fuel tank cavity can drain out to the aft live well through a new drain tube and thence drain to the transom via another new drain tube. This added drain path keeps the fuel tank cavity dry. In this method there are two removable, round, deck access plates, and there is a drain tube that drains into the transom.
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Phil T
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Re: Fuel Tank Fastening System Retrospective

Postby Phil T » Tue Jan 31, 2023 10:43 am

The new trend emerging is to re-foam the tank and fiberglass the top to keep all water out.
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Vance's Revenge
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Re: Fuel Tank Fastening System Retrospective

Postby Vance's Revenge » Sun Feb 05, 2023 10:10 pm

Phil, If I were to [redo the installation of a new fuel tank] again. I would foam-in the tank and [apply a sealing top coat] over the top [of the foam] using fiberglass [resin and cloth].

It was a tremendous amount of work to prevent water from accessing the fuel tank cavity from all directions intended by the original design. I succeeded in the process with the wall blocking the rigging tunnel (upper left figure 3) and the fuel fill and vent manifold (upper left figure 2).

To offset lost strength for not re-foaming, I reinforced the bottom of the fuel tank cavity and screw points for the aluminum mounting structure.

I also added a drain and inspection tube at the bottom between the fuel tank cavity and rear fish box so any water that did make its way in could be drained. I have used the boat now for over four years and there is rarely water in the fuel tank cavity. I the little water I find is passing through the two deck plates on the floor above the fuel tank.

It was also necessary to fill large gaps under the fish box cover so water in the fish box couldn't splash between the port stringer and the bottom side of the cover into the port rigging tunnel.

To foam in the tank, trim off the foam to tank level and glass over the top to prevent water access would be far easier.

The foam and fiberglass will make the area stronger than not foaming in the tank.

I do question whether the newly installed fuek tank cavity would need a vent for expansion and contraction. Adding a vent would be easy enough with an aluminum or fiberglass tube and vent hose. I just wonder if it is needed.


Vance