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[Backerther]

In addition to JimG's theoretical explanation, I have researched and studied some experiments ever done by some boaters as well as actual  jet boats when I was thinking about where to set the nozzles level on the transom against the water surface.


From my trial runs, the water jet over the surface could give me some confirmation to be more excellent than semi-under water
jet propulsion.  Top speed has become clearly faster than ever.

This is not a conventional type of screw propeller to thrust in the water, but a water jet propeller to thrust so massive volume
of water from the nozzle over the water surface.

[jaymac]

Not on  the Pibbers

[Backerther]

Oh jaymac, you have a Pibbers don't you,? which I once wanted to get in vain since it was too late for finding it already in the market at that time...
Therefore, I decided to obtain such a jet boat as yours by converting Lindberg 1/32 PT109.

Well then, it's about the time to exhibit the video of the 5th trial run made with a powerful 3S lipo and brand-new brushless motors on a very calm lake. Those who are interested in the motion images of the trial run, watch it.
As a static pic already posted show, two jet water could be seen clearly come out over the water surface powerfully in the video thanks to the trimtabs that might have raised the stern up, especially at speed.

Lindberg 1/32 PT109 with jet drive system sailed on a very calm lake powerfully. - YouTube

 

[Backerther]

Hi fellow RC boaters,
It's been a very happy and fruitful year for me as to have enjoyed the RC boating and building throughout the year.!!
It's totally and simply because I could have been healthy enough to have done such activities as the above.
For keeping a good health to enjoy and spend a wonderful time in any aspects of life including above, I have kept on practising
athletics including occasional swimming, not to say daily activity, but 7 through 10 times a month at the most. 
I do intend to continue this habit until 90 years of age for Rc boating, not to say until 100 years.!!
Here are my lovely queens and kings active on the water of the year.!!!!

How about your queen getting along on the water??

Wishing you a very happy New Year to you all and your families from Japan.!!
It's the New Year's Eve today. !!!

[swiftdoc]

That looks like a really good setup now, Kiyo!
I enjoy modelling very much as you do. Today we had the last sail for 2024 at our club pond. One of the club mates has an underwater drone and we found the submarine which got lost several weeks ago. The sub will be rescued in 2025.
Wishing you all a very happy new year which allows you to continue enjoyable modelling!!!!


Kindest regards


Arno

[Backerther]

Arno,
A happy New Year.!!!!      And thank you so much for sharing nice and unusual photos with us.
The underwater drone looks a practical and industrial machine developed to use for observing something in the water, doesn't it? judging from the image of the scope of the drone..   And the image of the sunk sub looks so clear..
I am looking forward to having some pics of recovery operation as to how it is made actually...??
And it seems toooo cold from the pic of the observation image in which lots of shrubs beside the road were stuck with ice.!!
It's so amazing for me to have seen such an activity as to enjoy ? the RC boating in such a terrible conditions.
What on earth, how cold it was then there.....???  All of the participants might be so energetic to RC boating....

I was a bit annoyed by green algae stuck around the impellers shafts as seen in the pics and I removed them after coming home.  The lake was unusually dirty with those algae on the 5th day trial run.


At any rate, let's have a wonderful boating and building as well as improving, repairing in this year, too!!?

Kiyo

[Backerther]

If I should conclude the status quo of this jet MTB under development made so far, it would be as in the pics below at a glance.


Pic 1/2; Jet nozzles were set like these against water surface, namely about 2/3 high of nozzle diameter.
        3; In the case of real missile boat of Japan navy.  Nearly same as mine.  
     4/5; Aluminum Trimtabs were set like these.
     6/7; And a powerful water jet was thrusted nicely just over the water surface massively and totally.
         8;To conclude, the boat has come up with a much faster and real runner on the water.

       However, above doesn't necessarily mean that there are no problems at all still now, against which I am currently  struggling to improve.!!!!!!   But it's worth challenging, mates.!!   It's the very hobby, isn't it.???!!!


           "There is no royal road to model boating."'(Backerther said!)
       

[swiftdoc]

Well said, Kiyo
Photo no. 6 looks very impressive, she is performing very well on the water!
Meanwhile I am still having a little amount of water ingress in my model. You told me, that you needed 7 attempts to fix the problem; I now have reached attempt no.5
Referring to your last statement: we will get there in the end!

[Backerther]

Yes, indeed. We shall overcome whatever should stand in our way to success.!!
Aluminum trimtabs are working very well to lift the transom up(or to refrain the transom down excessively)
And the tabs may have made the water surface around the nozzles so smooth and flat on which a powerful jet came out long
and low on the water, by which the boat might have been faster. If the jet was thrusted in the water, the boat might have been much slower.

"There is no royal road to learning"(an ancient Greek mathematician, Euclid said)
while
"There is no royal road to model boating"(a current Japanese old man, Backerther said)

[swiftdoc]

 

[Backerther]

I could have a nice weather yesterday to be able to ENJOY the Rc boating in the form of trial run that have amounted to 6th day of improvement test up to the day.
The weather was fine enough and calm to try the test run aiming at reliability on the water.
Through the test run up to today, the boat could be OK to run on the water in terms of good sailing behavior, its top speed and
sailing stability generally, not to say complete.
On the other hand, she is not necessarily reliable due to the motor itself or its selection, or cooling defect..
A water ingress at any parts of the hull has been blocked completely.


Judging from the above, it should need more months to resolve the above or to reach a compromise-able level of results, one or two months?
But it will be interesting and partly enjoyable for me to cope with such problems that will surely lead to a finally successful
model.!!!! 
Here we go with lots of pics of the test run as usual.


1; Typical splash at speed, neat shape of wave is impressive.!  Awesome form of pic to symbolize its high speed, Wow !!
2; imagine the high speed by the long drain water.!
3; At full throttle,!!!!        The wake is looong and low as compared with those at low speed. Compare with Pic7.
4; The drains are confirmed clearly by this pic to come out at both sides.
5/6; At slow speed
7; Typical wake at slow speed raising like a rooster tail.
8; At middle speed
9; The pics show that powerful jets are projected clearly on the smooth water surface made by the trimtabs and hull.
   The waves of both sides have been driven clearly outwards by the bilge/chine effect neatly.
10; The same as above though this is at low speed.

Have you already made and enjoyed a New Year sailing, mates ?

 

[Backerther]

I made an analysis of status quo of the latest improvement of the boat as seen below.

Pic1;wake at slow speed with 3S lipo
    2;Wake at middle speed with 3S lipo
    3;Wake at top speed with 3S lipo in the latest trial run omJan05.  The stern was clearly raised at this speed.
    4;wake at top speed with 2S lipo in the 1st rial run. The stern was too low.
 
   From these pics, it has become quite apparent that faster the boat, the longer and lower the wake is left behind the transom as a phenomenon.
  On the other hand, energy consumption of the lipo has become rapidly fast as the boat went faster, namely around 4 minutes at most if she should have run at higher speed as seen in pic3.
 While keeping the middle speed, she could enjoy the run time of 6-7 minutes.
   

[Backerther]

I made a video clip as attached of the 6th day of trial run in which my PT109JP was running so powerfully than ever before
on a very calm lake.   The video may tell all that she has done in the sailing test vividly even if a long wordy cordial
description was not attached any more in this post.

Lindberg 1/32 PT109 converted to a jet drive boat made a full throttle test on a calm lake.


Pic; "You did a very good job this time and a nice and safe return from the severe test."

[Backerther]

Additional repot of the trial run of the day is as per attached below.
Pic1; Many waterfowls gathered to observe seriously, silently and curiously my jet boat to pass in front of them at speed.  
        They were truly gazing at the boat.!!!???    How about your impression, Derek !?   Stupid even to comment?
    2/3; On the other hand, a huge number of crows was doing the same on the trees, sometimes noisily among a few birds as          if they were criticising my boat like " Oh it's so fast..", or " No, not so fast, we are much faster!!"
    4/5; This time, the water was so calm that cooling water drain was clearly taken and confirmed by my camera as being
          done as expected to be powerful enough.!
       Yes, seeing is really believing in this point too, isn't it ??!!
     
       The wakes, splashes and waves generated by this model boat do give me an impression and scale realism peculiar to a fast MTB. 
       One of the scale realism I feel from the sailing scenes is the very wakes, waves and splashes as well as its dynamics around the hull.!!!   In this sense, not only scale details can afford to supply the model with scale realism, especially on the water, needless to say, if it's a really practical RC runner.
It should be likened to a well-dressed beauty walking on the pavement so uglily that does not match her static beautifulness nor
spoil her static charm.   Haven't you seen such a beauty so far?  I have often seen in the street and still now.
     The above is my own part of understanding from what I think a scale realism is in RC boating.
       

[Backerther]

Hi there mates,!
I could find a very nice weather today and went to the usual lake for confirming the performance of the improved PT109JP
in terms of speed and reliability if she has become a really / practically serviceable RC fast boat on the lake.
The result today was so so.    
I am attaching so impressive pics below of the test run reaching 7th day as trial.
As you may possibly feel something fast and powerful from the pics, she has really done an improved job this time as well, not
to say perfect to my expectation or image I have in mind...
However, my camera woman has told me later that she was warned in the video monitor screen frequently as to be so fast to move the video-camera. 

I think the sailing performance and its scale realism of a scale RC (fast) boat could be judged to some extent by the wake, wave and splash caused by her, although my PT109JP is a fictitious boat.    Finally it was too cold even in Tokyo.

[swiftdoc]

When you posted the first video, the performance was not bad in my eyes. But when I watch the current video, you have improved it really to some big extent. She really looks very powerful and fast, just what you were aiming at

[Backerther]

Hi Arno,
I' m so glad to have your friendly comment and interest in the boat.
Today I post the video for you as follows together with additional /impressive still images I took for analysis of the sailing conditions.

PT109  jet-driven MTB converted from Lindberg sailed in the mid-winter powerfully and fast.

As you know very well, this kind of fast RC scale boat (though this PT109JP is fictitious) normally takes comparatively
long time to get it to run well as a serviceable / satisfactory model boat on the water...and unless having a successful result of a good performance on the water, the value of the model as an actual running RC scale boat might be diminished to some extent.
However, it could be worthy sufficiently of runnable RC scale boat to be kept in a room.
Therefore, I have been repeating many times of trial run to make it looked a scale like Rc runner on the water, not like toy level of RC runner on the water.
In such circumstances, this boat is still on the development stage and I doubt serviceable level of sailing performance may come before this spring... But promising too...  
A RC scale model had better be a RC scale model even/naturally in the sailing performance to match its good appearance, hadn't it..!!??

[Backerther]

Hi
I improved the power train to gain more effective output and heat resistance of the powerful brushless motors by which I have thought that the reliability and speed will be drastically increased.
One of the improvements is a heat-resistant spacer to set between the motor and its mounting bracket of the jet pump unit.
This spacer is intended to contribute to a proper alignment between the motor shaft and the coupling, and the bracket has been damaged largely by heat through not a few of severe test runs at speed.
In other words, I just rebuilt the mounting brackets for getting a correct alignment using the spacers.
Anyhow, a brushless motor is really powerful enough to get the boat to run fast which is normally impossible to do by a conventional brushed motor....   The motor I am using is 500W.
The spacer is about 1.0mm thick made of a metal and wood.

[Backerther]

Well then, in the next place. I have changed my mind to stick to coiled water cooling style finally, though this coiled style is I still think very useful for the conventional brushed motor from my RC boating experience.
However, the coil jacket doesn't seem to have contributed largely to cooling in this kind of brushless motor which I have thought
is possibly basic cause of malfunction of the boat through many test runs....
Therefore, I have set a pair of cylindrical type of water-cooling jackets as seen below.
The brushless motor is like a wild mustang at higher revolution.!!
Instead it has contributed largely to high speed.

I just feel as if I took a detour for cooling problem.....
New spacers are also well fitted to the motor mounts.

[Backerther]

This time, I took countermeasures against subtle vibration of the motors especially at higher revolution, by setting motor supports
just beneath. I am generally reviewing the power system totally to see if respective part is secure for a fast jet boat.
The motors are installed very unstable on the vertical mounting walls with only two screws each briefly.....
On the other hand, the motor is like a wild mustang when in fast sailing.... The screws are apt to be loosened to some extent comparatively easily. The powerful mustang has to be suppressed only to use the advantage of the power for a nice sailing boat, hasn't it.!!
With these supports, the motors have made more normal and tamely sound with much less vibration.
I should have done such easy countermeasures earlier....But it simply came so as the options of countermeasures have been left gradually very few among which are these supports.....

[swiftdoc]

That is looking good, Kiyo. Should I come across a similar problem, I would have to change the drive system to inrunner motors (at the moment I have mounted outrunners). The Kehrer system looks rigid though, using M4 screws. I am still fighting against water ingress, but was able to reduce that to an amount of only a few drops. If I cannot find the reason for that, I shall live with it.

[Backerther]

Arno,
Thank you for always friendly comment.
M4 screws may be quite OK to install such large brushless motors as yours, while mine are M2.5 !! to set smaller motors.   Mine are cheap Chinese-designed/made  while yours are well engineered German-made??
I think there is no need deeply to worry about a few drops of water ingress which is so negligible small amount of volume for me unless solved.

By the way, additionally to reinforce the suppression of the motor vibration, I fastened the motors with a 0.1mm thick steel bands as seen below.
Through several countermeasures mentioned so far against subtle motor vibration and hellish heat, the motors have been GREATLY  improved as if they were reborn, especially heat problem is done nearly perfect.

The revolution sound of the motors is like a music for my ears, not an irregular noise.
The motors are easily touchable even after 6 minutes high speed run in the bathtub test.
In addition, electric consumption is also greatly improved to half in spite of two times longer run time than before which will be possibly incredible in general.
This fact may prove to be improper setting of power train of the boat having been done so far.

These wild mustang-like motors seem to have become tame but powerful ponies.
Not hot but warm level of motor which is quite OK as the bathtub test, and it is promising to reproduce it again on the lake.!
If so and the same is done repeatedly several times on the water, it is what I say is serviceable and practical RC boat on the lake.!!!!   That means truly success of this project.!!!

[Backerther]

I could have the best and very satisfactory time than ever in 8th day of trial run yesterday.!!!!
The video will be exhibited later that may show you vividly how actually she behaved on the water.
I have just posted still images today of dynamic scenes of the jet MTB that will not be able to tell you exactly the dynamism
truly, though..
This is partly because of no sound and no movement, and such elements will contribute to represent the dynamism largely for us.
Since this is a RC running model boat on the water.

All the pics below is at full throttle level.
So, pay attention especially to the looong ,low and whitish stripe-like wake left behind the boat that will apparently appeal the very speed to us.

I enjoyed this day 4 rounds of trial run successfully with no serious problems unlike previous trials made so far.
Each run time was about 5minutes due to battery capacity and very high speed.
This is, so to speak, the boat seems to have passed the entrance exam. imposed on her to become a serviceable and practical RC boat, though not graduated from yet....

She has just really become a jet MTB literally.!   Wow, Wow Wow!!

[Backerther]

Hi RC boaters,
As I predicted yesterday about the video, I am so happy to be able to post it proudly as the following.
The you-tube video will surely and exactly tell you how the boat behaved on the lake for close to 5 minutes with no cut.
 The full throttle scenes may come up from 1:30 past.

Lindberg 1/32 PT-109 water jet MTB sailed stably at full throttle.!!

Just  comments on this sailing;
1:Acceleration is seen clearer than before firmly.
2;Motor sound is heard normally as the speed has gradually been built up.
3;Sailing behaviour is stable at speed which is partly natural though...
4;Actual run time exceeded 5 minutes easily keeping a nice speed to the end.
5;The motors were a bit warm level after the sailing which was the largest and remarkable improvement.
6;No loosened screws at all.
7;A small spoonful of water ingress was found.....this is actually only one point to be corrected later.
   This ingress is thought to have taken place at full throttle speed judging from the prior test run in the bathtub...

This result of sailing is so compromise-able for a mere pla-model converted RC scale jet boat to sail on the lake in my understanding.   Not to say perfect level, though.
 
Well then, enjoy (or enjoyed already? )the video of jet MTB sailing powerfully on the lake by the full screen of your PC.!!!

[swiftdoc]

Very impressive, Kiyo   I like the sound of the motors accelerating up to full speed! Sounds like music!