Pontoons hide their problems below the deck

A pontoon that "sits low on one side" or "feels sluggish" usually has water inside a log (toon). Aluminum logs are chambered; a leaking chamber can hold a lot of water before anyone notices — and hundreds of pounds of trapped water ruins performance and stresses the deck structure.

Water-in-log diagnosis

1. On the trailer, look at the boat level side-to-side; a listing pontoon on dry land already tells the story.
2. Rap along each log with a knuckle or rubber mallet — a dull thud instead of a hollow ring marks the waterline inside the chamber.
3. Most logs have threaded drain plugs at the rear of each chamber; with the bow raised, open them carefully (pressure or vacuum can exist — crack them slowly) and drain. Measure or estimate what came out for the customer.
4. Find the leak: common entries are popped rivets or cracked welds at the nosecone seams, keel abrasion from beaching, cracked weld at motor-mount or strake attachments, and corroded fittings. Soap-bubble testing with low-pressure air (a shop vac in blow mode is plenty — never high-pressure compressed air, which can balloon a chamber) shows the leak.
5. Repairs range from re-sealing plugs, to weld repairs (marine aluminum welder territory), to nosecone reseals.

The rest of the pre-season walk

• Underdeck: hanging wires, loose cross-member bolts, corroded fence-rail bases, and the transom pod welds around the engine mount.
• Engine mount and transom pod: cracks around high-stress welds — more common as owners hang bigger engines on older pontoons.
• Deck: soft spots near gates and the bow (plywood decks rot from the fastener holes down).
• Electrical: nav lights, bilge pump in the pod if fitted, battery secured and covered.
• Furniture and gates latched — a swinging gate underway is a real injury source.

Common mistakes

• Pressure-testing a log with shop air at full pressure
• Draining the water but never finding the entry point
• Ignoring underdeck fastener corrosion in salt or brackish use

When to walk away

Widespread crevice corrosion of the logs (white bloom lines along welds, pinholes on the keel line) is a re-tube conversation — patch-welding a lace-work log wastes the customer's money.

Safety: never work under a pontoon supported only by a trailer jack — use stands rated for the load.