Relationship of performance loss and engine hours

[Cobalt Bob]

I am aware of the many factors that can negatively impact a boat's peak performance ie. hull warp if stored on trailer, dirty hull, chipped or bent propeller(s) etc.

However, discounting the above factors, is anyone familiar with the gradual reduction in performance (maximum boat speed) based on the hours on a boat engine?

When new, my Cobalt 226 with 7.4 engine ran at 4600 RPMs and between 59-61 MPH. The boat is now 15 years old with 415 hours on the engine. The current top RPMs is 4300 and top speed is 57MPH. Does this seem to be normal considering age and engine hours?

Thanks in advance for your thoughts!

Cobalt Bob

 

[Scott Danforth]

the motor's hours are actually low (your usage is about 20 hours a year). for example, I put on about 150 hours a year and I dont get out anywhere near enough. I also drive my boat like I stole it.

life expectancy for a properly maintained marine motor is over 3000 hours.

your loss in performance should not be from 415 hours, however there are hundreds of reasons you have lost 300 RPM and 2-4mph.

look at the stickies at the top of the forums for low WOT RPM.

 

[alldodge]

I am aware of the many factors that can negatively impact a boat's peak performance ie. hull warp if stored on trailer, dirty hull, chipped or bent propeller(s) etc.

However, discounting the above factors, is anyone familiar with the gradual reduction in performance (maximum boat speed) based on the hours on a boat engine?

When new, my Cobalt 226 with 7.4 engine ran at 4600 RPMs and between 59-61 MPH. The boat is now 15 years old with 415 hours on the engine. The current top RPMs is 4300 and top speed is 57MPH. Does this seem to be normal considering age and engine hours?

Thanks in advance for your thoughts!

Cobalt Bob

Might also need a tune up, maybe prop needs to be checked

Need to also ask is this the speed=o on the boat or GPS

 

[airshot]

Yep, I would look at other issues as well.....my 1983 3.0 is still all original with exception of normal maintenance items, it still runs 4600 rpm and 34+ mph with a gps. and that is 32 yrs old, have no idea on hours but I do know that it has a bunch....But then again has always been maintained!!

 

[HT32BSX115]

is anyone familiar with the gradual reduction in performance (maximum boat speed) based on the hours on a boat engine?

When new, my Cobalt 226 with 7.4 engine ran at 4600 RPMs and between 59-61 MPH. The boat is now 15 years old with 415 hours on the engine. The current top RPMs is 4300 and top speed is 57MPH. Does this seem to be normal considering age and engine hours?

Thanks in advance for your thoughts!

Cobalt Bob

Howdy Bob,

Welcome aboard!

Loss of performance *could* be roughly described as "due to age"........... but age is not necessarily a "cause"........... but it could cause you to investigate further.

A good list of items to consider is HERE: http://forums.iboats.com/forum/engi...ves/302506-list-of-possible-causes-of-low-wot

Since we're talking about "AGE" or hours, #9 (compression) would be of particular concern . But many engines with more than a couple thousand hours have been known to have excellent (within new limits) compression(and power output) . Low compression would cause a reduction in power output...........

Low compression is one of many reasons why you might not be making full power. (I'll also add a severely worn out [flat lobes] camshaft......which is the problem I had in a BBF with excellent compression that was unable to achieve MAX RPM) )

Once you do a compression (or cyl leak-down) check and find that it's within limits, your low observed RPM it likely due to something else or a combination of "things" (including a faulty TACH and/or pitot speedometer)

Cheers,


RIck

 

[H20Rat]

To go along with what HT above me had, it some cases engines will INCREASE power as they age... All the various parts are getting worn in and the tolerances are opening up. Bearings/seals spin easier, the water/oil pumps are easier to turn, and the various other sources of friction internally in the engine have been polished down. Many times, a drop in performance can be attributed to some maintenance item.

400 hours in a boat is the same as 30,000 miles on a 1/2 ton truck pulling a trailer on the highway. Certainly it has some age on it, but no where close to being worn out.