Rudder "breaks loose" at high speed

S

SAILWRITER

Member
I took the Sunfish out for a couple hours at Gulfport Yacht Club today. Great breeze from the south. Some holes in the wind, but gusting to near 30. Average around 18.
I love this stuff and do well in it.
But, on a reach in the big puffs, while really going fast, the rudder 'breaks loose," cavitates.
I tried the usual quick stab to leeward with the tiller to reattach flow.
I checked for weeds.
I let the main out some more, but that only slowed me down, of course.
On a normal fast plane, no problem.
At "hyperspeed", problem.

New out of the box rudder. Lower boom set at 24", as far as I usually put it in a blow. Boom held down with the main halyard.
Hiking out. I suppose flattening the boat would get rid of some weather helm. But I'd need a trapeze in those conditions!

Any other suggestions?
I hate to round the leading edge of the rudder more, as it is brand new.

Anybody out there solve this?
Or is it just a fact of Sunfish life.

Dave Ellis
79301
 
No comments, eh.
Maybe nobody else has gone so fast!?

I think it is a factor of the boom being way off to the lee side, by design, and high winds makes for weather helm.
At considerable speed the rudder loses its 'bite'.
I'll just deal with it.
Dave Ellis
 
I think people are still speechless at the wind gusts. That is the crosswind gust limit for my 130000 pound airplane! Anyway, as you mentioned, the rudder must be stalling, and with the hydrodynamic force that must be on it, who knows if there is a fix. I suppose, like our plane, there is a high speed stall number as well as a low speed. I'd be interested in what other extreme winds other members sail in
 
I come from a higher performance sailing background, starting with Suicides back in the day, then Flying Dutchman, Contender, Windmill and finally a Raider Turbo.
Recently got back into the Sunfish after twenty years away. Getting older (68) but can still sail this little boat.
Somebody said that they race in higher winds than most boats. I can see how.
But it must be Windward / Leeward courses.
Reaching is not real safe in that kind of wind.
Ironically, jibing was no problem. Just pick a good wave.
Go figure.
Dave Ellis
 
Well ,

I respect your skills in the high winds - to all folks in the thread . A stalling foil though - it would seem some things ought to be put on the table...

1. Is the rudder deforming under high speed pressure?
2. What about a more robust high speed rudder?

I'm currently designing a shallow draft rudder and frankly like playing with different foil profiles. Strictly amateur here folks but it would seem that a high speed rudder would be the answer here. Sure it might have issues at low speeds but on those robust gusty days you just may need a higher performance foil.

They are so darned easy to make its worth a try to give it a shot. I profile the foil with a random orbital sander with 60 grit sandpaper. Birch plywood is fine but there are numerous ways to go about this. I use west systems or MAS EPOXY and no lighter than 4 oz. glass and heavy reinforcement on the leading edge.

This could be a lot of fun. Personally I wonder if your rudder is beginning to twist under pressure. All fixable anyway.

Pete
 
Yes, I put the rudder on the boat while on the trailer here in the back yard. If I tie the tiller off to a tree and twist on the bottom of the rudder blade the liller gives a little, but the blade also twists. It is enough to notice. Obviously, it takes a bit of ooomph to make it happen. Just as a high wind reach does.
On the Suicide until the 1960s everybody had their rudders under the boat about four feet from the stern of the 22' boat. Never had any problem. End plate effect and all that.
I put my rudder on the back of the boat in the 1980s (with a push me pull you set of rods that went from a quadrent at the rudder to a quadrent at the forward tiller position, otherwise it would be an eight foot tiller.)
The first rudder 'broke loose' quickly at speed and was totally useless. I copied a Flying Dutchman rudder and had no more trouble.
On my Marstrom A-Cat there were two rudders (duh) and they never broke loose at a lot faster speeds than the Sunfish.
So, it is what it is. The Sunfish is beautifully designed to do what it is supposed to do.
I plan to just sail it as close to its potential as I can, with stock equipment.
Dave Ellis
 
A few years ago, the Class had a serious discussion about a new, or modified, rudder that would have more 'grip' on the water (my layman's term). Tests by long-term racers showed that the modified rudder did lessen pressure on the board when reaching and the tendency to head up. But it was decided not to allow this modified rudder so as to prevent extra expenses. And we do know that many Sunfishes are owned by less than wealthy people...
 
Oh, yes, we don't need any more expensive "upgrades."
A new style dagger board and a new 'glass rudder and a new sail, oh, and a new tiller and a ratchet block and fancy line and a carbon tiller exrtension.
Add it up and it costs about as much as I paid for my 2005 Sunfish. With Sietech dolly.
Its a Sunfish.
I'll enjoy it as it is.
See you at the old fogey, er Masters in a few weeks.
Dave Ellis
 
SAILWRITER said:
"...But, on a reach in the big puffs, while really going fast, the rudder 'breaks loose," cavitates. I tried the usual quick stab to leeward with the tiller to reattach flow..."
Click to expand...
As my screen-name suggests, I prefer light winds, so maybe I can't be very helpful.

When I was last caught "out" in extreme winds, my Sunfish mast snapped-off six inches above the deck!

There could be variables to account for this cavitation, and perhaps that's why the similar and popular Phantom has a different design of rudder. To be certain that's the problem, you could fashion an anti-cavitation plate—like outdrives/outboards have. Try it with the old rudder, of course.

Could it be the weight of boat+captain?

(Trying not to get personal! :p)
 
Yes, a cavitation plate that would keep air from migrating down the rudder would work.
But again, its a Sunfish!
You are 'talking' with a guy who has designed, built and modified sailing craft for 60 years. My pram had a bowsprit and jib in 1950.
But, now it is time to just go sailing, and racing, on a one-design.
185# is a bit much for a Sunfish, but not extremely so.
In the 1989 (?) Sunfish Masters Worlds in Clearwater I was leading by eight points after windy races. Only to lose in the last drifter race that was shortened to three legs. Got 18th in that one with small Linda Tillman winning it. Dropped me to third. Then when the trophies were given out, third was a brand new white sail. Whooohooo. Sold the boat then and just now getting back into the class. Same weight. Same light air problem.
Dave Ellis
 
Linda T is one tough lady in light air. She still is
:) Of course, hubby knows a bit about sailing as well.
 
Not the same gal.
Linda Tillman sails the Sunfish. Her husband Dick Tillman (yes, THE Dick Tillman) has sailed Lasers and Sunfish (and J-24, etc.) forever.
They are both excellent sailors and now in the Great Grand Master catagory.
It is always a pleasure being on the same waters with each of them.
Dave Ellis
 
I have taken my Phantom out in wind conditions mentioned here with no rudder problems. As LVW said, the rudder design is different from a Sunfish. Also, the hull is wider and flatter than a Sunfish. There are other considerations that may not make this a good data point. The rudder I was using was not an original. It came with the boat, but I cut it down and reshaped it close to the original design. I try to avoid high wind speeds because one time, with gust close to 30, the deck seperated from the hull in three places. I'm interested to see how my Viking will do this year (it's closer in design to a Sunfish)
 
Back to the original topic of this thread, unless the rudder blade itself is defective (warped, deformed etc.) I have to think that the problem is weather helm, and the resulting angle of attach problem is causing the rudder blade to go into a high speed stall and loss of steering control. The usual fixes are: blade out the mainsail with tight outhaul and cunningham. Move the gooseneck back to as much as 20" from the intersection of the boom and gaff. Use your halyard over the gooseneck to boom vang the boom down. Hike harder but ease/feather the sail as needed. The idea is to get the hull moving faster with less heel allowing you to keep the tiller mostly centered. Weather helm is a vicious circle of event. The more weather helm you have, the slower you go and the more weather helm you generate. Sailing may be the one sport where the faster you go, the more you are in control. Odd, huh?

Alan Glos
Cazenovia (awaiting yet another snow storm.)
 
Thanks for the reply.
Be aware that all these suggestions were used, and is what any high performance boat sailor would have to know.
While it is known that it is weather helm that causes the rudder to "load up", I have come to the conclusion that there is no way to negate the effect completely on a Sunfish.
I'm running the Midwinters of the Flying Dutchman and Contender classes this weekend. I've owned and campaigned both of these boats in the past. No problem with weather helm when the boat is set up coreectly. As a matter of fact, I capsized more often to WINDWARD in the Contender when a wave suddenly induces a LEE helm when trapeze reaching.
But the Sunfish has the boom WAY out to leeward simply due to the lateen rig configuration, even when the boom is set 24" aft at the mast. Blade the sail out as much as you can and it is still rather full. I pull down on the boom really hard (vanging) but there is still some twist. I hike my 185# flat out from the back of the cockpit. I have a brand new, glass rudder.
Weather helm still there in the gnarly gusts.
It is just the way things are.
Today I sailed along with a bunch of Contenders practicing for tomorrow's first day of the regatta. Winds 16 - 25 mph. No problem with the rudder breaking loose. I once had to 'stab' the tiller down to re-attach. But that worked great.
It is just in the above 25 mph gusts of the other day that the problem occurred.
Rumor has it that no RC would set reaching legs in that stuff anyhow.
Hmmm.
I think I would, just to watch the show.
eh eh
Dave Ellis
 
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