Prop question

[Jay c]

Quick prop question for you gentleman.

Is it possible to take a 24x25 nibral down to 24 square safely?

Thank you.

 

[djmarchand]

Yes, 2" is usually the limit.

David

 

[F/V First Team]

4" if you're daring
6" if you're insane

 

[Jay c]

Stubborn and a bit of a hammerhead on a lot of things.
But not daring or insane on Anything mechanical.

Found out this particular prop was 24 x 26 and already tuned down to 24 x 25 - trying to decide if it would work.
We swing a 24x24 now, and thinking about a new nibral, when this one popped up. (the odds of finding a new lefty prop in close to the right size are pretty slim, so i thought its worth a shot to save a lot of dough).

 

[F/V First Team]

I've had my Nibral propeller worked and reworked quite a bit this past year, took it like a champ.

Don't let just any monkey with a hammer take a swing at your prop, take it to a professional.

We wound 3" into it with a fairly severe cup, no problemo

 

[Jay c]

Thanks guys.
Definately pro's only for working on the running gear.

 

[captainlarry84]

1 is recommended max for nibral 2 recommended max for bronze. You can go more if they heat the wheel up cherry red at the hub and then let it cool naturally. I have watched them do nibrals that way at one of the premiere propeller shops on L.I. They do not recommend it however on owner request they will do it.

 

[F/V First Team]

yeah... let's not use fire on propellers
any good propeller shop should have hydraulics to twist the blades, no heat needed.
never heard of the one inch rule, guess thats one of the rules that were made to be broken huh?

 

[captainlarry84]

Re-pitching

These are all rules of thumb and I am sure all propeller shops had different methods to accomplish there requests.

Correct heat is never good, however when pushing the envelope for that extra 1 of pitch plus or minus heat can help.

I watch how they do it:

The propeller is placed in a very large padded vice

Next heat is applied at the base of the hub

Once the 1st blade hub is cherry red the correct propeller shaft is placed into the bore of the propeller.

The blacksmith then applies pressure onto the shaft gently twisting the blade at the base.
The twist is done by eye and feel.

Next the wheel while still hot is drop onto the cc machine and the dial indicator measures the pitch for the correct amount of pitch.

The wheel is then adjusted until the 1 or 2 of pitch is achieved.

The process is then repeated on each blade until the approx pitch is achieved.

Once completed the propeller is allowed to cool naturally

Once cooled the propeller is then placed on the cc machine and measured again.

The final adjustments for that perfect pitch match is then done by hand and without any heat.

Once completed final load adjustment can be achieved by adding a little cup if needed.

On re-pitching heat is only used when you really need to over extend the pitch increase or decrease. That is why it is very important to know the history of the wheel before you start to re-pitch it.

When wheel are cased the patters are made in every inch of pitch. So when buying a new wheel it is always nice to get one that is in the original shipping box which gives the serial number and original pitch & diameter.

In most cases on wheels that have never been re-pitch the stamp of diameter and pitch is between the blades. On a re-pitch it usually goes on the face of the hub base. The reason being is that it is easier to re-stamp on the flat surface as apposed to in between the blades.

Lastly cutting a wheel to reduce load is never a good idea. The tips of the blades do the best work and once cut down it can not be changed.

 

[F/V First Team]

Yeah... heat

If I ever saw a torch being applied to my wheel, or finding out about it after the fact, that particular propeller shop would be purchasing me a new wheel and paying for all modifications to it - which would be done at a different shop.

That is such a bad idea I cannot even begin to explain

 

[captainlarry84]

If you want 3 of pitch you will need a little heat helper, like I stated it is in those cases where you excide the limit of metal stretching and Nibral will crack with out help of some heat on a 3 stretch. Is it good of course not, that is why it is important to get the correct size wheel plus or minus 1.

When we repower some of these DE boats that are hard to figure out close we always like to start with a bronze propeller. You have a lot more freedom of bend to get it correct. Once we are on target then we advance to nibral.

 

[F/V First Team]

To each their own
Over 3" on a Nibral wheel with no heat with no adverse effects on my own boat