[Public-List] Mast Sheave Bolt

Wed Mar 11 06:15:09 PDT 2020

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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