Kelvin

[Timleech]

 

My J transmission creeps out of engagement when in ahead. Seems to be working ok but a few hundred metres up the cut you realise the boat seems to be going ever slower, and the engine getting quieter. The reason being that the clutch is slipping and the prop shaft is only turning at about 75% of engine speed. Nipping the gearwheel properly back into ahead position turns out to be necessary. Dick Goble mentioned to me this happens to his J transmission and he carries a weight to hang on the gear wheel to keep it engaged. I now do the same.

 

My question is though, do they ALL do this or is it a fault? Surely it's a fault? Does anyone know how to cure it please? I'm guessing it's going to be expensive.

 

Many thanks.

 

Mike

 

I'm not familiar with that type of Kelvin gearbox (RG12 & RG32 are more my thing), but a lot of that general style of box rely on propellor thrust to keep the clutches in engagement. If there's a reduction box, sometimes helical gears in the box transfer some thrust across between the low- & high- speed shafts.

 

Tim

Edited December 19, 2010 by Timleech

[koukouvagia]

 

 

My question is though, do they ALL do this or is it a fault? Surely it's a fault? Does anyone know how to cure it please? I'm guessing it's going to be expensive.

 

 

My K2 has this habit too. I use a cut down lead window weight which hangs on the gear wheel. I'm not sure what causes the creep, but it only occurred on mine after I fitted a centaflex coupling. I've learnt to live with it and regard it as just another example of a Kelvin idiosyncrasy.

[MtB]

My K2 has this habit too. I use a cut down lead window weight which hangs on the gear wheel. I'm not sure what causes the creep, but it only occurred on mine after I fitted a centaflex coupling. I've learnt to live with it and regard it as just another example of a Kelvin idiosyncrasy.

 

Interesting. Yours is K transmission but mine's a J! Does anyone have a Kelvin that DOESN'T do this?? I also have a Centaflex coupling.

 

I'd quite like to obtain a second J transmission as the clutch cones in mine are almost worn out. I'd like one to dismantle and rebuild at my leisure rather than have the boat out of action for however many weeks/months it ends up taking for the research, metal-spraying and regrinding, bearing replacement, reassembly etc. Does anyone know of one for sale?

 

Tim,

 

It's a 1:1 transmission with cone clutches, and yes it supposedly relies on prop shaft thrust to stay in gear. The problem is that mine clearly does not, despite the prop shaft sliding correctly.

 

My knowledge of how J & K transmissions work is currently virtually zero, but I need to understand. Once I understand properly how they work I'm expecting the answer to become clear. I'll get up to speed on this soon. (Geddit? Haha!) I'm just beginning my research now :-)

 

Mike

[Davidss]

An interesting situation.

What I know about cone clutches comes from experience in cars, specifically overdrives in the 1960+70's, although I also know they were used in early cars, when they were still working out how to make clutches when the linings were generally cork or leather.

 

A cone clutch doesn't have a spring loaded cover to keep the two plates (cones) engaged. In order to get the cones to grip each other you made sure there was a 'noticable' speed difference between the two cones as they were brought into engagement, AND you made sure there was enough load on the slow cone to ensure it wouldn't be easily accelerated as the fast cone hit it. The inner cone would therefore screw into the outer cone, and it was the force developed across the clutch as this engagement took place which ensured the cones were joined tightly together, and did not slip.

In a car the load on the slow cone was the weight of the car (which had to be accelerated), and provided the tyres didn't spin on the ice, everything worked well. The instructions with the overdrive specifically warned AGAINST easing the throttle as the overdrive was selected as this would reduce the loading across the cones as they engaged.

 

Now put that into your boat experience.

The load on the slow cone is a prop which slips in the water, and to make it worse you fit a shock absorbing drive which cushions the shock load as the two cones meet. I also suspect that most Kelvin owners are mechanically sympathetic and thus engage gear gently, with an engine at slow speed.

So what's that, four reasons why your cone clutch doesn't engage properly.

You can also see why a weight on the gear wheel (clutch engagement mechanism) is necessary to keep the cones in tight engagement.

 

You are not going to like my suggested answer, because it involves removing the cush drive, doubling the engine speed before you engage gear, and winding the gear (clutch) into engagement with some vigour. You will know it's right when the drive train jolts as the drive is taken up. And yes, once engaged you may need to reduce engine speed to suit the boat handling requirements.

 

Engaged properly, cone clutches last an awful long time. Let them slip and you find they quickly wear out because they have so little friction area.

 

Or you carry on with the weight on the gear change mechanism, but at least now you know what it's doing, and why it's necessary.

 

And no, this brick boat doesn't have a Kelvin engine and whatever gearbox - I've explained where my knowledge comes from and if that isn't good enough for you I can only hope you enjoy spending time and money on your clutch changes :-)

 

HTH

[Heffalump]

Does anyone know where I can find out all about the Kelvin series of engines? Like a Kelvin Wikipedia. Yes, I did try Wikipedia!

[Timleech]

Does anyone know where I can find out all about the Kelvin series of engines? Like a Kelvin Wikipedia. Yes, I did try Wikipedia!

 

You can look here for a start:-

 

http://www.sky-net.org.uk/kelvin/diesel/index.html

 

Tim

[MtB]

Does anyone know where I can find out all about the Kelvin series of engines? Like a Kelvin Wikipedia. Yes, I did try Wikipedia!

 

Mike Skyner's site is about the nearest thing to a Kelvin wiki you're going to find....

 

http://www.sky-net.org.uk/kelvin/diesel/index.html

 

 

Mike

[Heffalump]

Thanks chaps

[MtB]

An interesting situation.

What I know about cone clutches comes from experience in cars, specifically overdrives in the 1960+70's, although I also know they were used in early cars, when they were still working out how to make clutches when the linings were generally cork or leather.

 

A cone clutch doesn't have a spring loaded cover to keep the two plates (cones) engaged. In order to get the cones to grip each other you made sure there was a 'noticable' speed difference between the two cones as they were brought into engagement, AND you made sure there was enough load on the slow cone to ensure it wouldn't be easily accelerated as the fast cone hit it. The inner cone would therefore screw into the outer cone, and it was the force developed across the clutch as this engagement took place which ensured the cones were joined tightly together, and did not slip.

In a car the load on the slow cone was the weight of the car (which had to be accelerated), and provided the tyres didn't spin on the ice, everything worked well. The instructions with the overdrive specifically warned AGAINST easing the throttle as the overdrive was selected as this would reduce the loading across the cones as they engaged.

 

Now put that into your boat experience.

The load on the slow cone is a prop which slips in the water, and to make it worse you fit a shock absorbing drive which cushions the shock load as the two cones meet. I also suspect that most Kelvin owners are mechanically sympathetic and thus engage gear gently, with an engine at slow speed.

So what's that, four reasons why your cone clutch doesn't engage properly.

You can also see why a weight on the gear wheel (clutch engagement mechanism) is necessary to keep the cones in tight engagement.

 

You are not going to like my suggested answer, because it involves removing the cush drive, doubling the engine speed before you engage gear, and winding the gear (clutch) into engagement with some vigour. You will know it's right when the drive train jolts as the drive is taken up. And yes, once engaged you may need to reduce engine speed to suit the boat handling requirements.

 

Engaged properly, cone clutches last an awful long time. Let them slip and you find they quickly wear out because they have so little friction area.

 

Or you carry on with the weight on the gear change mechanism, but at least now you know what it's doing, and why it's necessary.

 

And no, this brick boat doesn't have a Kelvin engine and whatever gearbox - I've explained where my knowledge comes from and if that isn't good enough for you I can only hope you enjoy spending time and money on your clutch changes :-)

 

HTH

 

David,

 

Thanks for your insight, much appreciated. I was never rich enough as a youngster to afford a car with overdrive!

 

I'm entirely happy to listen to your wisdom. I'd like to air the questions that pop up in my mind having read your post through. Not because your knowledge is 'not good enough', but because I want to understand properly.

 

1) The cone faces in my gearbox clutch are steel. Is there a lubrication medium in between the cones (i.e. gearbox oil) or do they engage 'dry'?

 

2) What angle is the taper on the cones likely to be? Presumably considerably steeper than a Morse taper or they would lock securely and never disengage, but the principle appears to be similar from what you say.

 

3) You suggest the Centaflex is stopping the cones engaging properly. This isn't quite consistent with the symptoms our clutch displays. I have actually tried the stuff you suggest, i.e. shoving it robustly into gear at sometimes quite high engine speeds. The gearbox carries a brass plate warning against doing this! It seems to engage very well in fact often it is very difficult to disengage from ahead after a firm engagement. The problem comes after five minutes of running it ahead. No matter how securely I make sure it is in gear, five minutes later the gearwheel will have rotated 5 to 10 degrees back and the clutch will have started to slip badly when it wasn't initially. The problem seems not to be getting it engaged, but making it STAY engaged over long periods of time. So, is subsequent disengagement of a previously securely engaged cone clutch still under load a problem on classic car overdrives?

 

I'll absorb what you've sold more fully over the next day or so then discuss it my mate who lives, breathes and repairs classic cars for a living. He has some amazing stuff in his workshop! He'll be very familiar with overdrive cone clutches and may have more insights to offer.

 

Thanks again,

 

Mike

[Timleech]

 

 

1) The cone faces in my gearbox clutch are steel. Is there a lubrication medium in between the cones (i.e. gearbox oil) or do they engage 'dry'?

 

2) What angle is the taper on the cones likely to be? Presumably considerably steeper than a Morse taper or they would lock securely and never disengage, but the principle appears to be similar from what you say.

 

3) You suggest the Centaflex is stopping the cones engaging properly. This isn't quite consistent with the symptoms our clutch displays. I have actually tried the stuff you suggest, i.e. shoving it robustly into gear at sometimes quite high engine speeds. The gearbox carries a brass plate warning against doing this! It seems to engage very well in fact often it is very difficult to disengage from ahead after a firm engagement. The problem comes after five minutes of running it ahead. No matter how securely I make sure it is in gear, five minutes later the gearwheel will have rotated 5 to 10 degrees back and the clutch will have started to slip badly when it wasn't initially. The problem seems not to be getting it engaged, but making it STAY engaged over long periods of time.

 

 

Mike

 

Those symptoms suggest to me that the two cones are running slightly out of line with one another. I expect there's a long bronze bush carrying the output shaft where it leaves the box and allowing it to move fore & aft to engage/disengage the clutches. If this is a bit worn the clutches won't necessarily be truly co-axial, and a flexible coupling will allow the output to oscillate around the centre line and work the clutch cones apart.

 

Tim

[koukouvagia]

Those symptoms suggest to me that the two cones are running slightly out of line with one another. I expect there's a long bronze bush carrying the output shaft where it leaves the box and allowing it to move fore & aft to engage/disengage the clutches. If this is a bit worn the clutches won't necessarily be truly co-axial, and a flexible coupling will allow the output to oscillate around the centre line and work the clutch cones apart.

 

Tim

That sounds logical. We now need to hear from Kelvin owners without Centaflex couplings.

[Davidss]

I can't comprehensively answer points 1, 2, and 3, because my experience doesn't go into that much detail.

1/ I don't know.

2/ I don't know the exact angle, and your gearbox clutch predates my direct experience, but I'd expect the taper to be much steeper than a Morse taper, it certainly was in the overdrive.

3/ What I was trying to suggest was that instead of the slow cone being held against a hard stop (the tyres on the ground) the slow cone was held against a soft stop (the flex drive) so the fast cone didn't have a fixed surface to screw into. It wasn't that the flex drive 'prevented' engagement, it's that the flex drive absorbed the shock loading which (I feel) is a necessary part of the engagement procedure. Perhaps it's all in the terminology.

 

"It seems to engage very well in fact often it is very difficult to disengage from ahead after a firm engagement."

I think your experience after 'firm engagement' supports my suggestions. I'd expect it to require more effort to disengage (compared to disengagement after a soft engagement).

 

"I have actually tried the stuff you suggest, i.e. shoving it robustly into gear at sometimes quite high engine speeds. The gearbox carries a brass plate warning against doing this!".

Could be a question of degree (how high is high compared to normal speed), and I'm not familiar with the detail of the engine or box. Re the brass plate, perhaps the self disengaging clutch was a known problem, and the boatmans 'solution' was also known. Perhaps the box isn't strong enough to withstand the abuse if the procedure was carried out to excess, all day every day. 'Excessive' being an engine speed of twice tickover, rather than just above tickover. I'm not being specific there, just making a comparison.

 

"is subsequent disengagement of a previously securely engaged cone clutch still under load a problem on classic car overdrives?"

Hmmm, define a Classic car. In the overdrive I was used to, if the engagement pressure was increased then stiffer disengagement (throwout) springs had to be fitted. I believe in older cars (Veteran?), where the main clutch was sometimes a cone clutch, then yes, I think they could require 'firm' pressure to disengage.

 

The suggestions from Tim Leech seem reasonable.

 

Someone who works on Classic Cars for a living outguns my 'qualifications' :-)

Does he work on Classic cars, or Veteran cars?

 

Good Luck, sorry I can't be more precise.

[MtB]

That sounds logical. We now need to hear from Kelvin owners without Centaflex couplings.

 

I agree. Given that my Centaflex is fitted between the plumber block at the forward end of the propshaft, and the transmission output shaft, there is nothing to stop the output shaft waggling about in the 30 thou or so clearance it has in its white metal bearing. I'll investigate getting a solid component made to replace the Centaflex and see if the problem disappears.

 

Another possibility is plumber block alignment. Given the shortcuts I've found in other areas of the engine installation I've no confidence that the plumber block will have been aligned properly, or even at all. I think I need to check this urgently!

 

Mike

[MtB]

David,

 

Could be a question of degree (how high is high compared to normal speed), and I'm not familiar with the detail of the engine or box.

 

We're talking slow speed engines. By 'high' speed I mean 300rpm. Tickover is 160rpm, max speed 750 rpm.

 

 

Hmmm, define a Classic car.

 

A car made between, say, 1955 and 1985 counts as 'classic' to me. Or alternatively, anything old enough to have come with the option of an overdrive unit bolted onto the tail of the gearbox instead of a five (or six) speed box in the first place.

 

 

Someone who works on Classic Cars for a living outguns my 'qualifications' :-)

Does he work on Classic cars, or Veteran cars?

 

Good Luck, sorry I can't be more precise.

 

Classics, definitely. Last time I was there he had a Sunbeam Lister Tiger in his workshop (fastback body), two 1970s Ferraris, a Ford Anglia 1200, Nissan Skyline and a couple of Beetles. And a load of normal stuff in the yard.

 

Dunno when I'll be over there next though. Next time my van breaks down I expect :-)

 

Mike

[billh]

Interesting. Yours is K transmission but mine's a J! Does anyone have a Kelvin that DOESN'T do this?? I also have a Centaflex coupling.

 

Mike

Hi,

We run a Kelvin F4 , the gearbox arrangement is similar to the J , the cone clutches are exactly the same size as the J (but not interchangeable!). It never drops out of gear under way unless it wasn't engaged properly in the first place.You can feel a definite "bite" as the clutches engage and sometimes if the engine is used at full power the clutches stick and you need to tug the change wheel quite hard to dis-engage. There is a flexible coupling in the drive train and apart from taking some of the shock out of engaging gear , it does not have any effect.

During the engage process , there is gearbox oil on the clutch surfaces which has to be squeezed out , this cushions the shock as well.I strongly suspect that you are being too gentle with the change wheel - slow the engine down to idling turn the wheel and apply enough leverage until the wheel goes solid, so it won't turn any more. How many turns of the wheel between forward & reverse? If it's more than one and a half, the clutches are worn , but you can get more life from them by inserting a suitable sized washer behind the reverse clutch.

Speaking of which- if anyone has a spare J type reverse clutch ( the one with the gear teeth integral) in reasonable nick I would be very interested.

Bill

[Timleech]

I agree. Given that my Centaflex is fitted between the plumber block at the forward end of the propshaft, and the transmission output shaft, there is nothing to stop the output shaft waggling about in the 30 thou or so clearance it has in its white metal bearing. I'll investigate getting a solid component made to replace the Centaflex and see if the problem disappears.

 

Another possibility is plumber block alignment. Given the shortcuts I've found in other areas of the engine installation I've no confidence that the plumber block will have been aligned properly, or even at all. I think I need to check this urgently!

 

Mike

 

There could be a clue there

 

Tim

[BEngo]

David,

 

Thanks for your insight, much appreciated. I was never rich enough as a youngster to afford a car with overdrive!

 

I'm entirely happy to listen to your wisdom. I'd like to air the questions that pop up in my mind having read your post through. Not because your knowledge is 'not good enough', but because I want to understand properly.

 

1) The cone faces in my gearbox clutch are steel. Is there a lubrication medium in between the cones (i.e. gearbox oil) or do they engage 'dry'?

 

The cones run in the gearbox oil. When they engasge they squeeze the oil out from between them. There are two sorts of J/K box- the original unlined version, which you clearly have and a version where the cones are lined witha Ferodo type of material rivetted on. The two sets have different drawing numbers so I assume that an unlined set of cones can only be replaced with a complete lined set.

 

2) What angle is the taper on the cones likely to be? Presumably considerably steeper than a Morse taper or they would lock securely and never disengage, but the principle appears to be similar from what you say.

 

From memory the included angle is about 30 degrees. The metal cones were renowned for sticking IN gear after a long run and many thrust boxes bear the signs of having been hammered out of gear at the end of a day's fishing. 3) You suggest the Centaflex is stopping the cones engaging properly. This isn't quite consistent with the symptoms our clutch displays. I have actually tried the stuff you suggest, i.e. shoving it robustly into gear at sometimes quite high engine speeds. The gearbox carries a brass plate warning against doing this! It seems to engage very well in fact often it is very difficult to disengage from ahead after a firm engagement. The problem comes after five minutes of running it ahead. No matter how securely I make sure it is in gear, five minutes later the gearwheel will have rotated 5 to 10 degrees back and the clutch will have started to slip badly when it wasn't initially. The problem seems not to be getting it engaged, but making it STAY engaged over long periods of time. So, is subsequent disengagement of a previously securely engaged cone clutch still under load a problem on classic car overdrives?

 

What I think is happening is that the cones are not properly in alignment- the 30 thou you write below of as play in the back bearing may be combining with the flexibility of the Centaflexto allow the cones to meet slightly off a strainght line. As a result the male cone will' wobble' in the female and tend to work itself out. This wobbling also wears the cones out of shape and will eventually make the problem a lot worse. I have a lined J box witha solid shaft and apart from when I get a load of cr@p between the prop boss and the stern post it puts itself into gear and stays there. No weights, no springs, just the thrust. The gearwheel will rotate back about 1/4 turn, but it is supposed to do that, to take the load off the thrust box.

 

 

Another possibility is that the cones are now so badly worn that there is not enough shaft travel to get them properly engaged before the collar on the output shaft has gone as far forward as it can. How thick is the gasket between the gearbox and the crankcase? If this is too thick it will space the cones further apart and need more shaft travel to get ahead gear properly.

 

I'll absorb what you've sold more fully over the next day or so then discuss it my mate who lives, breathes and repairs classic cars for a living. He has some amazing stuff in his workshop! He'll be very familiar with overdrive cone clutches and may have more insights to offer.

 

Thanks again,

 

Mike

 

 

See comments interspersed above in italics.

 

The Kelvin Box is pretty simple: Two back to back male cones sit on the output shaft ( called a clutch shaft in the parts book) between two female cones. The front female cone is directly driven by the crankshaft whilst the rear female cone is driven off an upper shaft. This upper shaft is driven by a double-row chain from the crankshaft at the front and drives the reverse cone through gears at the back. The reverse cone thus goes round the opposite way to the front (ahead) cone. There are thrust bearings in the crankcase for the ahead thrust and at the back of the gear case for the astern thrust.

 

The clutch shaft runs in a long whitemetal bearing in a bush at the back of the box. The outside of the bush has a coarse thread ( 2 tpi I think) on which the bronze thrust box turns. There is a collar on the clutch shaft which is pushed and pulled by the thrust box.

 

When the thrust box is rotated clockwise it moves forward and pushes the ahead male cone into the ahead femal cone on the crank. As the shaft starts to turn the prop thrust then slides the shaft forward to complete the engagement. The thrust box will follow the shaft if you keep turning it, but it doesn't have to- the prop will do the work.

 

When the thrust box is rotated anti clockwise it first pull the ahead cones apart, then pushes the astern cones together. Once again, as the prop starts to turn the astern thrust completes the engagement by pulling the shaft fully back into the female cone.

 

My lined box has been working like this for 21 years now without problems, except when I had it relined. The new linings were of such thickness that there was a very small mid-gear position and the slightest nudge of the gear wheel was sufficient to start the prop turning and engage either ahead or astern. A little wear soon eased the problem, though it has not entirely gone away.

 

I note you may be looking for a box to refurbish and then replace yours. If you buy another box do ensure that you get the ahead cone and chainwheel from off the crankshaft with it. Otherwise you will need your original to be removed to be matched to the gearbox male cones, which would rather negate the idea of a drop-in replacement!

 

When removing the ahead cone from the crankshaft it is secured with a FO big nut (2in BSP IIRC) and the drive is through two pairs of keys on either side. The keys are arranged as folding wedges and you belt the top one forwards into some lead and that pushed the bottom one backwards, freeing up the clutch cone. The arrangement is shown in the J manual, together with a warning not to refit the keys without some new lead key stops. this is a serious warning. If the clutch and keys are fitted without the stops it all goes together nicely, but it is an absolute bar steward to get them apart again- the bottom key , instead of separating, just goes forward with the top one, or there's no room to drive the top key away from the bottom key. If you just pull the cone then the folding wedges work like they are meant to and the whole thing stays firmly put. You end up trying to drill out one of the keys on either side. The access to do this is not good and it means making new key pairs! Been there (but not on my own engine), done that, have the t-shirts. I have a mould for the lead key-stops should you need any and original Kelvin drawings of the back end of the box and whitemetal bearing.

 

Drop me a PM if you wish to talk and I'll send you my phone number.

 

Regards

 

N

[MtB]

See comments interspersed above in italics.

 

The Kelvin Box is pretty simple: <snip>

 

Drop me a PM if you wish to talk and I'll send you my phone number.

 

Regards

 

N

 

 

Thanks for a most excellent reply BEngo. Very much appreciated. I'm still digesting it, too much information to swallow whole! :-)

 

Thank you for your kind offer to speak on the phone about it. I'll PM you in a while if I may, once I've learned in preparation as much as I can from looking and reading.

 

Have a good Christmas!

 

Mike

[MtB]

Well I think I may have solved the problem of the clutch cones partially disengaging. I'm ashamed to admit it but on checking the gearbox oil level, I found there was none in there.

 

After adding 1/6th gallon of SAE 30 it seems to stay in gear on testing (running against the pontoon as the marine is still totally iced up). I'll report again once get the chance to take the boat out on the mainstream for a proper run.

 

Anyway I'm also here to report I've finally (more or less) finished the engine installation and engine room and I REALLY pleased with it! I've just posted more videos on youtube of the finished engine room than a normal person would want to watch, so here's a link to my youtube channel so anyone still interested can have a look :-)

 

http://www.youtube.com/user/MiketheBoilerman

 

Mike

 

(P.S. I posted a link to my channel because I still can't see how to post a link to a single video without the whole video itself becoming embedded in the post. How do I do that? Can anyone explain?)

Edited January 2, 2011 by Mike the Boilerman

[Derek R.]

Very nice Mike. Looks like you have a decent length of swim there.

[MtB]

Very nice Mike. Looks like you have a decent length of swim there.

 

Thank you Derek.

 

Swim is slim and exactly 4m long. Boat still won't steer in astern though!

 

The engine room (and hence the engine) is rather too near the stern, giving the impression of a very long swim. The back cabin measures 5'6". The K1 weighs 1 1/4 tons and the uxter plate is 3" under water with no ballast at the stern, and more than enough in the bows.

 

Mike

[Derek R.]

'Yarmouth' was (is) 60' long and I had an 18' swim built when the 'surgery' was carried out in '86. This was typically vertical plate with no reverse tumblehome to the chine. She wouldn't steer much in astern either, though went forward beautifully and stopped quickly. Yet 'Sentinel' at 70' has a little less swim, but rather barrel shaped down to the chine - it steered perfectly in astern. There are several elements involved I feel, such as rudder area, prop diameter, pitch, and chosen speed of prop rotation. Depth of water too. 'Tycho' is barrel shaped below water line with a 10' swim (or thereabouts) but only now and then will she go exactly where steered astern. Being only 45' in length doesn't help. Length, I feel, stabilises the fore end and being shorter is inclined to want to whip about a bit. She's also deeper at the back which doesn't help - the 'pivotal point' is further back.

 

Derek

[MtB]

'Yarmouth' was (is) 60' long and I had an 18' swim built when the 'surgery' was carried out in '86. This was typically vertical plate with no reverse tumblehome to the chine. She wouldn't steer much in astern either, though went forward beautifully and stopped quickly. Yet 'Sentinel' at 70' has a little less swim, but rather barrel shaped down to the chine - it steered perfectly in astern. There are several elements involved I feel, such as rudder area, prop diameter, pitch, and chosen speed of prop rotation. Depth of water too. 'Tycho' is barrel shaped below water line with a 10' swim (or thereabouts) but only now and then will she go exactly where steered astern. Being only 45' in length doesn't help. Length, I feel, stabilises the fore end and being shorter is inclined to want to whip about a bit. She's also deeper at the back which doesn't help - the 'pivotal point' is further back.

 

Derek

 

Hmmmm yes, reversing and stopping, both things my boat now does apallingly.

 

Stopping used to be brilliant with the BD3 tug engine. The boat would stop from full speed in half a boat length sending a noticable swell up ahead of us. Now the narrow-bladed 'Kelvin format' prop made for our engine by Crowther has virtually no bite at all in astern. Just before the ice closed in I actually hit the pontoon we moor against because I engaged reverse too late - about a length away at a slow walking pace and the boat just would not stop in time. This behaviour is very disappointing. I might ring Crowthers and see if they have anything to suggest.

 

This boat has never steered in reverse though. Odd because at 68ft I expected better in comparison to our previous boat, a 40ft Black Country Narrowboats hull with about 7ft of swim which steered superbly backwards. I could steer backwards for hundreds of yards before eventually cocking it up provided I kept up a good pace. But in this current boat, no directional control whatsoever despite the fine swim. Its as though fat stubby swims actually help steering in astern.

[Derek R.]

Clearly many factors involved! For the record, Yarmouth had a 24" diam. x 27" pitch equipoise prop, driven by a Petter PD2 rated 20hp @ 1500rpm, with 3:1 reduction on the box.

[Speedwheel]

'Yarmouth' was (is) 60' long and I had an 18' swim built when the 'surgery' was carried out in '86. This was typically vertical plate with no reverse tumblehome to the chine. She wouldn't steer much in astern either, though went forward beautifully and stopped quickly. Yet 'Sentinel' at 70' has a little less swim, but rather barrel shaped down to the chine - it steered perfectly in astern. There are several elements involved I feel, such as rudder area, prop diameter, pitch, and chosen speed of prop rotation. Depth of water too. 'Tycho' is barrel shaped below water line with a 10' swim (or thereabouts) but only now and then will she go exactly where steered astern. Being only 45' in length doesn't help. Length, I feel, stabilises the fore end and being shorter is inclined to want to whip about a bit. She's also deeper at the back which doesn't help - the 'pivotal point' is further back.

 

Derek

 

Sentinel goes forward quite well too! Interesting you saying about length as the best boat I ever steered in reverse was when I had Usworth. It went exactly where you wanted it to - could almost do figure 8s in the marina (not that I tried of course!). It was only 33ft long but would go backwards as well as it went forwards. It was well ballasted and pivoted nicely in the middle.