Jump to content

Kelvins and Geaboxes


AndyV

Featured Posts

My last boat, which I sold a year ago, had a Kelvin K2. I loved the engine but never really liked the gearbox. I tried two gearboxes, one with the old "solid" clutch plates and one with Ferodo linings. My main issue was that both would "back out" of ahead gear because, I assumed, that unless I wanted to tow water skiers there was not enough thrust in the shaft two hold it in.

Now I am looking at the next boat and, as usual, I am starting with the most important question first. SWMBO can deal with everything else, I get to choose the engine?

Trouble is, I can't find anything I like more than the K2 or K3, or possibly a J3. I'm just not sure I want to trust the gearbox on a boat that we intend to cruise extensively.

Now the question that, I am not sure, might be an offensive one to some. Is it possible to fit a Kelvin with a different gearbox or even, dare I say, hydraulic drive? Has anyone already done this? I did think I might even get a hydraulic drive unit that would fit inside the Kelvin gearbox casings.

Any thoughts welcome.

Andy

Link to comment
Share on other sites

As you probably know a Kelvin box relies on the shaft being free to move. In head gear the thrust from the propeller pushes the clutch firmly into engagement. Rather than a tendency to come out of gear their are well attested stories of Scottish fishermen, when returning from extended trips when the engine had been in head gear for days at a time, travelling round in circles whilst hitting the shaft with a heavy hammer in order that the clutches would part company. where the engine had probably been in head gear for days at a time. Gardner with a similar box used a system where the box was held in gear with , I believe, an external screw. In order to fit a thrust box and cardan shaft when using a Kelvin F2 we developed a system where the box was locked into gear without using propeller thrust to hold it there. It is a system that needs further work but it does work. Regards, HughC.

Link to comment
Share on other sites

Similar problem on our J2 which we are just about coping with.

Phil Trotter at RW Davis at Saul Junction has I believe fitted a hydraulic drive to a Kelvin. He offered me this option recently, which I declined. I might need to go back some time if I can't find a more" traditional" solution?

 

The problem is compounded slightly by our clutch wheel being on the small side, so it needs a fair bit of effort to "torque" the clutch fully home before locking off with the lever. It's a bit of a handful when manoeuvring back and forth in a restricted area - involves 3 hands and a knee!

 

Chris Bennett at Pyrford Marina apparently had a hydraulic gearbox fitted to his previous K powered boat - I think he said it was fitted by Richard Powell (RLWP of this parish).

 

I'm a relative beginner on Kelvins, so I'll also also be interested in any advice from the seasoned Kelvin guys.

Link to comment
Share on other sites

We also have this problem on our J3. My eventual solution was to drill and tap a thread in the bracket that supported the gear change rod and put a thread in there with a bit of bar welded to it. Once wound into gear I lock the the rod with the screw. Simple, effective...as long as you remember to unlock before winding out of gear. Reverse gear tends to stay put! I think that they slip because at canal speeds the engine is running slowly. Out at sea, their designed environment, they would almost certainly run far faster and I've heard stories of sea going boats being stuck in head gear after prolonged running.

Link to comment
Share on other sites

Just a thought. Resolute is the title picture on my Facebook page. The red wheel visible inside the hatches is the gear change, the red rectangle just visible forward of it is the locking screw. A quick tweak and the rod is locked.

 

Dave

Link to comment
Share on other sites

I've been to the boat this morning and taken a picture of the locking arrangement, in case anyone was wondering...

 

Dave

Hi

 

I have a J2 and the gears work there way out as mentioned, I have a similar set up as the red wheel although I have a screw tapped into the back of the wheel and use a hook fixed to the hatch opening which locks it in place. A quick flick of the hook releases it when changing gear.

Link to comment
Share on other sites

I tried arrangements like this when I still had the boat, albeit they were a bit more crude involving bits of wood wedging the wheel off the hatch side. This did work most of the time but was awkward. I never liked this though as it meant that the thrust bearing (I guess that's what it's called) in the collar on the shaft would be under constant load and it wouldn't have been designed for that. I consoled myself that it would be easier and cheaper to fix than the clutch (though I might even have been wrong about that?) but I still have an aversion to using kit in a way that it wasn't designed for.

Link to comment
Share on other sites

40+ years experience of using Kelvin gearbox here. Unlined iron cone clutches on F2(15HP) and F4(30HP) engines, dropping out of gear on its own is never a problem, sticking in forward very occasionally , though that is because of some other external influence. It may be that you are not using the correct size (i.e. original) hand wheel for that particular model , the correct size allows the right torque be applied to engage the cones and squeeze the oil out from the clutch surfaces.

As regards hydraulic drive: the Kelvin gearbox is the most mechanically efficient design, being direct drive, that is, the prop is driven directly by the crankshaft,losses in the transmission therefore very low. I have used a hydraulic system with a Lister HR2 (29HP) and experience tells me that although the system is very robust, the efficiency is quite low- a lot of engine power goes into heating the hydraulic oil rather than turning the prop.The big advantage with hydraulic is if the prop stalls due to something fouling the blades, the pressure relief valves open and prevent any mechanical damage to the system. Also, the prop can be reversed at full power without damage, again the relief valves protect . But it's all quite complicated , much simpler to persist with the proper Kelvin set up.

Bill

Link to comment
Share on other sites

I'm with Billh on this one. After 27 years with a (lined clutch) J2 I've never had it work out of gear either before or after I had the clutches re-lined. If it comes out of gear either the prop shaft is too stiff or not straight, the engine is incorrectly aligned or the clutches are worn out of round. If it only does it in ahead it is just possible the box back bearing is misaligned. The shaft should be solid (no UJ's needed) and slide to and fro easily when not connected to the gearbox- if it doesn't then look at the pillow blocks supporting the shaft, the stern-tube packing and the general alignment again.

 

My problem is the opposite one. The box occasionally decides it would prefer to be in gear and winds itself in, usually forward. OK in a lock, usually, but a right bugger if you just hopped off to close a gate and have not taken a rope ashore!

 

Fitting a different (hydraulic or manual) gearbox is difficult. There is no flywheel at the rear to bolt a drive plate to and the crankshaft has a peculiar shaped end, to fit the ahead clutch, with big cut-outs for the two tapered keys on either side- no SAE splines in 1930's Scottish design offices, so it's very hard to get a drive plate on the crank directly- it would be a case of making a special. This then has to be thick enough to take the gearbox shaft as well as the tail end of the crankshaft.

 

A housing would need to be made for the drive. This also needs to deal with any oil that passes the rudimentary rear oil seal on the crankcase. It could bolt to the existing gear box mounting holes though. In removing the Kelvin gearbox you will also remove the starting handle.

 

If you fit a gearbox after the existing box then, apart from space and mounting considerations, you need to work out how to keep the existing box in gear when there is no thrust from the shaft. You will be able to remove the reverse chain and the upper shaft, provided again you are happy to do away with the hand start.

 

 

All in, it's much easier to find what is not right with the existing set-up.

 

N

Link to comment
Share on other sites

I am really interested to find that there are some (thanks billy and BEngo) who are not having the problem. I had always though that it was installation in a narrowboat, and so very low thrust most of the time, that was causing the problem.

The shaft on my boat did seem aligned and could be moved by hand but it did back out of gear with two different gearboxes. The problem was much worst in reverse though. The control wheel was certainly on the small side so perhaps this was the issue.

Link to comment
Share on other sites

  • 1 month later...

One disadvantage of a Kelvin gearbox, where the whole prop shaft moves backwards and forwards, is what happened to me this week.

I picked up what appeared to be a part of a wedding dress, a length of rope and a fender as I emerged from Blisworth. I put the engine in reverse and the tangled mass wedged itself between the blade and the stern post.

 

I thought I'd returned the shaft to the neutral position, but I hadn't realised that the engine was still in just in reverse gear as I stepped off the boat to chat to friends at SB. Fortunately, I was holding on to a line which I wrapped around a bollard. Otherwise the boat would gently have reversed itself back towards the tunnel.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.