Prop talk

[Island Time 1,235]

Have you tried heat, a puller and a slide hammer to remove? It will come off....If the hammer is big enough! 

That last prop listed - The Kiwi Prop - that is cheap if it is the right size and rotation...

[wheels 543]

Sorry, I got the last in the list wrong. I have rectified that now. It was the Briski for $425 that I was referring too. It would want to be in real good condition for that.
Yes the Kiwi-prop is a steal. But I noted it was large in diameter and could be too big.

Getting it off the shaft, yep wrap a cold water soaked Towel around the shaft and then heat the prop where it is on the shaft. If you have a puller, put that under tension. If you don't, get a sledge hammer against the prop body and give the opposing side a smack with a heavy hammer. They usually pop straight off with one good wack. I have often used boiling water to heat the prop and that has worked fine. But a Gas torch maybe needed in your case.
 

[Steve Pope 243]

Not a great expense to swap out the to large blades on the Kiwi Prop with ones more suitable to your boat / engine. So long as the shaft size and taper suit. At the price of the one on trademe plus the cost of 3 x new blades it would still be attractive.

[too_tall 15]

An interesting analogy re spinning versus fixed props, A helicopter when the blades are in auto rotation (no power) comes down with the blades spinning from their passage through the air and acting as a brake, it will land hard but generally in one piece.. A Helicopter with the blades stopped drops like a brick!

Autorotation is building momentum in the blades and transmission that is useful in an emergency. Firstly, it allows for a controlled descent which is vital for the second part of the landing to be successful, where the energy that has been gained in the form of momentum ( rotational, in this instance ) can be utilized to arrest the downward velocity of the helicopter.

 

I have been in an autorotation landing and it was as controlled and soft as a powered landing, although the ground did approach alarmingly rapidly. Timing is everything!.

[El Toro 97]

Anybody got any thoughts on the 3 bladed Gori with overdrive prop?

Good bad and the ugly?

[Tiller 2]

I have a 2 bladed Gori prop brand new 14" x 9.5 RH on 1" shaft for sale if interested

[wheels 543]

 

 

I have been in an autorotation landing and it was as controlled and soft as a powered landing, although the ground did approach alarmingly rapidly. Timing is everything!.

Yes timing is. Hence why RNZAF no longer have any working Sioux choppers. In their last years, they did however have many separate Tail sections and Canopy Sections, in a somewhat bent format.

I noticed that they don't seem to teach Autorotation landings at Whenuapai. Or none I have ever witnessed anyway. Probably because we can't afford to lose the few Seasprites we have.

 

Gori Props. Great props. Expensive new. Very expensive. Very good mechanism.

[Dtwo 157]

Anybody got any thoughts on the 3 bladed Gori with overdrive prop?

Good bad and the ugly?

My understanding of the "overdrive" feature is that to engage, you motor along in forward gear.  Then, pretty much slam it into reverse before the prop has a chance to reset.  Seemed hard on the gearbox when I witnessed it.

[El Toro 97]

My understanding of the "overdrive" feature is that to engage, you motor along in forward gear.  Then, pretty much slam it into reverse before the prop has a chance to reset.  Seemed hard on the gearbox when I witnessed it.

Yep thats the one, could you give me soe more info on that....interested to hear, do you think it improved performance (after ripping the gear box out!?)

[Dtwo 157]

Yep thats the one, could you give me soe more info on that....interested to hear, do you think it improved performance (after ripping the gear box out!?)

I wouldn't like to sound like I know too much - just witnessed on a mate's boat.  I will ask him but I have a feeling that he stopped using the overdrive?

[Nzgrant 19]

My understanding of the "overdrive" feature is that to engage, you motor along in forward gear.  Then, pretty much slam it into reverse before the prop has a chance to reset.  Seemed hard on the gearbox when I witnessed it.

 

Wrong way round. You engage reverse gear (low revs) then kinda slam it into forward gear. This engages the overdrive. There are some good utube videos of how it works. My understanding is that it gives you essentially a different pitch to your prop.

We have one and basically seems to give more bite in the water for less revs. Great for manouvering around the marina.

[El Toro 97]

What about long distance motoring NZgrant?

Do you find it faster/lower revs/better feul economy?

We do alot of motoring for a boat with a mast unfortunately, and am keen to eek out a little more speed, am pondering them, but ye gods they are expensive

[John B 106]

I like the idea of them , the way it was explained to me was if you were in the light or motor sailing you use it as an overdrive,ie keep speed , lower revs.. The owner of the boat I was talking to had an Elliot cruiser and was ticking along at 9 odd knots  and at comfortable revs.

Of course I can't quite see how that would make an engine manufacturer happy, as they inevitably INSIST that their engine should be able to reach full rpm with the correctly pitched prop. This is so that the engine is not overloaded . Of course a lot of cruisers do set their drive trains up slightly over pitched anyway, just so they can do their comfortable cruising speed at  sweet spot revs( usually around that 24... 2600 mark)

 If you can select an overdrive then you could easily  overload the engine if you misused it.So  I wonder what the engine guys think about Gori.

[wheels 543]

Re the full speed part and an overdrive prop feature.
A Diesel engine has two points to consider. It has set dose of Fuel and RPM to achieve Hp. Max Hp is at full RPM. Ruffly, 50% of full RPM would be 50% of Hp. VERY RUFFLY!!
Being able to achieve Full RPM within 10% (in gear) means your engine is matched to the load perfectly. Too much load causing the Engine to never reach for RPM (outside of the 10% rule of thumb) means the engine is overloaded. Excessive Fuel is being squirted into the Bore and results in the dilution of the Lubricating oil and Black smoke from unburnt fuel. Excessive load causes wear on big end bearings and other areas. It is the excessive load causing the engine to not rev correctly that causes the damage. Not that the Engine is running at 50% throttle. Idling a Diesel for long periods is not great either. But you can as long as you give it a good hard burst for awhile and go back to your idle work.
Overdrive with the Gori prop is OK, providing it is not overloading the engine. You may be able to drop the revs back 50%, save 50% in fuel and still have the engine running quite happily all day. Just like driving a Diesel Vehicle on the road, you use full throttle to get up to speed and then back off and may run at about 75% of full throttle. If you are climbing a Hill or into a head wind that is. And that is why you want to be able to achieve full RPM with the engine, for the times you are sailing into a Wind or up a "Hill" or when you need to move around in the Marina.
 

[waikiore 399]

Well since you asked... I can clear up some of these points on Gori props

The overdrive feature, (on three blades only) is engaged only by going in reverse at say half a knot then shifting into forward and off you go with approximately 15% more pitch. It is designed for motorsailing or light weather - as can happen around our summer or half way to the islands.

No slamming from gear to gear necessary.

To disengage just shift to neutral wait for shaft to stop rotating then into forwards again, the engine will not reach max rpm in overdrive so you don't ask for that from the throttle, however the boat will reach hullspeed at much lower revs than normal giving quieter and more economic steaming.

These props are very easy on saildrives as they are not trying to drive the leg under sail as they fold completely behind the leg, a well known problem with cats.

These are a precision bit of kit, and the engine should always be able to attain max revs in normal pitch for warranty sign off, many of the importers and some engine dealers do not understand how they work and I have often been called on to demonstrate so that the owners can benefit from these and other features.

[waikiore 399]

Wheels is correct re engine details, these particular props just give the knowledgeable owner another option, combined with good manoeuvring thrust at low revs around a marina and less prop walk in reverse, (the blades are propeller shaped not flat paddles and have the same leading edge for forwards and reverse. Calculations have to be made for every boat taking into account all the variables which I do to ensure the engines power is utilised correctly. 

[ballystick 72]

My 2 blade folding Gori prop is excellent and reverses quite well too

[ex TL systems 63]

I have 2 3 blade folding Volvo props and shafts available , I think 1.25 inch shaft off a 38ft cat and hardly used, as boat has gone to outboard power.