Most 40' cats have 60' masts, right? Again, that's what google says, I know nothing.

Maybe, but most of them weigh several tonnesand only have one mast.

Good point. the HP's have way less mass, but have a huge lever arm.

50-60% of the length, similar to most modern cats..

So the expected center of mass of a HP is the center of the boat? Interesting, I was expecting a more ww bias.

Depends on all the variables, bit 60/40 ww/w is 'normal'

Wait, if it is a 60ww/40lw split, then the HP has a 10% greater arm then a Cat, right?

For the same weight and beam , the HP has a higher righting moment.  The cat rm is 0.5 x weight x beam,  (say 4 tonnes x 6m = 12 tonne metres), the HP rm is beam x weight carried by the ww hull.  (0.6 x 4 x 6 = 14.4 tonne metres).

20% higher, not 10%.

But you have an honest limitation/point. A modern HP is much lighter than a typical cat.

I am not sure how per $ comparison would be made.

But, the ability to add weight and remove it easily and quick, to ww water tanks, at 2x the moment arm, is neat. so in a blow, this is easy to do, i guess. add huge margin when needed?

Not unless it is light to start with.  The beams and rig are sized for the payload in the windward hull.  This should not be exceeded.  Capsize is not likely if you sail sensibly.  One of the great things about harryproas is they can be sailed with minimal sail and speed as a) the rudders are large, b) the boat is easy to balance with sails and rudders and c) it does not need speed to tack.   Therefore, reducing sail in marginal conditions makes far more sense than adding weight.

Sure it does. For any reasonable sailor, it does.

But, if one imagines racing, then it could be a useful trick the other guys cannot do. Just adding just 5 or 10% is huge for stability, in a gusty windy race.

So, its like a bucket list trick, right?

Yeah, as long as the ww hull is not loaded past the design limits.

Well, as that Shuttleworth notes, composites have a 10x design factor in order to have a near infinite fatigue life. So a short term loading should be OK, right?

But I am not sure how adding this weight effects raft stability, but my early guess is positively, for certain hull orientations, as it can lower the ww hull wave impact energy?? assuming ww hull is wave impact hull

Raft stability is huge, a bit of water will make no appreciable difference.    Wave impact will be more of a problem with a heavier boat and/or a boat with excess leeway prevention.  Lift the rudders and it is almost impossible to capsize by wave action.

Even crest energy?

Yes. Unless the wave is breaking due to shallow water, when it will be steeper than at sea. Would still need to be a very large wave, at least the beam of the boat..

How did you decide on the mast height on the 24m?

The same as on all the boats.  Started with the required Bruce Number (sq root of sail area in sq' divided by cube root of weight in lbs) and worked from there.  The 24m needed a BN at least 1.3 when fully loaded (10 tonnes, plus 3 tonnes of boat = 29,120 lbs.  Cube root is 30.1).  So SA is 30.1 x 1.3 squared = 1531 sq ' = 142 sq m. 2 sails of 71 sq m each.   Rectangular sail, boom length 4m, aspect ratio of 4:1 = 17.75m luff.  

Excellent.

So, assuming I know nothing, is not all the Bruce number and these ratios based on traditional observations of typical boats?

It is a power to weight ratio.   The actual number chosen is a combination of weight, ease of build/use, cost, windage when reefed/anchored and experience.  No reason why individuals cannot have more or less if they want it.  The rigs and beams are engineered to resist capsize, so bigger/smaller rigs do not affect this.

Ya, but SA on stayed masts in one thing, SA on an unstayed mast is a different thing, in that the cantilever beam deflection curve makes SA not constant, right?

Yes.

So the Bruce number changes for the HP in heavy wind, but cannot for a typical cat.

Unless the cat reefs, eases the sheets or luffs.  

Hey, that's cheating! we are looking at capsize wind speeds, not what to do when approaching capsize wind speed.

my point is the capsize number gets higher slower as the wind speed rises vs what this formula would show.

Yes, an advantage of unstayed masts.

My point here is a typical designer/engineering number is kinda broken for weird boats.

The number remains relevant, but you need to include the weird factors.   A cat with low aspect ratio keels will have a higher windspeed capsize number than one with daggerboards.  

ya, that's better. weird factors.

Have you a set of weird factors for the HP?

Not really.  The whole strength/stiffness/loads exercise has so many fudge factors in it that the answer is pretty imprecise, so adding more does not achieve much.  

Like what beam deflection do you expect for the self made CF masts? And do you have an approximation of how that deflection effects SA?

On the C50, the mast tip deflects 3m at capsize and 1.6m at 30 knots apparent.   Maybe 50-70% (your guess is as good as mine) of the sail on this section of mast is not contributing to the heel due to twist and lay off, so the centre of effort is lowered by 2m at capsize, 1m at 30 knots.  Plus minus the increased wind as distance above the water increases and the amount of roach on the sail that is not working.

neat.

Increased wind at height is another typically ignored factor. it seems a negative for stayed rigs and a positive for yours. although perhaps if the HP rig is very much taller than a comparison boat, it might change.

But, as I see it every effect we have postulated about only positively effects stability.

Can you see a negative stability effect of your masts vs typical rigs?

It seems way more legitimate, perhaps to just my mind, to use more direct measurements like righting moment and the moment of a dangerous 'gust'. Does something like that exist?

Sure.  See about 1/3rd of the way through http://www.shuttleworthdesign.com/NESTalk.html   A similar formula is on Wharram's and opther designer's pages.  They are based on  Drag of a flat plate at 90 degrees to the wind equals 0.5 x area x (wind speed squared) x the coefficient of drag, which is near enough 1..   This is assumed to push half way up the rig (variations include wind sheer, underwater shape and mast bend, especially for unstayed masts) vs the righting moment.   Make sure all your units are correct.  The answer is usually somewhere between 20 and 25 knots for a harryproa, without allowing for the mast bend.  

Ya, but, all the assumptions in these formulas do not directly apply to HP's. Or at least, not as constants.

They don't really apply to any boats.  They should be looked at as comparative guides, nothing else.  As the boats compared get less similar, the results are less relevant.

Fair point.. But the lecture is literally on Cat vs Tri. Now, to be fair, the source article its not really about calculating heeling moments, but on showing how to understand heeling moments. And it has really done that for me. Thank you much for pointing me at it.

The author did not bother to detail many weird factors to compare a Cat to a Tri.

It would be an interesting article to replicate as HP vs Cat. Detailing the weird factors would be fun.

The difference between HP, cat and high buoyancy float tri configuration in a capsize scenario is no different.  What is different is the rigs.  Put an unstayed rig on the cat or tri and it will have the same effect as on a HP.

Does not the triangular raft shape, wave impact, and wind drag, assuming bare poles, favor the HP? In that the orientation in a storm would like put the HP in the most favorable orientation?

The 'Stability in wind' section assumes symmetrical boats and boats without the ability to positively effect stability in high wind via water tanks. Which adds displacement which the formula suggests reduces stability.

Weight is not mentioned, except in terms of righting moment.  Add weight to the lee hull of a cat or a harry and the rm doesn't change.  Add it to the ww hull, it changes twice as fast in the harry, assuming same beam.

The SA and CE are constants, where they reduce as wind climbs in a HP, making it more stable in higher wind than the formula suggests.

yes.

The curve in the 'Stability curve and stability in waves' section, plotted for a HP, especially a self righting one, would be kinda weird, but fun.

Yes.

Side note Rob. Why do you do a beam = 1/2 LOA? Why not less or more?

It is not fixed.    Windage, beam length/stiffness, helm balance, deck space are all considered.  The prototype 24m cargo proa is 9m wide.  The 21m Bucket List was 8m wide (at least in one of the iterations).

I can see the helm balance effected as you widen. And as it widens you need bigger beams to maintain stiffness, as larger moments.

How far forward would a typical cruiser expect to see the wind come? if its not that far, then the beams wont really add much at sail, right?

Right..  The min angle will be about 30 degrees.  

So is the windage more about at anchor or under motor?

Windage is a big deal upwind.   Shuttleworth has a good article about this as well.   At some point, extending the beam becomes counter productive as the boat becomes unsafe fore and aft.

BAH! Ya, upwind! Silly me.

How does it become unsafe fore and aft? And when do you expect that to happen?

Why do we not use an aerodynamic profile of the beams? Although I did read about Steinar adding covers to them?

Also, when I look at the Harry, say vs. the Ex40, the shapes early on seem significantly more aerodynamic. Probably an artifact of bending flat panels. But it seems aerodynamics are secondary in modern HP's. Steinar's custom excepted.

have you any thoughts on this?

If the free labour and overheads are still on offer after the lockdown, the most expensive part is the carbon, then the foam.  Using a truss structure, the beams can be made from glass rods which are easier to infuse than carbon, cost very little and although they have to be a little bigger to compensate for the lower stiffness, should still have less windage..  

Getting away from foam requires much smaller hull panels and maybe some form of corrugated core, which I am experimenting with this week.    Otherwise, the hull construction will be solid glass with easily built f'glass I section stringers.   Fairly thick glass (max 10 layers of 400 gsm uni in various directions) is required for toughness and to stop the small cross section hulls bending excessively, so we should get away with only one stringer per panel.  Building the hulls in half moulds, the join will act as the stringer on the deck and bottom.    10 layers of infused 400 gsm weighs 6 kgs per sq m..  20mm H100 (recyclable PET or similar) foam with 1200 glass each side also weighs 6 kgs per sqm, has better panel stiffness, is less tough, requires extra laminate at the beams and is a lot more costly.

hey, i was talking up reducing the foam costs before it was trendy!

;-)

If you are looking at protruded rods anyway, have you looked at half rods,square tubes ,or flat plates to corrugate your panels?

Yes, but all are heavy

Sorry to go back to this, but, if you laid a half rod every so often you could really stiffen the solid glass panel, right? And half rods should be easy to layup?

is the weight any worse than your solid glass hull?

Didn't our friend in the northern European country have F700 for very cheap per m^2? have you decided against it? Apparently they are not locked down.

yes, but not as cheap as corrugated glass, if it works..  Picking up the mould today, might get the first piece laid up tonight

PICS!

Will do.   Attached is a screen shot of what i am thinking of.  The blue and grey corrugations are glued together, probably during the cure of the grey sheet, then if required, the red flat sheets are laminated on each side.  Lots of variations with fibre direction and type, and on long skinny hulls whether corrugations in both directions are required.  Big problem for hulls is how to infuse it all in one shot.   However, as I am not paying for labour, it may be worth doing it in multiple shots to reduce costs.  

re corrugation, how about  https://www.math.wisc.edu/~miller/old/m223-96/progs/sin3.gif which may make it one infusion for the core, plus flat laminations.

Would Biax drape over that?

No.  

Would anything?

It would have to be a very loose weave, in which case it would probably not span the humps.

I guess you could press it between male and female molds

Fibreglass doesn't stretch.

I wondered if the tow could slide along each other, as some shift into the peaks and valleys and others stay sorta straight. I imagine that leaves the ends frayed

Probably better with corrugated

One could adjust the actual shape. but it only gives a fraction of the support against the outside skins that the corrugated does. However it does handle loads better.

Egg crate material is used for reinforcing moulds built with chopper guns.  Works well, although it cannot be rolled to remove the air bubbles.

How do you vac infuse the grey AND glue on the blue? wet layup?

Yes.   Or infuse them both, then sand and spot glue, which might be a good solution if some means of accurately applying small amounts of glue can be worked out.

Peel ply strips along the peaks and troughs?

Straight edge along the peaks and mark the touch points then cake bag them with dabs of thickened resin? I guess that would give a little structure to the touch point and spread the load?

The corrugations are 1.5" apart.  That is a lot of glue dabbing.

Is this mostly for bulkheads?

How are you doing the corrugated mold?

Roofing iron.  

How do you seal the edges for infusing?

The bag either seals to the mould, or encloses the mould and seals on itself.  

How do you stop the hollow corrugated core filling with resin when the hull is infused?

No idea..  Have to seal the ends somehow.  Even then, the risk of a pin hole would make it a pretty silly exercise.

Do you plant to fill it with resin? or just have not got that far?

 

How do you seal the corrugated core edges?

No idea.  For bulkheads, it won't be required.  

Perhaps the price of foam will drop after all this?