shaft brakes

mate of mine made one,using a wide timingbelt,fitted it round the shaft,tied a rope to it which then went round a pulley block and was then tensioned up on a cam cleat all controllable from the cockpit.
i guess it depends on how much room you have and how much exposed shaft ,i always thought about running an alternator of mine.maybe another project,
i think however its done ,it has to be easy and quick to release,
 
I read something somewhere on the web about using a car, motorbike or mountain bike disc brake system with a microswitch to release it when the engine is running. Also, was speaking to one of the engineers at Swanwick Marine Engineers (who all used to work for Moody's before setting up on their own) and something along these lines is how they used to do them at Moodys.

I eventually plumped to go for one of these http://www.shaftlok.com/cover_photo.htm after finding one at a bargain price.
 
oh ... to add one more comment ... you might get some 'know it alls' on here claiming that if you get a Bruntons autoprop you won't need a shaftbrake. Ignore such comments as they are cobblers. I know from experience! And yes, before anyone tries to justify otherwise, the prop was working correctly.
 
a nice bit of kit but you need to get to the shaft/engine to release it, the idea of the mountain bike disc system is intresting though and could be operated remotely .also would take up less space hmmmmm,thinking cap on for the afternoon, ,wonder wether swmbo needs two brakes on her bike,
 
"a nice bit of kit but you need to get to the shaft/engine to release it" - I assume you mean the ShaftLok. If so, note it is operated remotely which is perhaps not clear from their brochure. I've located the control knob at the helm. Nice bit of kit that does what is says on the tin, but it does need take up a a lot of space as the disc is approx 12" in diameter.
 
OK, I'll bite. I thought that with an Autoprop you just left the box in forward gear. Well that's what I do with ours. I assume that for the particular type of box you are talking about tihs is not sufficient to lock the shaft.
 
That would work with a mechanical box but not with Hydraulic. This comment from the website mentioned above mirrors my own experience:

"Max-Prop and AutoProp, feathering propellers, require that the prop shaft be held stationary momentarily while the blades feather. Henry K. of Victoria, Canada 10/24/02 tells us: Because AutoProp sets its own pitch it tends to open at speed if it is not locked."

In case anyone is interested, there's a page on that website discussing if a freewheeling of locked prop has more drag. I found it quite interesting ... but then again I am a bit of a nerd when it comes to technical stuff!
 
Ah hydraulic boxes, well outside of my domain, and yes, APs have to be locked all of the time otherwise feathering or not they will spin.

Finally, oh God, please don't start the freewheeling vs locked debate again.

I understoood that it been established that locked blades, self pitching or no, offered less resistance than revolving. The analogy that convinced me was that a helicoptor drops like a stone with fixed blades yet floats down (ie more drag) with revolving blades. But thne I'm easily convinced of most things...
 
[ QUOTE ]
please don't start the freewheeling vs locked debate again

[/ QUOTE ]

Agreed - but .. .. Not according to the paper, previously a free download but now subscription only (I think) "A comparison of ten Sailboat Propellers" by Lurie & Taylor. They concluded folding props (inc Autoprop) should be locked and fixed blade props should freewheel. PM me if you want me to send the pdf file.
 
Well, that's interesting 'cos before the AP we had a huge fixed prop (RS used to be a charter boat) and locking the box in reverse used to increase boatspeed in light airs.
 
The analogy that convinced me was that a helicoptor drops like a stone with fixed bladesyet floats down (ie more drag) with revolving blades. But thne I'm easily convinced of most things...

.......................................................................................

Whever told you this!!!!!!!!!!!!! They drop like bricks and do anything but float down.......The pilot builds up stored energy in the rotor blades as he drops like a brick by making them spin as fast as possible and then when he thinks he is the right distance from the ground he applies collective pitch and uses that stored energy to slow down the descent as the helicopter reaches the ground and slowing down the blades in the process . DO it too high and whoopsie !!! The tail falls off and maybe a few sore bums or worse when it accelerates the last few feet /forums/images/graemlins/laugh.gif
 
I'd appreciate the pdf file....shall I PM you or is it available on line?
 
Erm, I think that you just agreed with me, the rotating blades have just stopped the heli from hitting the deck hard OK I was being a bit loose with the floating down bit the the principle still holds or am I missing something.

And if you want another analogy, a sycamore seed whirs slowly to ground whereas a similar sized pea will hit the deck a fair bit harder. MOre drag from the whirring blade.
 
Thanks for the paper. I shall enjoy reading it in detail but it clearly shows what I expected....freewheeling fixed props reduces drag, let them spin. OK, there is wear, but then again everything wears in time. Boats are not maintenance-free items. It's like refusing to use the traveller to save wearing the bearings on the pulleys /forums/images/graemlins/wink.gif
 
... and the paper (almost) justifies the Autoprop we fitted last year. Though the reason we fitted it was to improve the handling, particularly going astern, which it certainly does!!
 
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