Removing folding props.

[B00B00 310]

I am trying to change to a slightly bigger prop from my 14X9 hinkley folding prop. Tried to get the old on off today (in a bit of a hurry with an incoming tide) but couldnt.

There is a barrel type nut inside the shaft, (which im guessing expands to shaft and locks the prop on) but there doesnt seem to be any way to move it, just a round hole in the center that seems to have a thread in it?

I kinda thought i would be able to figure out how it came off and then put the new one on the same way but it seems to be harder than i thought!

Anyone got any advice as to the correct way to do it as i dont want to damage any part of it but using too much brute force.

See attached photos.

[B00B00 310]

a few more

[wheels 543]

No it's a locking screw BB. It locks the next part from unwinding unlocking the prop.

[Bimini Babe 0]

Seem to remember I had the same problem when I replaced my folding prop. Partner spent best part of an hour breaking drill bits on the end of the prop shaft (thought there was a screw in there...), until I went and found a friendly engineer who came and got it off in about 2 minutes flat.

[Battleship 100]

looks like the locking grub screw is already out, you should be able to get a socket drive (looks about half inch) to fit straight in (see how the inside is square).

[wheels 543]

As Willow said, plus, you sure it's not a Henley??

[SloopJohnB 323]

In your second photo there's Scotch key at 4 o clock. Remove the set screw and use a square drive to remove the recessed lock nut. You might need a wheel/gear puller to lossen the hub.

 

Nothing changes in 40/50 years.

 

Use plenty of anti seize grease when assembling the unit.

[Battleship 100]

forgot to mention that despite appearances it is pretty much a normal nut not barrel shaped but cylinder shaped they dont expand onto the prop or anything like that but can sometimes get a bit seized, I used to boil the jug and pour it over which freed it up.

[wheels 543]

Darn, willow bet me again. Boiling water is a great trick.

Use plenty of anti seize grease when assembling the unit.

 

Never ever on the saft though. The mating surfaces MUST be kept clean or they will never pull up properly. Coating the shaft in something thinking it will help remove the prop later on, has been the cause of many loose props. The keyway and locking nut/bolt is only there as a backup and mechanical means of shock not allowing the prop from ever working loose. They should never be a primary means of holding the prop onto the shaft. That is done by the morse taper. The key stops the prop from ever spinning and losing that contact. A prop puller and some boiling water and maybe a sharp crack from a hammer, although always use a wooden block between hammer and prop. Smacking the prop with a metal hammer is a real no no and the prop guys will give you a real teling off if they see you have done that.

[B00B00 310]

Thanks for the advice guys, I think I had the concept compleley wacked.

Will have anorther go today and let you know how it goes.

I had another thought, thenew prop is exactly the same so I might just see if I can swap the blades over and leave the hub on there, any reason why this is a bad idea? New prop is 16 x 12.

[SloopJohnB 323]

WOW are you going line up against a Mac 25?

[wheels 543]

Cheap scate BooBoo. Exactly what I would do. As long as nothing is worn.

[Bill 0]

Should work fine if all you're doing is changing blade size and there's nothing missing from the hub. Most folding prop makers will sell the blades separately for this reason.

[B00B00 310]

All done, blades fitted straight in. Still about 15-20mm clearance at the hull so I hope that's enough. Will go for a motor trial at high tide once off the grid so if anyone sees the cordite doing warp speed out of the weiti river then you know its gone ok!

Thanks everyone for the help.

[B00B00 310]

For anyone who is interested, tried out the new prop today. It certainly has a whole load more bite, perhaps alittle too much. We are on hull speed (guessing around 6-6.2kts) at only 3/4 throttle, much more throttle and it doesnt seem to go much faster but there is quite a bit of black smoke. no smoke up to 3/4 throttle thou.

I imagine pushing the boat into a seaway it might load up a bit much but in flat water its mint.

Idealy i would reduce the pitch slightly but keep the same diameter. Does anyone know if you can repitch the prop and if so how/where and whats the aproximate cost?

We changed from a 14x9 to a 16x12, its a big jump but it was what i had available at the time so thought it was worth a try, will run it over Easter like that and see how it goes.

If anyone has a 16x10 or 16x11 prop or blades for a 'Bri-ski' folding prop i could be interested.

[Guest mental outlook]

Waterline length is so inconvenient!

[wheels 543]

Careful Booboo. You do not want to overprop.

You MUST be able to reach within 10%, the maximum Engine RPM when engaged. So out of gear, you open throttle and see if engine reaches rated max RPM. Yes it is safe to do so. Then take it for a run and open to max throttle. Best scenario is not quite making it to max RPM. Worse is making it there with ease, or having the engine black smoke and not getting as close as 10% of the max.

Diesel Hp is all about Revs. So if you never make full revs, you will never have the full available Hp when you need it. Continuos Hp is where you engine is wotrking at it's most efficient. Black smoke means it can not make it's proper rev range to fuel dose and you will eventually cause damage, not to mention wasted fuel and poor Hp.

The next issue you need to be careful of is Diameter. You do not want to have the clearance between Tip of blade and Hull less than 10% of Blade Daimeter or you will cause a hammering effect and affect the efficiency of the blades at that point.

Hull speed is Hull speed. You can not push past that. There is a basic rule of thumb formulae of square root of the WLL x 1.5, but it is better to use 1.3 to get a mnore realistic speed. That is because that last little effort of speed becomes more and more exponential as you climb the bow wave. So you can actually work out best case pitch to Engine RPM to boat speed on paper instead of just trying blades and having a guess to it being close or not.

Also remember, while diameter gives you more blade in the water, it also requires more Hp to turn it. You have far more friction, so you end up spending more poswer just top spin the blade rather than giving you more of the go fast. It can sometimes be better to keep the blade smaller and increase pitch. Once again, there are compromises between a launch and a yacht and what you are trying to achieve is the big question. As in, are you looking for more control in the Marina? or more boat speed? or???

[Guest]

We only have 5mm between the hull and prop.

It was a signed off isnstallation by the Volvo agent.

We still pull 8kn at full revs, and no wash or hammering issues.

We have a mini skeg so there is more gap to the hull.

[wheels 543]

There always has to be one that blows all the rules and theory out of the water, doesn't there.

[Guest]

It doesn't sound like Booboo has a rev counter, so cannot know how close he is getting to full revs.

Best get a handheld rev counter on it to check what maximum revs it can reach in FWD.