Boat engine V car?

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Warpa

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Can an IBOB run at full power for say 1hr without probs? I have my truck tuned and do work it, and cant help doing the same when on water. The last boat had an old Johnson 55 OB and seized on my 1st trip after running it flat out for about 20 mins which i thought was shocking.

Will the serviced mercruiser 3.0 on my new boat take a pounding? The way i see things, if i pay good money for anything i expect it to do what it should (work for me) i doubt i will run it at full speed often, but if im on the IOW and heading back to Southampton and keen to get home for whatever reason i expect (sea state permiting) to run full chat all the way back on a regular basis.

Is this asking too much, if so why are marine engines so weak? if not then great:D Either way, i know i will wind her up to the max on every outing, that is why i own her :eek::cool::)

I have been told the engine i have if serviced is near bullet proof?
 
One of the reasons for marine engines being more expensive than the same engine used in road applications is claimed to be as they are "heavy duty" designed for prolonged use at high or maximum RPM/ load. Whether that is true or not, who knows? The 3.0 litre 4 cylinder engine still used is pretty old by now (as is the 4.3 V6 and the 5.7 V8), I'd have expected Mercruiser or Volvo Penta would have dropped them by now if there were unreliability issues.

In having 5.7 V8 boats (10 years) I have run at maximum RPM for probably 20 minutes per season, basically just for the hell of it and sea conditions allowing it
 
In development, car engines run a durability burst test for 400 hours on a test bed, as part of their sign-off procedure. I'm not sure marine engines, when converted, do the same, as I have no experience, but I have my doubts, because I do not believe the investment levels are the same, hence you see niggly problems when new engines are launched.

I would therefore be very careful of running for extended periods over 80% throttle. Short bursts for a couple of minutes will be ok though, unless there is a cooling/ignition/fuelling issue.
 
I doubt even a car engine (petrol) would be that happy running for an hour nudging towards the rev limiter , think about it, you own an M5 and would want to run at max rpm for an hour every other time you took it out, that's not a car I would be happy buying a couple of years down the line, it will have been thrashed most of its life.

Interestingly I just sold my sports car to through a fellow forumite hereabouts who specialises in such marques. His guys put a computer on the car and it told them that I had touched the rev limiter 42 times which equated to 6 minutes on the limiter (or such, I can't quite remember the numbers), they said that is reasonable enough but if it had somewhere near 15 minutes they wouldn't take the car, it would indicate the car had been either tracked or I had been blatting the thing everywhere like nutter.

I don't see why marine petrol engines are any different.
 
there are a number of factors at play that need to be recognised -

1. marine 4 st petrol engines are basically the same engines used in cars - but uprated powerwise from the set up installed as standard in production cars. There are fewer models in use and failures tend to get noticed. Overall this applies to all marine engines. Failures associated with installation, cooling systems etc are another matter - but less applicable to your boat/engine combination (ie. I would expect yours to 'fail' with issues around the exhaust risers, water pump and general internal corrosion rather than load related running)
2. production cars rarely run at max revs under load in the same way as a boat engine - to simulate this you would probably have to put it in 3rd or 4th gear on a slight up hill (or load it up weight wise and put a huge roofrack/airdamm on the top) then floor it for a few hours - not represenative of most driving!
3. whilst diesels in the leisure market generally have a WOT 1hr rating, and a 90% revs fast cruise rating, petrols do not have such 'limits' - as has been suggested your wallet is normally the limiting factor.
4. 2s OBs are purpose built and will run WOT (subject to correct proping etc) within their designated WOT rev range for as long as you can stand the noise, afford the juice etc

I've run 4 and 6 cylinder OBs at WOT for extended periods (well over your hour) and 4 cyl turbo diesels at WOT for up to an hour - then back to 90% for another 2.

The nature of UK boating waters tends to be against long running at WOT in small engined craft - in the US inland waters it's much more prevalent.

Properly loaded, cooled and lubricated there is no fundamental reason you shouldn't run it the way you indicate. However, if you are concerned, you should ask Mercruiser themselves - if they have limits they will be listed in the user manual for the engine.
 
I'd be tempted to buy you a tin of dayglo paint and a flashing light so that other people can see you coming.

You are verging on the edge of irresponsibility.
 
Warpa said:
Is this asking too much, if so why are marine engines so weak? if not then great:D Either way, i know i will wind her up to the max on every outing, that is why i own her :eek::cool::)
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Warpa mate, you will be worn out before the engine:D
By all means give Her a good thrashing now and again, they say boats are like Women:D

Charging about flat out everywhere soon becomes tiring.
You will find out eventually.
Plus the number of times conditions are that you can run WOT for a good length of time will be few and far between.
So I wouldn't worry about your engine self distructing too much.

Enjoy a few blasts to get it out of your system but remember , if you get any! that the passengers might get a bit fed up of hanging on for dear life too:)

Plus as mentioned the fuel costs will soar when you give it stick.
You might need the extra cash to replace the bits that will shake loose and hit the briney whilst you terrorise the neighbourhood:D
 
Duncan - that was aimed at the OP Warpa, who seems to have a personal issue with the throttle control of his boat.

Not at you in any way.


I hope the people who provided his new engine have seen this thread.
 
sarabande said:
Duncan - that was aimed at the OP Warpa, who seems to have a personal issue with the throttle control of his boat.

Not at you in any way.


I hope the people who provided his new engine have seen this thread.
Click to expand...

ah - the wonders of threads. The post came up as a response to my reply rather than the OP.

Was only really concerned as I thought I had passed that edge a log time ago.... :)

I would tend to agree that a presumption that WOT will be used on every trip is somewhat of a concern - I would probably start out now with the presumption that I won't use WOT on any trip; and be pleasantly surprised if the opportunity presents itself appropriately.
 
Kawasaki said:
By all means give Her a good thrashing now and again, they say boats are like Women:D
Click to expand...

I'm a little puzzled about your analogy, Kwakker. Do you mean you wouldn't run a woman at WOT for more than an hour, or that you wouldn't get a second hand one that had been run on the rev limiter for more than 12 minutes? Or do you mean that you wouldn't thrash one all the time because the passengers might not appreciate being tossed around?
 
Back to engines: the answer to the original question is to look at the manufacturer's datasheet.

I am indebted to latestarter1 for this for my engines:

"Intermittent Rating: This power rating is intended for Intermittent use in variable load application where full power is limited to two (2) hours out of every eight (8) hours of operation. Also, reduced power operation must be at or below 200 RPM of the maximum rated RPM. This rating is an ISO 3046 fuel stop power rating and is for applications that operate less than 1500 hours per year"
 
Warpa said:
I have my truck tuned and do work it, and cant help doing the same when on water. The last boat had an old Johnson 55 OB and seized on my 1st trip after running it flat out for about 20 mins which i thought was shocking.
Click to expand...
Mechanical sympathy. That's what you need.
Run an old outboard WOT on you're first trip out with it? It'll be OK or it will bust. Yours did.
If you buy an old car you expect it to be a bit fragile until you get to know it and prove otherwise.
Well, obviously, you don't.
 
We had a 7.4 V8 in a 27ft Bayliner which would do 42 knots on WOT. The engine seemed fine, however as has been said, fuel consumption was eye watering and when we stopped it looked like we'd had burglars in the cabin.
From memory the fuel tank was 60 US gallons which got used up on a round trip to Ramsgate from the Medway or if I reigned myself in would get us from the Medway to Eastbourne.
 
sarabande said:
I'd be tempted to buy you a tin of dayglo paint and a flashing light so that other people can see you coming.

You are verging on the edge of irresponsibility.
Click to expand...

Please re read through my original post, then ask yourself was there any need for your reply;)

This part in particular;

i doubt i will run it at full speed often, but if im on the IOW and heading back to Southampton and keen to get home for whatever reason i expect (sea state permiting) to run full chat all the way back on a regular basis.

Now from where i will be launching to the IOW is about 5-7 mins, hardly reckless in calm water, and really not working the engine for long.


Now back to the topic, as i have an Americam boat that was designed primarily for the vast river areas in the states, one would presume the engine is one of many matches to the boat and expected to be pushed and quite often. I know how uncomforatble it is having your fillings rattled out in less than flat water :)
 
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Today all parts i in a engine is calculated in 3d programs. To avoid fatigue and have the possible highest output the manufaktuer can say: above this stresslevel 50 000 000 cycles and at lower stress no fatigue.

To optimize power output the dealer says for plessure use max 300h and 1 hour out of 10 100% speed rest below 90% or 75% power. A boat diesel like Volvo Penta have an expekted lifte time of 5000h. Plesure use is 300h/year
30h full power. That means 450h full power in 15years and 75% power or less 4500h. So if user chip tune the engine or use it for more than 450h at full load the engine might brake down du to fatigue. (Also high temp fatigue)

If VP sell MCR power they have to reduse the output a lot. A user that are running 4000h each year won't buy a D6 or D4.

When i choosed base engine for my boat i was driving a lot on the german autobahn. Lots of small trucks were running 140-150km/h. I knew this was maximum speed . If a engine can take whole day at autobahn at max rev it is good enough for my boat. I rented such a car for a measurement trip in europe
The cars could take hours of full rpm. Downhill we were driving the taco out of range! So small trucks like Touota Hiace, WW LT, Mercedes Sprinter,Fiat Ducato,Ford Transitt are all driven to maximum for hours on the autobahn.
 
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