Bending hard brass.

[navarcus]

I have a 10" piece of 1/2" by 1/8" hard brass as a skeg for a Hartman Bunker Boat.

And it needs to be 3/4" lower at the middle to clear the prop -- sort of a short in height,

but long in length "Z". Is there a trick to how I bend it?

[Bob Cleek]

I'm sorry. Maybe it's me, but I can't figure out the bend you are contemplating. A picture is worth a thousand words sometimes.

 

I'm not sure how you want to bend it. If you're trying to do what I think you are trying to do, I'd have to answer "No can do."

[Scottish Guy]

I agree with you Bob, a picture would be helpful. But I think he´s talking baout a boat like that (even if you can´t see the hull properly on that picture.

 

 

There have been model ships sold as Hartman Bunker Boat which were based on the Menhaden Fishing Trawler (1900 - 1920)

 

 

The USCG used those as well as. There is a Wikipedia Log for the SP-328 USS Margaret which is also based on a Menhaden Fishing Trawler (1912-1919). I guess hes talking about one of those. But since we can´t see the hull I just don´t know exactly what he want´s to know, therefore I can´t provide any help.

 

Micha

Edited April 21 by Scottish Guy

[Bob Cleek]

1 hour ago, Scottish Guy said:

But I think he´s talking baout a boat like that (even if you can´t see the hull properly on that picture.

It's not about the type of vessel or style of hull.  He has as 10" x 1/2" x 1/8" piece of "hard" brass to use as a skeg which he wants to bend in order to make it "3/4" lower at the middle to clear the prop."  If the stock is to be a skeg, given it's dimensions, I'd expect he wants to know how to bend it 3/4" across the 1/2" wide vertical face of the skeg.  "Hard" brass can easily be annealed with a torch, but there are limits to "bending across the flat" which would seemingly be exceeded in this scenario.

 

[GGibson]

9 hours ago, navarcus said:

...sort of a short in height, but long in length "Z". Is there a trick to how I bend it?

 

8 minutes ago, Bob Cleek said:

"Hard" brass can easily be annealed with a torch, but there are limits to "bending across the flat" which would seemingly be exceeded in this scenario.

 

 

Totally NEWBIE input here, but from how "drastic" he is needing the brass bent into a Z shape, would it be better to simply solder three pieces in that shape rather than attempt to bend, even with the annealing process? 🤷‍♀️👍

[Bob Cleek]

30 minutes ago, GGibson said:

Totally NEWBIE input here, but from how "drastic" he is needing the brass bent into a Z shape, would it be better to simply solder three pieces in that shape rather than attempt to bend, even with the annealing process? 🤷‍♀️👍

Probably.

 

For a good example of brass skeg fabrication see: 

 

Edited April 21 by Bob Cleek

[Dr PR]

Like everyone else I have no idea what he is talking about. "Z" dimension? Is that vertical, longitudinal or transverse? Short in height? Lower in the middle?? Is the propeller amidships?

[allanyed]

Looking at drawings of various trawlers and boats I still cannot figure out what Navcus is looking for.   Attached show skegs that are below the prop so I assume (usually a bad idea) it is this area.  If the skeg has to be bent to clear the prop it seems like the prop reaches below the keel which is odd for these boats.  Hope he or she posts a drawing as now I am curious.🤔

Allan

 

      

 

Edited April 22 by allanyed

[navarcus]

I was hoping to use brass (in a simpler form) for this instead of pine.

 

[Toolmaker]

It might be worthwhile getting a larger piece of brass and machine the part you require. Saw and files or power tools if you have them. I think this method would be more easily controlled and offer you a better chance of success. Brass is quite soft and files to shape quickly.

[allanyed]

Angel,

It looks like your prop is in the wrong place or the diameter is too large.  Is it possible to relocate the propellor shaft or go with a smaller diameter prop?  Also, you can add a piece similar to the sketch below although it is probably not a good solution.  If the ship had a wooden keel then this would work well and could also take a false keel across the entire length of the ship as well.  

Can you tell us which vessel this is?

Thanks

Allan

Edited April 23 by allanyed

[navarcus]

So I remade the pinewood skeg with hard cherry.

Steam engines love big props.

No longer trying to bend hard brass.

First step of many.

[allanyed]

4 hours ago, navarcus said:

Steam engines love big props.

Hi Navarcus

Memory may not serve here, but from what I do recall from my marine engineering courses the type of engine had nothing to do with the diameter of the propellors.   I sailed on steam ships as well as diesel propulsion with prop diameters up to about 19 feet.  The azipods found on today's ships are upwards of 20 feet in diameter as well. There is a practical limit on the diameter no matter the type of propulsion which is possibly one of the reasons larger ships have multiple props.  

Allan

Edited May 10 by allanyed

[Dr PR]

Propellers are intended to push a vessel through the water. The faster a propeller rotates, the greater the push. Increasing the size (diameter) and area of the propeller blades produces more push for a given RPM. The larger the diameter the faster the end of the propeller blade rotates at a given RPM. If the end of the propeller blade moves too fast it moves faster than water can move. As it turns it leaves holes or vacuum bubbles in the water. This is called "cavitation" and it causes two problems.

 

First, there is a lot of energy involved and cavitation can rip bits off the trailing edge of the propeller - and even cause pits in the blade surface. This will create imbalance in the propeller, and that creates vibrations in the prop shaft that can wreck the foundations in the shaft alley and even destroy the turbine or motor turning the shaft. This is considered a bad thing.

 

The second problem is noise. When the cavitation vacuum bubbles collapse they create a popping noise. This is like going into the reading room of a library and banging on a pan with a hammer. Everyone within hundreds of miles can hear cavitation. It is anti stealth!

 

So if you can't have one big propeller turning really fast to get the push you need, the solution is multiple smaller propellers turning slower than the speed that causes cavitation. And modern "twisted blade" propeller designs were created to minimize cavitation.

 

 

[navarcus]

One of the responses had this pictured design.

Since I had the huge shiny brass prop in my stash from long ago....

And since the deadwood was already drilled for the shaft, I went with hard cherry for skeg's strength.

Procrastination probably beats cavitation as my biggest problem -- like McClellan, I have a bad case of the slows.

 

 

[KeithAug]

On 4/21/2024 at 1:52 PM, navarcus said:

I have a 10" piece of 1/2" by 1/8" hard brass as a skeg for a Hartman Bunker Boat.

And it needs to be 3/4" lower at the middle to clear the prop -- sort of a short in height,

but long in length "Z". Is there a trick to how I bend it?

I think I recognise the picture immediately above.

 

I know that this may be a little late but to answer the question "how to bend hard brass"?

 

Brass is quite easy to bend but needs to be treated as follows.

 

Heat the area you want to bend using a blow torch until it glows cherry red.

Let the brass cool down to room temperature (no need to quench it).

Now start to bend the brass (you may need to create a jig to bend it round)

As you work the brass it will start to harden again - this is called work hardening.

Repeat the process of heating to cherry red followed by cooling - the brass will soften again and you can continue bending. 

Repeat the heating / cooling / bending process until the desired shape is achieved.

[paul ron]

you can soften the brass by heating it with a torch. you can tap the curve over a metal bar.

 

the z dimention is noted as... x y z im sure.

Edited July 15 by paul ron

[tmj]

What Keith said. Shape of material doesn't matter. Perhaps this will also be of some help. Don't force it. If it feels like it doesn't want to bend easily anymore, stop and reheat, etc. otherwise it will crack/break.  

 

 

Edited July 15 by tmj

[KeithAug]

Keeping the heat on as in the video isn't very easy with small parts unless the modeller has asbestos fingers. The heat then cool technique works just as well and doesn't hurt.

[tmj]

Hard brass is a pain, period! I hate working with the stuff unless I am forced to do so. Soft brass is soooo much easier to deal with! 

[Nirvana]

3 hours ago, tmj said:

Hard brass is a pain, period! I hate working with the stuff unless I am forced to do so. Soft brass is soooo much easier to deal with! 

Heat it up prior bending, makes it easier

[KeithAug]

16 hours ago, tmj said:

Hard brass is a pain, period! I hate working with the stuff unless I am forced to do so. Soft brass is soooo much easier to deal with!

It must be a personal preference thing. My preferred metal for machining operations is brass. I never like working with soft brass for any machining operation. Hard brass cuts beautifully and produces an excellent finish. Soft brass tends to push away from the cutting tool leading to binding and poor surface finish. This can be mitigated to an extent by keeping the tools very sharp. I only ever soften brass to ease bending operations.

[tmj]

I agree Keith, 100%! I wasn't talking about machining the brass, only bending it.