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Nigels Profile
Nigels Profile

Posted: Thu Nov 27, 2008 8:44pm

Post Subject: Propellor Whine /loss or propulsion

I had a new propeller fitted 6 months ago. From the outset it has suffered from a pronounced whine between 1100 and 1400 revs. I've been told that the back edge requires grinding to a thinner profile. Recently i've also suffered a degredation in speed for given constant revs along with significant water disturbance around the stern and with lack of stream being push away from the boat, even increasing revs significantly had no effect. There was nothing around the prop and no change in depth. If the neutral is selected and the wash around the stern is allowed to calm down, revs slowly increased again a more normal flow out from the stern and propulsion is restored. Is this perhaps to do with the propellor sucking in too much air?. The engine appears to be ok smooth running etc.

Tony-B
Tony-B

Posted: Fri Nov 28, 2008 9:38am

Post Subject: Propellor Whine /loss or propulsion

Dear Nigel, lets deal with the easy one first. Is this your first boat? The loss of speed at this time of year is absolutely typical of fallen leaves packing around the prop. When you stop the prop they all get washed away by the boats remaining speed so you never find them. However when this happens give the boat a short burst of reverse. This displaces the leaves and you will see a great cloud of them as you move ahead again. The prop is far more difficult. First ensure the prop has about two inches of clearance between the blade tips and any part of the hull. If you have less then I am afraid the wrong sized prop has been fitted. I think that what you have is known as a singing prop and the "cures" are many. It is usually attributed to the blades being so similar with very close natural vibration frequencies that as soon as one blade starts to vibrate the others also vibrate in sympathy. The "cure" is to make the blade vibrate at different rates so attacking any part of the blades with an angle grinder may well alter the blades individual weight/profile/balance sufficiently to stop the sympathetic vibrations. I have heard that bending one tip with a large adjustable spanner has a similar effect and you might be able to do this via the weed hatch, but please take care and do it in small stages. It is also possible that putting the stern aground in shallow, gravely water and giving a good burst of ahead might burr each blade sufficiently differently to stop the noise (at your own risk). I trust this helps. Tony Brooks

Nigels Profile
Nigels Profile

Posted: Fri Nov 28, 2008 11:45am

Post Subject: Propellor Whine /loss or propulsion

Thanks tony, It did get worse when entering areas with leaves on top. It's my first boat which i've had over 2 years. This is the first time that i've had this problem (i was based around Napton and now i'm moored below atherstone locks) perhaps there's more leaves about in this area. the new prop was recommended by sam cole of colecraft (who supplied the original. It's 20 x 15 RHS fitted to a 58ft noat with beta 43 and PRM 150 gearbox.

Tony-B
Tony-B

Posted: Mon Dec 01, 2008 1:08pm

Post Subject: Propellor Whine /loss or propulsion

Dear Nigel, sorry for the delay in replying but I have been at the Earls Court show. I have some concerns about that prop size. I am sure Colecraft have produced all sorts of hulls with all sorts of dimensions but at 58ft it sounds like a fairly standard hull and my 54ft Colecraft (1991) only has about a 20" sternpost meaning I can only swing a 16" prop without expecting problems. Please take a steel tape and gaining access via the weed hatch measure the distance from the top of the skeg to the underside of the uxter (swim) plate close to the prop. If you find 24 inches or more then a 20" prop is fine, but if you find significantly less then all sorts of odd noises could result so short of having the prop cut down you may never cure the noise. Tony Brooks

Hisnayres
Hisnayres

Posted: Tue Dec 09, 2008 9:13pm

Post Subject: Propellor Whine /loss or propulsion

hi, we took delivery of a new narrow boat from the new company, -aqualine madison - 6 months ago and right from the start we had prop whine at similar revs. A local boat builder sugested grinding the leading edge of the prop! by how much i don't know. We have not had the boat out of water yet to try but when we do we will let you know the outcome. Or if you beat us to it please inform us of your results. Good luck Rob

Tony-B
Tony-B

Posted: Wed Dec 10, 2008 9:31am

Post Subject: Propellor Whine /loss or propulsion

To all our other readers - now we see one builder says try grinding the front edge and another the back. This is a good illustration of how difficult it is, and thus how expensive it might turn out to be, to sort out singing props. This is why I originally suggested tweaking the tip of one blade via the weed hatch, at least that is a diy job and as long as you only do it a little it should knock back into place when the boat is out of the water. This seems to be more common problem than many people realise. Tony Brooks

Hisnayres
Hisnayres

Posted: Wed Dec 17, 2008 9:20pm

Post Subject: Propellor Whine /loss or propulsion

Hi Nigel, just thought you might like to know I did as Tony suggested with regards to the prop whine, by just fractionally bending the tip of one blade and found the noise much reduced. Once i have taken her for a trip down the river if not fully cured I will try doing it again on another blade. By the way the water at this time of year is ****** COLD. Have some warm water ready in the sink if you try it. Good luck Rob.

Tony-B
Tony-B

Posted: Thu Dec 18, 2008 9:10am

Post Subject: Propellor Whine /loss or propulsion

Thanks for the feedback Rob, it's not only nice to know when I get something about right but it also shows other readers how to deal with a problem. I must confess that tip is not mine, I got it from a contributor to possible the best Internet (not magazine) based Canal Forum. I should have said that if anyone needs to straighten the prop tip then hold the mooring hammer hard against the back of the kink and then tap the front with an ordinary hammer. In this weather (Dec.) I would also take the chill out of the kink with a blow lamp, but I suspect that does more for my mind than actual good. Tony Brooks

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