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Both boards are fully down throughout this video. That was not perceived as a problem by the helm. When the biggest gusts hit he was not totally happy with rudder response (he is a former Swedish A-cat champion sailing Marström boats -- very skilled but a bit spoilt when it comes to build quality).

 

Afterwards I calculated bow-down and forward tilt and figured that during maximum acceleration even the lee rudder operated almost totally in the wake of the hull: the lowest point of the hull being almost as deep as the tip of the rudder.

 

Hence the plans for new rudder blades.

 

Note that this is sailing under full sails and spi. Doing these speed and more under storm jib and two reefs (on a lower rig) in much more wind many, many years ago there was no bow-down or control issue. The lower centre of effort and, I think, less fierce gusts relative to base wind strength meant the boat was just skidding along without nose-down tendencies. (I wish I had had a GPS to record that run but that was well before GPSs became available.)

 

/Martin

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Guest Ketchup

Thanks for putting thought into it Ketchup.  Definitely the bows rode higher as speed increased.    They are pretty high once on plane, partly due to the rocker I think.    The rudder blades are fully in the water at speed.  

 

There are no thru hulls or anything ahead of the daggers or the rudder.

 

I Intend to raise those daggers at my next high speed opportunity.

 

wildfire7.jpg

it a tricky situation when hitting high speeds, the helm goes light and there is little or no control. It suggest that other things are overriding the helm. (Sails / rig set up, hull shapes, boards..)

 

One thing that is for sure is that if you are going down wind and the next mark is well to leeward then having the boards up will allow the boat to slide off to leeward and take away any tendancy to roundup or get excessive weather helm (Or fly off into a gybe)

 

I remember ailing a tornado cat downwind, at speed in 25-30 knots of breeze when suddenly both rudders sheared off (shitty cedar/glass blades). Because the boards were up we just tracked along and with quick mainsail trim just slowed and rounded to windward. I am sure with the boards down we would have been toast!

 

A key thing to realise is that the sails in conjunction (position in relation to) with the foils and hull shape determines the boats balance and the way it handles at speed. Rudders and thier size/shape are just there to control all these factors and get you around the course.

 

Rudders are also a compromise to cater for a huge scope of speeds and loadings. Again take a look at a plane. It has wings (centre boards) and rudders (all that kit on the tail) to control a plane efficientlay from 0 - 800 knots. Now you cannot design one foil to cover that scope of speed and loadings, thus they have flaps, flaperons on the wings to optimize the shape for differing speeds, balance, and loads etc. on the tail they have rudder and flaps to "week" the direction and balance.

 

The same could apply for yachts but the difference is the lower speed ranges and the different friction coefficient of water versus air (easier to stay attached due to density). Thus your foils, on the boat right now, might be great up to 18 knots but another shape/size might be better above this?.... ( I think boat/ boards trim could overcome a lot of the issues at speed. For example if the boat @18.5 knots dived of to leeward then either more mainsail or less A Sail would reduce this (boards up would for sure)

 

Food for thought Mk2...

 

Imagine at that moment you hit 18 knots you had no rudders at all - what would the boat do?....(the effect of the sails over the hull and dagger boards)

 

1. If the sail area (all sails loaded up)forward of the dagger boards (the boats pivot point) is greater than aft of the boards the boat will dive to leeward!

 

2. If the sails area was greater aft of the pivot point it would round up to windward.

 

Either way if the rudders have lost control then the balance of the sail area or trim will control the boat. (Just as the wings, flaps... will override the rear rudder flap on a plane).

 

Note:- the wings on the plane are the pivot point and the rudders and flaps on the tail are like rudders on a boat.

 

However - if the boards were up the pivot point is removed then what would happen.. :-) ....

 

You can trim the boat out of these control issues but it takes a good strong trimmer to pull big sails in fast enough. (Easy on a 12 foot skiff but hard on a 50 foot racing cat)

 

For example...

 

in 1. Above. If the main sheet guy pulled in the main and the A sail trimmer eased out the Asail at the moment helm control was lost then the boat would "balance" better and drive straight (Subject to hull shape)

 

Finally T foils are a good solution to controlling water flow in the horizontal plain. A Normal rudder has control in the verticle plain (left to right) but the T section gives another dimension and can assist. (Mainly in foiling and lift assist)

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Guest Ketchup

Forgot to add the best bit...

 

If, when flying downwind, your boat has a tendancy to want to "dive off to leeward" then pulling the leeward board up and keeping the windward board down will help reduce this.

 

Why?....

Well the windward board, in effect, is creating drag which in turn slows the windward hull down (in comparison to the leeward hull with no drag).

 

Beause the faster leeward hull cannot advance on the windward hull(well not to much depending on beam / lateral resistance of beam/structure) this has the effect of "pivoting the boat" around the windard board and driving it to windward.

 

The reverse applies too.

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Sailing the GBE last night upwind with enough breeze to fly a hull.

On one tack, helm was pretty neutral, with a bit of weather helm coming on when we started to lift a hull.

On the other tack, there was a lot more weather helm before we even got close to getting a hull out of the water

 

Any suggestions as to whats going on?

Both boards were down, jib sheeting was the same, traveller trim was the same.... :roll:

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Sailing the GBE last night upwind with enough breeze to fly a hull.

On one tack, helm was pretty neutral, with a bit of weather helm coming on when we started to lift a hull.

On the other tack, there was a lot more weather helm before we even got close to getting a hull out of the water

 

Any suggestions as to whats going on?

Both boards were down, jib sheeting was the same, traveller trim was the same.... :roll:

tide and/or sea state?

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Guest Ketchup

Sailing the GBE last night upwind with enough breeze to fly a hull.

On one tack, helm was pretty neutral, with a bit of weather helm coming on when we started to lift a hull.

On the other tack, there was a lot more weather helm before we even got close to getting a hull out of the water

 

Any suggestions as to whats going on?

Both boards were down, jib sheeting was the same, traveller trim was the same.... :roll:

To clarify, ( not meaning to be condescending) by weather helm you are talking " let go of the helm and she rounds up into the wind?... or is the helm just feeling heavy?

 

Some people get mixed up on this.

 

I presume weather helm.

 

... weather helm is only really generated by having the CE (Centre of effort) of the sail area aft of the CLR (centre of lateral resistance or pivot point of the Boat) thus as the wind pressure increases on the sails the stern is pushed to leeward and the bow to weather. (This is How a windsurfer actually steers)

 

so... if the sails are trimmed the same from tack to tack and the boards and rudders are all raked evenly and the rigs rake is even from tack to tack (check that) then there is something weird going on.

 

I would usually suspect either a rake issue or a sail sheeting/ballance issue.

 

For example just easing the jib 3-4 inches will move the CE aft and induce weather helm. Taking the jib of completely will give even maker weather helm. Are you sure the sails were trimmed to the same tension (twist) and angle of attack?

 

Are you running a canting rig, or a rotating mast? Both these can effect the mainsail power (leech) and rake (depending on steup)

 

I presume the mast is straight in both fore/aft and sideways dimensions.

 

 

If the mainsail is powered up more on one tack then this can contribute to a weather helm comparison difference.

 

Weather helm before the hull lifts is weird. Are you sure its not just a heavy helm (like when the rudder has been raked aft)

 

I suspect the rig has a issue with more rake (weather helm) and less power (hull not lifting) on the bad tack.

 

I would be getting the measure tape, level, and a laser level out (or theodolite)

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To clarify, ( not meaning to be condescending) by weather helm you are talking " let go of the helm and she rounds up into the wind?... or is the helm just feeling heavy? - rounds up into the wind

 

Some people get mixed up on this.

 

I presume weather helm.

 

... weather helm is only really generated by having the CE (Centre of effort) of the sail area aft of the CLR (centre of lateral resistance or pivot point of the Boat) thus as the wind pressure increases on the sails the stern is pushed to leeward and the bow to weather. (This is How a windsurfer actually steers)

 

so... if the sails are trimmed the same from tack to tack and the boards and rudders are all raked evenly and the rigs rake is even from tack to tack (check that) then there is something weird going on.

 

I would usually suspect either a rake issue or a sail sheeting/balance issue.

 

For example just easing the jib 3-4 inches will move the CE aft and induce weather helm. Taking the jib of completely will give even maker weather helm. Are you sure the sails were trimmed to the same tension (twist) and angle of attack?

 

Are you running a canting rig, or a rotating mast? Both these can effect the mainsail power (leech) and rake (depending on steup) -Rotating mast with a restrictor, so the mast rotates to the same angle on each tack, its definitely rotating

 

I presume the mast is straight in both fore/aft and sideways dimensions. - yep

 

 

If the mainsail is powered up more on one tack then this can contribute to a weather helm comparison difference. Main is sheeting in hard and cleated, trim is done via the traveller, so sheeting is consistent tack to tack

 

Weather helm before the hull lifts is weird. Are you sure its not just a heavy helm (like when the rudder has been raked aft) - it is neutral on one one tack, i.e. i let go of the tiller and she sails in a straight line, on the other tack if I let go of the tiller we would round up 

 

I suspect the rig has a issue with more rake (weather helm) and less power (hull not lifting) on the bad tack. There is no lack of power on the bad tack, we were still easily flying a hull

 

I would be getting the measure tape, level, and a laser level out (or theodolite) Hmm, not planning on hauling anytime soon so theodolite and level are out. Also remember that being a with a wide shroud base and rotating mast rig tension is minimal. because we were towards the limit of the full main wind wise we had already dropped off the top mast stays and backstays to let the top of the main blade off. I will do a quick check with the halyard to the back corners to check the rig is square when unloaded.

 

If I had weather helm on both tacks I would indeed be looking very carefully at the rig. 

we were on the no2 jib, and sheeting was consistent, its was on every tack that port had weather helm, starboard was finger tip control.

 

If it was a foil or rudder rake, I would expect to feel it on both tacks, but I'm not (cassette rudders by the way, so no chance of kicking back.

 

It seems to be pointing towards a foil twisting when loaded in a particular direction, time for a close look at the rudder cassettes and daggerboard cases for cracks

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When I read your post Ed, my first thought was rig leaning over or possibly not actually on center ( I had to put an adjustable rig in a 5o5 for a customer who only went fast on one tack. Turned out the mast gate at deck level was built off centre. We measured from the chainplates and all seemed well, as the chainplates were offset too!).

 

I also thought about foils etc, much as suggested earlier. One other possibility could be a curved rudder blade. Not likely, but possible. I remember leaving my starling rigged with the rudder on and going to lunch when I was a kid - when I came back I had lee helm on one tack and major weather helm on the other. The blade had warped in the sun.

 

There are so many variables, could even relate to the platform twisting differently on each tack.

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which tack was best ed? we were noticeably better on starboard last night than port. I have 2 mismatched centerboards and wonder if it is that, or possibly shrouds of different lengths.  but as i read the above, i wonder about mast rotation too!

mine is restricted by different purchases on each tack, so that could also be it.  

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Guest Ketchup

You say the weather helm was coming on before the hull liftedn(on port tack). and there was virtually no weather helm on th the other tack (dispite heal).

 

Is the leeward (starboard?) rudder blade out of verticle alignment? (The tip angled into the centre lone)

 

Also compare leading edges of both rudders for any differences.

 

A twisted or badly shaped rudder foil is a possibility. Rare to have such a big effect like this.

 

I Would still double check the rig, Jib tracks/b haulers etc.they have the biggest influence on weather helm.... but? you may be getting getting a stall (one side) situation on the leeward rudder that acts like weather helm on the tiller.

 

can you swap rudders and/or cartridges over and see if the same thing happens?

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When I read your post Ed, my first thought was rig leaning over or possibly not actually on center ( I had to put an adjustable rig in a 5o5 for a customer who only went fast on one tack. Turned out the mast gate at deck level was built off centre. We measured from the chainplates and all seemed well, as the chainplates were offset too!).

 

I also thought about foils etc, much as suggested earlier. One other possibility could be a curved rudder blade. Not likely, but possible. I remember leaving my starling rigged with the rudder on and going to lunch when I was a kid - when I came back I had lee helm on one tack and major weather helm on the other. The blade had warped in the sun.

 

There are so many variables, could even relate to the platform twisting differently on each tack.

Yeah I had that mast gate issue once on a production boat.

 

I got a laser level and went over the rig and had to move one chainplate forward and up, and the mast gate 12mm to starboard.

 

Found out later they had put the deck on out of alignmen.

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Guest Ketchup

which tack was best ed? we were noticeably better on starboard last night than port. I have 2 mismatched centerboards and wonder if it is that, or possibly shrouds of different lengths. but as i read the above, i wonder about mast rotation too!

mine is restricted by different purchases on each tack, so that could also be it.

 

agree on rotation. on tornado,s we used to tension up pre bend in the rig (though the spreaders) and this combined with rotation could make a big difference to mainsail shape/power from tack to tack if the pre bend and rotation were out on one side compared to other.

 

Do you guys rely on mainsheet tension, up wind, to tension the forestay?

If so then the main sheet tension being out by a small amount between tack can have a huge influence on both mainsail and jib shape (Fore stay sag opens up the jibs leech and drives shape aft. Which has an effect on moving the CE aft and thus weather helm)

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You say the weather helm was coming on before the hull liftedn(on port tack). and there was virtually no weather helm on th the other tack (dispite heal).

Is the leeward (starboard?) rudder blade out of verticle alignment? (The tip angled into the centre lone)

Also compare leading edges of both rudders for any differences.

A twisted or badly shaped rudder foil is a possibility. Rare to have such a big effect like this.

I Would still double check the rig, Jib tracks/b haulers etc.they have the biggest influence on weather helm.... but? you may be getting getting a stall (one side) situation on the leeward rudder that acts like weather helm on the tiller.

can you swap rudders and/or cartridges over and see if the same thing happens?

The rudder blades are pretty good, nothing major on either.

It's not a stall, the reason I say that is earlier in the race we sailed through a wake or something that tripped the flow on both rudders, wierd feeling, like there as nothing attached to the tillers. A quick wiggle of the tiller, the flow reattached and we were again.

 

We didn't have any issue boosting downwind with the kite on either gybe, so I'm thinking more and more its a daggerboard issue

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The rudder blades are pretty good, nothing major on either.

It's not a stall, the reason I say that is earlier in the race we sailed through a wake or something that tripped the flow on both rudders, wierd feeling, like there as nothing attached to the tillers. A quick wiggle of the tiller, the flow reattached and we were again.

We didn't have any issue boosting downwind with the kite on either gybe, so I'm thinking more and more its a daggerboard issue

Would'nt a rudder or foil issue replicate the problem own hill?

 

A foil shape or setup issue, at a certain speed/s, will be there no mater what direction you sail!? mind you downwind you have a A sail up and more CE (sail area/power) In front of CLR (pivot point) so this would offset any weather helm issue from rudder.

 

Swap,rudders over?

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Guest Ketchup

Maybe Plan B had a lump of weed, fishing line with a fish or bucket, stuck  on a center board.

That will not cause weather helm.... just turn a cat into a dog? :-)

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bah! - Blew up another cassette Saturday!   Again, moving 12 knots+ rounding a downwind mark (no jibe) and BLAM! The tiller had no undue pressure either way before the break.   I think the lower forward rake of the rudder, which is likely in an overbalanced state, led to the rudder suddenly taking over.   This blew out the back and side of the cassette....

 

So now I've had a chance to rebuild both cassettes.

 

I intend to run my rudders at half height from now on and see what we get.  I haven't had a case where either rudder threatened to lose bite with that 20 foot beam, and at speed, I'm thinking half rudders are sufficient.  And the full 1.2 meters of leverage that the fully deployed rudder provides is killing me.

 

This failure was a bit tricker.   It was a lee shore and winds rising, but we managed to get a hook down 5 meters of water. In a rising seaway, I removed the undamaged blade from the shattered cassette from there motored to the pier on the remaining rudder.

 

Building new rudders might be in the cards next year....

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