BETA BJ3 v BETA 43

[nicknorman]

It will stop our boat dead in half the length that a Beta 43 takes for a similar boat. I've tried on friends boats.

 

But that is nothing to do with the engine and everything to do with the gearbox ratio, prop size and to a lesser extent hull shape.

[trackman]

But that is nothing to do with the engine and everything to do with the gearbox ratio, prop size and to a lesser extent hull shape.

Of course Nick it is to do with what you say. But then our JD3 throws a 22x22 prop which a less torquey engine couldn't handle. So it is to do with the engine as well.

[FadeToScarlet]

Of course Nick it is to do with what you say. But then our JD3 throws a 22x22 prop which a less torquey engine couldn't handle. So it is to do with the engine as well.

A less torquey engine could handle it with the correct gearbox.

[nicknorman]

Torque curves of each engine:

 

 

 

The 43 has significantly more torque and power at the lower end of the rpm range enabling it (with the right gearbox ratio) to swing a bigger prop than the JD3.

Edited August 29, 2015 by nicknorman

[dmr]

Torque curves of each engine:

 

image.jpg

 

image.jpg

 

The 43 has significantly more torque and power at the lower end of the rpm range enabling it (with the right gearbox ratio) to swing a bigger prop than the JD3.

 

A friend has a modern engine with a 3:1 box and a big prop, and it works very well, but you do have the drawback(s) of higher engine revs at cruising speed.

 

Looking at your torque curves is interesting.

The torque absorbed by a prop rises with speed (square law???) so an optimum boat engine torque curve would have peak torque at maximum speed (pretty much what the JD3 does). With the Beta 43 if we choose the prop to match peak torque then that will limit the engine speed to that speed, and likely give excess speed at tickover, so the prop should be sized to match the torque at maximum speed However ultimately you are correct, the 43 produces more power than the JD3 so with a suitable ratio box could swing a bigger prop.

We are always told (especially by the Vintage engine fans) that Torque is everything whilst really its maximum Power that controls maximum boat performance (as long as we choose a suitable drive ratio) but this might be at the expense of pleasant cruising conditions.

 

I personally would never swap my JD3 for a 43! (but could be temped by 2L2 or even a Kelvin if it would ft))

 

...........Dave

[dmr]

Of course Nick it is to do with what you say. But then our JD3 throws a 22x22 prop which a less torquey engine couldn't handle. So it is to do with the engine as well.

 

Is 22x22 not a tiny bit big? Beta suggest 20x20 and we have a 21x20. I think we don't quite get to full engine speed (1200?), though full engine speed s a moving goal post as the John Deere can actually rev to 2400?

 

Surely if the prop is too big you don't get the full available power from the engine? and go too fast on tickover???

 

.............Dave

[MtB]

 

A friend has a modern engine with a 3:1 box and a big prop, and it works very well, but you do have the drawback(s) of higher engine revs at cruising speed.

 

Looking at your torque curves is interesting.

The torque absorbed by a prop rises with speed (square law???) so an optimum boat engine torque curve would have peak torque at maximum speed (pretty much what the JD3 does). With the Beta 43 if we choose the prop to match peak torque then that will limit the engine speed to that speed, and likely give excess speed at tickover, so the prop should be sized to match the torque at maximum speed However ultimately you are correct, the 43 produces more power than the JD3 so with a suitable ratio box could swing a bigger prop.

We are always told (especially by the Vintage engine fans) that Torque is everything whilst really its maximum Power that controls maximum boat performance (as long as we choose a suitable drive ratio) but this might be at the expense of pleasant cruising conditions.

 

I personally would never swap my JD3 for a 43! (but could be temped by 2L2 or even a Kelvin if it would ft))

 

...........Dave

 

 

Are you? I don't think so.

 

I'll grant you that occasionally a vintage engine fan who doesn't understand the relationship between torque, angular velocity and power might say this, but usually he gets pulled up on it.

 

It's very rare though and I can't remember that last time such a thing was claimed...

[Mrs Trackman]

I know nothing about engines (One of the many reasons I keep Mr Trackman! ). However when we were looking for a boat I was amazed how difficult it was to find a boat with an engine room. We keep coats, folding bikes, oil etc in there. We also have a washing line criss crossing so that washing dries from the engine heat. The engine also adds heat to the boat. I'm sure all of these can be dealt with without needing an engine room but I feel it's worth giving space to the engine.

I love the sound of our jd3 but it's certainly not quiet.

[dmr]

 

 

Are you? I don't think so.

 

I'll grant you that occasionally a vintage engine fan who doesn't understand the relationship between torque, angular velocity and power might say this, but usually he gets pulled up on it.

 

It's very rare though and I can't remember that last time such a thing was claimed...

 

Have a look in some of the canal mags and even some canal boat books.....not everywhere is the level of expertise equal to this forum. But then you are correct, these arn't really engine people.The high torque thing is to a large extent true of course..., a low revving high torque (and hence high cubic capacity) engine is much more suitable for a narrowboat than a smaller higher revving engine (especially so for a trad type boat)..

Some motor bike engines produce over 100bhp but don't want one in my boat, regardless of the gearbox ratio!.

 

...............Dave

[nicknorman]

, but you do have the drawback(s) of higher engine revs at cruising speed...

 

...........Dave

In absolute terms, yes. In relative terms, no. A 43 cruising at 1200 rpm is smooth and quiet, barely above idle, whereas a JD3 at 1200...?

 

Presuming the JD3 is a 120 degree triple it is of course in perfect primary and secondary balance but with a rocking couple. The 4 cyl 43 is not in perfect secondary balance, though not sure it if has a balancer shaft?

 

But I think because the JD3 is a fairly long engine with heavy moving parts the vibration from the rocking couple is more pronounced than that from the secondary out of balance on the 43, with the latter being more easily absorbed by the rubber mounts whilst the JD3 I think in general is solidly mounted?

 

As an aside from Trackman's post when we first got our Hudson one of the more noticable handling characteristics compared to previous boats was that it stopped on a sixpence. We then met another one with a JD3. Their main complaint was that it was hopeless at stopping. So I maintain it is all down to the prop and gearbox!

Some motor bike engines produce over 100bhp but don't want one in my boat, regardless of the gearbox ratio!.

 

...............Dave

Hayabusa-engined narrowboat! Now you're talking (well except that it's petrol I suppose)!

 

Edited August 29, 2015 by nicknorman

[trackman]

 

Is 22x22 not a tiny bit big? Beta suggest 20x20 and we have a 21x20. I think we don't quite get to full engine speed (1200?), though full engine speed s a moving goal post as the John Deere can actually rev to 2400?

 

Surely if the prop is too big you don't get the full available power from the engine? and go too fast on tickover???

 

.............Dave

Dave you're correct about what Beta say. Our boat's builder did trials with the JD3 and different props in a boat the same as ours. He said they were done for Beta.

Despite what Beta still say, he ended up fitting a 23 square prop on his own boat iirc and went for 22 square on the boats he built for sale.

We've not found it to limit our engine speed, in deep water it tops out at pretty much what Beta suggest. I haven't found that we get any more complaints about out tickover speed than with previous boats either.

I do think that it may cause the engine to be a bit more smoky though.

I'm happy to trade that for the ability to shove the boat into a strong current or stop it on a sixpence!

[Doug the Tug]

Slightly off topic,I know. But whilst we are talking about JD3's, does anyone have a reference number for an air filter?

[MtB]

As an aside from Trackman's post when we first got our Hudson one of the more noticable handling characteristics compared to previous boats was that it stopped on a sixpence. We then met another one with a JD3. Their main complaint was that it was hopeless at stopping. So I maintain it is all down to the prop and gearbox!

 

 

That's odd. One of the BEST things about the BD3 I used to have in Aldy was the truly awesome stopping power. It could stop the boat from five knots in half a boat length easily.

[nicknorman]

That's odd. One of the BEST things about the BD3 I used to have in Aldy was the truly awesome stopping power. It could stop the boat from five knots in half a boat length easily.

I'm sure it will have been prop-related rather than anything to do with the engine.

[MtB]

It's the only thing I miss about the BD3.

21 x 19 blade.
PRM 2:1 (approx) gearbox

[PeterG]

In absolute terms, yes. In relative terms, no. A 43 cruising at 1200 rpm is smooth and quiet, barely above idle, whereas a JD3 at 1200...?

 

 

That is the point though as the JD3 fast cruises at 650 which is much more relaxed with masses of usable rev range in reserve, if and when you can find a canal with enough water to use it.

[dmr]

That is the point though as the JD3 fast cruises at 650 which is much more relaxed with masses of usable rev range in reserve, if and when you can find a canal with enough water to use it.

 

That's the River Weaver!

Wide. deep, almost no flow, and very few boats if you go beyond Northwich.

Even better it has a 6mph speed limit so you can take a JD3 to full revs (onset of black smoke) and still be just about legal.

 

.............Dave

[GUMPY]

Black smoke!

My beta 50 pushes Loddon along at 6mph at 1750rpm with another 1000rpm to go before full throttle which is just shy of 8mph

[dmr]

Black smoke!

My beta 50 pushes Loddon along at 6mph at 1750rpm with another 1000rpm to go before full throttle which is just shy of 8mph

 

I have never managed to properly measure our top speed, but estimate it to be over 6mph but probably less than 7.

The JD3 is only 30 to 35 horsepower, and we are a big boat (71 foot, about 32 inches deep and maybe 24 ton), so if you can use your full 50 with a decent sized prop you should be faster, 8mph would be impressive..

 

.............Dave

[MtB]

When I had the BD3 in Aldebaran, 68ft and 20 tonnes, I was thrashing it up the Thames at Reading one day. A friend of ours who saw us from the bank said the trough behind the bow wave was so deep they could see the baseplate!

 

This must have been the day I took it up 1300 rpm, the highest I ever revved it to.

[GUMPY]

 

I have never managed to properly measure our top speed, but estimate it to be over 6mph but probably less than 7.

The JD3 is only 30 to 35 horsepower, and we are a big boat (71 foot, about 32 inches deep and maybe 24 ton), so if you can use your full 50 with a decent sized prop you should be faster, 8mph would be impressive..

 

.............Dave

For a modern boat Loddon has very sheer lines underwater, I have only clocked 7mph at just over 2000rpm going upstream on the River Nene with little flow. Have also been flagged twice for speeding by EA on the Thames as 6 seems to be its natural cruising speed on deep water.

[MtB]

For a modern boat Loddon has very sheer lines underwater, I have only clocked 7mph at just over 2000rpm going upstream on the River Nene with little flow. Have also been flagged twice for speeding by EA on the Thames as 6 seems to be its natural cruising speed on deep water.

 

 

I'm reasonably sure the speed limit on the Thames used to be 8 knots. Or has that changed?

[GUMPY]

 

 

I'm reasonably sure the speed limit on the Thames used to be 8 knots. Or has that changed?

8k is correct but the K stands for kilometers in other words 5mph

[MtB]

8k is correct but the K stands for kilometers in other words 5mph

 

 

Blimey that's a bit misleading! Did you get fined, or what happened?

 

I'd say 8km/hr is widely ignored by GRP cruisers on the upper Thames. How is one supposed to comply anyway, when boats don't have speedometers?

And I'd say on red boards the stream easily reaches 4mph in places, so with a bit of forward movement through the water it would be hard not to exceed the speed limit!

[OldGoat]

EA are unofficially relaxed about the actual speed - it's the WASH that counts and NBs tend not to make much of that, even when punching upstream in moderate to high flows.

 

There are hotspots in the summer when there are a lot of cruisers moored, but most of these are downstream of Reading.