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Post by Deleted on Oct 31, 2016 16:34:22 GMT
I have had a look at the propeller on my launch and could not see any size markings on the side view I had through the weed hatch.
The diameter seems to be about 20 or 22 inches. 1.5" shaft. I can't measure the pitch but the boat has a 50hp engine (perkins p4 slow type) revving to about 2000rpm afaik and there is not much "bite" so I don't think it has a big pitch. Prm160 2:1 box.
Prop is very knocked around with bent tips and this causes vibration.
I'm wondering if to put a 16x12 4 blade prop on there as I have seen one for sale which I think would suit it.
Would this make it pull better? It goes OK but doesn't seem to have the bite and the engine revs very readily indicating a lack of load.
Boat was built for hire originally and I have heard that hire boats were sometimes deliberately under propped for battery charging and speed control reasons.
Boat has very good underwater lines with plenty of water getting to the propeller. Its the 40x9ft launch I mentioned in another topic.
Any advice gratefully received as always.
I've always liked "4 leafed clovers" and when I went on the bantam tug Ilda it was impressive what they can do but not sure if it is necessarily the right plan for this boat.
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Post by JohnV on Oct 31, 2016 16:45:24 GMT
 This may take some time |
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Post by Gone on Oct 31, 2016 16:48:30 GMT
There is a guy in the other place who knows a lot about propellers, admittedly aircraft, but it is still a fan in a fluid.
So if you don't get a good answer here, you could try there, or even entice him over here with your question....................
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Post by JohnV on Oct 31, 2016 16:52:53 GMT
There is a guy in the other place who knows a lot about propellers, admittedly aircraft, but it is still a fan in a fluid. So if you don't get a good answer here, you could try there, or even entice him over here with your question.................... Dalslandia ? |
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Post by tonyqj on Oct 31, 2016 16:54:17 GMT
There is a guy in the other place who knows a lot about propellers, admittedly aircraft, but it is still a fan in a fluid. So if you don't get a good answer here, you could try there, or even entice him over here with your question.................... Deslandia? I guess he's be good to invite 😀 Edit - snap! |
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Post by Deleted on Oct 31, 2016 16:54:43 GMT
Dalslandia. Yes he's very knowledgeable (a trip boat skipper on the continent I believe). I'm not really doing CW at the moment but might be worth putting my oar in for this topic. Thanks for the suggestion chewy  |
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Post by bargemast on Oct 31, 2016 16:59:50 GMT
Dalslandia. Yes he's very knowledgeable (a trip boat skipper on the continent I believe). I'm not really doing CW at the moment but might be worth putting my oar in for this topic. Thanks for the suggestion chewy It may be a good idea to invest a little bit of money to buy yourself an "Endoscope-camera" www.ebay.com/bhp/endoscope-camera to have a better look under water of the sides of your prop, this to see if you can find any useful information about size and pitch, as if that's the case, prop calculations will be a lot easier then by guessing.
Peter.
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Post by Deleted on Oct 31, 2016 17:06:07 GMT
I could see the sides very clearly as I had a waterproof torch and clear water. I think the measurements might be stamped on the end where the nut is. Or possibly the other end but not enough room for a scope.
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Post by Gone on Oct 31, 2016 17:08:27 GMT
There is a guy in the other place who knows a lot about propellers, admittedly aircraft, but it is still a fan in a fluid. So if you don't get a good answer here, you could try there, or even entice him over here with your question.................... Dalslandia ? I forgot his name, but that sounds about right, and if anyone asks a prop question he often joins in the replies. |
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Post by JohnV on Oct 31, 2016 17:10:11 GMT
That's also the name of his trip boat I believe ...... on one of the Swedish canals
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Post by Deleted on Oct 31, 2016 17:10:23 GMT
The 4 blade prop I had seen on ebay seems to have a 16:1 taper and from what I can gather almost all UK canal boats have 12:1 taper. So it might not fit anyway.
L3.5" . taper 1.3/8 > 1.1/6 is what's written on the advert. My prop has a 4" boss length so may be completely different.
Not sure really.
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Post by Graham on Oct 31, 2016 17:10:37 GMT
Have you tried any of the online sizing sites?
What is the distance from the Utxer plate to the top of the skeq?
Engine HP at max revs?
Length at waterline?
Number of bearings between the the engine and the stuffer box?
Weight
Beam
Draft
Gearbox ratio 2:1
Think that is about all you will need
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Post by JohnV on Oct 31, 2016 17:12:44 GMT
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Post by nipper on Oct 31, 2016 18:18:56 GMT
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Post by Deleted on Oct 31, 2016 18:30:07 GMT
Thanks for that nipper I always thought that a 4 blade prop made a big diffence but running that calculator it doesn't seem to be that significant. What it does say is that it would need 75hp to reach hull speed on a 40x9ft boat weighing about 16T (8.5 knots) and that the max speed with 50hp engine would be 7.5 knots. I don't know the weight but its definitely a displacement boat ! The fact I can only get 6 knots and the engine gets to full revs very quickly with lots of magimix type fizzing seems to indicate an undersized prop. |
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