Engine installation

[Chewbacka]

The figures quoted in the HMI literature are the engine manufacturers data sheets,not the performance of the marinised units.Obviously,there may be some disparity in the setting of engine rev. meters. Unless the meter is cross checked against a test meter,you can not be sure of the accuracy of the electronic unit. I can confirm that my 4L.42 unit will not pull more than 2,000rpm on factory setting.. I checked with H.M.I.who confirmed that this is correct. Obviously the engine is capable of running at a sustained 3,000rpm(as in the spec sheets) in an industrial unit. There are many Isuzus fitted to hire boats. I would be interested to hear whether any of these will pull at over 2,000rpm?

So is the governor set to 2000rpm or is the prop a bit too big??

Edited November 19, 2016 by Chewbacka

[Sea Dog]

I would be interested to hear whether any of these will pull at over 2,000rpm?

Thanks for coming back on this one, Neb, as it seems strange but is an interesting issue. I couldn't/can't see why the marinised Isuzu's would be restricted to 2/3 of their available rev range thus limiting the maximum available torque and power. Might we not be seeing the effect of over-propping?

 

 

 

ETA like Chewy also thinks more quickly, I read!

Edited November 19, 2016 by Sea Dog

[Murflynn]

The figures quoted in the HMI literature are the engine manufacturers data sheets,not the performance of the marinised units.

the figures in the data I linked to are specifically for 'canal boat engines'.

 

when I had a Scouse built boat with an Isuzu 42hp unit it revved to 2800.

[FadeToScarlet]

Ey? Find brum one of the best places if im honest

OK, Willow is 71'9" at the water level, so 72' overall.

 

Run with one tipcat only, no bow button to get up or down Farmer's bridge, Aston etc. All fenders removed for Minworth and Curdworth. Can't wind by CTS at Norton Canes where you can wind 71'6". The crow short for length, along with I think Spon Lane too.

 

Also things like having trouble sharing Bishop Mill lock in Loughborough.

 

None of which are dealbreakers, but there are disadvantages to being full, full length, especially if you don't know what you're getting into. We knew, so none of this is a shock, but other people might not.

[nebulae]

It may be helpfull to know prop size in order for the origional poster to judge whether the Isuzu engine is set up correctly.. Acording to Nigel Warrens guide to propellers(some members of this forum are probably familiar with these),a 40hp engine ,1,500 prop rpm will require a 17.3 inch dia and 11.4inch pitch prop at 50% efficiency. This would give a theoretical max speed of 8knots(Probably not achievable for a narrow boat.) My boat has the nearest size available 17 by 11with a 4L.42 engine. G.P.S gives me a max speed in still water of just under 6knots@2,000rpm,Obviously,hull form may make a difference between different boats .In practice,if my engine revs increased above 2,000rpm the boat would not go any faster(50ft boat). My engine rev counter has been checked,so I believe it is accurate. As to whether these engines are all limited to 2,000,I can not say.All I can tell you is what I was told by H.M.I.,the mariniser.

[nebulae]

Have just checked the power and torque graph for the4L42 Isuzu engine. Max power of 42hp is achieved at 3,000rpm.Max torque is achieved at between 1,800 and 2,000rpm. Torque drops off sharply after this. Power at 2,000rpm is in fact,almost exactly 30hp.Hope this helps.

[Sea Dog]

Acording to Nigel Warrens guide to propellers(some members of this forum are probably familiar with these),a 40hp engine ,1,500 prop rpm will require a 17.3 inch dia and 11.4inch pitch prop at 50% efficiency. This would give a theoretical max speed of 8knots(Probably not achievable for a narrow boat.) My boat has the nearest size available 17 by 11with a 4L.42 engine. G.P.S gives me a max speed in still water of just under 6knots@2,000rpm,

My Beta 43 with 2:1 reduction through a PRM150 is fitted with a 17 x 11 prop. It will pull 2800 RPM easily on a river if asked. I think it's a wee bit under propped - Beta suggest 18 x 12, but add a disclaimer to say they're not prop experts.

[mrsmelly]

My Beta 43 with 2:1 reduction through a PRM150 is fitted with a 17 x 11 prop. It will pull 2800 RPM easily on a river if asked. I think it's a wee bit under propped - Beta suggest 18 x 12, but add a disclaimer to say they're not prop experts.

 

My last narrowboat with a beta 43 70 footer had a 18 x 12 and was spot on. This boat has similar size isuzu and same box also 18 x 12 prop only a tiddly boat this one at 68 feet and revs to around 2500 ish if I recall tho never get above 1100 on the local ditches at my present mooring. I had an 18 x 12 on a 57 footer and a 65 footer I have owned they seem a good prop to have in the spare parts box.

 

Tim

[nebulae]

Interesting to hear other peoples experience .I did not mention in my posts as it was not relevant,but I have de-restricted my Isuzu so that it revs to 3,000rpm(where it should be giving 42hp). In the best test conditions I can arrange,my Isuzu 4.42 will not pull more than 2,200rpm against a load,with a 17"dia and11"pitch prop.Between 2,000rpm and 2,200rpm,there was zero increase in speed through the water,which is the result of many factors,particularly,I suspect,to the drastic reduction in toque at over 2,000rpm.My normal canal speed is an average of 3mph at 1,200rpm.

[lazyboy]

During my four years working for the HMIsuzu mariniser in Gloucestershire,changes were not made to Speed settings or governed torque output after marinisation. The engines were as set by the Japanese manufacturer to their published torque output figures for industrial engines.

[Sea Dog]

 

My last narrowboat with a beta 43 70 footer had a 18 x 12 and was spot on. This boat has similar size isuzu and same box also 18 x 12 prop only a tiddly boat this one at 68 feet and revs to around 2500 ish if I recall tho never get above 1100 on the local ditches at my present mooring. I had an 18 x 12 on a 57 footer and a 65 footer I have owned they seem a good prop to have in the spare parts box.

 

Tim

Useful info Tim, thanks. I've had half a mind to get a bit of pitch added next time she's out. 17 x 13 will be just a little less than an 18 x 12 I believe.

[nebulae]

Well,I have learned something from this thread. Will check with the engineer who made my engine rev out to full revs.to see what he did. Not sure why I was told that it was o.k.when it was fitted. Dont think it makes any practical difference as the engine will not pull more than 2,200rpm in my boat. Hope the origional poster found the discussion usefull.

[RichardN]

I have a memory that there used to be an Isuzu 38 which was actually 41hp. Indigodream ( Isuzu 42 ) is over 10 years old and again from memory the engine range was about 2 or 3 years old at that time so the 38 in a 12 year old boat could be the older engine model? I did have a manual for the older range somewhere but I have looked through 2 old hard disks and it is not there. I will look elsewhere and see if I can locate it.

 

Squelchy: Where are you based? If you are within reach of the Nantwich area then talk to Neil Coventry, fabulous Engineer. We only get to see him every 3 or so years but he is the only person who can service the engine and subsequently my better half gets on the helm and not only notices that the engine has been serviced but comments how much better it feels. I service the engine, " you done anything?", I get someone who knows what they are doing, Sue does not notice, Neil plays with the engine, it is instantly noticed and commented on (and I agree).

 

I have uploaded the original engine brochure (for the "newer" range) - it is here. I am curious about the 2000 max rpm.

 

* The brochure suggests that we get peak torque at 1800 rpm.

 

* The engine will carry on revving under load over 1800rpm, we do squeeze a bit more speed out, bit noisier but also smoother plus the cruiser deck covers stop rattling so a nice speed on tidal river with an 18" x 12" prop.

 

* I always feel that at my top speed I am hitting hull speed, even with more power I feel that I would not get any more speed out of the boat. No proof of that except that we seriously moving and hard to imagine being able to push a narrowboat faster.

 

The maximum rev counter reading we get under load is 2000 rpm.

[Murflynn]

I doubt you could push a narrowboat to anything approaching hull speed.

 

for a 49ft boat hull speed is 1.34 x 7 = 9 knots.

[RichardN]

Hi interesting point. I googled and got the same answer as you.

 

My memory may be playing tricks but I thought there was a discussion here about hull speed, I followed the links, got to a more complicated formula which include displacement and hull shape and that gave an answer of just over 7 knots for a 60 foot boat.

 

If the 1.34 formula is right then I need a bigger engine! I see there is an 8 cylinder Gardner for sale on eBay. . . .

[Murflynn]

careful - we may be inventing a new breed of narrowboats, capable of making hull speed.

 

if they don't sink all the moored boats they will probably swamp themselves especially when coming down off max speed.

 

 

Hi interesting point. I googled and got the same answer as you.

My memory may be playing tricks but I thought there was a discussion here about hull speed, I followed the links, got to a more complicated formula which include displacement and hull shape and that gave an answer of just over 7 knots for a 60 foot boat.

If the 1.34 formula is right then I need a bigger engine! I see there is an 8 cylinder Gardner for sale on eBay. . . .

hull speed is the point where there is a single long wave between bow and stern, with the second crest supporting the stern; go any faster and the stern crest moves behind the boat, the stern squats and the boat is permanently trying to climb a hill.

[nebulae]

Apparently,the chap who altered the max rev on my engine just altered the throttle stop. It was still covered in blue paint when he altered it. I was reluctant to touch any settings,as I am not familiar with the Isuzu 4L.42. Maybe the max revs of the engine should be checked when the engine is installed? In any case,the engine in my boat will not pull more than 2,200rp m.Not sure max speed is that important,unless you are making a passage such as Sharpness to Bristol. One thing slightly unusual for a narrow boat is that my engine is cooled indirectly by raw water. This is because the boat was converted from air cooled,so saved installing keel cooling tanks. We had a problem at first,due to the design of the exhaust injector. After this was modified,the engine will run all day flat out with the temperature steady in the middle of the gauge. Any blockage of the intake can usualy be cleared with a cunningly modified wire brush on a stick.