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Model profile · for Great Loop buyers
Mainship 390
The published record on this model and what owners report, with the
questions worth asking while a boat is still a listing. This page covers the model.
Every boat still needs its own homework.
Semi-planing 350/390. She wallows in a following sea and the integrated swim platform does not fix it. Owners call it an annoyance, not a fault. No measured air draft exists for this hull.
The Mainship 350 and 390 are semi-planing trawler-style cruisers, popular enough on the Loop that resale is one of their real strengths (at a slight premium going in). Two things dominate the model layer, and neither appears on a listing. The swim platform is an extension of the hull rather than a bolt-on, and the originals were sealed foam with no inspection access, so they take on water at the rub-rail joint and lose buoyancy right aft. And she wallows in a following sea: the integrated platform was effectively the experiment that tested whether more length aft would cure that, and a former owner of the modified variant says it did not. Owners are consistent that this is a handling characteristic rather than a defect. One owner of fifteen years says they “just wallow a bit.” The standard mitigation on the smaller Mainship 34 is speed, but that fix is unreachable on the low-powered version of THAT hull, and nobody has tested the same logic against the 350/390 power options. What speed a given 390 actually makes is an open question per boat. Engine checks mean opening the salon floor, which is a livability question a survey will not raise. No measured air draft exists for this model, and there is no sourced material on the accommodation layout.
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How to read the tags on this page.
PATTERNtwo independent sources agree; confirm it on the boat you're looking at
CLAIMstated by one source, not yet confirmed
QUESTIONopen, and settled by looking at the boat itself
CONTEXTbackground on how this model is built or used
Sources are linked where published.
From owners
CLAIM
Water got into the swim platform bustle at the seams, the drain plug and the trim-tab wells
On a 1999 390, the owner found the bustle's foam had been removed years earlier. Both mounting seams had failed, the drain plug had failed, and both trim-tab wells had cracked at the edges, and the platform deck was soft at purchase. The fix was three large deck hatches, recoring, and heavy glass work over the seams, the drain and the tab wells, about $30,000 in all, with no water getting in since.
src:
Owner report: Greg White aboard Tug & Chug, 1999 Mainship 390 (Oct 2026). Their YouTube channel: Gnafloat
Swim platform
CLAIM
The swim platform is a hull extension, and the originals flood
On the 350 and 390 the swim platform is an EXTENSION OF THE HULL. It displaces water and contributes buoyancy. So a platform full of water is not just weight far aft, it is lost buoyancy at the stern, which is why it moves draft and trim more than you would expect. The originals were foam-filled with no inspection access; water leaks in at the joint under the rub rail and saturates the foam. The foam slowed complete flooding but never kept them dry. Most have since been modified with access hatches, drains, or standalone bilge pumps.
src:
a Mainship 34 MK1 owner who operates a 390, Trawler Forum, 2026-07-23
QUESTION
Has the swim platform been opened up with access and drainage, or is it still original sealed foam?
An original sealed platform is a latent water-saturation risk: weight, trim, and eventually structure. A retrofitted one has been addressed. A listing will never mention this and a survey has no particular reason to look.
src:
a Mainship 34 owner who operates a 390, Trawler Forum, 2026-07-23
Your move: Ask whether the platform has been opened, and look for hatches, drains or a dedicated pump. If it is original, ask when it was last checked, and check the trim at the dock.
Handling
PATTERN
She wallows in a following sea, and the integrated platform does NOT fix it
Semi-planing hull; owners describe wallowing in a following sea. A Mainship 34 buyer asked whether adding an integrated swim platform would cure the same behavior on their boat, and was told the 350/390 already ran that experiment. A 390 operator: “it would increase the distance from the rudder to the back of the hull, decreasing steering effectiveness. This is basically what was done on the 350/390 and they don't handle any better in following seas.” A former owner of a 390 with the integrated platform: “it was still a bear in a following sea or a beam sea.” The platform looks like an improvement over the 34's bolted-on one, and on draft and displacement it is; on following-sea handling it is not, and it may cost steering authority.
src:
a 390 operator and a former 390 owner, Trawler Forum, 2026-07-28
CONTEXT
Read the wallowing as a characteristic, not a defect
The buyer who started that thread said the boats “struggle” and no owner agreed with the word. One owner, fifteen years in one: “they just wallow a bit.” Another owner: “ok in following seas.” A 390 operator: “while it may be an annoyance, the boats have been in operation for close to 50 years now and they manage ok.” It is a handling characteristic with known mitigations, and the advice owners gave the worried new buyer was to go use the boat before modifying anything.
src:
two owners and a 390 operator, Trawler Forum, 2026-07-28
QUESTION
What speed does she actually make at cruise, and has anyone run her in a following sea?
On the Mainship 34 the standard mitigation for following-sea wallowing is SPEED. One owner: “Speed cures that. If you can get it to 11 knots it smooths it out… if it's a 200 hp or more version.” And another owner: “the early MK I with the 160 hp engine is only an 8 knot boat at cruising speed.” So on THAT hull the standard fix is unreachable on the low-powered variant. Nobody has tested that logic against the 350/390's power options and we hold nothing on it. The 34's 11-knot threshold does NOT transfer. The 390 is a heavier, much beamier boat. What speed a given 390 actually makes is an open question per boat.
src:
two Mainship 34 owners, Trawler Forum, 2026-07-28
Your move: Ask what she cruises at, what she will do wide open, and whether the owner has run her in a following sea. If the answer is single digits, the standard fix for a known handling trait may not be available on this boat. Ask about autopilot instead, which is what owners of the low-powered 34 fall back on.
Fuel & range
CLAIM
2 to 3 NM/gal at 7 to 8 knots, per Power & Motoryacht
Power & Motoryacht's review of the 350/390 says the hull runs efficiently at 7 to 8 knots and gets 2 to 3 nautical miles per gallon depending on the engine, with 14 knots possible on a single engine and up to 18 on twins. It's a general figure from a review, not a measured test.
src:
Power & Motoryacht review (Pierce Hoover), reprinted by Denison Yacht Sales
Livability
CLAIM
Engine checks require opening the salon floor
True of both the 34 and the 390. You cannot do a morning engine check without asking everyone aboard to clear the salon and pulling the hatch. An owner of the 34 who operates a 390 names this as the thing they would most want to change about the boat. Good engine-room access generally needs a bigger boat. Worth actually performing a morning engine check before buying and deciding whether you would do it daily. It is a livability failure a survey has no reason to flag.
src:
an owner of the 34 who operates a 390, Trawler Forum, 2026-07-23
CONTEXT
Much bigger than the 34, mostly on beam, with stairs to the flybridge
The 350/390 is a much bigger boat than the 34, primarily on beam, and the 34's storage is limited enough that living aboard it would be a challenge. A 390 operator also notes the 350/390 has stairs to the flybridge rather than a ladder: “it will spoil you” and make it hard to go back. Minor, but a real ergonomic difference and invisible on a spec sheet.
src:
a 390 operator, Trawler Forum, 2026-07-23
CONTEXT
Cruise-and-fish, not a fishing boat
Nice cockpit, and she will idle slow enough to troll for anything you would target en route, but the cruise speed makes a long run to a spot. Buy her to fish opportunistically while cruising, not to go fishing. A 390 operator also notes the superstructure makes noise trolling across waves for extended periods.
src:
a 390 operator, Trawler Forum, Jul 2026
Draft and trim
CLAIM
Loading barely moves her draft, but confirm the number anyway
A 390 operator, answering a direct question: “I doubt the draft is impacted very substantially when loaded down for cruising, the hull is quite wide and you would have to really load it down to see more than a couple inch difference.” The mechanism is hull form: a wide, beamy hull has large waterplane area and therefore high pounds-per-inch immersion, so a cruising load sinks her only a couple of inches. THIS NARROWS THE EXPECTED DELTA. IT DOES NOT REMOVE THE NEED TO CONFIRM THE FIGURE. The listed water draft is the design draft; the delta is a function of hull form, not a constant, and you do not know it until someone measures. Confirm the number. Never assume it is worse, and never assume this claim means you can skip it. They also name the bigger variable: the swim platform holding water.
src:
a 390 operator, replying to a direct question, Trawler Forum, 2026-07-23
Buying
CONTEXT
Loop popularity is both a resale strength and an entry premium
A 390 operator rates resale as possibly the model's greatest strength: Loop popularity makes them easy to resell and holds their value, but you pay a slight premium at entry. Not a defect, a trade: buyers rarely price the premium in, and it is offset by exit liquidity.
src:
a 390 operator, Trawler Forum, Jul 2026
CONTEXT
Do not read 430 reviews as 390 reviews
One forum member calls the 430 a different, faster, “basically planing” hull, distinct from the 350/390/400. A 390 operator independently describes the 350/390 as semi-planing. Two independent sources agree the 430 is not the same animal, though a competing semi-displacement framing of the 430 still stands. Reviews and owner reports of the 430 are about a different boat.
src:
two forum members, Trawler Forum
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