Looking for sources to fabricate a steel centerboard

[jpatrick]

I think the prices being talked about here are way off base. The OP needs to contact a couple of supplier/fabricators local to him and get a quote for the steel, cut to shape. Then talk to them about having the nose profiled. The cb only weighs a 150 pounds, more or less. So the overall cost will be mostly in the cutting. It is important to tell the supplier what the thing is for and that it must be flat. The best cutting will be via plasma on a water table or using a water jet. Don't cut the plate with a conventional gas torch.

If galvanizing is possible then go for that. Otherwise, use paint.

Doing the profile oneself is possible but maybe not a job many would like to do. It is a dirty and loud operation to grind that much steel. And it's not a lot of fun after the first inch or so.

To the OP.... Stop thinking about this. Just make some calls.

Jeff

[DeanP]

A shop in Hinesburg, VT could for sure do the basic shape & probably any bevels. They've done a lot a "interesting" projects - including oddly shaped stainless water tanks for my boat.

Giroux Bros. is the name - talk to Steve. You could tell them Garret Mott sent you, but you'll get "Oh s*** - this'll be something weird" along with en eye-roll & grin. Their grandfather started the business as a wagon works & wheel wright shop.

Thanks for this lead. Many years ago, I lived in Shelburne and would love to have another excuse to visit Vermont. I will give Steve a call and drop your name.

[Garret]

Thanks for this lead. Many years ago, I lived in Shelburne and would love to have another excuse to visit Vermont. I will give Steve a call and drop your name.

Cool - hope it works out.

[Gordon Bartlett]

If the chosen material is ordinary low carbon steel, the perimeter can be quickly and easily cut on pretty much any metal-cutting band saw. At 12mm thick, the board only weighs about 90 pounds minus whatever material is later removed to create the foil shape.

[DeanP]

Well, the centerboard has been fabricated and I picked it up on Friday.

In the end, I elected to go with 304SS. I wanted to use 316SS, but decided the cost differential did not justify the improved corrosion resistance. I had the board quoted in steel, too, with the thought of having it hot-dip galvanized, but here I decided to pay the delta for the 304.

I talked to 5 places, asked 3 to quote, and actually received to quotes. One was half the other and the more expensive supplier would not give me any assurances on the resulting flatness.

I went with Rennline Manufacturing in Milton Vermont. I had never heard of them, but someone I spoke with recommended I give them a call. They specialize in waterjet cutting and seemed to understand my needs. I gave them (and the others) a CAD file of the profile and they quoted $565 in steel, $1300 in 304SS and $1480 in316SS. As with the other quotes, these numbers included material and cutting of the profile and the addition of 3 holes (1 for the pivot pin and 2 for a line to retract it into the centerboard well, per the designer). Rennline also included some press time to flatten the part should it exhibit any bow or curl. Briefly, I considering making the part from silicon bronze thinking it may be less expensive and easier for me to fair. Atlas Bronze quoted me $6400 for a blank plate large enough to make the board. It was so expensive, relative to what I expected, I call the company to check that it was correct. It was.

None of these prices included any fairing work (at the leading or trailing edges). Anything I do from here will be me with a grinder or at additional expense at a machine shop with a multi-axis mill.

Here's a photo of the board as received. The water jet cut edges have not had any secondary operations. The cut is very clean right from the machine.

IMG_0925.jpg

I convinced my buddy it was a nice day for a flight to Vermont so we took his Cessna to Burlington and loaded the board into the plane.

CBoard loading_2.jpg

The centerboard will probably just sit in my basement and collect dust as I work on other pieces, but it is a step in the right direction. Thanks to all for the help and suggestions for getting this made.

[Garret]

Sounds great! Wish I'd known you were coming - I'm 1/2 mile from the Milton, 15-20 from the airport line & coulda ferried you about.

[Spot]

Has anyone inquired about foiling a wooden pattern and having it done in cast iron?
I know OP is past that but it would be interesting to see where it falls into line with the other materials in cost considering the up front work on the pattern and not much work after casting.

[DeanP]

Sounds great! Wish I'd known you were coming - I'm 1/2 mile from the Milton, 15-20 from the airport line & coulda ferried you about.

Thanks for the offer! I wish I had known you were so close. We were able to get an Uber to Milton, but Burlington doesn't seem to have many Uber drivers, yet. We were able to get a ride back to the airport from the shop in Milton.

Has anyone inquired about foiling a wooden pattern and having it done in cast iron?
I know OP is past that but it would be interesting to see where it falls into line with the other materials in cost considering the up front work on the pattern and not much work after casting.

That's an interesting idea. It's too late for me, though I would have liked to evaluate that option. I have absolutely no idea how much it costs to have a custom cast iron part made from a supplied pattern.

[gray duck]

For trailer boat 304 is probably fine but there is this-
IS 304 STAINLESS STEEL A GOOD CHOICE FOR MARINE ENVIRONMENTS?

Clinton offers SAE 304 stainless steel, which can also be found under the name A2 stainless steel or 18/8 stainless steel. 304 is the most popular stainless steel alloy available on the market. It is an austenite steel, meaning that it is non-magnetic in nature. This alloy was first developed by Firth Brown Steels nearly a century ago. It was originally sold under the trademark Staybrite 18/8, because of the presence of chromium (at around 18%) and nickel (around 8%) as alloying agents.304 steel has a eutectoid point that occurs at 727 °C (1,341 °F). While it is not a good choice for applications that require electrical or thermal conductivity, it is well known for its excellent formability. With a carbon maximum of .03 percent, this alloy is also ideal for welding operations under 800 degrees F. While heat treatment is not an option, cold working can be performed to make the material both harder and stronger.When it comes to corrosion resistance, 304 steel is generally an excellent choice. Its molecular composition protects it from all kinds of environmental damage, including intergranular corrosion (This is a kind of corrosion that results from stress relieving or welding). The chromium content of 304 makes it more corrosion resistance in oxidizing environments, while its nickel content helps protect it from organic acids.However, 304 stainless steel does have one weakness, and that is it does not perform well in chloride environments, in particular, seawater. It is susceptible to corrosion in these cases. If marine corrosion is a major concern, a better choice would be 316 stainless steel, which has 2 percent molybdenum added to it. This difference is what makes it especially effective in marine applications.

source: 304 Stainless Steel in Seawater - Clinton Aluminum

[DeanP]

For trailer boat 304 is probably fine but there is this-
IS 304 STAINLESS STEEL A GOOD CHOICE FOR MARINE ENVIRONMENTS?

Clinton offers SAE 304 stainless steel, which can also be found under the name A2 stainless steel or 18/8 stainless steel. 304 is the most popular stainless steel alloy available on the market. It is an austenite steel, meaning that it is non-magnetic in nature. This alloy was first developed by Firth Brown Steels nearly a century ago. It was originally sold under the trademark Staybrite 18/8, because of the presence of chromium (at around 18%) and nickel (around 8%) as alloying agents.304 steel has a eutectoid point that occurs at 727 °C (1,341 °F). While it is not a good choice for applications that require electrical or thermal conductivity, it is well known for its excellent formability. With a carbon maximum of .03 percent, this alloy is also ideal for welding operations under 800 degrees F. While heat treatment is not an option, cold working can be performed to make the material both harder and stronger.When it comes to corrosion resistance, 304 steel is generally an excellent choice. Its molecular composition protects it from all kinds of environmental damage, including intergranular corrosion (This is a kind of corrosion that results from stress relieving or welding). The chromium content of 304 makes it more corrosion resistance in oxidizing environments, while its nickel content helps protect it from organic acids.However, 304 stainless steel does have one weakness, and that is it does not perform well in chloride environments, in particular, seawater. It is susceptible to corrosion in these cases. If marine corrosion is a major concern, a better choice would be 316 stainless steel, which has 2 percent molybdenum added to it. This difference is what makes it especially effective in marine applications.

source: 304 Stainless Steel in Seawater - Clinton Aluminum

There's no doubt that 316 is better. I thought through this trade, and while I do expect to someday keep this boat on a mooring, it will most likely be on Lake Champlain. In fresh water, it should last a long time. If I end up in the ocean, I may have to re-think the decision.

All the hardware on the boat, so far at least, is silicon bronze. Had the cost been more reasonable, I would have used this for the board, too, as its (salt water) corrosion resistance is even better than 316. I have read that repeated wet/dry cycles is harder on stainless than either one alone (submerged or above water line) which would suggest that a retracted/partially submerged centerboard could be a challenging environment. Time will tell.

[Edward Pearson]

Dean,

I've wondered about routing steel but never done any. Your stainless might have different working characteristics but if you're looking to round over the nose and the rest in case you upturned and handing it etc then here's an option.

This guy uses a round over carbide bit in his wood router to round over his steel table top edges pretty quickly...

[DeanP]

Dean,

I've wondered about routing steel but never done any. Your stainless might have different working characteristics but if you're looking to round over the nose and the rest in case you upturned and handing it etc then here's an option.

This guy uses a round over carbide bit in his wood router to round over his steel table top edges pretty quickly...

Ed,

Thanks! I've been searching for such a tool to go in my router, but have been unsuccessful until now. I had been searching for this cutter using woodworking terms. Calling it a "bur" has identified new options. The Pferd website lists only a 1/8" radius, while I would like a 1/4". Tomorrow, I will call the company and see what they can offer and confirm this tool will cut stainless.

Hopefully, I will soon post some photos of a nicely rounded leading edge!

Dean

[sp_clark]

Hoo... wear eye protection, maybe gauntlets when you put carbide router bits to steel.

I 'faced' a lead brick a few weeks back with a router & 1/2" carbide rabbeting bit. Chips were HOT and I'll leave it to you to imagine the mess.

Steel'd have to be markedly worse, chips might be near red hot coming off a bit.

Better option, and best not used at typical rpm of a woodworking-type tool.

[Andrew2]

I am about to do one similar for a Sharpie 600.
10mm thick and I can easily cut it out with my plasma.
As for the profiling: The leading edge needs a section that will round it to 20mm back from edge.
The trailing edge will get a taper at about 80mm from the edge. That is enough for a thin board. A 9 inch angle grinder is fine for the job.
I would expect a wood router and esp the bits, to self distruct very quickly. Big mill is the tool, if you can find one locally.

[DeanP]

I am about to do one similar for a Sharpie 600.
10mm thick and I can easily cut it out with my plasma.
As for the profiling: The leading edge needs a section that will round it to 20mm back from edge.
The trailing edge will get a taper at about 80mm from the edge. That is enough for a thin board. A 9 inch angle grinder is fine for the job.
I would expect a wood router and esp the bits, to self distruct very quickly. Big mill is the tool, if you can find one locally.

Hi Andrew,

Is the board for your Sharpie steel? Can you profile as you describe with a 9" grinder in a reasonable amount of time? I've never done anything like this on steel and am concerned it could take forever. I do plan to look for a local machine shop with a mill large enough for my centerboard, but am worried about the cost. Also, I have no basis for assessing the performance impact of just using the board as-is (with square edges). Would it be noticeably slower or noisier? Still lots to learn...

[sp_clark]

Rounding the leading edge & tapering the trailing will have benefits, yes.

Square edges will cause drag, which may or may not affect what you get out of having this 'board' (when is a board not a board but rather a plate?) deployed whilst under sail.

Taking the metal down to a NACA profile cross-section may not be at all necessary.

Then there's what we might settle on as to what 'reasonable' might convey....

If the steel's not hardened, a 9" grinder may be way overkill yet certainly faster than a 4-1/2".

Using one of those, fitted with an abrasive 'flap' type wheel, I've seen lawnmower blades taken down well past sharpened in a matter of a minute or two. Given a decent supply of coarse & medium wheels (along with some patience and suitable PPE) I'd think you could ease the edges of that plate nicely in an hour or three.

Biggest advantage to having a machine do the bulk of the work would be in uniformity I'd think. Done by hand, some measure of fortitude will be evident in achieving a 'reasonable' degree of evenness.

Back 60 years ago in high school metal shop we used blueing to find high spots when hand-filing projects. There may be better products now for this yet their purpose is the same.

[Andrew2]

Hi Andrew,

Is the board for your Sharpie steel? Can you profile as you describe with a 9" grinder in a reasonable amount of time? I've never done anything like this on steel and am concerned it could take forever. I do plan to look for a local machine shop with a mill large enough for my centerboard, but am worried about the cost. Also, I have no basis for assessing the performance impact of just using the board as-is (with square edges). Would it be noticeably slower or noisier? Still lots to learn...

Yes, plain mild steel. A 2x1 mtr x10mm plate costs about 400 euro with tax. I might get it out of a half sheet with some of the sticky out bits welded on.

Back when my father designed several boats with plate boards, he didn't do other than reccommend just taking the sharp corners off, though, as an aerodynamics grad, he was well aware of foils. Many(most?) of the boats were built by amateurs and back then, no angle grinders.
I would think a 2000watt 9" would shape the leading and trailing edges in a noisy afternoon (with rests..) Say a couple of hours. I will let the panel know how I get on It won't be right now, but it sounds like you have a bit of time?


Flat, unshaped boards have a habit of vibrating, but just doing the edges as described above gets round that mostly.

[sp_clark]

Flat, unshaped boards have a habit of vibrating, but just doing the edges as described above gets round that mostly.

My surmise is the NACA section's lend a higher ability to point up, all else being optimized. They can generate lift rather than merely presenting resistance to drift.

The square-edge plate's vibration modes are turbulence made plain, why simply easing the edges to give water a smoother path 'round is advisable. After all, birds & airplanes don't fair well with square-edged wings....

Were I doing this I'd go the rounding route first, just 'cause it's fairly simple & ought to yield benefits over square edges if for nothing else than when handling the beast, and making paint easier to keep stuck onto. Later on, taking more off the back ought not be an unreasonable prospect if what may be a modest gain in performance is desired.

[Andrew2]

Yes, but a NACA section would need to be a lot thicker to have any benefit with lift, so best just limit the turbulance by rounding (ovalizing) the leading and tapering the traling edges. No need to finish the trailing edge sharp, in the 10mm one, I am leaving the edge at 2mm with 'corners' rounded.

I do a bit of SS fabricating and use flap discs on a 125mm (5") grinder to tidy up and polish, round off sharp edges. But I wouldn't think of trying to remove a lot of 304 with one. Decent 9" and a proper grit disc to get it down, then polish with a flap.

[jpatrick]

As one who's spent a fair amount of time grinding steel... I think this profiling can be done, but it will take a fair amount of time. It will certainly take more than an afternoon. The process is also without danger. A 7 or 9 inch grinder is no tool to be careless with. And they are LOUD and the dust will be considerable. Wear a respirator and ear protection. If one attempts to do the job in an urban environment, expect some disgruntled neighbors.

But perhaps I have a low tolerance for unpleasant work.

Jeff

[sp_clark]

Yes, but a NACA section would need to be a lot thicker to have any benefit with lift, so best just limit the turbulance by rounding (ovalizing) the leading and tapering the traling edges. No need to finish the trailing edge sharp, in the 10mm one, I am leaving the edge at 2mm with 'corners' rounded.

I do a bit of SS fabricating and use flap discs on a 125mm (5") grinder to tidy up and polish, round off sharp edges. But I wouldn't think of trying to remove a lot of 304 with one. Decent 9" and a proper grit disc to get it down, then polish with a flap.

Right... I had to read back a few posts before 'remembering' the OP'd chosen 304 over plain mild steel or 316. And yes, with as wide and thin a plate as has been sourced for this part, a true NACA cross-section's not at all possible.

Done by hand with power tools, it will be a noisy, dirty operation indeed removing that metal, but not impossible. For the money invested in material it's got to be a savings over what a 'board out of wood and fiberglass would cost in both money and time, with an added benefit of not insignificant weight where it'll count.

[NeilMB]

As the aspect ratio of the cross-section goes up (it gets thinner relative to its chord) then the lift and drag benefits of a better profile go down. https://www.mdpi.com/2077-1312/8/9/677 is a nice paper on the subject and the profiles that Mik Storer specs for his OzGoose come from Neil Pollock (https://catalogue.nla.gov.au/Record/680180/Holdings appears to be the original source, but my National Library of Australia library card is in my other pants).

http://www.boat-links.com/foils.html Has Pollock’s equations and this intriguing comment: “When the foil is really thin, it acts as a flat plate. There isn't much you can do to affect its performance. Analysis of even 6 per cent thickness shows much less sensitivity to shape than thicker foils. A limiting situation is model boats with sheet metal keels. Just round off the edges enough that they are safe to handle.”

6% thickness is about an 18:1 aspect ratio, or anything thinner than 2/3” on a 12” chord. My reading of this literature is that unless you have a purposely portly rudder/center/dagger/leeboard, then many of the plank-like foils that we use on small boats are getting towards the ballpark of vanishing returns on careful profiling. I think then just round the leading edge and taper the trailing edge over as long as you can stand.

[sp_clark]

Interesting stuff NeilMB, thanks for posting that. Still looking to see you pop in sometime in Viroqua.

You around during lunchtime, we can do lunch at the Driftless Cafe maybe....

[Andrew2]

Right... I had to read back a few posts before 'remembering' the OP'd chosen 304 over plain mild steel or 316. And yes, with as wide and thin a plate as has been sourced for this part, a true NACA cross-section's not at all possible.

Done by hand with power tools, it will be a noisy, dirty operation indeed removing that metal, but not impossible. For the money invested in material it's got to be a savings over what a 'board out of wood and fiberglass would cost in both money and time, with an added benefit of not insignificant weight where it'll count.

Agreed.
I started a 21ft Dix design. It had a steel plate. But, a builder in UK used a wooden board with lead to bring it up to weight. Thicker, so profiled with a NACA section.
Thinking similar, I built the case to allow for the thicker board. But built it with a steel frame with the intention to clad it in 4mm in a NACA section, then put enough lead to bring it up to weight.

Projet got a reality check and I still have the plate frame hiding in a corner.
Life is like that.

[pez_leon]

The discussion of shaping steel is interesting and also very clear: this would be a lot of work. I know that this comment is too little and far too late for the boat currently being beautifully built by Dean, but for posterity, I wanted to suggest that those committed to a weighty metal board might consider adding wood cheeks to a metal core. Wood cheeks would definitely reduce the amount of metal to be removed. With a thin metal core you could probably get away without shaping any metal at all. Wood cheeks would also likely change the width of the board. Added width, if appropriately shaped, can offer an incremental hydrodynamic benefit. It's a change you'd want to plan for from the first steps of the build, but it might be worth considering.


- James