weight of wooden masts

zodiac3813 · 10-06-2007, 16:31

Hi everyone!

I am in the process of purchasing a Hanna Tahitiana ketch. She seems to roll more than I would expect (while moored, walking from one side to the other) given her beam and keel weight. She has solid timber (oregon pine I think) masts, the main being fairly tall.
Would an aluminium mast lessen the rolling tendancy? (I'm considering sacrificing the mizzen & lengthening the boom if necessary in order to build a wheelhouse/dodger/shelter of some kind in the future.
Any opinions would be most appreciated.

Cheers

delmarrey · 10-06-2007, 17:01

Weight of wood!

http://www.engineeringtoolbox.com/weigt-wood-d_821.html

seaclusion · 10-06-2007, 18:05

Without going into a lengthy treatise on stability, the short answer is that a 'rolly' boat as you describe tends to have lower initial stability and higher ultimate stability. A 'stiff' boat tends to have higher initial stability and lower ultimate stability. In a sailboat you usually want high ultimate stability for carrying sail and tolerate the lower initial stability to achieve this. Therefore your Tahiti Ketch is probably set right for ultimate stability and you should probably not be trying to change the stability characteristics without consulting a naval architect or at the least doing a roll period test.

Second, the ketch was designed with a specific sail area for the main and mizzen to set the 'center of effort' of the sails in the proper releation to the 'center of lateral resistance'. Removing the mizzen will cause the 'center of effort' to move forward and impart undesireable sailing characteristics such as much more weather helm. Increasing the length of the boom to add more sail are aft will help but probably not return the 'center of effort' to it's original location.

Richard

zodiac3813 · 10-06-2007, 18:32

Thanks people for your prompt response.........I wouldn't be too worried about going to al. masts & spars, as many Tahitianas already have them. I take on board the principles regarding the sail plan; as the boat is steel, it may be possible to to build a steel wheelhouse with a roof that can be walked under at each side to go forward, and step the mizzen on it's roof? I saw a steel canoe-stern yacht with that setup at a local yard recently. The mizzen shroudswere attached to the sides of the roof, with vertical posts to carry the loads. Thanks again, Jim.

10-06-2007, 16:31	#1
zodiac3813 Registered User Join Date: May 2007 Location: Tasmania, Australia Boat: Swanson 28 Posts: 9	weight of wooden masts Hi everyone! I am in the process of purchasing a Hanna Tahitiana ketch. She seems to roll more than I would expect (while moored, walking from one side to the other) given her beam and keel weight. She has solid timber (oregon pine I think) masts, the main being fairly tall. Would an aluminium mast lessen the rolling tendancy? (I'm considering sacrificing the mizzen & lengthening the boom if necessary in order to build a wheelhouse/dodger/shelter of some kind in the future. Any opinions would be most appreciated. Cheers

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10-06-2007, 17:01	#2
delmarrey Registered User Join Date: Mar 2003 Location: Puget Sound, WA Boat: Choate 40 Posts: 3,456 Images: 115	Weight of wood! http://www.engineeringtoolbox.com/weigt-wood-d_821.html

10-06-2007, 18:05	#3
seaclusion Registered User Join Date: Jul 2006 Location: Florida Boat: 36 gulfstar Posts: 67	Without going into a lengthy treatise on stability, the short answer is that a 'rolly' boat as you describe tends to have lower initial stability and higher ultimate stability. A 'stiff' boat tends to have higher initial stability and lower ultimate stability. In a sailboat you usually want high ultimate stability for carrying sail and tolerate the lower initial stability to achieve this. Therefore your Tahiti Ketch is probably set right for ultimate stability and you should probably not be trying to change the stability characteristics without consulting a naval architect or at the least doing a roll period test. Second, the ketch was designed with a specific sail area for the main and mizzen to set the 'center of effort' of the sails in the proper releation to the 'center of lateral resistance'. Removing the mizzen will cause the 'center of effort' to move forward and impart undesireable sailing characteristics such as much more weather helm. Increasing the length of the boom to add more sail are aft will help but probably not return the 'center of effort' to it's original location. Richard

10-06-2007, 18:32	#4
zodiac3813 Registered User Join Date: May 2007 Location: Tasmania, Australia Boat: Swanson 28 Posts: 9	Thanks people for your prompt response.........I wouldn't be too worried about going to al. masts & spars, as many Tahitianas already have them. I take on board the principles regarding the sail plan; as the boat is steel, it may be possible to to build a steel wheelhouse with a roof that can be walked under at each side to go forward, and step the mizzen on it's roof? I saw a steel canoe-stern yacht with that setup at a local yard recently. The mizzen shroudswere attached to the sides of the roof, with vertical posts to carry the loads. Thanks again, Jim.