Jul 17, 2015, 09:58 PM Registered User Minnesota, USA Joined Aug 2002 3,461 Posts Question Keel bulb design for specific weight are there any tables that show keel bulb design/dimensions for specific weight? I am looking for tables where you can enter desired final bulb weight, and the tables will provide (I hope) the length and diameter for a bulb to hit or come darn close to the design bulb weight,. I thought there was one but haven't been able to find it. Any help or links appreciated. Thanks in advance. Dick
 Jul 17, 2015, 10:22 PM Registered User Auckland New Zealand Joined Sep 2010 253 Posts http://www.onemetre.net/design/bulbcalc/bulbcalc.htm All you need. Takes a bit of learning how to drive it though. found it in http://onemetre.net/index.htm There is always a tradeoff between length/dia (surface area) and drag. I've seen a chart of surface area vs drag relationships but can't find it. I seem to remember for lowest drag the diameter is around 8 to 10% of length. Makes delicate ballasts though. Last edited by KIWINB; Jul 17, 2015 at 11:03 PM.
 Jul 17, 2015, 10:32 PM Registered User Minnesota, USA Joined Aug 2002 3,461 Posts @KIWINB Thank you. I believe this was the one I was looking at some time back, and forgot to bookmark the URL. Will give it a go and see what kind of shape & size I wind up with. Appreciate your quick response. Dick
Jul 18, 2015, 05:44 PM
Rusty
Auckland, New Zealand
Joined Feb 2006
1,286 Posts
Attached is a non-lifting, parallel bulb calculator and lifting profile drag analysis for completeness.

# Files

 Jul 19, 2015, 11:32 AM Registered User Minnesota, USA Joined Aug 2002 3,461 Posts Thanks for the calculator. I am hoping to take a chunk of cedar and turn it on a lathe in garage. I was thinking that I wanted a diameter and a length that would = desired weight. My initial guess is the first response will provide that - or - a darn close ball park shape to begin. Want to get away from the # 5 or #6 shape (Image above) and head towards the #1 or #2 shape. I have no issue in finding the best total bulb weight - just visualizing how much lead needed to make a good bulb shape. I prefer to be close on the wooden turned plug, rather than having to try to reduce a lead bulb.
 Jul 28, 2015, 10:32 PM Registered User Joined Feb 2013 10 Posts Bulb Moulds Has anybody tried making moulds of portland cement.Plaster of paris is just to fragile!Maybe even chopped fiberglass in cement.
 Jul 29, 2015, 08:17 AM Registered User United States, FL, Cocoa Beach Joined Jan 2010 1,288 Posts bulb mold The best material I found for making bulb molds is alumina ceramic. You can use a wood plug and make a small box out of balsa to pour the mixed ceramic into with the wood plug inside. After a few hours it will be ready to go. A bit expensive if you buy the material from McMaster-Carr: \$85 for 10 pounds, part #8498K35. You can use a mold made out of this stuff dozens of times with no degradation. Last edited by DLord; Jul 29, 2015 at 08:58 AM.
Jul 29, 2015, 08:23 AM
Registered User
Minnesota, USA
Joined Aug 2002
3,461 Posts
I have been looking at this stuff. Haven't purchased as yet.