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Old 25-09-2019, 12:17   #31
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Re: Help me re-engineer my Catamaran lifting drive leg

Rumpi,

Thanks for your detailed response.

I had looked at trying to use a CV joint, but all solutions seemed to involve exotic parts or custom machining.
I like your idea of using parts from FWD car, but I think there would still be a lot of custom machining required.
I was trying to achieve constant velocity at the prop-shaft by using two U-joints at equal angles; Would that work ? Those components are available off the shelf and can be bolted together.
I am also under the impression that smaller angles for u-joints are better as long as the angle is greater than zero ?

The shaft currently swings sideways to avoid interfering with the rear ramp when it is lowered.
I don't quite understand how to implement the gimball you mentioned ?

Cheers,
JM.

Quote:
Originally Posted by Rumpi View Post
JM, since you have multiple problems I will try to explain this in steps so it's clear, and offer some solutions:
Problems:
1. Vibration: this has two sources wiplash of the long shaft and the U-joint not beeing CV.
2. Axial load: having the torque bearing after (or before if you count from the motor) articulation. U-joints can carry some axial load, but they are not happy doing it.
Solutions:
1. The elegant one is to replace the U-joint with a CV-joint designed to transmit all axial loads. Such things exist but are speciality items.
2. Move the torque bearing before the articulation and use a true CV-joint that does not carry axial loads. This will require articulation of the thrust block.
3. Remove whiplash by adequatly supporting the propshaft. This you already figured out but there is room for improvement.

I will deal with wiplash first. In order to support the shaft adequatly put a bearing every foot. If you want waterlubed bearings (cutless) you have to insure they get enough water, meaning a pressure system is needed injecting water at every bearing. A superior system is to use sealed roller bearings, in wich case you need to fit a waterseal at the prop end. Every single outboard and saildrive uses one so it's not as if it can't be done. Since most of the propshaft is not submerged you can also use a cutless at the prop end and sealed roller bearings for the rest. To assure a rigid shaft I propose: take two 1-2" fiberglass tubes and glue them togheter like the barrels of a shotgun. One will serve as water pickup, the other as exhaust. On this double tube you can now glue roller bearing carriers to support the driveshaft. Then the whole thing gets a fiberglass fairing glued onto it that aditionally stiffens the assembly and cuts the drag. Think of it as building a wingmast, rudder or daggerboard.

Now for the rest. The brutal option is to use the biggest U-joint you can find (something from a big truck maybe) to transmit the axial loads to the thrust block. It will still vibrate and be unpleasant but will last another circumnavigation. Not something I endorse but possible. You don't need another U-joint on the motor side, you already have a flexible coupling there.
You have to decide by yourself if you have the money for the elegant option.
Articulating the thrust block is not so complicated as it seems and can be acomplished cheaply. If the shaft is to only rotate up and down you simply mount the thrust block on a round bar that pivots on the frame in plain bearings. If you want it to also pivot sideways you need those plain bearings mounted on pivoting arms, basicly creating a gimball. The propshaft - motor connection is via a true CV joint, if necessary with additional length compensation. You can have the whole thing custom made in stainless steel or you can go cheap and use automotive components. Front wheel drive cars have all components you need on the front wheel. Power comes from the motor via a driveshaft with CV-joints at each end. The wheelhub is a bidirectional thrust block. The hubcarrier is made to rotate in two directions. A double whisbone suspension with kingpins would be the best for adapting to your boat since all you need to do is mount it on it's side.
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Old 25-09-2019, 17:33   #32
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Re: Help me re-engineer my Catamaran lifting drive leg

[Using a double cardan in place of your existing simple U-joint will reduce vibration. Achieving true cv depends on the exact geometry.

Using a FWD driveline will require 2 couplers and 4 brackets. One coupler to connect the transmission to the driveline. If you are lucky you can reuse the existing one. Second coupler connects the propshaft to the driveline trough the thrustblock. This is essentially a flange with a hollow stub. The flange gets bolted to the wheelhub using the wheel mounting holes and the propshaft is inserted into the stub and clamped or pinned. Anyone with a lathe can make it but yes, it is custom machining. It could also be a flat plate welded directly to the propshaft or other arrangements.
You also need brackets to mount the wishbones to. For that you cut the existing ones from the donor car and weld them to a plate that you bolt to the engine frame (the metal bar where the blue thrustblock sits now, and another one parallel to it). Depending on exact geometry it could be necessary to shorten or lengthen the driveshaft or modify the support frame.

The gimball function results from the double wishbone suspension geometry. I have attached two pictures, one a parts diagram to see what is actually there (it is a older model with kingpins, modern suspensions use ball joints instead) and a diagram explaining the function. The yellow part is the hub carrier, it pivots left-right so you can steer. The arms (blue and green) pivot up-down to allow the suspension to work. In the boat you mount it on it's side, the arms pivot port-starboard and the hub carrier pivots up-down. That is because you need more travel up-down than a ball joint provides. A suspension like the one in the other diagram could probably be mounted the normal way.
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Old 25-09-2019, 22:58   #33
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Re: Help me re-engineer my Catamaran lifting drive leg

@NahanniV

Have you considered contacting Gunther at Seascape as I mentioned in the other thread? His experience is Wharram specific too.

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Old 26-09-2019, 05:43   #34
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Re: Help me re-engineer my Catamaran lifting drive leg

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@NahanniV

Have you considered contacting Gunther at Seascape as I mentioned in the other thread? His experience is Wharram specific too.

Gunther seems to use hydraulic drives on long prop-shafts.
The drive is fixed to the shaft and pivots with it.

I'm just looking to rebuild my existing mechanical drive, with a few improvements if possible.
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Old 26-09-2019, 07:36   #35
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Re: Help me re-engineer my Catamaran lifting drive leg

Fair enough, at least you have explored this and understand the options
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Old 28-09-2019, 15:43   #36
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Re: Help me re-engineer my Catamaran lifting drive leg

Still refining the design....

Here is a diagram based loosely on ideas put forward here (TrentePiedes, JimBunyard).

It moves the thrust bearing to the lifting leg.
I would still use an automotive drive-shaft with length compensating spline and two u-joints to try to achieve constant velovity.

Comments welcome
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Old 14-10-2019, 09:57   #37
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Re: Help me re-engineer my Catamaran lifting drive leg

This is what I'm going to have fabricated:
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Old 02-01-2020, 16:36   #38
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Re: Help me re-engineer my Catamaran lifting drive leg

Moving ahead slowly with this project...
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Old 02-01-2020, 18:16   #39
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Re: Help me re-engineer my Catamaran lifting drive leg

Will be interesting to see the results, thanks for the update.

Watch out for sunburn, welding is a source of intense UV radiation... ask me how I know. (hint, south La. summer)
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Old 04-02-2020, 02:37   #40
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Re: Help me re-engineer my Catamaran lifting drive leg

hi John
You have a great boat, I went on board not long after Hans built and launched her and he showed me around.
I would be most interested to hear more of the progress with your shaft rebuild and the performance when installed. I have a 40 foot Wharram and have used a long shaft for several years connected to a hydraulic drive from the diesel engine. My shaft is a stainless tube 13.5 feet long with 60.33 mm OD and a wall of 2.77mm. There is a cutlass bearing on a short one inch diameter stainless shaft at the prop end and a UV joint at the upper end with a thrust bearing in the junction box with the hydraulic motor. There has been increased vibration of late especially at lower speeds due to some distortion of the shaft and I am intending to rebuild with an improved system.
Interestingly I saw a large Wharram in Vanuatu last year which had a shaft system very similar to the one you are building now. It had been in use for nine years and I understand was built and installed by Gunther at Seascape.
There was an outer stainless tube about 14 feet long supporting inside it a stainless drive shaft with a cutlass bearing near the prop end , a plain
brass (? ) bearing mid shaft with a grease nipple and a bearing , presumably a thrust bearing at the upper end before the Pivoting yoke and a UV centred on the pivot axis line , with direct drive from the diesel engine.
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Old 13-03-2020, 19:54   #41
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Re: Help me re-engineer my Catamaran lifting drive leg

Finally finished this project.
It runs smoothly.
So far I have about 15 hours of run time on it.
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Old 14-03-2020, 01:02   #42
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Re: Help me re-engineer my Catamaran lifting drive leg

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