Optimal rudder angle and weather helm for speed

[wingssail]

Originally Posted by Quebramar

I recall having read somewhere that a slight angle working «*against*» where they boat wants to go (into the wind) helps lift the hull and therefore reduce the slowdown effect of the water.
Would this also explain the benefit a weather helm?

Yes, for sure. And if you get enough lift you can really reduce the slowdown effect of the water.

[Dockhead]

Originally Posted by MicHughV

. . . A skeg hung rudder has the leading edge of rudder, parallel to the hull centerline, so when the rudder is turned...say...5 degrees...the skeg and rudder combined give a nice " foil" shape...such as it were...

Except that rudder and skeg at different angles create the opposite of a "nice foil shape". Skeg rudders have horrible hydrodynamic qualities, generating a great deal of drag when the rudder is at any angle. Even semi-skeg rudders like mine are far worse than spade rudders, generating vortices and drag at all the joints between skeg and rudder. Nearly all big ships built today have spade rudders. That is not a coincidence. Spade rudders are far more efficient.

[Allied39]

Shee's, I am humbled.

I recently wondered what 6 inches of rotation on my wheel related to actual rudder angle.......well it turns out.....not bloody much!

To be within a few degrees of rudder angle....well....very well done fellows, very well done!!

[wingssail]

Originally Posted by MicHughV

...
A skeg hung rudder has the leading edge of rudder, parallel to the hull centerline, so when the rudder is turned...say...5 degrees...the skeg and rudder combined give a nice " foil" shape...such as it were...

A wing sail, such as pictured below, is much like a skeg hung rudder. Except that the skeg can also rotate. If only the back part was movable, like with a skeg hung rudder, it would befar less effective.

My last boat has a deep spade rudder...it likes to be parallel to the hull centerline, for optimum performance.
The leading edge of the rudder is somewhat ahead of the rudder post, but when turned....say 5 degrees, I can tell that it is trying to stall, hence it is happier straight ahead.

I would say that this is unusual.

Having said all that, sailing to weather is a different animal from sailing downwind, and if sail trim is not correct, it too will affect rudder performance.

That (your last sentence) is why I love sailing to windward, and downwind I end up reaching because it feels so good. Sailing downwind we want leeway, it's good. And we use the helm to compensate for rolling.

[Dave_S]

IMHO

I disagree with the"find the groove" technique, I think that is comfortable, not fast.

I believe at any time the sails are creating lift (not down wind) you need to share the righting moment work underwater as evenly as possible across all foils. Matching lift/drag ratios between rudder and keel.

If there is no rudder angle there is no work being done, just drag, similarly, if you have lots of rudder angle and no keel angle you have exceeded the efficiency of the rudder and have comparatively too much drag. You must have some rudder angle or you are wasting potential and increasing drag on your keel and visa versa. Drag increases to the square and lift increases linearly so if one is doing more work than the other your combined lift/drag ratio is worse. You need to balance them for best efficiency.

Contrary to this, some sail imbalance is an advantage. Imbalance is ok if the extra sail area is creating more power than the additional drag underwater is loosing. The greater the imbalance above the water the greater the imbalance must be below the water. If you have an adjustable keel or dagger boards you can adjust to some degree to suit the sail imbalance and increase your potential. If you don't, or run you run out of adjustment on your dagger boards you should accept the drag increase up to the point where the drag below the water exceeds the extra power/motive force of the greater sail area.

Each boat will be different, even between the same make and model so you need to experiment.

[chris14679]

When the boat is heeled over, there is more curved hull in the water on one side than the other. The curved shape of the hull tends to turn the boat up to windward.

You can balance that in the design of the yacht by putting the mast (or more correctly, the centre of effort of the sails) further forward, but then it will be unbalanced (lee helm) when the boat is sailing level. The correction will also be less effective to windward than on a beam reach.

The other factor causing weather helm is that the sails provide the driving force on one side, not in the centre of the boat. The thrust from the sails is always trying to rotate the boat, even when the boat is level. When the boat is heeled the sails are more out to the side so the rotational effect is stronger (this feedback situation can cause a broach).

You can further compensate this with sail trim - in simplistic terms, tight jib sheet and loose main sheet will reduce weather helm but could also reduce performance.

So there's a compromise to be struck - you can eliminate weather helm with sail trim but perhaps at the expense of performance.

Your weather helm will constantly vary depending on your angle of heel so you can only eliminate it if the wind is very steady and/or the boat is very stiff.

It depends very much on the shape of the boat - a boat which is fat in the middle, slender at the ends, with rounded topsides (eg. a double ender) will have much more weather helm when heeled than a more straight sided boat.

So there's no right answer, some boats just have a lot of weather helm and there's no much you can do about it, if you fix it at one angle of heel you'll be out of balance at any other angle.

A bit of weather helm can certainly help with self steering and with steering by feel, you can more easily find a "balance point" when you feel the boat is in the groove. It may be less efficient (turbulence off the rudder) than steering with the rudder balanced but ont he other hand you can steer straighter so you might get there sooner!

[wingssail]

Originally Posted by chris14679

...You can further compensate this with sail trim - in simplistic terms, tight jib sheet and loose main sheet will reduce weather helm but could also reduce performance.

So there's a compromise to be struck - you can eliminate weather helm with sail trim but perhaps at the expense of performance...!

No, I think proper sail trim to reduce excess weather helm adds to performance, not reduces it

I guess I can be thankful for the genius of Doug Peterson who designed our boat. We have very little weather helm up to about 12 knots of true wind (20 apparent). At all wind speeds there is a little, not too much. Our windward performance is excellent by any measure. By 12 knots of true wind we want to change to a #2 or #2 jib, and then we still have little weather helm, just enough to keep the foils working, however if we hold off on the sail change, for whatever reason, flattening the main and/or easing the traveler removes the excess weather helm and OUR PERFORMANCE INCREASES. Cruising we are using a smaller main and a working jib. Weather helm is rarely an issue.

We have one of those boats with a fat middle and narrow ends, particularly compared to modern boats which should be even better in this regard.

So, if you are sailing a boat designed with performance in mind, chances are it will sail upwind faster with a little weather helm, not too much, and easing the main to keep the helm under control won't cost you any performance.

BTW, When I bought my boat, out of San Francisco, where the winds are stronger than Puget Sound, I took out a couple thousand pounds of internal ballast and rocked the mast tip aft 11 inches to get the best light wind performance. It worked and surprisingly, it still fine in a breeze (of course I added 2000lbs of liveaboard stuff).

[Searles]

Having sailed and raced several c 42mk2 ,over 20yrs and thousands of n m,the mast rake the rig tension the design and condition of the sails ,has as much control as the ability at the helmsman ,but one spoke of helm on those vsls is about right I.e about 5dg .⛵️⚓️

[Stu Jackson]

Originally Posted by wingssail

the rudder must be angled a little bit, and I will feel that on the helm. So, no we don't really want a neutral helm with no pressure. If there is no pressure on the rudder I feel like I just can't steer and I complain to the trimmers.

When I "find the groove," the rudder (wheel or tiller) is already "offset" meaning that it is already that 5 or so degrees off, and THAT is where the pressure DISAPPEARS and the boat sails itself.


It's where the rudder is BALANCING the sail's attempt to turn to windward.

[Dave_S]

Originally Posted by Stu Jackson

When I "find the groove," the rudder (wheel or tiller) is already "offset" meaning that it is already that 5 or so degrees off, and THAT is where the pressure DISAPPEARS and the boat sails itself.


It's where the rudder is BALANCING the sail's attempt to turn to windward.

Do you mean there is no weight on the rudder ? If there is no weight, it's not doing work and you surely are loosing some potential.

[MicHughV]

Some years back I got to sail on a homebuilt ferro-cement Pinky schooner. The boat did not have a keel per se, more like a full length extension of the hull. The rudder was a barndoor affair bolted onto the stern with a pronounced reverse rudder strake. The actual tiller arm must have been 8' long, and it required this length to muscle this boat around. It was a beast to sail in a straight line, despite having a full length keel. It really required two people on the tiller, and brought home the fact the enormous pressure a rudder must be able to with stand..

Some modern boat designs now employ twin rudders....

I remain a fan of the skeg hung rudder in that it provides some protection to the rudder in the event of a collision of any sort.

There are several Youtube video's on rudder designs, performance, etc, You could spend all day reviewing data.....opinions on the matter are all over the map.

[AKA-None]

Originally Posted by Dave_S

Do you mean there is no weight on the rudder ? If there is no weight, it's not doing work and you surely are loosing some potential.

It means you aren’t forcing the rudder to generate turbulence beyond that required to hold you straight if that helps

[wingssail]

Originally Posted by AKA-None

It means you aren’t forcing the rudder to generate turbulence beyond that required to hold you straight if that helps

No AKA-None, I think that for a keel to be effective it requires some "angle of attack", usually caused by pressure on the sails being aft of the center of lateral resistance. That aft pressure would cause the boat to turn up into the wind and continue to turn up into the wind until it is head to wind. The rudder is what stops that and most all rudders will load up the helm while correcting the tendency for the boat to round up.

If there is no load on the helm the rudder isn't doing anything, and therefore there can't be any "angle of attack" happening on the keel, therefore IT isn't at its most effective.

We aren't accepting excess turbulence from the rudder, but we are expecting it to be doing something and it will have some weight on it.

The trick is to get it just right.

[MicHughV]

this topic should really also include keel design....hull design....prop struts or apertures, distance from rudder...prop size and diameter, sail trim, etc...etc...etc.....all these things, plus more, affect a boat's performance...which in turn dictates rudder requirements..

interestingly, I note the the new 125' yacht, Skorpios, features twin spade rudders with scalloped edges on the forward lower edge of the rudders.....can't say I've ever seen this before or why they are there...

[Bowdrie]

The difference between the CE of the sail plan and the CLR of the hull/keel is one of those things that designers fret about/toil over.
It is referred to as "lead", or perhaps more accurately as "leede" and is generally expressed as a percentage of the WL length.
In the older days of the CCA, (with small winches and cotton sails,) boats had more problems with weather helm due to the issues of having huge mainsails and not enough sail area forward of the CLR.
It's also why we see so many of the boats from the '60s>'70s where their have been anchor platforms/short bowsprits added,, something to increase the lead and move the CE of the sail plan forward,, the designer didn't give enough lead to the CE.
Depending upon hull/keel shape, the lead of the CE usually falls in the range of ~7>15%,, the exception is the schooner rig, where it's common to find a negative lead, (that's why the mainsail is the first to drop or reef).
In the days of 12 meter racing ~2 degrees of rudder was thought of as optimal weather helm.
Interestingly, in real light air a bit of lee helm can be useful in working to weather.