I poured 6 bulbs yesterday. The first one bubbled and steamed, not real vigourously but for quite a while(maybe a minute). The rest went almost flawlessly. This is with a mold made from 1/3 Portland cement, 2/3 Plaster of Paris and a big handfull of 1/4" chopped strand glass. Dried it until it stopped losing weight(about 2 weeks in front of the stove). The mold has some minor chips but it looks like it’s good for at least another 10 or so bulbs. I’m satisfied with this method. I think I will make another mold before this one self destructs so it has time to dry. Although 6 bulb should last awhile.
Don
Hi Row, yes two halves are clamped together and I figured on pouring lead quickly & smoothly into the “pre-heated moulds” to prevent gassing & bubbling, but I made two sets of moulds, just in case it fails, then I can pour in halves and bond together, but prefer not too of course !
Both halves are not perfectly flat to each other, can see small amount (hair-line) of daylight when clamped together, which may help the moulds vent when pouring.
Wow Don!.. you give me hope mate !!! only first pour bubbled, others didn’t ? was mould temperature a factor or was it your quick hands or other secrets ? 
Cheers Alan.
I pre-heated in the oven at 300f for an hour. Just the first one bubbled. After that it was perfect, no bubbles. I didn’t really have to rush between pours.
I did get a slight void/depression at the base of the forward sprue. Maybe the sprue could have been longer.
The picture was taken after the 6 bulbs were poured. You can see a bit of chipping here and there. I scraped off the sharp edges before the first pour so the bulb would come out easier.
Don
Don,
Congratulations on you bulb successes - can you post any pics of the initial cast state of the lead?
Also, assuming that your mold material is reasonably liquid when it’s first mixed & poured, I found that placing the mold box on an upturned power sanded (switched on of course!!) really helped to bring air bubbles to the surface (vibration), thus giving a better overall finish to the mold and then by definition, also the lead.
Another quick question for you, did you use sheet lead cut up into small pieces for melting down or ‘ingots’ - & what did you use as the heat source for melting? Although I have my system that seems to work I thought others who haven’t tried casting would value the additional info.
Cheers,
Row
Unfortunatley I have sawed off the sprues but here’s some pictures anyway. There is no need for vibration, the mold is smooth. With the cement and POP mixture there really isn’t time to vibrate anyway. I use tire weights and scrap lead. I made a melting pot by welding a cap on some old pipe. I stand it on a pile of bricks and aim a thing we call a “Tiger Torch” at it. See this link http://www.youtube.com/watch?v=lAMMKR_xK2M
I do this outside with everthing on the ground. That way if I spill it can’t splash much.
I only got one small burn on my thumb. All in all a good day.
Don
Ok confession time … I came across Robert in Dutch forum as he was looking for NZL-92 plans & I offered to lend my NZL-92 mould, after few e-mail exchanges he asked to pull female moulds and offer them to Dutch forum members to help quick start AC-120 group in Holland.
http://www.modelbouwforum.nl/forums/zeilschepen/155460-iacc-120-a.html
Cut long story short Robert now has 4 of my moulds (including NZL-20) as professional laminator in return, he will give me 3 laminated hulls …win-win situation, unfortunately as I had prepared the plugs with wrapping tape for release, poor Robert needed to take it all off again and re-sand and paint them ready for polishing and waxing.
All four moulds finished today ready for next stage & here’s the pics 
Claudio looks like I will have just about caught up with you my friend 
and central European fleet growing quickly with new Dutch group 
Cheers Alan :zbeer:
You’re bit if a demon there Don, no wonder had no problems pre-heating the moulds :lol:
No words for Don, Robert and Alan !!!
cheers
ClaudioD
For those interested, Robert has opened a new threat on the Dutch Forum on “How to make female mould” http://www.modelbouwforum.nl/forums/showthread.php?p=2480174#post2480174
Don has provided great contribution on “How to make a bulb” from the U.S. This is turning into an international build project !!! hey Jim maybe we can have you in the threat in “How to make custom carbon mast” in Valencia next ! 
And then I asked Tiziano from TD model to pitch-in with “How to make professional Keel fins” from Italy 
ok ok … I have abandoned my search for the truth and am now looking for a few good fantasies.:lol::lol::lol:
Cheers Alan :zbeer:
Canada, Not U.S. :):)
Don
:tapedshut sorry
Hi All, Just quick update on this project …it is not fizzled out, Robert in Holland has been set back with family priorities, so my hull moulds with him, are on on hold for awhile, family comes always come first and pass on best wishes for Robert & his family.
Claudio in waiting for me before completing our dual NZL-20 project, in the mean has come up with a great new 1-2-3 design that looks like possible futuristic new AC 90 mono-hull that looks fast on the bench…another new build to add to my already too long list of things-to-do…we should be completing NZL-20 build following completion his 1-2-3 build.
Big thanks to CapeCodJim who found two very rare AC books in a book sale in New England and was kind enough to think of & send them on to me …thanks Jim ! great reading and inspiration of some forgotten teams, like team Nippon campaign (91-99) and JPN-26 that sailed against NZL-20.
Cheers Alan
Weather is now improving and decided to pour bulbs from moulds made earlier, pre-heated moulds while melting lead and then clamped two halfs together.
First bulb I used house flashing lead which felt little thick in the pot, only after pouring molten lead did I realise how much slag was in it and aborted the pour halfway, can see slag beside the mould in the pic.:rolleyes:
Second attempt was using old bulbs (minimum slag) and pour went well until I plugged the pouring hole with lead leaving me with ¾ of the bulb :mad:
Two failures in one day so gave up for the day and went sailing instead….will try bulbs again next weekend
Cheers Alan
Alan !!!
you have a design error in your mold !
You forgot to insert the air escape hole.
Lucky you that did not exploded for air entrapment !
You should for the next time add the holes aside the melt lead entrance. see marks on the picture if the mold shall stay in the upright position !
Cheers
ClaudioD
Thanks Claudio … will rectify that asap !
Error comes from (or lack of) grey stuff between my ears !
Ok finally managed to have couple of good bulbs without any problems this time, but next time I would most definitely go for the foundry sand over the furnace mortar, following this exercise I’m now convinced it is worth. it.
Cheers Alan
I finally managed to drive to Holland and pick-up my 2012 plugs, albeit Robert had no time to laminate hulls, he did manage to prepare the plugs with some “candy colours” in prep for vac bagging.
With little colour hopefully now begin to see the difference between each of hulls, like women I never get bored at looking at beautiful lines [i]all great designs from Claudio.
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As Claudio is working through his 123 project, I will be finishing another project for a friend and then will start preparing for latex lamination of NZL-20 hull (red plug) that will be end of July.
Cheers Alan
Great information on the molds for the bulb but what happened to Claudio’s build project NZL20. We were just finishing the plug? Love this info. Maybe my build will go good the first try. Thanks to all!
Claudio has NZL-20 project on hold until his other project 123 is completed, I’ve got my part on hold too, looks like few more weeks before continuing with this project.
Cheers Alan
Hello , I am curious did this boat get completed ? I Grew up in southern California and attended the Americas Cup in San Diego, and NZL-20 was a stand out boat to me and should have Sailed against America3 for the cup. This is a boat that I have wanted to build for some time. I even contacted Bruce Farr’s office and could not get any info on the Boat. I understand for the IACC 120 Class The hull shape had to be altered, for the reasons I have read in this build log. Does anyone have info on the correct hull shape and bowsprit length. I would love to build a scale replica that could be Sailed ( for fun )
Best Regards,
Pete