The only piece of ply in the whole damn boat...breaks

[Thorne]

Should have known -- mixing dissimilar woods has gotta be like mixing metals -- so I guess the fir and oak just dissolved my ply centerboard.

http://www.luckhardt.com/brokenCB1.jpg


http://www.luckhardt.com/brokenCB2.jpg

Before breakage:
http://www.luckhardt.com/cb-painted.jpg

Actually I suspect that I had some leakage around the lead inserts, even though they were epoxied in quite heavily, and that must have weakened the ply. All the excitement at the Vallejo Pirate Festival did the rest, including some serious ferry wakes and a lot of very thin water.

No wonder I had problems reaching when we sailed her back to the ramp after the event. Tempting to try a metal one with ply sides to make up the proper foil shape, but I'll probably end up with either white oak or more ply.

[Paul Girouard]

Polly just typ. plywood failure a lil water in the wrong place goes a long way.And once one drop gets in the next , and next and next just flow on in and never dries out , just does it's thing promoting / supporting rot , mold decay.

Jim Ledger did a hell of a job rebuilding Sea Rover's rudder , very similar to that center brd. in it's construction.

Here's that thread,

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=65548

Good luck!

[mmd]

If you build it out of ply again, try cutting it out of the sheet so that the plies run forty-five degrees to the chord axis rather than perpendicular/normal.

[George Ray]

Wow! 45deg tip is a biggy. It is hard on the pocketbook but makes HUGE structural sense.

[mmd]

Sorry for the wasteful use of other people's plywood. <wink> If "cut on the bias" is too extravigant, at least orient the board on the ply so that the exterior skins' grain is parallel to the chord, not perpendicular as the old one was.

[paladin]

contrary to popular belief, plywood ain't stronger than a good board...it's just more dimensionally stable.....;)

[Tom Lathrop]

Using plywood for a cantilevered application is not a proper use of plywood even if I and many others have done it gotten away with it. Not the fault of the material, just the user.

[Thorne]

What about making a CB from stainless steel? My wife works for Seaport Stainless here in Richmond, so I could get restaurant-grade SS fabbed up for very little cost.

It wouldn't be the marine-grade SS, and since they don't work with anything thicker than about 1/8", I'd have several blanks made up and epoxy them together - with a bolt or two to make sure they stay attached. The boat never spends more than a few days in the water, so the usual issues of unlike metals and crevice corrosion shouldn't be a problem.

What does the Collective Wisdom(tm) of the Forum think about that?

;0 )

[S/V Laura Ellen]

Not everyone is down on using plywood. This vessel; has a very liberal use of plywood to great success.

http://www.imagestation.com/picture/sraid225/pa280616099e39c3f0ea786cd3cf501f6/e8bfe7e2.jpg

[mmd]

'Twould be a bear to shape into an airfoil section....

[Thorne]

I hear you on the foil shape, but sometimes wonder how much difference it makes in a trad dinghy that sails as slowly as mine.

Seems like I could make ply cheekpieces for the SS centerboard (itself made from 3-4 layers of 1/8" SS), then glass over the whole layered construction to get the NACA0008 section foil shape.

[George Ray]

When you consider how many rudders and CB's are made from ply and how few break and VERY importantly how easy it is to fair because of the ISO level lines. GO WITH PLY. Do the plys at 45deg to chord axis as 'mmd' suggests and you got it. Only question is 'which ply to use'?

[gert]

There are huge lateral forces on a center board; how much lateral movement did the board have? If it "rattled" the repeated lateral slamings would eventualy break the plywood fibers. A solid lumber CB would definatly be stronger, or at least its trailing and leading edges; say a 1x3 front and back. I broke a plywood rudder once (not convenient) and have a 1/4" galvanized steel CB with large nylon "cheeks" to eliminate lateral rattling. The steel CB is very economical and the edge work can be done with a grinder. The galvanizing is charged by the pound; I don't think the whole thing cost more than $60; it has never failed to go down,and adds a bit of weight where it's usefull.

[Thorne]

It wasn't loose at all -- no rattling or sideways twisting in the case. I'll start pricing ply and SS and see what happens.

What thickness and make of marine ply would the 'pro-ply' crowd recommend purchasing? The broken CB is 5/8" thick, CB slot is 1" wide, and at the pivot pin I used large SS washers on the CB and nylon washers inside the case to hold the CB firmly in place.

The site I used for the chord info -
http://www.philsfoils.com/designTips.html

[mmd]

You probably can't go much thicker - if you bump up to 3/4" ply, by the time you have added some 'glass & epoxy sheathing, fairing compound and paint, you'll be thick enough to risk jamming in the centreboard case. I'd suggest good quality 5/8" / 16mm marine hardwood ply cut on the bias, shaped, sealed, 'glassed (fabric should be cut on the bias, too), filled and painted. I'd also suggest that you round over the outer edges of the centreboard slot with a generous radius so that when the board gets pressed against the bottom of the boat the load on the board will be distributed evenly over a "soft" area rather than a sharp, hard edge.

[Rick Starr]

Wow. That is a very long, very skinny board. I would say you got yeoman's service out of it. I would have felt better with a metal one or one that is at least twice as thick.

If you were to rebuild the trunk, could you get all the pieces you need out of one sheet of good thinly veneered ply? Otherwise I'd visit my local metal shop. Computer/plasma cut SS shouldn't be too expensive in your area and wouldn't involve too much downtime. Simple swap-out and some grinding roundovers would do you. Foils really can't be justified in your case, seems to me. The advantages of a metal board in labor and weight and perpetual minimal maintenance would outweigh the tiny (probably immeasurable) benefit from foil shaping a 5/8" appendage.

Good luck

[Don Kurylko]

Thorne, really. All you need is a ¾” solid wood board for your boat. Shape it, sand it, epoxy coat it, paint it and you're off to the races. Cheap, simple and much stronger than any of the above alternatives. A nice piece of Fir, African Mahogany, Oak, Ash, etc, will do the trick. For ballast, use a 4” to 6” hole saw to create a cavity and pour some lead into it. Once cooled, fill the inevitable void around it due to shrinkage with Epoxy resin. Then fair the lead nice and smooth and coat with epoxy resin and paint. Epoxy sticks really well to lead, no worries there.

[mmd]

C'mon, Don! Where's the fun in that?! No sense in proposing a common-sense, suitable solution when there are so many bizarre and complex alternatives yet to explore. I was just working up a suggestion for a NACA-foil form vacuum-bagged female-form-moulded foam-cored double-diagonal skin Honduras mahogany with external uni-directional carbon fibre stiffening let into the surface plies board. And you're suggesting common sense and proven materials? What's with that? <wink, grin>

I'd go with spline-joined solid ash for the flexibility and strength, myself.

[JimD]

Mmd, with all due respect, where's the kevlar?

[mmd]

Sorry. I was going for the "natural" look. Skin it out with Kevlar set in bismaleimide resin. That's the ticket...

[Lewisboats]

What about a stainless core with UHMD outer cheeks. You can shape the plastic with a grinder and flap wheels easily but nothing on there will ever rot. Have a center layer of 1/8" steel, a layer on each side slightly smaller (to help with foil affect) steel welded on and ground down, then the cheeks shaped and formed for you foil.

Steve

I built a stainless steering system for a canoe that I converted for sailing...works like a champ. I just used 10 guage for the blade tho...not much stress so not real thick. 3/8" of stainless should be pretty durn stiff.

[JC 72]

Thorne, Sorry about the CB. I'm with Don with the solid wood alternative. Get a piece of good DF stair tread. 4/4 stock. It is usually about 11.5" wide with a nice round over on the nose side. McBeths has it, White Bros., Truite and White. If you need to plain it, I can do that for you, as long as we don't go over 12.5" wide. If you need wider we can edge glue with Smiths, which I have. John

[Thorne]

C'mon, Don! Where's the fun in that?! No sense in proposing a common-sense, suitable solution when there are so many bizarre and complex alternatives yet to explore. I was just working up a suggestion for a NACA-foil form vacuum-bagged female-form-moulded foam-cored double-diagonal skin Honduras mahogany with external uni-directional carbon fibre stiffening let into the surface plies board. And you're suggesting common sense and proven materials? What's with that? <wink, grin>

Ooooooh -- sounds like fun, and sexy too! But wot: no embedded electronics, sensors, LED-fish-warning lights, SONAR dishes, and the like? How about a Lexan CB case to show it all off?

I'll price out the SS option, but suspect it will be more than my modest budget, so I'll go for either marine ply or white oak.

I have a hand power planer and trusty belt-sander, so I should be able to shape the oak correctly. I hate working with glass fabric, but will do it on this CB to cover the lead weights and edges.

[Jim Ledger]

Thorne, if you make a solid wood board why would you glass over the lead?

I'd be careful of white oak for reasons of warpage. VG D.Fir might be more stable.

[John Meachen]

How about leaving out the lead?

[Thorne]

Can't, CB case is closed-top, no rod or lever to force CB down and I like it that way. So lead is needed to pull CB down when sailing.

[few3]

Would G10 work for a CB?. You could get a 12 x 48 x 3/4 inch sheet for the bargain price of $272.00..........:D

http://k-mac-plastics.net/g10-fr4-sheets.htm

[paladin]

If you will machine a 3/8ths wide groove about two inches long in the board when you finish it, I can have a daisy chain of blinking LED's ready to do sequential or random blinking. By using a 4500 mah battery it should last several months and make pretty red/blue/yellow blinks underwater....:D ...just cover it with clear epoxy....
other wise.....I would split some regular straight grain fir planks so that the pieces are 1/4 of an inch thick, keeping the grain straight, overlapping the seams when epoxieing them together, cut your airfoil shape, sand well so that the finished board is a bit less than 5/8ths of an inch thick, then cover with 2 layers of Xynole fabric in MAS epoxy. the xynole will be thinner (less bulky) than fiberglass, but more impact resistant...then add your washers to the sides. The fir will be easier to work with. After planing to shape do not sand the wood....paint it with a thin coat of epoxy, then sand the epoxy and add the Xynole....

[Lewisboats]

Hey Lewis,
That material UHMD mentioned, is it same as UHMW plastic?
That stuff is slicker than snot.. I haven't found anything that bond to it..
Its make a good skid plates on the bottom of some boats, I don't see why it wouldn't work as cheek plates for centerboard.. It'll be great as it won't let the board to stick (hang up) inside of case...


Yeah...same stuff. Density/Weight...however you want to call the last letter. We use 3/4" boards of the stuff at the meat packing plant as cutting boards. When the surface gets too cut up we plane it down until clear and use them again. If you use a Stainless or Lead core and thru bolt you should have a functional and virtually rot free foil that can be shaped with common woodworking tools. Those 3/4" boards are TOUGH...but can take a set sometimes. There are various hardnesses...some are so hard they chip when we plane them and sometimes break the blades, so those get tossed out. The ones I like are the middle of the road ones...they plane well and last a long time. The softer ones cut too easy and I suspect would show too much wear from groundings and such. It would probably make an awesome case too...been thinking of making a daggerboard case out of it...just can't figure out how to get the old ones past security :rolleyes: :D

Steve

[Don Kurylko]

Oops, sorry MMD! I forgot that you have gone over to the “dark side” and can no longer opt for the easy solutions! Bummer. :p

Chuck, does them blinkin LED’s things attracts sharks? :D

Thorne, FG on Oak? :rolleyes:

[Excalibur]

Silly question Thorne. Was the previous CB made of marine ply or standard exterior? Is it possible that it was exterior ply and the glue dissolved?

As an aside, is there an ironwood species that you could use and leave out the lead? My vote, BTW, is for a titanium/kevlar composite with active angle adjustment for that ultimate advantage in going upwind

On a more serious note (and I'm asking for my own education, since I don't know). Is it possible to make the CB too robust? What happens if you make up the Ultimate High Strength CB and then have a large swell ground you hard in skinny water?

[Andrew]

Just to throw another idea into the mix. Start with two thin SS plate. Tack a rod 1/3 the distance aft. Clamp and weld the for and aft edges. Voila, a SS foil shaped board!

[JimD]

And a couple turns of the tape, for insurance.

http://www.jnkproducts.com/images/gorill1.jpg;)

[Thorne]

Excalibur -

Not a silly question at all. Embarrasing, unfair and untimely -- but not silly.

;0 )

It wasn't marine grade ply, but it had no voids, and was soaked in CPES and then coated with epoxy. Does "Seemed like a good idea at the time" cover it?

Since the boat never spent more than 3 days in the water, I think it was inletting the lead that caused it to fail, as that removed nearly half the thickness of the 5/8" ply. So I'm guessing more of a structural than glue failure, but who knows?

If I go the ply route again, should I buy a sheet of thin MARINE ply and lam up something roughly 5/8" thick? Heck, I could even route out some ply and put a couple of SS rods running the length of the CB for additional strength...

[Excalibur]

I've yet to build a CB. I have built a number of shields designed to be beat on by large people trying to hit me tho. I used 6mm marine ply and built it up as you described, and then molded thin sheet metal over the edge with a hammer from a cheap auto body shaping kit and a layer of epoxy over all. Done that way, they lasted as much a 6 months before failing. One bad thing about faring the ply after layup is that you expose the inner layers over a large area. I expect that compromises the edge strength a lot. I used thin sheets for shields because I could cold mold the ply into a curved shape. You could do the same thing. Take foam (or a plank) and carve it into the airfoil shape you want. Then cold mold ply on the outside to dimensionally stabilize the CB... Or, just go ahead and make one from glass and foam. At least you wouldn't need to pour the lead :)

[Thorne]

I have the armour but just borrowed the shield back in the day -- but always preferred combat archery...you know...shoot 'em in the back and run awaaaaaaaaay. Now I do mostly black powder.

Went down to McBeath's at lunchtime and picked up a 3/8" 1/4 sheet of Hydro-Tek Meranti marine ply. Will cut it in half lengthwise and epoxy it together tonight using filler (thank you, WB Forum!), then shape when it is cured. Priced the SS option and it was a gazillion dollahs even with the woife's discount.

I'll also pick up some Xynole to cover the board.

Thanks again, everyone!

[John Meachen]

The reason I suggested leaving out the lead is that the contribution to stability is minimal but in order for the lead to be inset,you had to sever all the fibres in the face veneers of the plywood.If you wish to retain the aspects of the system that suit your preferences,it might be better to use a smaller amount of lead on the tip of the board and persevere with the policy of sealing the wood.

[Thorne]

John -

I'm with you, but my problem was that initially I used too small amount of lead, and the board wouldn't drop properly -- and would fold back when sailing fast -- not good.

So I had to double the amount of lead, and that meant cutting another hole through half of the ply with my router before epoxying it all in place. I agree that it ain't good to be cutting holes in something that takes the sort of forces that a CB has to handle, but don't know how to get the weight where it needs to be.

The only alternative is a weighted shoe like you sometimes see in the UK -- puts the weight at the tip plus provides protection against hitting rocks. I'll see what I can fab up shoe-wise, but I usually just use some sheet lead that I've got sitting around for CB and rudder weights.

Here's one idea -- two pieces of sheet lead glued (and screwed) together to form the shoe at the tip of the CB -- sort of a flattened "C" shape. I could then use two thin strips of SS to wrap under the shoe and run up maybe 4" on either side to attach it to the CB, bolting them through the CB like plumbers tape.

All of this would be faired smooth, with the SS strips let into shallow cutouts in the CB's surface, then epoxied over and glassed (or Xynoled).

[Philip Maynard]

My last 1-1/2" 2 X 12 board for (Redmond's Bluegill), I ordered 3' (min order) of 3/4" lead wire (6 lb and just barely enough) and drilled 3/4" holes and then hammered the lead into the holes. The only bad part was chiseling the rod into all those short little pieces. I could then hammer it to conform more or less to the curved face of the board and then thickened epoxy over the lead and glassed the whole thing. Regardless of solid or plywood, glass or no glass, if you leave it clear finish then you will see any rot develop. Also weight at the tip is more effective at dropping the board and keeps the board intact at it's greatest stress which is just where it enters the CB case.

[Lewisboats]

Just to throw another idea into the mix. Start with two thin SS plate. Tack a rod 1/3 the distance aft. Clamp and weld the for and aft edges. Voila, a SS foil shaped board!

I gave that a try last night...except I used a 1/2" stainless rod for the leading edge, 3/4" rod for the spacer...2" back... and then clamped the aft edges and TIGed everything together... looks great (but will it work?). I went with 16 gauge SS for the sheet metal, 18" long and a 6" chord for a 3:1 ratio. I'll be using this as a rudder blade. I'll post a few pics tomorrow. I am wondering tho...should I drill holes to let it fill with water...or will the weight compensate for the buoyancy of the sealed air chamber that it will become when I weld on the end plates? :confused:
And speaking of end plates...should I leave the bottom one a bit wider than the sheet metal or shape it to match the foil shape exactly. The reason I ask is that I know that lift is lost around the bottom of a foil for about 25% of the length of the foil and that end plates can reduce this loss.

Steve

[gert]

I think it must be a slow day at the office; any one here remember...KISS? ;)

[Andrew]

I think it must be a slow day at the office; any one here remember...KISS? ;)

Gert, it is simple if you're only suggesting someone else try it.

Lewisboats, I think the hole would be more important to insure the water gets out.

[Thorne]

Steve -

I'd be tempted to fill it with something waterproof -- maybe one of the huge tubes of PL Premium or ?? And you could add some lead shot to the bottom fill so it will hang down but still kick up when needed.

Gert - I tried it as simple as possible and it didn't work (cheap ply, lead weight, epoxy covering). So now we are checking out other options. The marine ply with Xynole and epoxy coating should work fine, just gotta figure out how to get the weight in place without weakening the CB too much.

[Jim Ledger]

Thorne, calculate the buoyancy of the board to decide how much lead to add. Don't rely on a guesstimate or you might end up with a board that doesn't want to go down, a real annoyance especially when you have to re-do what you just built.

I know it sounds simple but it's a mistake I made with the Sea Rover's board and getting the board in and out of that boat was a major undertaking.

Put plenty of lead in. Melted and poured is the best as you get the densest concentration of weight.

[Philip Maynard]

Thorne, I find this an easy way to make a fairly efficient board for a small boat, my kitchen floor is 12" squares for reference. This is before glass and lead. It's just 2X12 with 3/8 brass plumbing nipple for an axle. The 1/8" brass cover plates are screwed to 10-24 ss tee nuts set flush with the inside face of the trunk, I glassed the inside of the trunk before putting the 2nd side on. Your 5/8 thickness is such a handicap it might be advisable to make a new wider trunk by making new thicker spacers and enlarging the slot and cutting back the frames that let into into the case.
http://www.pmaynard.lunarpages.com/temp/bluegillCB.jpg

[JimD]

Hey Thorne, I hope Phillip's Mrs doesn't mind when you show up on he kitchen with your busted centerboard.

[Thorne]

Too late, I've already glued up the marine ply, shaped it into a NACA0008 foil and am letting the first coat of CPES cure...

http://www.luckhardt.com/newcb1.jpg

http://www.luckhardt.com/newcb2.jpg

http://www.luckhardt.com/newcb3.jpg

I'll also be adding about 6-7 lbs of lead, so it will be sure to pull all the way down -- made the error of not adding enough weight on the last one, which is why I had to later inlet another chunk of lead, which may have been why it broke...