Has anyone considered installing either a "Python Drive" or "Aqua Drive" between their engine and prop shaft? Would appreciate hearing any pro's or con's. Ernie
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flex coupling
Ernie, can't address those brands but last year I installed a PYI flex coupling on our 356-3GM30 with an Autoprop. I was concerned about cutless bearing wear because the yanmar mounts seemed really soft and we were getting wear even though the alignment seemed correct. The pyi coupling only takes about 1 1/3 inches of space, is really robust, and seemed to reduce vibrations and shaft movement a lot. after haulout, there was no additional wear on the cutless. so I think it helped.
Ernie, can't address those brands but last year I installed a PYI flex coupling on our 356-3GM30 with an Autoprop. I was concerned about cutless bearing wear because the yanmar mounts seemed really soft and we were getting wear even though the alignment seemed correct. The pyi coupling only takes about 1 1/3 inches of space, is really robust, and seemed to reduce vibrations and shaft movement a lot. after haulout, there was no additional wear on the cutless. so I think it helped.
What is involved in the installation ?
Does the shaft have to be shortened for this installation ? If it does, is it a simple hacksaw job, or a machine shop job ? Thanks....... Jeff
Does the shaft have to be shortened for this installation ? If it does, is it a simple hacksaw job, or a machine shop job ? Thanks....... Jeff
Shorten Shaft?
I have the same question about shortening the shaft. Is seem that the upper limit for the distance between the aft side of the strut and the front side of the prop hub should be 1.5 x shaft diameter (thus 1.5" for a 35), and my L35 currently has about 1.25" of space. So adding a flex coupling probably does require shortening the shaft. The keyway at the coupling end of the shaft appears to be ~1" longer that needed (on my boat) which might mean that cutting the shaft will still leave enough of a keyway to use. If it possible to have the shaft extend through the shaft flange and into flex coupling, then cutting might not be necessary, but that depends of whether the shaft hole goes right through the shaft AND if the flex coupling also has a hole. I think the R&D coupling (which I have on order) has metal shear plates that block the potential hole. If there is not enough keyway in the shaft at the flange end, then simply cutting it off will be a problem and probably requires a shop to do the job. Chris
I have the same question about shortening the shaft. Is seem that the upper limit for the distance between the aft side of the strut and the front side of the prop hub should be 1.5 x shaft diameter (thus 1.5" for a 35), and my L35 currently has about 1.25" of space. So adding a flex coupling probably does require shortening the shaft. The keyway at the coupling end of the shaft appears to be ~1" longer that needed (on my boat) which might mean that cutting the shaft will still leave enough of a keyway to use. If it possible to have the shaft extend through the shaft flange and into flex coupling, then cutting might not be necessary, but that depends of whether the shaft hole goes right through the shaft AND if the flex coupling also has a hole. I think the R&D coupling (which I have on order) has metal shear plates that block the potential hole. If there is not enough keyway in the shaft at the flange end, then simply cutting it off will be a problem and probably requires a shop to do the job. Chris
Cannot be a hacksaw job
Jeff, You cannot hacksaw the propeller end of the shaft as you would cut through the threaded part and also change the dimensions of the tapered part making it impossible to re-insert the prop. You might be able to hacksaw the shaft on the coupling end (assuming your shaft is 1", hacksaw cutting through SS is going to be long and difficult), but you still will need the key way to be re-machined ! Because of the small increase in total lenght, most people that I know that went to a flexible coupling used the same shaft without any problems. Of course they had the necessary room to do so.
Jeff, You cannot hacksaw the propeller end of the shaft as you would cut through the threaded part and also change the dimensions of the tapered part making it impossible to re-insert the prop. You might be able to hacksaw the shaft on the coupling end (assuming your shaft is 1", hacksaw cutting through SS is going to be long and difficult), but you still will need the key way to be re-machined ! Because of the small increase in total lenght, most people that I know that went to a flexible coupling used the same shaft without any problems. Of course they had the necessary room to do so.
Me too on PYI coupling
I too installed the PYI coupling and it works well on my Beneteau 400 with the M50 engine. Installed as advertised, kept the original bolts in case of breakoff of the sacrificial bolts furnished. EAsed vibrations, provides me with a fail safe in case of propeller seizure from lines or other obstructions.
I too installed the PYI coupling and it works well on my Beneteau 400 with the M50 engine. Installed as advertised, kept the original bolts in case of breakoff of the sacrificial bolts furnished. EAsed vibrations, provides me with a fail safe in case of propeller seizure from lines or other obstructions.
I did it
Did just this in 1996 on my H376. Fitted the PYI flex coupling and it just moved the prop back enough to enable me to fit a rope cutter - great. No need to modify the shaft. However we caught some discarded fishing net in fog, no wind and whilst crossing the shipping lanes. I worked desperately on the coupling trying to turn it with a long screwdriver. After an hour I got the prop to move about 2 turns so fired up the engine, revved up and selected gear. Much vibration and lots of polyprop netting came out from under the counter and we were able to move at 2 knots. 60 miles later we were home. 8 years afterwards I discovered one web of the coupling was split. Maybe it ran like that since our moment of excitement. No way of knowing as we had no signs of anything wrong. Makers say it protects the gearbox in case of something wrapping round the prop. It sure does yet still remains functional. I just bought and fitted a new coupling last year and now all is well. Highly recommended. No problems from additional overhang of prop-shaft.
Did just this in 1996 on my H376. Fitted the PYI flex coupling and it just moved the prop back enough to enable me to fit a rope cutter - great. No need to modify the shaft. However we caught some discarded fishing net in fog, no wind and whilst crossing the shipping lanes. I worked desperately on the coupling trying to turn it with a long screwdriver. After an hour I got the prop to move about 2 turns so fired up the engine, revved up and selected gear. Much vibration and lots of polyprop netting came out from under the counter and we were able to move at 2 knots. 60 miles later we were home. 8 years afterwards I discovered one web of the coupling was split. Maybe it ran like that since our moment of excitement. No way of knowing as we had no signs of anything wrong. Makers say it protects the gearbox in case of something wrapping round the prop. It sure does yet still remains functional. I just bought and fitted a new coupling last year and now all is well. Highly recommended. No problems from additional overhang of prop-shaft.
usually no need to shorten shaft
the coupling is thin enough that you don't need to shorten the shaft if you have clearance. the main effect of just moving the shaft back might be more cutless wear, because the prop is on a longer lever arm-but in our case it seemed to improve cutless wear, and we've got more room for cooling water flow around the cutless. On the 356 Hunter uses a shaft that has splines into the flange, and threads and a nut inside the flange so the shaft can't pull out. the shaft can't be shortened, we'd have to get a custom replacement.
the coupling is thin enough that you don't need to shorten the shaft if you have clearance. the main effect of just moving the shaft back might be more cutless wear, because the prop is on a longer lever arm-but in our case it seemed to improve cutless wear, and we've got more room for cooling water flow around the cutless. On the 356 Hunter uses a shaft that has splines into the flange, and threads and a nut inside the flange so the shaft can't pull out. the shaft can't be shortened, we'd have to get a custom replacement.
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