1995 Outrage 24: Install New Non-OEM Replacement Fuel Tank

[NLA01]

In mid-March 2020 I am going to install a non-OEM fuel tank in my 1995 OUTRAGE 24 boat. I purchased a 111-gallon Moeller-brand plastic tank. The bottom of the new non-OEM tank is not an exact match to the bottom of the fuel tank compartment. The new tank has a flat bottom in the middle and v-taper on the sides. The fuel tank compartment on the boat has a sharper V-angle, and there is no flat bottom at all. I need to create a support under the tank.

I am looking for ideas for fitting the new plastic tank into the existing fuel tank cavity on 1995 OUTRAGE 24.
Thanks

Can rubber mats be placed under the new plastic fuel tank as shims to help support it and fill the gap to the fuel tank cavity underneath the new tank?

I thought of trying to cut plastic lumber to use a shims, but I still think it will not be a perfect fit. Plastic lumber is super hard to cut straight because of the slippery material. I am not as worried about the sides as I am about the bottom.

I could use Douglas fir 2 x 4 lumber to make a V-wedge, which will fit under the tank like a plug. And to fit the V-section too,

I have also thought of poured foam. But poured foam would be hard to cure with the tank on it, and the [pressure of expanding foam] may buckle the tank. Foam would only be under the tank not on the sides.


Archie

[jimh]

Contact the manufacturer of the new non-OEM plastic fuel tank to find out what is required to support the tank.

If the tank requires continuous sidewall and bottom support, you will have to implement some sort of continuous shimming of the sidewalls and bottom. If the manufacturer permits the tank to be supported only at certain intervals, you will be able to use intermediate frames to create a cradle in the existing fuel tank cavity onto which the new non-OEM tank can lay, with the frames spaced apart as the manufacturer requires.

The use of an expanding foam surround to fill all the spaces between the fuel tank and the fuel tank cavity actually sounds (to me) like a very good approach.

[Phil T]

Archie-

What is the dimension of the V wedge you need to make. Looking for 3 measurements: Top width, side widths and the length.

Can you make a rough drawing of the shape of the cavity and the shape of the new tank. Use your phone, take a photo and attach here (or email to me)

Based on the dimensions, I will give you suggestion on materials and construction.

[quickenberger]

I'd probably use 2 part polyurethane foam since it'll expand to support the whole surface. If it does get water in the foam then it shouldn't affect the plastic like it would on aluminum tanks. 2 part expanding foam cures by chemical reaction and doesn't need to "air dry".

Pour part A and part B in two different plastic cups and dump contents of each cup in one gallon size plastic bag. Knead the mixture very well and cut a small corner of the bag to be able to squirt out the foaming mixture. That method has worked well for me to get the foam in a difficult location. You can use smaller bags to get the hang of mixing before going for larger quantities. It can be done in small batches too. Wear gloves. It's nasty stuff.

[NLA01]

Thanks a lot everyone. I may need to make a support shelf under the tank for the V-part. This is a rough drawing of what the support will look like at a cross section view and will run the full length of the tank which is like 75-inches:

Fig. 1. Sketch of necessary support for new fuel tank bottom surface.

tank.jpg (13.29 KiB) Viewed 4607 times

These measurements are estimates right now. During Spring break I am doing the whole project. The notch in the bottom will run full length for water drain.

Phil-- you have any ideas?

I am thinking of using PVC lumber from Lowes or marine plywood and Douglas Fir 2 x 4 lumber cut to make a shelf.

--Archie

[Phil T]

In replicating the dimension of the triangle using A4 paper (8.5x11) and visualizing the length of the run, the results are telling.

Keeping in mind the triangle shaped "structure" under the tank will need to take some load, the use of composite or non-wood lumber will be problematic due to the ~11" width and the weight bearing requirements. Perpendicular stringers would be needed. In mapping this out, it is appears construction of the supports to be rather time consuming, requiring substantial materials, many cuts and many fasteners

While the above is feasible, I believe the use of 4-lbs expanding foam would accomplish the same end result, bear the weight evenly, and only require moderate work in shaping and leveling the foam. Sealing the foam once cured would add an extra layer of protection from water ingress.

Breaking up the lineal distance into 4-6 sections would allow more control of the pour. You can make a test form section of the upside down V (2 to 3-feet long) to determine how much foam is needed for each section.. You can make the form out of plywood for the distance of the pour and reuse it over again for the other sections.

Once the fill line is determined, you can mark the side walls of the V of the cavity with a fill line to reach the desired finish height (slightly above to allow for finishing). This will allow easy pours.

By doing one pour at a time, you have more control and have the ability to get the desired height.

Does this make sense?

[jimh]

Phil's idea of making a mold for the necessary forms needed to support the tank, and then pouring the foam into a mold instead of molding it in place in the boat's fuel tank cavity is an interesting approach.

It reminds me of the Bob Dougherty method used in his Edgewater and later Everglades boats. Bob pre-cast the foam for the double-bottom hull space in molds outside of the hull. Then the foam could be inspected and determined to be free of air spaces or voids. The pre-cast foam was them placed into the hull and fixed in place with an adhesive.

Also, by pre-casting the forms, as Phil also suggests, you can coat the foam forms with a sealer, probably epoxy resin, so they will be much less likely to be able to absorb water.

[Phil T]

Having slept on it, I have a further refinement.

Purchase the foam and cut to the shape.

Vendors:
https://www.universalconstructionfoam.com/products/polystyrene/marine-floatation.php

https://www.taylorfoam.com/products/dock-flotation

https://www.dockbuilders.com/dow-styrofoam-billets.htm

You could even visit Home Depot/Lowes to view their EPS foam
https://www.homedepot.com/b/Building-Materials-Insulation-Foam-Board-Insulation/N-5yc1vZbaxx

[biggiefl]

I like Phil's second approach as that was what I was going to mention. Like making a surfboard. Gonna be messy but will work well and should be cheap as you can use smaller blocks and fuse together.

[NLA01]

Phil thank you for the great ideas. I am not sure about using a styrofoam based material since I will not be able to seal it and it is not impervious to gas and resins.

I really really like the idea of the poured-in foam with a reusable mold and to do a section at time. This is really a great idea, moving the mold and doing each section at a time. I could us plywood and then paint it with a mold release. I could place the mold in one section with weight on it and pour in foam through a hole in the top or on the end. Then once the foam is in place I could seal the whole thing with resin.

I could cut a 4 inch PVC pipe in half to make the channel for water and put in the bottom before I start.

Will the poured-in foam be able to support the tanks weight over time? In other words, is the foam structurally enough?

I love the poured-in foam in a bag method. What kind of bag should be used used?

What do I put between the tank and the base to let water run through? Is rubber Ok?

Thanks--Archie

[jimh]

If using a pre-cast foam from a mold, the mold will need to be quite accurate so that the tank-side of the mold is a very good fit to the tank walls.

[Phil T]

In my mind I was envisioning the mold would only have a vertical face and two sides that kept it plumb.

On the intial pour, you would need to tape the straps to the tank wall. Once the section had cured, you move the form forward and the two straps would rest on the cured section. You could use duct tape to seal the edges of the form to the cavity walls.

I was thinking you would seal the top of the foam and not have any drain or pipe. Additionally, I was thinking you would not foam in the sides or ends of the tank and could allow moisture to escape by opening the inspection ports when the boat was not in use.

See my horrible drawing below.

[Big Bend Brian]

Acassidy I have a 1994 24 Outrage and last year I had to have my fuel tank replaced on account of pin holes. I don’t have any input on how to help you fit the new plastic tank but I can tell you the new 195 gallon tank cost $1,800 wackers. Best of luck buddy.
Brian