custom stainless straps, plates etc

[SimonGH]

Does anyone have a good source for 316 SS plate, either waterjet, laser, or CNC cut?  Would need to be pretty thick.

I want to fabricate straps (similar to chain plates) for stern drogue fastening.  From what I can see that would be preferable over using the existing cleats...

I was hoping that I could send a CAD drawing and have them fabricated.

What are others doing to attach stern drogues?

Thanks

Simon

 

[SVArcturus]

What are others doing to attach stern drogues?

Large stern cleats. 

Online Metals will have the metal, but not the machining.

 

[IStream]

I've had good luck with 3DHubs:

https://www.3dhubs.com/

Upload your drawing, spec your material and thickness, and get an instant quote. Parts arrive a few weeks after order.

Another good one is xometry.com and I've heard good things about protolabs.com.

 

[El Borracho]

Will the force be pulling the plate thru the transom? Or along the plate, like a proper chain plate, pulling the bolts sideways across the deck? This detail is often confused. Backing plates on cleats often have no beneficial effect as the cleat tears the bolt bodies along the deck. When is a cleat ever loaded upwards?

My drogue bridle would go to a pair of cockpit winches as there is nothing particularly strong aft. However that has never been tested...

 

[sail69]

General Supply in New Bedford, MA

 

[SloopJonB]

Cleats on the aft deck would be better than chainplate type things on the transom.

Drogues exert enormous forces and could rip a transom open with huge snatch loading in tension.

Cleats on deck would be in shear and are intended to withstand snatch loading.

Make them big - way bigger than even an anchor cleat.

 

[SimonGH]

I was envisioning long straps along the aft hull sides, with the rings protruding beyond the transom.  Quick sketch shown, it’s a 41.1 and I honestly don’t think the cleats are anchored particularly well.  The Jordan design specs want ~12,000lbs capacity.

 

[SimonGH]

Will the force be pulling the plate thru the transom? Or along the plate, like a proper chain plate, pulling the bolts sideways across the deck? This detail is often confused. Backing plates on cleats often have no beneficial effect as the cleat tears the bolt bodies along the deck. When is a cleat ever loaded upwards?

My drogue bridle would go to a pair of cockpit winches as there is nothing particularly strong aft. However that has never been tested...

See my sketch.  I’d want the bolts in shear...

 

[SpongeDeckSquareFoil]

White Water Marine in MI can do what you want. https://whitewatermarineinc.com/

I've used them for various special designs. Always good work.

 

[slug zitski]

I was envisioning long straps along the aft hull sides, with the rings protruding beyond the transom.  Quick sketch shown, it’s a 41.1 and I honestly don’t think the cleats are anchored particularly well.  The Jordan design specs want ~12,000lbs capacity.

View attachment 413937

If the object being towed veers 45 degrees... your tang will fail 

you are better off using a winch as the dead end, with a open or closed chock to

leed the tow rope

 

[longy]

Winches are not very strong, check the specs. And getting/keeping a fair lead going through stern pulpits/etc is next to impossible. On a Shannon 50 when asked to install something for a Jordan, after much research (both literature & looking at how boat was built) I installed two of Harkens largest padeyes on the transoms, through bolted to 1/2" thick, about 8x8" aluminum plates to spread the load.

 

[SloopJonB]

I was envisioning long straps along the aft hull sides, with the rings protruding beyond the transom.  Quick sketch shown, it’s a 41.1 and I honestly don’t think the cleats are anchored particularly well.  The Jordan design specs want ~12,000lbs capacity.

View attachment 413937

That looks about the best possible way to install them.

 

[SloopJonB]

If the object being towed veers 45 degrees... your tang will fail 

you are better off using a winch as the dead end, with a open or closed chock to

leed the tow rope

It's for a drogue, not a tow.

 

[SASSAFRASS]

You might want to have them break a L bracket that pics up the transom then put a heavy horizontal eye on the aft piece. Same profile as your pic on the side just wrap it on the transom.  You will be able to use lighter material for the doubler maybe 1/4" and heavy for the eye 3/8" or 1/2".  It will take loads from all directions well.

 

[LionessRacing]

It's for a drogue, not a tow.

And you've never had your boat slew with a following sea? 

 

[SVArcturus]

I was envisioning long straps along the aft hull sides, with the rings protruding beyond the transom.  Quick sketch shown, it’s a 41.1 and I honestly don’t think the cleats are anchored particularly well.  The Jordan design specs want ~12,000lbs capacity.

How will you do the adjustments to the drogue lines from that chainplate setup?  Cleats allow for easy trim of the bridle.  They just have to be substantial.  If the deck is too thin, lay up some additional layers in the immediate vicinity.   Doesn't have to be large (a sq ft or so should be plenty).

Winches allow easy adjustment also, but you'd want to be sure you wouldn't need them for anything else (and note that they aren't necessarily setup for those loads either).  You don't want an override with something carrying those loads, so leads would be critical.  Plus, whatever fairleads are required are gonna be a chafe problem you have to deal with.

You're gonna want one of them to retrieve the drogue anyway.

 

[longy]

Drogue Design Load
The design load for each drogue configuration is adjusted for the displacement of the yacht.
The design load is the ultimate, once in a lifetime, peak transient load that would be imposed on the drogue in a “worst case” breaking wave strike. The working load during a severe storm is about 10 % of this value.







MONOHULLS


 


MULTIHULLS




Displacement


Design Load


 


Displacement


Design Load




10,000 #


  8,000 #


 


  6,000 #


10,000 #




15,000 #


10,000 #


 


12,000 #


12,000 #




20,000 #


13,000 #


 


18,000 #


14,000 #




25,000 #


16,000 #


 


30,000 #


19,000 #




30,000 #


19,000 #


 


 


 




35,000 #


22,000 #


 


 


 




40,000 #


25,000 #


 


 


 




45,000 #


27,000 #


 


 


 




50,000 #


30,000 #


 


 


 








Bridle Legs
The design loads for each of the bridle legs are 70% of the drogue design loads.

Attachments on the Hull
The hull attachments for the drogue should be as far outboard and as far aft as possible.
I have no information on the ultimate strength of a typical sheet winch installation, and it would be difficult to evaluate each structure. Unfortunately, a winch is not an ideal structure, since the load is applied above the deck line and tends to overturn the winch and pull it out. The optimum attachment for the drogue is clearly a strap similar to a chainplate, bolted to the hull at the corners of the transom and extending aft with a shackle.

For a load of 14,000 lbs, a strap ¼ x 2.25 x 18 inches attached with six 3/8 bolts would provide a conservative design.

A large steel cleat would be acceptable if the deck is thick solid fiberglass and a steel plate is provided underneath.



Some serious load values here. And even though they claim "normal" loads at 10%, do you want to have a system that destroys stuff on your stern if max loads are hit??






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[SVArcturus]

And you've never had your boat slew with a following sea? 

You know, the more people raise various issues, the more it seems like bollards on the quarters might be a good approach.  If well placed, no fairleads needed, strong enough, line adjustment not bad.  

Also, no problem with your stern docklines have a secure attachment point. 

 

[longy]

IIRC, (it was many years ago) on the jordan set up I worked on, we ended up with a 3/8" poly rope off the end of the drogue to use as a retrieval line. Pulling in on that ine would reverse the cones