Renegade-27

Rudders and roundup

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15 minutes ago, 10thTonner said:

A little weather helm actually is faster! At about 3 to 5 degrees rudder angle, the increased drag is more than compensated for by sailing higher, so there’s your best VMG. Boats that are absolutely neutral usually don’t go to windward very well. 

Bullshit.

Driving around with the brake on is faster you say.  Mmmmm

The fastest VMG is when the boat is balanced on both foils.  But you go with 5 degrees, I'll drive over the top of you.

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33 minutes ago, 10thTonner said:

A little weather helm actually is faster! At about 3 to 5 degrees rudder angle, the increased drag is more than compensated for by sailing higher, so there’s your best VMG. Boats that are absolutely neutral usually don’t go to windward very well. 

I agree with the 1st & last sentences in the quote, but the middle one could be a little different.

Weather helm means that the rudder & keel (or centerboard) are sharing the loads, so any increase in rudder-drag also involves a decrease in keel drag. Since the induced drag is a nonlinear function of the load, this sharing results in a net benefit. However, induced drag is only part of the total, so other factors can mask the benefit (or even negate it).

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I'd like to hear more discussion on how hull shape effects (affects?) round up tendencies. Might learn something.

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2 hours ago, astro said:

Bullshit.

Driving around with the brake on is faster you say.  Mmmmm

The fastest VMG is when the boat is balanced on both foils.  But you go with 5 degrees, I'll drive over the top of you.

A few degrees weather helm can be faster.  Depends on the boat.  It's also a lot easier to drive with a bit of helm, most drivers do better with a few degrees of rudder angle and a bit of pressure on the helm to react against.

The J120 is notorious for having lee to neutral helm in light air upwind.  To give the skipper feel, I used to crank the shit out of the backstay in light stuff upwind and then the runners to keep the main full and we would ease a few turns off the forestay before the race if the forecast was light to keep the jib luff with a bit of curve.   We would toast all the other J120s upwind in light stuff.  Getting a bit of pressure on the rudder by pulling the sailplan aft made a world of difference.

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3 hours ago, 10thTonner said:

A little weather helm actually is faster! At about 3 to 5 degrees rudder angle, the increased drag is more than compensated for by sailing higher, so there’s your best VMG. Boats that are absolutely neutral usually don’t go to windward very well. 

Totally agree.

Trouble with lee helm is that the rudder works against the keel (keel exerce force toward windward whereas rudder toward leeward) increasing load on keel hence total drag.

If helm is neutral, at times you will have to actually push (rather than let go) toward leeward hence slow down the boat.

OK, that's my theory but I think that you should be able to steer only varying how much you pull the tiller with the tiller as lightly loaded as possible.

So in short, IMO to be fast, the boat should be set up with just enough weather helm so that it climbs slowly to windward when you let off the tiller. For self steering, you need to be able to somehow lock the rudder.

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On 7/24/2020 at 7:27 PM, Kenny Dumas said:

A non-obvious relationship is that displacement hulls turn opposite the direction they lean. That’s what generates the weather helm. Exactly opposite a planing hull or surfboard 

Say what?

 

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I think the rutter should be in line with the keel. And should share the lift-load so it’s not just drag. That means the helm is amidships but has some pressure on it and will head to weather if let go.
 

My outrigger canoe mast tilts fore and aft and the steering oar lifts clear out. It’s magic when balanced. 

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2 minutes ago, KC375 said:

Say what?

 

I did. Non-obvious. Try it under motor on a calm day 

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It's complicated. The keel is operating in a few degrees of flow because the hull is necessarily making a few degrees of leeway. Otherwise, with no angle of attack, it would be doing nothing of use except counteracting heeling. The rudder is operating in the lifted flow from the keel. So to be neutral in that flow it will be angled a few degrees to windward. As noted above, a centered rudder is likely contributing unhelpfully to leeway. The keel is automagically at a beneficial angle of attack due to the hull making leeway. The rudder is in the water making drag so one might as well make it do some work by giving it a few more degrees angle of attack. This also means the underwater center of lateral resistance is between the keel and rudder where the designer intended it to be...everything behaves better. Works out to 5 to 10 degrees of windward helm.

Of course it all depends on everything else, too.

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1 hour ago, Bob Perry said:

I'd like to hear more discussion on how hull shape effects (affects?) round up tendencies. Might learn something.

It was always my understanding that a flat bottom on a boat + very curved sides (a wider boat) increases the amount a hull would want to head up as the boat heels due to the curved section being in the water on one side and the flat section on the other side.  But you probably know a hell of a lot more about it than I do.

How much affect the location of the sail plan, rudder, and keel center of efforts change as the boat heels probably complicates the whole thing way beyond my simplistic thinking.

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1 minute ago, Kenny Dumas said:

I did. Non-obvious. Try it under motor on a calm day 

Yes but you said  " A non-obvious relationship is that displacement hulls turn opposite the direction they lean.... Exactly opposite a planing hull or surfboard"

All the planning hulls I've sailed (limited to a fairly large number of dingies) turn to port when heeled to starboard...which is the same behaviour I've experienced with keel boats.

I'm no expert surfer (actually I'm very bad) but on both my windsurfer and my not very impressive surfing efforts the turn to starboard while heeled to starboard is a function of the rotation applied to the board by my feet. 

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1 hour ago, Bob Perry said:

I'd like to hear more discussion on how hull shape effects (affects?) round up tendencies. Might learn something.

That must be a complicated subject. As the boat heels the sail effort goes to leeward. On most hull's the drag probably follows that to leeward as well. But the keel and rudder drag goes to windward. The hull at speed has considerable shape-induced downforce which rotates to windward. Depending on where that downforce is longitudinally there will be some turning tendency.

??

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KC:  Fair enough. Maybe at low speed they’re in displacement mode . But water skis and surf boards clearly carve turns. I regularly steer my flat bottom skiff like a ski at low and high speeds with weight trim. 

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El B:  I don’t see the lifted flow from the from the keel any more than a lift from a boat directly in front of me. And 5-10 degrees of helm is slow. 

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15 minutes ago, El Boracho said:

That must be a complicated subject. As the boat heels the sail effort goes to leeward. ... 

This becomes incredibly more complicated if you are trying to understand the dynamic effect  - like the forces and center of effort changes when hit with a gust.  

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4 hours ago, 10thTonner said:

Boats that are absolutely neutral usually don’t go to windward very well. 

Hell of a lot better than one with 20deg of high load.

Trying to make the point that you should be able to, I agree a a little rudder lift is optimal.

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4 minutes ago, Kenny Dumas said:

El B:  I don’t see the lifted flow from the from the keel any more than a lift from a boat directly in front of me. And 5-10 degrees of helm is slow. 

When the keel is operating as a foil it definitely turns the flow. What the rudder feels depends on speed and how far back it is. Rudders are usually more efficient than somewhat stubby and bulky ballasted keel foils so therefore may operate at higher angles of attack.

Carrying a few degrees of windward helm in a breeze was SOP on the keelboats I raced. It is so taught in the racing texts. I should have said 3-7 degrees of weather helm...I was visualizing my wheel position vs. a tiller...

 

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Are we confusing weather helm with rudder angle? 

On the wind most boats will show a few degrees of rudder angle to weather at their neutral balance point, something to do with leeway and waterflow over the hull I imagine.

As a helmsman it is usually faster to drive the boat down slightly for speed and come up with the apparent. Having a little helm load greatly assists with this, its an art.

We are talking a few degrees max and minute loads and movements, with tiny adjustments to the main, the subjects boat is running at 20deg with a gorilla hand, the problem is not the rudder.

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1 hour ago, Bob Perry said:

I'd like to hear more discussion on how hull shape effects (affects?) round up tendencies. Might learn something.

I have tried to figure out why this rudder sucks air at high speeds. The bottom of the boat along the center line is real flat. Once the bow section ends at it's curve it is flat to the keel. Then the flat carries back after the keel.

Back in the 70's and early 80's many boats had this forward of the pivot point to help balance the rudder. No doubt it is still in use today but not in such extremes on high performance boats. After viewing the shots, I can (having sailed the boat and talked to the previous owners) only think that when the boat is powered up on reaches and the boat heels a bit. The driver pulls a bit of helm, the forward section of the rudder grabs air and control is lost as the rudder ventilates.

When I talked to the previous owner, he said that at times when on high speeds, sometimes the rudder would just lose grip and the boat would spin out. But always at high speeds. So I can only guess it is the balance part of the forward rudder that grabs air because it jets out pretty far.

The photos are linked because the are hi res.

Flat front end

Balanced rudder

Fat rudder head

This shot really shows how flat the bottom is. Taking pictures from a wheelchair is difficult at best. Notice how they all aim up. :)

When I look at the rudder, it does seem to be a bit far from the transom. The previous owner said you could not turn the rudder hard to maneuver in tight spots so I think he made new mount points farther back. I do know that when we get up on a big wave and start flying, the forward part of the keel becomes exposed, it's almost like ice skating.

Here is something I do not have online. It shows some design info.

746467849_designinfo.thumb.jpg.f6e5edca20604907785c362f22d04620.jpg

So to wrap it up, I got a template from a new rudder made for a Pocket Rocket. It needs to be lengthened and widened. but it is pretty nice looking. I'm not sure this will help.

 

Flame away.

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Bob:  I’ve always thought of it as bow steering from submerging the big curved topside when heeled so should scale with beam. Maybe that’s why the hollow forward on the Tiger works?

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Back sailing Ensigns one design we would heel and hike the shit out of ourselves the more weather helm we induced by our methods and the boats all slid sideways up the windward legs.

A sailmaker from Louisiana sailed with us in ‘02 and we cleaned up the whole fleet on every leg because we sailed the boat dead flat as much as possible. I never sailed with any heel if possible from then on.
 By sailing with flat main and Genoa with the boom a little above centerline and pointing to the point of pinching, we could get the masthead over to the windward side of the boat and it would pull us up to weather while all the other boats were dragging around the old way.
From the start, if we didn’t get a great start, we could work up beside a windward boat from below and behind and take advantage of their leeward wind pressure and slip past them and then get quickly to windward and ahead to the next boat. Also, we would never fall off in a header. With 3,000pounds of full keel, the boat could continue though a header and when the wind shifted back for a lift, we were already there and would get higher and higher towards the mark. 
 

So, any weather helm,  in my opinion, is too much and induces drag and kills true pointing ability. 

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On my skiff, the bow is above water so maybe ski steering takes over?  I’ll put the GF in the bow to see what happens. 

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KC, yes, that’s exactly what I do. It turns towards the weighted side, which for sake of clarity let’s call ski steering. I’ll try weight forward and lower speed to see if it transitions to bow steering. 

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50 minutes ago, Kenny Dumas said:

Bob:  I’ve always thought of it as bow steering from submerging the big curved topside when heeled so should scale with beam. Maybe that’s why the hollow forward on the Tiger works?

I used the term hollow here once and was corrected by SJB and Bob to fine entry...

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48 minutes ago, Meat Wad said:

I have tried to figure out why this rudder sucks air at high speeds. The bottom of the boat along the center line is real flat. Once the bow section ends at it's curve it is flat to the keel. Then the flat carries back after the keel.

Back in the 70's and early 80's many boats had this forward of the pivot point to help balance the rudder. No doubt it is still in use today but not in such extremes on high performance boats. After viewing the shots, I can (having sailed the boat and talked to the previous owners) only think that when the boat is powered up on reaches and the boat heels a bit. The driver pulls a bit of helm, the forward section of the rudder grabs air and control is lost as the rudder ventilates.

When I talked to the previous owner, he said that at times when on high speeds, sometimes the rudder would just lose grip and the boat would spin out. But always at high speeds. So I can only guess it is the balance part of the forward rudder that grabs air because it jets out pretty far.

The photos are linked because the are hi res.

Flat front end

Balanced rudder

Fat rudder head

This shot really shows how flat the bottom is. Taking pictures from a wheelchair is difficult at best. Notice how they all aim up. :)

When I look at the rudder, it does seem to be a bit far from the transom. The previous owner said you could not turn the rudder hard to maneuver in tight spots so I think he made new mount points farther back. I do know that when we get up on a big wave and start flying, the forward part of the keel becomes exposed, it's almost like ice skating.

Here is something I do not have online. It shows some design info.

746467849_designinfo.thumb.jpg.f6e5edca20604907785c362f22d04620.jpg

So to wrap it up, I got a template from a new rudder made for a Pocket Rocket. It needs to be lengthened and widened. but it is pretty nice looking. I'm not sure this will help.

 

Flame away.

Looks like the original keel was replaced - I like the new one much better.  Those very short tipped keels King came out with in the late 70's sounded like a good idea, but the boats that had them never seemed to be stellar performers, although other factors may have come into play.  IMO the hull could use some more rocker.  The deepish forefoot reminds me of the Chance designed Tartan Pride 270.  Never seems to work that well on really light boats.

As you mention the extended gudgeons sets the rudder too far back IMO.  As you also mention, it has a really ft rudder head - I am guessing at least 2.5 inches  Assuming the front side of the rudder head is flat and with the notch set back 2-3 inches from the transom corner, that's a pretty wide brick being exposed to the water at speed.  But hard to tell without better photos of the detail there

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On 7/23/2020 at 10:30 AM, Renegade-27 said:

 Rudder goes over hard - at 30 degrees nearly always stalls - I try to keep it at 20 +/- but the boat often just flips through the wind.

Can you clarify - is that rudder angle or wheel angle? Depending on your gear/cable reduction there is a pretty big difference between the two. 

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My current boat came from factory (for various reason) with a rudder smaller than the designer called for. She used to round up / spin out like a demon even with aggressive easing of main sheets.

Most of the owners have replaced the rudder with one made by CCI that was designed by the the original NA and is 15% bigger in all plan directions.

The boat handles completely differently now much more stable with little (if any) change in speed potential and no rating hit.

It might be worth a try.

Lost

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On 7/23/2020 at 12:48 PM, Renegade-27 said:

Hi all - cruising boat/weekend racer here - a lifelong sailor with lots of experience.  I have a 35' 'production' boat shoal draft that I'm just not happy with its sailing characteristics.  Specifically, it rounds up constantly.  Other than alway pushing on how much sail we carry, I've come to believe this is because the rudder for this shoal draft version is cut short as well as stalls out easily even at 15 kts apparent.

What does the group think about replacing this with a deeper rudder to keep steering control in an upwind blow?

Also, is there more to it than depth and width?  Would I be able to use a well chosen rudder from a different boat - say a C&C110 rudder on a Beneteau 35?

The rudder depth could go from 4'9" to 6'... would this be enough of a difference to be worthwhile?

Who knows 

 

you haven’t posted a picture of your boat 

 

it’s hull form ...  extra wide stern ? 

 

Rudder distance  forward of the  stern chine

 

 

the rule is a rudder must always stay wet 

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On 7/23/2020 at 4:39 PM, lydia said:

Fuck, never sailing one design like Etcheels with some the people here!

But there's no reefing on an Etchells.

All you can do is tighten the uppers and lowers, shorten the fore stay, crank on some back stay, cunningham, out hual, and add vang to flatten the hell out of the main.  Then you have to ease the traveler and main in the gusts.   Of course this assumes you set up the mast step correctly.;)

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1 hour ago, svitale said:

But there's no reefing on an Etchells.

All you can do is tighten the uppers and lowers, shorten the fore stay, crank on some back stay, cunningham, out hual, and add vang to flatten the hell out of the main.  Then you have to ease the traveler and main in the gusts.   Of course this assumes you set up the mast step correctly.;)

isn't that what you're supposed to do, when your boat can't handle the wind velocity? :D   and don't forget to hike out..

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5 hours ago, bgytr said:

A few degrees weather helm can be faster.  Depends on the boat.  It's also a lot easier to drive with a bit of helm, most drivers do better with a few degrees of rudder angle and a bit of pressure on the helm to react against.

All weather helm does is that, give the helmsmen something to guide him.

Basic physics is that two foils inline are less drag than having one of them not.  The trade off is what is slower, a draggy rudder or a helmsman 'feeling' around for where the groove is.

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1 minute ago, astro said:

All weather helm does is that, give the helmsmen something to guide him.

Basic physics is that two foils inline are less drag than having one of them not.  The trade off is what is slower, a draggy rudder or a helmsman 'feeling' around for where the groove is.

Maybe.  If you are going in a straight line and don't require lift from the foils, then yes you have less drag if they are in line.  Assuming you are talking about upwind, then having the rudder operate in the wash of the keel can be more drag depending on the specifics of the boat, and the required rudder angle to achieve balance of forces.  Most designs, the rudder is partially clear of the keel wash upwind with the boat making 3-4 degrees leeway.

Yes it is definitely easier to steer with a bit of helm pressure from weather helm.

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If the rudder is loaded at the same angle as the keel (= leeway angle). Then it should have some feel / load when centered. Unless the keel changes the incident flow on the rudder, which is a good question. 

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1 hour ago, slug zitski said:

Who knows 

 

you haven’t posted a picture of your boat ...

 

This is it - not my hull, but I think the pic is pretty telling...

 

On 7/24/2020 at 2:43 PM, ryley said:

But here's me :)

IMG_1194 (003).jpg

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12 minutes ago, astro said:

 

Basic physics is that two foils inline are less drag than having one of them not. 

Yes two foils inline create less drag, but they also create less lift.

Are there no circumstances where this lift is beneficial?

I know some of the 12m AC boats had trim tabs on the back of the keel which increased drag but added lift on the keel.

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6 hours ago, Bob Perry said:

I'd like to hear more discussion on how hull shape effects (affects?) round up tendencies. Might learn something.

The unbalanced waterline would, I believe, create forces that push the boat to leeward.  Longer waterline on the low side - Bernoulli's principles - would create a vacuum there relative to the high side.  Whether that imbalance would create a net force toward the stern or bow resulting in a turning moment would be important and dependent on the two waterline shapes (?).  First principles.

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Here’s the scoop on the boat specs

25AE4DBE-5E57-4B62-960D-99B0751B54D9.png

7E42EE06-E31E-48D1-9BCB-69B1BBDAD0A1.jpeg

AFACD329-C945-4EAF-82F3-79B8FD51EFFF.jpeg

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22 minutes ago, astro said:

All weather helm does is that, give the helmsmen something to guide him.

Basic physics is that two foils inline are less drag than having one of them not.  The trade off is what is slower, a draggy rudder or a helmsman 'feeling' around for where the groove is.

It is basic physics that that drag you write of produces prodigious amounts of lift to windward. I.e. a good thing. And they are only "inline" in some perfect (boring) DDW situation.

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3 minutes ago, El Boracho said:

It is basic physics that that drag you write of produces prodigious amounts of lift to windward. I.e. a good thing. And they are only "inline" in some perfect (boring) DDW situation.

Weather helm has nothing to do with lift/drag other then it drags.

Edit: a foil can be in balance and have great lift.

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3 minutes ago, astro said:

Weather helm has nothing to do with lift/drag.

?? They all are intimately related.

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I'm injoying the novitiates instructing the abbot.

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18 minutes ago, Renegade-27 said:

 

This is it - not my hull, but I think the pic is pretty telling...

 

But here's me :)

IMG_1194 (003).jpg

Difficult to see the rudder position 

 

as you can see from the picture of this modern hull form , the designer has moved the rudder forward so that it stays wet when the boat is heeled and powered up 

7C43C543-27DA-4B7F-AE7D-765A82AD1CA4.png

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This should help understand the position of the rudder - along with my computer measurements to see how much deeper the other rudder is!  The rudder is right at the waterline.  The hull aft of the rudder is almost board flat.

image.thumb.png.918be605c03d8e6564a21c428c9a63e6.png

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I chartered a Sun Odyssey 35 about 15 years ago, and it was ridiculous about rounding up. I'm sure the blown out charter sails did not help, but it would round up even with a double-reefed main and full genoa from a broad reach. I suspect the wide stern, when heeled or lifted by a wave, would just lever enough of the rudder out of the water for it to suck air and lose effectiveness.

If it were my boat I would play around with mast rake, decent sails, etc., but given the severity of the problem, I think it was inherent in the design. The OP talks about 30-degrees of rudder angle -- how does he know it's 30 degrees if it has a wheel? or is it 30 degrees of wheel rotation? I don't recall extreme angles for the rudder, the helm would start loading up as the boat started to round up, and then it just gave up. 

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20-30 degrees as measured from my rudder position sensor part of the autopilot.

You can see relatively new sails - with the original sails it was virtually impossible to sail upwind at all.

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43 minutes ago, astro said:

Basic physics is that two foils inline are less drag than having one of them not. 

Actually just thinking about this again, this assumes that the boat is not making any leeway. If the boat is making leeway, then the keel is not aligned to the flow of water, and i would suspect that there is less drag if the rudder is aligned with the water flow rather than with the keel?

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26 minutes ago, El Boracho said:

?? They all are intimately related.

Weather helm, or too much of it, is telling you that the boat is unbalanced.

The amount of tells you how much drag you have. 

 

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3 minutes ago, JohnMB said:

Actually just thinking about this again, this assumes that the boat is not making any leeway. If the boat is making leeway, then the keel is not aligned to the flow of water, and i would suspect that there is less drag if the rudder is aligned with the water flow rather than with the keel?

See my post above.  Both foils should have lift going the same way regardless of the water flow.

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7 minutes ago, Renegade-27 said:

20-30 degrees as measured from my rudder position sensor part of the autopilot.

You can see relatively new sails - with the original sails it was virtually impossible to sail upwind at all.

At 20-30 degrees rudder angle, it has completely stalled and is in-effective. You need to ease the main and traveller well before you get there or head down in a puff.

a deeper rudder might help, but then first time you run aground you’re buying a new rudder.  

 

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I had a 35r first that had that same aft rudder position and even as deep as it was, that boat would round up if loaded and downwind it would be happy broaching all day if you weren’t careful.

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Symmetric foils like keels and rudders need some amount of angle of attack (e.g. 3 degrees) to generate lift, which typically appears as a bit of weather helm. Lift also induces drag, so it's all about maximizing lift while minimizing drag.   

But as noted above 20-30 degrees is certainly a stall, with no lift and lots of drag.  

https://en.wikipedia.org/wiki/Airfoil#/media/File:Lift_drag_graph.JPG

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8 minutes ago, astro said:

Weather helm, or too much of it, is telling you that the boat is unbalanced.

The amount of tells you how much drag you have.  A foil with a few degrees of weather helm has the lift going in the opposite direction than you seem to think it is.  Has low pressure on the lee side while the keel has it on the weather side.  Low pressure has to be on the weather side of both foils for speed.

 

 

That is absolutely correct. That’s the premise of the post I made earlier about keeping the boat flat. And by heeling the boat to windward at that point like a dinghy, the pressure is even lower on the windward side and actually vacuums that side in the form of lift to windward.

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20-30 degrees is a ludicrous amount of rudder angle.  I think that amount would be enough for the rudder to stall even if it is not ventilating. I guess at that point something went wrong when you only had a little bit of rudder angle, but then you start chasing the problem with more rudder angle until the whole thing just drags through the water and becomes useless. You mentioned that the mast had some rake. Try standing the mast straight up and see if you get anywhere. the JSO 35 is a nice looking boat, and we liked everything about it except its sailing characteristics in decent breeze. I hope you find a solution. It will probably need to be a combination of solutions, such as deeper rudder (maybe with a fence), less mast rake, reefing early (main first), etc. 

On boats with a tiller, I could get a chance at correcting a round up by putting the rudder briefly back to centerline in hope of re-attaching the flow, but I'm not sure you can react that quickly with a wheel.

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59 minutes ago, Renegade-27 said:

 

This is it - not my hull, but I think the pic is pretty telling...

 

But here's me :)

IMG_1194 (003).jpg

Your Genoa looks weird to me. Why is it so high up? The foot should be below the top lifeline. Also its  leech looks really tight to me whereas the foot doesn't.

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On 7/23/2020 at 10:30 AM, Renegade-27 said:

Jeanneau Sun Odyssey 35.  New(ish) sails with very good shape.  Experienced sailor.  Some rake back, adjustable backstay, bocks back for flat jib, leaches twisted off, traveler down, weight out of the bow, all of that. Rudder goes over hard - at 30 degrees nearly always stalls - I try to keep it at 20 +/- but the boat often just flips through the wind. I *do* try to carry too much sail but this is a poor sailing characteristic.  

I'd love to find a rudder from a full-draft JSO35, but they were imported from France at the time and almost all were spec boats with shoal draft.  I can buy one from the factory and have it brought over.  Seems like lots of places to get rudders made, but I'm also wondering how much difference 6-9" would make as well.

Pics of the main please.

 It develops a lot of weather helm with heel so the main has to be draft-forward(ish) and bladed. Once the draft moves aft on the main it creates a lot more weather helm...and you're screwed. 

 

 EDIT: I see the pics above. Looks pretty deep. Offshore cut? Anyway you get a flatter main it will help. 

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The roller furler is actually very high which gives cruisers better visibility (I am told :blink:).  Jib could be in better shape - although I can flatten it out, the leach is starting to develop a permanent curl.  Foot is pretty tight with the block in an aft posion.

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42 minutes ago, Renegade-27 said:

This should help understand the position of the rudder - along with my computer measurements to see how much deeper the other rudder is!  The rudder is right at the waterline.  The hull aft of the rudder is almost board flat.

image.thumb.png.918be605c03d8e6564a21c428c9a63e6.png

For obvious reasons

 It’s not recommended  to have a rudder deeper that the keel 

 

your boat is what it is 

I’ve sailed plenty of shoal draft boat and rounding up was not a big issue 

You might double check sail trim , headstay length and the position of the mast head fore and after 

 

a common rudder ventilation, loss of bite ,  issue is caused by an air breathing thru hull locate too close to the leading edge of a rudder 

 

 

 

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13 hours ago, spirit28 said:

We have a 39' Sun Odyssey - strictly cruising, but have the occasional fun race.  Compared to other boats I've had or sailed on, have found this one to be rather tender with a tendency to round up if hit by an unanticipated gust especially close reaching in 15+ knots.   Half the issue is the main sheet comes back to a cabin top winch which is under the dodger and you have to put your beer down to stand up and take it out of self-tailer to ease it out, but usually too late to to have any impact.

Wonder if the shape of the main contributes to round up/heeling effect :huh:  photo shows 10 year old factory supplied quantum with 1 reef in 20 something knots.   Yes the reef line was tight along the foot, but the longer the sail stayed up, the worse the stretching got.  Have a new main sitting in the garage waiting for summer with the old one now used as a drop sheet for painting.

 

 

1563518232_OldMain.thumb.png.bb0db8759b0f4cbbe8092434b9c090e6.png

The luff is full and the leach is bubbled ? 

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1 hour ago, Sail4beer said:

That is absolutely correct. That’s the premise of the post I made earlier about keeping the boat flat. And by heeling the boat to windward at that point like a dinghy, the pressure is even lower on the windward side and actually vacuums that side in the form of lift to windward.

You two (@astro) have lost the program. " Weather helm" is the positioning of the steering tiller towards the weather. That causes the rudder foil to generate lift in the direction of the weather. That lift being at the stern of the boat causes a leeward turning force. I.e. that tries to rotate the bow of the boat to leeward.

You can forget about vacuums and water pressures. Too esoteric. Just stick to forces. Foils generate forces when angled in a flow. They simply try to go the direction they are pointed. The drag and force increase in relative proportion until drag suddenly increases (shuddering), followed by lift vanishing (spinning), followed by the boat rounding up (swearing).

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2 hours ago, astro said:

Basic physics is that two foils inline are less drag than having one of them not.  

Do you know how to read?

I'm all but incompetent and barely have a second-rate third-grade education, and even and I can see the point, politely made by multiple people on this thread, that the foils can't be "in line" if you're making any leeway at all.

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Study some Farr designs:

Larger rudders than most

Intended rudder angle for optimum upwind: 3 to 4 degrees in the 10 to 20 tws range

Rudder contribution to total sideforce (i.e. leeway resistance) is around 40 to 45%

Design leeway around 3 degrees.

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11 hours ago, 10thTonner said:

A little weather helm actually is faster! At about 3 to 5 degrees rudder angle, the increased drag is more than compensated for by sailing higher, so there’s your best VMG. Boats that are absolutely neutral usually don’t go to windward very well. 

Yup 

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5 hours ago, Renegade-27 said:

 

This is it - not my hull, but I think the pic is pretty telling...

 

But here's me :)

IMG_1194 (003).jpg

Main leech looks really tight.

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8 hours ago, Sail4beer said:

I used the term hollow here once and was corrected by SJB and Bob to fine entry...

I may not be too bright, but I try not to forget!

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4 hours ago, El Boracho said:

You two (@astro) have lost the program. " Weather helm" is the positioning of the steering tiller towards the weather. That causes the rudder foil to generate lift in the direction of the weather. That lift being at the stern of the boat causes a leeward turning force. I.e. that tries to rotate the bow of the boat to leeward.

You can forget about vacuums and water pressures. Too esoteric. Just stick to forces. Foils generate forces when angled in a flow. They simply try to go the direction they are pointed. The drag and force increase in relative proportion until drag suddenly increases (shuddering), followed by lift vanishing (spinning), followed by the boat rounding up (swearing).

Except...

 

1BA663CB-16BC-4CB1-B58E-6B8301CBCE69.png

F94895D5-AE6A-48E1-A70B-CCBB1B0D25EA.png

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And the geeky evergreen I post whenever this subject comes up. 
 

If you can sail a boat like a dinghy, you’re going to win the Silver dish thingy...

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Hey Renegade, use that ME and fluids knowledge and add some water ballast. Strap a couple kayaks to the shrouds with some bilge pumps and hoses and make a modern Q ship. Take pics 

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1 hour ago, Sail4beer said:

Except...

 

1BA663CB-16BC-4CB1-B58E-6B8301CBCE69.png

F94895D5-AE6A-48E1-A70B-CCBB1B0D25EA.png

This image is correct in that it points out that the two vectors combine. It is incorrect in implying that they combine to form a perfectly straight-ahead vector - in reality, I'm pretty sure you still make at least some leeway in the vast majority of circumstance, as any comparison of true and apparent headings close-hauled will show.

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1 hour ago, Sail4beer said:

Except...

 

1BA663CB-16BC-4CB1-B58E-6B8301CBCE69.png

F94895D5-AE6A-48E1-A70B-CCBB1B0D25EA.png

Trimming the jib might help that vector diagram.

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12 minutes ago, Left Shift said:

Trimming the jib might help that vector diagram.

Watch that terrible embarrassing video twice and you won’t know how to sail anymore.

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3 hours ago, Sail4beer said:

Except...

 

1BA663CB-16BC-4CB1-B58E-6B8301CBCE69.png

F94895D5-AE6A-48E1-A70B-CCBB1B0D25EA.png

Except...

Sails create an applied (active) force while the keel generates a reactive force

A resultant force is a single force that applies the same effect as the original system of applied forces.

At constant velocity, the active and reactive forces cancel each other out (i.e. Sum of Active - Sum of Reactive = 0)

In that state, side force (sails) and lift (keel) are equal and opposite.  Same thing with drive (sails) and drag (all sources).

I won't get into the torque balancing.

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3 hours ago, Ncik said:

Main leech looks really tight.IMG_1194 (003).jpg

A lot going on here

That is full hoist? Main and Working Jib? To my eye, about the correct SA for a much smaller boat,,,,  Beautiful but also very tall dodger, short boom, sheeted in front of the dodger. Can you get to the travelor , easily/quickly? Vang = almost as far aft as the booms sheeting blocks. SA for the main = equivilent of 1+ reef to begin with before any shortening, kinda like a center cockpit boat. Why is the tack for the jib soooo high? And though many of us are advised to sheet in our jib leads as much as possible,  in this case you may want to try going outboard and back a bit, with the jib leads to open up the proverbial "slot" to aid flow and lessen turbulence between the main and the jib. It looks like you have so much to play with and have fun improving you boat's performance.

1. Stand the mast up, minimum rake like many have posted

2. You need MORE power!! Could you live with a smaller dodger or without it in nice wheather? Lower the gooseneck and add roach or maybe a fat top main?

3. You're sails look "strapped", too much halyard tension and leechs too tight even though the foot(s?) look good on each sail

4. Rethink your past understanding of where the power in your sails come from, Your boat is POWERED by the jib/genny, increase that SA and think of your main as trim. You may have a revelation or at least be pleasantly surprised by how much this will help with your helm.

5. You do NOT need an old style 150% decksweeper but a nice ~135 with a relatively high clew might do wonders re: overall balance, and with a fairly high cut clew, leave you acceptable vision forward, and you could keep the furler, (maybe just trick it out somehow, to get the tack down lower)

I love this thread, and my 2 cents are that the existing sailplan, for multiple reasons, is not balanced with the hull. I can understand why the OP is triming what he has, the way he is, but it seems to me like an underpowered rig trimmed and straped down for anticipated round ups , without giving room for possibly a larger range of more effective adjustments.

There is just so much here to have fun with!!!

 

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7 hours ago, slug zitski said:
18 hours ago, 10thTonner said:

A little weather helm actually is faster! At about 3 to 5 degrees rudder angle, the increased drag is more than compensated for by sailing higher, so there’s your best VMG. Boats that are absolutely neutral usually don’t go to windward very well. 

Yup 

There are some really stupid post on these boards.  This is one of them.

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I forgot to say that there is nothing sweeter than a nice balanced boat that can be sailed to windward fast, no effort, by watching the tell tails on the heady for direction.

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About hull shape and rounding up, try to imagine this

take a wedge of cheesecake, nice and flat on the plate - a perfect representation of the typical modern wide ass boat. Pointy bow, wide stern, rudder in the middle of the widest part.

now cant the wedge over 15 - 20 degrees and see what happens.

Your cheesecake is leaning on its bottom edge - which is pointing in a different direction than the 'centreline' of the cake! That direction is the opposite of the direction of heel - the result is instant round up!

Then look at where your rudder went - the middle of your 'transom' has lifted away from the water by a substantial amount - thus leading to aeration of the foil and reduced effectiveness - losing its ability to counter the round up.

You can mess around all you like with foil size and sharpness, sailtrim, and even mast position, but that won't change the basic behaviour of the hull.

SAIL IT FLAT!

Boats like these were built to function as caravans, don't expect them to behave like race cars

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Hey everybody - I love the general physics of sailing discussion, but really appreciate the specific comments.  

I also like seeing the pic of my "Sugar Mountain" (you can't be 20..).  I do love her, while she steps on her foot dancing once in a while, serves as a fantastic hotel and swim platform.  :D

 

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8 hours ago, alphafb552 said:

About hull shape and rounding up, try to imagine this

take a wedge of cheesecake, nice and flat on the plate - a perfect representation of the typical modern wide ass boat. Pointy bow, wide stern, rudder in the middle of the widest part.

now cant the wedge over 15 - 20 degrees and see what happens.

Your cheesecake is leaning on its bottom edge - which is pointing in a different direction than the 'centreline' of the cake! That direction is the opposite of the direction of heel - the result is instant round up!

Then look at where your rudder went - the middle of your 'transom' has lifted away from the water by a substantial amount - thus leading to aeration of the foil and reduced effectiveness - losing its ability to counter the round up.

You can mess around all you like with foil size and sharpness, sailtrim, and even mast position, but that won't change the basic behaviour of the hull.

SAIL IT FLAT!

Boats like these were built to function as caravans, don't expect them to behave like race cars

Now cut the sides of your cheese cake into a curve, tip it up 15° or more and see what it wants to do when you try to push it straight.  

E.G.  The fastest J-24  (a round-sided tub if there ever was one) is the one sailing dead flat and has a helm that feels like a dead fish.

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9 hours ago, alphafb552 said:

Your cheesecake is leaning on its bottom edge - which is pointing in a different direction than the 'centreline' of the cake! That direction is the opposite of the direction of heel - the result is instant round up!

 

1 hour ago, Bob Perry said:

Thanks Alpha. That's exactly what I was getting at.

The way I finally got it was sticking my hand out the car window in the highway, fingers pointing forward. Flat hand is a symmetrical hull shape. Cup your hand - an asymetrical hull profile moving through a fluid - and you're hand is immediately pushed downward (a turning moment)

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21 minutes ago, Breamerly said:

 

The way I finally got it was sticking my hand out the car window in the highway, fingers pointing forward. Flat hand is a symmetrical hull shape. Cup your hand - an asymetrical hull profile moving through a fluid - and you're hand is immediately pushed downward (a turning moment)

That more properly describes a foil moving though a fluid rather than a hull.  And when your hand is pushed down, it is solely due to force - there is no turning moment applied to your hand. 

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18 minutes ago, 12 metre said:

That more properly describes a foil moving though a fluid rather than a hull.  And when your hand is pushed down, it is solely due to force - there is no turning moment applied to your hand. 

Right but I'm pretty sure if your hand were a hull with a keel, presenting one curved face, that force would *result in/manifest as a turning moment.

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so I haven't read every post in this thread, can't be arsed, but I think I did see a pic of a dingy without a rudder. 

One of the things we used to practice on my j35 was locking the rudder amidships with the autohelm and going thru various sailing evolution with using it. 

taught us a lot about balancing the sails and lateral weight placement. we could tack and gybe and do everything we needed to be able to do without the rudder. 

(not at a pace we'd need in a race, but we could steer the boat) 

Sail trim/balance and crew weight placement might be able to solve your problem without redesigning your boat. 

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