Hi Stu
Just checked the 4mm prop shaft bearing housing and it's 20mm long.
I tend to use the longer prop shafts in my builds and the 5mm shaft/10mm outer is a bit of a beast! Fine in the Swordsman but it's not right for the svelte Huntsman 31 (much too heavy and doesn't look right) so I've got a 4mm/8mm for that. For long prop shafts it's often recommended to go for 5mm but as Raboesch is quality stuff and I'm guessing they wouldn't make a long 4mm if it didn't work.
All my motors are lower kV than yours as I tend to choose within 800 - 1100kV and then choose the LiPos to give me around 10/11k. revs which is safely within the 15k. max.
I just fancied using the maintenance free prop shafts but the conventional ones, especially the better quality ones, are obviously fine as the speed merchants, Harry (Canabus) and Bob can verify.
Chris
Yup - pleased to verify that Chris.
I have used an M5 Maxi-Shaft inner from MBB in my Rapier and I have taken the inner shaft out to check it and re-grease it after a good season of high speed action - and despite me opening the bearings up (the olde 2BA shaft had a slightly smaller diameter) there is no visible "play" in the bearings at either end that can be seen or felt.
All of the new shafts that I have bought for my Swordsman, Huntsman and Javelin are M5 Maxi Shafts - no chance of any "shaft whip" or "twisting" when using a good quality M5 shaft - and they are reliably solid and run "flat" when tested on glass.
I would not use an M4 shaft on any of the above mentioned boats using the brushless motors that I have chosen to fit in my hulls - I like to have some power to spare and know that when I do choose to "wind it up" the drive train will take it.
Even with an M5 shaft, I still avoid fitting a shaft any longer than it absolutely has to be to give less revolving mass and to allow the motor to be fitted as low as possible in the hull.
My original Swordsman ran for many years on a plain bearing M5 shaft with a '61 glow power motor ....and this included racing off-shore in the sea as well as on river and canals. No shaft bearing wear or failings to report.
I also ran a fast grp "flatty" hull with an OS 40 marine engine with an M4 shaft (inland waters only) - and that shaft did wear its bearings out fairly quickly, and both shafts were aligned carefully so I prefer to use M5 for any fast boat or one that has a powerful motor.
My scale models (such as my TID Tug) run very happily (year after year) with M4 shafts, but they are not being run at speed.
Aligning the motor and shaft correctly is essential to avoid premature shaft bearing wear.
Bob.