Cutting Through Precious Wood for Fuel Tank Removal....HELP!!

[asmith2378]

Ok we have an old Challenger 40 sailboat, built in 1973. The 200 gallon tank is located next to the engine under the floor, and it has a small access hatch to view connections and such, but now it appears that the aluminum has rusted and the tank is leaking. We need to replace it so that we can get our boat sold. I've never taken on a project this large and we have no clue how to go about cutting up the floors to get this tank out/ how to make it look pretty again when we finish / how to make sure that we don't mess up the integrity of the boat. ANY and ALL help or advise would be greatly appreciated. I'm attaching some pics of where the tank is located. We aren't sure how far under the flooring the tank actually goes just fyi. Thanks in advance!

[5BTM]

Before you cut anything take apart as much of the interior as possible.

Look for signs of wood plugs used to cover screw holes; eood grain in different direction, different color, circular grain, etc.

[asmith2378]

Originally Posted by 5BTM

Before you cut anything take apart as much of the interior as possible.

Look for signs of wood plugs used to cover screw holes; eood grain in different direction, different color, circular grain, etc.

Take apart as much of the tank? Using a saw I'm assuming?

[coopec43]

Have you floated your question on the Owner's Forum?

https://www.cruisersforum.com/forums/groups/5-challenger+owners+group.html

[5BTM]

Originally Posted by asmith2378

Take apart as much of the tank? Using a saw I'm assuming?

No.
You want to take off the teak and holly sole

[mako]

200 gallons sounds like a huge tank for that sized tank. What capacity are you planning on replacing it with? If you’re okay with a small tank of 40-50 gallons for example, can you locate the new tank in the lazarette or under the cockpit sole and then abandon in-place the existing one?

[asmith2378]

Originally Posted by mako

200 gallons sounds like a huge tank for that sized tank. What capacity are you planning on replacing it with? If you’re okay with a small tank of 40-50 gallons for example, can you locate the new tank in the lazarette or under the cockpit sole and then abandon in-place the existing one?

We were planning on a smaller tank around 100 gallons but I'm not opposed to the idea of fitting an even smaller one onboard. It is supposed to be blue water capable which is why the original was so large.

[asmith2378]

Originally Posted by coopec43

Have you floated your question on the Owner's Forum?

https://www.cruisersforum.com/forums/groups/5-challenger+owners+group.html

Excellent idea. Thanks

[wrwakefield]

Unrelated to your specific boat, but another option to consider [and what was done on our boat]:

If you can gain access to just the top of the old tank, consider removing the top [after removing as much fuel as possible] and placing the new tank[s] inside the old.

This could be a fuel bladder, or new plastic or metal fuel tank[s].

Our port tank was done this way. They cut off the top of the empty tank; repaired the leak with epoxy, then lined it with a thin waterproof carpet like liner [blue in attached photos]. They then set the two new tanks in place [custom fabricated; white in photos; showing interconnection with a large diameter fuel hose at the bottom to make one virtual tank of slightly less capacity than the original; down to 86 gal from original 130 gal.]

Two new, smaller, interconnected tanks were used because much more ‘remodeling’ would have had to be done to fit in a single tank of near original size.


FWIW

Best wishes with your project.

Cheers, Bill

PS: A small drain fitting with a valve was installed in the old tank bottom as a tell-tale if the new tanks ever leaked…
PPS: The heavy canvas/sail sewing machine nests perfectly between the 2 new tanks…

[asmith2378]

Originally Posted by wrwakefield

Unrelated to your specific boat, but another option to consider [and what was done on our boat]:

If you can gain access to just the top of the old tank, consider removing the top [after removing as much fuel as possible] and placing the new tank[s] inside the old.

This could be a fuel bladder, or new plastic or metal fuel tank[s].

Our port tank was done this way. They cut off the top of the empty tank; lined it with a thin waterproof carpet like liner [blue in attached photos], then laid the two new tanks [custom fabricated; white in photos; showing interconnection with a large diameter fuel hose at the bottom to make one virtual tank of slightly less capacity than the original; down to 86 gal from original 130 gal.]

Two new, smaller, interconnected tanks were used because more ‘furniture’ would have had to be dismantled to fit in a single tank of near original size.


FWIW

Best wishes with your project.

Cheers, Bill

PS: The heavy canvas/sail sewing machine nests perfectly between the 2 new tanks…

What is the purpose of using the old tank at all? If you've already cut up the entire floor why not just remove the tank? Also, do you have any recommendations for cutting through the floor and making it still look good with the end result? Like any specific tools or bits you used for creating the opening

[wrwakefield]

Originally Posted by asmith2378

What is the purpose of using the old tank at all?

In our case, the old tank was well secured to the vessel and still structurally sound with the exception of a small area of weld corrosion in one bottom corner- causing the leak. The tank was cleaned out and the corroded corner repaired with epoxy to make the tank leakproof. This makes it somewhat of a a fail-safe against future leaks from the tanks installed within.


If you've already cut up the entire floor why not just remove the tank?

Removing only the top and cleaning out the tank was much less work than removing the entire tank [which would have been done if the tank was not still structurally sound.]

Also, do you have any recommendations for cutting through the floor and making it still look good with the end result? Like any specific tools or bits you used for creating the opening.

If the sole cannot be removed by dismantling the originally installed pieces, I would measure 100 or so times and then make a quality cut using my Festool plunging track saw and guide; cleaning up the corners with either a very carefully used multi-tool or Japanese hand saw. The removed piece of sole would become a new fuel tank access hatch which would require additional carpentry under the sole to support it when put back into place.

I hope this helps.

Cheers, Bill

[rls8r]

asmith2378 -

What 5BTM said in Comments #2 and #5. Take up the sole. You may have to take out the settee, table and berth opposite the settee - but even with that ... you'll save time, money and effort in the long run. Trust me on this one - I've been faced with exactly the same problem. You can then replace the tank with a smaller one or one of the same size, or do the tank-in-tank that wrwakefield mentioned. Another plus for this approach is that you can refinish the sole while it's out of the boat.

If you have your heart set on cutting up the sole - I'd suggest that you use any athwartship seams that are already there - and just cut the sole in the fore-and-aft direction between them. It looks like your sole may be made of teak and holly lumber instead of veneered plywood. If so - then use the multitool (or Festool) saw that wrwakefield suggests and cut along one of the seams between the holly and the teak. That way you'll have a better chance at making a straight cut that will not show after re-assembly. Chances are, the holly/teak joint is tongue-and-groove, so you'll have to (at least) remove the holly strip. You can then, with the aid of a router, make another, ever-so-slightly wider holly strip to replace the one you removed so the saw cut will not show. Long holly boards are around, you just have to look for them - and it's not the cheapest lumber in the world.

If the sole is veneered plywood then I can't think of an approach to cutting the sole that will look good when you've finished. Of course, there are others on this forum with more experience in this sort of thing than I have - so perhaps we both can learn.

[ahun]

Don't kid yourself, it will be a big job.

[rls8r]

asmith2378 -

Yes, it will be a big job, no matter how you approach it. But ... it's really not that complicated. You just have to take a lot of things apart - remember how they go together (take pictures and mark the pieces) - and then put things back.

Some soles have the screw holes plugged - like 5BTM mentioned. They're easy to remove with a small screwdriver - and easy to replace. Buy teak plugs at any chandlery - or online is cheaper. A possible hiccup may happen if the sole is screwed down with bronze screws (as many boats of your boat's age were). Some of the bronze screws may have corroded - in which case you'll have a heck of a time getting them out. That's just life. Buy a pair of vice grips.

I recommend putting things back together using 316 stainless steel screws. The stainless steel screws you find at most chandleries (including West Marine) are 304/18-8, which are OK, but they are less corrosion resistant than 316. McMaster-Carr is your friend here. Many Ace Hardware stores also carry 316 stainless steel fasteners.

Another thing to be aware of is the floors under the sole. The tank may be under the floors, so you'll have to remove the floors. Make sure that you remember how they go back. Number them, and mark port and starboard ends. Depending on how your boat is built you may have stringers to deal with, too. Same advice as for the floors.

While you have things apart - it's a good time to check any wiring and hoses that run under the sole. Perhaps you'll take the opportunity to clean the bilge and give it a nice, fresh coat of paint.

As I mentioned before - it's also a good time to refinish the soles.

ahun showed you a photo of (I suppose) his boat with the sole removed and the tank exposed. The picture below is my main cabin with most of the sole removed to expose my fresh water tanks. The tank on right has been removed; the tank on the left is on its way out. Please excuse the mess of hoses and cables in the space where one of the water tanks used to be.

Like we said ... it's a big job, but not one that's technically complicated. Good luck. Have fun!

[mlydon]

Step one is to map out how big the tank actually is. It looks like the sole is plywood - somewhat poor pictures, but it looks like the aft-facing pic shows a panel ( I presume the connection access?) and just to the left a seam running all the way back to the companionway. Where is your bilge access? Get a peek under the sole from those points to see what’s under the plywood supporting the sole. Mechanics mirrors and a $30 bore scope from Amazon will help.

Your boat looks ‘stick built’ as opposed to a fiberglass liner. I have the same. It’s likely there are joists athwartships bonded to the hull, then 3/4 ply laid on that, with nice teak/holly ply on top of that. IF that’s the case, you can just cut a large panel out of the whole floor slightly larger than the tank, lift it out, change out the tank, then face the hole’s edge with teak, face the panel the same after cutting it down to allow for the facings, and put it back.

That’s a simplification, a lot depends on what you find down there after you investigate. Let me know….

Matt