Author Topic: JET BOAT HORRORS  (Read 4472 times)

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Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #15 on: November 17, 2017, 12:26:32 AM »
Wow, you really 'dug deep' to get results. My units both were fixed with bolts, meaning that the plate that's embedded in the hull bottom fiberglass has holes which are tapped.
Interestingly I had considered fitting them with studs as the repeated removals over the years have caused several of the threads to not be that great and so I cant really snug up all the bolts anymore.
I also noticed in some of your pictures that you seem to be able to leave the bolted down piece in place while being able to remove the reactor housing etc. That is definitely not possible in mine, but would be really great as I don't have good gaskets and so I bolt the unit down using bedding compound (s) (have experimented with several forms of silicone based compounds to get a good lasting seal).

Offline BN

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Re: JET BOAT HORRORS
« Reply #16 on: November 17, 2017, 10:06:40 AM »
Hi and welcome to OSB.

The jet unit is fitted by studs to the mounting base plate. The mounting plate is set firmly into the boat hull at the layup period, so not removable without cutting it out as I have. The problem with studs is that the jet housing had seized onto the 24 studs, so it was not possible to lift the jet out, that is why I had to cut it out and start again.

At the moment, I am trying to refit the 'base plate' (for want of a better name) into the boat hull again. I am trying to find a fibreglass technician who has sufficient knowledge on how to bed the plate in because the stresses on it are considerable, let alone the leak risk, which is a weakness on the UK built Dowty I am finding. There is no other way that I can see how to update the base plate unfortunately.
1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB

Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #17 on: March 06, 2018, 01:13:14 AM »
What were the specifications on the cutless bearings you used in your restauration and did you find a good supplier?

Offline BN

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Re: JET BOAT HORRORS
« Reply #18 on: March 06, 2018, 08:30:06 AM »
The cutlass bearing I used was a canal barge steering bearing. I then had to cut it down to make the bearing fit, including the inner rubber section.

The hidden part is that there is a recess on the outside of the brass so that it slides into the housing easier. I did not notice that at first and the first bearing became damaged on insertion, so I had to start again.

Attached are the pictures of the old bearing and my new one. I also had to make an extractor.

Hope that helps.
« Last Edit: March 06, 2018, 08:32:13 AM by BN »
1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB

Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #19 on: March 10, 2018, 08:00:41 PM »
yes, great, thank you, good pictures.
I found some bearings that seem right but are 6" long instead of the 4 3/8" the others seem to be.

Also I am still amazed at the pictures I saw of a pump disassembly while the main intake housing remained bolted to the hull, my boat definitely doesn't allow that. Which is too bad as it is bedded in pretty good and every time I remove it for any reason I get the sense I am weakening the fiberglass'ed in base plate.
Also my base plate definitely has tapped holes and the unit is bolted down, I wonder if yours is a better system as you don't wear out the threads in the holes although yours seems to corrode to the unit or something.

Do you know what happened to Kurt Hansen in Nova Scotia? He had a great site with drawings and manuals on the Dowty Turbocraft?

Offline BN

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Re: JET BOAT HORRORS
« Reply #20 on: March 11, 2018, 12:51:37 PM »
Do you mean like the attached picture. If yours is all one piece it is a later model and better re reduced leaks. Take a look on my Dowtyboats site, all is there. My system is a nightmare and the bolts seize in the alloy, so make removal really dreadful. I am working on a mod at the moment, but it is slow.

Go to this site: http://www.oldspeedboats.co.uk/dowtyrestorationpage4.html you will need to browse through the pictures.

Also look and my other site, which is better: http://www.dowtyjetboat.co.uk/

No idea what happened to Kurt, but I have as much as he had, because I managed to get mine from Dowty in Gloucester before the offices burnt down. The rest, I have done myself and documented on the my Dowty site.
1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB

Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #21 on: March 11, 2018, 06:22:21 PM »
Yes I don't understand how you were able to remove the activation unit, while leaving the intake housing bolted down, I'm not sure I can do that, but sure would be handy though and easier on the hold down bolts. No Mine is a 3 stage with 3 sections that are all bolted together but the only way I have been able to take it apart is by first removing the entire assembled jet unit.
I would love some of those original manuals so I can print them off, do you have these scanned in at all?

When assembling the unit the things that is unclear to me is the lock washers that seem to be needed where the shaft fits in the capsule bearing and where the fairing meets the first impeller or actually the first sleeve. There isn't a lot of info on what size these are.
In my unit I never put these back in at first which changed the total length of pieces on the drive shaft and so when tightening the nuts on either end of the shaft I ended up forcing the impellers to close to the reactor housing etc. I was able to solve it by re-introducing some spacer in the place of the lock washer but it specifically seems to mention lock washer. The reason I at first didn't put these back is that they had disintegrated (both) and the bits had gotten into the capsule bearing on one side.

Offline BN

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Re: JET BOAT HORRORS
« Reply #22 on: March 11, 2018, 07:18:30 PM »
I will try to locate the relevant diagrams.

There is very little advice on most of the unit, because they were built in NZ and shipped over as a unit. The only thing that had to be done was the thrust shim; and I have no idea how they worked that out just yet.

Re the input housing, I had to cut it out, which left the grate in the bottom. It still has to come out, but it was only held in by 8 self tapping screws to a piece of aluminium which was set into the hull at first build. I now have another plan to set bolts through the hull to do the dame thing, but better and easier to remove. I still have to set my input housing back into the boat, but now have a new base plate, which a friend has moulded in alloy for me.

The lock washer is an Imperial size, but I cannot recall the size right now. The spacer is a tiny thin piece of brass and is very hit and miss, or trial and error. It is also very time consuming, because there is no way to test it for gap.

Attached are pictures of the jet unit. The cut away is the 2 impeller version and the other the 3. The diagram shows the intake housing and gasket. The base plate that is embedded into the hull fits below that. The last picture is the original base plate, which has tapped holes for studs, I now have a new one which is stronger.
« Last Edit: March 11, 2018, 07:27:39 PM by BN »
1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB

Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #23 on: March 13, 2018, 12:03:26 AM »
Thanks.
Its so interesting to see how many different versions or iterations exist under the Hamilton-Dowty-Buehler umbrella model names.
I can see that your intake housing has an inspection hole or at least a place in the mold where one could have been, in mine no such thing, mine also doesn't have the bolt locations for the engine mount at the rear of the intake housing.

But as I might have said before the issue you are facing intrigues me, as you have studs that pretty much seem rusted or corroded into your intake housing, making it very difficult to remove the housing.
In my case they are bolts, and the plate is molded into the bottom of the boat and has threaded holes. My problem is that the thread in several holes isn't that good anymore and I was considering studs. I even thought to loc-tite some of them as needed.
But my worry is that I then have no wiggle room to put the unit in or take it out. Right now due to lack of a proper gasket I use some form of bedding compound and slide it part into the transom hole and then try to lower it in place right on top of the holes.
I worry that if I use studs maybe that will impair my ability to slide it into the transom hole.

I own 2 units, from 2 different production periods. My current one is a Dowty built in Ajax, Ontario, Canada and my previous unit (now just for parts) is a true blue Buehler Turbocraft from Indiana USA.
Being in Canada makes me feel ok with the Canadian unit :-) but mostly because it actually came with the first incarnation of a reverse bucket as opposed to the drop gate with the Buehler. The buehler was supposed to have hydraulics which mine doesn't have.

I'm rambling, sorry.

I just ordered 2 of the Cutless (rubber) bearings, I could only get them in 6' length so I will have to find a way to shorten them in a professional manner.
I also did some serious measuring on my 3 stage shaft setup in terms of all thicknesses etc and I saw that in the manual that Hansen had at the time on his site (I only have a scanned in version after it had been used a lot) that there are 2 spots where there is that lock washer, I found some stainless ones that are 1" inside diameter and are 1/16" each, which seems to bring me close, only 1/16" needed to shim, if I did it right.
The run-out at the impeller shaft caused my gland seals to leak at higher rpm, not into the bearing it seems but came out of the weeping hole, not at lower speed.

Offline BN

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Re: JET BOAT HORRORS
« Reply #24 on: March 13, 2018, 10:02:17 AM »
The problem with the Dowty, Buehler and Hamilton, they were all franchised by Hamilton to each country, so in each country they did what they wanted, whether it was cost, quality or design. None of the designs for installation are what I call good for a boat that was originally built to be a water bourne Land Rover or Jeep as they are so difficult to repair. Concept excellent, fun brilliant, reliability dubious, repair very difficult, that is why there are so few left.

Dowty of course are the suppliers of most aircraft landing gear, so how they became involved, who knows. Dowty then sold the boat side to Boulton Paul in the UK, a contract house and factory building company?

Re the inspection mould on the top of my housing, the earliest did have a glass access, but they frequently smashed with stones, so that was stopped. This lead to the more difficult shimming which I still have difficulty with as no one has any data or how to do it easily.

Re the re-homing of your unit, perhaps you could mould them in like mine using an alloy base plate. I had mine professionally moulded, but in hindsight, I could have used a chunk of alloy and hand cut it. but it would have had to be 1 inch thick, so I chose casting. Re the studs or bolts, they will last a few years, but with regular service, and brass nuts, they may survive a little better. The two studs on the back of my housing are a night-mare to remove the nuts from, unless the rear units are removed first as they are hidden.

The reverse bucket was a great improvement on the 'shutter' which is useless. I was used to no reverse with my direct drive, no reverse and no neutral Albatross, so did not concern me.

Lining up the impellers is a true nightmare; and that does not include the thrust shims. I have no idea how other than by trial and error, which involves setting up, measure, remove, make shim, re-install etc etc.

I am struggling now due to old age a heart condition and few skilled engineers in this country now. I have a toolmaker, fabricator and a foundry, but nothing else and I am lucky. All the best BN

1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB

Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #25 on: March 14, 2018, 11:42:37 PM »
Yeah the reverse isn't what it was cracked up to be in the old brochures. Bucket or not, it isn't very effective although it does assist in slowing down. Really douses the passengers in the rear seats, treats them to a big shower s the bucket wasn't ideal shaped yet :-).
Its interesting though especially when looking at some older experiments by Hamilton where they actually used a clamshell design, but must have abandoned that for a while.

I think I figured something out about the disassembly mystery. I noticed in the British Manuel from Kurt' site in the past that the reactor casing seems shoved in through the transom from outside inward and the clamps mounted inside to the transom.
The Canadian model mounts by being inside the boat and shoving it from inside to outside through the transom, mounting a ring on the outside of the transom and then using the clamps on the inside.
This explains why I couldn't figure out how you guys could remove the reactor housing without removing the intake piece.
I wish mine was like that, it seems like a better setup for maintenance so you don't have to remove the intake all the time.

I also noticed the shims you mentioned in the drawing of Kurt's British manual, whereas the Canadian model doesn't have shims but 'lock washers' one between the fairing and the bushing for the first cutless bearing and 1 between the spacer tube (immediately behind the fairing) and the bearing centre in the capsule bearing housing.
I have been able to establish that in mine there is a discrepancy of 3/16" and so between the 2 lock washers and o-ring between the fairing and the spacer tube, they need to be exactly 3/16" or so it would seem.

I understand now also why your capsule or thrust bearing housing assembly looked so different from mine. The British manual shows your exactly but the Canadian one shows what I have.
That all confirms what you said, they made them all different.
Wouldnt want to be able to interchange parts aparently.


You better take it easy on the heart there, got only one of em....

Offline BN

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Re: JET BOAT HORRORS
« Reply #26 on: March 15, 2018, 09:48:43 AM »
The reactor casing is pushed through from the outside and a pair of 1/2 moon clamps are fitted to the inside, with a gasket (cork in my case), which fits on the outside between the hull and rim of the reactor. Cork was used because the thickness was unknown until fitment, so layers were glued together. That causes the main problem of the thrust washer thickness, which is my biggest problem.

Other issues are with the thickness of the hull and exactly where the intake housing is fitted in the hull. I am trying to work out how I can assemble the whole unit and then drop it into the hull and slide the jet (as a whole), forwards and backwards up to about 1/4". Sounds simple, but proving very difficult. If I could do that, the seal and spacer between the reactor and the housing would be sorted on the worktop in one go. I have attached the twin impeller setup, possibly like your.

I have also attached the assembly of my model, only they all varied dramatically. For instance mine as the 1/2 moons near the rim and the other end has a slot and another pair of 1/2 moons to fit into the jet intake. Hard to explain, but I plan to assemble the whole lot on the bench and the make an adjustable base plate to drop it all into the boat. In theory I could then clamp the reaction unit to the outlet pipe, sandwiching the hull in between.  ::)

815 is a alloy and anodised unit. Mine is now stainless steel.
831, 827 and 821 are also alloy and anodised. All of them, including 815 and 820 I had to remake.
917 and 918 are the tiny shims
832 is a seal that sits inside 821.

908 BTW fits near to the rim of the reaction unit and should be a pair of half moon items. I had to make these as mine were missing. Most of the diagrams are incorrect no matter what country they are from as all was trial and error at the time.
I hope some or all of this helps.

I think it is this boat that is causing the cadio issues  ;D
« Last Edit: March 15, 2018, 10:02:42 AM by BN »
1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB

Offline ltdlandau

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Re: JET BOAT HORRORS
« Reply #27 on: March 20, 2018, 10:30:37 PM »
Well thanks for all the info BN, its funny how what you describe as what you would like to see:
but I plan to assemble the whole lot on the bench and the make an adjustable base plate to drop it all into the boat. In theory I could then clamp the reaction unit to the outlet pipe, sandwiching the hull in between.
that is how mine is...  :)

and what I described as what I thought to be more ideal for maintenance purposes:
This explains why I couldn't figure out how you guys could remove the reactor housing without removing the intake piece.
I wish mine was like that, it seems like a better setup for maintenance so you don't have to remove the intake all the time.

That is how yours appears to be...

So, I'm taking your advice and am not switching to studs but for some of the bolts where the thread isn't too healthy I might loc-tite a few in and keep the rest bolts, however I'll have to experiment as I think mine needs to be slid in the last bit, into the transom, in which case studs are out for me, in that case I have to re-tap some of the ones that no longer hold, get larger bots, drill the holes in in the intake larger etc etc.

I think the diagrams aren't too too bad when considering the different builds around.
Thanks for all your info, and the great site with the very helpful pictures.
There isn't a lot of great info around otherwise.

Offline BN

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Re: JET BOAT HORRORS
« Reply #28 on: March 21, 2018, 08:55:55 AM »
I think between us, we have uncovered by simple discussion, the difference between the two builds in different countries, even though on franchise, what ideas emanated from each company in each country. I have to say, I am with your designs, rather than our designs.

As far as I know information like this has never been done before; and what a shame, because the boats are great, they are solid and excellent for what they were built for in the first place.

I am now working harder on a design that will allow easier fitting of the jet unit and far easier adjustment and repair. So many of these great boats have been lost over here because of the difficulty and cost in repairing them back to original. For a boatyard to work on them, was prohibitive in man hours, hence the loss of the boats.

Thank you for the discussion and I hope it helps others, I certainly have learnt a lot more, which will be passed on in this forum  :D BN
1953 Albatross
1958 Dowty Turbojet
1965 Mitcham Jetboat
1968 Mitcham OB