Design to avoid Broaching

[Guillermo]

Here an explanation from Umeda and Peters:

"While a ship in waves normally experiences a periodic motion, broaching is a transition from a stable periodic motion to a non-periodic motion. This transition can be explained as hetero- or homoclinic bifurcation by executing invariant manifold analysis of an unstable surf-riding equilibrium as a saddle. The trajectories connecting two saddles in different wave slopes, which appears only at heteroclinic bifurcation point, looks like a periodic orbit but has a period of infinity because the velocity on a saddle in eigen direction asymptotically tends to zero. Thus this trajectories can be regarded as a limit of periodic orbits and under the control parameter beyond this point no periodic orbit exist. This is the reason why the heteroclinic bifurcation represents the transition between periodic and non-periodic responses."

Could it be more clear?
Cheers

[masalai]

Very concise and understandable Guillermo, Thanks for the very illuminating definition - - - Huh?

[tspeer]

Originally Posted by farjoe

That is certainly very true but it is not easy to always find sufficient crew to do so.

You may need to reef or sheet out earlier. When the heel angle exceeds a threshold that experience tells you says the boat is in danger of broaching, then reef even if you don't feel the conditions really warrant it. This may be the penalty you have to pay for the benefits of the tenderness in lesser conditions.

Should one aim for lee helm in the upright position so that when the boat does heel, the weather helm is not so heavy?

I think lee helm is the wrong way to go. But a deeper rudder may be in order. It would shift the lateral area aft and give you more control when the boat heels.

When reefing, should one reduce the main first rather than the genoa to push the forces ahead of the keel again to try and counteract this source?

I think this sounds like a reasonable approach. It's a matter of learning what you need to do to adapt to your boat's peculiarities.

These seem to make logical sense to me but what is sure nobody does this whilst racing.

[farjoe]

Originally Posted by Earl Boebert

This subject was extensively studied by model yachtsmen in the free-sailing days. PM me with your email and I'll send you a paper I wrote on the topic.

Cheers,

Earl

Earl,

I have read ( several times actually ) your interesting paper about hull balance.

Do you know if designers today apply these methods in their job?

It is very hard to mentally relate modern cross sections with the rule but it seemsmost modern wedge shaped desgns would not pass the rule.

[Earl Boebert]

Originally Posted by farjoe

Earl,

I have read ( several times actually ) your interesting paper about hull balance.

Do you know if designers today apply these methods in their job?

It is very hard to mentally relate modern cross sections with the rule but it seems most modern wedge shaped designs would not pass the rule.

The real designers on this forum would have to answer that. I just play with model yachts and read a lot :-)

Cheers,

Earl

[Splash Gordon]

Originally Posted by farjoe

...only during gusts... the boat gets overwhelmed. Otherwise the boat is quite balanced with just a little weatherhelm...

IMHO, the gusts are where it counts. If she's being a tart in the gusts, is the main-hand playing the traveller enough? The depowering (heading down to counteract the tendency to head up) with the rudder is counter-productive- it costs speed! Traveller-work through the gusts should increase to the point of making the main-hand's life a misery, and they should be bleating about running out of track before you reef, and even then I'd look at putting a flattener-reef if you're allowed them in your rules! Oh- and if the rail-meat can't keep her upright, get more meaty rail-meat!

Originally Posted by farjoe

Maybe the rudder is too small?

But big blades are expensive- much more than buying a few pies to keep the rail-meat heavy! Is your rail-meat in a position to come back and play the jib-cars or the toast-rack? Dumping the cars in a gust really helps the main de-power, and as the apparent wind comes back in the gust, the open jib keeps the action hot on the telltales.

Originally Posted by farjoe

...a more experienced helmsman would be able to handle the situation better. However my observations were made after noting how the boats handled under the control of 3 different helmsmen

Was the crew the same? If so, try a cooking-hot mainsheet-hand and a fresh pair of paws on the backup to trim the jib-cars. Maybe try get the jib-trim led to the rail, if you can.
What's the speedo say? Are you getting sailing-lessons on the beats or are you in the mix? If you're a rocketship humouring a bunch of 4ksb's (Anarchy-terminology I like), just sail above your handicap and take a wheelbarrow to collect the trophies, but otherwise, if you're an "also-ran" in a fleet of legends, look at borrowing some rockstars for beercan-racing to see if the trim can be fixed.

[Stumble]

This sounds to me like more of a trim problem than a design one. If we are talking about a modern racing boat, part of the modern theory is to use larger mains and smaller fractional jibs. This design reduces the amount of force in the jib, and increases the tendancy of the boat to round up in puffs due to the significantly larger main.

The advantages of this design are significantly increased upwind performance, particularly pointing ability. The downside is normally either a smaller fractional kite, or moving to assymetrical chutes.

The problem as you have experienced is that as puffs come on the boat has a tendancy to drive into the wind. The answer to this is drop the traveller as the puffs come on, bring it back up as the puff starts to pass. In effect the traveller becomes the gas petal, constantly being played up and down to keep the boat at the same heeling angle. this of course is exhausting on the main trimmer, and on a similar design we actually traded of main trimmers every race to keep people from getting burned out.

Of course there are design methods for avoiding this as an issue, but as with all designs there is often a compromise that was made. In this case it was to improve upwind angles and give more sail area down wind, But at the expense of making a boat harder to keep in trim.

[Brent Swain]

Hull shape is the problem , wide stern and lean bow boats do that.
Brent

[daiquiri]

Hello,
this problem was addressed few days ago in this thread:
Tendency to broach during beat or close reach