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#11
TSBB General Talk / Re: Is Dymax = Dyneema?
Last post by Doug SC - Dec 12, 2025, 11:39 AMCB is spot on as usual. I have done some stuff with Dyneema lines and soft shackles. Not just sailors but ultra lightweight backpackers also use the lines to save weight with their hammock setups. The locking Brummel and long (importantly tapered) buries are needed when splicing. Lots of YouTube videos on how to do this.
#12
TSBB General Talk / Re: Is Dymax = Dyneema?
Last post by Brian N. - Dec 12, 2025, 10:32 AMWow - Thanks Charles. You always are so well informed. I am not planning to use Dyneema anytime soon, but the info is interesting. What I do know about UHMWPE (Spectra and Dyneema) comes from archery bow strings, another hobby of mine.
#13
TSBB General Talk / Re: Is Dymax = Dyneema?
Last post by Charles Brennan - Dec 12, 2025, 09:28 AMDale, I'll give it a shot! 
Dyneema was the first of the Ultra-High-Molecular-Weight Poly-Ethylene ropes (UHMWPE) to get manufactured and marketed, so much like Kleenex and Formica, the brand name eventually became a generic description for the product. A good example of brand names getting appropriated by different manufacturers, is Amsteel calling their UHMWPE rope: "Amsteel Dyneema"
Dymax is just another UHMWPE rope made by a different manufacturer, no different than say, another manufacturer making tissue paper, instead of Kleenex.
SK-XX:
Dyneema fibers are produced in several SK ranges, including SK60, SK65, SK75, SK78, and the newer SK99.
Basically, as the number kicks up higher it has an increase in tensile strength, at the cost of a little more stiffness. Another factor in UHMWPE SK ratings is "creep", a measure of how much the line moves over time. Since Dyneema type lines are very slippery, you have to tie it with special knots like the Estar knot:
https://www.animatedknots.com/estar-stopper-knot
Fun experiment:
Tie a reliable jamming knot, like a square knot with two pieces of Dyneema and then pull!
Yeah, slippery.
For that same reason, eye-splices need to be "locked" with (for example) a locking Brummel splice and further, require much longer "buries" in the eye splice.
Those SK-XX numbers are generally of far more interest to high-performance racing sailors and larger boats, than for boats in our size range. In practical terms, you could use most any SK number UHMWPE with complete safety on boats in our size. Another consideration for you to think on, is that ⅛-inch Dyneema type ropes are a little stiff to splice at that diameter, for example, typically requiring a doubled over wire instead of a fid, to do splices. In your case, the SK65 rating would be much easier to deal with, in ⅛-inch diameters than say, SK78.
In summary, the SK rating is a measure of characteristics, not quality.
Hope this helps,
Charles Brennan
Dyneema was the first of the Ultra-High-Molecular-Weight Poly-Ethylene ropes (UHMWPE) to get manufactured and marketed, so much like Kleenex and Formica, the brand name eventually became a generic description for the product. A good example of brand names getting appropriated by different manufacturers, is Amsteel calling their UHMWPE rope: "Amsteel Dyneema"
Dymax is just another UHMWPE rope made by a different manufacturer, no different than say, another manufacturer making tissue paper, instead of Kleenex.
SK-XX:
Dyneema fibers are produced in several SK ranges, including SK60, SK65, SK75, SK78, and the newer SK99.
Basically, as the number kicks up higher it has an increase in tensile strength, at the cost of a little more stiffness. Another factor in UHMWPE SK ratings is "creep", a measure of how much the line moves over time. Since Dyneema type lines are very slippery, you have to tie it with special knots like the Estar knot:
https://www.animatedknots.com/estar-stopper-knot
Fun experiment:
Tie a reliable jamming knot, like a square knot with two pieces of Dyneema and then pull!
Yeah, slippery.
For that same reason, eye-splices need to be "locked" with (for example) a locking Brummel splice and further, require much longer "buries" in the eye splice.
Those SK-XX numbers are generally of far more interest to high-performance racing sailors and larger boats, than for boats in our size range. In practical terms, you could use most any SK number UHMWPE with complete safety on boats in our size. Another consideration for you to think on, is that ⅛-inch Dyneema type ropes are a little stiff to splice at that diameter, for example, typically requiring a doubled over wire instead of a fid, to do splices. In your case, the SK65 rating would be much easier to deal with, in ⅛-inch diameters than say, SK78.
In summary, the SK rating is a measure of characteristics, not quality.
Hope this helps,
Charles Brennan
#14
TSBB General Talk / Is Dymax = Dyneema?
Last post by Captain Kidd - Dec 11, 2025, 11:41 PMI'm wanting some 1/8" dyneema. I see this on Amazon. Described as 100% sk65 fibers. Is this a brand name for dyneema? Or a inferior knockoff? Seems I read about some sk78 fibers somewhere.
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#15
TSBB General Talk / Re: Second sail on the Navigat...
Last post by Doug SC - Dec 11, 2025, 08:14 AMQuote from: Krusen on Dec 08, 2025, 11:03 PMThe end of the sprit boom does not get moved up and connected to the reef reinforcement? It seems that the pull out at the end of the sails foot, rather than the corner of the working portion would result in poor sail shape.
The snoder line is eased so the boom moves forward. In the photo I posted below you can see a jiffy reef line that brings the clew reef reinforcement down to the end of the sprit boom after lowering the main. The down haul is released and reattached to the corresponding tack reinforcement. Then the main is raised and the snoder line tensioned to yield the desired sail trim. Pulling on the snoder line will flatten the sail. Easing it does the opposite.
#16
West Wight Potter Yachts / Re: Serge Testa at the South B...
Last post by Wolverine - Dec 09, 2025, 10:00 AMI read his book some years ago. Quite the adventure.
#17
TSBB General Talk / Re: Second sail on the Navigat...
Last post by Krusen - Dec 08, 2025, 11:03 PMThe end of the sprit boom does not get moved up and connected to the reef reinforcement? It seems that the pull out at the end of the sails foot, rather than the corner of the working portion would result in poor sail shape.
I am assuming that the downhaul connects to the reinforcement at the mast when reefed, but have never sailed such a rig.
I once considered building such a rig for my sailing surfboard, resulting in a taller mast and more sail area when not reefed, and fully reefed, less area but higher aspect ratio than the normal sail.
I was calling my proposed rig a Gunter rig.
I am assuming that the downhaul connects to the reinforcement at the mast when reefed, but have never sailed such a rig.
I once considered building such a rig for my sailing surfboard, resulting in a taller mast and more sail area when not reefed, and fully reefed, less area but higher aspect ratio than the normal sail.
I was calling my proposed rig a Gunter rig.
#18
TSBB General Talk / Re: Second sail on the Navigat...
Last post by Doug SC - Dec 08, 2025, 10:44 PMQuote from: Krusen on Dec 08, 2025, 04:51 PMHow does the main outhaul function when reefed? It is not obvious how that is tensioned with the regular rigging.
In the photo below what I think it is called a sprit boom which runs from in front of the mast and is attached to the clew of the mainsail. The snoder? line runs through a hole in the end of the boom left of the mast (in the photo) to a block on the mast. It then runs down the mast to a block and lead back into the cockpit where it can be pulled to force the boom back against the clew which flattens the sail like an outhaul, and sort of acts like a vang because it angles down to the clue rather than following the foot of the sail.
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#19
TSBB General Talk / Re: Second sail on the Navigat...
Last post by Riley Smith - Dec 08, 2025, 09:54 PMNorman we even get loons down on the Gulf Coast. Sonya and I had one swim very close by us once in Pensacola and I couldn't get the camera without scaring it and so I just watched it swim by without a pic.
#20
West Wight Potter Yachts / Serge Testa at the South Bay Y...
Last post by George16 - Dec 08, 2025, 09:00 PMAhoy Skippers,
Serge Testa will speak at the South bay Yacht Club about his book "500 Days: Around the World on a 12 Foot Yacht" on Thursday 12/11 at 7:00 PM. Please invite friends with a boating interest and come hear about this amazing adventure!
Alone aboard "Acrohc", the tiny yacht he designed and built, Serge Testa sailed around the world and into the Guinness Book of Records. Exotic landfalls, cyclones, encounter with whales, and a nearly fatal fire at sea makes this a gripping story. Told with understatement and humor, this account of a unique voyage of discovery and endurance appeals to the adventurer in all of us.
Also, the event is free to join by Zoom. This invitation comes via SBYC Commodore Lisa Bickford, who also sails a P-15 named Harry and is a proud Potter Yachter.
Address:
South Bay Yacht Club
1491 Hope St
Alviso, CA 95002
Join Zoom Meeting
https://us06web.zoom.us/j/2080110813?pwd=UDdsRmlQdnpXV1E2bFJMQi9IWWtUdz09&omn=82702562674
Serge Testa will speak at the South bay Yacht Club about his book "500 Days: Around the World on a 12 Foot Yacht" on Thursday 12/11 at 7:00 PM. Please invite friends with a boating interest and come hear about this amazing adventure!
Alone aboard "Acrohc", the tiny yacht he designed and built, Serge Testa sailed around the world and into the Guinness Book of Records. Exotic landfalls, cyclones, encounter with whales, and a nearly fatal fire at sea makes this a gripping story. Told with understatement and humor, this account of a unique voyage of discovery and endurance appeals to the adventurer in all of us.
Also, the event is free to join by Zoom. This invitation comes via SBYC Commodore Lisa Bickford, who also sails a P-15 named Harry and is a proud Potter Yachter.
Address:
South Bay Yacht Club
1491 Hope St
Alviso, CA 95002
Join Zoom Meeting
https://us06web.zoom.us/j/2080110813?pwd=UDdsRmlQdnpXV1E2bFJMQi9IWWtUdz09&omn=82702562674