CB 90 HEX Hjärtrud.

This is the building forum for the Combat Boat 90. If you are interested in the STL's for this project, they are available to those who help me by contributing 15 Euro. Then you get access to a sub-forum where STL's, instructions and mods are located.
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Joined: Wed Jun 20, 2018 7:13 pm

CB 90 HEX Hjärtrud.

Postby Mazzarin » Fri Mar 06, 2020 2:13 pm

I gave up trying to make one 1/10 scale because of costs and issues with my big printer.

SO HERE WE GO! This time in original scale!

I have as long as i remember wanted to make a rc CB 90 in the Hjärtrud ambulance paintscheme and features. My dad was the commander of the boat from when i was 3 years old to a couple years ago.
Im now 15 and have all neccesary equipment and skills to fullfill this dream.
As the hull is 1mm thick I used a 0.5mm nozzle on the printer for it not to make impossibly thin lines.

Some backstory:

Before Hjärtrud was converted to ambulance, she had been thrugh a bunch. It all started as an order from the Malaysian government. Docksta shipped her to Malaysia where she got a damage and that ultimately led to her being still for very long. Docksta months later then decided to take the boat back and use it as a demo boat for the CB 90 HEX model. Later the german police wanted to rent her to stop climate activists from reaching the g8 meeting.

Video of the defence.

Then she was sent to a boatyard in sweden where she was converted to an ambulance for the gothenburg archipellago where she did 8 years of service before Northern Offshore Services NOS took over the role a few years ago.
The New boat:
Nos.jpeg (7.83 KiB) Viewed 17480 times
Feel free to comment!!!!!!
Last edited by Mazzarin on Sat Mar 14, 2020 3:54 pm, edited 7 times in total.

Posts: 10
Joined: Wed Jun 20, 2018 7:13 pm

Re: CB 90 HEX Hjärtrud.

Postby Mazzarin » Fri Mar 06, 2020 2:19 pm


I first printed the hull pieces 1,2,3,4

Sanding,Sanding, Sanding
Sanding was done using my favourite sanding tools in the world! Sandvik Sandplate!!!
IMG_20200302_215847.jpg (2.78 MiB) Viewed 17543 times

Posts: 10
Joined: Wed Jun 20, 2018 7:13 pm

Re: CB 90 HEX Hjärtrud.

Postby Mazzarin » Sun Mar 08, 2020 7:15 pm

The day before yesterday!

-I printed the cabin and front top parts
-I sanded them as much as I endured that day!
-Installed A small FPV camera system in the Cabin! First fpv project EVER!
-Epoxied the outside of the hull.
IMG_20200303_163905.jpg (2.16 MiB) Viewed 17535 times
Filled in the middle Window
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-Modified the motor mounts to not look like v8 (Scania Dsi-14) engines but inline 6's (Cat 3406e) Like the CB90 HEX model came equipped with.
- Epoxied and glass fiber'd the inside of the hull

-I printed some small pieces like the 2 centrifugal cooling pumps (totally unnecessary!),
-"Aft engine room box"
-"reversing bucket"
-"impeller duct"
-"guide vane chamber"
-"Steering nozzle"
-Epoxied and Glass fiber'd the outside of the hull.

The glass fiber was cut from a cardboard template.
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Masking tape was used, Well, to mask the epoxy off: :lol:
IMG_20200308_182301.jpg (3.91 MiB) Viewed 17535 times

Then the glass fiber and epoxy was carefully applied:
IMG_20200308_185958.jpg (2.97 MiB) Viewed 17535 times
Since glass fiber has a lower density than epoxy it will float, and thus being very prone to hydraulic slip, wich would definately ruin my careful alignment! So I soaked all the residual epoxy off with some toilet paper. AND makes the model more dimensionally accuate!

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I'm not too worried about covering the intakes for the cooling pump as it will initially run off of the pressure from the WaterJets! I forgot to order the motors for the pumps :(
IMG_20200308_190831.jpg (600.36 KiB) Viewed 17535 times
Soon my yellow paint will arrive!!!!!!!!!
More to come!!!!!!


I recieved the flourescent yellow paint.
A bit too much clear in the paint but i will medigate that with painting the boat white first.
The paint I used:
The paint I should've used:
Ehhr I dont know!

I also sanded and epoxied the hull once again!
Then I applied a thin coat of epoxy all over the hull Again!
The remaining epoxy was mixed together with the "Micro glass balloons" to remove some staircase effect notisable on the front deck and besides the cabin.

I had used masking tape to prevent the epoxy from entering the jet intake, that turned out to be a very bad idea as i had made the masking tape larger than the intake the epoxy stuck to the tape and i had to cut all of it out. So i needed a way to make the intakes flush with the hull with glass fiber on it. I used the "micro glass baloons" I had mixed earlier.

Epoxy cures overnight.
The day after Tomorrow!

I started sanding the newly added epoxy filler putty.

lost track of the days :lol: 03-14

-Applied spray putty on the hull-
-Sanded and applied another coat. Great weather today so the putty dries quickly!!

Engine Mounts
-the mounts were painted using Humbrol Enamel ((yellow) mixed with (black))
Note these motor mounts were later scrapped, I will make new ones when buy more spray filler.
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cat3406sd.jpg (39.37 KiB) Viewed 16979 times
Last edited by Mazzarin on Tue Mar 24, 2020 10:16 am, edited 2 times in total.

Posts: 10
Joined: Wed Jun 20, 2018 7:13 pm

Re: CB 90 HEX Hjärtrud.

Postby Mazzarin » Tue Mar 24, 2020 9:16 am


I had paused this project for a couple of days now, since the 3d Meetup was canceled. Sad news. Anyway meanwhile i had the project on hold I experimented on another boat!
Screenshot_20200324_101450.jpg (229.62 KiB) Viewed 13153 times
Video of "another boat"

This boat is quite the opposite, It almost doesent have any printed pieces at all (except for the 3d printed Jet drive) and instead consists of epoxy and glass fiber. I learned a Lot from this boat, Laying up glass fiber nicely, intake considerations, hull design, high speed hydrodynamics, impeller design etc. The boat didn't perform properly at first, It porpoised A term taken from how some mammals like dolphins swim in the water, meaning it jumped and had an aggressive angle between the bottom of the hull and the water. Making it very ineficcient and slow, the intake also lost the waterflow.

Using hot glue i could test details such as "ride plates" "guide steps" for the intake, "Planing steps" I had an idea of Instead of relying on the "scooping effect" the intake usually has, and instead rely on "Ram pressure". I became slightly obsessed periodically with "ram pressure"!! (read more here! https://en.wikipedia.org/wiki/Ram-air_intake)

And decided to utalize it on the "rideplate" too! Like an "interceptor"
Ram pressure.png
note: Picture totally ripped off from "Zipwake's" website
Ram pressure.png (39.42 KiB) Viewed 13141 times
(read from the implementors in this field! http://www.zipwake.com/)
This is used on many boats worldwide.

Though I certainly won't Need a rideplate on the CB90 (because of the length/width/beam) It is good knowledge to take into consideration in the furture! But I will certainy benefit from all i have learned regarding intakes.

I also found while researching different theories of jet drive propulsion a great youtube channel discussing everything Boat related! Go watch!!!
Especially this video!!

Back to the model!!!!!!
- I applied some spray putty (almost an entire can!)
- Started sanding to shape.

Please comment
Last edited by Mazzarin on Fri Jul 03, 2020 11:35 am, edited 1 time in total.

Posts: 10
Joined: Wed Jun 20, 2018 7:13 pm

Re: CB 90 HEX Hjärtrud.

Postby Mazzarin » Tue Mar 31, 2020 9:05 am

Update 2!
Intake grate!
I designed and printed some grills for the intake.
-Pm, Me if you are interrested in the files.
The paint plays a critical role in the boat's appearence, I have yet to decide on a sigle paint I can use. I think I will contact Rescuer (the new ambulance boat) It is stationed very close to where I live.

I have come to like Humbrol's paints. They stick well and gets very strong once dry.
Though they have a very limited range of colors.
I have not checked, but they may have a good green, their yellows are not close.
I found an old wiper pump. They are high pressure, self priming gear pumps used for windshield wipers on cars, boats, etc.
-they are terribly heavy though, so i have cut down on mine, the motor does not have to be that big. While i'm not sure if i want it in the boat, I would still want to install a lighter, brushless motor.

The primary idea is still to use Depronized's own cooling pumps, Maybe even both cooling pumps AND an intake thrugh the stator of the jets Using a T coupler.

I'm Not scared of problems!! :lol: :lol:

I have yet to find a good vendor for the silicone hoses and motors for the cooling pumps.

Site Admin
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Joined: Thu Jan 11, 2018 7:46 pm

Re: CB 90 HEX Hjärtrud.

Postby admin » Wed Apr 01, 2020 1:29 pm

Interesting with the gear pump, I spent too much time trying to design a small cooling pump for this project. I ended up scrapping that and going for passive cooling. Maybe a smaller 3D-printable version of the wiper pump would be possible to build, is your one possible to disassemble? do you have any picture of the interior?

I think one of the problems with my small one was that it was simply too small, so the water surface tension was even too much for it to overcome, and the high rotation speed meant that if PLA surfaces touched with no water in it, it would weld itself shut. :S

As you can see in this clip, it cannot prime itself but once it has water flowing through, it pumps really nice.

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Joined: Tue May 22, 2018 10:46 am

Re: CB 90 HEX Hjärtrud.

Postby Matsa » Tue Oct 13, 2020 5:39 pm

Mr Mazzarin, how is it going with your build?


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Joined: Wed Jun 20, 2018 7:13 pm

Re: CB 90 HEX Hjärtrud.

Postby Mazzarin » Fri Nov 06, 2020 6:07 am

Matsa wrote:
Tue Oct 13, 2020 5:39 pm
Mr Mazzarin, how is it going with your build?

I'm not quite happy with the bow. Some parts shoud have been glued before oneanother.

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