Engine over revving

[oGaryo]

Hi, during the sea trial of the new boat, I noticed the RPM at WOT was between 5200 and 5400 on the gauge.. on checking the spec it should sit between 4600 and 5000. Is this simply a case of installing a prop with high pitch or should I be factoring in other things?

I guess the concern is whether a lower pitch prop has been fitted to get her on to the plane quickly to the detriment of crusing economy.

I did ask and was told a 16 pitch prop is fitted which seems to agree with the recommendations in the Mercury Prop selector tool when using weight etc as the data input... will try putting in WOT RPM to see what that states.. one of the conditions of sale is that I get to give the boat a thorough check over once out the water.

I guess the question will ultimately be whether it would be cheeky of me to ask for a new, higher pitch prop to be fitted as part of the sale.

p.s. I don't intend to have a survey carried out due to the excellent service history and it having a recent hull and engine survey.

 

[Wiggo]

Personally, I'd be tempted to get a stainless prop that's a shade finer to reduce the revs. That way, you always have the option of swapping them, as well as having a spare prop if you damage one and need to send it away for repair (Sod's law says you'll have a dinged prop and be unable to go out for the best weekend of the year otherwise...)

 

[capsco]

Personally, I'd be tempted to get a stainless prop that's a shade finer to reduce the revs. That way, you always have the option of swapping them, as well as having a spare prop if you damage one and need to send it away for repair (Sod's law says you'll have a dinged prop and be unable to go out for the best weekend of the year otherwise...)

I think Wiggo meant a coarser pitch, [NOT FINER] if so I would agree that this is the way to go.

 

[Wiggo]

I think Wiggo meant a coarser pitch, [NOT FINER] if so I would agree that this is the way to go.

Well spotted that man! I was wondering when someone would spot the deliberate mistake. Take last Tuesday off as a reward!

 

[oGaryo]

thanks guys... Graham may have been referring to blade thickness rather than pitch?

Also reading up on trim settings as I didn't think of checking that during the sea trial,, I do know the led indicators were off so presume they were set in the up position... am reading that trim settings can increase RPM too.

I don't think this is a show stopper, just a case of optimising things.

btw, the current prop fitted is a 3 blade prop. will be giving the owner a call to find out the excat detail of the prop fitted so I know pitch, diametre, make and model etc

 

[capsco]

Well spotted that man! I was wondering when someone would spot the deliberate mistake. Take last Tuesday off as a reward!

Yes, as I was expecting the error, I already did, and can I now please book last years holiday early?

 

[Wiggo]

thanks guys... Graham may have been referring to blade thickness rather than pitch?

I was thinking in terms of quality - one should be looking for a fine gentleman's propeller...

 

[tinkicker0]

thanks guys... Graham may have been referring to blade thickness rather than pitch?

Also reading up on trim settings as I didn't think of checking that during the sea trial,, I do know the led indicators were off so presume they were set in the up position... am reading that trim settings can increase RPM too.

I don't think this is a show stopper, just a case of optimising things.

btw, the current prop fitted is a 3 blade prop. will be giving the owner a call to find out the excat detail of the prop fitted so I know pitch, diametre, make and model etc

As far as I am aware, although it has been known for me to be wrong even pitch (10, 12 etc) props are four bladed and odd pitch (17, 19) are three bladed. 16 is an even number........It may have been re pitched at some point.

Merc props appear to be anyhow.

 

[Wiggo]

Is the tacho actually reading correctly? 5400 rpm for a big American V8 lump sounds awfully high. I'd be tempted to check that with a hand held tacho on the crank pulley or somewhere similar. £30 for a bit of test gear is better than £300+ for a prop... http://www.virtualvillage.co.uk/dig...er-for-engine-rev-measurement-001480-003.html

 

[oGaryo]

Is the tacho actually reading correctly? 5400 rpm for a big American V8 lump sounds awfully high. I'd be tempted to check that with a hand held tacho on the crank pulley or somewhere similar. £30 for a bit of test gear is better than £300+ for a prop... http://www.virtualvillage.co.uk/dig...er-for-engine-rev-measurement-001480-003.html

will do... I have one of these....

http://www.metershack.com/electrica...up-to-12000-rpm-with-rs-232-pc-interface.html

....which I can use with the engine cover up whilst underway. the cover has a hydrolic lift mechism so should be ok to run it with the cover held partially open and the meter on the cockpit floor.

 

[MapisM]

Finding a better prop wouldn't be my main concern. Btw, I don't think a s/s prop is worth the additional cost on this kind of boat.
The point is, did you have the engine ECU scanned?
Aside from confirming the total number of engine hours, you should read the hours done at various RMP ranges.
On such boat/engine/drive you should normally see just minutes (if any) above 5k RPM, but if the prop allowed the engine to be overreved, it might have been pushed harder than the block is supposed to run, and this could indeed be a show stopper.
Mind, the "partial" readings at the various RPM ranges can be zeroed via software. If the sum of each RPM range doesn't match the total, I'd be worried.
All the very best, the boat looks lovely indeed.

 

[oGaryo]

Good point that.. the current owner has had her for 4 years and in that time has logged every trip and also fitted a fuel flow interface thingy that couples in to the Navman Plotter.. I wouldn't be surprised if I can pull some data off that thing to give an indication of whether the engine's been thrashed.. I doubt it to be honest as he's fitted the fuel flow meter to gain an understanding of best speed for ecomony which he changed from 22Kts to 24Kts after fitted.. Doesn't strike me as a chap that wants to bomb about all over the place. I'd epect the only time he'd go near WOT is to get on to the plane.. again, worth checking but will probably end up taking a punt based on the engine ticks over perfectly, is responsive, well maintained and clearly is able to get the revs up... will also check the recent survey to see if that had engine data checks carried out.

first check though as stated is to use an accurate rev gauge as it may be a red herring, will also carry out compression checks but recognise that'll not cover all potential evils.

 

[moonraker 36]

I was thinking in terms of quality - one should be looking for a fine gentleman's propeller...

try ron hill of america for s/s prop's..
i have a 5blade 14-quarter/23"" on alpha 1 gen 1 leg..
you wont want one this big though..
dont go up in pitch if you go for more blades..

 

[MapisM]

Good point that.. the current owner has had her for 4 years and in that time has logged every trip and also fitted a fuel flow interface thingy that couples in to the Navman Plotter.. I wouldn't be surprised if I can pull some data off that thing to give an indication of whether the engine's been thrashed..

Yup, most navman plotters are SmartCraft compatible, so he might have bought the SC/Navman gateway, plus a SC cable, connecting the plotter to the SC plug on the engine. I did something similar on my boat, though I only fitted the small LCD screen 'cause she doesn't have (nor need, for the lake) a plotter. A couple of hundred bucks well worth spending.
If that's what he did, actually you have much more than just a fuel flow interface, because it allows you to see on the Navman screen all the engine data in real time (RPM included), thus giving a chance to cross check the accuracy of ALL other gauges, not just the tacho. No need for any additional revmeter.
You can find more details about all that on this user manual if you're interested.

But back to the engine log: you should also be able to check the TOTAL engine hours reported by the ECU through the SC interface, but unfortunately I'm sure (well, almost) that you need the Mercury scanner or a portable PC with the proper software and SC interface to check the hours logged at each RPM range, which in your case is the most interesting data I'd be interested in.
Any Mercury mechanic MUST have such equipment, and with it the reading is a 5 minutes job.

 

[MapisM]

try ron hill of america for s/s prop's..
i have a 5blade 14-quarter/23"" on alpha 1 gen 1 leg..

At 23", s/s props might begin to make sense (just).
But at the pitch (hence speed) the OP is talking about, I rest my case: s/s is not worth the additional cost, and it only increases the risk of damaging the leg in case of collision with floating objects.
According to the numbers previously posted, I'd try an Alpha 4 18", to start with.

 

[oGaryo]

Yup, most navman plotters are SmartCraft compatible, so he might have bought the SC/Navman gateway, plus a SC cable, connecting the plotter to the SC plug on the engine. I did something similar on my boat, though I only fitted the small LCD screen 'cause she doesn't have (nor need, for the lake) a plotter. A couple of hundred bucks well worth spending.
If that's what he did, actually you have much more than just a fuel flow interface, because it allows you to see on the Navman screen all the engine data in real time (RPM included), thus giving a chance to cross check the accuracy of ALL other gauges, not just the tacho. No need for any additional revmeter.
You can find more details about all that on this user manual if you're interested.

But back to the engine log: you should also be able to check the TOTAL engine hours reported by the ECU through the SC interface, but unfortunately I'm sure (well, almost) that you need the Mercury scanner or a portable PC with the proper software and SC interface to check the hours logged at each RPM range, which in your case is the most interesting data I'd be interested in.
Any Mercury mechanic MUST have such equipment, and with it the reading is a 5 minutes job.

thanks, that's an interesting bit of software/hardware for the techy geek in me.. he certainly showed me a page on the Navman that indicated flow rate, range, tank level (bar reading format), real time MPG and it looked similar ish to that in the manual.... he swore it was more accurate than the analogue gauge.... will have a good look at it when back down there for final inspection and handover.. thanks for the tips, very useful

 

[MapisM]

he certainly showed me a page on the Navman that indicated flow rate, range, tank level (bar reading format), real time MPG and it looked similar ish to that in the manual.... he swore it was more accurate than the analogue gauge....

It should be, 'cause it takes those numbers directly from the engine control unit.
One thing you'll have to remember is to reset the fuel meter upon refill, because it works very differently from the traditional analogue gauge: it stores the tank capacity in memory, knows when it's full based on your input, and deducts the fuel burnt to show the residual amount of fuel left.
Very accurate and handy, particularly for real time MPG and residual range. Will make you wonder how you got by without it before.
I'd love to have something like that instead of sight gauges, on my sea boat...

 

[enterprise]

Hi Gary,
I wouldn't worry too much at this stage, once you have gear onboard and a bit of growth on the hull it will knock the cruise RPM down to acceptable levels.

The prop that's on would probably been installed due to both of the above by the previous owner, better to be able to reach the recommended revs without full throttle than not to reach them at full throttle if you know what I mean!
Just keep an eye on your RPM's when applying power.

Looks to be a well looked after example, couldn't imagine the previous owner not tackling an over revving engine problem if it occurred.

 

[oGaryo]

Hi Gary,
I wouldn't worry too much at this stage, once you have gear onboard and a bit of growth on the hull it will knock the cruise RPM down to acceptable levels.

The prop that's on would probably been installed due to both of the above by the previous owner, better to be able to reach the recommended revs without full throttle than not to reach them at full throttle if you know what I mean!
Just keep an eye on your RPM's when applying power.

Looks to be a well looked after example, couldn't imagine the previous owner not tackling an over revving engine problem if it occurred.

Just had an email back from him and he's stated exactly that so I think it'll be ok as you say

 

[duncan]

Hi Gary,
I wouldn't worry too much at this stage, once you have gear onboard and a bit of growth on the hull it will knock the cruise RPM down to acceptable levels.

The prop that's on would probably been installed due to both of the above by the previous owner, better to be able to reach the recommended revs without full throttle than not to reach them at full throttle if you know what I mean!
Just keep an eye on your RPM's when applying power.

Looks to be a well looked after example, couldn't imagine the previous owner not tackling an over revving engine problem if it occurred.

this would be my interpretation as well

sea trial is one of the situations when a boat is probably as clean, empty of **** in lockers, low levels of water in tank, with probably not a full fuel tank either!

I would expect it to be right at the top end of a rev range - and I wouldn't be concerned if it was 2-300 over it; unless all the tanks were full etc of course