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Slow boat, do I have a problem


Dignity

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I've always been happy travelling slowly,but last year I seemed to upset quite a few people who couldn't wait to overtake.A couple of them pointed out it looked like my prop was fouled due to the large fan tail wash I was producing. Checking showed all was clear. Interestingly if I stick the gearbox into reverse as if to clear the propellor and then back forwards again the wash tightens up for a while. Does anybody have an idea what's happening here, is there a problem.

It's a vetus 4.14 engine with a ZF Hurth gearbox that is operating normally.The propellor when I looked via the weed hatch seemed tight and un damaged.

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I've always been happy travelling slowly,but last year I seemed to upset quite a few people who couldn't wait to overtake.A couple of them pointed out it looked like my prop was fouled due to the large fan tail wash I was producing. Checking showed all was clear. Interestingly if I stick the gearbox into reverse as if to clear the propellor and then back forwards again the wash tightens up for a while. Does anybody have an idea what's happening here, is there a problem.

It's a vetus 4.14 engine with a ZF Hurth gearbox that is operating normally.The propellor when I looked via the weed hatch seemed tight and un damaged.

This wouldn't have been around autumn time perhaps? Sounds like the way my boat behaves when the cut is full of leaves.

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I've always been happy travelling slowly,but last year I seemed to upset quite a few people who couldn't wait to overtake.A couple of them pointed out it looked like my prop was fouled due to the large fan tail wash I was producing. Checking showed all was clear. Interestingly if I stick the gearbox into reverse as if to clear the propellor and then back forwards again the wash tightens up for a while. Does anybody have an idea what's happening here, is there a problem.

It's a vetus 4.14 engine with a ZF Hurth gearbox that is operating normally.The propellor when I looked via the weed hatch seemed tight and un damaged.

At the same revs do you go the same speed in reverse as forward?

Ian

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This wouldn't have been around autumn time perhaps? Sounds like the way my boat behaves when the cut is full of leaves.

It fooled me the first time I experienced leaves. Slowed down and I was convinced the prop was loose. Looked down the weed hatch and nothing on the prop, started off normally then slowed down again. Of course, as soon as you stopped or went into reverse, all the leaves fell off the prop so it appeared clear.

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I don't see why you think you've upset people who overtake, as long as you let them past with a cheerful wave when they obviously are moving faster than you. My boat has a natural speed of about 3mph and if it goes much slower the whole thing vibrates horribly, so I tend to either go past real slow movers or if I can, stop and have a cup of tea and then catch them up again. I do get fed up with the "You in a hurry" cracks or the people who just sit doggedly in the middle at 1mph and won't let you past while a queue builds up behind them. Some people, especially on a short hire boat holiday, do have a schedule which us boat owners don't have.

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The leaves wrap themselves round and round and form a sort of "doughnut" and it doesn't take much to reduce the efficiency of the prop. When we were cruising last October this was a major problem on the Staffs & Worcs which has a lot of trees. Why it affects some boats more than others I don't know, maybe the prop size, clearance etc etc.

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Another vote for leaves on the prop. During October and November I was dropping it into reverse for a second or two almost every 200 yards. It's fairly obvious when there's something on Kendal's prop, slight loss of power but the wash is a real tell-tale, water being churned up and off to one side rather than a smooth straight 'bubble'.

 

I regularly drop into neutral and glide through bridge holes anyway, then give a quick burst of reverse just to clear anything that may be on there. There's more chance of picking something nasty up at a bridge hole and the longer it's there the worse it will get.

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Just let them pass and be nice.

 

Two years ago I spent a whole morning following a boat that just wouldn't accept that my proximity to his stern was an indication that maybe I was keen to travel a bit faster than his 1 to 2 mph. I sat it out until he eventually pulled over and moored up.

 

My respectful suggestion, made as I passed him, that perhaps he should have given way, was met with the accusation that I had been trying to dictate his speed of travel. He completely overlooked the fact that by not giving way, he was doggedly dictating mine! In hindsight, I should have got her indoors to take the tiller, walked on ahead, and had a walking-pace conversation on the matter!

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So long as you stop/slow down regularly when there is a boat behind you who wants to overtake, I can't see the problem in it. If you are going slow but are unaware of it, or aware of it but too belligerant to let them overtake, its a problem. Its exceedingly difficult to overtake narrowboat-narrowboat except with cooperation.

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Our old boat was a fairly slow boat. We always let people past, with the exception of when a lock flight was less than one mile ahead.

 

It amazed me on the odd occasion that we caught someone up, when they adopted the blinkered, eyes forward approach. They eventually glance over their shoulder, then ignore you for the next few miles, by which time you have another two boats behind you.

Edited by MHS
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If you are concerned that you're not getting enough power out of your engine might be worth looking at the prop.

 

In deep water (not most canals), I was only able to get 1900rpm in gear from a 3000rpm engine. It turned out it was over-propped. I had the pitch reduced and now I get about 2250rpm and a lot more power.

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If you are concerned that you're not getting enough power out of your engine might be worth looking at the prop.

 

In deep water (not most canals), I was only able to get 1900rpm in gear from a 3000rpm engine. It turned out it was over-propped. I had the pitch reduced and now I get about 2250rpm and a lot more power.

I'm of the opinion that most narrowboats are over-propped. I think it's a combination of over optimistic engine data and owners who like to pretend they have a slow revving engine. I met a guy a couple of years ago that had a bmc 1.5 with a 20" prop and he had the tickover screwed right down so it sounded "like a trad" (his words). He was telling me all this and at the same time complaining that since the engine had been rebuilt it was smoking a lot more...

 

I think this might be a contributory factor in the dead leaves issue. I know my boat is overpropped from trying to push a strong flow up the Severn last year and when she comes out in April I'm changing it. According to Crowthers the prop is 2" too big (dia).

 

I suspect most owners never discover their prop is too big because the boat is never exposed to the conditions where maximum power is needed.

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I'm of the opinion that most narrowboats are over-propped. I think it's a combination of over optimistic engine data and owners who like to pretend they have a slow revving engine. I met a guy a couple of years ago that had a bmc 1.5 with a 20" prop and he had the tickover screwed right down so it sounded "like a trad" (his words). He was telling me all this and at the same time complaining that since the engine had been rebuilt it was smoking a lot more...

 

I think this might be a contributory factor in the dead leaves issue. I know my boat is overpropped from trying to push a strong flow up the Severn last year and when she comes out in April I'm changing it. According to Crowthers the prop is 2" too big (dia).

 

I suspect most owners never discover their prop is too big because the boat is never exposed to the conditions where maximum power is needed.

I guess it depends on your setup but Crowthers told me to reduce pitch rather than diameter. Apparently on an overpropped boat 1" of reduced pitch increases revs by about 250 rpm while 1" of reduced diameter only increases revs by 100rpm and will adversely affect stopping power. Obviously there are limits to reducing pitch. You can't make the prop too flat.

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I'm of the opinion that most narrowboats are over-propped.

 

Indeed, and one consequence is that many boats cannot travel slowly enough at tickover speed.

 

I like being slightly under-propped. In my discussions with Crowthers when I changed my prop I chose this feature deliberately. Not only doers it mean that my speed at tickover is acceptably slow, it means that the engine rarely labours, even when there is a build-up of rubbish (or leaves) on the prop, because it has a reserve of power to deal with the situation - particularly because I specified a 3:1 gearbox which gives me the extra torque to turn a steeper-pitched prop slowly which gives a double bonus if I get rubbish on the prop because it too only turns slowly - needing less effort - and the increased torque makes this easier too.

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Thank you folks, it was indeed end of summer and there were plenty of leaves around. Five years and I'm still learning stuff.

Speed and control at tickover is perfect and I wouldn't want to change that. I tend to travel with the revs around 1100 ish, you can hear when the engine is starting to over rev itself at about 1500.I'm going to keep on waving you all through. Oh and the forum name is after the Deacon Blue song.

Edited by Dignity
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I guess it depends on your setup but Crowthers told me to reduce pitch rather than diameter. Apparently on an overpropped boat 1" of reduced pitch increases revs by about 250 rpm while 1" of reduced diameter only increases revs by 100rpm and will adversely affect stopping power. Obviously there are limits to reducing pitch. You can't make the prop too flat.

That's interesting, I suppose on a (relatively) big heavy widebeam or indeed a long or particularly heavy narrowboat you do want the "widest" prop the engine will handle.

 

 

Indeed, and one consequence is that many boats cannot travel slowly enough at tickover speed.

 

I like being slightly under-propped. In my discussions with Crowthers when I changed my prop I chose this feature deliberately. Not only doers it mean that my speed at tickover is acceptably slow, it means that the engine rarely labours, even when there is a build-up of rubbish (or leaves) on the prop, because it has a reserve of power to deal with the situation - particularly because I specified a 3:1 gearbox which gives me the extra torque to turn a steeper-pitched prop slowly which gives a double bonus if I get rubbish on the prop because it too only turns slowly - needing less effort - and the increased torque makes this easier too.

I actually considered keeping the "big" prop and just fitting a 3:1 gearbox and looking at the new prop quote from Crowthers I might reconsider it!

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That's interesting, I suppose on a (relatively) big heavy widebeam or indeed a long or particularly heavy narrowboat you do want the "widest" prop the engine will handle.

 

I actually considered keeping the "big" prop and just fitting a 3:1 gearbox and looking at the new prop quote from Crowthers I might reconsider it!

 

"Problem" with a 3:1 gearbox is that I am doing 1800 rpm to achieve 3 mph and over 2000 rpm to achieve 4mph.

Fuel consumption is over 2 litres per hour

(Lister LPWS4 in a 45 foot Reeves)

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"Problem" with a 3:1 gearbox is that I am doing 1800 rpm to achieve 3 mph and over 2000 rpm to achieve 4mph.

Fuel consumption is over 2 litres per hour

(Lister LPWS4 in a 45 foot Reeves)

 

Of course, a 3:1 box will only be useful if the prop matches it, In my case it's Crowthers 18x14 high-efficiency (the 19" prop that was originally fitted, was too close to the counter, kept getting things jammed in it and was very noisy) and with that the engine does 450 rpm per mph on canals or 400 rpm per mph on deep water.

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The OP doesn't seem to suggest that the problem is confined to the autumn. His description seems more like cavitation to me. As the boat builds up speed and the water profile around the hull changes, air is being sucked down into the prop. The prop is then thrashing lots of very elastic air and throwing it out the back. Stopping or going into reverse breaks the cycle for a while before it returns again.

 

Add some ballast to the stern, or take some out of the bow. A simple test would be to put a big plastic dustbin the back deck and fill it with water.

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