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roll reducing fins-a long post


richarddalaska
 

We have completed the installation and initial testing of roll reducing fins (aka roll chocks or bilge keels) on Lilliana. Since this topic has been of interest I will give a report from our initial test drive and overnight anchoring experience. I have uploaded several photos of the fins. They are i an album labeled “Liliana" in the photos section of this site.

cost: the materials cost was $1010 . this was dominated by 9 gallons of epoxy ($812). I could have used polyester for half that cost.
Labor was $1700 which covered one master fiberglass person and his assistant working for almost 5 weeks. They typically worked about four hours each day because the epoxy required curing time after application. 

Construction: Each fin is made from two shaped pieces of 3/4” plywood epoxied together. They are covered with three layers of fiberglass and attached to the hull with thickened epoxy and 3 or 4 layers of fiberglass tabbing. They feel very sturdy. Total thickness is slightly less than 2”. The outboard edges of the plywood were beveled to a 1/2” radius. The bevel extends about 2.5”. With hind site I wish I had made them knife edged because after covering with fiberglass the edge is probably about 7/8”. Sharper is better to encourage turbulence upon rolling.The fins are about 11” wide and 12ft long.

The most difficult part of construction is matching the curve of the hull such that fore and aft lines on the fins are parallel to the water and the outboard edge needs to be parallel to the center line of the keel. This is done to minimize drag as the boat  moves though the water. A more sophisticated shape would have the fins curved and following a streamline. However knowing the streamlines requires a sophisticated computer analysis. Luis Soltero (from the Trawlers and Trawlering site) had such an analysis performed for his non-willard hull. That analysis shows that toward the center of the hull the streamlines are not very curved. So I concluded that straight fins would be satisfactory.

Initial test: Since launching Lilliana, we went out for a test drive and overnight anchoring in a bay that would be open to moderate but short swell on the beam. I can make only qualitative comments on performance because there is no practical method to compare the motion with and without the fins.
1. The boat feels noticeably stiffer. When passing a side wake the roll is not very large and recovery is rapid. No  underdamped rolling. 
2. At anchor with beam-on waves of period near 3 or 4 seconds the rolling seems less than normal but the more rapid recovery makes for a larger deceleration. Some people might prefer more roll but slower recovery. Note that since the natural roll period of a W40 hull is about 3.5 secs. this is the worst possible type of beam sea at anchor.
4. Underway in moderate conditions, about 15 knots of wind and beam sea of about 2ft at 3-4secs, there is still considerable rolling, although it seems less than without the fins. The  only real measure of the fins effectiveness is to observe after  considerable cruising if we use the paravanes less than without the fins.
5. While rolling at anchor I could observe turbulent upwelling at the water's surface. This indicates that the flow perpendicular to the fin edge is turbulent, which is exactly what we want. The turbulence transfers the  energy in the rolling hull into eddies in the water.
6. Underway in beam seas there is an occasional thump that is felt under the hull. A friend with fins on a similar hull noticed the same effect. This may be caused by trapped air under the fins collapsing, or possibly trapped water making a sort of water hammer.
7. I anchored again in a spot with a longer period swell. Here the rolling was clearly less than normal. The sea of Cortez is a particularly nasty place regarding rolling and pitching because the typical waves come at 3-4 secs intervals On the ocean the wave period is at least three time longer.
8. I could detect no difference in the boat's steering characteristic. Backing out of our slip requires a a 90 degree turn to port in a fairway about 80ft wide. I could make that turn using the usual “bump and stop” technique. The boat's speed at 1650 rpm seems unchanged. So I am guessing that fuel consumption will not be noticeable changed. Note that the forward cross section of the fin is only 1/12 of a sq. ft and is tapered. That is much smaller than the area of a paravane. The surface area of the fin is a small fraction of the surface of the hull. The main drag would come from any change in turbulence in the stern wave. 

I want to mention that Luis Soltero gave me invaluable advice and encouragement on this project. I hope he will write up his experience with roll reducing fins for some boating publication.

These are just my first impressions of the roll reducing fins. My opinions may change when we use the boat more. At present due to the extreme (for me) heat we won’t be doing much boating until next winter. I can’t imagine how you boaters on the East Coast, especially south of the Chesapeake, can survive the summer.. I understand why so many people have air-conditioning on their boats.  

Richard



--
Richard P
Willard 40 -Lilliana-Sea of Cortez, Mexico
Willard 30- Puffin- SE Alaska
Tiffany Jayne 34-sailboat- Dancer- SF Bay


Sven
 

Hi Richard,

I just revisited your message after a night that saw us tear the lines in both our Magna flopper-stoppers while at anchor.  The flopper-stoppers are of unknown age so the lines were probably weakened but the rolling in the anchorage was perfectly tuned to LAGOM at about 3-4 seconds,  often broadside due to tidal currents.  Before the tearing the lines showed no signs of parting and the rest of the lines don't look bad at all.

Right now it is just a random musing but what I'm wondering is what adding a 2' deep keel to our 40' PH might do.  To keep the keel from interfering with lift-straps would limit the length to just under 15',  overall.  The drawback of a 6' draft would probably be easily justified by a more seakindly motion.  The rolling is really the only thing we don't love about LAGOM.  Assuming a 2' keel entry at the bow we'd be adding 54 square feet to the wetted surface which is not negligible but probably not a huge deal compared to the dynamic drag of wave action.  The design should be a lot easier than your bilge keels,  but again,  we'd be adding draft.  In the Bahamas the draft would matter more than here on the west coast.

It would be strange to once again have a sailboat's draft,  but if it would make LAGOM more seaworthy and comfortable it sure would be wonderful.



-Sven


Pease, Dan
 

Assuming that you will be ballasting that additional 2 feet of draft, that may "quicken" or shorten the roll period, possibly to the dreaded "snap roll" effect.
Remember, a sailboat has a tall mast which dampens the motion.
This is one reason why people don't typically just turn sailboats into trawlers, they motion becomes uncomfortable after removing the mast .

Dan

On Sun, Aug 16, 2020, 23:03 Sven <southbound@...> wrote:
Hi Richard,

I just revisited your message after a night that saw us tear the lines in both our Magna flopper-stoppers while at anchor.  The flopper-stoppers are of unknown age so the lines were probably weakened but the rolling in the anchorage was perfectly tuned to LAGOM at about 3-4 seconds,  often broadside due to tidal currents.  Before the tearing the lines showed no signs of parting and the rest of the lines don't look bad at all.

Right now it is just a random musing but what I'm wondering is what adding a 2' deep keel to our 40' PH might do.  To keep the keel from interfering with lift-straps would limit the length to just under 15',  overall.  The drawback of a 6' draft would probably be easily justified by a more seakindly motion.  The rolling is really the only thing we don't love about LAGOM.  Assuming a 2' keel entry at the bow we'd be adding 54 square feet to the wetted surface which is not negligible but probably not a huge deal compared to the dynamic drag of wave action.  The design should be a lot easier than your bilge keels,  but again,  we'd be adding draft.  In the Bahamas the draft would matter more than here on the west coast.

It would be strange to once again have a sailboat's draft,  but if it would make LAGOM more seaworthy and comfortable it sure would be wonderful.



-Sven


Peter P
 

Sven - surprised to learn you lost not one but two flopper stoppers. I lost one several years ago at Cojo Anchorage, beneath Pt Conception near Santa Barbara. I don't recall what parted - could have been a knot, but I don't recall. Took me a while to find a replacement as they were made by a guy in the San Diego area (long since out of business). 

What's your best thinking on the point-loads and stressing? I am re-designing my flopper stopper pole setup as we speak and am curious why yours broke.

Peter
--

M/V Weebles
1970 Willard 36 Sedan Hull #40

Ensenada, MX


Sven
 

Hi Dan,

No,  I see no need for ballast.  We have no sail/mast so no need for additional righting moment,  unless we turn turtle :-)

I just want 28 sq. feet of flopper-stoppers permanently mounted under the hull.  Our Magma flopper-stoppers are 5.5 square feet each but the moment arm is almost 17' with the paravane outriggers out.  So 5.5 times 17 gives 93.5.  If I assume the rolling axis is one foot under the waterline (does anyone here know where it actually is ?) that means that the 28 square feet would be on a moment arm of 4 feet or 28*4 which equals 112.  

We do have two flopper-stoppers but each one is only active when pulling up so the keel would have more rolling resistance than the flopper-stopper by almost 20%.

Dang,  I'm almost talking myself into a keel !!



-Sven


Pease, Dan
 

I'd hate to lose your draft advantage.

How about this?

On Mon, Aug 17, 2020, 11:31 Peter P via groups.io <pete_pisc=yahoo.com@groups.io> wrote:
Sven - surprised to learn you lost not one but two flopper stoppers. I lost one several years ago at Cojo Anchorage, beneath Pt Conception near Santa Barbara. I don't recall what parted - could have been a knot, but I don't recall. Took me a while to find a replacement as they were made by a guy in the San Diego area (long since out of business). 

What's your best thinking on the point-loads and stressing? I am re-designing my flopper stopper pole setup as we speak and am curious why yours broke.

Peter
--

M/V Weebles
1970 Willard 36 Sedan Hull #40

Ensenada, MX


Sven
 

Dan,

It was Richard's post about his bilge keels that made me pick up his thread.  Since we've lived with keels almost forever it doesn't seem like that big a loss,  but it is still somethiung to think about.



-Sven


Richard A. Miller
 

The hull naturally wants to settle down length-wise in the trough of any waves.  A spring on the anchor rode can be used to change the orientation of the boat in the water so that the bow faces into the waves and rides over them.

Richard Miller,
W40FBS ADRIA

On Aug 16, 2020, at 10:03 PM, Sven <southbound@...> wrote:

Hi Richard,

I just revisited your message after a night that saw us tear the lines in both our Magna flopper-stoppers while at anchor.  The flopper-stoppers are of unknown age so the lines were probably weakened but the rolling in the anchorage was perfectly tuned to LAGOM at about 3-4 seconds,  often broadside due to tidal currents.  Before the tearing the lines showed no signs of parting and the rest of the lines don't look bad at all.

Right now it is just a random musing but what I'm wondering is what adding a 2' deep keel to our 40' PH might do.  To keep the keel from interfering with lift-straps would limit the length to just under 15',  overall.  The drawback of a 6' draft would probably be easily justified by a more seakindly motion.  The rolling is really the only thing we don't love about LAGOM.  Assuming a 2' keel entry at the bow we'd be adding 54 square feet to the wetted surface which is not negligible but probably not a huge deal compared to the dynamic drag of wave action.  The design should be a lot easier than your bilge keels,  but again,  we'd be adding draft.  In the Bahamas the draft would matter more than here on the west coast.

It would be strange to once again have a sailboat's draft,  but if it would make LAGOM more seaworthy and comfortable it sure would be wonderful.



-Sven


Sven
 

Richard,  the springline works if you are being turned by the wind or waves.  If you are being turned by the shifting wind and shifting tidal currents it is not so easy.

We have had times when the anchor rode is actually running down behind us,  maybe 130° from straight ahead.   You see that even more if you are in an estuary.  When we were on our sailboat down in La Paz the non-intuitive movement and heading out in the anchorage was referred to as the Malecon Dance.  I get a headache when I try to figure out how the current and wind are teaming up that way.



-Sven


Richard A. Miller
 

The Willard 40 was designed to carry a mast and boom used to lift a dinghy on and off board, to fly a steading sail, and provide antenna and flag halyard mountings.  If you don’t have a mast, it has been removed.  That will be a contributing factor in your discomfort from roll.

Richard Miller W40 Adria

On Aug 17, 2020, at 12:31 PM, Sven <southbound@...> wrote:

Hi Dan,

No,  I see no need for ballast.  We have no sail/mast so no need for additional righting moment,  unless we turn turtle :-)

I just want 28 sq. feet of flopper-stoppers permanently mounted under the hull.  Our Magma flopper-stoppers are 5.5 square feet each but the moment arm is almost 17' with the paravane outriggers out.  So 5.5 times 17 gives 93.5.  If I assume the rolling axis is one foot under the waterline (does anyone here know where it actually is ?) that means that the 28 square feet would be on a moment arm of 4 feet or 28*4 which equals 112.  

We do have two flopper-stoppers but each one is only active when pulling up so the keel would have more rolling resistance than the flopper-stopper by almost 20%.

Dang,  I'm almost talking myself into a keel !!



-Sven


Richard A. Miller
 

Very interesting!

Now I know why I enjoyed the East Coast so much.  Never had to face such conditions!  And had lots of sheltering options.

Richard M 

On Aug 18, 2020, at 1:28 PM, Sven <southbound@...> wrote:

Richard,  the springline works if you are being turned by the wind or waves.  If you are being turned by the shifting wind and shifting tidal currents it is not so easy.

We have had times when the anchor rode is actually running down behind us,  maybe 130° from straight ahead.   You see that even more if you are in an estuary.  When we were on our sailboat down in La Paz the non-intuitive movement and heading out in the anchorage was referred to as the Malecon Dance.  I get a headache when I try to figure out how the current and wind are teaming up that way.



-Sven


Sven
 

On Tue, Aug 18, 2020 at 12:22 PM, Richard A. Miller wrote:
Now I know why I enjoyed the East Coast so much.  Never had to face such conditions!  And had lots of sheltering options.

Dan and Kika on Uma talk about the problems with wind versus currents in the first couple of minutes of their latest Sailing Uma episode,  from the Netherlands:

https://www.youtube.com/watch?v=R9_JX_0xh6M

We definitely envy you the East Coast archipelago !


-Sven & Nancy



PS  Sailing Uma is the only video blog we follow religiously,  especially now that we are no longer sailing ourselves !