Fairing in bulb to foil

[slowpoke]

Hey guys, how did you handle the transition from bulb to keel foil? I'm fairing it in with a 1/2" radius, but I was wondering how many of you faired it, and how many just let the transition form a 90*?

[jeff.dalsin]

I smeared 410 filler in the joint with a tongue depressor. So that's probably a 1/4 radius. Gave everything a coat of neat epoxy after is was fair and before primer.

Jeff

[jray]

Just going there myself very soon, I plan on a radius for the transition area. No supprise the hole boat is a transition. I don't think there are many sharp edges on the hole build, there are some though. As for the right thing to do I believe the proof will be there later and it is a easy change if needed.

[Kevin]

MIne has a very small radius. 1/16" probably. Here is my theory. The larger the transition, the more drag that will be created. Why, because transitions create turbulence. Your keel is either splitting the water away from it's buddies, or you are letting them come back together. So the water coming around the top side of your bulb hits your keel. Now what, well you want to make it's decision easy, left or right. Not complicated; Left, or right or left and up or right and up. The ones going up will run into the straight around dudes going around the keel and now you have turbulence disrupting your flow. And that just slows you down.

Kevin.

Note: this is based on my own understanding of flow theory and what makes sense to me. I'm not an engineer by trade and I accept the fact that my advise could be completely wrong. As usual, it's worth what you paid for it, which is not much.

[jerome]

İnteresting discussion since İ am also just about to complete this task. İ like Kevin's descrition of little buddies running all around but İ am also faced with another issue: i intend to cover the whole bulb + bulb-to-keel join with one layer of fiber. The point is that if İ leave a very small radius, close to nothing, than İ know İ will not laminate that bub-to-keel join properly. İ just found it impossible to laminate over hard angles without living bubbles. Wrapping that cloth around nice rounded edges is easy, but not doable over 90 degrees angles.
Point in case : İ already laminated my cockpit, rounded the edges of the upper deck-to-hull joints and had no issue whatsoever. But İ forgot to rund the edges of the cockpit sole-to-transom edges. Result ? Large bubbles all over the edges. İ sanded everything down to clear the bubbles and know have the plywood edges exposed. No big deal but İ will , for sure, round off those edges and then re-laminate.

This leads me to another question. İ guess İ will have the same issue with the hull panel edges. Did you guys rounded off those edges before laminating ? İ sure intend to do so to avoid the possibility of bubbles.

[Kevin]

Jerome, You're right on the money. If you are glassing the way you plan to, then a 1/8" ~ 3/16" radius minimum is probably needed to get the glass to lay in that joint. If you run the glass on the bias instead of square to the joint it "may" lay down better because each fiber can use a longer angled arch instead of the perpendicular arch.

On your transom, you could round it off and then run your transom piece of glass up and around onto the sole.

I rounded my chines for glassing and then used fairing compound to shape the finished chine the way I wanted. There are about as many theories as their are builders on what is the best treatment of the chine.

Kevin.

[jerome]

Good input Kevin. İ'll do just that for my chines. Tks
Ps: and that is one more good building tip to add to our database

[Chad]

These guys hire pretty good designers , and they all seem to agree that no radius at the bulb/foil joint is best:

bulb1.jpg

bulb2.jpg

bulb3.jpg

[Kevin]

Dang, that middle picture is sexy as hell. What an awesome picture.

[Chad]

mybulb.jpg

Yeah, they were no doubt inspired by my work.

[jray]

Hard to argue with that. Nice job Chad!! Hope mine turns out looking something like yours did. Plan on casting the bulb halfs next Sunday.

What has everyone used to through bolt the half bulbs together on the strut? I seem to remember something about stainless steel not working well when it's encapsulated.

[jeff.dalsin]

Stainless Steel needs oxygen in order to "stain less". I used bronze bolts to fasten the two halves together. I'm sure that the two halves are still together at the bottom of Lake Michigan. On the second bulb, I was pressed for time to get in the water for the Epoxy Cup so I went with regular old zinc plated. In any case, the entire bolt should be well protected from water given all of the filler, etc. present.

Jeff

[admin]

did you notice the dimples on that last shot? what a bunch of amateurs.

[Kevin]

I thought those are speed dimples

[Chad]

Hey now, it's just primer, with the fresh-off-the-roller orange peel, not sanded yet. Gotta see it for what it will be, not what it is.

At least that's what I keep telling myself.

[Kevin]

Chad, it will look awesome when you are finished with it. I'm sure of that. We were just giving you a hard time and playing on Nortorious' comment earlier. I'd recommend you keep it white so you can see the weeds on it and such. Those AC bulbs are pretty awesome, but black hides everything include the kelp you are dragging. Very huge and many different ideas on each of them. Those days are gone with the new AC cats though.

[admin]

my apologies, Chad!!!

I did not read the captions well enough. I thought it was one of the shots of from the Oracle/Alinghi series! You do superb work and I am sure yours will make the AC bulbs look like the surface of the moon.

sorry sorry sorry!

[Chad]

I'm not the least bit offended at having my bulb mistaken for even a badly finished AC bulb!

Weed, huh? Plenty of kelp where I play these days, but I have very little freshwater experience. Whaddaya guys have in those middle of the country lakes and rivers? Should I be planning a weed cutter?

[jerome]

Chad, so how did you go about that bulb to foil transition ? Did you laminate that area with fiber glass ? İf so, how did you avoid the bubbles on such a hard angle ?

[Chad]

My foil is inserted into a shallow notch in the top of the bulb, glued with a toughened epoxy, and bolted from below with two 5/8" (16mm) stainless rods that extend about 8" (200mm) into the foil. There's no sheathing on the bulb, and no fibers in the corner. Without a radius there, I don't think fibers will do any good- they would be progressively loaded in the peeling direction. All the load the fibers see is concentrated along the line of the tight radius, trying to peel them off the bulb or foil, and if that line of adhesion fails the load is transferred to the next line of adhesion, and so on- classic zipper type failure.

For places where you do want a tight radius, it works to use an appropriately shaped stick wrapped in parcel tape and clamp it into position over the laminate.

[jray]

Is there some reason besides the strut being shallow in the bulb that you secured it from the bottom instead of cross bolting? I have to pick a direction to go with soon. How did you secure the rods in the strut so they don't pull through? Lots of questions.

[Chad]

The hole for the foil to pass all the way through the bulb displaces about 30 pounds of lead. I wanted to get as much of my allowable 185 pounds in the bulb as I could, so I chose an attachment design that allowed a more solid bulb.

I drilled the end of my foil with oversize holes, wet out the holes, wet out the rods, partially filled the holes with thickened epoxy, and pushed the rods in. Just typical hardware bonding techniques. A shallow foil-shaped recess in the top of the bulb is still very important with this method, so that the bulb doesn't push sideways on the rods where they exit the foil. I cut the recess with a pattern-following cutter in a router, about 1/16" oversized to allow room for glue.

Note that this is a slightly more aggressive construction method, and needs to be done carefully to succeed. It's hard to mess up with cross-bolts, but there's a couple opportunities to make it go wrong with my method. Choose your level of risk/reward.

[Chad]

For the sportboat that has everything, the ultimate Christmas present:

blingbulb.jpg

Might need to knock over a couple of those "cash for gold" kiosks at the mall first, though.

[jray]

Great picture Chad, and I even like the color.

Nortorious the auto racing scheme will look trick. I'm having fun with two colors and can't imagine the work you are planning. Keep us posted on the progress.

[Kevin]

I used a cut off from my keel for the recess for the foil in the bulb. As I recall it was about 3" tall total and not in good shape when I was done with it. Soak it in water before lead touches it. Anyway, I didn't go all the way to the bottom of the bulb with the slot. The 2 halves didn't exactly mesh together perfectly. Jeff did a second pour of lead to fill the gaps between the halves after they were bolted together. I used lead shavings in epoxy for the same purpose. I think Jeff got a better result and less head aches. If you cross bolt the bulb on, it really shouldn't go anywhere in relation to the foil. Something super major has to go wrong for the 2 to separate. I filled and faired the joint like any other without using fiberglass.

Of note, I drilled the smallest hole I could for the nuts and bolt heads. I used a screw driver and a mallet to tighten them up because a socket wouldn't go in the hole. I covered everything in epoxy and silica as I assembled to fill voids. I used a grinder here and there to get it all below the surface of the bulb. The thought of taking it apart some day is unthinkable to me at this time. Maybe I'll do if for try #2 some day. Have to get the rudder back in shape first though.