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Ocean Dreamer
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Discussion Starter #1 (Edited)
Let's say I had a 40' sloop that lost its mast in a storm and that mast was difficult or impossible to find and the cost of a new one was prohibitively expensive. Couldn't I just buy another used mast with the same dimensions and specs and use that mast with some minor modifications to the standing rigging?
 

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Master Mariner
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A well designed vessel is a combination of weights and measures, to put it simply, that make that vessel operate properly.
For instance, were you to replace a carbon fiber mast with an alloy one, the whole motion and sailing characteristics of that boat would change, just as they would if one were to lop off a foot of the draft. If you need to do either, for financial reasons or because you bought a home with too little water at the dock out back, it would be best to either sell that vessel and buy one designed with the features that suit your needs, or hire a Naval Architect to design a new sail plan or keel for that boat.
Boat design and construction is not free form art.
 
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Ocean Dreamer
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Discussion Starter #3 (Edited)
But if I had a 46ft mast, I could not simply put another 46 ft mast in its place, as long as the standing rigging and sail plan remain the same? I understand that there are differences in rigging designs and that they vary greatly from boat to boat depending on the design of the boat and its intended purpose, but a mast is essential a rolled piece of aluminum, in this case, and mast manufacturers sell them fairly standardized. I would think that a modified masthead would be about all I would have to do if the height and material performance are the same. I know that it is not a free form art, but people do modify their masts and rigging for different missions. It would seem to me that with some basic math. I could simply replace the mast itself, copy the original rigging, and with some modifications to the masthead, or a newly fabricated masthead and possibly spreader mods, I would have the same sail plan I started with. Of course, this is just my own uninformed theory.
 

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Ocean Dreamer
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Discussion Starter #6
It was looking at Dwyer's website that gave me the idea. If Masts are built kind of like Legos, then I could just buy a used mask that was similar.
 

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If essentially the same height, same weight with the same sail plan, that's just replacing OEM with aftermarket. I'd want to know the new stick was quality, but no reason it can't be.

The step may be different, which might require some surgery or leave edges of the old footprint visible. That would be less than fully desirable. I would not get into altering spreader angles or standing rigging. Find something that replicates what you have. Not sure why the mast head would need modifying, but that's not a big deal.
 
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Hello

I think it can be used with the necessary arrangements. You can continue the tours without any problem. I recommend working with a good master.

John Cameron
 

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If you find another stick with similar wall thickness, width, depth, same spreader set up, and step, keel or deck, and roughly the same length, shouldn't be any problem swapping it into the boat.

If you are talking hot rod race boat with absolute lightest tallest mast and rig and want to duplicate it best to get an engineer and spar maker involved.
 

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But if I had a 46ft mast, I could not simply put another 46 ft mast in its place, as long as the standing rigging and sail plan remain the same? I understand that there are differences in rigging designs and that they vary greatly from boat to boat depending on the design of the boat and its intended purpose, but a mast is essential a rolled piece of aluminum, in this case, and mast manufacturers sell them fairly standardized. I would think that a modified masthead would be about all I would have to do if the height and material performance are the same. I know that it is not a free form art, but people do modify their masts and rigging for different missions. It would seem to me that with some basic math. I could simply replace the mast itself, copy the original rigging, and with some modifications to the masthead, or a newly fabricated masthead and possibly spreader mods, I would have the same sail plan I started with. Of course, this is just my own uninformed theory.
With all due respect, that is partially an uninformed theory but also mostly correct. To explain, depending on rig geometry (single or double spreaders, straight or swept spreaders, spreader lengths, fore and aft lowers vs aft lowers and a babystay, vs mast pre-bend and aft lowers only, shroud base width, height of the boom, vang type and geometry, keel stepped or deck stepped, and so on), there can be very big differences in the loads experienced by the mast. To replace a mast from a different source than the original the structural characteristics need to match pretty closely or some engineering performed.

Ignoring the minor differences between different aluminum alloys, the critical structural characteristics are described by:
(A) Area of the section which controls axial loads (compression)
(S) Section Modulus which controls the strength of the section in bending in two axis (Sx and Sy)
(I) Moment of Inertia which controls the stiffness of the section in bending in two axis (Ix and Iy)

Generally, these are published for any given spar section. To make a substitution, you ideally need to figure out the make and model of your original spar. That's usually not too hard to do since the profile and characteristics of most spar sections ever made are still available online and so it comes down to making careful measurements and comparing them to those sections. Sometimes it requires enlarging the profile (or several similar profiles) to full scale and holding the profile up to the spar itself.

Once you figure out what your spar actually is, you should be able to find the published A, Sx, Sy, Ix and Iy for your spar. When evaluating a substitute mast section, you need to carefully measure that section and figure out what is it's make and model as well, and then compare the A, Sx, Sy, Ix and Iy for that spar to your spar. Small deviations (5% or less) usually are not all that critical. Bigger variations would need to be engineered around.

Jeff
 

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New or used you are still pretty much building a custom mast and I don't think there would be any financial advantage in doing so.
 

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I have changed a few masts in my day and they all came out ok. changed a wood mast to aluminum on a 32' PC sloop. changed a islander 32 telephone pole to a 5' longer thinner mast, changed a 35' racer to a carbon mast, never saw any of the major differences that are always talked about . the differences in how they sail were very hard to determine. my current boat was offered with three different mast options from the factory. it is very hard to tell the difference in how they sail. Aluminum, Carbon cruising and carbon race mast. only difference i could feel was in my wallet. each one $20k more then the next option. and each option needing more expensive maintenance then the last. anodized aluminum lasts 25 years or more, carbon mast needs to be clear coated or painted every 5 years. and they are easier to brake.
I went with the aluminum because of durability. and gave up about .001 knot in speed
 

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New or used you are still pretty much building a custom mast and I don't think there would be any financial advantage in doing so.
If the original poster already has all of the rigging, and he can find a used mast section with the right properties and length, then there should be a major savings between a new spar section and a used one. Used spars can often be purchased for what the aluminum is worth for recycling. Depending on the particular mast section and supplier the cost for a new mast tube can be $100-200 per foot or more.

Jeff
 
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