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Kelvin j3


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Yes. The gear change on the reversing gear is a Reynolds chain gearwheel around the output driveshaft, which needs rotating approx two whole revolutions to go from fully ahead to fully astern. If you can easily devize a push-pull mechanism to do this, you're a better man than most boatyard engineers!

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24 minutes ago, MtB said:

Yes. The gear change on the reversing gear is a Reynolds chain gearwheel around the output driveshaft, which needs rotating approx two whole revolutions to go from fully ahead to fully astern. If you can easily devize a push-pull mechanism to do this, you're a better man than most boatyard engineers!

Other than take off the gearbox and replace it with a hydraulic drive you mean...!


Alec

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Before you buy,  inquire if the gearbox has lined clutches or metal to metal ones.  The former are fine.  The latter can be a right b@st@rd to get out of gear after a spell in ahead gear.  It can be disconcerting to approach a lock or swing bridge and find that there is no elegant  way to stop quickly.

 

N

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33 minutes ago, agg221 said:

Other than take off the gearbox and replace it with a hydraulic drive you mean...!


Alec

 

True, I have a Velvetdrive on the back of my K2! 

 

Still have a vestigial wheel to control it though :)

 

 

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15 hours ago, MtB said:

If you can easily devize a push-pull mechanism to do this, you're a better man than most boatyard engineers!

The principle would be fairly simple:  a suitably high helix angle nut driven by a matching threaded rod which in turn rotates a chain wheel.  Something like the insides of a Hatton paddle gear.  Pull and push the rod rotates the nut.

 

A Bugger to make without some fairly specialist kit,  though one might possibly be able to adapt  a worm type steering box from an elderly vehicle.

 

 An alternative would be a rack and  pinion, but that would give you the problem of changing the plane of rotation between the pinion and the Kelvin gearbox.  Bevel gears would be needed.

 

OTOH, the gear wheel is easy to get used to, and it will teach you to manoeuvre gently and to think ahead. It certainly is not as quick to use as a push pull set up.

N

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3 minutes ago, BEngo said:

a suitably high helix angle nut driven by a matching threaded rod which in turn rotates a chain wheel.  Something like the insides of a Hatton paddle gear. 

Wear a blue shirt and a life jacket when you liberate the Hatton paddle gear internals. Put a yellow CaRT sack over the remains when you leave.

The perfect crime. 😀

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Oates has a J2 with a hydraulic drive. We took it off the Trent on Saturday, on to the T&M which was our first real outing with it. The rod hydraulic drive transition works very well - to the point where stopping was surprisingly quick even allowing for letting the engine revs drop. It doesn't half shift in reverse too! The wheel geared approach would require a bit more planning and thinking but I don't think it would take long to get used to.

 

Alec

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Wheel gear change was standard on all the Grand Union boats built with Russell Newbery and National engines fitted with a Brunton's gearbox. Many of those boats still have it fitted, whether still connected to a Brunton box or adapted to control other models. It's not hard to use, and as BEngo says, teaches you to think in advance about your manoeuvring. Just because you can bang a lever or rod operated box straight from forward to astern doesn't mean you should!

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The  wheel change means you don't run the risk of knocking the  Chief Engineer/ERA  out with  the push pull system😀.

Wheel is more positive with less slack than the various linkages and levers 

 

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6 hours ago, BEngo said:

The principle would be fairly simple:  a suitably high helix angle nut driven by a matching threaded rod which in turn rotates a chain wheel.  Something like the insides of a Hatton paddle gear.  Pull and push the rod rotates the nut.

 

 

I thought the idea of a worm drive was to prevent the worm turning the nut which is why vices and bolts work

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I ran a J3 in my old boat for almost 20 years. Lovely motor, the measured triplet on tick over was delightful. The gear change was by wheel, never a problem. The engineer who fitted it preferred it to the Gardners he usually installed.

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14 hours ago, ditchcrawler said:

I thought the idea of a worm drive was to prevent the worm turning the nut which is why vices and bolts work

It usually is, hence why I said "a suitably high helix angle", and why it is hard to make.  Hatton  paddles are one example where the weight of the paddle and  threaded rod drives the nut whist the paddle is self-closing.

Early motor cars also had worm and wheel drive to their back axles and they have a suitable high helix angle  worm/wheel to allow the inertia  of the vehicle to drive the shaft on overrun.  Otherwise  the back wheels would stop every time the throttle was closed.

N

 

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3 hours ago, BEngo said:

It usually is, hence why I said "a suitably high helix angle", and why it is hard to make.  Hatton  paddles are one example where the weight of the paddle and  threaded rod drives the nut whist the paddle is self-closing.

Early motor cars also had worm and wheel drive to their back axles and they have a suitable high helix angle  worm/wheel to allow the inertia  of the vehicle to drive the shaft on overrun.  Otherwise  the back wheels would stop every time the throttle was closed.

N

 

 

As would the engine, unless the clutch was depressed too!! 

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3 hours ago, BEngo said:

It usually is, hence why I said "a suitably high helix angle", and why it is hard to make.  Hatton  paddles are one example where the weight of the paddle and  threaded rod drives the nut whist the paddle is self-closing.

Early motor cars also had worm and wheel drive to their back axles and they have a suitable high helix angle  worm/wheel to allow the inertia  of the vehicle to drive the shaft on overrun.  Otherwise  the back wheels would stop every time the throttle was closed.

N

 

The long helix should work, but you may need a rather long throw on the rod. The longest I have encountered on a rod was about 2' from full forward to full reverse, which was quite tricky to feel for inside the cabin roof when wanting to reverse.

 

I think if I was trying to do this, I would go for either rack and pinion or a con-rod onto a wheel, the latter needing to be put round a 4:1 ratio to gear it up for two full turns. I would also be inclined to look at pulleys and v-belts to take the rotation down from the control rod to the engine as they the half twist could be introduced directly without any gearing.

 

In practice, I would leave it as wheel and wheel!

 

Alec

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On 04/10/2021 at 11:25, Jen-in-Wellies said:

Wear a blue shirt and a life jacket when you liberate the Hatton paddle gear internals. < snip >

I was wearing a blue T-shirt and a life jacket when I came down Hatton last month.

 

Got mistaken for a locksmurf.........twice!

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50 minutes ago, Victor Vectis said:

I was wearing a blue T-shirt and a life jacket when I came down Hatton last month.

 

Got mistaken for a locksmurf.........twice!

You must have been drinking a mug of tea and looking gormless. 😄

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1 hour ago, jaime66 said:

So wheel and wheel it is then ! cant bloody wait !!!! 

 

 

Yes, it really is no trouble at all. 

 

So you're getting a J3 then?! Congratulations, I'm well jealous!!!! 👍

 

 

Edited by MtB
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