This is the fourth of a 10-part series on how to buy a boat.   If you have not already seen it, check out Chapter 3 – Best Places to Shop for Boats.

Once you have found an interesting boat listing or two, the first thing to do is contact the seller to get additional details and possibly arrange a time to check out the boat.  The goal at this stage is to learn more about the boat and the seller to help you decide whether it is worth your time to go see it.


There are over a dozen key questions I believe you should ask the seller before deciding to check out a used boat.  You can get my full list of pre-inspection questions and boat evaluation checklists here: Used Boat Buyer Checklists.

The following are some of the main questions to ask the seller initially and why.

What is the model year of the boat, motor and trailer? Sometimes these differ but only one year is provided on the listing.  However, the actual age of each item has an obvious impact on the depreciated value.

How many hours are on the engine?  This is a case where too much AND too little can be cause for concern.  Mechanical items like engines do best when they are run regularly.  Otherwise, things like rust could build up in the cylinders or fuel could degrade causing major problems and possibly a catastrophic failure if the proper procedures are not followed before running the motor.  Here is an excellent video that describes how to treat an engine that has been sitting for years.

Where was the boat used?  If used in saltwater, hopefully the seller will describe what precautions he took after every usage.

Why are you selling the boat?  Though the seller might not tell you directly, the answer to this question provides important clues as to whether he/she is getting rid of it because they are unhappy with the boat, they are not using it enough, they want a completely different type of boat, or some other reason.

Describe the condition of the boat.  What defects or issues have you had with the boat, motor and trailer?  If the answers to this question do not align with your observations when physically inspecting the boat later, it raises questions regarding the trustworthiness of the seller.

What equipment and accessories are included?  Does it come with a trailer?

Do you have the title and are there any liens on the boat?  If your state requires a title, do not pursue the boat if a title is not available.  Note that some states require a separate title for outboard motors and trailers.  Also, if you are hoping to take the boat home the same day, ask whose names are on the title because all parties would need to sign-off in order to legally transfer ownership.


Assuming the seller’s answers to the pre-inspection questions were satisfactory, the next step is to physically inspect the boat.  Start by checking out the boat on the trailer. Then, if you are still interested in purchasing it, you will want to do a “sea trial” afterwards which will be covered in a subsequent chapter.

As you look over the boat, realize that nearly every used boat will have some issues. However, your goal is to clearly identify what those issues are and understand their severity so that you can make an informed purchase decision and base your offer accordingly.


The boat’s hull, including the transom, are extremely critical to carefully inspect because defects in this area might be difficult and expense to repair.  Naturally, some of the things to look for differ depending on whether you are shopping for an aluminum boat or pontoon vs. a fiberglass boat.

Aluminum and Pontoon Hulls

If you are looking at an aluminum fishing boat, the first thing to take note of is whether the boat is welded or riveted (pontoons are welded). There are pros and cons with each, and both are generally acceptable. However, welded boats are often thought to be slightly stronger and less likely to leak.

Besides the obvious things like scratches and dents, some key things to look for in an aluminum exterior are as follows:

  • Are there any missing rivets or broken welds? This could cause a leaking problem.
  • Are there and dents or patches that might indicate prior damage?

Fiberglass Boat Hulls

With fiberglass boats, there are some additional things to inspect:

  • Oxidation – if the finish appears dull or chalky, this indicates oxidation has occurred which is common in older boats.  Here is a picture of one of my boats that has oxidation due to sunlight hitting the gelcoat on my boat lift. Prolonged exposure to UV rays can cause the gelcoat to break down.  This is largely a cosmetic issue and, in many cases, can be addressed if not too severe by polishing with some sort of fiberglass compound and then waxing.  However, a newish boat with considerable oxidation is likely indicative of a boat that sat outside or was not well taken care of (e.g., not properly covered and periodically waxed).
  • Blisters or “Chicken Pox” – These are small dimples that can appear when water seeps in between the gelcoat and fiberglass. This is typically a cosmetic issue and should be fairly easy to address.
  • Cracks or Chips in the fiberglass – This can be caused by a number of factors such as hitting an object, hull flexing (especially in rough water), too much or too little gelcoat used in the build process, improperly mounted or stress at hardware/fittings, expansion and contraction due to weather changes, age (gelcoat can get brittle over time), or voids in the transom, stringers or core material.

Understanding the probable cause of the cracks or chips is key to determining whether it is something to be concerned about.  Small hairline or “spider” cracks or small chips in the gelcoat are fairly common and are usually not a big deal provided that the underlying fiberglass or structure has not been compromised.  On the other hand, if the cracks are larger or deeper (can fit your fingernail in them), penetrate the underlying fiberglass, or appear near the transom or splash well, these could be signs that the transom and/or stringers are failing which is a much bigger concern and worth investigating further.  A couple additional checks you can do are as follows:

  • Do the tap or “percussion” test. Take a hard object such as a small hammer or the handle of a screwdriver and gently tap throughout the fiberglass hull.  Listen for a consistent, solid sound – much like finding a stud behind drywall.  However, if the sound changes from one spot to the next and has more of a hollow “thud” to it, this could mean that the underlying structure has degraded.
  • Buy a relatively inexpensive moisture meter like this one here. Use it without the prongs (to avoid scratching the boat) and run it along the hull.  Look for relative changes in the moisture level that could indicate that water has penetrated the transom or stringers/core.


Though technically part of the boat’s hull, the transom is addressed separately given its importance.  This is a high-stress area that could weaken or degrade over time – especially if there is a leak somewhere on the boat or if the engine, drive system or other items mounted to the transom (e.g., transducer) were not sealed correctly.

One helpful thing to know up front is what the transom (and stringers) are made of.   The boat seller might not know and so it is a good idea to research this online beforehand.  If made of wood (typically encased in fiberglass/resin) which is fairly common, extra diligence is needed because a leak in the hull could rot or weaken the transom.

Some key things to check are as follows:

  • Are there any cracks in the fiberglass or aluminum (or broken welds) in the transom or splash well?
  • Are the engine mounting bolts pulling in? (suggests potentially rotting core)
  • Trim the motor all the way up and note whether the transom flexes when pushing down on the cavitation plate. Another approach is to tilt the engine all the way up and then push the trim button down in short bursts to see if the transom bounces.
  • Are there any gaps between the motor bracket and the back of the transom? (transom could be bowing or the engine is pulling away)
  • Are there rust/brown stains below screws, bolts or fittings in the transom? (could indicate rotting wood/moisture oozing out)

Do the “percussion test” mentioned earlier with a small hammer or the handle of a screwdriver across the entire transom.  If you hear changes in the tone as you move along and get a hollow thud, that could mean that there is a void or weak section in the transom.  Also consider scanning the entire transom with a moisture meter and look for relative changes in the moisture content which might signal a saturated area.


Whether made of wood (and covered with carpeting or vinyl) or fiberglass, you will want to check the entire deck to ensure that the material is in good shape and the supporting structure (stringers & core material) are in tack.

  • Walk around the deck/floor – if soft/spongy in some areas, this could mean that the floor material has rotted or, worse, the underlying stringers/core has degraded (significant repair).
  • On pontoon boats, look underneath at the deck for discoloration. If black, this could mean that the deck is rotting.
  • On fiberglass boats, look for chips or cracks in the fiberglass. As noted in the fiberglass hull section, small “spider” cracks or chips in the fiberglass are often not a major issue provided that the underlying structure is solid.  Larger cracks that you can put your fingernail in are a bigger concern and should be investigated further.  As described previously, do the “tap” test and/or check with a moisture meter to determine whether the stringers or core might be failing.


In addition to obvious things like cuts or tears, here are some other things to look for with the boat’s upholstery:

  • Touch all of the upholstery. It should feel soft and supple – not papery or brittle.  The use of harsh chemicals or over-exposure to UV rays can degrade the fabric.
  • Gently separate all of the seams to see if stitching is holding up.
  • Check for mold and mildew. These fungi are very difficult to treat and will often return once they get into the cushions.
  • Sit on all the seats to assess comfort. You will often be on a boat for an extended period of time so it is good to have comfortable seating for you and your guests.

One thing to note about vinyl colors – darker shades or accents might look appealing but can be very uncomfortable to sit on during warm summer days – even in cooler climates.  Though not a deal breaker, it is something to be aware of going in.


If the boat is equipped with carpeting or vinyl floors, look for cuts or stains or loose sections.  Vinyl is becoming increasingly popular, especially on pontoon boats, because it is easier to maintain.  However, replacing the flooring material (whether carpet or vinyl) on some boats like pontoons can be a big job since the top deck might need to be disassembled in the process.

Storage Compartments

Ideally, most boats should have separate wet and dry storage locations.  Wet storage is for things like anchor lines or built-in coolers, while dry storage is good for clothing and personal items (phones, wallets, etc.).

It is important to open all storage compartments and check for the following:

  • Are seals (rubber gaskets) in place in dry storage locations?
  • Are there stains inside the storage compartments that might indicate standing water (e.g., failed gaskets for dry storage areas or wet storage areas not draining properly)
  • Do lids/hatches fit properly? If not, these might rattle while underway.
  • Do the hinges appear sturdy?

The good news is that these are usually fairly minor issues that can be addressed without a lot of expense.


  • Fasteners – are there any screws or bolts loose or missing? If unable to tighten, could indicate that the screw is stripped OR that the core material is rotting (bigger issue).
  • Windshield – Check to see if it closes and latches properly. If loose or ill-fitting, it will likely rattle in waves.  Could also indicate that the hull has flexed/distorted (e.g., boat in a lift with straps for an extended period).
  • Bimini – deploy to ensure it is sturdy/working properly and the canvas is in good shape (if frame bent, could indicate bimini was left up at high speeds or while trailering). Note how easy it is to stow & deploy.  Also pay attention to the size of the bimini – larger is often desired in warmer climates for health and comfort reasons.
  • T-top – Common on saltwater boats, grab ahold of the top along the upper frame edge and shake it. Too much flex could rattle while underway, dislodge rods in rod holders (if installed), or potentially break welds.  Also inspect the quality and condition of the welds and how securely the top is mounted to the boat.  If the top is covered with canvas (vs. fiberglass), look for rips or tears at the seams and whether it has a good, snug, fit that won’t flap around in the wind.

Wiring/Electrical System

  • Wiring – Is it neat and secured in place (to reduce chaffing) or more like a “rats nest” and hard to trace wires? Are marine-grade wires and connectors used?
  • Batteries – Are terminals clean and corrosion free? (green build-up indicates corrosion) How old are the batteries (most need replacing approximately every 3-5 years)?  What type of battery(s) is installed (lead-acid is most common but bonus points if AGM or Lithium are installed – longer lasting and more vibration resistant)?  Is a battery cut-off switch installed (provides peace of mind to prevent accidental draining)?  Having an on-board battery charger is a nice convenience feature.
  • Fuse Box/Breaker Panel – is it fairly neat and accessible? Fuse boxes are common in older boats but breaker panels are often used in newer or more expensive models.  They tend to be more convenient because you do not have to replace a fuse when a breaker is tripped.
  • Switches – at the console, try all systems (lights, bilge, horn, aerators, etc.) to make sure each is working properly.

Installed Accessories

  • Power up each item (fish finders, VHF radios, stereos, etc.) to make sure they operate properly. You might have to repeat this step during a sea trial to check things like fish finders that will not work properly on land.
  • Ask age of installed accessories (did it come with the boat or added afterwards?). Some items like fish finders may be out-of-date and need upgrading.

Canvas and Covers

If the boat is equipped with snap-on canvas pieces or a mooring cover, it is a good idea to check these too because they can be fairly expensive to replace.

  • Snap-on Canvas Pieces (e.g., bow or cockpit covers) – If this is something you will be using, attach the pieces. Look for tears or stains (e.g., mildew) in the covers or missing/damaged snaps.  Also, canvas may shrink over time making it difficult to snap to the boat.  Since these are custom pieces, the canvas is expensive to replace (although snaps can be replaced fairly easily).
  • Mooring Covers – Having a properly fitting mooring cover is important to protect the boat’s interior from bugs and harmful UV rays – especially if the boat will remain outdoors for an extended period. You will want to attach the cover as well to note the canvas condition, the quality of the fit (custom covers will naturally fit better than aftermarket versions), and how it attaches (some use a ratchet system which is easy to use and provides a snug fit; others require ropes or bungees to secure).  Unlike snap-on canvas pieces, mooring covers are not too expensive to replace (typically, a few hundred dollars for an aftermarket version).


For most used boats, the engine is the single most important item to inspect.  It often represents about half of the boat’s value and can be expensive to repair or replace.   Before you even begin your inspection, ask or confirm the number of hours on an engine.  Also ask how often the boat has been used.  While fewer hours is often preferable, this isn’t always the case.  An engine that has sat for a long time without use can develop issues as noted earlier.  Check out this video for some precautions to take if you have an engine that has not been run for a long time.

Next, examine the engine while the boat is on the trailer.  Key things to check are as follows:

  • Powerhead/Engine Compartment – remove the engine cowl or open the engine hatch to check the cleanliness (indication of how well it was maintained) and to see if corrosion is present (especially important if used in saltwater or kept in a coastal area). Also check for a cracked or worn timing belt (non two-stroke engines) or fuel line/primer bulb (outboards).  Squeeze the rubber hoses on top of sterndrive or inboard engines to see if they are soft and supple or in need of replacement.  Be sure to do this with a cold engine as the block and manifolds could be very hot otherwise.

While you are in there, also check the oil and fluids.  If the levels are too high or too low, or if the color of the oil is very dark in color (four-stroke engines), this could be a sign that the engine was not carefully maintained.   Also be sure to ask how often the engine had been maintained, when the last oil change had occurred, and who typically does the routine maintenance.

  • Lower unit corrosion – If there are white blotches, the paint is blistering, or the metal surfaces are pitted, this likely indicates that galvanic corrosion has occured. Also check to see if the sacrificial anodes are in tack.  These are small, unpainted metal objects made of zinc, aluminum or magnesium that serve as the “trim tab” and/or are attached near the cavitation plate.  They are designed to take the brunt of the corrosion so that your lower unit is spared.  However, if they are heavily pitted or greatly reduced in size, they need to be replaced (easy to do) in order to provide protection.

If the lower unit metal surface is not badly pitted, the corrosion can often be successfully treated by stripping/grinding off the old paint, filling the pits, and then repainting the surface.  Also be sure to reinstall the proper set of sacrificial anodes.

  • Trim system – trim the engine all the way up and down to see if it operates properly. If the boat has a sterndrive engine, also check the bellows (rubber gasket around the drive unit) when the drive unit is fully trimmed up.  Turn the steering wheel from side to side and look for any cracks or tears that may result in water intrusion that could damage the boat and drive unit.
  • Steering system – While standing behind the engine or drive unit, try moving it from side to side. If there is a lot of “play” (over 1” or so), this could mean that there is a broken mount or leak in the hydraulic steering system.
  • Propeller – look for obvious signs of damage. Also, if the prop has been repaired, additional numbers (besides the original manufacturer number) might be stamped on the hub.  Stainless steel propellers, of course, are more valuable and durable than aluminum.
  • Prop shaft – With the engine in neutral, spin the prop and look to see if there is any wobbling. A bent prop shaft will cause vibration and damage the lower unit.
  • Skeg – Look for cracks or damage. However, paint that has rubbed off is not uncommon and likely not a big concern.
  • Gear lube – the drive (sterndrives) or lower unit (outboards) has a screw under the gearcase “torpedo” that is used to fill with gear lube.  There is also a vent/overflow screw up above (if you are not sure which one it is, ask the boat seller).  Remove this upper screw and insert a clean Q-tip or twisted corner of a rag to sample the gear lube (slightly loosening the lower screw while the top screw is in place is an even better way to sample the gear lube but many boat owners might be hesitant to let you do this for fear of draining the gearcase and causing a mess).

When fresh gear lube is added, it will likely be either blueish-green (Mercury/Quicksilver) or golden-brown (Yamalube).  Over time, the gear lube will naturally darken.  If your Q-tip or rag comes out a dark shade of its original color, then you are fine (if it is really dark, the gear lube likely hasn’t been changed in a while).  However, if it is milky in color that indicates that water has entered the gear case (likely due to a damaged seal).  This might not be a major problem yet (since some gear lube remains) but is something that will need to be fixed soon.  However, if it has a grayish tint, that means that there has been some sort of gear failure and metal shavings are now mixed in with the gear lube (major issue).

These are just the initial things to inspect with the engine while the boat is on the trailer.  There are many more things to evaluate during a sea trial which will be discussed in a subsequent chapter.  Note that it is not necessary to put on the “earmuffs” and start the motor on the trailer if you intend to do a sea trial (highly recommended).  Running the engine on the trailer will not tell you how the engine performs under load and so it is not a good substitute for an actual test drive.


If the boat is equipped with a trailer, you will want to inspect it carefully.  This is because a trailer in poor condition could damage your boat and/or pose a safety risk and is fairly expensive to replace.  Much of the inspection can be completed with the boat on the trailer but a few items are best examined without the boat – perhaps when the boat is in the water for the sea trial.

The following are the key trailer components to examine:

  • Frame – Look for signs of corrosion. Some surface rust is Ok but significant corrosion around the bolt holes could lead to failure.
  • Tires – Any uneven wear or cracks along the sidewall suggests the tire is going bad. Though tread depth is important, most trailer tires fail because of age, not mileage.  Look at the DOT number on the sidewall which indicates when it was manufactured (after the letters DOT, there will be some letters and/or numbers and then a four-digit number in an oval.  The first two digits indicate the month of manufacture and the last two denote the year).  Trailer tires should be replaced approximately every three to five years, regardless of mileage. If the trailer was stored outside, the tires will degrade quicker unless they were covered.
  • Winch – Make sure that it cranks properly in both directions and that the strap is in good shape. There should also be a safety chain attached in case the strap ever fails.
  • Jack – Crank the jack up and down to make sure it works properly. Also take note of the condition of the wheel – especially if you will be moving the boat around while on the trailer.
  • Lights – With the trailer connected to the seller’s vehicle, have him go through all the functions (lights, turn signals, brakes and emergency). Also pay attention to the type of trailer connector used (round vs. flat, number of pins).  Should you decide to buy the boat, you will need the right kind of connector to trailer it home.
  • Brakes – Many boat trailers are equipped with surge brakes although larger vessels might have “Electric-over-hydraulic”. If the boat has a tandem trailer with surge brakes, an easy way to see if they are working is to place a piece of wood in front of a tire and have the boat owner pull the trailer forward so that one of the tires is on top of the wood while the other is spinning free.  Then, chock the tires on the other side and disconnect the tow vehicle.  Spin the free tire and then push in the actuator at the front of the trailer (you should be able to compress it slightly).  The tire should immediately stop if working correctly.  Alternatively, you could jack up one side of the trailer and do the same thing but that is a bit more work.
  • Hardware – Crawl under the boat (having a piece of cardboard is handy for this) or, better yet, wait until the boat is off the trailer for the sea trial and check that all the nuts and bolts around the leaf-springs and elsewhere are in place, not rusted out, and tightened securely.
  • Bunks – This check is also best when the boat is off the trailer. Most boat trailers have carpeted bunks.  Inspect the carpet for tears that could end-up scratching the boat hull.  Also examine the wood itself to see if it has rotted or if any of the lag screws are loose or missing.  The good news is that replacing the carpeting and/or bunks on boat trailers is easy and inexpensive to do (provided that you have a place to park the boat while you work on the trailer).
  • Wheel Bearings – With the boat off the trailer, grab ahold of a trailer wheel and try to wiggle it. If the wheel has “play” in it, it could mean that there is a loose bearing which could add up to trouble soon.  Repeat this for each wheel.

One last thing.  If the boat is not equipped with a spare tire, you will definitely want to get one if you plan on trailering your boat a fair distance.  Otherwise, you might end up leaving it on the side of the road if you get a flat and no one wants to do that.

Get a Printable Used Boat Evaluation Checklist

To receive a comprehensive checklist of the items mentioned above in a printable format along with what to look for during a sea trial, click here: Used Boat Buyer Checklists.

Special Thanks to Robert Grantham

Robert is a friend and former colleague who contributed to this article.  He has been around the Boating industry even longer than me with “tours” at Mercury, Suzuki, Baja boats, UFlex and various others.  He is the best “product guy” I know.  Whenever I have a problem or question with my boats, Robert is the first person I turn to for advice.  Besides being a wealth of knowledge on most things boat-related, Robert has a natural curiosity regarding how things are made or designed and was a tremendous resource in the writing of this article.


In addition to help from Robert Grantham, the following are some of the many sources that helped to inform this article:

Gasmire, Charlie. “Riveted vs. Welded Jon Boat (What is It and Which is Better).” Web Blog Post.  Jon Boat Planet

Landry, Chris. “The Smart Buyer – How to tell if that core is wet.” Web Blog Post.  Soundings. 2 November, 2014.

Everything You Need to Know About Wet Transoms.” Web Blog Post.  Seaworthy Inspections.

Seeing Water In The Bilge? 14 Reasons Why & Easy Fixes.” Web Blog Post.  Boating Valley.

Rudow, Lenny.  “Buy the Best T-Top for Your Boat [Signs of Boat T Top Quality]” YouTube Video.  BoatUS.

HOW TO SAVE A OUTBOARD THAT’S BEEN SITTING FOR YEARS.” YouTube Video.  Team Reelin The Blues.  2019.

Stopping Boat Engine CORROSION!!!.”  YouTube Video.  Born Again Boating. 2022.

What Color Should Lower Unit Gear Oil Be?” Web Blog Post.  Born Again Boating.

When to replace your trailer tires.” YouTube Video. 2016.

When to Replace Trailer Tires.” YouTube Video.  Family Handyman.  2017.

Please note that I provided a link to a product (moisture meter) above for your convenience.  If you click on a link and buy the listed product or any other, I will receive a small commission that will help support BoaterInput and would be greatly appreciated.  Thank you for visiting my site.

Jerry Mona - BoaterInput

About the author

Jerry Mona is an avid boater and angler and long-time boating industry insider. With over three decades of experience, he is often considered to be the leading research expert with boaters and has helped numerous manufacturers and trade associations to understand the needs, wants, attitudes and behaviors of boaters. He now shares many of his insights about boats and boaters for free on his website.

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