Are our engines unnecessarily powerful?

[Theo]

Just looking at page 56 of the June Tillergraph. The article says that about 1hp/ft length is about right. I thought to myself "That sounds a lot!" then I wondered what Theodora has in the way of hp. I rather think that she has about 25 horses concealed in the BMC 1.5. Am I right?

 

If I am right then I have been risking life and limb plugging up the Thames from Duke's Cut to Shifford in the high winds and moderately high waters of March 2008.

 

N

[Guest]

Engines just seem to get bigger in relation to boat length. 33 Japanese horses in our 57ft NB, and I bet I only ever use 10 of them. Have moved another 57 NB alongside with same engine needing just a little more throttle. I suppose in these days of large electrickery usage on board, and triple alternators etc, a few more horses might be needed. I am not convinced my particular boat would achieve greater speed with a bigger engine fitted, though it might stop quicker.

 

I used to have a 32FT NB with a tiny one pot Yanmar fitted (10hp IIRC) and it got along very nicely, being amazingly good on diesel.

[Paul's Nulife4-2]

I also think that as our Electrical demands increase, by adding 1 then 2 Alternators, a Power Pack, Bigger Prop ect, ect it all takes HP from the Eng to run, & then we only use maybe 30% of what's left for propulsion.

But from a manufacturing point of view, a say 30 Hp Eng could quite happily go in a huge range of inland craft.I suppose.

[John V]

Probably, I think is the answer. It's something that gets discussed quite regularly when out for a beer with my mates. We're talking about offshore rather than inland but the same principles hold

.

You can get to your hull speed with quite minimal power and you need a bit in hand to cope with punching a tide or current nothing like the power that seems to be installed nowadays

.

The old barge boys would make progress when they could and use the tides and currents to help, anchoring up when conditions were adverse.

 

When I bought my old Humber barge she was fitted with a Glennifer 4 cyl of I believe about 48 hp. She used to carry about 80 ton and was rigged with a proper towing hook for towing a dumb barge. Her last trading route was from the Thames up the East coast to the river Stour

 

(I must confess that she has a much more powerful engine fitted now but that was because someone made me an offer I couldn't turn down)

 

 

ONE day I'll not have to make a fat finger edit!!!

Edited June 7, 2014 by John V

[Guest]

I remember some years ago on the L&L where a bloke was using a Seagull outboard to move a wide beam shell. Far from ideal, but it shows what a few horsepower can move.

[RLWP]

Just looking at page 56 of the June Tillergraph. The article says that about 1hp/ft length is about right. I thought to myself "That sounds a lot!"

 

Well, quite. Clearly our BMC 1.8 isn't capable of producing 70HP, and we never run it flat out with the governor on max. That figure is nonsense

 

Richard

[Naughty Cal]

I remember some years ago on the L&L where a bloke was using a Seagull outboard to move a wide beam shell. Far from ideal, but it shows what a few horsepower can move.

Indeed. Our 6hp outboard pulls NC along quite easily. I guess a 2.5hp would pull it along nicely once the initial momentum is gained.

 

(We found out our outboard pulled NC when we fell victim to the Witham weed about a mile from Washingborough moorings . Easier to tow it there to sort out!)

 

Well, quite. Clearly our BMC 1.8 isn't capable of producing 70HP, and we never run it flat out with the governor on max. That figure is nonsense

 

Richard

I don't think ours would quite work with 25hp!

[RLWP]

 

I don't think ours would quite work with 25hp!

 

It would work, I don't think it would be anywhere near as much fun

 

Richard

[nb Innisfree]

We used to have 33bhp in our 60' nb, struggled a bit at times with alt on full output (100a @24v = approx 6bhp) but stopped in 3/4 boat length with batts on float charge.

 

Now we have 40bhp which still stops in 3/4 length with alt on full output or float.

 

So for us 40bhp is a few horses overpowered.

[Paul's Nulife4-2]

It's not so much the getting going, as momentum builds & builds it gets easier &easier.

It's the getting STOPPED that the extra HP is handy for.

[Guest]

It's not so much the getting going, as momentum builds & builds it gets easier &easier.

It's the getting STOPPED that the extra HP is handy for.

A bit of extra HP comes i useful when maneuvering too.

[nb Innisfree]

It's not so much the getting going, as momentum builds & builds it gets easier &easier.

It's the getting STOPPED that the extra HP is handy for.

Strictly speaking it gets harder and harder as drag increases, but I know what you mean!

 

Drag is the enemy when moving but a friend when stopping.

[blackrose]

It depends what kind of waterway you're moving on. If you're just on canals then even a small outboard will move a 70ft boat (it might have trouble stopping it though!)

 

For a widebeam like mine I think the 1 hp/ft ratio is probably the minimum for rivers. Having said that, unless many modern high-revving engines can reach maximum engine revs in gear then they will never actually achieve their maximum stated hp. My Isuzu 55 only revs to 2250rpm in gear in deep water, so according to the power curves it's only achieving about 45 hp maximum.

[colmac]

I have a Lister LPWS3 in my 45'NB. It produces 28 horses and is more than adequate for our needs. We fair zip along but there always seems to be someone behind us who wants to go faster. However, viz a viz the original topic, there are so many factors affecting the power output/speed ratio such as; depth below the keel etc. a standard speed seems to be difficult to compute. Tried it a few weeks ago by timing ourselves between the mileposts on the Shroppie but moored boats kept knackerin me speed/time calculations so we just contented ourselves with what we do best, ambling along.

[Theo]

As I thought. Anyone have any idea how many horses my BMC 1.5 actually has?

 

N

[Ricco1]

My 35ft has a 12hp Vetus. I can tootle along at 3 mph without having to go above half revs. On full revs it only does 4mph so not worth the bother. It doesn't stop so quickly but at 3mph, are there many situations where not having fast 'braking' can result in damage? I suspect not.

 

So I'd say that the power I have is perfectly adequate for the canal and has the benefit of doing 2 hours to a litre of fuel, 3 when charging. Not for a river though.

[John V]

My 35ft has a 12hp Vetus. I can tootle along at 3 mph without having to go above half revs. On full revs it only does 4mph so not worth the bother. It doesn't stop so quickly but at 3mph, are there many situations where not having fast 'braking' can result in damage? I suspect not.

 

So I'd say that the power I have is perfectly adequate for the canal and has the benefit of doing 2 hours to a litre of fuel, 3 when charging. Not for a river though.

 

Your entry surprises me. I would have expected you to have better performance than that.

I have the same engine in my cruiser (28.5') it's fitted with a PRM gearbox and swings a 12 x 7 prop

she does 3mph at a fast tickover and about 6 kts at full revs

I expect you have a greater displacement and possibly blunter entry but that should be somewhat countered by the extra waterline length

Do you know what your prop size is?

Edited June 7, 2014 by John V

[Theo]

It's not so much the getting going, as momentum builds & builds it gets easier &easier.

It's the getting STOPPED that the extra HP is handy for.

I rather suspect that unless you have a decently designed swim aft and a largish prop then stopping power is poor whatever engine power you have. Theodora has a short swim and a smallish prop matched quite well to the BMC. Her stopping power is similar to that of a horse boat. The long centre line and a convenient bollard for strapping to a halt is often useful.

 

N

[Marjorie]

Someone I met the other week, who has had I think 4 narrowboats over the past lots of years (lets say 20 - I can't really remember), said that if he was to recommend that I do one thing, it would be to get a slightly bigger engine than I think I need to help with manoeuvrability and rivers.

 

(don't shoot the messenger)

[Theo]

Someone I met the other week, who has had I think 4 narrowboats over the past lots of years (lets say 20 - I can't really remember), said that if he was to recommend that I do one thing, it would be to get a slightly bigger engine than I think I need to help with manoeuvrability and rivers.

 

(don't shoot the messenger)

I quite see the practicality of this but I have to confess to taking a rather perverse pleasure in coping with the idiosyncrasies of my beloved boat.

 

N

[FadeToScarlet]

Fantastic, I must have a 72 horsepower engine for my 72' boat. A Gardner 4LW would do it....

 

....oh, it got along quite fine with a 10 horsepower engine when it was built? And when it would carry 30-35 tons of cargo as well? No, that can't possibly have been true....

[MtB]

Just looking at page 56 of the June Tillergraph. The article says that about 1hp/ft length is about right. I thought to myself "That sounds a lot!" then I wondered what Theodora has in the way of hp. I rather think that she has about 25 horses concealed in the BMC 1.5. Am I right?

 

If I am right then I have been risking life and limb plugging up the Thames from Duke's Cut to Shifford in the high winds and moderately high waters of March 2008.

 

N

 

Never mind 1hp per foot!

 

Back in the day we got by perfectly well on 1hp per boat...

 

 

MtB

[Lockie Junior]

The article says that about 1hp/ft length is about right.

 

Just to buck the trend. One of the boats I use at cadets has a 23hp engine (Lister TS2) in a 16ft hull. It is extremely over powered (and I think over propped) for what it is, but boy does she stop quick! An almost identical boat with a smaller, newer, more "appropriately sized" engine (Yanmar) doesn't, as I found out during my first coming alongside of the (brand new) jetty...

 

Regards,

Lockie.

Edited June 7, 2014 by Lockie Junior

[mattlad]

I'm running 1hp per metre.

[MtB]

I'm running 1hp per metre.

 

 

That sounds about right to me!

 

MtB