A method, worked on one real listing. The boat is the illustration — the tiering and the questions are the point.
Worked 1 August 2026, on a 2003 Mainship 390 listed in Biloxi, Mississippi at $149,000.
She may well be sold by the time you read this, and it doesn't matter. This is not a recommendation and it isn't a listing — it's the method, run on a real boat so you can see what it produces. We are not involved with the boat, the seller or anyone selling it, and we've never seen it. Everything below comes from the public listing and from owners talking about this hull family.
Because "owners report" is where most boat advice quietly stops being checkable.
| tier | what it means |
|---|---|
| FACT | Measured or documented. |
| CLAIM | One credible source said it. |
| PATTERN | Two independent sources agreeing. |
| QUESTION | Something to go and find out. |
| CONTEXT | Calibration, not a finding. |
⚠️ The last two are not a lower grade of confidence — they're a different kind of thing. A question is not a weak fact. Rank all five on one ladder and the questions fall off the bottom, which is exactly where the useful work is.
| gate | status |
|---|---|
| Air draft — 19'6" | Unverified, and we can't fix it from here |
| Water draft — under 5' preferred | Design figure not stated in the listing text — ask |
| Range — 250 mi, Alton→Paducah | Depends on tankage and speed. Ask both |
| LOA | 39' — inside every practical limit |
There is exactly one clearance on the Great Loop you cannot get around: 19'6" on the Illinois River at mile 300.6. Everything else has a way through. That's the air-draft page.
We hold no measured air draft for any Mainship 350 or 390. It is the oldest open gap in our own notes on this hull family, and we are not going to invent one from a brochure.
⭐ That is the correct answer, not a dodge. The number that matters is this boat, with the antennas down, the arch as it sits, and whatever the last owner added on top. A tape measure on that specific hull beats any published figure, and nobody has ever measured a boat by reading a spec sheet.
Low hours reads as low wear. On a boat this age it usually means something else.
Rate and recency beat the total. 1,600 hours over twenty years is about 80 a year, which is healthy, regular use. 33 a year is a boat that spent most of its life tied up.
What sitting costs, and none of it shows on the meter: impellers, hoses, exhaust components, seals, injectors, fuel that has aged in the tank, and a raw-water side that has been wet and still for two decades.
⚠️ This is not "don't buy it." It's the single question to put first:
"When did she last run regularly — not when did she last start?"
⚠️ And the counterweight, because it's real: she's a Yanmar diesel. A 750-hour figure that would frighten you off a gas boat means something different on a diesel — these run into the thousands. An hours number with no fuel type attached is not a number. That's the engine-hours page, and this is it on a real boat. The concern here is sitting, not wear.
⭐ The listing helps, and it's a genuinely good sign: a bottom job in 2025, and new electronics, cushions, dinghy and outboard in 2025–26. Somebody has been spending money on this boat recently. Whether that came with regular use is the thing to establish.
Tier ceiling for this whole section: pattern. All of it is owner and owner-adjacent testimony — no measurements, no surveys, no documents. We describe who said each thing rather than writing "owners report."
On the 350/390 the swim platform is a hull extension — it displaces water and adds buoyancy. So a platform full of water isn't just weight aft, it's lost buoyancy at the stern, which moves trim and draft more than you'd expect. The originals were foam-filled with no inspection access; water gets in at the joint under the rub rail and saturates the foam. Many have since been retrofitted with hatches, drains or a dedicated pump.
Source: an owner of a Mainship 34 who also runs his parents' 390.
Has the swim platform been opened up with access and drainage, or is it still original sealed foam?
A listing will never mention this and a survey has no particular reason to look. Ask; then look for hatches, drains or a standalone pump. If it's original, ask when it was last checked, and look at how she sits at the dock.
Semi-planing hull, and owners consistently describe wallowing in a following sea. When a Mainship 34 owner asked whether adding an integrated platform would cure the same trait on his boat, he was told the 350/390 already ran that experiment — it moves the rudder further from the back of the hull and costs steering authority. A former 390 owner with exactly that platform: "it was still a bear in a following sea or a beam sea."
Two independent sources, one of them an owner of the modified variant.
🔴 Do not read the above as a defect. The buyer who raised it used the word "struggle", and no owner agreed with him. One with fifteen years in the family: "they just wallow a bit." Another: "the boats have been in operation for close to 50 years now and they manage ok."
It's a handling characteristic with known mitigations, not a fault. The advice owners gave the worried buyer was go use the boat before you modify anything.
On the smaller Mainship 34 the standard fix for following-sea wallowing is speed — but owners report the low-powered version tops out around 8 knots, so the standard fix is unreachable on that variant.
⚠️ That threshold does not transfer to the 390 — heavier, much beamier, different numbers — and we hold nothing on what a 390 actually makes.
⭐ Which is why this listing is interesting: 390 hp is real power for this hull. So the question is answerable on a sea trial rather than academic:
What does she cruise at, what will she do wide open, and has the owner run her in a following sea?
⭐ And note the new autopilot. On the low-powered boats, autopilot is what owners fall back on when the speed fix isn't available. Here it's a bonus rather than a crutch.
True of the 34 and the 390. No morning engine check without clearing the salon and pulling the hatch. The owner-operator we drew on names this as the thing he'd most want to change about the boat.
Perform one before you buy — physically, on the day — and decide whether you'd do it daily. It's a livability failure a survey has no reason to flag.
"I doubt the draft is impacted very substantially when loaded down for cruising — the hull is quite wide." The mechanism is hull form: a wide, beamy hull has large waterplane area, so a cruising load sinks her only a couple of inches.
🔴 That narrows the expected delta. It doesn't remove the need to confirm the figure, because the delta is a function of hull form, not a constant — and you don't know it until someone measures.
The 390's reputation as a Loop boat makes it easy to resell and holds its value — but you pay a slight premium at entry. Not a defect; a trade. Buyers rarely price the premium in, and it's offset by exit liquidity.
The Mainship 430 is a different, faster, essentially planing hull — two independent sources agree it isn't the same animal. When you go looking for owner reports, check which boat you're reading about.
⭐ "Deck access is made easy for shorthanded cruising with a starboard helm sliding door."
That's a bigger deal than it sounds. Handling the Erie Canal's hanging lines shorthanded needs a boat you can leave instantly — a side door, a boat hook and a bow thruster. A helm door on the correct side is one of the three, built in. That's on the single-handing page.
Recent money, all in the last two years: bottom job 2025 · new electronics with autopilot 2026 · new dinghy and outboard 2025 · new bridge cushions 2026 · exterior wax and detail 2025.
⚠️ Recent work is evidence of care, not of condition. Cosmetics and electronics are what people do before selling. The bottom job is the useful one — it means the running gear has been out of the water and seen by someone recently. Ask what the yard found, and note that it's the same lift a survey needs. What a survey costs, and when to book →
🔴 That last section is the one worth copying. A write-up that has no gaps in it either covered everything or stopped looking, and only one of those is common.
The public listing, and owners of this hull family talking about their own boats — an owner of a 34 who also runs his parents' 390, a former 390 owner with the integrated platform, and an owner with fifteen years in the family. We didn't collect that testimony — we found it, read it together, described who said it, and marked how far it goes. We haven't seen this boat.
If we've got something wrong, tell us and we'll fix it — support@caniloop.net. A correction from someone who has actually run it is worth more than anything we can write.