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Fin keel with ballast bulb

Name: Fin keel with ballast bulb dimension sheet
Creator: Xem Studio
License: https://creativecommons.org/licenses/by/4.0/

Why do racing yachts and RC sailboats use a thin fin with a bulb? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: bulb keel, fin keel, keel bulb, rc sailboat keel, IOM keel, ballast bulb, fin and bulb, torpedo keel, lead bulb rc yacht, keel draft

Exact dimensions. True size, with no printing tolerance added.

sizes: 5 in table

Notes

A bulb keel puts the ballast in a teardrop at the bottom of a high-aspect fin, as low as possible for maximum righting moment (Wikipedia, Bulb keel). The thin fin supplies lateral lift with little drag.
The penalty is draft, so bulbs suit deep, thin keels and are not used where shallow water matters (Wikipedia).
The IOM RC class limits the bulb to 2500 g of lead and 420 mm draft on a 1000 mm hull with 4000 g minimum displacement (onemetre.net).
Used on: International One Metre (IOM), International 110.
The file is a reference example built by Xem Studio from the numbers above (Depth = IOM max draft; chord and bulb shape illustrative (IOM fin/bulb shape free).). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Fin keel with ballast bulb size chart

parameter	value or range	source
IOM hull length	1000 mm	onemetre.net
IOM max draft	420 mm	onemetre.net
IOM min displacement	4000 g	onemetre.net
IOM max bulb	2500 g lead (62.5% ballast ratio)	onemetre.net
International 110 bulb	300 lb cast iron	Wikipedia (Bulb keel)

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Wikipedia	Bulb keel	web	Publisher's page; dimensions are facts
onemetre.net	The IOM class	web	Publisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

fin-keel-bulb-appendage

fin keel bulb: 420 mm deep, 60 mm chord, NACA 00-series foil, bulb Ø40 × 180 mm

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Plain text: sheet.txt · JSON: /api/geometry?object=fin-keel-bulb