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[1967Brutus]

I'll try to make a drawing of the later Raboesch design for the yoke attachment to the shaft. It's pretty cleverly designed and should in theory be "unbreakable". It was back then a very difficult to manufacture design (faillure percentages in the machining process, which all was done manually, about 30%), but he told me, nowadays they can achieve a much better accuracy with near zero machining faillure, using CNC controlled spark erosion.

This is that design: four recesses are cut in the shaft, and four tangentially placed holes drilled in the yoke. The hardened pins are placed with Loctite, and the connection between shaft and yoke should theoretically be as strong as the shaft itself.

[JimG]

The newer design looks to be more secure. I probabbly bought the Rivabo vp prop around 40 years ago to replace the reversing gear setup I had originally made for the tug. This worked ok but with straight cut steel gears it was noisy and gave a loud clunk every time iit changed from forwards to reverse or back, there was also no proper neutral position so the boat couldn't be stopped.
Jim

[1967Brutus]

I had no option for a reversing gearbox, for reasons that I would then end up with a boat that would have a fairly high minimum speed due to the fact that there is a limit to how slow an internal combustion engine at this size can run, and of course gear reductions can lower that minimum speed, but then higher speeds or stump pulling bollard pull would make the boat sound like a Formula One car, and that would totally ruin "the experience"...


And without that, this boat would have nothing going for it...

[1967Brutus]

The newer design looks to be more secure. I probabbly bought the Rivabo vp prop around 40 years ago to replace the reversing gear setup I had originally made for the tug. This worked ok but with straight cut steel gears it was noisy and gave a loud clunk every time iit changed from forwards to reverse or back, there was also no proper neutral position so the boat couldn't be stopped.
Jim

By the way, and just out of curiosity WRT longevity of such mechanisms... Is that tug still active or at least that prop still in operattional condition?

[JimG]

I'me afraid the tug has not been active for many years, it was rather large and awkward to carry on a motorbike so has been lying in the workshop for quite a while. The steam plant has been out of action as it doesn't have  a boiler certificate so I can't run it. It was fully hydraulicaly and steam tested after I made it but there was no one at the club who could officially test it for a certificate.As far as I know the prop is still working OK although I have not looked at it for some time. It probably had around 5 to 10 hours running in total over the time I used it.
Jim

[1967Brutus]

It probably had around 5 to 10 hours running in total over the time I used it.

I probably go through that in one, maybe 2 months...

Bummer about that testing you guys have...

[Colin Bishop]

Is the basic problem that the gasoline engine is simply putting too much stress on the mechanism? Would an electric motor have worked better. Maybe the gasoline engine really needs a more robust gearbox/clutch mechanism rather than relying upon the built in variable prop components which were probably never designed to accept a motor of that type.

Colin

[1967Brutus]

Is the basic problem that the gasoline engine is simply putting too much stress on the mechanism? Would an electric motor have worked better. Maybe the gasoline engine really needs a more robust gearbox/clutch mechanism rather than relying upon the built in variable prop components which were probably never designed to accept a motor of that type.

Colin

these props are advertised as suitable for steam engines. A twin double acting compound runs quite a bit chunkier than this fourcylinder I am using, which runs remarkably vibration-free, also in the torsional sense.

But as stated, the prop I have, appears to be of a really old design from Raboesch, which was extremely flawed. In hindsight, now that I know how it was constructed, I could have twisted this locking pin basically by hand allready.

The tiny 5 cc single cylinder runs quite a bit rougher judging by the rocking action of the boat when in neutral, and that prop is made of 40 year old plastic.
According to the current owner of Raboesch, who worked in production during the last years of production of these props, there was zero doubt that these props should be able to handle any type of powerplant that would be capable of running it at 4K. But he was NOT aware of this old design.

So it stands to reason that once modified to the new design, it should hold as long as I make sure it never exceeds 4K, which should not be very complicated since I still intend to use a governor.

[1967Brutus]

A few cosmetic changes:

The wheelhouse windows were a horrible orange colour (can't imagine why anyone would want to do THAT...) and are replaced for clear glass.



And the slide hatch on the rear deckhouse was a horribly poor fitting ugly piece of black plastic, now a proper wooden hatch. It only needs some darker colour (woodstaining or something) and a coat of laquer.

[1967Brutus]

Telemetry for the coolingwater temperature is installed. This sensor is ALSO going to control the servo that opens or closes the bypass over the cooler.



For temperature control, this location is less ideal: rapid loadchanges will show rapid temperature changes, and that tends to lead to a valve overcontrolling.
A sensor in the expansion tank would be better.
But IF the coolingwater pump drivebelt snaps, the temperature of the expansion tank will not change, but this location will se virtually immediately steam, AKA a very rapid jump in temperature to 100 deg C.

On the other hand: I have two temperature channels availlable, I could fit a second sensor on the outlet of the xpansion tank, and use one for alarm, the other for control.

More work, but perhaps worth it. Not sure yet. Going to test without control first anyway, just to see where temperatures end up.

[1967Brutus]

And THIS:








is how you make a variable throttle, otherwise known as a controlvalve, with the bare minimum in materials, tooling and cost.
I will be using this as a variable bypass on the bilge-coolers, in order to control engine temperature, IF necessary.

 

[1967Brutus]

Talked to Hanco (owner of Raboesch) this morning, the guy that was to make the shaft reported sick this morning, but with a bit of luck, I will have my prop back somewhere in the coming week.

Fingers crossed...

So now  out with the old Ducati to work on its electrics (and no, I know their reputation, but this 38 year old bike does not have issues, it's an upgrade to LED headlight that I started a few weeks back and still have to finish).

[1967Brutus]

Darned flu epidemic is keeping me from getting my prop back... 

[1967Brutus]

YESSSS!!!!!

Just got news from Raboesch, my prop has been repaired.
Cost me an arm and a leg, but who cares?

Only frustrating thing right now is that I just yesterday began another 2 week shift on board, and by the time I get back (9th of April, Raboesch is closed for almost a week... Dammit!

But in 3 weeks, I'll be fitting back that darned prop!

[1967Brutus]

And TRIPLE YESSS!!!

I have my prop back, and it appears to be a solid repair.



This was the culprit..

This USED to be one single pin, only 1,5 mm diameter, which couldn't cut it therefore it got cut...



The small boss at the forward end of the prophub has a press fit in the sterntube, and I did not, of course, want to mess with this fit, so I had to figure out a way to get it in the tube with as little friction as possible.
So the shaft and hub went into the freezer at -20 deg C for half an hour, and I had to devise a way of heating the tube without damaging the Epoxy that holds it in the hull.

The tube is 8 mm inner diameter, so I took an old drillshank and iserted it in the tube, resting a plugged in 75W soldering iron on the drill.
This turned out to provide gentle heating, it took about 40 minutes toi reach 50~60ish degrees C.
The shaft being so cold that when I applied an anaerobic sealant on it, that sealant basically froze, but it allowed for simply pushing the hub home, where within 5 seconds it locked in place.
I am pretty sure, this will hold until the next time I need to get it off. Which hopefully is never.

There is about 2 hours of tool-time in it to reconnect everything, adjust and check, cure the threadlocks (I use Loxeal 85-21, pretty strong stuff).

With a bit of luck, There will be a bathtub testing session this evening, and if so, possibly tomorrow (weather permitting) a careful maiden.

[1967Brutus]

With a bit of luck, There will be a bathtub testing session this evening, and if so, possibly tomorrow (weather permitting) a careful maiden.

Still FAR from p[erfect, and a long way to go...


https://www.youtube.com/watch?v=XsUOplituBA

And VERY promising:

https://www.youtube.com/watch?v=FyKuIq1pNKA

[1967Brutus]

Anyone wondering where the pics went, the forum they are hosted on, is currently under maintenance, and they should reappear later today.

[1967Brutus]

Meanwhile, while still quite a way to go, At least I am getting some control over the mixture under load changes.
Ithis is achieved by placing an orifice in the airfilter, restricting airflow just a tiny bit, just enough to generate a slight underpressure at the air intake when the throttle is opened. This tends to linearize fuel draw through a single metering valve, more in line with the increase in air consumption.
It is a bit of a "bandaid solution" but it did work well in my earlier single cylinder boat.

First vid, it was still a bit too rich, hence cutting short the test.

https://www.youtube.com/watch?v=TpzFsvcesJM

But there definitely was improvement in the engine not shutting down, so a touch leaner and...

https://www.youtube.com/watch?v=uZ2tDX4aUIk

[1967Brutus]

Still a lot of work to be done, but the maiden voyage was all in all a resounding succes!

in total maybe 35~40 minutes of runtime, the first 25~30 were non-stop to see if the engine kept running reliably.
It did... It kept running without any serious issues, and I had to shut it down to get it to stop. Which I did, and restarted, etc etc. Working brilliantly!

The superstructure, it turns out the boat fills with exhaust gas, and the engine increasingly started to labour and lose power.
So most of the testing was done without superstructure, but here it is:

https://www.youtube.com/watch?v=EWfugslE3_8

She is quite fast, although I do not have that on video, she easily exceeds "hull-speed", and I haven't yet pushed her to the limit.

https://www.youtube.com/watch?v=cF-NWFQT-Xg

Bollardpull was tested, not measured, I wanted to know first if the boat would be controllable under tow, and she is.
It FELT like approximately 1 kilo, not even at full power, but the prop pulls airt too easily, it needs ballast.

https://www.youtube.com/shorts/hLom8fwTScc

If I had to estimate, there could be between 1,5 and 2 kilo of bollardpull, but that remains to be seen, also because there still is a lot of work to be done getting the combination between prop-pitch and throttle functioning.

The cooling, it HAS to be luck, was "goldilocks".... Júst right....

Free running, I saw between 68 and 74 degrees and during the bollard pull test, about 1,5 minute in, I saw 79 degrees Celsius.

I am an extremely happy chappy...

[1967Brutus]

Meanwhile, no posts did not mean I did not do anything...

As stated in previous post, the superstructure apparently affected how the engine was running, within 10 minutes from start during the maiden test, engine seemed to struggle, which as by flicking a switch dissapeared when running the open boat.
Initially, I thought it was exhaust gas leakage internally displacing oxygen and suffocating the engine. This suspicion was supported when I found the pressure tap of the Notro car muffler had come loose.
So yesterday, I tested with the repaired exhaust. The engine held out longer (approx 18 minutes, but then it started to bog down again. What was more remarkable, after running the boat 5 minutes without the superstructure, I placed it back and the engine bogged down within 2 minutes/ This made me think, heat could also have to do with it.
After all, there is an engine block at 70 degrees radiating heat, there is a 100 ml expansion tankof the same temperature radiating heat, and there is an exhaust muffler of maybe 150~200 deg C. And the only ventilation would be the engine drawing its air from inside the boat.

I still had the 62 mm electric cooling fan that came with the Engines accessory kit, and I decided to install that above the engine, blowing down at the carb area, but in general ventilating the entire boat at a decent rate (I have no fan data, but if I had to guess, something like a full airchange every minute or so)

I decided to place the fan in the superstructure, and feed it from the starting battery. That would allow me to camouflage the intake as an open Engine Room skylight.
Since the fan turns out to consume only about 400 mA, and the starting battery is a 2500 mAh 3S LiPo, that should result in PLENTY capacity to be able to runthe fan basically all day and still start towards the end of the day.


opening the skylight hatches... I did not yet know if I would need one or two, but one was sufficient in the end.


Constructing an airduct/fan base


The open skylight...


the fan, installed under its airduct, in the superstructure

Off I went testing. Started the boat, placed the superstructure from the get-go, and for 22 minutes I had a very consistent engine behaviour, when the pitch control linkage malfunctioned at half ahead, which forced me to bring the boat in, shut down the engine and take it out of the water.
This turned out to be just a linkage pin that had worked itself loose, and that was a 2 minute fix.


Boat back into the water, and off we went again. another rather uneventful 41 minutes later, I was wondering how long the fuel (normal filling capacity approx 250 ml) would last, because I noticed the engine leaning out a bit.
Bringing the boat in, there was about 50 ml of fuel left. Not bad.

So we have the following figured: Fuel capacity appr 250 ml., consumption appr 200 ml/hr, theoretical 75 minutes endurance.
Ignition current draw 200 mA, Ignition battery 1000 mAh, theoretical endurance (taking max allowable depletion of LiPo into account) of 4 hours
Fan current draw 400 mAh. battery 2500 mAh, so theoretical endurance until max depletion 5 hrs
Starting current is 2 sec bursts of 12 A, the equivalent of 7 mAh per start, so that does not do much
RX/servo consumption still to be determined, will edit in later, but estimated around 600 mA average, expected runtime about 3 hrs. EDIT: 1 hr of running the boat  resulted in a recharge of 635 mAh  for a 2000 mAh RX battery. So there is roughly 3 hours of operating time there as well.

All in all a boat very usable for demo days and such.

[1967Brutus]

Just hit a snag...




This is the cup of the engine side dogbone coupler, and it has wallowed out severely.
This limits the fore/aft movement of the shaft considerably, as well as that it transfers axial loads on the crankshaft.

Big bummer.

Going to ask a friend to make me a cup from hardened steel.

Also going to try and fabricate damper rubbers in the drivetrain, apparently the torque is not as constant as it seemed when the engine was on the testbench.
No idea yet how to do that (making a torsional damper, I mean).

Crap!

[Martin (Admin)]

 
Abstract art...?

[Martin (Admin)]

How about ....

[1967Brutus]

How about ....

The shaft travels some 5~6 mm in forward/aft direction when pitch is being adjusted, and there is a very shallow angle (less than 5 degrees). The dogbone coupler was the one supplied with the prop when I bought it, so I was hoping it could handle it. My hope was in vain.

[Martin (Admin)]

True.... why do the must hopeful wrong paths take so long to be discovered !