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chris95040

Taper mast base to fit mast step

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I need to make a new deck-stepped aluminum mizzen mast fit into my undersized mast step.  The 5.25 inch (longitudinally) mast section needs to fit in a hole that is only 5 inches.  
 

While I assumed the only answer would be a mast shoe, a rigger is suggesting i simply cut a vertical channel along each side of the mizzen mast,  port and starboard, about 6 inches tall by about a half inch wide,  at the bottom of the mast.  
 

 With those two channels cut (channels cut with a rounded top to avoid a stress point) they suggest I simply squeeze the front and back of the mast together at the base to squish it to the necessary dimension and leave it that way.

I understand why tapering at the base,  in general, is ok (as long as enough material remains for the compressive loading,  buckling failure is not an issue right at the confined base) but I’m curious what people think of this method for achieving the taper.

Crappy diagram attached.

 

 

CC2D5E71-F7BA-4464-86A3-8FC4073374B8.png

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Was a new mast step not an option?

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New mast step is definitely a smart option - there are a number of reasons (about 5200 of them) why this will be my last choice after exhausting all other options. 

 

 

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Top mast tapers are done by taking out a V section on each side and welding towards the end.

I guess you could do that but it should be longer taper rather than just squeezing the end down where you risk a horizontal wrinkle.

Is there a reason not to use the correct base?

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11 hours ago, chris95040 said:

New mast step is definitely a smart option - there are a number of reasons (about 5200 of them) why this will be my last choice after exhausting all other options. 

 

 

Sounds more like one reason. If you think that a new step is the last option, you would be kicking yourself if you went through the trouble to cut slots in the mast tried to bend it and whatever else and then ended up getting a new mast step anyway. 
I’d ask the spar maker about their thoughts about this taper idea, but I tend to be a little more than cautious. 

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I’m an engineer, and I’m telling you: fire that rigger and either get another mast step to fit the mast or another mast to fit the step.

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1 minute ago, Max Rockatansky said:

I’m an engineer, and I’m telling you, fire that rigger and get another mast step to fit

^^^^^^^^^^this!!!

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It's only a quarter inch off.  Wouldn't it make more sense to grind an eighth from each of the two ends of the step, and leave the mast intact?  A welder could add material to the outside of the step if it was needed to re-strengthen it. 

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Spoke with the spar manufacturer.

They said the method the rigger suggested would be OK but that it would be preferable (stronger) to leave the sidewalls intact and just carve off the fore and aft segments that interfere with the step instead.

Makes sense to me,   that channel cut feels sketchy as hell.

To those of you who can’t get your head around removing material from the mast base,  the mast section is sized to prevent buckling failure and this results in a section with dramatically more material than necessary for a purely compressive load.    The load at the step is almost entirely compression, or so I’m told,  so you can get away with an awful lot of shenanigans there.

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7 hours ago, Max Rockatansky said:

I’m an engineer, and I’m telling you: fire that rigger and either get another mast step to fit the mast or another mast to fit the step.

Yeah but I don’t get to spend your parents money the way you do,  I just get to fuck your mom.

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1 hour ago, chris95040 said:

Yeah but I don’t get to spend your parents money the way you do,  I just get to fuck your mom.

That makes you á necrophiliac and a douchebag. Fuck off and break your mast, asshole

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1 hour ago, Max Rockatansky said:

That makes you á necrophiliac and a douchebag. Fuck off and break your mast, asshole

Sorry,  I thought this was how the overprivileged little misogynistic shits talked to each other on here.  My mistake!

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4 hours ago, Bruno said:

Make a g10 transition piece

I do like that idea,  but i think I’ll just hack off the ass end of my mast step and stick a pin through it for this year.  (Turns out I’m too chicken to attack the mast section.) Next year maybe I’ll put in fancy fit mast step.

 

Thanks everyone for the responses,  including the punk who thinks it’s ok to use Mel Gibson as his avatar.

 

 

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   On 6/25/2020 at 1:20 AM,  Max Rockatansky said: 

I’m an engineer, and I’m telling you: fire that rigger and either get another mast step to fit the mast or another mast to fit the step.

Yeah but I don’t get to spend your parents money the way you do,  I just get to fuck your mom.

 

I'm with Max. He gives you a valid reply and you respond like an arsehole.

The sectional shape gives a lot of strength under compression. Just think about how you can stand on a empty beer can... but the moment you dent it, it collapses. Cutting the slot and bending has a similar effect to denting the can. So unless the section is massively over the strength required I wouldn't try it. As soon as part of the section wall is no longer in line with the compression force the compression force will continue to try and bend further.

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4 hours ago, thorpecameron said:

 

I'm with Max. He gives you a valid reply and you respond like an arsehole.

Well,  to be clear,  he suggested buying a mast to ‘fit the step’ which is ridiculous -  enough has changed in the rig configuration that to choose a section in that manner would be like designing a seatbelt around the print on my tee shirt.  “I’m an engineer!”  Lol ok.

And anyone who walks around with a Mel Gibson mask on is begging for a punch in the face.     

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Pretty sure Max was recomending the only two proper solutions, A get the right Mast step and B if what one can only assume is a inability to deal with "5200" bedding compound then get the right Mast.  The unsolicited douchebag response you gave above aside don't you live within a stones throw of 20 some rigging shops?  Maybe start there for second opinions.

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On 6/24/2020 at 6:22 AM, mad said:

^^^^^^^^^^this!!!

 

On 6/24/2020 at 6:20 AM, Max Rockatansky said:

I’m an engineer, and I’m telling you: fire that rigger and either get another mast step to fit the mast or another mast to fit the step.

WHAT MAX SAID, really bad idea to cut the base of mast as you asked about.

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bad idea cutting the mast like your rigger suggests.  I'm a structural nav. arch. (going on 31 years).  Don't do it.

Figure out a new mast base to fit the mast or make a transition piece, or perhaps modify the deck fitting to accommodate the mast.

The base of the mast can and will develop other strain/stress mechanisms.  If you have vertical slots such as you describe, the mast base will want to spread due to poissons effect.  This will induce a stress concentration at the top of the slot- estimate by a factor of 3 over the far-field stress.  Any other purely non-axial load component (which is a certainty from mast flexing, vibration, stretch in the shrouds, etc.) will induce another level of uncertainty in stress direction which will likely be cyclical- meaning fatigue problems.  Aluminum is notoriously bad in fatigue and I'd expect cracks to develop at the top of the proposed slot.

Do whatever you can to keep the circumference of the mast intact at the base.

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On 6/24/2020 at 9:38 PM, chris95040 said:

Yeah but I don’t get to spend your parents money the way you do,  I just get to fuck your mom.

You come here and ask for advice!!! 

Go fuck yourself, hope the rig falls over.<_<

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On 6/25/2020 at 12:20 AM, chris95040 said:

Sorry,  I thought this was how the overprivileged little misogynistic shits talked to each other on here.  My mistake!

It was sound advice, the fact that you're unable to understand it, is your issue.

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2 hours ago, mad said:

It was sound advice, the fact that you're unable to understand it, is your issue.

It wasn’t that I misunderstood it,  it was two imperatives with no explanation.  The fact that it came from a little brat with a famous racist for an avatar led me to answer in a way I felt was appropriate.   Go away.  Other people are contributing real things.

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3 hours ago, bgytr said:

bad idea cutting the mast like your rigger suggests.  I'm a structural nav. arch. (going on 31 years).  Don't do it.

Figure out a new mast base to fit the mast or make a transition piece, or perhaps modify the deck fitting to accommodate the mast.

The base of the mast can and will develop other strain/stress mechanisms.  If you have vertical slots such as you describe, the mast base will want to spread due to poissons effect.  This will induce a stress concentration at the top of the slot- estimate by a factor of 3 over the far-field stress.  Any other purely non-axial load component (which is a certainty from mast flexing, vibration, stretch in the shrouds, etc.) will induce another level of uncertainty in stress direction which will likely be cyclical- meaning fatigue problems.  Aluminum is notoriously bad in fatigue and I'd expect cracks to develop at the top of the proposed slot.

Do whatever you can to keep the circumference of the mast intact at the base.

Appreciate the explanation,  thanks for taking the time!
 

 I did chicken out on cutting the slots,  the mast manufacturer had a better idea for tapering the mast without introducing so much stress but in the end I decided to hack off the rear end of the mast step and use a pin to prevent the mast from sliding aft.

The mizzen’s step is a pretty complicated affair involved in securing the main sheet traveller assembly as well so if I end up rebuilding the step it’ll be an off season project.

 

 

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Repeat after me, ban the asshole, or should I be PC and refer to the OP as "whiny little bitch".  If you ask for advice and then proceed to trash those who are offering you constructive help expect to get flamed.  HTFU!

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38 minutes ago, zenmasterfred said:

Repeat after me, ban the asshole, or should I be PC and refer to the OP as "whiny little bitch".  If you ask for advice and then proceed to trash those who are offering you constructive help expect to get flamed.  HTFU!

Ummmm... I think everyone's gonna be OK my man. 

 

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23 hours ago, chris95040 said:

It wasn’t that I misunderstood it,  it was two imperatives with no explanation.  The fact that it came from a little brat with a famous racist for an avatar led me to answer in a way I felt was appropriate.   Go away.  Other people are contributing real things.

Whiny little fuck!

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