At Last I Have A Dowty (photos may not be visible to none regisitered members)

[BN]

Here's a request to the imaginative engineers please:

Attached is a diagram of my jet unit nozzle. Since I have sand blasted it, I find that there is a reduction shim (866) and I need to remove it. BUT as usual the dreaded corrosion has virtually welded it into the housing. I have drilled out the locking bolts, but the shim is stubborn. Any ideas please 

[enginuitytriumph]

Hi Brian,
it does depend on the materials & the fragility of it, but as ever the only way is heat!! Again depending on the material, an inductive heat might be a less aggressive way of getting the bl~~dy thing HOT!!
I've found there is little else to shift things quite like it    Mark

[BN]

Hi Brian,
it does depend on the materials & the fragility of it, but as ever the only way is heat!! Again depending on the material, an inductive heat might be a less aggressive way of getting the bl~~dy thing HOT!!
I've found there is little else to shift things quite like it    Mark

Thanks Mark, the material is cast aluminium and circa 1956. I think it is solid enough to give it some heat and a bit of aggression, but as always with these situations, it was over engineered and primitive. I will get a company in Corby to see if they can heat as you suggest. If it does not work, then it is a, 'somehow' cut it out and make a modern plastic insert.

[BN]

So far so good. The jet-ski nozzle is now fitted and you all say, not pretty is it, you are right. Well I want the mod to be able to be reversed back to normal in an instant and what I have now will do that. In addition, I (possibly), have a very steerable Dowty now with the addition of a nozzle that will put out a solid jet as apposed to the original confused jet. It is also adjustable up and down to give more push on lift out and then straighter on the plane. It will also allow a little trick driving 

When it is powder coated in shiny black, it will look a lot better. Also I can use simple control cables instead of the 12 foot by 1 inch radiator pipe which the original is. Still a work in progress and there is a reverse bucket to be fitted as well 

[enginuitytriumph]

I've always been a bit curious about the nozzle side of jet drives... the Castoldi has rudders a bit like yours, but every 'modern' jet unit has nozzles. Is it to speed the water up? or perhaps make the water go up above the water line (I've heard that works well)?? Does it steer better ? Sorry, but Castoldi still now seem to continue the 05 with rudders, so I am perplexed!    thanks Brian !! Mark

[BN]

Hi Mark, I am learning about jets a lot recently. It appears that the jet at full speed, should be just above the water level. Obviously on 'pull out' it is beneath, then the nozzle bottom is on top of the water.

In an effort to get better performance, I am experimenting with an old Bombardier Jetski nozzle with variable pitch. By that I mean it can be dipped to push the bow down quicker than a straight nozzle. Then when on the plane the nozzle can be adjusted to level out just above the water level. It will also make 'trick' driving and shallow water driving far more interesting (I hope).

Re the nozzle, nearly all modern jet units have a round nozzle, exactly like a power hose of a Fire Engine jet. In fact Hamilton jets were used in fire engines with a car engine in the 1960's. The pressure outlet pressure was increased by straightening out the water in the jet tube and exiting via the round nozzle put even more 'umph' into it.

Take a look at this brilliant video: https://www.youtube.com/watch?v=bC8tbBXEhdo
 
If you look carefully, the jet is just above the water on its fast manoeuvres. I know my Dowty can do most of the manoeuvres, but with the modified nozzle, I hope to be able to do more, especially with the variable pitch up and down 

[BN]

Just to clarify what I am trying to achieve:

https://www.youtube.com/watch?v=JEWxIeHBMy4

The real bit to see is at 1:18 on in the video.

[BN]

More progress, slow but sure.

Attached is the adapted Dowty jet outlet (circa 1956 and alloy) using a Bombardier jet nozzle (unknown years) and an unknown bucket from unknown boat or jetski. You can see the ability (or will be), to tilt the jet nozzle and of course steer it. I had to make a couple of bolts to attach the bucket to the original Dowty nozzle, which now needs the final adjustment and shimming. The reverse bucket should give a good stop power, we will see 

It should also give a good turning ability and hopefully a 360 degree turn in its own length, something that the Dowty could not do, although it was good. When finished and sprayed to a uniform colour, it should even look reasonable.

[BN]

Here is a crazy detail, I have driven about 50,000 miles in the 8 years I have been restoring my 3 current boats  just to get the parts made, modified or collected.

[BN]

[BN]

This is the box end of the bearing that I adapted for the Dowty Cutlass Bearing. Because the Dowty had so many bespoke items, the bearing will have to be trimmed down and about 1mm taken from the outside of the bearing, leaving at each end the same amount as the holder has in the Activation tube. See details below in previous posts.

The reassembly is about to start before paint and I think the weight is over 76kg and the length over 1.2 metres, its a monster.

[BN]

Now to start the very complex re-assembly. I will try to put pictures, but it is a nightmare already. I have absolutely no details of spacers or gap settings. To top the lot, spent all morning looking for an important part of the drive shaft. Then realised, I had made it out of stainless, rather than alloy 

Everything is so heavy, I have no idea how I am going to get it all back without the original 'jig' that Dowty used to fit all the vital fixing points of which there are over 75 

If you want seals, Walker Rubber in Norwich are fantastic. I use them all the while. I needed a 'nitrile, gasket to sit between the activation tube and the jet intake, so it has to be good. Over the phone they took details and I should get 3 bespoke gaskets next week, all laser cut.

More later 

[BN]

Found out what the spacers are for, but need to find out how they are set and how many 

[BN]

Found out what the spacers are for, but need to find out how they are set and how many 

OK, so I think I have it now.
Attached is the only diagram I have showing the tolerance BUT, there are no tolerances written on it 
The 'prop-shaft tube' is made of alloy and is 214mm long and slides onto the drive shaft, with a water seal in the end and around the shaft, which is never seen unless you take the whole assembly out; and that is no mean feat either.

When assembling the unit, as the shaft goes in assemble normally. (I will write that up later as it is not easy). It is not quiet as simple as a simple assembly either because for the job two people are required.

More later when I get my head around how to put it down accurately and in a succinct way.

[BN]

The part that was eluding me was that all the massive 'thrust' pressure is placed onto the very thin thrust bearing holding plate, where the jet unit links to the engine via a very short prop-shaft.

Attached is the thrust bearing plate and it can be seen how thin it is. I may make a new thicker one and if possible, put a slim thrust bearing in. These are the type with the rollers placed inside like a clock face?.