Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 31-12-2013, 18:00   #76
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 7,906
Re: Mantus chain hook

Quote:
Originally Posted by Cotemar View Post
...
Your numbers are all wrong as usual....
Is it possible you are not referring to the same rubber snubber design? There are many out there. Explaining which numbers are wrong may bring clarity.

However, unless they can stretch 4-6 feet at loads of 1000-2000 pounds, the math is in favor of a long nylon snubber. He has presented numbers, you have delivered unquantifiable anecdotes; I suspect your rough anchorage and your boat are both different from his.
__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Old 31-12-2013, 18:05   #77
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Mantus chain hook

Cotemar - if that is your experience then I am sure you are right.

Jonathan
JonJo is offline   Reply With Quote
Old 31-12-2013, 19:01   #78
Registered User
 
Cotemar's Avatar

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Mantus chain hook

My 5/8 inch diameter 3 strand nylon bridle snubber has a tensile strength of 11,650 lbs.
The rubber snubber with three turns is rated for storm surge conditions.
The proper rubber snubber not only stretch’s on the three turns, but also coils and compresses the rubber core in 3 dimension’s.

When I back down on this cat bridle snubber with two 30 hp diesel engines at 2800 rpm with 3 bladed props, These rubber snubbers are at 1/3 stretch.

This compact 20 foot cat bridle setup accomplishes the same snubbing power as JonJo’s climbing lines running down his decks to his stern cleats, But I will not kill anyone as my Bridle snubber is all forward of my Seagull Striker cross beam.

Wind and wave shock loads are gone.
Attached Thumbnails
Click image for larger version

Name:	Snubbers Cotemar 1.jpg
Views:	132
Size:	432.9 KB
ID:	73093   Click image for larger version

Name:	Snubbers Cotemar 2.jpg
Views:	126
Size:	431.4 KB
ID:	73094  

Cotemar is offline   Reply With Quote
Old 31-12-2013, 20:26   #79
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Mantus chain hook

Cotemar

I am interested, seriously, in your rubber snubbers. You mention they are rated for storm surge conditions with 3 turns, the 3 turns as illustrated in your image. The restricting feature of your snubber are the 3 turns - the snubber simply cannot stretch more than the '3 turns'. Consequently the 'rating' for a storm surge does not mean very much in that as long as you keep the 3 turns the snubbers will take whatever load the cordage will take (you will never stretch it beyond whatever those 3 turns restrict it to).

The cordage will stretch - but in terms of the length of the 3 turns - not very much. Basically beyond about 30 knots any excess load is taken by the cordage - not the snubber.

My data is based on actually testing a 1 inch by 18 inch rubber snubber As far as I can make out there are a number of manufacturers and the products are all similar - but your snubber seems slightly higher priced and might be different. I have checked Taylor Made, Forsheider and Unimer (not sure of the spellings) and they are all the same specs. Max stretch is about 60% - and there are very few polymers that would be applicable and cheap that are better then this.

West Marine sell a 1 inch by 18 inch rubber snubber for around $50 and you can buy 30' of 3/8th inch Mega Plait for around $39. This snubber (and this is similar to the one I tested) will absorb around 250 joules of energy and that is at the limit of stretch suggested by the manufacturer. The 30' of 3/8th nylon at 50% of breaking load absorbs over 7,000 joules. 50% of stretch is excessive and not to be used - but 30' of 5/8th inch nylon can absorb 4,000 joules at 20% of stretch so a better option at higher loads and has no need for a rubber snubber - the nylon does it all by itself and works through the complete wind range. Recall that a 5t yacht at 1 knot develops 1250 joules, a 10t yacht twice that at the same speed. A rubber snubber is very effective at low wind speeds but then depends completely on the strength of the cordage beyond 30knots (and I think stops working below this wind speed).

My view is rubber snubbers are great in a marina application, they are more expensive than cordage, they are heavy for what they do (could not check the weight so this comment is subjective) and they reach the limit of their energy absorbing ability (when used as an anchor snubber) at relative low wind speeds.

But none of this matters - if your chain (size and length) deployed, combined with your nylon snubbers + the rubber snubbers works for you and you are happy then that is all that matters. There are other options which are cheaper and maybe more effective. None of these items, chain, nylon, rubber, works in isolation - but the 'loss' of chain catenary and the rubber snubber both lose effectiveness just as you actually need it.

But if you can advise the specific brand of snubber I would be very interested to check it out.


I note your comment about safety - and a comment well made.

There is conflict with multis (and monos come to that) as to how to get a 30' snubber into the rode system. If you have it all outboard then in light winds the snubber/chain attachment rubs on the seabed, chain hooks fall off and the snubber potentially abrades (nylon is not very abrasion resistant). If you have it all inboard and it fails you have a cable that would seriously injure someone. (Though I'm not sure that someone standing on a yacht bow is immune from having an arm cut off (or worse) if 30' of snubber fails outboard). We run our snubber/bridle through the deck stanchion bases- its basically contained to 5' lengths. On a mono you could run it through Dyneema loops tied to the toe rail - containing the snubber is not an issue. But to have a snubber much shorter than 20' and you will lose energy absorbing potential.

Jonathan
JonJo is offline   Reply With Quote
Old 31-12-2013, 20:35   #80
Registered User
 
NorthPacific's Avatar

Join Date: Feb 2010
Location: La Paz Baja Sur
Boat: Dufour35 1982
Posts: 824
Images: 5
Re: Mantus chain hook

40-15 to Jonathan
__________________
www.SouthPacificEngagement.com
NorthPacific is offline   Reply With Quote
Old 31-12-2013, 20:40   #81
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 7,906
Re: Mantus chain hook

Quote:
Originally Posted by Cotemar View Post
My 5/8 inch diameter 3 strand nylon bridal has a tensile strength of 11,650 lbs.
The rubber snubber with three turns is rated for storm surge conditions....
Cool, numbers! I should have caught the snubber description in your earlier post, and I did not understand that you had one in each leg.

Your description above makes it sound as though the snubbers are 1/3 extended with motor, perhaps 800-1000 pounds, and probably fully extended at full load. Perfect. (tesing could establish this)

I'm estimating that they extend about 12-inches, based on basic dimensions and 3 wraps around a 1" core. That's how much line they consume in twists. Any additional stretch would occur anyway (nylon).

Assuming linear elasticity (probably not, but gotta start somewhere) they would absorb about 70% x 3000 pounds x 1-foot/2 = 1050 foot-pounds each, 2100 ft-pounds total, or about 2900 joules. The 70% is the per-leg load division; I'm guessing because I don't know the exact apex angle, but I bet it's close.

Climbing rope can absorb a max of about 1000 foot-pounds per foot on slow pull and about 400 ft-#/ft at the target load. Your line can prbably absorb about 1/2 that (fatter line is stronger but stretches less) or 200 ft-#/ft, or about 400 x 40 = 16000 ft-pounds on a bridle of your size. Put another way, depending on line size, the twist snubbers act like another 4-5 feet of rope.

A much simpler approach is to consider that the nylon will stretch about 20% at this load, so 4-5 feet of rope will stretch the same amount as the snubber under the same load. It's good when 2 unrelated calculations give the same answer.

Really interesting idea, better for a cat because you can run 2 of them. The trade off is a clunky bit of rubber vs. extra line on the side decks. Fewer chafe challenges but substantially less energy absorption capacity. Same cost, perhaps, unless the snubber line is free (often is retired anchor rode or other free line--I've never bought any).

Development continues.

(missed JonJo's last post; was calculating and typing)
__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Old 31-12-2013, 20:45   #82
Registered User
 
NorthPacific's Avatar

Join Date: Feb 2010
Location: La Paz Baja Sur
Boat: Dufour35 1982
Posts: 824
Images: 5
Re: Mantus chain hook

As to the elasticity of nylon rope. I can attest to this from personal experience as a rock climber. After an initial brutal blow to the privates, it does stretch somewhat, the idea being that you are not cut in half. The old 3 strand stretched much better than the strand rope until they built in more elasticity, then on a long fall it would get thin in the middle Not that I ever fell that often:-) .Thought this may be of help next time you guys are anchoring up. Happy New Year folks. Nice (polite fireworks display)
__________________
www.SouthPacificEngagement.com
NorthPacific is offline   Reply With Quote
Old 31-12-2013, 21:38   #83
Registered User
 
Cotemar's Avatar

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Mantus chain hook

JonJo,

Here’s the deal, you and I know that 3 strand nylon bridles are used on 95% of boats anchoring around the world today and they work very well.

Now add two rubber snubbers to that same 3 strand nylon bridle to make a Cat Snubber Bridal. Now you’re going to have a winning combination in the same 20 foot package. The shock loads to the boat from strong wind and waves disappears.

This cat bridle snubber cost me $55 usd for the 3 strand nylon line and $60 usd for the rubber snubbers for a total of $115 usd. This is all new gear. Not used or hand me down crap.
Attached Thumbnails
Click image for larger version

Name:	Snubbers Cotemar 3.JPG
Views:	135
Size:	167.3 KB
ID:	73095  
Cotemar is offline   Reply With Quote
Old 31-12-2013, 21:56   #84
Marine Service Provider

Join Date: Jul 2011
Location: Myrtle Beach..for now
Boat: Marine Trader 36 Sundeck
Posts: 388
Re: Mantus chain hook

Quote:
Originally Posted by Cotemar View Post
WOW, Staniel Cay.
Mind If I drop in for a week and wax your boat for you.
Well it's a big cat, it may take me 10 days.
Crewed on an A class sloop today, the Lady Muriel. We won overall beating Tida Wave. Got a nice jacket for winning. Come on down, but you may be hooked as we are. Gonna be tough to leave here..
__________________
Cruisin' again....
Sid at SailAway is offline   Reply With Quote
Old 31-12-2013, 22:01   #85
Registered User
 
Cotemar's Avatar

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Mantus chain hook

Quote:
Originally Posted by Sid at SailAway View Post
Crewed on an A class sloop today, the Lady Muriel. We won overall beating Tida Wave. Got a nice jacket for winning. Come on down, but you may be hooked as we are. Gonna be tough to leave here..
I am hooked already. I love Staniel Cay
Cotemar is offline   Reply With Quote
Old 31-12-2013, 22:33   #86
Registered User
 
CarinaPDX's Avatar

Join Date: Jan 2010
Location: Portland, Oregon, USA
Boat: 31' Cape George Cutter
Posts: 2,762
Re: Mantus chain hook

I have to note that the discussion gives snubbers a pass in marina applications. In fact they have the potential to cause great damage. Some marinas (Marina Bay, Gibraltar is one example) there is a surge, where the water will suddenly flow inwards for 5-10 seconds, then reverse and flow out. If the boat is moored on the inside, the inrush moves the boat inshore and stretches the snubber (rubber or spring steel) thus storing energy. When the current reverses the boat is accelerated outward with the combined force of the snubber and flow and can stretch the mooring line holding the boat off the dock (in this case a cement construction). A lot of damage can result. I got rid of my snubbers in Gibraltar and never looked back. For anchoring I use braided nylon which works great.

Greg
CarinaPDX is online now   Reply With Quote
Old 31-12-2013, 22:46   #87
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 7,906
Re: Mantus chain hook

Quote:
Originally Posted by Cotemar View Post
JonJo,

Here’s the deal, you and I know that 3 strand nylon bridles are used on 95% of boats anchoring around the world today and they work very well.

Now add two rubber snubbers to that same 3 strand nylon bridle to make a Cat Snubber Bridal. Now you’re going to have a winning combination in the same 20 foot package. The shock loads to the boat from strong wind and waves disappears.

This cat bridle snubber cost me $55 usd for the 3 strand nylon line and $60 usd for the rubber snubbers for a total of $115 usd. This is all new gear. Not used or hand me down crap.
Overhand loops? Huh.
__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Old 31-12-2013, 23:08   #88
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Mantus chain hook

Quote:
Originally Posted by Cotemar View Post
JonJo,

Here’s the deal, you and I know that 3 strand nylon bridles are used on 95% of boats anchoring around the world today and they work very well.

Now add two rubber snubbers to that same 3 strand nylon bridle to make a Cat Snubber Bridal. Now you’re going to have a winning combination in the same 20 foot package. The shock loads to the boat from strong wind and waves disappears.

This cat bridle snubber cost me $55 usd for the 3 strand nylon line and $60 usd for the rubber snubbers for a total of $115 usd. This is all new gear. Not used or hand me down crap.
Cotemar,

I've already said - if it works for you, great. In fact we used to have a set up identical to yours, a rubber snubber each side and braided nylon but our lines were shorter. Once I'd made all the calculations I realised that the rubber was not adding and that I could achieve a much better - and I think significant - effect, simply using climbing rope as it works fairly consistently through the complete wind range. You could use 'all' rubber snubbers - but to achieve what nylon offers you need 5 of them, each side (plus the nylon to carry it) which we did think of but balked at both price and weight. We are twitchy about weight (though not when stocking with wine, but then we carry it amidships).

Climbing rope simply will not work for many - their yachts are too big. It comes as a maximum of 11mm (someone correct me if this is wrong) and beyond about a 45' yacht climbing rope starts to look too small (certainly when conditions are arduous). Anyone with a bigger yacht, or not able to get climbing rope (cheaply) could use 3 strand or anchor plait - which comes in almost any size one could ever want.

Your solution is fine, though I think I'd rather longer lines of lower diameter - but if it works for you stick with it. I'd be twitchy about the snubbers on the seabed - but if you can live with the possible abrasion, again, stick with it. We actually tend to anchor in deeper water (maybe like you) too close to shore in an ocean anchorage and swells build or steepen - much better further out.

Jonathan
JonJo is offline   Reply With Quote
Old 31-12-2013, 23:10   #89
Registered User
 
Cotemar's Avatar

Join Date: Dec 2007
Boat: Mahe 36, Helia 44 Evo, MY 37
Posts: 5,731
Re: Mantus chain hook

Quote:
Originally Posted by thinwater View Post
Overhand loops? Huh.
All Figure 8 knots
Attached Thumbnails
Click image for larger version

Name:	Figure 8 knot.jpg
Views:	110
Size:	26.2 KB
ID:	73096  
Cotemar is offline   Reply With Quote
Old 31-12-2013, 23:14   #90
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Mantus chain hook

Quote:
Originally Posted by CarinaPDX View Post
I have to note that the discussion gives snubbers a pass in marina applications. In fact they have the potential to cause great damage. Some marinas (Marina Bay, Gibraltar is one example) there is a surge, where the water will suddenly flow inwards for 5-10 seconds, then reverse and flow out. If the boat is moored on the inside, the inrush moves the boat inshore and stretches the snubber (rubber or spring steel) thus storing energy. When the current reverses the boat is accelerated outward with the combined force of the snubber and flow and can stretch the mooring line holding the boat off the dock (in this case a cement construction). A lot of damage can result. I got rid of my snubbers in Gibraltar and never looked back. For anchoring I use braided nylon which works great.

Greg
We live and learn

We keep 'Josepheline' on a swing mooring, we anchor whenever we can and restrict marinas to refueling - fear of paying money unnecessarily. I do see snubbers, stainless springs and rubber, in use on moored yachts (and have seen some commercial lines with rubber incorporated into the build of the cordage) - but our marinas, or the ones I know, sound a bit more comfortable than yours - another reason its called the Lucky Country?).

Jonathan
JonJo is offline   Reply With Quote
Reply

Tags
Mantus, Rubber Snubbers, Snubbers, Soft Shackles, mantus

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Anchor Chain Preservation Method heintje23 Construction, Maintenance & Refit 31 28-09-2013 07:24
Dumb Question, Chain Hook? BozSail Anchoring & Mooring 49 14-06-2013 08:20
Anchor Chain Hook Poll Cotemar Anchoring & Mooring 135 17-03-2013 16:11
Getting Chain into the Bilge JonathanSail Anchoring & Mooring 32 15-01-2012 17:22

Advertise Here


All times are GMT -7. The time now is 12:21.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.