Who has owned a cat with daggerboards?

[etoimene]

Originally Posted by Chotu

Note: the large faces of the board have multiple layers of triax strategically placed to take the side loading of the boat under sail, but these have nothing to do with the board’s strength on impact from an underwater object.

Hmmm ... nothing?

[Chotu]

Originally Posted by etoimene

Hmmm ... nothing?

Literally nothing. Think about it.

In a severe impact at speed, the force vector comes from the front/leading edge of the board. The extra triax to handle side loading handles forces that are 90 degrees to this force.

What happens when you apply a huge Impact force to the edge of a composite panel?

It easily delaminates, the core falls apart and the skins fold up.

The board will break apart on an impact like people are discussing. The triax on the large faces of the hydrofoil will fold up like the flimsy house of cards it is when impacted on edge. It only has strength athwartships.

I’ll also add the leading and trailing edges of mine are 12oz cloth (2x 6oz layers). So those are soft too.

You can make a new board in a couple days. Making a new trunk or hull or taking on water? That’s a nightmare. So a well designed and built boat has boards that are well designed too.

This eliminates any concern of damage from impacting your boards at speed.

[rob denney]

Originally Posted by tcpbob

rob, i hate to say it but that is alarmist. it is obvious you have a barrow to push here but don't let your personal, perhaps financial interests get in the way of common sense.

your array of unsupported assertions are embarrassing. build your boat anyway you want but respect others who differ, who are about a million to your one.

You are shooting the messenger.
Which assertions are unsupported? What do you think will happen when a boat with daggerboards or a fixed keel hits something just below the surface/forefoot at a "performance cruiser cat" speed?

If owners have not considered this possibility, then 'alarming them' is probably a good thing.

Does tcp in your name stand for The Coastal Passage? A great read, including the part about Bare Bones hitting a log at 10 knots, spinning the boat around. What happened to TCP?

Catsketcher,
Sensible thinking, good to see that you have considered it.
Slowing down in case you hit something is a good solution, but takes you out of the 'performance cruiser' bracket I was talking about.

Imagine the boat hits something solid at your reduced 10.5 knots speed with board more than 300mm down. There will be a small time while the bows submerge and the board crushes into the back of the case, but then anyone standing up will be launched forward at near enough boat speed. Running speed for an average man is about 6-8 knots, so it is not inconceivable that the result will be running into a bulkhead as fast as you can run. That is "worth a few design compromises" in my opinion.

Did you do any tests to confirm the 500mm (?) long glue join will sheer off in a head on collision? As opposed to it peeling off in a grounding.

Chotu,
Also a good solution, if you don't mind building new boards and carrying around the extra weight to beef up the cases. What do you use for a sheer web? And how does it fare in the imagined collision?

[fxykty]

How often does a sailboat hit something solid such that it comes to a stop? While sailing, coastal or ocean? Such that the crew are injured?

Answer: very rarely, similar to getting hit by lightning. Or even much less common than getting hit by lightning.

Next question: how often do performance CRUISING cats sail as fast as or faster than 10 knots on average?

Answer: not that often - 250+ mile per day distances for cruising boats in cruising trim are not very common. The times it happens are exceptional, not usual.

Due to those two answers, Rob’s assertions of the probable danger of hitting something at high speeds (which of course isn’t limited to cats with daggerboards, but for some reason he focuses on them) absolutely is alarmist.

Some further questions:

Has there ever been a case of a cat with daggerboard cases that have failed?

Are daggerboards typically designed to fail at a lower force level than their daggerboard cases? Is this a fuse fallacy in the same category as standing rigging that is less strong than maximum righting moment? Or is this something that can be reliably designed, engineered and tested as some posters have said?

[Chotu]

I’m sorry. I missed Rob’s response.

If we are talking about a shear web inside the foil, the foam and skins take up that purpose. It’s not hollow. It’s a giant piece of foam shaped into an NACA foil.


The boards are nothing more than NACA foils wrapped in glass, but with the right amounts of glass in the right spots to both support the lateral forces on the board and give way on impact. They were actually my first resin infusion practice project, along with the rudders. The foam core just absorbs energy and deforms on impact. For those that have never worked with foam, just picture impacting styrofoam insulation. What happens? It absorbs the energy. Just like my boards.

I had to build new boards anyway since that’s part of building a boat, so I did it right.

Yes, I took a little weight penalty for making stronger cases. I felt it was an ok trade off. We are talking maybe 10lbs.

[Tupaia]

Reality check.

There are almost no fast cruising or racing boats that will do 20 knots to windward, the only time that a daggerboard needs to be down so this is an alarmist response.

We have hit a container doing about 12 knots at night on route from Panama to Galapagos. The board had the tip down which is angled at 45 degrees and it rode over it. The rudder was hit about 2ft below the surface and it sheered the plate and kicked up. There was a bang that is all, no noticeable deceleration. After a few checks we replaced the plate and sailed on.

Seven months later when hauled in NZ we discovered the rudder bearings on that side were worn. Further inspection identified a tiny notch in the leading edge of the rudder and the 2.5 inch solid ss shaft was very slightly bent. It was rectified on a hydraulic press and the bearings replaced. The system did what it was supposed to.

Is rob suggesting boats need to be fitted with bulkhead airbags to prevent people running into them from being injured. This wouldn't prevent being run down and sunk by a ship that could happen to any vessel, proas included, or monohulls sinking due to rusty keel bolts that is probably more common.

Sailing is not guaranteed to be safe in the same way that road transport to which most people are exposed to on a daily basis is proportionally much more dangerous.

[rob denney]

If you really believe there is nothing out there to hit and even if there was, it is not worth worrying about it, then you go for it. *My comments were aimed at people who hope for the best, but prepare for the worst and are interested in discussing design solutions to boat problems, which is the purpose of this forum.

*

Originally Posted by fxykty

How often does a sailboat hit something solid such that it comes to a stop? While sailing, coastal or ocean? Such that the crew are injured?

No idea, but those are the wrong questions.
Try: Are there objects where I sail that are big enough to stop the boat if they are hit? * How much damage would be done to the crew and boat? *

Originally Posted by fxykty

Answer: very rarely, similar to getting hit by lightning. Or even much less common than getting hit by lightning.

In most of the world, more boats hit something in the ocean than are hit by lightning. * In lightning prone areas everyone takes precautions, whereas with daggers, the mind set is often that nothing will happen. *

Originally Posted by fxykty

Next question: how often do performance CRUISING cats sail as fast as or faster than 10 knots on average?

This is not an exercise in statistics, it is about damage limitation and personal injuries. Consider the likely damage at the top speed on an average 10 knot speed day, not the average. Or don't. *Your decision.

Originally Posted by fxykty

Answer: not that often - 250+ mile per day distances for cruising boats in cruising trim are not very common. The times it happens are exceptional, not usual.

15 knots is common, according to "performance cat" owners posting on this site. *And some of them advocate doing so with their boards down. *If you asked them, most would claim regularly hitting much higher top speeds. *

Originally Posted by fxykty

Due to those two answers, Rob’s assertions of the probable danger of hitting something at high speeds (which of course isn’t limited to cats with daggerboards, but for some reason he focuses on them) absolutely is alarmist.

Daggers is what the thread is about, but I include any boat with appendages that will cause it to stop in a collision. *Alarmist is not my intention, try "thinkist". *ie, to get people to think about the chances. *If you have and concluded they are not an issue, go for it. *

Originally Posted by fxykty

Has there ever been a case of a cat with daggerboard cases that have failed?

Several, but it's not pertinent. * if the board or case doesn't fail, the boat stops, but the people don't. *
Richard Woods: we were sailing off Nicaragua, and we were sailing at eight knots. We hit a reef with the daggerboard and the boat stopped dead. In fact, my wife fell over. It was driving a car at 10 miles an hour into a wall, sort of effect. * *Double that and be standing behind a bulkhead (8 times the effect according to CT49). *Or on the bow. *Or sleeping with your head forward. Or on an elevated helm chair.

Originally Posted by fxykty

Are daggerboards typically designed to fail at a lower force level than their daggerboard cases?
Is this a fuse fallacy in the same category as standing rigging that is less strong than maximum righting moment?

The fallacy is the same for both. *It is simple to design a rig or board to break at a given speed, hull lift, impact or other specific data point. *But it is impossible to make it happen reliably, due to safety factors, build variations and varying operating inputs (waves, loads, weight location, rig settings, etc). *

Originally Posted by fxykty

Or is this something that can be reliably designed, engineered and tested as some posters have said?

Many have said it, none have tested, or proven it, afaik. And it is harder in the fore and aft direction of a daggerboard than sideways.

Chotu,
Thanks. I don't know the loads or the size of your boards, but I would be wary of only using H80 foam for the shear web on a big daggerboard, particularly at the slot exit where the sheer loads are increased by the crushing loads. Core deformation/delamination is bad news in this area as the unis on the sides get out of column and buckle on the compression side. This is probably the most common cause of board breakage. The heavier the foam, the less it will fail like styrofoam, especially along the chord.

[rob denney]

Tupaia,
Sorry, missed your post. It's great that you recognised the problem, devised a plan and it worked. This is what I am trying to encourage. Well done.

Maybe read the comments on boards down and speeds reached in the 'light air speeds expectation' thread (and others) and people's denial that there is a problem before deciding whether the topic needs discussing.

[smj]

In regards to lightning, how does one take precautions?

[Training Wheels]

Originally Posted by smj

In regards to lightning, how does one take precautions?

I find a copious amount of rum helps.

[smj]

Originally Posted by Training Wheels

I find a copious amount of rum helps.

Probably the most sensible precaution. That and a good supply of adult sized diapers.

[SVNeko]

We hit an uncharted rock in the Las Perlas with our daggerboard and rudder. Motoring at about 8 knots, the impact slowed us down to a near stop. Glass was crunched up pretty good. We were glad Switches have solid stainless rudder stocks and it did not bend. Board was many layers vinylester with a wood core. Core was ok, glass LE was destroyed. Had a hell of a time finding someone in Panama to fix it, as it has to fit in the slot precisely. NB: We informed Eric Bauhaus of this uncharted rock, and we now have a rock named after us in his later charts - Neko Rock.

[Chotu]

I wouldn’t worry about it. Here’s a video of us hitting a shipping container at Warp 9.

The starboard nacelle took a bit of a hit but no damage to the board or rudder.

Everyone was fine.

Just a bruised ego on the part of the navigator.

[GRIT]

Originally Posted by Chotu

I wouldn’t worry about it. Here’s a video of us hitting a shipping container at Warp 9.

The starboard nacelle took a bit of a hit but no damage to the board or rudder.

Everyone was fine.

Just a bruised ego on the part of the navigator.

Love it.

Cheers.
Paul.

[fxykty]

One rule of thumb on any boat that can sail fast, particularly on racing multihulls, is always sleep feet forward. If an athwartship bed, hopefully it is king size and you can turn yourself 90 degrees. Decelerations are always many times faster than accelerations, so it makes sense to protect yourself from the bows stuffing into a wave.

Hitting a container or whale or reef at higher speed, when heading downwind with boards up (thanks for someone else pointing out that most higher speed time is spent reaching or downwind where boards aren’t needed (excepting foiling boats, which I assume don’t qualify as cruising boats)) will most likely result in the bows riding over the object and ripping off the rudders on one or both hulls. Plus skin friction (especially a reef). So I don’t think there would be an instant stop.

We have hit a rock with one bow at 4 knots - that was a hard stop and bounce back. No injuries but did break one wine bottle (red, a real pain to clean off soft furnishings) and splintered a bunch of solid fibreglass in the bow knuckle - our thanks go to the designers for creating crash boxes in our bows. At double the speed that collision would’ve been much uglier.