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Old 20-12-2005, 10:49   #16
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This is a very difficult and complex argument. It's one reason why there are so many engine makes. Each maker has a different reason and purpose to their design. Some designs tend to get used slightly outside there specs and original design purposes, some are spec'd particularly for there actual use.

One simple rule. All engine manufactureres measure their engines with different specs. None are the same.
It's kinda like saying a piece of string is 1000mm, 10cm or 1m long. It's all the same length, but measured with different techniques. Then you could add that 1m is 3.3ft. It still could be argued it's the same. But there are subtile differences in the length.
Engines have different ways of being rated. No manufacturer is wrong, nor right for that matter. They just see the world their engine is being used in, just a little differently. Then you add in the design. Every manufacturer has a different design goal. Once again, no one being right or wrong. But the design goal cross links to the way the designer has published his specs.
Perkins have several ratings. The maximum continuose rating is for a max period of 1hr ONLY. And it will get hot. It will send most normal boat operating temp readings off scale. Alarms will sound if they are conected. The engine should NEVER be run in this area. It is a rating ONLY and determins many other figures that you would normaly being using.

A few other points, cooling systems are not ALL the same either. So many variables come into play there as well. For instance, if water temp is above 70F, then you would add about 25% to your cooling size. If you have a wet exhaust, you add about another 25% to your cooling size just because of the back pressure and so on. There are just so many variables outside the imediate fault of the engine.

If another manufacturer say's their engine's max is X and you can run it there for an extended period of time, then chances are, it can go even higher than that yet again. But the manufacturer has simply not given you those figures.


For God so loved the world..........He didn't send a committee.
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Old 09-01-2006, 12:57   #17
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from the sellers point of view...

It might be unfair to the current owner to blow up his engine even if it does prove a point. A fair alternative might be to require an engine survey rather than force the issue.

If I were the seller in this case I might be inclined to walk away from the deal. Another buyer might not be quite so demanding.

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Old 16-01-2006, 12:59   #18
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I would think it reasonable to test at Max power, Maybe not for 30 min. but at least bring it up to rated max power It would give the buyer a clue to any possible problems, like vibration, overheating, ect. Most of the time a problem does not show at lower rpm.
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Old 31-01-2006, 04:38   #19
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From: Yanmar Pleasure Boat Marine Engine Help:


A seatrial is the final step where all that agro you went through to build your boat slides into obscurity. This is the point where everyone's ideas float, or don't float, and where everyone you know, who knows you, who thinks they know you and who wants to know you, turn up for free beer.
Let me give you a couple of tips:

* Don't do the sea trial on launching day! (That's the free beer day.)
* It is still the boatbuilder's boat until the seatrial is finalized. He / she is the person responsible for giving you what you paid for.

Now that's over, we can get on with it.

* How should the trial be done? Let's assume the boat has been in the water overnight, the engine(s) have been run and the electronics work almost as advertised. You have an anchor with a warp that is tied to the right bits at both ends.
( Check it, 9 out of 10 times the warp wont be tied to the anchor let alone the boat! )
* Check the chart and see where you are going to go, if you have a power boat you will need 30 minutes at full power so you don't want to run out of sea room! Many harbours have a 'measured mile' ( 1 nautical mile) where you can check the boat speed. The boatbuilder may already have this local knowledge. If there is no 'measured mile' you can measure the distance between two points on the chart and take the time between them.
* 1 Nm in 2 minutes = 30knots, in 3min = 20knots, and variations thereof, etc.

* OK, homework done, let's check for leaks, water, fuel and exhaust gas! Ask all the dumb questions now because the 'experts' aren't going to be there soon and you want to know what you're looking for when you open the engine room to do your preflight. Everything secure? Engine room is clean? (You are now about to use your XXX hp vacuum cleaner(s) and you don't want all that boat building rubbish going into the filters.) You also don't want that nice, very expensive furniture flying around the boat in a rough seaway because they aren't really ready yet. If it isn't ready, ask them when it will be and go away, come back when they said it would be OK.
* The boat should be full of fuel, water and other ballast and have all the necessary tradesmen on board, leave your mates at home! If this is a final engine acceptance seatrial the boat must be fully loaded to it's maximum operating weight.

* OK, everyone is ready! Start the engine(s), check the boat moves in the right direction when you operate the controls, if all is well untie the mooring lines and get moving, don't idle at the dock for longer than you need to check that the engine is running and you can untie. Prolonged idling of diesel engines is not good for them. (this is not a truck!)

* Maintain idle to 1500rpm until the engine temperature has stabilized. At this point, if you're legal, you can push the 'go' lever until you have 50 - 60% rpm.

* A planning hull may need lots of power to get on the plane, use it and then slow the engine down again. Before doing any speed tests, with turbocharged engines, increase the rpm by 200rpm every 5 minutes or so until you have reached full power. The engine tradesman should be measuring the rpm with a * hand held tacho, he will tell you when he is ready and you can increase the rpm.

* On non turbo engines you can move a bit faster to full power, take about 15 minutes.

* If the engine can't reach its correct maximum rpm then slow down, return to the dock if necessary and have it fixed before trying again.

* With turbocharged engines carry out a 30 minute full power run after the maximum rpm has been checked and is OK. Keep an eye on the engine temperature, turbocharged engines can rise in temperature, but not into the red section of the gauge during this run. If it does, either the gauge is faulty, there isnt enough cooling water or there is something wrong with the engine.

* The oil pressure may drop as the engine gets hot, that's OK.
* Check the exhaust for smoke.

* Running in Finally, when the engine rpm is correct, the seatrial is over and you've got rid of the hanger-ons, run-in the engine. (Yes, I know, we just gave it a good workout!) For the next 5 hours running don't operate the engine at more than 85% rpm or less than 2000rpm and every 20 minutes change the rpm up or down by 200rpm. When the 5 hours are up you can do what you like.

* he may use an optical tacho or a tacho that counts the pulses on the injector pipes or other similar devices that can be read remotely, he no longer has to deal with the rotating machinery in a heaving seaway. Just be sure he is not using the boat tacho to set up your turbocharged engine. Non turbocharged engines are not so critical.

* MAXIMUM LOADED RPM: Make sure the following criteria are met before checking the maximum engine rpm:

* Weight - the boat is fully loaded
* Clean - the hull and appendages are spotlessly clean
* Measuring devices and distances are accurate
* Throttle lever on the engine touches the maximum rpm stop
* Speed - before taking a reading, make sure the boat is up to speed

Engine model: Hand held tacho ~ Boat engine tacho
GM series: 3550-3650 ~ 3650-3750
JH and JH2 series: 3600-3650 ~ 3750-3800
JH3 series: 3800-3850 ~ 3950-4000
LH and LY series: 3300-3330 ~ 3450-3480
LP series: 3850-3950 ~ 4000-4100
CX-ETE: 2700-2730 ~ 2850-2880
CX-GTE2: 2900-2930 ~ 3150-3180

* Note that later, when the boat is not fully loaded, the engine will rev higher.
* Count from '1' to '10' while moving the throttle lever between idle and full power.
* Maximum loaded RPM is adjusted by altering the Propeller


Tho' this was written for a new boat/engine, it applies equally to a used boat purchase.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 31-01-2006, 06:37   #20
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Thanks Gord!! I'm going to print this out, roll it up and poke the broker in the eye with it!!

Learning to trust my instincts / navy experience more each day.....

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