Removing a floor for bilge access

[newbie-]

I am preparing to buy a skill saw, set it to 3/8", and start driving it up and down the floor to slice it up and remove. At least 3' x 5' of it.

My aluminum water tank is leaking. I thought I patched it up from the damage I could reach but it's leaking somewhere else too. So I don't think I can save it. There's no access. Without taking the interior apart.

So my plan has two goals:

1. Gain access to that section of the bilge. Cut out the floor.
2. Remove and replace the old water tank.

Finally, cut new 3/8" plywood to size and rebuild the floor. This time the flooring will be removable.

There's no way the 3/8" plywood floor is structural right? It's marine grade wood. And coated in epoxy. But It's totally safe for me to start cutting a gigantic hole in the middle of the boat?

[tkeithlu]

Just watch out for structural stiffening. It is possible, if the sole (floor) is not already liftable, that it has been used to stiffen the hull. That should be evident from the materials used, because stiffening requires stuff that is really stiff and really anchored to bulkheads. That doesn't mean that you cannot cut it out, replace the tank, and restore it. It just means that you may have to abandon the idea of having a lift-out floor and instead screw down to the bulkheads for and aft of the tank.

[newbie-]

Okay that makes sense. I'm OK with screwing down the access floorboards. I'd prefer that since it would make the floors more stable and less squeaky.

[Don C L]

This is in a power boat, right? I kinda doubt that 3/8" would be structural. But before you start cutting, are you sure it is the tank itself that is leaking?

[newbie-]

Originally Posted by Don C L

This is in a power boat, right? I kinda doubt that 3/8" would be structural. But before you start cutting, are you sure it is the tank itself that is leaking?

You're right actually. I mistyped. The floor is thick stuff. Probably 1" ply.

Access is really bad under the tank. I can just reach my fingers under the aft side. I felt around and found a spot that had holes in to the tank. Under what felt like a broken weld from a tank brace.

After some thought, I decided I'd just clean the area as best as I can and patch it with some jb waterweld. A few days later I tested the tank with fresh water and.. the repair held. But there was another leak. I can't find where it's coming from but I'd bet it's another section where a brace failed. The tank completely empties so wherever the leak is - it's at the very bottom.

I'd love to find a way to solve this without removing the tank or cutting up the floor. I'm also guessing the tank will not fit through the doorway. So once it's out, I'll have to slice it up.

[MV Caroline]

First off, I believe you are talking about removing portions of your cabin sole.
Floors on a boat are beams or timbers running athwart-ships between the frames or ribs at the keel area and typically will support the cabin sole. You also don't state whether the sole is a fiberglass or composite liner structurally situated to take the place of floor timbers in a molded boat.

As has been said, be careful of just hacking away at the cabin sole or any other part of a boat without knowing the structural compromises you may be incurring in the process. Best to have someone with some real knowledge look at it first. I have seen so many uninformed boat owners ruin a boat by DIY projects without any experience in boat building or engineering.

Hire a surveyor or really good shipwright to look at it before you start hacking away.

[newbie-]

No keel on this one. I have two boats. A SV and MV. This particular problem is on a 46' power boat.

Noted on having it looked at.

[Mlp48]

I have installed --with good help-- access holes and panels. Decide on the decking and then measure carefully in relation to all surrounding where access should be. Remove floor and inspect re marks and measurements, and then cut decking if all is clear or OK. The cut out can be saved and placed in the very same spot if a supporting shoulder can be added. It lot depends on how often you want to revisit but an access hole makes it convenient if going in is frequent,

[MV Caroline]

Even powerboats have a keel. It is the basic backbone for the rest of the hull structure. The keels in some Fiberglass boats are established when the the two halves of the hull are joined and bonded together. Molded (fiberglass) boats and even some strip-planked and cold molded composite boats may use keels and frames added after the monocoque hull has been laminated either over a form or mold. Some are designed to use longitudinal stringers to carry carlin style floor beams to bear the cabin sole loads. There are many different ways to build, some strong and some pretty weak.





If boats were built like houses, we'd all be dead or at least pretty wet.

[Manateeman]

It would be a really good idea to find more about the construction before cutting.
Are there any drawings, similar repairs on line. Who built it, where. Sometimes you can find old boatbuilders who remember what was done.
I’d exhaust the research before cutting.
Then careful mouse holes where they cannot bee seen and can do no damage.
It’s the no damage which is the hard part.
Somebody, somewhere knows.
What boat, when built, where. These three might get answers here.
Happy trails to you.
M and the crew.

[sinnerman]

Check out Ronco Plastics website for a possible replacement plastic tank.

They made the water & holding tanks in my boat.

www.ronco-plastics.com

[stormalong]

If you are careful and neat you may be able to re-use the piece that you cut out.

First determine just how thick the sole really is. Drill a small hole (about 1/4") and use a wire with a bend at the tip to feel the bottom of the hole. Bend the wire at the top of the hole to mark the depth. Set your circular saw to about 1/16" over that depth. Use the thinnest blade that you can find. Draw clearly visible lines for your cuts on the sole. Start with plunge cuts and carefully follow your lines.

After you have removed the sole screw strips of plywood around the perimeter of the cutout to form a ledge to rest the cutout on when you are ready to replace it. Seal the newly cut edges to prevent the wood from swelling.

Counter bore the screw holes and use bungs that match your floor and you will hardly notice the new cutout.