Looked at the Visby vid again Rowen, and it did go pretty well. 2 should work ok in a bigger model. I had seen reviews on some of the small jets being a bit lacking in performance when I was looking at choices for my Hartley, that's why I went for the 28mm, but yours must be one of the better versions. My model is quite heavy, so needed a bit more grunt.

JB

Hi JB,
Used them in my Visby and the performance is good. The instructions advised fitting the aluminium impellers when using 3S cells.
Original intention was to use 3S, until the trail runs showed 2S more than adequate. Left the impellers in as did not want to replace and then have leaks to resolve.
Service from the Tilkea shop supplier is also good.
Used the flap reversers and they work quite well, also resemble the Visby type reversers.
The CB90 reversers are a different style and, whilst am trying to make my own, can always fall back on these if unsuccessful.
Rowen

Hi Rowen, I've seen a vid of one of those units in a plastic racer being trailer launched, that flap reverse worked quite well. The aluminium impellers are meant to be better, (supposed to be CNCd ) as they are finer and apparently are a better fit. Interested to see what you do.

JB

Thanks JB,
Good points. Luckily my diameters slowly increase from the waterjet nozzle outlet, hope will be no choking.

Will modify the inner nozzles as suggested. No point in directing water at the transom!

Used the following jets on my Visby as could accommodate them readily. They worked well, so plan on using them on this project, except with my own reversers

https://ae01.alicdn.com/kf/H87446bf2ec6d4ac3acf9ed81e3d79316Q/22mm-Water-Jet-Boa

Hi Rowen, looks like a good start👍. A few points I would suggest,- don't reduce the outlet size with the stepped fitting ,- I tried this with a similar fitting on my 28mm jet and it restricted the flow too much. Also, if you can, get a 3 blade prop slightly larger than the internal bore, and trim it to a close fit (say.3mm max) as the props they give you are usually too small and lose half the thrust. Search for Tilkiea model in Ali Express, they have a great range of props, or DT Hobby store- go for the type pictured and skim it down. You may have to trim the back of the blades, if they interfere with the flow directors in the plastic nozzle.

Your outer reverse nozzles should also be pointing downwards to push water forwar under the hull in reverse, not at the transom, (ie cancelling the effort) You also only need cheap aircraft ESCs, as you don't need reverse😊

With a few mods, you can make them much more efficient. The type of motor is important as well, - needs good torque and high revs (eg 2800kv 3000kv) to get anywhere. Jets are totally different to exposed props, and require precision fitting of the impeller and good power, as they are a pump not a screw (relies on the amount of water it can move out the back to push the boat along (nothing to do with the jet flow pushing on the water behind the boat at speed). With the small improvements to mine, it can now pull about 40A static, as against around 28A in original form. Another mod is to make the intake grille bars vertical to reduce drag.

All depends on how fast you want to go.😁 Might be harder with the smaller jets though, but worth a crack.

JB

Hi Rowan
Very impressed in your fabrication.
That must have taken some time to work this out.
I looked at a similar arrangement but because of the two drives I was pushed for space.
So I compromised by diverting the jet under the boat. To be honest they are hardly used.

I will get back to you on the boat dimensions.

The design was a model boat mag, however it used props rather than jets.
The boat performs well,

I had a few problems with leaks around the drive, also had a problem with one drive , internal prop moved within the assembly resulting in loss of power.
You also have to ensure you ballast the boat to ensure the jet are under water or they will air lock.

The motors do heat up, so running time is limited.
I found out later that the motors can be water cooled using the water jet that comes out of the top of the jet.

I am not sure of the purpose of this jet maybe somebody in the group can enlighten us.
I note jet skis have this jet as well.

The jet units themselves are quite flimsy
and in my opinion not very well designed for fitting in the stern of a boat.

Robert

Nice bit of fabrication Rowen.

Cheers,
Stephen.

Robert,
Meant to add on my note, what are the significant dimensions and weight of your model. How well does it perform?
Just finalizing the size of my CB90, which is similar, so would find your experience and insight helpful.
Thanks Rowen

Thanks Robert, it did.
Have come to the same conclusion.
In the size I need (22mm), "bucket" reversers similar to yours in concept are available. However, I need the "T" shaped reverser.
The only source (somebody suggested on either this or the MB Mayhem sites was Ocean Works in Hong Kong. They make the reverser I want, but not in that size.
Also quite expensive.
Have embarked on making my own using small copper pipe fittings.
My first attempt is attached. Needs fettling to bring up to standard buy looks promising.
Rowen

Hi, is this the kind of drive you are enquiring about.
I bought the 32mm jet drive on wish.
This did not have the reversing buckets.
I tried to find the drives with reversing buckets but was unsuccessful.
I made the buckets from brass sheet.
The buckets are weighted so that they drop by gravity and are held up by the servo via nylon cords.
When held up the buckets are clear of the jets
Hope this helps.