Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 29-07-2013, 18:47   #1
Registered User
 
zboss's Avatar

Join Date: Sep 2011
Location: On a boat
Boat: Cabo Rico 38
Posts: 3,428
Davit Blocks are Twisting

Hi,

We have a davit system with a triple block set on one side and a double block set on the other side. The side with the double block pulls up the dinghy just fine but the triple block seems to always have a twist to it that only becomes more pronounced when we try and raise the dinghy. Finally, it binds and the lines get mangled.

When I move the blocks by hand, the swivels and the sheaves all seem to spin fine, but when I release them, they just swivel back into the twisted position.

I was thinking that the lines are just old but I don't want to go out and buy more line unnecessarily.

Any ideas?

- z
__________________

__________________
zboss is offline   Reply With Quote
Old 29-07-2013, 19:14   #2
Registered User

Join Date: Apr 2011
Location: Cruising the east coast and Bahamas
Boat: Pearson 422
Posts: 228
Re: davit blocks are twisting

I have the same problem. Comes from the line getting twisted as the dink is lowered. There's enough weight to pull the twists right thru the blocks. Then when raising the dink, the twists jam the blocks.

Couple things that help.

- prevent twists by using a 'figure 8' coil instead of a 'round' coil
- occasionally raise the blocks all the way without the dink, then untwist the line and let it pay out smoothly back down to the water. That will get rid of the twists already in the line
__________________

__________________
Greg Long
s/v Paperbird
www.paperbird.us
Paperbird is offline   Reply With Quote
Old 29-07-2013, 19:20   #3
Registered User
 
montenido's Avatar

Join Date: Jun 2010
Location: Lying La Paz, BCS
Boat: 1979 Marshall Californian 42 LRC
Posts: 339
Images: 4
Re: davit blocks are twisting

Z,

I just installed davits with the 6:1 blocks on both sides. I had to look up how to thread the rope through and I found a diagram on Harken's website I think. Anyway, unlike the 4:1 set up. 6:1 requires the bottom blocks to be at 90 degrees to the top ones. I'll see if I can find the link for you. It takes a little work, because you have to run all that line through.

Cheers, Bill
__________________
M/V Ansedonia
'91 Californian 52 CPMY
Channel Islands, CA
montenido is offline   Reply With Quote
Old 29-07-2013, 19:24   #4
Registered User
 
ryon's Avatar

Join Date: Feb 2013
Location: Southern California
Posts: 588
Re: davit blocks are twisting

Quote:
Originally Posted by zboss View Post
Hi,

We have a davit system with a triple block set on one side and a double block set on the other side. The side with the double block pulls up the dinghy just fine but the triple block seems to always have a twist to it that only becomes more pronounced when we try and raise the dinghy. Finally, it binds and the lines get mangled.

When I move the blocks by hand, the swivels and the sheaves all seem to spin fine, but when I release them, they just swivel back into the twisted position.

I was thinking that the lines are just old but I don't want to go out and buy more line unnecessarily.

Any ideas?

- z
Has it capsized? This is really common on dinghy blocks, when someone forgets to choke the lower block when handling. Can you draw it up two-blocked correctly?
__________________
ryon is offline   Reply With Quote
Old 29-07-2013, 19:29   #5
Moderator
 
Hudson Force's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Lived aboard & cruised for 45 years,- now on a chair in my walk-in closet.
Boat: Morgan OI 413 1973 - Aythya
Posts: 7,894
Images: 1
Re: Davit Blocks are Twisting

I would assume that, since the triple block side uses far more line, the amount of twist is increaing as you coil the at lifting. Over time I would expect the same method of coiling the hauled line would produce a twist there too. I am aware of this tendency to develop a twist in my davit lines too. I continue to coil my lines in a manner that puts in a twist, but when I detach my lift lines after lowering my dinghy I always spin the twist back out until I see my blocks hanging aligned in the air. The other option is to raise the line without repeating the coils in the same direction or to produce the "figure eight" coil as suggested above.
__________________
Take care and joy, Aythya crew
Hudson Force is offline   Reply With Quote
Old 30-07-2013, 13:42   #6
Registered User
 
zboss's Avatar

Join Date: Sep 2011
Location: On a boat
Boat: Cabo Rico 38
Posts: 3,428
Re: davit blocks are twisting

Quote:
Originally Posted by ryon View Post
Has it capsized? This is really common on dinghy blocks, when someone forgets to choke the lower block when handling. Can you draw it up two-blocked correctly?
Yes, the two block comes up just fine.
__________________
zboss is offline   Reply With Quote
Old 30-07-2013, 15:05   #7
Registered User
 
ryon's Avatar

Join Date: Feb 2013
Location: Southern California
Posts: 588
Re: davit blocks are twisting

Quote:
Originally Posted by zboss View Post
Yes, the two block comes up just fine.
Sorry if you already know this, but two-blocking is when the two blocks come together so that they cannot be hauled any tighter. Do the lines correspond with their mates in the upper and lower blocks? It seems that you've answered that they are fine, but maybe you are referring to the double block being fine as opposed to the treble block and tackle which you are having trouble with? Is this where it binds and the lines get mangled? If so, it's capsized and should be straightened out.

Another twist would be as the blocks separate and the tackle lengthens. The blocks twist on their pendants as the load is lowered until there is so much chafing that they need to be overhauled (the individual lines hauled by hand). But you say it twists as the tackle is hauled, not slacked, so...

Is it the rope itself in the blocks that is twisting? I can imagine that the sheaves could push the lay of a very relaxed rope until it binds. But that should be obvious.

Aha! Maybe I have it. Are you using three-stranded line? All of the smallboat falls I can recall use woven. Maybe that'll do it!
__________________
ryon is offline   Reply With Quote
Old 30-07-2013, 18:17   #8
Registered User
 
Sailor Doug's Avatar

Join Date: Jan 2010
Location: Lake Erie
Boat: H36
Posts: 384
I have a double a single block on the bow end and a double block on the other. Both lines are lead through sheet stoppers to winches, very easy to lift. After 12 hauls the line is twisting so bad the single block end needs help to go down. Pulling the line out and un twisting it is the only solution I have found. Sure would like a better answer.
__________________
Sailor Doug is offline   Reply With Quote
Old 04-08-2013, 15:39   #9
Registered User
 
zboss's Avatar

Join Date: Sep 2011
Location: On a boat
Boat: Cabo Rico 38
Posts: 3,428
Quote:
Originally Posted by Sailor Doug View Post
I have a double a single block on the bow end and a double block on the other. Both lines are lead through sheet stoppers to winches, very easy to lift. After 12 hauls the line is twisting so bad the single block end needs help to go down. Pulling the line out and un twisting it is the only solution I have found. Sure would like a better answer.
I am wondering if a slippery synthetic line might be better for this type of application.
__________________
zboss is offline   Reply With Quote
Old 04-08-2013, 15:44   #10
Registered User
 
zboss's Avatar

Join Date: Sep 2011
Location: On a boat
Boat: Cabo Rico 38
Posts: 3,428
Quote:
Originally Posted by ryon View Post

Sorry if you already know this, but two-blocking is when the two blocks come together so that they cannot be hauled any tighter.
no... Did not know that!

Quote:
Originally Posted by ryon View Post

Do the lines correspond with their mates in the upper and lower blocks? It seems that you've answered that they are fine, but maybe you are referring to the double block being fine as opposed to the treble block and tackle which you are having trouble with?
Yes.. By the time the dinghy gets 1/3 of the way up, the line/blocks on the triple block side are already twisted. I can't lower them without untangling them. I was just on the boat... Should have taken pics.

Quote:
Originally Posted by ryon View Post
Is this where it binds and the lines get mangled? If so, it's capsized and should be straightened out.

Another twist would be as the blocks separate and the tackle lengthens. The blocks twist on their pendants as the load is lowered until there is so much chafing that they need to be overhauled (the individual lines hauled by hand). But you say it twists as the tackle is hauled, not slacked, so...

Is it the rope itself in the blocks that is twisting? I can imagine that the sheaves could push the lay of a very relaxed rope until it binds. But that should be obvious.

Aha! Maybe I have it. Are you using three-stranded line? All of the smallboat falls I can recall use woven. Maybe that'll do it!
The boat came with the line in the davits. It may very well be... I will look when I get back to the vessel.
__________________
zboss is offline   Reply With Quote
Old 05-08-2013, 18:52   #11
Registered User
 
capbillh's Avatar

Join Date: Feb 2008
Location: Runnemede, NJ
Boat: Jeanneau 409
Posts: 102
The twist occurs on all my double braided lines including the main sheet so I do a double loop/figure eight that helps.
__________________
Bill P.C. TOYC,
K2SDV
S/v Wind Dragon
capbillh is offline   Reply With Quote
Old 06-08-2013, 02:54   #12
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 1,376
Images: 7
Re: Davit Blocks are Twisting

You generally do not need swivels on the blocks used on davits if there are for and aft lifts. Use braided lines and lock the swivels so that the blocks are prevented from turning and allowing the lines to twist.
__________________
RaymondR is offline   Reply With Quote
Old 06-08-2013, 07:15   #13
Moderator
 
Hudson Force's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Lived aboard & cruised for 45 years,- now on a chair in my walk-in closet.
Boat: Morgan OI 413 1973 - Aythya
Posts: 7,894
Images: 1
Re: Davit Blocks are Twisting

This photo, though the blocks are partially obscured by the boarding ladder, shows these blocks on swivels.

I think that the line will be able to become twisted with or without the blocks on swivels. The twists originate with the line in your hands as it is raised and coiled. You can either change the method by which you hoist the line or remove the twist each time you lower and detach the dinghy. When I'm standing in my dinghy and the lower block is removed from the dinghy and hanging free, it will not hang in alignment with a twist. It's a quick task to spin the twist out of the line at this time.
__________________
Take care and joy, Aythya crew
Hudson Force is offline   Reply With Quote
Old 06-08-2013, 07:29   #14
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 4,350
Re: Davit Blocks are Twisting

Quote:
Originally Posted by RaymondR View Post
You generally do not need swivels on the blocks used on davits if there are for and aft lifts. Use braided lines and lock the swivels so that the blocks are prevented from turning and allowing the lines to twist.
Bingo!

One of my personal peves is the number of swivel blocks installed where they are not needed. Sure, they self-align with new line, but in time tangles happen. Sure, you can coil differently and use the correct line, but 80% of the time getting rid of the damn swivel is simpler. I find very few applications where a non-swivel block will not due if possitioned correctly; there is enough swivel inherant in the shackle.
__________________

__________________
Gear Testing--Engineering--Sailing

Writing full-time since 2014.
Bookstore:http://sail-delmarva.blogspot.com/20...ook-store.html
thinwater is offline   Reply With Quote
Reply

Thread Tools
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
Classic Blocks, Who Makes Them Anymore? Topsail Deck hardware: Rigging, Sails & Hoisting 13 22-12-2012 12:35
For Sale: Schaefer Blocks thesparrow Classifieds Archive 4 01-05-2012 15:40
For Sale: Lifting Davit Motormate Forespar $175 George P Classifieds Archive 1 17-11-2011 20:21
Antal Blocks FecklessDolphin Deck hardware: Rigging, Sails & Hoisting 2 08-11-2011 11:24
Merriman Snatch Blocks Delta Fox Construction, Maintenance & Refit 9 11-10-2011 18:59



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:46.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.