Why I'm Following Sven Yrvind

Gladis the killer whale and her gang of orcas out for revenge https://www.independent.co.uk/news/world/europe/gladis-whale-orca-boat-attacks-gibraltar-b2347572.html

"Although known as killer whales, endangered orcas are part of the dolphin family. They can measure up to eight metres and weigh up to six tonnes as adults."

Yep I guess that Yrvind in his tiny tiny boat could be toshed around quite a bit if he comes across a gang of those killer whales. Harshly actually and relentlessly if the whales take turnes bumping into his tiny tiny boat

Solution: buckle up and wear a helmet. That should do the trick.

 

I dunno, how does a foam boat stand up to a 6ton belly flop across the deck? I have no explanation of why they have been behaving like they have been, but seeing a rather thick glass rudder get chewed to bits, I have memories of pictures like these....








Obviously his boat is not shaped like a board. My guess is they would get bored after nudging it around for awhile......but who really knows?

 

Scary pictures.

Yrvind: Small = strong.

Yep.....who really knows?

Especially if it's some kind of kamikaze attack. Could mean curtains

 

I just found a video detailing first hand experience building and participating in the globe 580 "race".
(259) Jim Schofield - The Voyage of the Molly Claire - the Atlantic is Big - YouTube
Some good "data" about small boat ocean crossing
-strength is a non-issue
-the sail plan is not balanced. The fat head main rarely went unreefed and it seems silly the rig is fractional. "Race" fashion Sailplan sells plans, but doesn't deliver for cruise.
-such a small boat, so much wasted space. Out of the entire boat, the safe, desirable space to occupy would be described by a small cylinder aft of the mast centered on Gz!

Sharpie, you clearly have had something you have needed to get out of your system for years. I won't speak for you but I am not getting younger you should check yourself. I think Sven has lowered the bar -no shame. It sounds to me like you would build LARGER than the minimum.

This guy is showing real up to date capability in self designed highly custom cruiser. (260) Arctic SeaCamel - YouTube

If you want to know the current "state of the stunt" for short ocean crossing see. (260) Daredevil dad has set sail from Canada in a one metre boat | SWNS - YouTube

 

The same balance issue is found with the Setka, I think it has as much to do with the boats shape and waterlines, as concerns going downwind. Donn mentioned that just moving about below would upset the boats trim, maybe he should lose some weight?

The other guy in the 1 metre boat is done already. He got towed back into harbour after taking on water, it then sank overnight in the harbour, and when being raised by a crane, broke apart. Bloody good job as it turns out.

 

Tiny tiny madness. Blood in feet and without sleep.. Totally impossible.

 

About Globe 5.80

A cordial greeting to all, I am a small sailboat enthusiast and this case is painful for me

(A) Lateral Hydro Forces in a Sailboat are:

(1) Yaw moment due to Yaw
(2) Yaw moment due to Roll
(3) Yaw moment due to Pitch + Roll + Yaw

(4) lateral force of the Keel/Centerboard (which in most cases is a destabilizing force because it is forward of the center of gravity of the yacht)

(5) rudder force

The Rudder Stabilizing Force must be equal to or greater than the Sum of the Destabilizing Forces.

(B) On the other hand, there is the typical problem of an off-center sailboat: the longitudinal position of the Center of Bouyancy does not coincide with the longitudinal position of the Center of Flotation.

(C) If we also add the Sails Force which sinks the Bow ... and Waves

HydroDynamic disaster

If, for example, we look at the sharp bow ... It is easy to see that it will produce Lateral Force and will not produce hydroDynamic Vertical Force, moreover: it will not even defend the bow from a hydroStatic point of view.

 

From my point of view a lot of problems could be avoided by following a few logical rules:

(1) Longitudinal Balance: longitudinal Center of Bouyancy at the longitudinal Center of Flotation

(2) Center of Gravity of the Sailboat a little aft (2-3% LWL) of the Center of Bouyancy

It is not possible to take into account the full effect of the Downwind Sail Force (as it can be a force of about 10% of the Displacement) but at least an upwind/beating driving Force of say 4% of the Displacement can be taken into account in the calculations.

(3) A large Longitudinal Metacentre (may be 3 x LWL): big longitudinal righting moment

(4) Hydrodynamic Center of the Centerboard/Keel just below the Center of Gravity of the sailboat

(5) Calculate the rudder blade taking into account the Yaw Moment of the yawed and heeled hull

(6) A Carene that when accelerating tends to a bow up and stern down Attitude of the Hull that facilitates a quick transition between the 'displacement regime' and Surfing with big Waves.

 

Back to my value proposition from post #369 -Setka and the 580 are going for the image of box rule planing class designs. The proposition is "you can do what the big boys (6.50s) do but cheaper and by your own hand". Classic marketing -sell by telling them what they already believe is right. As an engineer and designer I judge it to be a failure for not delivering what was paid for.
It wouldn't bother me so much except that so many of these "ocean capable small boats" have proclaim that they are proving the status quo wrong.

Planing a hull takes power. To get that power from the wind you must divert a tall column of air. The taller you go the more the wind pushes the bow down. Getting enough volume in the bow is a problem as you get shorter. Not only is there too little length to get to full beam but the short length means that at hull speed the lift you get (proportional to V^2) is small.
The bottom line is that scaling down a 6.50 doesn't make a boat that planes easily or often.

Getting back to skipper weight, in a high performance boat this small body weight is a big portion of the total so its position is limited by the conditions. Don went below in a storm? By doing so he simultaneously trimmed the boat forward and reduced the righting. Greater heel from the loss of righting causes greater weather helm, and the autopilot correction (which doesn't have accelerometers like real race & offshore boats) causes greater drag and more bow pressure. As the boat goes slower than the wave train there is another problem, the wide transom gives the waves a great lever to lift and roll. In a boat like the 580 the only place to be is in a gail is the windward back corner of the cockpit and the right amount of sail is whatever it takes to follow the wave train.

If they had spent the same materials (25 sheets) making a slightly longer, narrower, sailboat with a pinhead main and masthead genoa it would have easily made the same trip faster and easier.

 

This old Sailboat

19,19 ft LWL
300 D/L

With an old sailor of the merchant navy sailed from the Iberian Peninsula to the Canary Islands ...

Planing/Gliding-Surfing Waves ...

Proyecto NOSEVE: De Barbate a la Graciosa -9- :: NAVEGAR ES PRECISO https://www.navegar-es-preciso.com/news/proyecto-noseve-de-barbate-a-la-graciosa-9/

And in the end reached Surfing a top speed of 20 knots = 4 (!) x 0.35 Froude

This is not sending a man to the moon. A small sailboat (5,7-6 m) can behave beautifully.

It's a matter of careful and loving design and a little bit of calculation.

(1) Longitudinal Balance
(2) Pitch resistance
(3) Lateral Force Balance
(4) Hull Attitude

"As the boat goes slower than the wave train there is another problem, the wide transom gives the waves a great lever to lift and roll"

E x a c t l y

A Mini Transat hoist about 40 square meters of sail per Ton.

A Mini Ton of 5.7-6 meters in length hoist about 15-20 square meters per Ton.

In slow sailboats the design errors are much more noticeable: the sailboat sailing in front of waves can even put the mast in the water by a violent sum of Pitch, Yaw and Roll.

 

If the sailboat has a wide stern/transom ...

Longitudinal Center of Flotation will be around 60% of its waterline (LWL)

and Longitudinal Center of Gravity of the sailboat should be around 62-64% LWL

and of course taking into account the Load and where the Crew sleeps

 

Gliding-Surfing (take-off, 0.50-0.60 Froude) Powered by the Earth Force thanks to the slope of the Wave

(1) hydroDynamic force (high pressure), say 1000 Newtons

(2) hydroStatic force, say 1500 Newtons

(3) Earth-Gravity Force, 10,000-11,000 Newtons

(4) hydroStatic force, ca. 10,000

(5) hydroDynamic force (Low pressure, suction) 1000 Newtons

Some old sailboats are transformed into prodigious Surfboards thanks to the Suction at the stern that sinks the stern into the wave providing the good attitude of the hull 'stern down bow up' for surfing down the wave

But to achieve this, the sailboat must

(A) have a good Longitudinal Balance and
(B) a good Balance of Lateral Forces (hull yaw moment, daggerboard lateral force and rudder force).

 

Gliding-Surfing

It may be based ...

(A) on the hydroDynamic high pressure at the bow forming a 'gliding plane' with the hull

(B) on the hydroDynamic low pressure at the stern

(C) Combinations of A and B

 

'Pitch Machine'

SF, Sail Force
GF, Gravity Force
WF, Wave Force

CF, Center of Flotation

Gliding-Surfing is the icing on the cake

but in any case to enjoy it first we have to deactivate the 'Pitch Machine'.

Moreover, in many cases, when the sailboat heels/Roll ... the bow sinks.

So there are three issues in the navigation of a small sailboat that is relatively slow in relation to the speed of the waves and wants to cross an ocean:

(1) disable as much of the 'Pitch Machine' as possible

(2) strict control of "Yaw" which is the other outlaw that must be controlled and

(3) the icing on the cake: a good Surfboard

 

When I was 11, I dreamed of taking my Opti across the ocean. I drew up a dodger type cabin to sleep in and thought of lining the gunnels with dock fenders for added floatation. My 11 year old mind couldn't figure out two major hurdles; 1 - how to carry enough food and water to cross an ocean within 7' of space, and 2 - There are fish out there that prey on fish the size of a pram.

Now that I'm almost 50 years older, I still have those same concerns, plus quite a few more.