Rudder balance

[MrChris]

Hi knowledgeable people!
My rudder drops hard to port or starboard rather than to a middle position.
I have recently acquired a long keel Colvic 27 with a skeg hung rudder.
My investigations to date revolve around changing the vertical angle by overloading the back end of the boat, this reduced the weight of the rudder swing to some degree but the boat was clearly trimmed too far aft already. I can only think that it would be the angle of the big heavy rudder blade hanging tilted too far forward at the top that moves the vertical centre of the whole thing too far.
BUT I don't know....
Any help would be much appreciated

[wingssail]

Originally Posted by MrChris

Hi knowledgeable people!
My rudder drops hard to port or starboard rather than to a middle position.
I have recently acquired a long keel Colvic 27 with a skeg hung rudder.
My investigations to date revolve around changing the vertical angle by overloading the back end of the boat, this reduced the weight of the rudder swing to some degree but the boat was clearly trimmed too far aft already. I can only think that it would be the angle of the big heavy rudder blade hanging tilted too far forward at the top that moves the vertical centre of the whole thing too far.
BUT I don't know....
Any help would be much appreciated

I'm guessing that you have a tiller and that your rudder pivot is not exactly vertical, (bottom gudgeon is farther forward) so swinging either to port or starboard allows the tiller to drop down a bit. It's weight is more than the weight of the rudder blade.

While underway I'd think that the force of the water flowing past the rudder would tend to keep it straight.

If your problem happens while moving the perhaps there is too much area ahead of the rudder pivot.

[tkeithlu]

Could you post a picture of the rudder? The pictures I can find of the Colvic 27 don't show anything unusual about the balance of the rudder. Something is just not right here, making me wonder whether the rudder on your boat is not where it is supposed to be.

[MrChris]

Hi, the stern overhangs so the pins are on a 40 degree slope, the balance I guess is a vertical line through the pins at the centre of balance of the whole unit.

Originally Posted by wingssail

I'm guessing that you have a tiller and that your rudder pivot is not exactly vertical, (bottom gudgeon is farther forward) so swinging either to port or starboard allows the tiller to drop down a bit. It's weight is more than the weight of the rudder blade.

While underway I'd think that the force of the water flowing past the rudder would tend to keep it straight.

If your problem happens while moving the perhaps there is too much area ahead of the rudder pivot.

[MrChris]

Hi, I am sure you are right, the rudder is original but has had work carried out in the past. It takes around 3 knots before water pressure keeps it midships, and even then it is not stable. It is a skeg hung rudder.

Originally Posted by tkeithlu

Could you post a picture of the rudder? The pictures I can find of the Colvic 27 don't show anything unusual about the balance of the rudder. Something is just not right here, making me wonder whether the rudder on your boat is not where it is supposed to be.

[TrentePieds]

MrChris:

We need to get more specific here, in order to help you :-) What, precisely, is "a long keel boat with a skeg hung rudder"? Such a description in antithetical. Do you have a drawing of the boat?

Quote: "... the stern overhangs so the pins are on a 40 degree slope, the balance I guess is a vertical line through the pins at the centre of balance of the whole unit."

40º?? That is almost inconceivable. 15º might be believable. But surely you are not taking about "overhang", but rather about "rake"? Rake" is the "slope” the transom has when you see the boat in profile. If the top of the transom leans towards the bows, the rake is positive. If the top of the transom leans away from the bows, the rake is negative. A Colvin-built boat of the late 70s and early 80s is almost bound to have a transom with a really nasty positive rake, but that is immaterial if your rudder is skeg-hung. So let's work away at this slowly and deliberately, making sure that we get the terminology right lest we be confused :-)

Now look at this boat - the inimitable "folkboat":

https://sailboatdata.com/sailboat/nordic-folkboat

You will see that it has considerable NEGATIVE rake, specifically 45º! BUT the "bottom hinge" of the rudder, which is mounted on what is called the "stern post", is WAY forward of the "top hinge". This means, due to the physics of the case, that the rudder will align itself with the centreline of the boat when it is lying dead in the water.

(By the way: The male part of a hinge, what you call the “pin”, is properly called the “pintle”. The female part of such a hinge is called the “gudgeon”)

The negative rake also means that as the boat heals under a press of wind, and begins to turn her head to weather, the weight of the rudder will compel it – the rudder – to “fall off” to leeward, thereby cancelling out the boats tendency to turn to weather, i.e. this rudder arrangement mitigates the need for the helmsman to haul the tiller to weather. In other words: it mitigates the boats weather helm. That is one reason the Folkboat is so pleasant to sail.

Now consider the case of POSITIVE rake: When the boat is dead in the water the rudder will fall off to one side or the other, just as you describe. However, when the boat begins to move, the water flowing past the rudder will, when the speed gets high enuff, exert enough pressure on the rudder blade that it will “trail behind” on the centreline of the boat. Yet, as the boat heels. this rudder will ALSO tend to "fall off" to leeward, and to the helmsman such a boat will now, in respect to helming, feel just like a boat with negative transom or stern post rake.

At low speed, however, when the pressure of the water flow is inadequate to straighten the rudder, it will fall off to one side or the other, just as when the boat is dead in the water, and the boat will feel “squirrelly” at low speeds. That is a price people who are keen on racing are willing to pay in order to achieve a slight “measurement” benefit under the racing rules to which such boats are designed.

IMO there is also a cost to be paid in terms of seaworthiness. But that's a long complicated argument, and of little import to those who only want to race in the sorts of waters that are home to both the Folkboat and to the Colvins. For the cruising man, however, it is a point worthy of attention.

So at this point it seems as if you are worrying needlessly.

Tell us, what is it , precisely, that you are worried about?

TrentePieds

[MrChris]

Worried about? The greatest concern is that it is impossible to let go the helm for even one second when manoeuvring as the helm instantly goes hard over, the second is that the autopilot seems to be under extreme loads, possibly countering this effect. As I sail single handed and intend long distances, both these issues matter.
I had not yet thought too much about the situation when heeling, can you elucidate a little on the advantage of the (unbalanced) rudder.
The boat is 30 plus year old Colvic, not the ufo Colvic BTW.

Originally Posted by TrentePieds

MrChris:

We need to get more specific here, in order to help you :-) What, precisely, is "a long keel boat with a skeg hung rudder"? Such a description in antithetical. Do you have a drawing of the boat?

Quote: "... the stern overhangs so the pins are on a 40 degree slope, the balance I guess is a vertical line through the pins at the centre of balance of the whole unit."

40º?? That is almost inconceivable. 15º might be believable. But surely you are not taking about "overhang", but rather about "rake"? Rake" is the "slope” the transom has when you see the boat in profile. If the top of the transom leans towards the bows, the rake is positive. If the top of the transom leans away from the bows, the rake is negative. A Colvin-built boat of the late 70s and early 80s is almost bound to have a transom with a really nasty positive rake, but that is immaterial if your rudder is skeg-hung. So let's work away at this slowly and deliberately, making sure that we get the terminology right lest we be confused :-)

Now look at this boat - the inimitable "folkboat":

https://sailboatdata.com/sailboat/nordic-folkboat

You will see that it has considerable NEGATIVE rake, specifically 45º! BUT the "bottom hinge" of the rudder, which is mounted on what is called the "stern post", is WAY forward of the "top hinge". This means, due to the physics of the case, that the rudder will align itself with the centreline of the boat when it is lying dead in the water.

(By the way: The male part of a hinge, what you call the “pin”, is properly called the “pintle”. The female part of such a hinge is called the “gudgeon”)

The negative rake also means that as the boat heals under a press of wind, and begins to turn her head to weather, the weight of the rudder will compel it – the rudder – to “fall off” to leeward, thereby cancelling out the boats tendency to turn to weather, i.e. this rudder arrangement mitigates the need for the helmsman to haul the tiller to weather. In other words: it mitigates the boats weather helm. That is one reason the Folkboat is so pleasant to sail.

Now consider the case of POSITIVE rake: When the boat is dead in the water the rudder will fall off to one side or the other, just as you describe. However, when the boat begins to move, the water flowing past the rudder will, when the speed gets high enuff, exert enough pressure on the rudder blade that it will “trail behind” on the centreline of the boat. Yet, as the boat heels. this rudder will ALSO tend to "fall off" to leeward, and to the helmsman such a boat will now, in respect to helming, feel just like a boat with negative transom or stern post rake.

At low speed, however, when the pressure of the water flow is inadequate to straighten the rudder, it will fall off to one side or the other, just as when the boat is dead in the water, and the boat will feel “squirrelly” at low speeds. That is a price people who are keen on racing are willing to pay in order to achieve a slight “measurement” benefit under the racing rules to which such boats are designed.

IMO there is also a cost to be paid in terms of seaworthiness. But that's a long complicated argument, and of little import to those who only want to race in the sorts of waters that are home to both the Folkboat and to the Colvins. For the cruising man, however, it is a point worthy of attention.

So at this point it seems as if you are worrying needlessly.

Tell us, what is it , precisely, that you are worried about?

TrentePieds

[MrChris]

I am having trouble uploading the pic I have just taken of the stern with rudder, maybe it will work a little later from my computer rather than phone. But the general layout below water is very similar to the folk boat in the link above

Originally Posted by MrChris

Worried about? The greatest concern is that it is impossible to let go the helm for even one second when manoeuvring as the helm instantly goes hard over, the second is that the autopilot seems to be under extreme loads, possibly countering this effect. As I sail single handed and intend long distances, both these issues matter.
I had not yet thought too much about the situation when heeling, can you elucidate a little on the advantage of the (unbalanced) rudder.
The boat is 30 plus year old Colvic, not the ufo Colvic BTW.

[TrentePieds]

Quote: "...it is impossible to let go the helm for even one second when manoeuvring as the helm instantly goes hard over,..."

Ah, "when MANEUVERING..."

Well, yes, of course! If you are making sternway ("backing up") so the water first hits what would normally be the trailing edge of the rudder, then obviously the rudder is gonna smack right over against the stops. And if you don't have solid stops, damage will be done...! That is true in all boats, and has nothing to do with rake or "overhang". In tiller-steered boats, that phenomenon can be powerful enuff to knock the helmsman off his feet. Nothing odd about that, and nothing you can do about it other than go astern slowly enuff to keep the forces within your strength to handle them.

In wheel-steered boats the steering gear is what absorbs the force, and the gear can indeed be damaged if you get too ambitious about your sternway!

Rudders that are hung on a sternpost or on a skeg are not (usually) "balanced" rudders. A "balanced rudder" is one that has a proportion of its blade area disposed forward of the hinge line, which is such boats is normally the rudder stock that goes through the bottom of the boat and carries the tiller. Balanced rudders are meant to alleviate the force necessary to deflect the rudder and therefore the tiller.

When you say "maneuvering" are you talking about the evolution that many Sunday sailors call "backing and filling", i.e. going forward and backwards in turn in order to, say, get into a "finger slip" at a marina?

As long as you are making headway (moving forwards) this disconcerting tendency of the tiller to "take charge" should not come into play. If it does, you have a problem that needs to be rectified.

As far as your auto-pilot is concerned, you need to have regard to the geometry of the setup and to the length of the sundry "moment arms" via which the action of the machine is transmitted to the tiller. Remember that as long as your boat is properly "balanced" i.e. the sails worn are those that are appropriate for your chosen course and for the prevailing wind and wave, the forces required to deflect the tiller are not really very great. If they BECOME great, you need to look to your sail trim and to the amount of sail you are carrying.

Just as a reference point: The rudder deflection required to maintain your steady course when sailing in a well-balanced boat it rarely more than 5º either side of midships. If you are engaged in violent maneuvering, or if you are going so slow that much larger deflections are required, you should disconnect the auto-pilot entirely and steer by hand.

TrentePieds

[MrChris]

Not during reversing, but going ahead at speeds under 3 knots. As you rightly say, this is a problem, and it is this problem I am trying to solve.

Originally Posted by TrentePieds

Quote: "...it is impossible to let go the helm for even one second when manoeuvring as the helm instantly goes hard over,..."

Ah, "when MANEUVERING..."

Well, yes, of course! If you are making sternway ("backing up") so the water first hits what would normally be the trailing edge of the rudder, then obviously the rudder is gonna smack right over against the stops. And if you don't have solid stops, damage will be done...! That is true in all boats, and has nothing to do with rake or "overhang". In tiller-steered boats, that phenomenon can be powerful enuff to knock the helmsman off his feet. Nothing odd about that, and nothing you can do about it other than go astern slowly enuff to keep the forces within your strength to handle them.

In wheel-steered boats the steering gear is what absorbs the force, and the gear can indeed be damaged if you get too ambitious about your sternway!

Rudders that are hung on a sternpost or on a skeg are not (usually) "balanced" rudders. A "balanced rudder" is one that has a proportion of its blade area disposed forward of the hinge line, which is such boats is normally the rudder stock that goes through the bottom of the boat and carries the tiller. Balanced rudders are meant to alleviate the force necessary to deflect the rudder and therefore the tiller.

When you say "maneuvering" are you talking about the evolution that many Sunday sailors call "backing and filling", i.e. going forward and backwards in turn in order to, say, get into a "finger slip" at a marina?

As long as you are making headway (moving forwards) this disconcerting tendency of the tiller to "take charge" should not come into play. If it does, you have a problem that needs to be rectified.

As far as your auto-pilot is concerned, you need to have regard to the geometry of the setup and to the length of the sundry "moment arms" via which the action of the machine is transmitted to the tiller. Remember that as long as your boat is properly "balanced" i.e. the sails worn are those that are appropriate for your chosen course and for the prevailing wind and wave, the forces required to deflect the tiller are not really very great. If they BECOME great, you need to look to your sail trim and to the amount of sail you are carrying.

Just as a reference point: The rudder deflection required to maintain your steady course when sailing in a well-balanced boat it rarely more than 5º either side of midships. If you are engaged in violent maneuvering, or if you are going so slow that much larger deflections are required, you should disconnect the auto-pilot entirely and steer by hand.

TrentePieds

[Cheechako]

So if I understand, the rudder goes to the side while moving forward slowly. That is pretty strange due to the force of water across the blade should want to make it straight, more or less. But maybe it is the prop wash doing it motoring? or does it do it sailing also?

[TrentePieds]

O-ho :-)!!

Now we are getting somewhere - but not to where we want to be :-)

So let's look closer. You say the underwater profile is "similar" to the Folkboat? We really need a picture, because as Cheechako sez - it's pretty strange. With the Folkboat's underwater profile, it simply CANNOT happen!

Can you find a picture on HolyMotherNet of the type of boat you have and give us a link? Colvins made a number of widely different boats, some of which were just fine, and some of which not so much, IMO.

That it "cannot happen" is always true when the rudder stock has negative rake. It cannot happen! However, if the stock has POSITIVE rake, and the blade is VERY heavy, then, conceivably, it could. Then you'd get that "squirelly" behaviour I was talking about.

So there are things we still need to know. Does this happen when the auto-pilot is engaged? Or when the AP is NOT engaged?

Precisely what kind of "maneuvering" are you doing when it happens?

Does it happen when you are under sail alone, or under power alone, or when you are "motorsailing"?

TP

[MrChris]

Hi, the rudder goes over going forward and as you say, it shouldn't. Completely still conditions it flops heavily one way or the other, so it is a balance issue, not a flowing water or prop issue.

Originally Posted by Cheechako

So if I understand, the rudder goes to the side while moving forward slowly. That is pretty strange due to the force of water across the blade should want to make it straight, more or less. But maybe it is the prop wash doing it motoring? or does it do it sailing also?

[MrChris]

It happens in all situations, included when moored and completely still.
Your assumption that it cannot happen due to the hanging rudder is not correct I think. The rudder stands on its bottom bearing supported in the middle and near the top. The balance must be around a line vertically through the mid point of all 3 points. If the centre line of the mass of the rudder passes forward of that line then it would behave as it does. So, I overloaded the back of the boat to move the top support further aft and this Did ease the issue but not enough to notice.

Originally Posted by TrentePieds

O-ho :-)!!

Now we are getting somewhere - but not to where we want to be :-)

So let's look closer. You say the underwater profile is "similar" to the Folkboat? We really need a picture, because as Cheechako sez - it's pretty strange. With the Folkboat's underwater profile, it simply CANNOT happen!

Can you find a picture on HolyMotherNet of the type of boat you have and give us a link? Colvins made a number of widely different boats, some of which were just fine, and some of which not so much, IMO.

That it "cannot happen" is always true when the rudder stock has negative rake. It cannot happen! However, if the stock has POSITIVE rake, and the blade is VERY heavy, then, conceivably, it could. Then you'd get that "squirelly" behaviour I was talking about.

So there are things we still need to know. Does this happen when the auto-pilot is engaged? Or when the AP is NOT engaged?

Precisely what kind of "maneuvering" are you doing when it happens?

Does it happen when you are under sail alone, or under power alone, or when you are "motorsailing"?

TP

[dfelsent]

Wowee. Is it possible that you have a really heavy tiller? Or that the rudder, rather than being denser than water, which would have gravity aid you, is floating and therefore has buoyancy against you?
Or a combination of the two?