SailNet Community

SailNet Community (http://www.sailnet.com/forums/)
-   General Discussion (sailing related) (http://www.sailnet.com/forums/general-discussion-sailing-related/)
-   -   Steel masts??? (http://www.sailnet.com/forums/general-discussion-sailing-related/11163-steel-masts.html)

Sasha_V 01-20-2005 11:09 PM

Steel masts???
 
I was just speaking to a friend on your side of the pond and the topic got onto steel masts. For a normal 34foot cruising cutter. My reaction was "You must mean an alloy mast"....only to be told that the aluminium mast is what he is planning to sell off in order to finance some of the work on his boat (Again, my reaction was; "???") and then buy a cheaper steel mast.

I do not think I have ever seen one of those in Australia (well, not except on a freighter). What is the deal with these? Do they actually work? how well?

I am decidedly confuzzled on this topic.

Sasha

TrueBlue 01-21-2005 01:26 AM

Steel masts???
 
Perhaps your friend was making reference to a Stainless steel mast to replace his aluminum? Stronger, costlier, but even if this was the case, being a heavier component, the center of gravity would undoubtably be higher (not a good thing on a sailboat). I have yet to see one at my marina.

Steve

Jeff_H 01-21-2005 05:53 AM

Steel masts???
 
I have only recently been running into discussions of using steel masts. It is based on the idea that steel is much cheaper to purchase than aluminum if purchased by the pound and that a dollar''s worth of steel is a lot stronger if measured as a simple unit of cross section than aluminum. But it is not that simple. In any given verssel, the items that control the strength of the structure of a mast, require a minimum wall strength and a minimum resistance to buckling, And there is the rub. To achieve a suitable wall strength and resistance to buckling, the steel mast ends up being somewhat heavier than the aluminum spar. This is a problem because it raises the center of gravity and can greatly increase the moment of inertia. That combination can result in what is referred to an ''excitation capsize''. This was very much a problem with older IOR era boats and was a major contributer to the problems encountered during the Fastnet Disaster. In effect what happens when you have a heavy spar is that the boat stores a lot of knetic energy when it rolls. This kinetic energy causes the boat to roll past the point that it would have if it had less inertia carried high. In a wave train that is close to the sympathetic harmonic of the boat the boat is likely to roll through every increasingly large angles until a knock down occurs. This higher moment of inertia can also contribute to a roll over in a single large wave incident.

Jeff

TrueBlue 01-21-2005 06:17 AM

Steel masts???
 
It is very curious that, giving the scenario of steel''s greater weight ratio over aluminum alloy, yacht designers find an advantage to use the material in spars, especially masts.

Steve

geohan 01-21-2005 07:23 AM

Steel masts???
 
TrueBlue....Steel masts aren''t new. I knew a fellow who used a tapered steel street-light pole for a mizzen mast. It even doubled as a chimney for his wood stove. No problem with draft (He kidded that he had to be careful with the stove lid to keep it from being sucked up the chimney)and it made a convenient hand warmer for the helm. While it may have looked odd on a cold day, the smoke didn''t bother his neighbors.(grin)

Sasha_V 01-21-2005 03:22 PM

Steel masts???
 
Wow...how...educational.

I have toi wonder about a few things though.
What type of steel do they use. I mean masts tend to flex and work a fair bit. If you use low carbon (mild) steel, then you are going to be putting a lot of weight aloft in sidewall thickness and in the end the masts will develop wrinkles.
If you use hi carbon or spring steel then you will work harden it and eventually develop brittle faults at the exact "working" points.

And it will not take long either.

The only solution I could come up with to these issues is to go with a hybrid steel manufacturing process so that you either have a spiral welded tube structure that tends to equalize stresses and reduce work hardening, or you can go with a pattern welded structure like old gun barrels used to be (A folded/layered combination of high and mild carbon steel) The cost of producing a mast length tube of pattern welded steel makes my brain cringe.
And I could put that steel to much better uses!

So what sort of steel is used for the masts? (the light pole notwithstanding, though it is a scary/cute concept).

If it is just a surface plated mild steel such as used for lightpoles, do they need to run about a gazillion shrouds and stays to try and keep the mast extra rigid so that the surface hardening doesn''t just crack off and fall to the deck?

I love steel. I work in steel everyday and have bought my house and boat on the proceeds of what I can make it do....But I think steel masts are one fo the dumbest ideas since concrete boats (or maybe they belong together).

More answers please....


Sasha

TrueBlue 01-21-2005 05:13 PM

Steel masts???
 
Steel on a sailboat mast . . . stainless, hi carbon, spring, hybrid or otherwise (lamposts??) . . . simply is not a logical choice.

It has been eloquently demonstrated by JH, and present company, that steel requires a relatively thick section throughout the mast''s length to equal the structural qualities of the aluminum alloy competitor that has less weight per foot. With the increase in weight and appreciative cost ratio . . . steel is more costly and increases the center of gravity.

Why even bother considering steel as a viable contender for sail applications?

Quagmire indeed.

Steve

jimrigg 02-24-2005 01:02 AM

Steel masts???
 
hi re steel masts, I have been searching for info as I am wanting to build one for my steel hull ( I must remember steel won''t float)I found a site by Dudley Dix designs explaining the use of steel in masts. I am wanting to build one for gaff rig so it won''t be a skyscraper has anyone built one using either 127mm x 3.00mm or 114mm x 3.2mm tube? thanks jimmy

Billpjr 02-24-2005 10:57 AM

Steel masts???
 
I know nothing about steel masts but it IS interesting that alum boat trailer weight is almost the same as a steel one. An al trailer mfg told me they had to beef up the extrusion size to match steel strength...but I don''t think they use 2024 on trailers.


All times are GMT -4. The time now is 02:33 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012