Question for an engineer ................

[Shayne]

I want to spend 3 grand on boat propeller shaft couplings but before i do i must identify the PCD of the output flange coupling .

It's not a standard part because its a bobbin used to clear a protrusion on the gearbox so couplings don't foul , though it probably is a standard size with regards to the flange .

The people who built my boat offer "it won't be nothing special so just standard" , the people who made my shafts could only guess it was the typical 4 bolt pattern 5" standard though for reasons we will never know the flange diameter of mine is 6" . The engineers based where my boat is whom i have paid a fortune to prevent me from making an income for 4 months said "erm dunno"

The people who supplied my engine and gearbox and probably made the bobbin though they have no record of it were the most helpful by offering that i should be using 7/16th bolts and the PCD should be 108x2 .

The people selling the coupling i need were happy to accept the 7/16th but questioned the 108x2 .

Could it be the technical head calculated the pdc as we spoke only giving me half the math and so it should be 216x4 , or am i just confusing things further ?

If it's of any use to someone who is bored the gearbox is a twin disk technodrive , 2 ratio , model TM93 .

Any help would be greatly appreciated .

 

[Towpack]

Is this any help?...........Measuring PCD

 

[Chris]

The pcd is the pcd regardless of how many holes the number of holes simply divides the 360 degrees up into 4,5, 6 etc which is usually uniformly spaced
So a 175 . 4 would have holes at 0, 90, 180 and 270.
however it’s perfectly possible to have a 175.4 but with the holes all crammed into the first 180 degrees so you’d have holes at 0, 45, 90, 135 and 180 but it would still be a 175 circle

 

[Shayne]

Thank you for that Chris my mind is a mess of frustration so i can't think but with a uniform pattern in mind and a pen and paper in hand i can see that 108mm is 4 and 1/4 inch so when drilled out to take 7/16th bolts evenly spaced the standard 5" flange would almost run out of metal hence whoever made the bobbin used a 6" flange .

Its another avenue to investigate anyway .