[Public-List] Mast Sheave Bolt

Gordon Laco mainstay at csolve.net
Wed Mar 11 09:10:40 PDT 2020 

Sure, but please amend my 3% stretch analysis to read 0.03 foot stretch PER FOOT.

Cheers - 

Gordon Laco
www.gordonlaco.com




> On Mar 11, 2020, at 12:09 PM, Greg Hounsell via Public-List <public-list at lists.alberg30.org> wrote:
> 
> Thanks Gordon!
> 
> May I share your email to another group that would appreciate the
> information?
> 
> Greg Hounsell
> 
> On Wed, Mar 11, 2020, 9:15 AM Gordon Laco via Public-List <
> public-list at lists.alberg30.org> wrote:
> 
>> Morning Gang,
>> 
>> 3% stretch on 35 feet is actually 0.03 feet…less than an inch which is not
>> much, and one can load up the halyard using a winch to negate that…
>> 
>> Most marine quality rope is prestretched and heat treated to lock it these
>> days…
>> 
>> Stretch in rope is an interesting subject.  My professional work
>> outfitting classic yachts and sailing ships causes me to look at
>> traditional rigging a lot, and that has led to some interesting revelations.
>> 
>> The first one, which seems heretical, is that good quality hemp rope (yes,
>> hemp) stretches LESS than polyester rope when made in the same diameter and
>> type (ie braided or twisted)  It is also just as strong…  we have had it
>> tested and the results are uniformly confirming of what I just wrote.  Yes,
>> that was startling.
>> 
>> Good quality hemp rope feels soft, like human hair… and unlike manila or
>> sisal, is unaffected by humidity with regard to dimensional stability.
>> Manila is ’twiggy’ and shrinks dramatically when wet… not good if one is
>> using it in shroud lanyards etc… and it swells in diameter, not good if one
>> is hoping it will run through blocks.
>> 
>> So why don’t people use it?  There are a number of reasons…
>> 
>> First, being natural fibre, its longevity at rated performance is
>> completely unpredictable.  Yes, when it’s new, and well made, it is better,
>> but after a season in service it might still be good, but nobody can tell.
>> In modern work, we cannot guarantee performance statistics for natural
>> fibre rope after it’s been in service, only when it is new.  Synthetic rope
>> can be counted on to be predictable in performance, even when older…
>> 
>> Second, it can rot in a variety of ways.  Up to WW2, it was common for
>> yachts to tar their rope with pine tar… it looks and feels like maple syrup
>> and when rope is impregnated with it, preservation is quite good… but it’s
>> messy and gets on sails and clothing even when dry.
>> 
>> Third, when synthetics came along, there was of course rejoicing because
>> it appeared that people were going to be spared the cost and toil of
>> replacing their rigging constantly, but there was also some evil on the
>> part of synthetic manufacturers.  The industry that grew and processed hemp
>> was literally demonized to the point where it doesn’t exist in North
>> America any longer.  The good quality hemp rope we supply now comes from
>> Holland.   And that is funny because we have farms near where I am writing
>> which grow hemp, but they ship their produce to Europe for processing
>> because we don’t do that on this side of the Atlantic anymore.
>> 
>> There are two kinds of stretch in rope… what I call ‘mechanical
>> elongation’, and ‘fibre elongation’.  The later is the actual elongation of
>> the stuff the rope is made of… the former is how the matrix of the rope
>> adjusts itself under load, and becomes longer.  Twisted rope has greater
>> mechanical elongation than double braided rope.
>> 
>> A word on knots vs splices.   All published data will confirm that a
>> splice retains a higher percentage of a rope’s strength than a knot.  One
>> day a number of years ago when I was teaching rigging at Georgian College,
>> I had just covered that in a lecture, and let my students out for a break
>> before resuming.   Outside I heard cheering and engines revving… I looked
>> out at the gravel parking lot and saw my students apparently rioting around
>> two pick up trucks tethered by their towing hitches… one was dragging the
>> other all over the place… finally the line connecting them broke.
>> 
>> My students had taken a piece of 1/2” nylon three strand… spliced an eye
>> in one end and tied a bowline in the other, then tried to break it.  Two
>> results came of that experiment.  First, the Ford dragged the GM pick up
>> all over the place.  Second, the line broke in the middle!  That is not
>> supposed to happen…haha
>> 
>> So there’s along and uncalled for lecture on rope…
>> 
>> Gordon Laco
>> www.gordonlaco.com
>> 
>> 
>> 
>> 
>>> On Mar 10, 2020, at 11:38 PM, Don Campbell via Public-List <
>> public-list at lists.alberg30.org> wrote:
>>> 
>>> So far, no one has mentioned that rope halyards are prone to stretch and
>> so if you do use rope halyards, and are not prepared to spend the bundle
>> for staset or other non-stretch line, you have the stretch on 35 feet if
>> you cleat on the mast or about 50 feet if you lead the halyard back to the
>> cockpit. Even a 3% stretch factor on relatively low stretch line will give
>> at least a foot on 35 feet,  double or triple that on more ordinary line.
>> Just make sure you check this factor regardless of where the halyards are
>> if you want to maintain mainsail shape. Wire does not stretch much at all
>> and the rope tail is very short if the wire is measured correctly.
>>> Don
>>> 
>>> -----Original Message----- From: Gordon Laco via Public-List
>>> Sent: Tuesday, March 10, 2020 2:16 PM
>>> To: Alberg 30 Public List -- open to all
>>> Cc: Gordon Laco ; George Dinwiddie ; Daniel Swords
>>> Subject: Re: [Public-List] Mast Sheave Bolt
>>> 
>>> By the way Daniel... did you see that the movie I was working on when I
>> visited you is being released in June?
>>> 
>>> G
>>> 
>>> Sent from my iPhone
>>> 
>>>> On Mar 10, 2020, at 1:19 PM, Daniel Swords via Public-List <
>> public-list at lists.alberg30.org> wrote:
>>>> 
>>>> 
>>>> BUT - as Gordon pointed out there are some definite potential failure
>> modes here and I would not recommend this system for hoisting a bosun’s
>> chair. This system works for me and has for many years without the use of
>> the mast sheave and without internal halyards but there are probably better
>> and safer ways to attach blocks to the masthead.
>>>> 
>>>> 
>>>> Sent from Yahoo Mail for iPhone
>>>> 
>>>> 
>>>> On Tuesday, March 10, 2020, 11:27 AM, George Dinwiddie <
>> gdinwiddie at alberg30.org> wrote:
>>>> 
>>>> Daniel,
>>>> 
>>>> If you send the photo to me, I'll be glad to post it on the website.
>>>> Include a description and I'll add that, too.
>>>> 
>>>> - George
>>>> 
>>>>> On 3/10/20 11:18 AM, Daniel Swords via Public-List wrote:
>>>>> I just happen to have a photo!  Who can I post it to?  Can I mention
>> “Fa—-b—“ on this site or would that be rude?
>>>>> 
>>>>> 
>>>>> Sent from Yahoo Mail for iPhone
>>>>> 
>>>>> 
>>>>> On Tuesday, March 10, 2020, 10:15 AM, Gordon Laco <mainstay at csolve.net>
>> wrote:
>>>>> 
>>>>> That’s exactly how our main halyard is rigged.  Nothing is internal…
>> just a traditional masthead sheave that carries the halyard from the
>> forward face of the stick to the after…
>>>>> Gordon Lacowww.gordonlaco.com
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> On Mar 10, 2020, at 11:13 AM, Jonathan Bresler <262alberg30 at gmail.com>
>> wrote:
>>>>> All halyards external?
>>>>> The masthead on Constance has two pins abaft the mast: one is used for
>> the backstay, and the other for the main topping lift.At least that is my
>> recollection.  The main halyard line is external but for the small part
>> passing over the sheave in the mast. Where do you hang a block for an
>> external main halyard?   Photos?
>>>>> Jonathan
>>>>> 
>>>>> On Tue, Mar 10, 2020 at 11:09 AM Gordon Laco via Public-List <
>> public-list at lists.alberg30.org> wrote:
>>>>> 
>>>>> I have all my halyards external in Surprise’s rig, as she was when she
>> was built.
>>>>> 
>>>>> We still win races, and I never worry about what’s going on inside the
>> mast that I cannot see.
>>>>> 
>>>>> Gordon Laco
>>>>> www.gordonlaco.com
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>>> On Mar 10, 2020, at 10:59 AM, Daniel Swords via Public-List <
>> public-list at lists.alberg30.org> wrote:
>>>>>> 
>>>>>> I have abandoned my mast sheave and internal halyards and replaced
>> them with simpler blocks and external halyards. You would have to provide
>> me with wind tunnel data to convince me that at 6.5 or even 7 knots of
>> speed the
>>> 
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