Changing pitch

[CDK]

The bronze 14x17" props I purchased for my tunnel drive project seem too heavy a load for my engines.

Someone suggested I had the pitch changed by a company called "Federal".
So far I have been unable to locate such a company, but is it possible to substantially reduce the pitch of a prop or is it just a quick way to ruin them?

[TollyWally]

From what I understand you can go about 2 " of pitch. I'm going to have my spare prop repitched as an experiment. It's tweaked anyhow so it won't cost me much to experiment.

I'm sure we can expect some confirmation or denial from the assembled brain trust.

[Eric Sponberg]

Originally Posted by CDK

The bronze 14x17" props I purchased for my tunnel drive project seem too heavy a load for my engines.

Someone suggested I had the pitch changed by a company called "Federal".
So far I have been unable to locate such a company, but is it possible to substantially reduce the pitch of a prop or is it just a quick way to ruin them?

CDK,

Here in the US, Federal Propellers is a brand name from Michigan Wheel Corporation. Here is their website:

http://www.miwheel.com/Propellers/In...s/Federal.aspx

Michigan Wheel could repitch your propellers for you, however, that seems a huge shipping expense to send them all the way over here. My suggestion is to try to locate a good propeller shop, perhaps in Italy. Any good propeller shop should be able to repitch your propeller for you. It is not an elegant process; usually it takes a good bit of hammering on the blades to bend them to a new pitch. As a result, there is a limit to how much pitch you can change, and 2" is about that limit. The alternative is to buy another set of propellers with the same diameter but different pitch. It might be worthwhile to consult with a naval architect or the propeller shop to see what they recommend for your boat. One that I can recommend here in the US is Platzer Marine Propulsion Inc. Their website is:

http://www.platzermarine.com/

I hope that helps.

Eric

[daiquiri]

CDK,
I've understood that you live in Croatia, so it would be much simpler for you to have the job done in Italy. I can recommend you a firm which have made several well-done prop re-pitch and re-size jobs for my clients. They are
"Fregonese Bruno e Figli" Officina Meccanica s.n.c.
and they are located at San Donà di Piave (VE) - near Venice.
Their phone number is
+39 0421 221080
The fax is:
+39 0421 222209
E-mail: fregonesesnc@libero.it

They have a vast on-field (or in-water? )experience with props and will be able to evaluate the ammount of pitch change necessary to achieve your goals.

Hope it will help.

[Frosty]

First get a big bowl of cement and bed the prop into it. Before it dries pull the prop out , this will be a base from which you will know how far you have changed or if you want to go back.

Then carefully decide where it should be hit. Carefully decide on what you are going to hit it against and with what,-- a big ball pain would be best.

To be honest changing the pitch will be the leading edge and trailing edge. This will seem like a change in pitch.



The thing is if they are no good to you what do you loose. If it improves it almost to where you want it the props can be melted down and re cast.

[daiquiri]

Frosty, changing a prop pitch is a job which goes well beyond hitting it with a hammer or whatever.
A prop has to be balanced statically, dynamically and hydrodynamically, and it takes right tools to do that.
Unless you are a fan of hull vibrations and worn-out shaft bearings...

[TollyWally]

Frosty,
If you are serious could you expand on that? I have seen some amazing things done with 3rd world technology before and seen some pretty impressive feats pulled off by old timers. While my first thoughts are similar to daiquiri's my mind is open to the possibility. I will admit I am a bit taken back by the thought of recasting a mistake but I get it. Do go on.

[gonzo]

You should consider if you have too much pitch or diameter. Propellers can be cut down

[Frosty]

I remember as a kid saving up for a new equipoise prop. It was a bit too pitchy so I took back this jewel like prop wrapped in a scratch proof towel.

They knocked the crap out of it with a hammer !!!!.

Since then I have altered pitch at the side of the river with a hammer myself.

I have talked to Sonni Levi who used to do the same thing.

Granted 14 inch is getting big. I don't know what the professionals use but I doubt if the hole in the hub could take the force required to re pitch a blade from its root, I think at best it would elongate the shaft hole.

Altering leading edge and trailing edge would get you a couple of inches and thats Max.

A car panel beater would understand how to hit the metal to make it respond the way it is required to.

Maybe I should'nt have started this.

Basically I don't know how they do it but just telling you how I do it.

The point being --if they are no good as they are now what do you loose.

[fasteddy106]

Cdk, I think you would be far better off selling your props on ebay or some similiar site and buying props with the correct pitch for your boat. Frosty, I shudder to think of what would happen to my 38 year old OMC Electric Shift if I used the method you just endorsed. One of the 40ft Vikings with twin diesels in our marina hit a bait bucket backing into his slip and the vibration from the bent prop made me want to take a leak every ten minutes when we went out the next day. Ended up diving and removing the prop and having it balanced. Cdk, if you are looking for just a bit more performance you would be better off having the correct props cupped. My boat originally came with a 14X14 prop. When I changed the engine to a custom built 205hp V6 that prop just made the engine rev way too high to get anywhere. I went to a 14X18 prop and now the boat tops out at 25mph @ 4000 rpm. That is an increase of 10mph over the old engine, a 145hp kaiser V6 and 5mph increase over the new engine with the old prop.

[Frosty]

No-No- No- you take the bloody things off the shaft first.

You have to very carefully decide where to hit them. It may take a long time to make something to hit them on , that is a very important part of it.

You know what ---leave them,--- buy some new ones geeeeez

[CDK]

Frosty, I do appreciate your attitude. If I ever find myself marooned on an uninhabited island I'd wish you were there. With a hammer of course.

Because no hammer in the world is big enough to change the angle at the base of the blades, the result of any pitch change is a compromise I guess. I do not know whether or not prop makers use a different cast for each type or set the pitch for 14x16, 14x17 and 14x18" using the same basic prop.
Would it be a more elegant solution to flatten the blades with an hydraulic press instead of a sledge hammer?

[Ad Hoc]

what power is going to the prop and at what rpm?

[Frosty]

No I did'nt say a sledge hammer and this is not third world get you out of the shit thing this is what they do. Thats what I said --you call it the base it is called the root, that can not be twisted but the leading edge and trailing edge can, -----theres a terrible echo in here.

I give up. Talk numbers and RPM then go buy new ones.

[tuantom]

Saw a show on making stainless steel props once - Mercury or maybe Michigan Wheel - and they really let the hammers swing on the props to adjust the pitch. Brand new. Takes a healthy shot to bend one up too.