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Old 05-03-2016, 10:15   #1
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Mast weight calculation

Good afternoon all - This is my first time and I hope you'll be gentle with me - I also hope I don't offend anyone! I own a 1939 12 ton Hilyard called Lady Corinne. She normally comes out @Birdham Pool in Chichester and they know just how to handle her. Unfortunately, due to developments at the marina they can no longer accommodate us and we are moving to the new shed in Chichester Marina. The people who would lift the mast have asked for the weight and I have absolutely no idea. I wonder if anyone might be able to help me please.
The mast is 49' of Solid Douglas Fir in total (It's keel stepped ) and goes from 7" diameter at the base to 4" at the masthead. All the standing rigging is oversized @ 10mm stainless and consists of:
Forestay with Roto stay furler
Inner forestay with Roto stay furler
Backstay
2 sets of solid Douglas fir spreaders
Masthead shrouds
Running backstays set around 3/4 of the way up
2 stays from the hounds on each side
I realise that this will be a bit of guesswork to say the least but would be very grateful for any sensible suggestions that you might be able to make

Best regards

Iain mac
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Old 05-03-2016, 10:33   #2
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Re: Mast weight calculation

I figure a bit over 8 cu ft of doug fir. At 31# per cu ft that about 250# for the mast only. Too lazy to do the rest for you though!
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Old 05-03-2016, 11:28   #3
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Re: Mast weight calculation

Quote:
Originally Posted by Cheechako View Post
I figure a bit over 8 cu ft of doug fir. At 31# per cu ft that about 250# for the mast only. Too lazy to do the rest for you though!
What he said, only I'd use, say 36lbs/cuft in order to account for fasteners & tangs. As to the other bits, it's pretty easy to run the numbers using the figures on www.RiggingOnly.com and www.Defender.com or www.Harken.com for the furlers... But, ballpark, you could use 2/3 lb/ft for your foil extrusions, & 25lb - 35lb for the other bits which comprise the rest of a furler, each.

Armed with said info, you'll get within 10 - 20lbs. That, & any guy used to lifting spars (which is what you want), will have a figure in his head already, once you tell him what your spar's made of, how (as in not hollow), & it's height.


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Old 05-03-2016, 11:55   #4
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Re: Mast weight calculation

Quote:
Originally Posted by Iain Mac View Post
Good afternoon all - This is my first time and I hope you'll be gentle with me - I also hope I don't offend anyone! I own a 1939 12 ton Hilyard called Lady Corinne. She normally comes out @Birdham Pool in Chichester and they know just how to handle her. Unfortunately, due to developments at the marina they can no longer accommodate us and we are moving to the new shed in Chichester Marina. The people who would lift the mast have asked for the weight and I have absolutely no idea. I wonder if anyone might be able to help me please.
The mast is 49' of Solid Douglas Fir in total (It's keel stepped ) and goes from 7" diameter at the base to 4" at the masthead. All the standing rigging is oversized @ 10mm stainless and consists of:
Forestay with Roto stay furler
Inner forestay with Roto stay furler
Backstay
2 sets of solid Douglas fir spreaders
Masthead shrouds
Running backstays set around 3/4 of the way up
2 stays from the hounds on each side
I realise that this will be a bit of guesswork to say the least but would be very grateful for any sensible suggestions that you might be able to make

Best regards

Iain mac
Simple weight of a column calc. I'm assuming a round, not square, mast.
Also assume mast is 7"diameter over whole length. It's not but we dont want calculate the weight of all fittings. I've rounded up after calculating to allow for all the rigging and mast mounted paraphenalia.

Douglas fir density = 530 kg/ m^3
Length = 49' assume 13m
Diameter = 7" assume 0.178m
Area of a circle=pi*(diameter/2)^2
A=0.025m^2
Volume of a cylinder=Area of circle * Length
V=0.025*13=0.32m^3
Weight=density×volume
W=530×0.32=170kg or 375#

So assume max lift weight of 500# (227kg or 1/4 US ton)

I would then use a crane and rigging gear rated for 10 x the calculated lift weight. 5 tonne crane with a pure vertical boom lift will be fine.

In reality any boatyard crane should be able to handle this weight. The biggest load may be cracking rhe mast free if its stuck. Lift height and boom reach and swing will also need to be calculated.

To be honest I dont know why the yard expects you to provide them with the mast weight. Is this their first lift?

I'd have the yard show me their calibration certs for the crane, lifting gear and crane operator. If they can't and I don't like the look of their gear then they don't lift it.

Sounds like a nice boat. How about a pic...

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
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Old 05-03-2016, 12:29   #5
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Re: Mast weight calculation

Thank you for taking the time to work all that out! I didn't have a clue where to start - here's a pic of the old girl on the scrubbing piles at Itchenor.

I wish I was clever like you!
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Old 06-03-2016, 06:56   #6
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Re: Mast weight calculation

Greetings and welcome aboard the CF, Iain.
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Old 09-03-2016, 11:43   #7
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Re: Mast weight calculation

Quote:
Originally Posted by Cheechako View Post
I figure a bit over 8 cu ft of doug fir. At 31# per cu ft that about 250# for the mast only. Too lazy to do the rest for you though!
Particular thanks to you Cheechako yours was a really useful answer - you shouldn't have gone to so much trouble!!!

Best regards

Iain
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Old 09-03-2016, 12:00   #8
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Re: Mast weight calculation

Quote:
Originally Posted by Iain Mac View Post
Particular thanks to you Cheechako yours was a really useful answer - you shouldn't have gone to so much trouble!!!

Best regards

Iain
No problem man, keep us posted on how it goes!
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Old 09-03-2016, 14:57   #9
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Re: Mast weight calculation

Quote:
Length = 49' assume 13m
Hey, Left Brain... that's a funny assumption, when 49 feet is just under 15 meters!!

Jim
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Old 28-03-2016, 11:18   #10
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Re: Mast weight calculation

Question is so silly that I would change yard immediately.

On a 65' mono, I witnessed 400kgfkgf of extra pull to detach the mast+shrouds of approx. 900kgf
Thus total pull was 1300kgf

Kgf = kilogram-force
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