10th Sep 2010, 01:29 PM #16
Howdy, I have been scheming something remarkably similar to your foil shaped-steel core idea. Vivier and I are working on a 6m Yawl. I think it can work if you use the right epoxy and Met weld by System Three, I think. Some research is surely needed. A very thorough sheathing of glass on the outside and annual inspection, it should be OK. But yes there will be differential rates of expansion. Now, the Romilly builders in the OK have a steel board encased in plywood which is then shaped. Their seem to be OK. Michael Storer here on this forum thought the steel core-foil idea was bad because once any moisture gets in, the board rusts and expands the assembly, forever jamming it inside the case.
I'll be watching what develops. What has Francois said?
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10th Sep 2010, 04:05 PM #17
I've seen some of your discussions on this topic on other forums and also a thread on your Yawl, hope you're going to run a blog on the build.
At the moment I'm waiting on a quote from a steel fabricator on a complete steel version of the centreboard, price will define which direction I take.
I've noticed though all the online discussion to date is pure conjecture with no one who has actually built a steel encased board offering up there experience. Therefore I think it is up to you and I to blaze the trail.
I'm developing some drawings at the moment to give to a fabricator. They are based on a 20mm steel core with 6mm plate welded onto the bottom edge and trailing edge. This is to support the hoisting and handling holes. I'll also get them to pre drill everything. I'm not expecting this to cost more than a few hundred dollars. This I'll then get galvanised, also not very expensive.
I intend to build up the timber layers out of 5mm marine ply. Any shortfall in overall weight I intend to make up from lead inserts. See how Francois specs his rudders Ė same technique.
Stay tuned to my blog and the woodwork forum and see how it all pans out. If it works I'll be able to give you any CNC files or drawings, as I'm guessing the Yawl will use the same centreboard as the Stirven.
11th Sep 2010, 11:46 AM #18
I meant to ask, is this board thicker than spec'd? Did you therefore neat to modify CB case assembly?
I see why you are doing the 6mm plate on trailing edge. Makes sense. A foil under SV and my yawl would do wonders. It remains so interesting, however, how set Vivier and his son and other builders of FV boats are: they swear by the flat steel plates. I just don't understand how they will work for the boat until the boat speed is way up. Where I am in the summer, winds are light and if I am beating out of the bay against a chop, I want a board working for me.
I am very interested in your work and results and certainly appreciate the willingness to share. I speak with Francois often so I do not mean to speak down towards his boards. In fact I think more of the steel boards since working with him. But for my own boat, I want a foil.
Another thought I had was to use Storer type boards. These are not as thick as a NACA foil, but have shaped noses and trailing edges with the middle section flat. This may be a nice compromise.
12th Sep 2010, 04:00 PM #19
As Clint says, Michael Storer uses these, but they were developed by a fellow named Neil Pollock. You might be able to find a reference to them and how to calculate a profile or perhaps Mik has a reference/ something you could scale up.
Ok, here's a reference to follow with a formula for calculating a (Pollock) parallel sided foil.
Design and Construction Of Centerboards and Rudders
12th Sep 2010, 09:33 PM #20
Thanks for that reference. I'd love to get a PDF of Australian Sailing Feb 1988, the issue Pollack has an article.
I'd like to do some homework and approach Francois with a parallel sided foil shape like MIK uses. It seems to be a very good compromise and would allow more steel core to be inside the board to keep the weight as designed.
6th Oct 2010, 03:06 PM #21
Rand have you worked on your centerboard design?
I need to figure mine out as we are working out the Jewell plans in December due to finish in March. I'll be building asap after that.
Since it is a new design, we can work around whatever foil shape works and whatever steel fabrication works with that shape.
I'm thinking parallel sided maybe 40mm thick, maybe more and shaped much like Storer's. My centerboard will only weigh 80kg so with a flat sided board it may be easier to fit the weight. I noticed that Nigel Irens Romilly is a 90kg board set in plywood and foil shaped + glass.
6th Oct 2010, 03:41 PM #22
I've got two new foundries quoting on the cast iron option at the moment. I literally got off the phone just then with one of them. They have asked me to make a small modification to my casting pattern ie remove the groove in the head of the board that guides the safety line, apparently this will simplify the mould making enormously, they have also recommended a particular type of Grey cast iron that is not as brittle as normal cast iron, perfect if you hit something. The foundry I'm dealing with know all this because they've done a few boat keels! Thanks to Darce who posted the link on a guy who publishes books on this type of thing. I sent him an email and he sent through the details of few foundries to contact
I should have pricing in by tomorrow or the next day!
I haven't abandoned the wood encased steel option, I just thought I'd give the casting option another go. Casting is my preference as I've been thinking the wood encased option may crack or split if I hit something (pretty likely knowing me!) though the way Francois designs his boards they will kick up if you do hit something.
On a different note I've ordered all the bespoke bronze items from Classic Marine in the UK, these are things such as
• Tabernacle and Mast Plate – Galvanised steel
• Stem Head Fitting
• Stem Head Fairlead
• Spinnaker Pole Mast Eye
• Spinnaker Pole End Fitting
• Mainsheet Horse
• Bowsprit Iron
• Boom Crutch Fiittings
• 3 Eye Bronze Plate
Given the Aussie dollar is going gang busters at the moment it's cheaper than getting them made locally and they already know how to make all the bits, should have this stuff in a few weeks.
Sorting these items has been the only diversion from the tedium of painting the interior which is taking forever!!!!
13th Oct 2010, 01:34 PM #23
Keep me posted. I only recently realized that SV was designed with a NACA foil, so you aren't reinventing the wheel much after all.
I need to do some work on my foil idea before my next chat with Francois.
1st Dec 2010, 04:18 PM #24
I've enjoyed reading about your build, well done and heres to a close launch day.
I've just purchased the plans for an Iain Oughtred "Grey Seal" and so your thread caught my eye. I have a few projects to get out of the way first before I start!!
Just a few questions if you wouldnt mind?
Iain specifies hardwood timber for all framing and we both know that could be a bit difficult( or expensive) here in Australia, so I was wondering what timber you have used, also which plywood have you used and what is your opinion of quality and price. I am probably leaning towards 1/2 inch hoop-pine marine myself.
Did you have any probs getting long lengths of timber for battens, mast etc.
Which Epoxy system did you use?
I notice you have ordered some fittings from Classic Marine in England. Have you received them yet and what sort of quality are they as far as casting, straightness and polishing standard?
Did you need to draw out your moulds full-size from reduced lines/sections on the plans ( I think they call it lofting )? On my plans they are 1/4 size so I have to draw a grid and transpose the points and bend battens around for the lines ( at least I think thats how it goes).
P.S. sorry about all the questions"World's oldest kid"
1st Dec 2010, 06:01 PM #25
I like questions, especially about where to get stuff, this has been hard won knowledge on my behalf.
On my Blog I've got a page on suppliers that might also be helpful.
Seeing you are in Melbourne this should be easy.
Re hardwood frames! No hardwood frames in a Stirven – all ply. Though I have used Oregon for any structural parts not made from ply – easy to order from Simply Oregon or Matthews Timber. Matthews Timber has some great timber selections, they have Oregon and spruce clears perfect for mast making.
With Simply Oregon I specified F11 Grade or clears and clarified it's for boat building. I found both places do there best to find nice timber I was able to get 7 metre lengths with up to 11 metre lengths available.
While at Matthews the other day I bought some Sydney Blue gum for the trim that will be varnished and had this milled to my specs at Baker & Davies Joinery. This is way more dense to work with than Oregon but I like the reddish look once varnished.
Re Ply, all mine has come from The Plystore which is just around the corner from Simply Oregon. I specified either normal marine ply which is a mystery bag of tropical hardwoods or Gaboon which is light and easy to work with. The Plystore have thicknesses from 4mm upwards. 15 or 16mm was the thickest I needed. All has been excellent quality and well priced. I found Hoop pine ply to be very heavy and quiet a lot more expensive than I wanted to pay. At the end of the day if you coat everything in epoxy and 2 pac undercoat it will all be fine.
Re Epoxy I have used Bote Cote throught, mostly because I'm familiar with it and the 2 to 1 ratio is easy to remember. This is available in a few places around Melbourne I get mine from Mc Donald Marine
Re the fittings from Classic Marine, everything I've ordered so far has been beautifully made and finished and cheaper than getting it made here! They would be able to make your Grey Seal fittings with their eyes closed. Just keep your orders below $1000 otherwise you get nailed on import duty. I learnt this the hard way.
All moulds I drew out full size from the dimensions in the plans. I drew these onto 3mm MDF then used those as cutting and routing templates on the final ply sheets. This has become my favourite technique for making accurate parts.
Hope all that helps. You are welcome to come and check out my boat anytime. It is in a warehouse near the Moorabbin airport.
If you're interested let me know.
1st Dec 2010, 08:36 PM #26
Thanks for the invite, I'd love to come have a look, perhaps in January after the dust has settled from work pre xmas. I'll PM you then and we can sort a time.
Also thanks for all the info.
Andrew"World's oldest kid"
25th Jan 2011, 05:17 PM #27
The Mighty Cast Iron Centreboard
On Christmas day Santa came through with the goods! I'm now the proud owner of 180kg of foiled cast iron!
In between the turkey, ham and beer the bros in law and I wrestled the beast from one Santa sleigh to the other.
It is going to be interesting moving this thing around to finish it off!
I would just like to thank everyone for all the advice and suggestions I received re foundries and alternate construction methods. In the end I ran with the cast iron option as specified by the designer and it has come out a treat. Thank you Billman's Foundry!
Final finishing and painting of the centreboard is still to come but the hard bits been done!
28th Jan 2011, 12:22 PM #28
Hey Rand. Great news, I will watch closely. Was it worth all the work? When you are going 7 kts to windward you'll be happy you did this!
I will need to decide whether to do something like this for Jewell, or to try some sort of wood/metal/glass hybrid. I will probably use the foil style you find on Michael Storer boats, a section developed by Neil Pollack that closely mimics NACA sections.
Note, my screen name has changed to CCBB. Here is Jewell that I referred to...
Jewell_SailPlans | Flickr - Photo Sharing!
28th Jan 2011, 12:52 PM #29
I had you and Jewell in mind when I did the Xmas post as I knew you were undecided about which way to tackle your centreboard build and thought this might convince you to go down the cast iron path. Was it worth the effort? Most definitely! Making the pattern was fun and interesting and you can get it as accurately foiled as you like using wood foam etc I did a post on this process on my blog One thing to consider though is my pattern was pretty trashed by the time the foundry had finished with it (Unusable for more boards)! Though I guess they could make a new mould from the finished board.
I still have to drill a hole for the axle and a handling hole as well as make a grove in the head for a safety line then paint it all. I'll do all this later as I'm about to start laying the hardwood deck which will be an interesting challenge in itself.
I saw the article in Watercraft on Jewell, I guess the pressures on to now get started if you haven't already.
31st Jan 2011, 01:28 PM #30
The truth, Rand, is that Jewell won't start until later this year. Too many paying projects to get out of the shop! But I sure look forward to it. You whole approach is worth considering and I will do just that as Francois and I decide how to go about the centerboard in Jewell.
I might actually have the plug for a cast board shaped on a CNC machine to a foil shape. A 5-axis machine could do it perfect, a 3-axis would leave steps and I'd fair those steps with fairing epoxy. That'd probably be the approach if I go cast, or at least I'd look into that approach first. The other way will be to make the Storer type board which allows us to use an NC cut plywood backbone (requires a thinner board) which is where the Storer board comes into play. Looking forward to seeing updates.
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