Can You Equate Boat Hours to Car Mileage

Does anyone know if you can equate a boat's hours to car mileage. I'm looking into purchasing a "new to me" boat. So is buying a boat with 500 hours on it like buying a car with 50,000 miles... 80,000 miles...? I realize there are a lot on variables involved but I would like to put boat hours in to a frame of reference I can understand. Are there any peeps out there that have a feel for a ballpark correlation.

Anyone???

I apologize if this has been discussed before.

I don't know if this theory is correct but I figure it should be pretty close, someone feel free to correct me if I am wrong. I figure the boat is usually at a running speed of 2800-3400 RPM depending on the boat and weight in the boat. If you figure that would probably equal about 80-90 mph in a car and then multiply the number of hours by 80 or 90 and you would have 40000-45000 miles. Not sure if that is correct but it works in my head.

Some try to equate the two, but it is hard. Cars have transmissions to reduce engine rpm into the torque curve. Most boats do not. Let me put it this way - I usually see 1500 hours as rebuild evaluation time (compression check, bore scope, etc.). 500 hours is 1000 hours away from that or 10 years of recreational use of 60-120 hours per season in the northern climates.

So percieve the boat as having 2/3 of its intended life span left.

Every 100 hours is equal to 10,000 miles. At least that is what I have heard over the years.

Whatever you do, don't check out:

http://www.wakeworld.com/MB/Discus/messages/3183/107144.html?1081568257

The thread starts at 'how often do you open it up' and proceeds through 'is it rpm or load that kills an engine' to 'you're a stupid freak'. In the process, we compare boat engine life to car engine life. Unfortunately, some of us were reasoning through stuff we don't KNOW and others were blindly following WHAT EVERYBODY KNOWS.

It'd be an interesting read if you were chained to a crapper in Madagascar.

Derek - Madagascar is very nice.

The general rule is that one hour is 100 miles. However I have rebuilt a few car engines (mostly an old race car) and a few boat engines.

A lot of miles in a car engine causes many problems, but theworst is the buildup of sludge from burned and contaminated oil. Overtime seals fail and allowcontaminants to enter the oil resvoir which then eatat parts and something eventually fails. When you pull the heads you will find amazingly buildup and scoring.

Marine engines do not typically have this level of buildup at the same point. For example a 350 V8 out of a suburban at 100,000 miles will have lots of buildup but the same engine after 1000 hours of marine use will not.

The higher RPM of a marine engine combined with usually lower operating temps (always pulling cool water for cooling) actually help to keep buildup to minumum. Marine engines also do not experience high friction starting in cold weather.

Here is where this gets not so good for the guys on this forum. Running any engine under load for long periods creates buildup. A wakeboard boat, loaded down will put a lot of stress on an engine. You can help alleviate this by spending some time cruising under light load with RPM between 2800-3500 and frequently (maybe every 20 hours, instead of 30) changing oil. Also, use synthetic unless the engine manufacturer recomends against it (some OEM seals will fail with synthetic motor oil.)

I am not an engineer, but have a shadetree mechanic liscence and hope this helps you to better understand the "miles" on your boat.

Derek- That thread was hilarious, just reinforces my belief to never take ANYTHING as fact that you learn over the internet because 99% of the people probably don't know what they are talking about.

I think the recommended oil change interval is every 50 hours.

my suburban has an hour meter in it...the sub has 35,000 miles and just over a thousand hours

my boat has an hour meter and the perfect pass has an odometer, if i remember ill see what the two say together. I believe the last time i looked i was in the 550 hour range with somewhere around 2500 miles but dont quote me till i get a second look.

I have around 400 hours on my boat and around 2000 plus miles. I'll look again next time out. Just remember, You run full out above 4000 rpms going to and from places and board under heavy load around 2600 rpms. 2000 or so rpms is likely where a car cruises at on the highway. So, I would say double the miles on the boat at least, they have to do something about the loading.

Jeff, are you laughing at me? Do I amuse you? Are you saying I'm funny? (Wish I could rip off the Pesche line at will, with the Tim Duncan poker face ;-)

All I was trying to say is that even though some things skew the wear curve a bit (extra-high or low rpm, rapid accel/decel, etc.), I just can't believe that number of miles on an odometer is any real measure of the work an engine's been asked to do. In this case, gallons burnt does. I do think there's merit to this argument even though I haven't made my case very clearly, and haven't backed it up with any research. A simple, original idea that IMO seems logical as a working hypothesis.

But yeah, funny as hell. Some boards are good at making me feel stupid. This is one of them.

Derek, Haha! No I wasn't trying to pick you out specifically, I didn't even notice you were up in that mess. I think all parties of that thread were partly talking out of there arse.

But I was definitly not trying to point you out at all, just making a more general statement. I'm new here so not trying to get on anybodies bad side in my first week of posting or anything!

I totally agree that miles on an odometer are not an accurate measure of work an engine has done and gallons may be a more relative measure.

Derek, Haha! No I wasn't trying to pick you out specifically, I didn't even notice you were up in that mess. I think all parties of that thread were partly talking out of there arse.

But I was definitly not trying to point you out at all, just making a more general statement. I'm new here so not trying to get on anybodies bad side in my first week of posting or anything!

I totally agree that miles on an odometer are not an accurate measure of work an engine has done and gallons may be a more relative measure.

Ok my new Subruban has an hour meter. I will go in the parking lot at lunch and tell you. I have been driving a pretty average type of driving. "a few long trips, city/traffic so it should be a pretty good guage. I have a feeling you are going to be surprised by it. I think I had around 300 hours for around 10,000 miles last time I looked. I will give you the exact nubers in an hour or so.

Jim,

I have tried to figure this correlation too, I like/agree with the one about 1500 being time for overhaul. My old S&S had 800+, was used heavily, and ran like a champ. The key was good ownership and maintenance.

The other side of the coin reminds me of the "stories" (never personally seen it) of the little old ladys' car with 8000 miles but needed overhaul because it never drove over 2 miles at a time and was full of sludge.

Our Fire engines typically have almost 4000 hours, for 60k miles of road time. This of course includes lots of idleing, and pumping under load. I bring this to point out that everything gets used differently.

I suppose a 10 year old boat, with only 100 miles may make me as suspicious as one with 1500 miles. These engines were made to work, not sit around. At least a high reading may be more honest too, since there are people out there that would gladly reset an hour meter to their advantage.

I would prefer an engine that was run at high speed through a course, than weighted with 3k lbs. But it depends on who put those hours on it.

Luckly, IMHO, there are many things you can look at besides hours - such as the scratches in the hull from when they ran up on the beach, signs of good regular maintenance and care, was it stored indoors/winterized...?

One more thing. Some hour meters start working at the turn of the key. Which means they are racking up time just sitting around, off.

Good luck dude. Send me pix.

Phil

Ok here we go, my engine on my new Suburban has 353 hours on it and I have 11,300 miles on it. So take it for what it's worth.

Okay, I already wrote this post once today and then the web gremlins killed it.

To summarize some stuff in this thread: the trucks average 32, 33 and 35 miles per hour. We'll call it 35. The boats average 5 mph.

A quick diversion: the truck averages 1/2 of its normal high-speed cruise, and 1/3 of its top speed. The boat on the other hand, averages 1/6 of its high-speed cruise and only 1/9 of its top speed. End diversion.

Okay, now to support the "1 boat hour = 100 car miles" rule. Take that 100 miles and divide it by the truck's average speed to turn miles into hours, and you can rewrite the equation as follows: "1 boat hour = 3 truck hours".

If we call 1500 boat hours the point at which we ask, "are we gonna start flowing money into this engine, or trade-in on a new one"....that will equate to 157,000 car miles (1,500 boat hours * the 3:1 car to boat ratio * 35 mph average). That's a reasonable figure in my book.

Of course, your wife will make the 1,500 hour decision for you - the whole rest of the boat will be looking ghetto as hell by then.

(Look, didn't even talk about mpg, gph, gallons burnt, rpms, final drive ratios or watts rms.)

Derek,

To add there is also a "load" difference - pushing 2.5 tons of mass through water is much different than 2 tons of mass on 4 wheels across pavement. Not sure how to add this into the calculation, but somthing to consider none the less.
In recent years with all the wakeboarding use i have seen 4 year old boats that run just fine with 1K+ hours. I think the wakeboard camp had a toyota with over 3K hours on it at one time, but that was the trusty toyota motor ;-)

Now you're trying to add qualitative descriptions (of how the engine was used), when we had just settled in on nice, easy quantitative descriptions (how many miles or hours).

The 60,000 mile pumper truck has worked as much as four Suburbans have at the end of their lifetimes. Sticking with the odometer (quantitative) would do you wrong there, "honey, I found a rig with only 60K, that's LOW miles!!!" It might also scare you away from a rural commuter that spends 98% of his time on the interstate. That engine MIGHT be getting broken in at 100K.

This is why I say that gallons burnt attempts to answer quantitative and qualitative at the same time. If the EPA or the mfr gave each boat/engine combo a recommended overhaul interval (expected engine life) like the FAA does with planes, but instead of quantifying it in hours or miles, chose gallons, I believe you'd know much better how much engine life has been used (maintenance practices and fuel type being held equal.)

Fuel burn takes engine loading, acceleration rate, speed, weight and drag into account. The greater the load, the greater the fuel burn, whether we're talking mpg or gph or mph/second.

And whatever you do, don't fall into the trap of thinking that transmissions change things MUCH. Their largest contribution is to miles traveled, to mechanical advantage if you will, not to loading. They do put the engine in a different RPM range, and engines are clearly happier (mpg-wise) at lower rpms, but I think that factor is more of a distraction in this case.

And the whole "everybody knows boats are under greater load" thing is weak in our case - we do not spend significant time at 90% throttle like ocean boats do. And what would happen if you drove your Suburbans at 90% throttle for extended periods?

We run our boats in the middle of the rpm range and once the weight's on plane at 23 mph, the load is not hugely significant, even with buttloads of ballast.

Gotta go get the boat ready for the first Havasu trip of the year ;-)

Also a Suburban has a transmision that changes gears and keeps the RPMs low. When I run at about 28-32 MPH cruising in my boat if I remember right my RPMs are around 3000 - 3200K. My truck hardly ever gets to 3000K unless I am accelerating. Usually it hangs around 2000K or even less.

"To summarize some stuff in this thread: the trucks average 32, 33 and 35 miles per hour. We'll call it 35. The boats average 5 mph."

BTW my Suburban keeps track of average MPH too, I will check that out and let you know. Also average Miles Per galloon...about 14 for the lifetime I have owned it. That includes all types of driving for the lifetime of the truck.

I have also heard that it's tougher on engines that run at constant speeds for extended periods. Like running a car on a Dyno. This might not be as important on a wakeboard boat though.

Let's make this simple:

Jim - what color is the boat?

Thanks for everybody's help. As I figured there is no clear-cut answer but this discussion has help to put a little perspective on the subject at least.

When you get your boat checked out by a certified boat mechanic they can also run the computer on the engine. It'll give you a better idea of engine hours. I had a 97 Maristar which had 490 hours on the dash meter. When the mechanic did his check on it he ran the engine computer and it showed it only had 425 hours. Big difference.

500 hours on a boat is nothing if it's been taken care of.