Stopping the prop!!??

We had exactly the same problem with that set up. When we brought the boat we found that the gearbox (TMP)was very noisy and needed a bearing replaced. The manufacturers, yes they are still going, said that the wear had been caused by the prop auto rotating whilst sailing, which deprived the bearings in the top of the box of oil. Their suggestion was to start the engine every hour or so, & let it run for a couple of minutes so as to circulate the oil. This also had the benefit of passing water through the stern tube. Despite that we fitted a Kiwi prop which has improved things, although we still get some auto rotation when sailing above 6 it's.
 
pcatterall said:
Thanks guys, feathering prop would have to wait until i have money and boat comes out of water.
Just out of interest what is a ball park price for the prop alone?

no real answqers to my question about the water feed to the prop seal ( the fact that there is no water going to the seal when the prop is free wheeling?

Thanks again
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I have a featherstream depends on size but I think it was about £1000. Like another post sugests I have forgotten the cost due to it being the best thing I could have done to the boat.
 
Gone sailing said:
I have a featherstream depends on size but I think it was about £1000. Like another post sugests I have forgotten the cost due to it being the best thing I could have done to the boat.
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I have just fitted one to replace a non-lockable (PRM gearbox) 2 blader. Ordered a 17" one last year to get a 20% early order discount and it was still £1500!! :eek:
 
Assuming that it does no harm to leave the stop handle pulled out, wouldn't it be neat to use the stop lever to pull a shaft brake on? Just needs an extra Bowden cable pulled by the lever that pulls in a simple brake.

Have I lost the plot?
 
Seajet said:
I believe it is correct to say a freewheeling prop creates more drag than a locked one; think of the turning prop as a solid disc...
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The trouble is Seajet has a point, and if you bother to read all the published research on this the answer to the drag question is not straightforward and that means not just cherry picking the conclusion of one paper.

Blade area is a huge element as is the speed through the water. So not all props are equal and add to that the effects of the hull and the whole system is chaotic, some published results go as far to suggest that mathematics and computer modelling is unable to provide a definitive answer. So the answer is a rather disappointing "it depends".

My own contribution to this debate is an experiment carried out in 1992. We didn't have access to strain gauges so the experiment was very practical. We did have a long tank and a 12v winch that pulled a "truck" on rails across the tank. We also had a ammeter in series with the winch so we could measure the current drawn by the winch.

The theory was that if we could pull a propeller attached to the truck through the water with the winch the ammeter would indicate how much power (amps) were required in each configuration. You will all appreciate that as the winch is required to supply more power the current will rise so the pass with the highest current would indicate the configuration that would sap the most power from a boat pushing THAT PROPELLER. A hypothesis that's not covered in the mathematics of attack angles and stall speeds, just a simple measure of raw power.

Sadly I no longer have the actual results of this very practical experiment however, I do remember the conclusion: that pulling the 3 blade propeller free wheeling used the most power (highest reading on the ammeter).

Truck on its own X amps Truck with fixed prop X + Truck with free wheeling prop X ++.

As far as I am concerned the best days work I ever did on this vexing question was to fit a volvo folding prop.
 
PCUK said:
The Volvo folding three blader gave us excellent performance. Coastal rides currently have a second-hand one for £150.
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That sounds amazingly cheap for something that costs over £1k new. Also not suitable for all boats, particularly the OPs where the prop is in an aperture.
 
I too have a hydraulic gear box on my Perkins. The solution is very, very easy and also will not damage the shaft if the engine is started while engaged. Take a small section of leather such as that found on a typical leather belt, about 12" long, wrap around the spinning shaft such that you are holding the two ends with the shaft supported saddle fashion. Take mole grips and pinch the saddle section of the leather, allow the mole grips to rest against a surface. The shaft will now be stopped. Try it, it works.
 
sailorman said:
Wrong, the blades self align when in neural & the boat speed alters their pitch
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Not quite, my SO37 had a NEW maxprop and that needed to be set in reverse gear to make the blades feather, my current Volvo Prop will windmill unless a gear is selected (reverse) but after I ve stopped it stays folded even in neutral until its under power again. When I stop the boat it feathers, I know this because when I dive under the boat its always feathered. So when the boat is driving the prop it wont always feather or fold. And if you read the thread you will find one contributor who claims his feathering prop rotates at boat speeds of over 6Kt - so in fact his never really feathers. I remember a PBO video test that showed that some of these devices didn't change pitch to enable a boat to go astern - a bit embarrassing to say the least.

So what it says on the box and what happens in real life are, in the world of folding and feathering props quite different in many cases.
 
Marsupial said:
The trouble is Seajet has a point, and if you bother to read all the published research on this the answer to the drag question is not straightforward and that means not just cherry picking the conclusion of one paper.

Blade area is a huge element as is the speed through the water. So not all props are equal and add to that the effects of the hull and the whole system is chaotic, some published results go as far to suggest that mathematics and computer modelling is unable to provide a definitive answer. So the answer is a rather disappointing "it depends".

My own contribution to this debate is an experiment carried out in 1992. We didn't have access to strain gauges so the experiment was very practical. We did have a long tank and a 12v winch that pulled a "truck" on rails across the tank. We also had a ammeter in series with the winch so we could measure the current drawn by the winch.

The theory was that if we could pull a propeller attached to the truck through the water with the winch the ammeter would indicate how much power (amps) were required in each configuration. You will all appreciate that as the winch is required to supply more power the current will rise so the pass with the highest current would indicate the configuration that would sap the most power from a boat pushing THAT PROPELLER. A hypothesis that's not covered in the mathematics of attack angles and stall speeds, just a simple measure of raw power.

Sadly I no longer have the actual results of this very practical experiment however, I do remember the conclusion: that pulling the 3 blade propeller free wheeling used the most power (highest reading on the ammeter).

Truck on its own X amps Truck with fixed prop X + Truck with free wheeling prop X ++.

As far as I am concerned the best days work I ever did on this vexing question was to fit a volvo folding prop.
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Well said Marsupial - simple minds need simple, catch-all answers, so the rather complex hydrodynamics are reduced to "Fixed props cause drag" - which all the Soton research proves to be a half-baked, half-correct answer.
Long-keelers with small prop orifices are the worst culprits (usually no room to fit a feathering or folding prop) and wear out gearboxes in short order, making an awful din when underway. If one has to have a fixed prop a two-blader aligning behind the deadwood is best fixed NOT rotating - saildrives and P-brackets folders of self-feathering (but the latter still need a fixed shaft to feather).
 
BlowingOldBoots said:
I too have a hydraulic gear box on my Perkins. The solution is very, very easy and also will not damage the shaft if the engine is started while engaged. Take a small section of leather such as that found on a typical leather belt, about 12" long, wrap around the spinning shaft such that you are holding the two ends with the shaft supported saddle fashion. Take mole grips and pinch the saddle section of the leather, allow the mole grips to rest against a surface. The shaft will now be stopped. Try it, it works.
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Basically what I did with the bike inner tube. Although I used a week link and strong point in case we forgot, mole grips flying would not of been friendly....
 
Can't you just pop it in reverse before you stop the engine. Not sure if it still holds with a hydraulic gearbox but I think it does. I have done that on many boats in the past and it's no problem. I've never had a problem restarting in gear either.
 
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