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Mainship 34 Trawler

2004–2009 · single Yanmar 370 hp · semi-displacement

Beam 14'3" · Draft 3'4" · Fuel 250 gal · ~20,000 lb dry · used market ~$150–200k

First — which boat? Two unrelated boats are sold as a "Mainship 34." Confusing them is the #1 buyer error, and listing sites mix them constantly. This dossier is the modern Trawler.

Modern 34 Trawler · 2004–2009

Yanmar 370 hp, semi-displacement, ~20,000 lb, ~$150–200k. The exhaust riser is the watch item. This dossier.

Classic 34 · 1978–1988

Perkins diesel, ~14,000 lb, ~$21–40k. Balsa deck-core rot is the defining issue. A different boat entirely.

GO for the Loop — a strong physical fit

She clears every hard Loop gate with real margin, and a single Yanmar makes for simple, economical cruising. The watch items are model-specific and checkable: the raw-water exhaust riser (the standout) and prop cavitation. Neither is a dealbreaker — but the riser is the first thing to confirm on any hull.

The gates

What a Loop boat has to clear

Gate	The number	Why it binds
Air draft	Under 19'6"	Fixed bridges on the Chicago route. Miss it and a third of the Loop closes.
Water draft	Under 4'6" loaded	Skinny water — the rivers, the Erie, parts of the Gulf ICW.
Range	Plan 250+ nm	The longest no-fuel stretch is debated (often the Mississippi near Hoppie's, ~200–240 mi) and shifts as marinas open and close — verify current fuel stops.

Scorecard

Gate by gate

Criterion	Status	The read
Air draft	PASS	Published at 16'5"–17' (top of the flybridge) — clears 19'6" with ~2.5–3 ft of margin before you drop a single antenna. Sources differ slightly; get a tape on the specific hull, but this is a comfortable pass.
Water draft	PASS	3'4" — well under the skinny-water line. Confirm loaded, but there's plenty of room.
Range	PASS	250 gal; at trawler speed (~7 kn, ~3 gph) that's ~500+ nm — easily covers 250 nm legs. Caveat below: only at displacement speed.
Diesel	PASS	Single Yanmar 6LYA-series, 370 hp. Simple single-engine ownership.

Risk 01

The raw-water exhaust riser

The one mechanical risk that defines this hull. Check it first.

Pattern

The stock exhaust riser/mixer sits low — a slug of seawater can back into the turbo.Widely reported. The riser sits only ~8" above the waterline where 12"+ is wanted; a following sea or shutdown surge can push water past it into the turbo. Documented fix: extend the riser (~16").src: owner forums (Trawler Forum), multiple threads

Question

Has this hull's riser been raised, and what's the turbo history?The single most valuable question to ask on a Mainship 34 Trawler.

Your move: confirm riser height · ask whether it's been extended · get the turbo's service/replacement history.

Risk 02

Prop cavitation

Pattern

Cavitation is commonly discussed — but inconsistent.Some hulls have it, some don't, some only in certain conditions. A clean bottom and fairing the deadwood sometimes help; truing the prop often doesn't.src: owner forums (Trawler Forum)

Question

Does this hull cavitate at cruise?Not a given — verify on the sea trial, at cruise RPM, and check the running gear.

Your move: sea-trial at cruise and listen/feel for it · inspect prop and deadwood.

Risk 03

Fuel tank & engine controls

Question

Fuel-tank corrosion is contested — not established fleet-wide.One surveyor reported corrosion on a tank bottom; a long-time owner said he'd never heard of a tank problem. Don't assume it either way — inspect the tank bottom rather than budget a replacement.src: owner forums (Trawler Forum) — conflicting reports

Pattern

Aging MicroCommander controls and poorly-grounded start relays.Owners advise refreshing the electronic engine controls/cables as they age; the start relays are a known (easy) grounding nuisance.src: owner forums (Trawler Forum)

Your move: inspect the tank bottom where it sits · budget survey time for the controls and grounds.

Risk 04

Read the boat right

Fact

It's a fast trawler, not a 7-knot-only boat.Semi-displacement — the 370 Yanmar will plane her to ~19–21 mph. Good to have, but the ~500 nm range math collapses the moment you run off displacement speed. Plan fuel at trawler RPM.src: published boat test + specs

Question

"34" is the hull length — LOA runs to ~38'10" with the pulpit/platform.Doesn't change the model name, but it can change slip and haul-out fees. Confirm the billed length.

How to read this

Every claim wears its confidence

Fact

Verified against published specs or a documented test.Checkable.

Pattern

Commonly reported across the fleet.True of the model — verify it on this exact hull.

Question

Your to-do list before an offer.Contested or unconfirmed — go get the answer.

No owner-verified facts on this model yet — those get added as real owners confirm them, with a name and a date. This is the research-grade starting point, tagged honestly. An inference doesn't become a fact through confident phrasing; it becomes one when someone who owns the boat answers.

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A real survey and sea trial still happen — this just keeps you from paying for one on a boat that was never going to fit.
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