Casting the bulb

[Chad]

It was a slightly bastardized Godfather quote.
Just being goofy...

[admin]

Doesn't matter where your sharing came from. Everyone who reads your post will send good thoughts your way.

Got that right!

[Chad]

How does a Godfather quote turn into a love fest?!?

Anyway, day three progress on the bulb plug. Cut a couple same-length blocks to support the spine very level. Glue the last two ribs to the spine with some 5 minute epoxy, using a square and block of wood to support them plumb and level- they're too fragile, and their notches too small to self-register on the spine. Cut some strips of foam, hack them to rough length, and glue them in between the ribs. I used Gorilla glue since it sticks nicely to the foam, and it the fills gaps, and it isn't too hard to sand. Add some weights to hold it all down:

half foam.jpg

This glue will dry in a couple hours, so I can do the other side this afternoon- the foam is already cut and waiting.

Time today, about an hour.

And I sanded half of my deck, about halfway. So it's not all charity work around here...

[Chad]

Day four.

Second half of the foam glued on yesterday afternoon:

IMGP2436.jpeg

Using a handsaw to cut the foam pretty close to the ribs. This feels like cutting fish fillets, somehow:

IMGP2437.jpeg

Using a surform tool to shape the foam just to the ribs:

IMGP2438.jpeg

And finally, using various sanding implements to sand the foam fair:

IMGP2440.jpeg

The tail is still a little fragile, and was challenging to shape accurately- I may knock out the last portion of foam and replace it with a hunk of filler-thickened epoxy. At any rate, I'll brush a skim coat all over it this afternoon, sand that back tomorrow, and it ought to be done.

Time today, about an hour. I was a little smarter today, starting with a sanding session on my deck until my arms went limp, then worked on the bulb, then had the energy to put in another session on the deck.

[ryderp]

Chad,

The plug looks great. Is there a mailing list yet?

Phil

[Chad]

Thanks, Phil.

I'm going to pull a mold off of it for myself (for a backup), then it goes to Noel in MA and then you, so far.

[Chad]

... although if Noel isn't ready for a bulb just yet, and Phil is almost done with his keel, maybe it makes sense to swap? Is that alright with you, Noel?

[noemar]

I'm Ready. Lead is awaiting.Thanks ever so much
Noel

[Chad]

Ok, sounds good! I'll pull my mold this weekend, and contact you early next week for an address.

[cstay]

Noel. I am headed down that way in the near future. I could give you a hand pouring and if you need any equipment I could bring it down.

[noemar]

Craig, I appreciate your offer. Chad has made an offer to let me use his latest keel plug and then. I will try a to make a mold. I have my lead and a plumber friend has agreed to let me use his lead melting equipment. Not sure what else I need but will keep you informed. When do you plan on being in SE Mass/Cape Cod area? I'm just about complete cutting out frames and panels and finishing up cradle supports.
Thanks again for your offer. Now if only the rest of the world could be like the I550 folks !

[Chad]

I caved, and added filler to the plug. I knocked out most of the foam at the tail section, and just cast it in epoxy/filler. Sanded it this morning, it looks killer. The trick is having a convex sanding block- a must for fairing the finished bulb as well.

I'll pour my first half mold this afternoon.

IMG_0250.jpg

[admin]

Beautiful.

[Kevin]

I concur. That bulb plug looks fantastic. Maybe some day I'll need a new keel and that bulb plug will make it's way to me. Until then, good luck to all that are lucky enough to put it to good use.

Cheers, Kevin.

[Chad]

Thanks guys.
I cast the first half of my mold yesterday afternoon. I suck at concrete- botched the mix and had super-soupy slop to work with. Hopefully it won't be so weak as to crack under its own weight! I'll do better with the second half.

I'm doing my mold in bottom half / top half fashion, so I won't get to test how hard it is to extract the beaver tail sideways from the mold. That'll be for the next guy...

Mold will be here and empty, Kevin. Just a short five hour train ride...

[Chad]

Thanks, Jon!
I don't need a new bulb yet either, but I'll be glad to have a mold already done and squirreled away should anything unfortunate happen to the current model!

No progress on the plug today- I spent the morning "boat time" putting together a sailplan to give my sailmaker. If he doesn't laugh too much at my whacky ideas , I'll post that here in a couple days.

Well, he didn't laugh at me, which is nice. So here's the sailplan. He's a little concerned about forestay tension in say the 12-15 knot range, where you don't have the mainsheet boned, but the forestay wants to be tight. I'll be standing the rig up during the boat flip, so I'll get a better sense of how things behave at full size, versus the little model I made several months ago.

That means I need to get those spreaders attached to the mast, and cut in my t-ball plates, and a bunch of other rig work. Exciting! -if I didn't also have to sand the deck, glass the cockpit, finish the boom, and on and on.

You'll notice this is craftily buried away here on a thread with an unrelated name, and the file is zipped, so you really have to want to look at it...

i550_sailplan7.jpg.zip

[jray]

Looks great Chad, I especially like how you are running the stays and adding the jumpers. Looks like you have lifted the jumper t-ball above the boom some. Above where Josh placed Shazza's. Just curious, how much pre-bend are you planning on? I'm running around six inches some are much more. Get her done, let's go sailing.

[Chad]

Alex suggested around 100mm/4 inches to start. I'll see how it feels when I rig the boat, and sails won't be finalized before that. The gnav stays just hit the mast at the top of the gnav, rather than at the gooseneck like a conventionally vanged boat. Alex said he thought the rig wouldn't need D1's with this setup, but there's laminate in the mast already if I feel the need to cut them in later.

Yup, ready to go sailing already! Groundhog might have seen his shadow, but the last week has felt like Spring here. I'm sure I have plenty of winter left to get my projects done though!

[ryderp]

Chad,

I'm just getting up to speed on rigging for the boat. A couple of questions:
What is the advantage of using running backstays on this boat? I have the old style runners on our e-scow, but I'm hoping to get rid of some complexity on this boat.
Am I correct in thinking that you'll set the pre-bend with the blue (in your drawing) shrouds before you leave the dock and the runners are just for supporting the mast and for adjusting tension while sailing?
I'm using a Dwyer DM4 rather than carbon mast. If I'm using aluminum, is there an advantage to this kind of setup rather than a more conventional rigging?

Thanks for sharing this info.

Phil

[Chad]

Phil,
If I said I knew exactly what I was doing my nose would be a yard long. I'm posting these drawings to share what I'm doing, rather than encourage others to do as I do. If my explanations make sense to what you know of sailing and rig tune, then feel free to use or adapt anything I've done. Chances are that some of my plans are more ambitious than good sense, so I'm not the least offended if you think I'm nuts.

How I got to my rig design: First, I wanted typical sport boat tuning characteristics, as you get from your typical swept-spreader, I-point shrouds, and nearly balanced (round tube, or close to it) mast section. But I also wanted to see if I could improve the aero of the round tube a little, incorporating an updated version of what Bethwaite did with his Tasars with spruce masts and balsa fairings- the spruce was nearly square or round so when it rotated it didn't get all stiff in the wrong direction like a solid wing mast does, and the balsa was light enough to be useful enough to justify its weight. That class has moved on from spruce masts, and Bethwaite's ideas lost traction. They sorta struck a chord with me though, so I wanted to have a go with today's materials to see how it could be made to work.

So the hounds high/I-point shroud that goes over the lower spreader (in green in my pic) is the string that will be adjusted with turnbuckles at the dock (or with difficulty on the water)- it sets the base prebend and rake. The gnav stay is probably just going to be set "a little more than hand tight" once the hounds spreaders are set. Then, with an adjustable forestay, pulling the forestay on will pull a little extra bend in the lower mast flattening the middle/lower part of the main and hopefully if the mast doesn't go noodley it will also increase headstay tension.

The blue topmast shroud (is that what you are calling the backstay or runner?) is also on-the-go adjustable, so I can play the upper part of the main shape upwind, as well as setting the point where the top mast falls off in response to a gust. I lead it to the base of the mast instead of the chainplates so that I could more easily adjust both sides with one tackle, and I think I can reduce the rotation friction with the geometry setup this way. I can also vary the point along the lower spreader where the topmast shroud bends, making a further tuning opportunity to either pull or push on the mast at that point. I honestly don't know which I will need more of at this point! I'm learning (from others, I haven't sailed one myself) that fathead or square top mains like stiff masts. Having a topmast shroud greatly stiffens the topmast (duh!), but also allows you to adjust the pressure where the topmast begins to deflect. With no shroud, the topmast is a simple spring cantilevered from the hounds. It will deflect in direct proportion to the pressure applied. If you add a stay and tension it, then the mast is "pre-stiffened" so that it does not deflect (much) until a higher pressure threshold is reach, and then it does deflect, to aft and leeward along the arc of the stay that is in tension, opening the upper leech of the sail and helping the boat go forward instead of heeling or staggering. That's ye olde "gust response". Somehow, it just seems like it will be hard to find that correct tension with a turnbuckle versus having the string in your hand and pulling a little on, looking, easing a little off, looking, etc. And if you know you'll have newbs for crew, it means far less instruction and hassle to get it set up.

As for the DM-4, here's how they compare to a Forte's carbon mast (I don't have the I values for C-Tech, which also has a 70mm/2.74" diameter but has a .10" wall thickness so should be similar to slightly less I value):

DM4.png

FORTE 2740.png

The DM4 is likely to be very similar fore and aft to the carbon masts, but a little softer side-to-side. I suspect this means you'll need to use a little less tension on the shrouds, use longish spreaders to help your geometry (increase the staying angles reduces the needed tensions), and set your chainplates as wide as you can. And do install the 2nd, I-point spreaders!

Some online references:
For classic sportboat rig tuning:
http://www.tboat.com/Editorials/Edit-de ... t-rig.html

Some other whacky options:
http://www.uk-cherub.org/doku.php/tech/rigging

[Chad]

To further obfuscate this rig discussion, let's bury it in between some more bulb talk:
The second half of the beaver bulb mold is curing! I'll pull the mold apart tomorrow afternoon and box the plug up and send it on.

IMG_0254.jpg

[noemar]

Chad is that a two piece form ie top and bottom?

[Chad]

Yup. I intend to pour my next (if ever) bulb in one piece like I did the first. I bolted my bulb on from the bottom, rather than inserting the fin into the bulb and cross-bolting.

First pour, with the plug wrapped in cling film:

IMG_0251.jpeg

Just before the 2nd pour, with cling film over the bulb and the first poured concrete:

IMG_0253.jpeg

If you plan to make left and right halves, I'd advise wrapping the plug in several layers of cling wrap to make sure it can be freed from the mold. Remember, it's no biggie to make the mold cavity too big- the lead is easy to fair back to shape, and in most cases the mold can be faired with some drywall mud. My mold currently has all kinds of cling wrap wrinkles, but it doesn't matter, as long as the overall shape is fair.

[cstay]

Its a bit late to tell you this but you put the cups in upsydown. Once the lead cures in those there will be no way of removing that part of the mold from the lead. If you want to save your mold i would use a grinder or file something to get those holes flat and not have the funnel shape. Chances are the mold will crumble after anyways. Also when you do your pour make sure you bolt the two sections together well. When i poured mine the weight of the lead floated the top section of the mold right off the bottom and lead poured all over the ground and we even had it bolted just not tight enough.

[Chad]

Yeah, I don't plan for this mold to serve for more than one pour- my last one didn't survive the un-molding process either. For me the funnel function is more important than preserving the slight chance that the concrete might be reused. At about $2 per 60# sack, I can remake molds a couple times a year without breaking the bank. The hard part is disposing of the pieces in several loads of trash, to avoid pissing off the trash man.

I used red RTV sealant (from an auto parts store) to seal the two halves of my previous mold, and had no leakage or floating problems.