Engine Trials.

[Degsy]

I used to go to truck racing when it was in its early days and those with low budgets for tuning were noted as opening to fuel up so much that the engine could become swamped with dense clouds of black smoke. There is an optimum point of fuel quantity or flow and perhaps you are getting too much, have you tried cutting it right back? Something not at all right there somewhere, do you know more than you are telling? I suspect this is another CW guessing game :rofl:

 

 

Of course he knows, he's already admitted they found the answer by accident, as I said before it's just another CW wind up.:argh::-D

[Guest catweazle (Banned Member)]

Of course he knows, he's already admitted they found the answer by accident, as I said before it's just another CW wind up.:argh::-D

:rofl::rofl:but we are all learning,its cold outside,and not a lot else happening on here to night,except for that trouble maker Burley:shocked:

Richard knows what was the problem he has just forgotten,he knows what bodge cured it as well.:-Dtrying to get a bit more video up.

Edited January 6, 2009 by catweazle (Banned Member)

[Richard Farrant]

:rofl::rofl:

Richard knows what was the problem he has just forgotten,he knows what bodge cured it as well.

:-D

 

 

Was Bodge involved? Don't recollect that..........got a lot on my mind at present

 

Ah yes :idea::idea::idea:.......got it :rofl:will say no more

[Degsy]

Are you listening Rupert CW's blaming you now:shocked::-D

[Guest catweazle (Banned Member)]

Are you listening Rupert CW's blaming you now:shocked::-D

:rofl::rofl::rofl:anything could happen in the next half hour.:-D

[Guest catweazle (Banned Member)]

From www.paxmanhistory.org.uk (see 'regulateurs europa') comes the following:

 

Engine governing is, of course, much more sophisticated than the above introduction may suggest. For instance in a turbocharged diesel the rate at which fuelling is increased during acceleration needs to be controlled. When accelerating there is a time lag between the injection of additional fuel and the turbocharger(s) increasing speed and charge air boost pressure. If too much extra fuel is injected before there is sufficient additional air to ensure its full combustion the results are emission of partially burnt fuel (in the form of smoke), fuel wastage, and potential engine damage. A properly designed governor will limit the rate of increased fuel injection to match the air available for combustion. This is just one example of the various refinements incorporated in modern governors.

 

I've highlighted a bit that I hadn't really appreciated before. Some interesting stuff on this site.

:tup:: as you know i can introduce the smoke by not letting the turbo catch up.They are huge and of course take a while to get going.I visited Paxmans in the 60s think it was at Colchester?,it was full of very big engines on test,inbetween each one was a man with a book sat on a stool with ear defenders on monitoring them.

Edited January 7, 2009 by catweazle (Banned Member)

[Guest catweazle (Banned Member)]

[Richard Farrant]

The port engine is running about 200 rpm faster than the starboard. Reckon there is a difference in the screws, think one is probably damaged.

 

I suggest using Belzona to build up the damaged area.

 

Any time you need any technical advice, just call :-D

[R Cubed]

What's with the Gauge below the Right hand Tacho on the right, its off the top end of the numbers !!!

Where the same gauge on the Left engine is not ??

[Guest catweazle (Banned Member)]

What's with the Gauge below the Right hand Tacho on the right, its off the top end of the numbers !!!

Where the same gauge on the Left engine is not ??

Well spoted.they are pressure gauges g/box,i had them made to match the originals,once done they told me they couldnt match the senders,so i refused to pay them or take delivery.a while later they came up with some,they have never worked and the whole episode lasted 18months.

still need to resolve this problem.They are Stewart warner .

[Guest catweazle (Banned Member)]

The port engine is running about 200 rpm faster than the starboard. Reckon there is a difference in the screws, think one is probably damaged.

 

I suggest using Belzona to build up the damaged area.

 

Any time you need any technical advice, just call :-D

Richard is correct,the props had suffered severe electrolosis,the surface was pitted with some pin holes right thro,I wouldnt of believed it but it stopped the engine reaching max revs,Andy did say it must be the props when we ran out of ideas,The boat was lifted for the usual anti fouling,the marina rang and told me there were holes i was surprised to say the least.

As a bodge for the round britain we shot blasted them and filled with Belzona ceramic filler.sanded to shape,we laughed saying it will all fly off and go thro the bottom of the boat,all my worries would be over.now what can i spend the insurance money on,A Shermam:idea: Well it stayed on and we were back up to top speed,i have had 2 new props made but as yet not fitted,we need to cure the problem of electrolosis first.I dont know much about the maths of a prop but still find it increadable it made so much difference.Maybe one of our aircraft chaps can shed more light on it.

[Richard Farrant]

Richard is correct,the props had suffered severe electrolosis,the surface was pitted with some pin holes right thro,I wouldnt of believed it but it stopped the engine reaching max revs,

 

we need to cure the problem of electrolosis first..

 

CW,

 

another bit of advice ( next time I am invoicing you :-D ) ;

 

The damage to the props sounds more like it is caused by cavitation. Is it possible that the engine power is too great for that type of prop?

[Guest catweazle (Banned Member)]

CW,

 

another bit of advice ( next time I am invoicing you :-D ) ;

 

The damage to the props sounds more like it is caused by cavitation. Is it possible that the engine power is too great for that type of prop?

Cavatation is a problem for some vessels.I think what was different for me was the fact that the boat heaters 4 big tube heaters were left on for 6 months to help preserve the vessel.This is the longest i have left them on.normally i would pull the plug on the mains when leaving.It all started with the battery charger that i now have on permantly,so why not leave the heaters on.The prop shafts were never bonded to the anodes so the yellow metal has been fizzing away merrilly.It could be another boat near by has a poor instalation which would affect any boats nr by,i need to buy a galvonic isolator to help protect the boat.I have fitted temporary bonding to the shafts for the moment.Have pics of the damage soon.cw.

[Richard Farrant]

I think what was different for me was the fact that the boat heaters 4 big tube heaters were left on for 6 months to help preserve the vessel.

 

Ah, I see now. I am I right in thinking this a a problem in marinas where boats are connected to electricity? Wonder why the other one was not affected, or was it?

[Guest catweazle (Banned Member)]

Ah, I see now. I am I right in thinking this a a problem in marinas where boats are connected to electricity? Wonder why the other one was not affected, or was it?

This is a big problem in Marinas,the other one was affected but because it wasnt as old it had more meat on it so fared a bit better.I go thro props quicker than people do tyres at £1200 a piece i must stop it.:-D

[Degsy]

Just googled 'propellor electrolysis' some very interesting stuff on there plus some possible answers to your problem.

[Guest catweazle (Banned Member)]

Just googled 'propellor electrolysis' some very interesting stuff on there plus some possible answers to your problem.

Its a facinating subject will have a look.:-D

[N.O.S.]

Just googled matching propellor to engine, and found this on the Caterpiller marine site:

 

www.marine.cat.com/cda/files/949240/7/Propellor%20Sizing.pdf

 

Talks around the tricky subject of matching the prop to engine power available, looks like there will be some more interesting stuff on there.

 

Have you jacked up the power output from the original set-up, CW?

 

Here is an extract from the above:

 

3. "I want more power." If you want to re-engine your boat to increase power and speed, chances are, you’ll need to increase the size (blade area) of the propeller. A prop can only absorb and distribute the power it was designed to handle. For example, if you increase horsepower 50 percent, you’ll probably have to increase blade area 10-15 percent, or cavitation may result. Cavitation is the creation of water bubbles against the propeller blades when it is asked to absorb more than its designed power. This leads to pitting and wear. Ultimately, the propeller won’t be able to demand the amount of power needed (or desired) and the boat will perform poorly.

[N.O.S.]

That link doesn't seem to work now, try googling 'matching propellor to engine' and hit a Cat site that comes up a few down. Only seems accessible via google (?)

[Guest catweazle (Banned Member)]

Cheers Tony,the props are capable of the power,they are like a mini destroyer prop,

The boat has a hull speed of 28 knots,so in theory it shouldnt go faster,in practise it does,we are whats called a semi displacement hull,the boat rides on the rear half so it maintains stability with speed in the rough.To go lots faster you need to get out of the water with a planing hull,its drawback is in rough weather you have to slow down,it then becomes a displacement hull and performs very badly.

This pic is a good example Cmdr Thorneycroft was a lot more skillfull than he gets credit for,It was obvious when i took over this boat that it needed to be going at a minimum 15 knts to benifit from his design.And the rougher it got the faster you went.Previous nelsons were underpowered

when ordered by trinity house for the pilots.This in effect made them very wet boats in bad weather,hence the nick name Bembridge submarine.

Many were lucky if they had 400hp in total.1000 hp would be good.:cool2:

I dont know how the props came about in the 60s but no firm today will guarantee me a 30 knt plus boat i have fell out with most of them,I have master copys which the foundry use when they cast mine.They all boast computor aided design and in reality cant come up with the goods,Gee is a good example it is still 7knots below there predicted top speed and 9 knots slower than it was on the old engines which were a lot heavier but same h/power.They have them back as we speak ,they dont know which way to go.Mind you the rudders they made are broke and the new Cummins are out of the boat with oil leaks.This modern stuff is crap.:argh:

[N.O.S.]

:tup:: It makes a little more sense now. Good luck with it.

Tony

[philb]

CW

 

I guess from post #38 you do know what you are doing, you just need to do it. If the shafts are stainless steel and the props are bronze, the prop will fizz if its shaft is not connected to an anode, as you say.

 

Assuming then that shafts(hence props), anodes and your electrical system common are bonded and connected to the marina supply earth, without an isolator, everything could fizz, by different amounts - it's a matter of luck (not strictly luck, of course, but practically so).

 

You should get a galvanic isolator and I suggest you get one with ac and dc leakage monitoring - to see if there is still current flowing. The reason for the monitor is that currents can be induced by effects, intentional or accidental, other than galvanic cells. Accidentally, most likely, by faults in other boats' electrics. Intentionally, as some vessels and marine installations are protected by active corrosion prevention systems (Not likely to be the case in a marina - unless you are near a naval dockyard? but everyone would have complained by now). Either can result in potential differences higher than some galvanic isolators will resist, and current still flowing through your suppy earth and so through your precious metal bits.

 

Cavitation is most likely to occur around the trailing edges and fast moving parts of the forward face of the propellor blades, where the water pressure is prone to fall sharply to create vapour bubbles. So, looking at the distribution of corrosion/erosion should give a good idea as to what the dominant mechanism was.

 

Good luck with the rest of the engine re-build and I hope you solve the puzzle of the failure.

[Guest catweazle (Banned Member)]

Hi phill,thanks for advice on isolator,there have been other complaints,one fishing boat about 50yds from me on a swinging mooring,steel pile,and even Gee on pontoon mooring 100yds from me has had some damage.I have spoken to the marina about it,they say they dont have a problem all the pontoon electrics were new a couple of years ago.We do have Mc Duffs the anode people nr by i would like to get them in and do some tests but it would have to be discreet,as we have an unsympathetic

manager.We allso have a very long steel bunkereing pier belonging to the navy.Dont stand a chance do we.cheers cw.

[Guest catweazle (Banned Member)]

Allthough these pics are only of the edge the damage went right to the centre hub.

[Degsy]

More wholey than Godly, looks like a piece of Gruyere cheese.......a bit more costly though:shocked: