FinDelta Anchoring Sail

[MurrayM]

Riding sails (a small sail on the aft end of a boat) have been used for centuries to reduce an anchored boats tendency to swing from side to side in a strong wind.

With todays nylon rode's that side to side motion is accompanied by a heavy yoyo bounce on the anchor: when the boat bounces back upwind on the stretchy nylon, it falls off the wind and gets pushed downwind with wind partially on the beam for another big bounce.

This FinDelta looks to be a 'slap yourself upside the head' for not thinking of it yourself kind of idea, and pretty amazing that nobody thought of it a thousand years ago:

https://www.bannerbaymarine.com/index.php?l=product_list&c=12

 

[MurrayM]

While the FinDelta might not work with the lower mast of a trawler, we’ll be scooping the design principle and plan to add a couple ‘fins’ to our current home made riding sail

(Have emailed them to see if they are interested in designing a FinDelta MV version)

 

[Group9]

We used one of these sails on our 42 Catalina sailboat (notorious for sailing at anchor).

Pros: It does work.

Cons: It's a lot more trouble to put it up than you would think.

 

[mvweebles]

What's the engineering theory on anchor riding sails? Untethered and adrift, a boat will sit roughly broadside to the wind, not point-up like a weather vane. Hunting/dancing at anchor is caused the anchor restricting that tendency. I can see where a sail placed well aft would change the natural wind/hydro induced orientation of an adrift boat, but is the effect a token amount or a meaningful amount? And how would one know?

 

[rslifkin]

What's the engineering theory on anchor riding sails? Untethered and adrift, a boat will sit roughly broadside to the wind, not point-up like a weather vane. Hunting/dancing at anchor is caused the anchor restricting that tendency. I can see where a sail placed well aft would change the natural wind/hydro induced orientation of an adrift boat, but is the effect a token amount or a meaningful amount? And how would one know?

It depends on the boat. For a typical trawler with the house fairly far forward, getting it to sit well is going to take more than it will on something with a raised pilothouse aft and minimal or no cockpit.

 

[Group9]

What's the engineering theory on anchor riding sails? Untethered and adrift, a boat will sit roughly broadside to the wind, not point-up like a weather vane. Hunting/dancing at anchor is caused the anchor restricting that tendency. I can see where a sail placed well aft would change the natural wind/hydro induced orientation of an adrift boat, but is the effect a token amount or a meaningful amount? And how would one know?

It was easy to see the effect with our boat. When it was up, at anchor, we couldn't look out the window and see our view changed 90 degrees every couple of minutes!

Seriously, it kept our sailboat pointed into the wind at anchor, and eliminated the yawing back and forth it did without it.

The problem, was that the thing was a lot more trouble to put up and take down, than I ever thought it would be. That might not be true on another boat.

My wife liked it more than I did. Because she never had to put the thing up!

 

[drf6]

We made a triple clewed steadying sail for our Pilgrim as it tacks around at anchor like crazy. It seems to dampen the action a bit but nothing will keep a Pilgrim from hunting other than being tied up at a dock. It would help if the mast was set further aft. We couldn't figure out an arrangement to have it attached to the back stay and be high enough to be above the fly bridge.

The "wings" fold flat against the sail when using it solely as a steadying sail while underway. It helps dampen the roll a bit.

 

[MurrayM]

We got surprised by a wind shift one day and had about 25 knot winds at anchor.

The bounce & yoyo effect described in the OP was very pronounced putting a big jolt on the anchor, which thankfully never moved.

I had previously put a long boom off our mast onto which a boat trailer hand winch was placed to raise our dinghy on the swimstep. This gave something to attach a small folded rain tarp onto.

The final size of the riding sail was about 4' long, 2' tall at the front and a few inches tall at the back. We still swayed side to side, but quite a bit less and it completely eliminated the bounce on the rode.

The two 'fins' of the FinDelta would make it work even better.

 

[MurrayM]

Here's some photo's showing the boom and the 'emergency' riding sail: (sorry...having issues with main computer & photos...couldn't find a closer one showing boom)