SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Dec 18, 2012, 05:32 PM
Registered User
Joined Dec 2012
17 Posts
Question
drop keel

Hi, I am scratch building a 43" shallow "V" hull sail boat, she is 12" across the beam. My drop keel will be aluminum flat bar of 2" x 3/16" x (L ?) any suggestions as to how deep the keel should be or how much weight I should attach? I am planning on using a torpedo style ballast. Is there a formula for determining these things?
Gramps1 is offline Find More Posts by Gramps1
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 18, 2012, 05:43 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
3,553 Posts
The area and height of the rig should be mentioned but the boat is obviously for relaxed sailing with probably a smallish set of sails. I'd go for a fin no longer than maybe 8-9". The weight is more a question of the designed water line. Put a weight in the hull equivalent to the rig, the radio etc. and do a flotation test in the bath to see how much additional weight is needed and where.
martin richards is offline Find More Posts by martin richards
Reply With Quote
Old Dec 18, 2012, 05:47 PM
Registered User
hiljoball's Avatar
Canada, BC, Lake Cowichan
Joined Jul 2011
531 Posts
Good luck with your project.

It is similar in size to the Star45 class boat and that weights 12 lbs, of which about 10 lbs is in the ballast.

See the Star 45 forum

http://groups.yahoo.com/group/Star45/

Here is a reference for bulb calculations

http://www.onemetre.net/Design/Bulbcalc/Bulbcalc.htm


I would recommend against just a flat plate for the fin. The hydrodynamics are really bad. I suggest that you plan to glue on two balsa cheeks and sand them to an airfoil shape, then cover with fibreglass cloth and epoxy resin.

John
hiljoball is online now Find More Posts by hiljoball
Reply With Quote
Old Dec 18, 2012, 07:14 PM
Registered User
Joined Dec 2012
17 Posts
Thanks Martin, I still have to decide on a fixed keel or drop keel. I'm building by guess & by gosh and was hoping to eliminate some of the guess work. Dave
Gramps1 is offline Find More Posts by Gramps1
Reply With Quote
Old Dec 18, 2012, 07:29 PM
Registered User
United States, MA, Wenham
Joined Jan 2007
1,526 Posts
Quote:
Originally Posted by martin richards View Post
The weight is more a question of the designed water line. Put a weight in the hull equivalent to the rig, the radio etc. and do a flotation test in the bath to see how much additional weight is needed and where.
This is the correct answer.
Good luck.
breakwater is offline Find More Posts by breakwater
Reply With Quote
Old Dec 18, 2012, 10:09 PM
Registered User
Joined Dec 2012
17 Posts
Thanks, I sort of figured it would come to that...Gramps1
Gramps1 is offline Find More Posts by Gramps1
Reply With Quote
Old Dec 19, 2012, 09:16 PM
Registered User
Joined Jan 2006
603 Posts
flat plate keels ie less than 1 or 2% thickness can work well in the Re numbers our models deal with. Problem is 3/16 is pretty thick and 2" is too narrow for the boat you are doing. You need to be more in the 4" wide range and .090 thick. A star 45 fin is 6" wide at the top, 4" at the bottom and about 11" deep for reference.
slotracer577 is offline Find More Posts by slotracer577
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Wanted Stratos nose keel AvB Aircraft - Sailplanes (FS/W) 3 Jun 05, 2012 08:21 AM
Discussion VM Madcap keel fin question Bassman41 Sailboats 4 May 24, 2012 01:31 PM
Discussion STEEL KEELS IACC100 rc Yachts SILVERFERN Sailboats 42 Apr 17, 2012 08:42 PM
Discussion Steam Harbour Tug Keel Questions Tug Hercules Scale Boats 9 Feb 27, 2012 11:47 AM
Discussion Keel Fin and Keel (fishing lead sinker) attachment? FalconXman Sailboats 9 Aug 26, 2009 08:14 AM