Halyard loads - how to estimate

[wiekeith]

Originally Posted by fallingeggs

Good luck there!

PS - Let me also mention that you may want/need to change the sheave at the top of the mast. I haven't personally seen this myself, but I hear that the sheaves used for wire halyards have a smaller groove (or something like a double groove) that may chafe rope halyards. I know this has been discussed on this forum in the past, so a quick search should tell you want to look for on your set up. Stumble or Uncivilized may even have a shorter answer for this.

Thanks
One of the reasons for going for a smaller diameter rope was to hopefully use the same sheaves, but there have been some comments about this in the past, as you mention.

[wiekeith]

Originally Posted by Hard A Lee

Just some other food for thought...Not sure how you're planning on attaching the line to the shackle, but if you use a knot, you can estimate a 50% reduction in strength. It may not always be quite that much, but in pull tests I've definitely seen even greater reductions depending on the knot and how it is dressed.

Thanks for pointing that out. I'm actually planning on an eye splice.

[UNCIVILIZED]

Sheave diameter = 8x rope diameter (minimum). But also check for burrs, sharp edges or grooves, basically anything which would rapidly wear a line, especially when under load.

[wiekeith]

Originally Posted by UNCIVILIZED

Sheave diameter = 8x rope diameter (minimum). But also check for burrs, sharp edges or grooves, basically anything which would rapidly wear a line, especially when under load.

Yep, I've had a good read of the info you pointed me to yesterday.

I've subsiquently checked with the boat builder, and they say the sheaves were sized for rope, so hopefully they'll be ok. I will have a good look at them though to confirm this and check their condition.

[wiekeith]

And the good news is: The supplier of the rope has kindly agreed to take it back and give me credit - very kind of them as it’s cut rope. The proprietor also called me to discuss my needs and to help me get it right. He seemed very knowledgable about boat rigging, and strongly suggested (as has been suggested here on the forum) that as a first-off, I renew my sheaves as they will almost certainly be damaged by the present wire halyard.

I’ve also been in communication with the boat manufacturer, who offered to order replacement sheaves for me. I’ve actually suggested he sends me the part numbers so I can get them ordered here in the UK - might make life easier.

I've not yet fully figured-out how I’m going to change the sheaves, but I guess I’ll need to secure myself to the masthead in order to take the tension off the halyard that’s raised me there in order to change its sheave. I think I need to get up there beforehand and have a good visual so I know what I’ll be up against.

I’m most grateful and appreciative for all the useful input that you guys have contributed to this thread - thanks :-)

[S/V Alchemy]

Not to question your original question, but if your main won't drop under pressure due to slug or car friction, I would say that you have less of a halyard problem and more of a track problem. While I haven't tested "trying to drop a full main in 50 knots" nightmare scenario, when we bought a new main last season, I installed a Tides Marine track and SS slugs...it's midway between a traditional slug and slot setup and a full-batten/batt-car setup in terms of friction reduction.

I also put in four 1/2" Dacron over 6 mm Dyneema core halyards and topping lift.

My initial take having run full main hoist to the low- to mid-20 knot AWS range (it's a steel boat and can cope with more canvas without struggle) is that not only does the Tides Marine setup allow far easier hoists (meaning I'm lifting more sail with less friction as a component of total load), but that the main douses with can only be described as alacrity. I have to pace it by hand or it just flakes itself, or would if I had lazyjacks rigged. I guess what I'm getting at is that the halyard strength is only one factor in main control: ideally, it's a solution arrived at holistically.

[wiekeith]

Originally Posted by S/V Alchemy

Not to question your original question, but if your main won't drop under pressure due to slug or car friction, I would say that you have less of a halyard problem and more of a track problem.

Yes, I totally agree. My halyard problem relates to me not liking/trusting the wire-rope splice!

But there is clearly something amiss that's introducing friction at the mast track. I'm using Rutgerson Battcars on a Selden mast, which allows me to raise and drop the main with relative ease, as long as I'm pretty much head-to-wind. As a short-term fix I added a downhaul, which is fed back to the cockpit, so I can drop the sail without going to the mast (I have lazyjacks too). However, I do need to resolve this properly - there's a reason why the sail is jamming and I need to identify it. The sails are off at the moment, but I plan on taking a closer look when they go back on, probably next week.

Thanks for your input though, I'll bear your solution in mind.

[wiekeith]

Originally Posted by S/V Alchemy

... when we bought a new main last season, I installed a Tides Marine track and SS slugs...it's midway between a traditional slug and slot setup and a full-batten/batt-car setup in terms of friction reduction...
.

I just took a look. Nice, and well thought out for retrofitting.

[TheThunderbird]

8mm is for coastal day cruising, and racing boats (with 78% dyneema).

Not handy

What you call "rule of thumb" is a SAFETY COEFFICIENT being used since mid1800 in structural engineering, in all application.

It is 4-7:1 for sailors