This is exactly were we are now with the current tipweight rule. And this is exactly what was intended when we incorporated this rule.

I worked on several updated F16 alu mast designs (none in production at this moment) and a 6 kg tipweight is impossible to achieve on any dependable alu F16 mast.

Stiffness is NOT an issue in this as you can pretty much have any stiffness you want for a given mastweight by adjusting the crossectional profile. The issue is truly strength as at a certain point the wallthickness will become so small that the wall will easily buckle under the compression loads resulting in a total failure of the mast (=collapsing and breaking). But interestingly enough this can be corrected to some measure by pressurizing the alu masts, however this is a different topic. (Compare this to the russion inflatable catamarans)

Carbon masts are the same in this respect. Personally I always wondered why carbon mast builders don't use plain glass cloth to beaf up their mast in (wall) buckling resistance without affecting the stiffness of the mast much at all. Also glass cloth is CHEAP ! And if they do (I know some do) then why not use a little more plain glass cloth to get up to the tipweight of 6 kg without affecting the stiffness much at all while making the walls alot more buckling resistant (=dependability).

I would really like to hear a carbon mast builder tell us why this can't be done.

Wouter

But Wouter, you are asking the mast makers to add weigh to their mast because the rules say so.

The figures I have are that they can make masts lighter if they were allowed to. The rule we have in place are forcing the makers to make their masts over they weight than can make them to (or in fact add lead to the top to make them measure to the current rules). The figures I also have suggest that they could make masts about 1-2 kg lighter (all up weight) and remain more than strong enough to cope with the loads applied.

Wouter

You asked for some data to corroborate the claims that carbon masts can be made robust at significantly lighter weight, well here is my 2 cents worth.

We have to date built over 60 F16 carbon masts, we have broken 6.
1 was driven into a pub whilst on it's trailer, 1 was driven over by a car, 1 was broken whilst flying a 21sqm mast head kite, twin trapezing with the main flogging trying to get round a headland, and 2 failed because we built them to a special spec. and the last one had a ridiculous amount of diamond wire tension.

The first masts came from Holland composites, we then bought the mast mould and continued building them to their specifications.

About 18months ago I revisited the spec that we used and came up with a new laminate, the old one was plenty strong enough but I wanted a stiffer mast.

The old spec did indeed have glass in it and there is no reason why this cannot be done, however although glass is cheap, pre-preg glass is not, indeed unless you buy very large quantities it is almost the same price as carbon.
And as you say you can pretty nuch put as nuch as you like in there without effecting stiffness.

Anyway the new mast spec gives a tip weight of 5kg, I just weighed one with diamonds main halyard, and spinnaker halyard in it 5.05kgs.

Purely by coincidence the guy who broke the last mast is a structural composite consultant, he works on very large multis, did Ellens boat and mast, and is doing some giant in Australia at the moment, his credentials are impeccable.
He wanted to ensure that his next mast was stronger and stiffer as he sails with his crew at 190kgs.

He ran the calculations on both our mast specs, the old one had a Euler buckling failure of 1.8 tonnes, and the new one is 3.3 tonnes.

Back to adding glass, the old mast had a significantly thicker wall than the new, carbon is just a hell of a lot stronger that glass, I see no point at all in spending more time putting glass in adding unnecessary cost and weight to a mast that is clearly more than strong enough. I am sure that my customers would not want to pay the extra for a mast that is stronger than it needs to be and heavier than it needs to be, they will simply strap on lead for events that require it and take it off for club racing.

For our mast which has a bigger cross section than the superwing it is a fact that we could reduce the weight and still be strong enough, however the mast would not be stiff enough for our purposes, so it would be slower, so from a strength point in order to get it stiff enough it is overengineered on strength.

You say that stiffness is not an issue since you can adust the cross sectional profile, and you are right, however to do this you need to build a new mould every time, this is not a practical suggestion.

Thank you very much John Pierce,

Finally somebody who is willing to go on record with this !

You've provided some very interesting info. I wonder if we can get some of the other carbon mast builders like Fibrefoam and Saarberg to contribute to this discussion in public.




Naturally I was commenting on the engineering side of the topic. Here stiffness is not a big limiting issue. I was not suggesting that customized stiffness distribution was to be implemented by using different crosssections. Basically what I was saying that a crossection can be chosen as to satisfy the most flexible mast bending requirement where the mast walls are solid enough to handle the loads and (off the water) abuse. From then onwards the customizing can be done by adding cloth were needed (making the mast more robust simultaniously). In effect the first case determines the mould and with this mould all customized masts can be build.

I write this in clearification of my comments earlier to other forum readers. Naturally you and I were on the same page already.

Again thanks alot for providing us with some hard data.

Wouter

And worse still, I'm asking the hull builders to add weight to the F16 hulls because the F16 rules say so as well !

But seriously, what you saying is actually the core principle of a formula class rule set. Some claim that 18 foot long hulls are way better for a singlehander, but the F16 rules demand the hull to be equal to or shorter then 5.00 mtr. Same with the minimal ready to sail weight, the Marstrom M18 has proven that an 18 foot long spinnaker singlehander with F16 specs for the remainder can be build at 80 kg ready to sail. Still the F16 class demands that the boats weight at least 104 kg in 1-up mode. All these limitations on what CAN be had technically were not the result of us not knowing any better a few years back. Under all rules there is a balancing between technical capabilities and economic c.q. perceptional considerations.

More often then not a formula rule framework asks the builders to build something to a lesser degree then can be had with cutting edge technology. This is the core intention of the rules and rule makers as this prevents an arms race and garantees economic feasibility. So I will argue that the fact that something CAN be build to more impressive specification is in itself not an sufficient reason to claim that a formula rule framework needs correcting. In most cases limiting this possibility was actually the intention of the rule in the first place.

A far more persuasive argument can be had whether the reasons for limiting this possibility are still present.

I feel personally that times maybe changing and a revision of the reasons that gave birth to this particular rule may be in order.

Wouter

Just a little about carbon masts that most people are unaware of.
Firstly most people relate breakages of carbon masts that occurred with A class masts in the past to the same way that aluminium masts broke. That is that the aluminium section under extreme bending/shock loadings folded on the compression side of the section and bent etc. With a carbon section although the end result may appear the same that is not exactly what happens. In layman terms we can say that carbon fibre has enormously good properties under compression but is far less strong under tension/stress/twist loadings, so that unlike an aluminium section that will “fold” on it’s compression side wall, in the same type of situation a carbon mast “breaks” on the other side of the section wall I.E the fibres are literally pulled apart on the tension loaded side. We extensively tested “to failure” several standard sections of carbon A class masts before we decided on a carbon laminate for our masts on the F14 and we found that in the vast majority of breakages that occurred to the A class masts all failed approx 600mm to 800mm below their hounds and had literally been ripped apart on their tension side. This 600 to 800mm distance is where the greatest load will occur on a mast when it is “slapped” onto the water forcibly. The hounds act as a fulcrum and the diamond wires restrict the section below the hounds in their ability to “flex” and disperse the shock as much as the unstayed section above the hounds. To obviate this potential failure in our sections we simply have added a section “patch” of 300gm/sqm of Kevlar to the laminate from just above the hound location to approx’ 1m below the hounds. This has to date proven completely successful and apparently seems to have made our mast sections “bullet proof”

May I ask what the unit weight of your masts are Darryl. Is it near the 1.1kg/m that has been suggested previously in the post?

With kevlar reinforcing the BARE mast section weighs 8.6kgs for a 25' length section (you can do the equivalent maths conversion - though somewhere near 10 to 11 kg for an F16 BARE length) the 25' length fitted is 10kg (plus or minus) for a section for an F16 the per metre weight would probably increase slightly as we would modify the ratios of the laminates

In this post I do the unit conversion and the math for our forum readers.
The statements in this thread do not convey my personal take on the issue in any way.





F14 carbon mast (25 feet long = 7.62 mtr) :

8.6 kg / (25 * 0.3048) = 8.6 kg / 7.62 mtr = 1.129 kg / mtr

If this particular bare mast were 8.5 mtr long (F16) then it would weight ; 8.5 mtr * 1.129 kg = 9.593 kg

Using the earlier stated rule of thumb : tipweight = 1/2 * bare mast section weight + 0.75 results in.

1/2 * 9.593 + 0.75 = 5.547 kg tipweight.

In my calculations I found that the fittings themselfs add 2.64 kg to the mast and 0.827 kg tipweight. If lightweight spreader arms are fitted (proctors are relatively heavy) then numbers are 2.40 kg and 0.75 kg. Hence the use of the 0.75 number earlier.

With this averaged info we arrive at a F16 carbon mast, based on the F14 specs, that have an overall weight of about 9.593 kg + 2.40 kg = 11.993 kg. = say 12 kg overall. And this EXCLUDES the weight from the halyards and trapezelines !

These halyards (main and spi) are about 200 grams = 0.2 kg per 16 meter. And so these add 0.2kg to the tipweight while adding 0.40 kg to the whole mast. 4 high tension line trapeze lines are combined 0.2 grams and add 60 grams = 0.06 kg to the tipweight. These are pretty much neglectable in the overall picture.

So our estimate of the F16 carbon mast based on the F14 carbon mast comes out at :

Overall weight = 9.593 + 2.400 + 0.400 + 0.200 = 12.593 kg = say 12.5 kg
Tipweight = 5.547 kg + 0.200 + 0.060 = 5.807 kg = say 5.8 kg

As a comparison : the Alu superwing (Taipan, Blade, Viper) mast has the officially measured (averaged) specs :

Overall weight : 18.0 kg (and 20 kg including the 4 mm thick stainless steel standing rigging)
Tipweight : 8.25 kg (excluding the standing rigging)

At 85-90 kg dry body weight I have never encountered problems righting my F16 (which is 121.8 kg ready-to-sail when fully sloop rigged)

The Stealth specs are given in the post by John Pierce earlier.



Also note that Darryl wrote :



Also note that some weight savings can be had by using very lightweight fittings and a push up mainsail. But also note that these change will not alter the calculated tipweight much as the above example shows.

Interestingly enough these calcs mirror closely the calcs that supported the 6.00 kg tipweight rules choice in the past.

Wouter

Using the data gethered in my post above we can estimate the difference in righting between an Alu and carbon mast, this may be of interest when balancing the pro's and con's.

Additional data is that a pentex mainsail itself will weight 5.5 kg with a centre of effort at about 4.150 mtr up from the mainbeam. With a mast angled downwards (10 degrees) in a capsized position the leverage becomes 4.150 + 0.220 mtr = 4.370 mtr= say 4.50 mtr. This results in an added virtual tipweight of about 4.5/8.5 * 5.5 = 2.911 kg

The 94.5 kg platform (using a 12.5 kg mast on a 107 kg ready to sail boat) is also angled at 10 degrees and thus also provides some additional virtual tip weight of (sin(10)*1.25*0.5*94.5) / 8.5 = 10.256 / 8.5 = 1.207 kg

So the total virtual tip weight of the whole craft on its side is :

Alu mast = 8.25 + 2.911 + 1.207 = 12.618 kg
Carbon mast (12.5 kg total) = 5.8 + 2.911 + 1.207 = 9.918 kg

In effect the carbon masted boat takes 9.918/12.618 kg = 79 % = say 80 % of the righting moment that the alu masted F16 does.

And a tipweight lowering of 1 kg results in :

5.00 + 2.911 + 1.207 = 9.118 kg tipweight => 9.118 / 12.618 = 72 % resulting in a 7 % gain in righting ability.

If 100 % equals a 85 kg skipper (me) then 7 % improvement of righting constitutes 5.95 kg less skipper weight needed to right the boat relative to the current tipweight rule.

It is to the class members to evaluate if this is enough of a reason to propose and support a class rules change.

To give some perspective to these calculations. If we assume that it takes at least 85 kg (=me) to right the alu masted F16 in ALL conditions including no wind and perfectly flat water (a very demanding condition) then it requires 67 kg to right the F16 with a carbon mast compliant with the current rules and a 61 kg skipper if we lower the tipweight rule to 5.00 kg.

Many of us have indicated that a little wind makes righting the alu masted F16 significantly easier, probably requiring only 75 kg to right the alu masted F16.

Wouter

So we are limiting persons to 61kg who can sail the boat single handed. There was a lady at the A class Nationals at Mumbles who was 58kg - so she cannot sail the boat !

Edit to add - Wouter, do you calcs take into account your height - if so we are limiting the boat to persons of 61kg the same height as you ?

Are we really ?

Is it impossible for a "61 kg or less" skipper to use shroud extenders, righting bags or other righting aids ?

In the end of the day there is going to be a threshold somewhere with individual sailors falling on either side.

The paramount reason for the formula rules is to equalize performance over boats of different make, not to garantee that some extreme skipper can right the boat without additional tools.

Wouter

It would be really neat to see an auto-trimming foil like shown in the attached sketch. The concept is similar to the Ketterman trifoiler, where the foils automatically generate negative lift on the windward hull when it wants to fly, increasing righting moment.

Glen;

My approach is similar, but uses cams within the foils to do it.

Foiling is not how it seems . It is the leeward hull that rises on a Ketterman Trifoiler, not the windward. The drawing you have added would lift the stern and bury the nose on the windward hull and the opposite on the leeward. If it were foiling it would raise that hull but that would be exactly what a foiler would not want. We dont foil on catamarans so trying to use a foil to balance the boat rather than sailing it balance must be couterproducetive. T foils temporarily correct an ill balanced boat. That is why they are so effective.

Have a look at the following for how the Ketterman works. It's very interesting.http://www.hobiecat.com/support/pdfs/trifoiler_manual.pdf

Maybe I did not make it clear. My design would create lift from the leeward ruddder and "drag" from the windward rudder. So pushing the stern of the leeward hull "up" and the pulling the windward rudder down. This will result in considerable twisting moment within the beams / hulls, this is why I believe the a new beam / hull layout would be needed to make the most of this.

When you say "drag" do you mean "suction" or "negative lift"?

Drag is usually the term associated with a force acting against the direction of motion. For lifting foils this is a horizontal force. This would not pull the windward hull down, generally speaking it would just slow the boat down and make it yaw to windward.

If you're talking about suction or negative lift then yes it will increase the righting moment of the boat.

I think he means "upwards" lift on one foil and "downwards" lift on the other, which are both positive "lift" but acting in opposite directions. (which would create quite large additional twist loadings to the beams and beam mountings if it was to be effective particularly with it acting at the stern(s))

YES, negative lift in order to create RM

it was late

But cats already are being twisted significantly under the rig loads. Off the top of my head, I think the T-foil would only reduce the twisting loads or maybe reverse them a little in special cases (high angles of attack on the foil).

What size foils are we talking about here. If you're talking about say 400mm * 150mm, you'd probably only get about 40kg of up/down force at an efficient angle of attack that doesn't create too much drag. If you want anymore force you're talking about foils on each rudder the equivalent of the total area under a moth (700*150 and 600*130 -ish)! They're gonna be very big, feasible but big. And I believe the foils are included in the beam measurement of the F16, so they will likely have to be L-foils, not T's, which will be even trickier because of the structural issues.

Just quickly read the rules again, I'm not sure if the centreboards or rudders are now included in the beam measurement. It says "overall beam" which I take to mean beam of the boat when taking everything into account in its normal position...can anyone clarify?

I'm need to think about these rudder foils some more...