Buying Used - What to look for?

So my buddy decided on that '01 Air Nautique and is going to check it out today. What would your check list be for looking at a used boat? Would you recommend a compression test or other mechanical tests by a mechanic? Thanks!

When we bought ours, we had the mechanic do a full checkup on the engine, compression test, the whole works. The seller paid for it.

Get the prop looked at too, we didn't and it turned out ours was bent beyond repair and had to be replaced (thankfully the seller paid for the new acme).

Look at the hull for scratches, and look especially near the bow to see if the previous owner beached his boat on sand a lot.

Good luck!

sounds like you had a good seller DB...

If it runs well, I wouldn't worry about a compression check on a boat of that age. Hours would a factor too. You're basically checking the valves and head gaskets. And you'd pry know if something was wrong there.

On an older boat, i'd be more concerned with it since the valves will pry need some work.

I did, Benjamin. Marc Valliant of Frontline Wholesale out of Post Falls, ID. Great guy to deal with! Which is important when you are driving 16 hours to pick your boat up sight unseen...

Look for any corrosion that could be caused by salt water, we bought a boat out of FL, "never been in Salt Water" B.S. haha We had to replace the entire engine and other parts.. Don't by FL boats.. haha

I think a compression check is not a bad idea if the boat has a lot of hours. If salt water may be an issue, closely inspect the trailer, prop / rudder area & engine area for rust or corrosion (stay away from boats with rust). Many say you can tell how well a boat was cared for by the condition of the teak swim step.

Start at the front of the boat and work your way around. Keep in mind that a good detail can fix minor scuffs. I personally don’t think beaching is a huge problem unless the boat has some significant damage to the keel. Look under the seats, check the batteries and asked for maintenance records.

Disclaimer--I am very anal about boat maintenance. Skip this post if you are not spending your own money for the boat.

I would get a compression test on any boat you consider buying. It is cheap insurance ($100) and provides a tell/tell of what is going on inside the cyliders. I had a compression test done on an 08 MCX and 2 of the cyliders read 114 and 135. The rest were in spec @ 185-190. This is a good sign that there is something going on in the engine (rings, valve seals, HG issue, or pitted cylinder walls). Oh yeah, the seller could not produce any maintenance records.

I would also strongly suggest you make a check list and follow it. It is very easy to get side tracked by the looks of a sweet boat and/or the seller's chatter about features. The following is a list i used when i inspected the boats I looked at.

Walk around and inspect Gel Coat
Inspect Running Gear
Inspect all seated surfaces and associated storage compartments
Inspect Bimini Top to makes sure it closes properly
Inspect Cover (does it have all poles, harware, etc)
Lift up carpet
inspect bilge and pump(s)
Verify Hours
Check Oil
Check Tranny fluid
Check all gauges
Check Blower
Check Bilge pump
Check Heater
Check Radio
Check IPOD connection
Check Running and anchor lights
Cycle VDIG and ensure all works
Check Perfect Pass Pro
Check Ballast tanks
Does the boat vibrate underway/under deceleration
Turn both ways
Does the trim tab work
Fold Tower
Do racks swivel/lock
Owners Manual
Keys
Maint. History records
Compression Test records
Check Trailer lights
Inspect trailer bunks
Inspect tires (pressure, Hubs, etc)
Air pressure and lug torque are within spec

Thanks guys. I will pass this along. Good stuff.

Shooter sums it up......Nice Post

I would defiantly ask for all service/maint records.

I would get the engine checked regardless of the hours... low hours don't always equal a "new" performing engine, esp if it wasn't broken in properly...

And I agree, I'm probably too picky about the "beaching" part... just makes me cringe when I see a nice boat scratching up against the shore...

Good advice here, not much to add.

Service records would be nice, but nowhere near as important as a mechanical checkout. Also if someone does all their own maintenance, their boat may be maintained very well but no service records. This would be my case if I ever sell my boat.

+1 IMO beaching on sand is NBD, but it really does set some people off.

Josh are your figures not in PSI, or does that MCX really have ~13.5:1 compression?

(Message edited by jtnz on August 06, 2009)

Jos... I am not talking about the actual compression ratio, but the rather the compression pressure of each cylider. A Compression Pressure test is measured in PSI.

185 psi would be about 12.5 times atmospheric pressure (~14.7 psi) or a ratio of 12.5:1

Seems very high, unless it is a diesel. Our 350 tests around 140 with 9.5:1 compression.

I guarantee he isn't anywhere near 12.5:1. Most marine engines are designed to run on either 87 or 89 octane. 12.5:1 with iron heads would be hell to make work on pump 93 in a light street car, no way it'd run without detonation in a weighted wake boat.

Compression ratio is simply volume of air at BDC to volume of air at TDC. Cranking compression is affected by a number of factors, namely intake valve closing. Whether detonation will occur is affected my many other factors including quench distance, chamber shape, surface texture, intake charge volume, spark plug type/heat range, etc.

Most factory marine engines in the 9:1 to 9.5:1 range. I've seen engiens with 12:1 compression that only give cranking pressure of 160, and I've also seen 9:1 engines that get over 200 psi cranking pressure. Neither engine had well matched components for the application and resulted in sub-par performance.

Point being, there were many marine engines made and who knows what has been modified, if the engine is original or has been rebuilt, or whatever. No way to know what's in an engine on an older boat.

The number most important to determining octane/pump gas feasibility is dynamic compression. Generally 8.5:1 is max for pump premium (93), generally to run pump 89 you can probably squeeze by at about 8:1 dynamic compression ratio on a boat. A car may take slightly more on 89 octane but this is due to different engine loading.

The point of the compression pressure check is to make sure all of the cylinders are within 10%+/- of each other. The compression ratio is irrelevant.

But for you who want to know.. the MCX has a factory ratio of 9.4:1 and the LY6 has ratio of 9.6:1.

... End of compression ratio Hijack.