TOPIC: Converting Engine Hours to Mileage

So you're considering buying a boat with an engine that has logged 1,230 hours. You're pretty sure that figure is accurate but what does that mean in terms we can relate to?

Car engines (nowadays) have overdrive transmissions and at highway speeds, turn right around 2,000 RPMs. Boats generally run in excess of 3,000 RPMs constantly, often higher and pulling 100% of the time, whereas cars coast a lot.

To put things into perspective, I multiply engine hours by 80 (for MPH) to get the "mileage" on a boat. 80 is a 33% increase over a normal 60 MPH speed limit which compensates for the higher RPMs and workload experienced with marine engines.

In this case, 1,230 engine hours would relate to 98,400 automobile miles...and mileage is always a factor to consider.

On a power boat mileage is far too subjective and not a very accurate measure of fuel economy. A far better measure is gals per hour. The fewer gallons per hour the better. My Sea Ray with a Merc 165 uses about 4 gallons per hour (I admit I have never accurately measure it but experience indicates that that is the rate.) On the far extreme other end my 2 hp Johnson had a 1 quart tank and would run for about 2 hours on that so it used a pint an hour. By the way, I did once translate that to mileage and at 3/4 throttle works out to about 20 mpg. But if I ran it at half throttle it used far less fuel. Same with the Sea Ray. If I keep the rpms at about 1000 (hull speed in displacement mode) it uses far less gas per hour than at planing speed (around 3000 rpms at 3/4 throttle)

The only really accurate way to do this is fill the tank with a known amount of fuel. Run the boat at the usual speed you run your boat (for most people that's about 3/4 throttle). Run it for a known amount of time. Accurately measure how much gas was used. That will give you gals/hr.

You seem to have missed the point. Please re-read my post, which had nothing to do with fuel economy. My point was that this idea is one way to estimate wear and tear on an engine. Using my conversion approach, the boat I used for an example had the equivalent of 98,400 highway miles racked-up. If I were buying a car with that mileage or in this case, a boat, I would expect problems with compression, bearings, valves, etc. and would anticipate having to either rebuild or replace the engine. My method of estimating engine condition simply offers a possible benchmark for making a decision to buy or pass. Additionally, one could assume that the engine(s) in a racing type boat (Formula, Cigarette, Stinger, Scarab, etc.) would have been run harder, longer and more often, in which case I would double the engine hours to calculate.

Get on the GPS, mark two waypoints several miles apart. Hop in your boat, open the sucker up, start your stop watch and then see how long it takes you to get from point A to point B. That will give you time (hours/minutes) to mileage (distance). Now that being said, if you started out with a full six gallon fuel tank just measure what is left in the tank when you finish your run. You will have accurate speed, fuel consumption and time to mileage figures. Now that being said again, take in sea/wind/boat passenger load conditions/number of skiers/tubers being pulled at the time of trials/water sloshing in the bilge and other assorted paraphernalia and sundries on board you will come up with the most confusing inaccurate numbers anyone could think of...in the end as someone once said "At this point, what difference does it make" you're out to have fun and enjoyment in your boat.

Ike, I understand the point of your post (not sure how this is being interpreted as MPG...he's talking about how many miles do you have on that thing...think odometer.

I just don't know how easy it is to convert hours into miles travelled. 300 hours spent putting around on a chain of lakes is very different than 300 hours spent pulling skiers on a show team.

The SeaKing I picked up last year does not have an hour meter on it. However, it is clear that it has been very well cared for during its life. The Century Cheetah I have sitting up in the barn only has 300 hours on it. It was rode hard and put away wet.

My grandfather had his old Imp for 35 years, used it all summer every year up in Minocqua. While is had some wear to it, it was very clean and well cared for.

I think it matters too if you are looking at an inboard or an outboard. Just too many variables. I agree, I would use the hours as one part of the decision when buying a boat, but if I found a very clean and loved 1000+ hour boat I don't think it would scare me away. Likewise, I have seen a few boats that looked trashed with less than 300 hours.

The real question is how many miles per gallon does she get

Ran my 1960 Glasspar G-3 110 miles down the Apalachicola river in 1965 with v-4 75-hp Johnson and it took every drop of 24 gallons of gas one-way!! Was running flat out most of the time!!

Made this trip (round trip again the next year)

Jim Savage

Pic of another 1960 G-3 with Merc 1000 that I now have. Just need a gas station to run this at 56 mph all day!!!!

LOL...Fellas!!!

His post is NOT ABOUT MILES PER GALLON!

Too funny.


He is pondering the conversion of the numbers on the hour meter to the miles traveled in the life of a car on the odometer.

Nothing to do with the gas tank, be it half full or half empty (depending on your perspective)

EUREKA! You've got it, Drb007!

There is no fair comparison. Consider two boats with identical motors. One is in a fairly light performance boat, the other in a heavy cruiser. Both are run for the same amount of hours, but the load and wear on the cruiser engine will be higher, since it has to work harder to push a heavier load. Hours only tell me how much time a boat was used, not how it was used over time.

By the same thought process, there is no way to determine how a car has been driven or whether is was used extensively for towing, climbing mountains, in/around salt water, etc. The odometer mileage is your only real indication of use, at least from the standpoint of time. Few people would buy a car with 200,000 miles, regardless of how it looked. If you use my idea to convert hours to miles, it puts things into perspective and may factor into the decision to buy or pass. It's not meant to be a panacea.

Agree that a boat engine's life is harder than a car engine's. A marine mechanic once told me that at a typical cruising speed its like driving a car up a hill at 80MPH. I average 40 to 60 hours a season with my 27 Owens.
We're out pretty much every weekend, but the length of our trips varies. Cruising speed is around 20 knots, 3450 RPM's at half throttle. I hope to get at least 1200-1500 hours on my motor before replacement.
On the other side of the coin, a properly maintained boat engine gets better maintenance than a car engine. I know of small block Chevy boat engines that have gone 3000 hours. I also have seen catastrophic failures at 500 hours. Go-fast boat motors typically are raw water motors 'cause they usually wear out or grenade before corrosion from being run with raw water cooling is an issue. Getting close to a 1000 hours on a go-fast boat motor would be doing pretty good.
I think that type of use and quality of maintenance are a better indicator of engine condition than just running hours.
Larry

Please throw some dirty oil on that engine. You're embarrassing the rest of us.

OK now we have the issue resolved let's take a break.

Sorry didn't get to this until now but thanks Jan great stuff. It makes for a good starting point. Boat condition etc all matter but have to be taken in perspective. Say '69 Chevy Nova SS, all original looks like showroom and engine not rebuilt with 3000 miles on it, sounds to be a great deal until you find out it's all straight line miles 1/4 mile at a time! Just an example.

Again great stuff Jan thanks.

Bob

I would also consider if the motor matches the hull. Mine is a 71 Kona, with a 78 Merc. I doubt the hull sat around for 7 years waiting for a motor. All the exterior decals label it as a 1150, but serial number has it as a 1500, likely a factory rebuilt.
Either someone was thrashing this boat around, or kept forgetting how to mix oil.

Will

Sorry for the confusions. I saw mileage and my foggy brain interpreted that as MPG.

You are right tho. Any way of estimating usage is useful, but the others are right too, it depends on how hard people run their boats. When I was running a USCG repair facility we used to overhaul the engines at 400 hours because the USCG runs those boats hard. However 1000 hours is not unusual on a recreational boat. But that really doesn't translate to mileage well. A good mechanic would probably be able to tell you more about the engines condition.

According to the previous owner my 72 Sea Ray sat on the trailer for at least ten years. But after cleaning up the engine and spraying some freeing oil in the chambers it turned over by hand, and after I replaced the alternator, starter and dist, and cleaned the carb it fired right up. It has pretty good compression on all cylinders. So it can't have been run very hard. My point is a good survey of the boat and engine will tell you more about it's condition than estimating it's use.