DIY tunnel drive

[Frosty]

The Upholstery needs replacement? well it a thought" its as good as what other professionals are coming up with ---may work.

[baeckmo]

Hello everybody; back again after 7 days of pouring rain in Ireland..... now I understand why there are so many pubs on that island....!

CDK: nice job you have done; it tells us that the engines are now running with fuel restricted by rpm-limits (i.e. centrifugal rpm map, NOT max fuel map)! The 0.4 mm bores are working fine; don't change anything there yet! Note; NO disappointment there due to the following:

If engines had been running on max fuel curve, the xh gas temp would have been 450 to 500+ centigrades in pipe (~120 deg. lower on housing surface), and pressure 0.6<>0.8 bar at max rpm. Note: A turbine housing without water-jacket is normally glowing in a dark cerise colour when at max load! Don't bother with wastegate! And if excessive xh back pressure had occurred with engine running on fuel max mapping line, the temp would have been equally high, but with low boost pressure and black smoke as a result.

The pic's from the boat show absolutely excessive aeration of props, which supports the conclusions above. (And Richard, sharp as ever, with his focus on details, noted the real problem before the rest of us. Shame I missed that.... How 'bout "Argus1" instead, Richard?).

So, performance is now restricted due to prop ventilation, with centrifugal regulator limiting fuel flow (and thus rpm). Are the locking devices intact on the throttle lever stops, or have these settings been tampered with?

And.... aah, yes I am still waiting for an independent calibration of tacho's!. If you still have the instruments installed, you may now provoke the engines to show a different behaviour if you run a "bollard push test", because it seems that the whole tunnel arrangement is submerged at zero speed, hence less aeration in that case, and probably higher values for xh temp and boost pressure.

[Ad Hoc]

baeckmo

aah yes, bollard test, good call. The most obvious does tend to elude us at times!

[apex1]

Jaja Baeckmo.

(And Richard, sharp as ever, with his focus on details, noted the real problem before the rest of us. Shame I missed that.... How 'bout "Argus1" instead, Richard?).

If only I could, I would change my nickname. This apex1 name has it´s roots in the early 80ies when I held shares in a computer and software developing company. We brought the first branch specific, integrated hardware/software system worldwide into the market, named apex1. Well, and sold ONE. Was too early for such stuff.

Sorry for the aside.

Richard

[CDK]

Originally Posted by baeckmo

Hello everybody; back again after 7 days of pouring rain in Ireland..... now I understand why there are so many pubs on that island....!

Yet somehow they manage to make TV documentaries with only sunshine. My wife wants us to go there with our motorhome but I've always refused.

CDK: nice job you have done; it tells us that the engines are now running with fuel restricted by rpm-limits (i.e. centrifugal rpm map, NOT max fuel map)! The 0.4 mm bores are working fine; don't change anything there yet! Note; NO disappointment there due to the following:

If engines had been running on max fuel curve, the xh gas temp would have been 450 to 500+ centigrades in pipe (~120 deg. lower on housing surface), and pressure 0.6<>0.8 bar at max rpm. Note: A turbine housing without water-jacket is normally glowing in a dark cerise colour when at max load! Don't bother with wastegate! And if excessive xh back pressure had occurred with engine running on fuel max mapping line, the temp would have been equally high, but with low boost pressure and black smoke as a result.

I measured the back pressure. It dances around 100 mm H2O @2000 rpm, at lower speeds measuring is hampered by the exhaust coughing up cooling water irregularly.

The pic's from the boat show absolutely excessive aeration of props, which supports the conclusions above. (And Richard, sharp as ever, with his focus on details, noted the real problem before the rest of us. Shame I missed that.... How 'bout "Argus1" instead, Richard?).

So, performance is now restricted due to prop ventilation, with centrifugal regulator limiting fuel flow (and thus rpm). Are the locking devices intact on the throttle lever stops, or have these settings been tampered with?

I didn't tamper with them (yet) and there is no need to because the throttle lever is at the end of its stroke approx. 2 mm before the stop is reached.
There is a minor change in behaviour I didn't mention before: the whole throttle stroke is active now until the end. If I also had the last few mm. available I think there might be another 100 rpm more.

And.... aah, yes I am still waiting for an independent calibration of tacho's!. If you still have the instruments installed, you may now provoke the engines to show a different behaviour if you run a "bollard push test", because it seems that the whole tunnel arrangement is submerged at zero speed, hence less aeration in that case, and probably higher values for xh temp and boost pressure.

The rev counter program confirms the tacho readings. I was a bit hasty the first time when I used the program as it was installed. But there are a few parameters that need to be set first, like a min/max setting and a conversion factor. Once that is done you get proper readings.

A bollard test has to wait until the tourists have gone. A fierce NE wind (bora) is also making life difficult for all boat owners in the area.

I found an interesting topic about increasing engine output here:
http://www.t4forum.de/wbb2/thread.php?threadid=90661

These guys want to drive dangerously fast with their old VW vans, so they install an intercooler, oil cooler and a waste gate bypass. But the extra power comes only from turning the "Mengenschraube" at the back of the VE pump.
This might be a solution for my boat engines to deliver the extra horses to get the boat over the hump and pull back the throttles before the whole engines start to glow in the dark.

Not visible in the wake pictures is the changed position of the hull at speed. I wrote several times that the bow lifts 6 degrees, but I also noticed that the stern digs in. At rest there is approx. 80 mm of anti-fouling visible at the flanks, at speed that is completely gone. Not a very objective observation I admit, because the bow wave raises the level along the hull.
There is also an increased level directly behind the stern, but I read in another post where Ad Hoc answered, that it is typical for a sub-critical wave pattern.

Funny that in 50 years of boating I always looked forward and now find myself staring at the stern most of the time. Must be old age.....

[CDK]

Originally Posted by Ad Hoc

baeckmo

aah yes, bollard test, good call. The most obvious does tend to elude us at times!

BOLLARD PULL TEST.

The only thing I could think of to indicate the pulling force was the use of nylon fishing line.
We used 20 strands of 0,5 mm, breaking strength 18.7 kg, loosely connecting two spliced lines, each 15 m. long. One end attached to the center of the stern, the other to a large bollard on a pier. There was also a 6 mm safety (650 kg breaking strength) line of 50 cm long to hold the ends together if the fishing line should snap.

That happened at approx. 1500 rpm, using only the port engine. The safety line snapped less than 1 second later because of the boat's momentum, while the rpm increased to 2000.

Not a very scientific setup I admit, but it tells us that one engine pulls with at least 375 kgf, so both engines generate a force of more than 750 kgf at zero velocity.

[Ad Hoc]

as a rough guide most boats/engines will get 750kg per 100hp

[CDK]

Originally Posted by Ad Hoc

as a rough guide most boats/engines will get 750kg per 100hp

Does that mean that the average 100 hp engine generates 750 kg at a bollard pull test or that an engine when actually delivering 100 hp during such a test will generate 750 kg pull? At the breaking point I saw only 1500 rpm, so the engine was unable to deliver full power.

[Ad Hoc]

"..Does that mean that the average 100 hp engine generates 750 kg at a bollard pull test.."

Correct

[baeckmo]

One of my issues with the BP test was to check wether the propellers, when fully submerged (as in static condition), would allow the engines to come closer to full load condition. As we still have a lowload condition when "steaming", due to aeration, this would be one way to ascertain that the engines now (after correction of return restriction et c.) are getting enough fuel and that thermostats, cooling and everything else is ok.

So, just put her stem to the quayside and try to move the island; full throttle! Don't worry about thrust, but check exh temp and boost pressure if possible. If engine data now indicate that this department is ok, we may proceed to seek a solution to the propeller problem, that fits your ambitions!

[powerabout]

take an accurate measure of fuel consumption and do the bsfc calculation.
Peak torque will be the lowest figure.

[pistnbroke]

sorry your bollard pull is unlikley to prove anything ..your assumption is that each strand took its share of the load .....if one strand was only 1mm shorter than the others it would take all the load and snap followed by the next shortest etc ....sorry I would love you to get this boat A1

[CDK]

Originally Posted by baeckmo

One of my issues with the BP test was to check wether the propellers, when fully submerged (as in static condition), would allow the engines to come closer to full load condition. As we still have a lowload condition when "steaming", due to aeration, this would be one way to ascertain that the engines now (after correction of return restriction et c.) are getting enough fuel and that thermostats, cooling and everything else is ok.

So, just put her stem to the quayside and try to move the island; full throttle! Don't worry about thrust, but check exh temp and boost pressure if possible. If engine data now indicate that this department is ok, we may proceed to seek a solution to the propeller problem, that fits your ambitions!

What bothers me about the test is that I didn't design the propulsion system to move the island. I regularly help tourists pulling their boats out at the slip and am witness of the smoke coming from the clutch and the rear wheels. For a boat the situation is comparable to a car with an automatic gearbox: no smoke from the clutch, but the strain is the same.

Anyway, the throttle setting at the 'moment supreme' was for 2000 rpm, while actually is was only 1500, so full torque must have already been there. I am willing to repeat the test and measure the boost pressure, but I do not expect any spectacular figures because the rpm will be insufficient for a noticeable boost pressure.

During the bollard test, there was again no black smoke, so I need to adjust the general fuel setting on the injection pump first.
I wrote about this on the German VW-T4 forum in a very detailed thread about tuning these specific (ABL) engines. As installed in a van, these engines produce no more than 50 kW; the identical engine in a passenger car delivers 55 kW because it has an aneroid on the injection pump and a small oil cooler under the radiator.

These guys squeeze up to 104 kW out of the same engine by changing the pump settings, installing an intercooler, an oil cooler and a bypass valve before the waste gate aneroid to raise the pressure to 0,9 bar. They also replace some cylinder head bolts with stronger ones (12 instead of 8.5).
I suggested that in my case the modifications could be limited because I do not need to double the output and will throttle back as soon as the boat reaches planing speed. But the general opinion is, that the engine is thermally already at its limits and will need a fresh water or blower assisted oil cooler before any other modifications are made.

I found a guy with a V8 powered new Searay who was willing to participate in an experiment where I would run my boat at full throttle and he would supply the extra power to pull my boat over the hump using a long line. That way I might have found out if the boat can sustain planing speed, but the next day the Searay suffered prop damage when the guy drove backwards and hit a rock, so we had to abandon the plan.

[CDK]

Originally Posted by pistnbroke

sorry your bollard pull is unlikley to prove anything ..your assumption is that each strand took its share of the load .....if one strand was only 1mm shorter than the others it would take all the load and snap followed by the next shortest etc ....sorry I would love you to get this boat A1

All strands were of equal length. I wrapped the fishing line around 10 times and only knotted the ends so each strand could slide and distribute the load evenly.

[powerabout]

I would have thought that peak torque is also max boost. If not you would probably end up with 2 torque peaks.

Without an anerometer on the pump I would have also thought you would get black smoke as the pump will assume you have boost.

What is peak torque rpm for your engine?

Cheers