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On my Cheoy Lee 44, when I raise the sails and kill the engine, the prop starts spinning if I get over about 5 knots. I've tried shifting into forward and/or reverse, but it has no effect whatsoever-- the prop keeps spinning. The engine is a 50HP Perkins 4.108 Diesel and the transmission is a Borg Warner Velvet Drive.
I know this can't be good on the bearings and the packing gland. Any advice on how to stop this?
Have heard of shaft brakes to stop spinning and save rear trans bearings. Do a google search and something should show up. Know that articles have been written on the subject.
Hi all
At 5kns the rotary moment indused by the draging force seams big enuff turning whatever holds your prop. So if you need a brake just for (against) that purpose, have a look at Kobelt Marine stuff etc.
If a free spinning prop would abuse your bearings you better get an other type! What do think a bearing has to stand when motoring day be day for years. By the way: fill up your accumulators using the drag by cuppling an generator to your prop shaft (see jareds adwise)
good luck elena http://www.kobelt.com/pdf/brochure_brake.pdf
Check to find out if letting the prop freewheel is bad for your transmission. For some it is, for others it is not. If your transmission doesn't care, then letting the prop freehwheel probably puts less drag on your boat and is a good thing. If not, the shaft brake is not unusual or complicated.
One other option, if your transmission can take the freewheeling, would be to attach a generator to the prop shaft. That way you leave it freewheeling, and it charges up the batteries for you!
A folding prop would also solve your problem. I don't know about your access, but vise grips on and off the prop (emergency - need to "hit the key") would be a pain for me.
The manual for my Universal diesel engine indicates that it is o.k. to leave it in neutral while sailing, so I was going to do that. But the manual for my Varifold folding propeller says I have to put it in gear to have the propeller fold up. So given these conflicting directions, what would you all recommend--in neutral or in gear? Would there be any disadvantage to keeping it in gear while sailing?
Thanks for any advice.
Frank.
You can not compare a fix prop with a foldable one! The first one reduces drag while spinning, the second by folding for less drag.
Stick your hand into the water while sailing and turn the hand 90° back and forth. You'll feel the difference!So what happens?
A free spinning prop is not good. If for no other reason, it will slow the boat. Either put the transmission in gear or if hydraulic install a shaft break.
he Borg Warner boxes needs oil pressure from the input shaft, engine on. to engage the clutches. I guess your engine is not of the newest model, so has it been spinning this long, let it spin but keep the box in neutral position. It was not recomended by the older Borg Warner to let the propeller spin but a shaft lock to be innstaled, but as I said has it been spinning for the last 20+ years (?) I would keep on unless You plan a circum navigation.
he Borg Warner boxes needs oil pressure from the input shaft, engine on. to engage the clutches. I guess your engine is not of the newest model, so has it been spinning this long, let it spin but keep the box in neutral position. It was not recomended by the older Borg Warner to let the propeller spin but a shaft lock to be innstaled, but as I said has it been spinning for the last 20+ years (?) I would keep on unless You plan a circum navigation.
Folding props can keep freewheeling, especially of you start sailing at speed before taking the engine out of forward gear. The resistance of the gearbox (generally in reverse) forces the prop to fold due to drag. Once folded, you can go to neutral again, but in most boats there's no need.
We have a Hurth gearbox, the recommendation is to put into reverse while sailing, and further not to let the prop drive the gearbox if the gear is in forward without the engine running. (I believe the input shaft must be powered to provide lubrication for the gearbox)
The locking of the clutch systems are different on the Borg Warner and Hurth. The hurt is purely mechanical, but the cluch neds the resistanse given by the propeller to lock. That gives that is has to be put in reverse to lock the clutc pack. This goes for all boxes with multiple disk clutch pack, Hurth, most Yanmar, ZF.
The lubrication is performed by the lower shaft splashing the oil around, no pressure, and the upper only rotates with the engine. The output shaft and bearings are not in oil and letting the prop shaft rotate means the bearing runs dry!
A free spinning prop is not good. If for no other reason, it will slow the boat. Either put the transmission in gear or if hydraulic install a shaft break.
This has been argued many times over the years, always without facts as far as I have seen. If anyone knows of any experiments or measurements I would love to know of them.
My belief is that a spinning prop offers the least resistance. If it offered more resistance, it would stop spinning. But that is just a belief, not even a theory.
But I can definitely recommend you not install a "shaft break". A shaft brake would be more appropriate.
A free spinning propeller will have the same drag as a solid disc of the same diameter. DO NOT LET THE PROP SPIN FREE. Shut down the engine in gear and this should be enough to stop the prop from spinning. If you are in gear and the prop still spins, youu need a shaft brake.
This is base on Aerodynamics, but it is essentially the same in Hydrodynamics. The point is "The propeller produces much more drag as it windmills than it would if it simply stopped turning."
i still think the example there doesn't fit the problem here.
for starters, the propellers on aircraft don't spin free. because they are usually atached directly to the crankshaft of the engine, a windmilling propeller has to overcome the engine's internal friction and compression. the power needed to do this produces drag.
as solution the blades are turned so they don't produce spinning force at all, reducing drag to the minimum.
it doesn't address the problem of a nonfeathered propeller spinning with no friction, or almost no friction, as only the friction of the bearings has to get overcome. and neither does it address the drag of a nonfeathered propeller stopped by a brake.
Actually there is NO FRICTION in a free spinning propeller on a turbine powered aircraft. There is no mechanical linkage between the propeller and the power turbine. If you watch a pre-flight on a turbo prop aircraft, you can free spin the prop like a windmill with no resistance what so ever. It is still detrimental to fully feather the prop as soon as you loose power to keep the dead windmilling engine from dragging the aircraft down. In fact if it is an air transport category aircraft it must have a AUTOFEATHER system to make the climb requirement after an engine failure on takeoff. ANYWAY..... Try this...Get a small prop from the toy store. Hold it out the window of your car while somebody else drives. Look at the difference in force aginst you with a spinning prop and a stopped one. You will be amazed how much drag a spinning prop makes!
still the only conclusion those articles offer is that a feathered propeller has less drag than a nonfeathered propeller, either stopped or windmilling.
don't get me wrong here, i'm not saying that you're wrong, just that those articles don't support your statement.
You seem to have lost contact with the 'sea' in the above discussion! The question is not what creates the less drag, the question is what the gear box may handle and tolerate. Most marine gearboxes can not tolerate free spinning due to lubrication problem!!!!!!!!!!!!!!!!!!
Comparing a propeller in air to one in water is like the apples/oranges deal. How many times more dense is water, than air? Air compresses, water doesn't. Dragging a stagnant prop through the water takes more energy than a free-wheeling prop. More energy is spen deflecting all the water, where if free-wheeling, some of the energy is stored in the prop as energy. This energy helps keep the prop at speed, thus deflecting less water......less drag.
As for lube, no bearing surface will tolerate a lack of lube for long, so it boils down to the design. Now, under power vs free-wheeling, a bearing will tolerate a great deal of free-wheeling since the load on the bearings is negligible, as opposed to the load when motoring. Still, there are limits. This is analagous to towing a rear-wheel-drive vehicle. Typically, if towing over 25 miles, give-or-take, the manufacturer states that the driveshaft should be removed to prevent transmission damage since the tranny isn't pumping lube when being towed.
Probably best to change to a folding prop? The comment earlier about a Velvet Drive requiring lubrication from the front with the engine running may have validity, it is certainly the case with auto trans in your car and the structures of the gearboxes are very similar. Borg Warner would be able to clarify that but as the earlier comment also says, if it has been running like this for 20 years, it must be OK.
The reason I recommend a folding prop? If you stop your prop from spinning, you'll knock as much as 1/2 a knot off your boat speed depending on the size of the prop and it's pitch. If you're into voyaging, that represents 12 miles a day!
Actually there is NO FRICTION in a free spinning propeller on a turbine powered aircraft. There is no mechanical linkage between the propeller and the power turbine. If you watch a pre-flight on a turbo prop aircraft, you can free spin the prop like a windmill with no resistance what so ever. It is still detrimental to fully feather the prop as soon as you loose power to keep the dead windmilling engine from dragging the aircraft down. In fact if it is an air transport category aircraft it must have a AUTOFEATHER system to make the climb requirement after an engine failure on takeoff. ANYWAY..... Try this...Get a small prop from the toy store. Hold it out the window of your car while somebody else drives. Look at the difference in force aginst you with a spinning prop and a stopped one. You will be amazed how much drag a spinning prop makes!
well, not too sure how people will interpret this, had one of those toy pinwheels, stuck it out the window cruising into work, it spun happily along with a fair bend on the stick for a 1/4 mile or so, pulled it in and tied the blade so it wouldn't spin, stuck it back out the window, and the blades plastered back for a second or two, then the stick snapped off.
My view, stick was strong enough with the blade spinning, but not strong enough with the blade stopped, stick never changed, only the blade spinning or not, so I'd have to say drag increased when the blade stopped.
is a pinwheel identical to a prop? No, but many of the same 'laws' are in effect, and yes the entire surface area of a pinwheel is much greater than a prop.
had thought about sticking my trolling moter out the window and measuring the stress with a fishing scale, but figured that may raise questions.
i guess the problem is that a prop that has a good efficiency under power hasn't neccessarily low drag without power, either stopped or windmilling.
some designs might compromise to one degree or another, trading efficiency under power against lower drag unpowered.
as omatako said, best might be a folding prop, second an adjustable prop.
question as always is how much money has to be spent on it, if the speed increase is worth spending it, or if the money is available in the first place and not needed for other items.
Ahoy, dis ere Pirate has shouted me challange before, why don't ye just take de blooming thing off and try sailing for real? I ain't never had a prop on me vessels and never will. What's the point? Iffin I'm half way to home and dwe wind dies I anchor and wiat for god to deliver me home. Iffin he don't,den i figger I wasn't meant to go home yet. On the other hand iffin ye know your going to be sailing for extended periods why not just take it off and put it pack on when ye needs to navigate a tricky channel or git home to yer overbearing wife?. What ye be afrain of a little underwater exercise? Training might come in handy some day, like when your mast goes in de drink .
Does anyone know who supplies a propeller shaft brake for a 1" diameter shaft?
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