I have read all of your replies and and considered them carefully. I think the key thing here...the crux of the problem is this: how much shock can a given material withstand before it will snap. Common ground tackle for commercial vessels in the Pacific NW has always been chain followed by cable. In order to mitigate shock the placement of a buoy along the rode can be deployed. Is it possible to determine how much shock a particular rode is likely to experience in the most horrendous conditions? 3/8 spectra has a working load limit of around 13000 lbs which is 3x that of 5/8 Novabraid. The only reason i want this to work is because I can fit 300' on my winch. I want that scope. Price is not a factor here. One thing is certain. If I do decide that spectra is the best fit for my particular operation I will certainly be deploying a buoy on the rode.
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Main Message Board / Re: Spectra vs. Samson double braid for anchor rode.
September 13, 2013, 07:35:47 AM #2
Main Message Board / Spectra vs. Samson double braid for anchor rode.
September 07, 2013, 09:05:59 AM
Hi Stu and other community members.
I have been perusing the anchoring, anchor sizing, and anchor tackle threads. I am looking for practical and theoretical evaluations comparing the working load limits of double braid nylon vs. spectra. I own a 38 foot combination fishing boat in southeast Alaska. In the winter months this boat serves as a harvest dive platform. We spend 70% of our time anchored up. Expected conditions during the working day while anchored with divers and hoses (both diver airlines and 2" water lines) extended out to 350 feet can be extreme. It is not uncommon to be working in 40 -50 kt winds and an 8 foot sea with attendant 2-3 foot chop. In between openings or waiting out a blow it is not uncommon to be anchored up inside a protected bay and have winds blowing a steady 70 or 80 kts with higher gusts. In these conditions you are always expecting to drag. My old anchoring system was a 60 pound bruce style anchor, 60 feet of 5/8 chain, 125 feet of 5/8 double braid. Many times I've seen that 5/8 double braid stretched down to 3/8 of an inch. This system was limited by the size of my anchor winch. I had a bigger winch built for the upcoming winter harvest season. (its still not big enough but I cant get anything bigger w/o compromising the floatation of the bow) My new anchor is a 60 pound Manson Supreme. Chain is 100' of ½ " galvanized. 300 feet of 3/8 spectra. Normally I size my tackle by looking at the different parts and say to myself "holy cats, that's some huge chain that ought to work." I chose the 3/8 spectra by actually comparing its strength to the old 5/8 double braid. They are very close. The spectra has a breaking strength of 14k lbs. and the Samson braid is 15k lbs. I have some concerns beyond the 'jeez that stuff looks small' factor. One of my fellow harvest boat operators told me that spectra is terrible for anchor rode because it wont stretch and this will cause it to snap due to shock in heavy weather. "Its good everywhere on the boat but don't put it on the anchor" he said. I was considering going up to 7/16 diameter spectra to give myself some peace of mind. Then I found the sizing and working load spread sheet on these forums. Now I'm very concerned. There is no rope size on the chart that meets design standards when u plug in a 40 foot boat in a 60 knot blow. According to the spread sheet, and the posted tables from Calder's, double braid has a breaking strength of 6,375 lbs. and a working load limit of 1,275 lbs. Is it possible that those figures are kilograms? Samson's tables gives their 5/8 double braid anchor line a breaking strength of 15,200 lbs. Despite this I am still going to use a rode above the chain to get some scope. I would like to use spectra because its strength to size ratio allows me to get more of it on the winch. Its working load limit is 5% its breaking strength, or 13,490lbs. Rocna's anchor sizing chart suggests a 3/8 inch chain for the 55 and 73 pound anchor. It should follow that the rode strength be very close to the chain strength. The strength of 3/8 chain according to the spread sheet is 16,200 lbs. This is for grade 43 chain. ( I wish I knew that before I bought.) To further muddy these murky waters I pulled up a chain strength and grade table. My ½" chain is grade 30 galvanized. The table says its breaking strength is 18,000 pounds and a WLL 4500 lbs. If I go up to 7/16 diameter spectra the breaking strength of the rode and the chain are close and the WWL are very disparate. If I keep the rode I have (3/8 spectra) the working load limit is double that of my ½" chain and is not then the weak link. Here are some pictures of my old anchoring system and the new one.https://www.facebook.com/MansonAnchors . The boat is the Ocean Point. I am not really worried too much about dragging anchor any more. The Manson Supreme seems to have solved that problem. I am worried about the rode snapping. I keep the old ground tackle in the lazz. Should I be very concerned using spectra as opposed to Samson double braided nylon.
I have been perusing the anchoring, anchor sizing, and anchor tackle threads. I am looking for practical and theoretical evaluations comparing the working load limits of double braid nylon vs. spectra. I own a 38 foot combination fishing boat in southeast Alaska. In the winter months this boat serves as a harvest dive platform. We spend 70% of our time anchored up. Expected conditions during the working day while anchored with divers and hoses (both diver airlines and 2" water lines) extended out to 350 feet can be extreme. It is not uncommon to be working in 40 -50 kt winds and an 8 foot sea with attendant 2-3 foot chop. In between openings or waiting out a blow it is not uncommon to be anchored up inside a protected bay and have winds blowing a steady 70 or 80 kts with higher gusts. In these conditions you are always expecting to drag. My old anchoring system was a 60 pound bruce style anchor, 60 feet of 5/8 chain, 125 feet of 5/8 double braid. Many times I've seen that 5/8 double braid stretched down to 3/8 of an inch. This system was limited by the size of my anchor winch. I had a bigger winch built for the upcoming winter harvest season. (its still not big enough but I cant get anything bigger w/o compromising the floatation of the bow) My new anchor is a 60 pound Manson Supreme. Chain is 100' of ½ " galvanized. 300 feet of 3/8 spectra. Normally I size my tackle by looking at the different parts and say to myself "holy cats, that's some huge chain that ought to work." I chose the 3/8 spectra by actually comparing its strength to the old 5/8 double braid. They are very close. The spectra has a breaking strength of 14k lbs. and the Samson braid is 15k lbs. I have some concerns beyond the 'jeez that stuff looks small' factor. One of my fellow harvest boat operators told me that spectra is terrible for anchor rode because it wont stretch and this will cause it to snap due to shock in heavy weather. "Its good everywhere on the boat but don't put it on the anchor" he said. I was considering going up to 7/16 diameter spectra to give myself some peace of mind. Then I found the sizing and working load spread sheet on these forums. Now I'm very concerned. There is no rope size on the chart that meets design standards when u plug in a 40 foot boat in a 60 knot blow. According to the spread sheet, and the posted tables from Calder's, double braid has a breaking strength of 6,375 lbs. and a working load limit of 1,275 lbs. Is it possible that those figures are kilograms? Samson's tables gives their 5/8 double braid anchor line a breaking strength of 15,200 lbs. Despite this I am still going to use a rode above the chain to get some scope. I would like to use spectra because its strength to size ratio allows me to get more of it on the winch. Its working load limit is 5% its breaking strength, or 13,490lbs. Rocna's anchor sizing chart suggests a 3/8 inch chain for the 55 and 73 pound anchor. It should follow that the rode strength be very close to the chain strength. The strength of 3/8 chain according to the spread sheet is 16,200 lbs. This is for grade 43 chain. ( I wish I knew that before I bought.) To further muddy these murky waters I pulled up a chain strength and grade table. My ½" chain is grade 30 galvanized. The table says its breaking strength is 18,000 pounds and a WLL 4500 lbs. If I go up to 7/16 diameter spectra the breaking strength of the rode and the chain are close and the WWL are very disparate. If I keep the rode I have (3/8 spectra) the working load limit is double that of my ½" chain and is not then the weak link. Here are some pictures of my old anchoring system and the new one.https://www.facebook.com/MansonAnchors . The boat is the Ocean Point. I am not really worried too much about dragging anchor any more. The Manson Supreme seems to have solved that problem. I am worried about the rode snapping. I keep the old ground tackle in the lazz. Should I be very concerned using spectra as opposed to Samson double braided nylon.
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