The Origins Of A Bulb

Things have been quite busy with the kids, the holidays, and work..but I've been able to find a bit of time to plug along on the boat project now and then.  I've continued fairing the keel fin and almost have it done.  I thought I was almost done last week, but with each layer of fairing compound, I'm excited to find I'm exceeding my expectations but that it's still not quite perfect..so I grab my template an add another layer of compound.  With the shop being kind of cold from the weather, it takes a while for each layer of fairing compound to cure.

So since I've been waiting between fairing layers, I've been taping seams on the inside of the boat and am almost caught up.  I have run out of 6" fiberglass tape so it looks like a field trip to Fiberglass Supply in the near future.

One cold night as the snow was falling and I didn't feel like heading out to the shop, I figured I should start thinking about the keel bulb.  So I poured myself some wine and I did. And what I thought was, there's no reason for me to re-invent the wheel and try come up with my own bulb shape.  Since this project is sort of similar to the i550, I've decided to use the bulb shape someone already designed for that boat..with only ever so slight modification. I found the bulb lines on the i550 forum and downloaded them.  The only problem is that the i550 bulb weighs 180lbs and I'm thinking I need this thing to weigh around 550 lbs  So I grabbed my calculator, scratch paper, another glass of wine and began measuring, calculating stuff, and running ratios.  By some method which my memory is not exactly clear on, I arrived at the conclusion that by enlarging the i550's bulb dimensions by 45% this new bulb would weigh precisely 550lbs.  I know when I did the calculations I was pretty confident that they were sound, however, I will consider any weight between 475 and 600 lbs a complete success.  And if it's way off, I melt it down, build a new mold, and re-cast!

The first step is to build a plug which I will use to cast a female mold in plaster or concrete.  I am building the plug out of plywood and foam which I will fair (arg!! there's that word again!) and cover in fiberglass.