Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 25-05-2022, 12:51   #1
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Cast Thimble Modification for Dyneema

Weve thought about fabricating a lashing dead eye using a cast thimble as a base. We would weld a bar across the wide part of the thimble so the lines would not climb over each other. This bar could also support a short section of pipe welded at 90 degrees to it for a pin.
Just an alternative to the aluminum terminal fittings.
We also thought about how to use plastic ...which was suggested before on the forum ...but we lost the post and are not sure which plastic would be ideal.
Looking forward to new ideas / suggestions.
Thank you.
Mark and Crew
Manateeman is online now   Reply With Quote
Old 26-05-2022, 16:15   #2
Registered User
 
Spot's Avatar

Join Date: Jan 2019
Location: Minnesota, USA
Boat: 21' trailer sailor & 8' sailing dinghy
Posts: 1,563
Re: Cast Thimble Modification for Dyneema

Hi Mark,
I am having a time trying to visualize what you are wanting to make.
Any chance the manatee crew could draw a sketch or make a reasonable facsimile out of discarded pizza crust?
__________________
Big dreams, small boats...
Spot is offline   Reply With Quote
Old 27-05-2022, 10:12   #3
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

OK. We all know what the usual and rather expensive dyneema terminal fittings look like...sort of old wooden dead eyes but flat and made in aluminum. Nothing wrong with them, just the cost for some people.
Plain cast thimbles in stainless have some advantages but the wide curve tends to squeeze the lashings together and on top of each other.
If you cross the wider end of the thimble with a piece of heavy stainless bar stock at 90 degrees to the shroud or stay, the lashings would not cross on top of each other. With two thimbles, the lashings would be parallel. The line around the thimble is squeezing the thimble in compression and the crossbar... to which the lashing is attached ...is trying to push the thimble apart.
I think the crossbar should be about the diameter of the outside of the thimble but it could be larger or it could be fitted with a roller. The diameter is not limited by the thickness of the plate used in the existing dead eyes. The advantage is much less friction and a larger radius turn for the lashings.
As to cost. A cast thimble. A crossbar with or without a roller. Two simple TIG welds. Cast thimble to mast thru bolts would just be a simpler design where a plate fills the interior space of the thimble. It could be drilled and a short section of pipe could be welded to the plate at any angle desired.
We began the thread as an appeal to the forum members for new designs.
We will post our drawing as soon as we can but we would love to see what others can design. To us, cast stainless thimbles are a reasonably priced starting point to which a lot of interesting components can be easily welded.
Or maybe plastics are the way to go?
Mark and the manatee crew.
Manateeman is online now   Reply With Quote
Old 27-05-2022, 11:19   #4
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

Drawings.Click image for larger version

Name:	9037B762-5B9C-4A20-9D51-704FFD5F87E7.jpg
Views:	63
Size:	415.5 KB
ID:	258484
Manateeman is online now   Reply With Quote
Old 27-05-2022, 11:59   #5
Registered User

Join Date: Mar 2016
Location: New England. USA.
Boat: McCurdy & Rhodes Custom 46
Posts: 1,337
Cast Thimble Modification for Dyneema

I wonder if the thimble would rotate slightly in the eye of the shroud. This would cause the lashings to slide to one side. This would cause more rotation and so on.
In other words this setup might not be stable.
You can test that.
dfelsent is offline   Reply With Quote
Old 27-05-2022, 14:25   #6
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

Rotation. Just dont see this as a problem. If you use a cow hitch for the lashings in the middle of the cross bar and work your way out toward the thimble, you can get a nice equal tension because you have far less friction vs a dead eye with smaller holes. Why would the thimble shift in the dyneema eye to begin with...just dont see why. Well you could wrap the dyneema in hockey tape.
The roller need not be straight across. You could cover the center with a series of little rollers...think a line of low friction rings. If the roller is plastic, its easy on a lathe. Maybe no roller, just scallop out the crossbar. It can be larger in diameter than the thimble is wide.
The current aluminum dead eyes dont impress us. If you just use plain cast stainless thimbles, the lashings touch each other on the sides and are squeezed together by the curve of the thimble. Lot of friction. With a straight bar across the thimble you reduce this when you tighten things up. Im more concerned with the best way to attach the dyneema lashing lines.
Looking for new thinking...new designs.
Testing will reveal the problems and the improvements.
The manatee pizza is done so well sigh off.
Mark
Manateeman is online now   Reply With Quote
Old 27-05-2022, 14:50   #7
Registered User

Join Date: Dec 2019
Location: Boston
Boat: Farr 50 Pilothouse
Posts: 984
Re: Cast Thimble Modification for Dyneema

If you can do the welding yourself, then this seems pretty reasonable. I think the crossbar should be as "low" on the thimble as you can while still having room for all your lashings side by side, this way it would inhibit rotational forces, if any. I don't know enough about synthetic lashings to know if a roller is necessary. The downsides of a plastic roller are that it's either a full cylinder and you'd have to cut and reweld to replace (assuming you could weld it in the first place without melting the plastic). If it's a split cylinder that you stretch around the crossbar, I'd be worried about the forces of the lashings shifting it out of place, or over time deforming it and loosening the lashings. For your mast fitting, again, if you have the welding equipment and the ability, that seems like a reasonable solution.
Muaddib1116 is offline   Reply With Quote
Old 28-05-2022, 07:59   #8
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

For now well take plastics off the table and return to a stainless crossbar. Welding it to the cast thimble is pretty straightforward and even if you bring the thimble to the shop, its not a lot of bench time.
We think the cast thimble with a single hole for a pin or a toggle would take much more labor but the cost might be worth the advantages of stainless over aluminum. It would be interesting to see prices for solid center cast stainless thimbles. You could drill out the pin size you need and weld in a short reinforcing tube or washer at any angle required. By solid center, we dont see the center plate thickness equal to the thimble width...just a plate. Not sure there is a good rule of thumb but some added strength would improve the current cast thimbles which are point loaded if you need to connect them to a pin in a toggle.
For example.
We have nice thick aluminum chainplates welded in the hull. From the mast, we now have a nice dyneema line hanging down with a manatee designs cast stainless thimble with welded in crossbar.
We would like to attach lashings between this thimble and the chainplates. So now we need one more cast thimble with crossbar and the smaller end now points down to the chainplate. We could add a double jaw toggle IF there were a reinforced hole in the thimble...or maybe a second crossbar.
If you had a second crossbar, you have a lot more options .
Thats why we posted the thread. What are the options besides flat black aluminum terminal fittings.
Hand tossed manatee pizza recipe for the best NEW suggestions or drawings.
Happy trails.
Mark and the crew.
Manateeman is online now   Reply With Quote
Old 28-05-2022, 08:28   #9
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

Drawings of alternative modifications to cast stainless steel thimbles.
Click image for larger version

Name:	48FCC6AF-920D-4811-8752-1456BA5C3F2A.jpg
Views:	56
Size:	412.3 KB
ID:	258508
Manateeman is online now   Reply With Quote
Old 28-05-2022, 08:42   #10
Registered User

Join Date: Dec 2019
Location: Boston
Boat: Farr 50 Pilothouse
Posts: 984
Re: Cast Thimble Modification for Dyneema

What are the two middle right sketches of? What is the purpose of the add-ons at the narrow part of the thimble?
Muaddib1116 is offline   Reply With Quote
Old 28-05-2022, 09:07   #11
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

The question marks indicate the two areas where we are not sure what to do.
Question mark 1 is the area inside the thimble. The two thimbles on the right are just suggested solutions. The middle one is a short second crossbar showing where a pin would be located on top of and at 90 degrees to the second lower crossbar. I just drew it as a cut piece, end view, just to show the position of the pin sitting on top of the second crossbar. The furthest right thimble has a plate with a hole for a pin which would be at 90 degrees to the top crossbar. One crossbar, one plate filling up the small end of the thimble.
Not shown would be the toggle or turnbuckle or plates connecting the chainplate in the deck to the lower thimble.
Question #1 is...what goes in this space.
Question #2 is...what connects the lower thimble to the deck chainplate.
Ill try to make and photograph some models as soon as I can.
Thank you!
Mark and crew.
Manateeman is online now   Reply With Quote
Old 28-05-2022, 09:52   #12
Registered User

Join Date: Dec 2019
Location: Boston
Boat: Farr 50 Pilothouse
Posts: 984
Re: Cast Thimble Modification for Dyneema

Oh, I see, you are trying to figure out the bottom fitting to the chainplate. I'm don't think the thimbles will be strong enough, without the dyneema spliced around it, even with some welded bars. I think maybe the best solution would be to use the lower thimbles as thimbles with a dyneema strop around the thimble, lashings around the two lengths to keep it tight to the thimble, and then two spliced eyes over a pin through the chainplate. Or a lower leg of dyneema with a thimble on each end, and the lower thimble attached to the chainplate with a shackle or something.
Muaddib1116 is offline   Reply With Quote
Old 28-05-2022, 10:19   #13
smj
Registered User

Join Date: Nov 2007
Boat: TRT 1200
Posts: 6,423
Re: Cast Thimble Modification for Dyneema

A simple way to go from turnbuckle to lashing?
Click image for larger version

Name:	IMG_6197.jpg
Views:	65
Size:	180.3 KB
ID:	258519
smj is offline   Reply With Quote
Old 28-05-2022, 15:32   #14
Registered User

Join Date: Oct 2019
Location: Kennebunk ME
Boat: Owner built 60 Aluminum Expedition Yacht.
Posts: 1,685
Re: Cast Thimble Modification for Dyneema

SMJ ...Looking at the very bottom thimble. Here you have a flat toggle against a curved thimble. The flat surface of the toggle rides on the curved inner surface of the thimble. Its a very small contact area. Its a sharp 90 degree flat bar against the round inner surface of the thimble.
This is exactly the kind of point loading Im trying to avoid.
It would be ok if it were welded, but it flexes.
Ive got to draw out the above post before I comment but I do very much appreciate the response.
Lastly, Wichard has a photo of a rather beefy thimble but no details. Its the thimble above their line clamps . The thimble has crossbars cast into it and a hole for a pin. Anyone recognize this thimble?
Operator manatee signing off for dinner.
Manateeman is online now   Reply With Quote
Old 28-05-2022, 15:43   #15
Registered User

Join Date: Dec 2019
Location: Boston
Boat: Farr 50 Pilothouse
Posts: 984
Re: Cast Thimble Modification for Dyneema

I'm not sure that's their product. The photo I found was for the clamp they sell. That beings said, I still think you need to have the load be born by the dyneema line that goes around the thimble, the thimble itself is not designed to be structural. So for the lower part of the lashings, I think you'll still need the thimble to be wrapped in dyneema and then attached to your chainplates somehow. In the photo that SMJ posted, if you remove the bottom thimble, and have two eye splices is the dyneema, each one on one side of a pin going through the chainplate, then you won't have a point load like with that toggle. Alternatively, you could maybe use a D shackle with the pin through the chainplate and the D through the thimble. You'll still get a point load, but on a rounded contact surface, which is probably better. That being said, I'm not sure that the point loading you see with that flat section toggle is a real problem. The thimble will deform a bit at the corner points, but the thimble is not the true load bearing structure, it is transferring the load to the dyneema line. Also, as you see in that photo, the lashings are all next to eachother in the curve of the thimble, and it doesn't look too crazy with overlapping and such. Are you sure you aren't going down an unnecessary rabbit hole because of theoretically un-ideal minor things.
Muaddib1116 is offline   Reply With Quote
Reply

Tags
dyneema

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
Best way to insert thimble in midpoint of Dyneema 12-strand? SailFastTri Deck hardware: Rigging, Sails & Hoisting 2 18-06-2016 05:52
12 strand nylon thimble splice. salticrak Anchoring & Mooring 4 15-08-2013 13:19
For Sale: Anchor Rode 1/2" with thimble $60 silverp40 Classifieds Archive 0 04-06-2012 17:13
Thimble Islands Ferry Financial Troubles Soundbounder General Sailing Forum 0 04-07-2011 07:17
Roll Swaging vs Copper Swage and Thimble Dove Deck hardware: Rigging, Sails & Hoisting 37 03-09-2009 09:08

Advertise Here


All times are GMT -7. The time now is 14:09.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2022, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.