Hull Shapes and Behaviour in Heavy Seas

[El Pinguino]

Some interesting thoughts here...
https://goldengloberace.com/talking-boats/

[Paul L]

Originally Posted by Cpt Pat

.....
Yes, a larger and deeper-draft boat has less risk of momentary rudder exposure, but the keel design affects how it will behave when the rudder doers get exposed. The bigger, more massive boat will also be perturbed by any given disturbance much more slowly than a smaller/lighter boat. It's that first year college physics formula for mass, force and acceleration. Keeping near perfect sail balance is the countermeasure. If when letting go of the wheel or tiller, nothing bad happens, and ideally the bow swings slowly to the wind ("weather" helm), then nothing catastrophic should happen with the rudder out of the water. If conditions are such that something bad will happen, it will happen more slowly with a full keeled boat. I consider that effect, plus improved course holding with a full keel, to be a factor in "seakindliness."

And the foil shape of the fin keel and balanced rudder will make the modern fin keeler feel like it is riding on rails. When my J/37 was offshore in 30-40kts and large following seas it would do some impressive acceleration. The boat would just lock into a dead straight course. The helmsman only needed to move the wheel 1 or 2 inches in either direction to make any turn.

....

As others above point out, a bigger presumably heavier boat is more seakindly - it's a better ride - all other things being equal. But others point out that modern lifeboats are small. And a lot of research has gone into the best hull form for a small boat to survive extreme conditions. I suggest taking a brief look at those hull designs. (Still, I'm sure the ride in those boats is horrible in heavy seas. I hope they carry plenty of seasickness bags.)

Lifeboats are well known for being one of the most seasick inducing places to be in a storm. This isn't a smooth ride.

No size of boat is immune from human error. The Titanic was a big boat. And when a big boat strikes something, it is much more likely to sustain catastrophic damage. My boat, at hull speed, striking the same iceberg with the same glancing impact as the Titanic hit, would make loud scrapping noises and bounce off. I might have to touch up the paint.

It's said that there are two kinds of sailors: those who have run aground and those who will. I've done it. I confess. "Hard" aground. The consequences (beyond my damaged pride) were that I had to wait eleven hours for the tide to rise and lift my boat off. There was no damage whatsoever because my long keel can support the boat while maintaining a level pitch and my keel-hung rudder doesn't extend below the keel.

You should consider the consequences of running a fin keeler aground in some strange and exotic place. Did you damage the keel attachment making the boat unseaworthy? Did the boat rock back on the rudder causing substantial damage? Will you have to just walk away from a mortally damaged boat?

If that's your argument for hull shape then hull material needs to be mentioned. Far better to have a heavy plate steel boat than either a fin or full keel tupperware GRP boat.

There's a huge range of cruising boats that do fine crossing oceans in mellow to reansonably bad conditions. Few experience truly life threantening storms. The biggest issue in general safety is crew preparedness and experience, along with some significant Neptune induced luck.

[NevisDog]

Very interesting reading Ping, from someone with experience of both types: "...I was involved in the RESCUE of French solo sailor ALAIN DELORD, sailing a fast, light modern fin keel 35ft yacht solo around the globe. He was unable to control his boat in a storm and then was dismasted 440 miles south of Hobart in Tasmania..."

But of course I'm being selective in my quote - better to read it for yourselves and let it all sink in.

[Paul L]

Originally Posted by El Pinguino

Some interesting thoughts here...
https://goldengloberace.com/talking-boats/

Interesting perspective. He mentions multiple times that the small full keel boats can be driven by windvanes in tough conditions, a requirement for GGR, while fin keel designs would require autopilots.

In either case the stats aren't good for either style in a Great Capes round the world.

[B23iL23]

Maybe, maybe not. Could be down that particular boat or down to the skipper just having enough. The article also compares the GGR to the Vendee Globe... from 2008.


A better comparison would be the 2017 where 18 finished and 11 retired. Couple of dismastings, couple of masthead problems (whatever that is), some rudder damage and one (I think) keel problem (swing keels I assume). Given the speeds the boats are doing, that damage does not surprise me.



So we have modern, ultra-lightweight racing boats with ultra complex rigs and systems and 18 of them made it home.



What all this means I still don't know.

Originally Posted by NevisDog

Very interesting reading Ping, from someone with experience of both types: "...I was involved in the RESCUE of French solo sailor ALAIN DELORD, sailing a fast, light modern fin keel 35ft yacht solo around the globe. He was unable to control his boat in a storm and then was dismasted 440 miles south of Hobart in Tasmania..."

But of course I'm being selective in my quote - better to read it for yourselves and let it all sink in.

[NevisDog]

Originally Posted by Paul L

And the foil shape of the fin keel and balanced rudder will make the modern fin keeler feel like it is riding on rails. ...

Absolutely, gives a wonderful feeling of (somewhat misplaced) confidence, until a big steep one lifts her rudder above the water, the nose dips - then all hell breaks loose.

[The worst, most pyramid-like waves are once the mid-ocean storm begins to abate - be prepared to hoist more sail in a fin keeler to regain some semblance of control.]

[NevisDog]

Originally Posted by B23iL23

...So we have modern, ultra-lightweight racing boats with ultra complex rigs and systems and 18 of them made it home.
What all this means I still don't know.

It means any boat fully crewed by professionals will survive - but will they survive in comfort? Are they in constant danger of being swept overboard? Can the hullform survive the conditions without constant hand-steering or autopilot? Must the occupants be strapped into their bunks with seatbelts? Can it be sailed by a solo voyager without unlimited backing?

[Cpt Pat]

Originally Posted by Paul L

If that's your argument for hull shape then hull material needs to be mentioned. Far better to have a heavy plate steel boat than either a fin or full keel tupperware GRP boat.

I fully agree.

My paragraph drew no comparisons between hull forms. I was writing only in reference to vessel size:

No size of boat is immune from human error. The Titanic was a big boat. And when a big boat strikes something, it is much more likely to sustain catastrophic damage. My boat, at hull speed, striking the same iceberg with the same glancing impact as the Titanic hit, would make loud scrapping noises and bounce off. I might have to touch up the paint.

[Paul L]

Originally Posted by NevisDog

Absolutely, gives a wonderful feeling of (somewhat misplaced) confidence, until a big steep one lifts her rudder above the water, the nose dips - then all hell breaks loose.

[The worst, most pyramid-like waves are once the mid-ocean storm begins to abate - be prepared to hoist more sail in a fin keeler to regain some semblance of control.]

I put a lot of offshore and inshore miles on my J. The only time the rudder came loose was when it was way over canvassed- think we should have taken tbe spinnaker down 2 hours ago. When it was "on rails" with white sails only at 10kts or so I was always really confident. Once I got rid of the Raymarine autopilot I had no problem leaving it on AP for days at a time. When it, very rarely, accelerated to 16-17kts it still felt like it was locked on rails but I knew it wouldn't take much of any driving mistake to have a spectacular wipe out.

As far as after a storm was concerned, one thing that a medium light, low underwater drag boat has over a heavy lots of underwater drag boat is low stress on the sails in heavy weather. I could put up a doubled reefed main and no headsail and the boat would sail easily. So to keep the boat moving at 4-6 kts to get good steerage you didn't have to start raising a bunch of canvas by a fatigued crew. Easily driven has sone advantages besides speed.

[boatman61]

Well one thing I draw from your observations on the Vendee.. the speed they are capable off means they can do the S Ocean at the optimum time of year and be in and out during the short window.. 110 to the latest 78 days start to finish.
These smaller traditional craft in the GGR dont have this luxury so spend months as opposed to weeks down there.. in fact the only decent weather they're likely to experience is maybe 25degrees either side of the equator.
Survial rate is better tho', 1 death (suicide) to date in both races I think.. finish statistics not so good..
So one could argue which is actually the tougher race.

[B23iL23]

Vendee Globe is single handed. Same a GGR except modern designs.

Originally Posted by NevisDog

It means any boat fully crewed by professionals will survive - but will they survive in comfort? Are they in constant danger of being swept overboard? Can the hullform survive the conditions without constant hand-steering or autopilot? Must the occupants be strapped into their bunks with seatbelts? Can it be sailed by a solo voyager without unlimited backing?

[Cpt Pat]

Deleted duplicate post. The CF server is having issues.

[boatman61]

Originally Posted by Cpt Pat

I fully agree.

My paragraph drew no comparisons between hull forms. I was writing only in reference to vessel size:

No size of boat is immune from human error. The Titanic was a big boat. And when a big boat strikes something, it is much more likely to sustain catastrophic damage. My boat, at hull speed, striking the same iceberg with the same glancing impact as the Titanic hit, would make loud scrapping noises and bounce off. I might have to touch up the paint.

The Titanic sank because the watertight bulkheads had no roofs so they flooded one overflowing into the other and cascading till she sank..
No one calculated the multiple watertight areas could be affected at the same time.. I think it was 3 or 4 watertight sections were exposed by the gash..
Will google n come back..

[Cpt Pat]

Originally Posted by B23iL23

Wow. So I'm relatively new around here, but I was reading another thread about why newcomers don't join in. To me your post is one of the reasons why.



A certain amount of civility and respect for others would be nice to see. Otherwise us newcomers just move on.

I understand, and I agree. I don't have a problem with anyone who wants to contribute here. My problem is with the nit-pickers and frankly, trolls, who can only post personally insulting comments. Civility is a two-way street.

The need to remain civil is balanced against the right to call someone out for not contributing anything but personal criticism.

I encourage you to post here. But be prepared that - if you write anything that challenges conventional wisdom, the closer you get to the truth the more venomous will be the personal attacks. Some of the crowd here are stuck in their ways, and they come out of the woodwork, armed to the teeth, when they see something unconventional. They expect continual validation of their opinions. They're the "we've always done it that way" crowd. Hardly free thinkers.

Even in formal debates, ad hominem attacks (attacking the writer - not the substance) is considered to be unfair. Get ready for it.

You'll understand when you spend an hour writing and researching something - only to have brief snarky comments posted against it containing name calling. I'm a professional writer and I've got a pretty thick skin. But snark needs to be called snark precisely because it does drive away the newbies.

I wish we could all be more civil. It's a diminishing art in our culture.

I'm not a newbie, but I still sometimes question why I bother posting here. I do it because there are some very good and knowledgeable people here. I could just lurk and not contribute, but that seems unfair to me.


Christmas is coming up and I'm going to give this forum a break. Best wishes to everyone for the holidays!

[NevisDog]

Originally Posted by B23iL23

Vendee Globe is single handed...

Oops - my mistake, was thinking of those Volvo ocean racers; those modern sleds all look the same to me, you'd have to pay me to sail in one (and that's not gonna happen).