Some boats roll more than others, why?

[Spyros]

Hi guys,

I am wondering why some boats roll at anchor like pigs while others feel a lot more stable and dont even swing?

I was on a Windy Ghibli 28 that is supposed to eat waves but unfortunately did not find anybut the boat was very sensitive at slow speeds and rolled like crazy at anchor.

On the other hand I was on a Chris Craft 28 that felt like a table since I first stepped on it and almost completely unaffected by movements.

Do deeper V boats tend to roll more than shallower boats? Is it a design characteristic that sacrifices seaworthiness somehow or is it something else?

 

[PowerYachtBlog]

Do deeper V boats tend to roll more than shallower boats? Is it a design characteristic that sacrifices seaworthiness somehow or is it something else?

Yes. The deeper the Vee the more a boat rolls to side waves, since it builds large momentum on the chines.

On the other hand flatter Vees or hulls tend to roll less.

It is also obvious there is other factor at play especially if the boats get bigger, like beam super structure and so on.

 

[Portofino]

Depends on the beam to length ratio and width of the chine flats and other flat surfaces .
Some have profound spray rails at the bow that ad they move aft morph into pretty wide surfaces and act as lifting strips .
The sum of the added flat bits mitigates the V but you need beam to fit all this in .
All adds drag so you need additional Hp , bigger engines , if you can mount them lower keep the CoG lower it all helps .
The Chris craft sounds like a typical Ray Hunt Sony Levi , evolution.

Outdrive boats are relatively low on Hp compared to shaft driven deep V s so narrow on beam , thin on chine flats and other flat surfaces .

Mine is very stiff doesn’t roll once moving , the faster you go the stiffer the set .Arguably a bit too much set .
Keeping the weight lower by having solid hulls , ie none cored also helps so maybe the Windy and Chris craft have differing hull construction? , the CC being able to keep its CoG lower compared to the W ?

Great to hear you are actually test driving them btw .That’s the only way to find out if it will meet your needs .Good on you .
Rather than buy via a brochure and static boat show or a gentle plod around in calm seas .

Have you tried an Itama 38 ? Is there a way of accommodating a larger boat .I know previously you have said they won’t fit in your target berth .
The deep V works better over 4 M beam upwards as I said they can add a lot more in .

 

[PowerYachtBlog]

Have you tried an Itama 38 ? Is there a way of accommodating a larger boat .I know previously you have said they won’t fit in your target berth .
The deep V works better over 4 M beam upwards as I said they can add a lot more in .

Itama 38 is 3.80 m wide.

 

[Portofino]

Itama 38 is 3.80 m wide.

Yes .
it’s getting up to 4 ish nearer than 3.4 or 3.3 or 3.5 or what ever the lower powered outdrives The extra 30-50 cm of beam for 11/12 M is critical.
How ever as you know there are even larger Itama , My 42/48 with 4.2 or a 46 with 4.4 m .That’s why I suggested he find a bigger berth ? So he can fit a Beamer boat in ideally over 4 M + a deep V for the ride comfort in waves …..which I understand he’s looking for ?
There are a few other candidates like the older Baia B 1 the 40 ftr ,

He‘s been looking for a few yrs without much success it seams = hence look else where at bigger + deep V .


Once you are over 4m or thereabouts, the roll thing thats noticeable in narrow deep Vs pointed out by Spyros , (by deep V I mean true excess of 20 degrees at the deadrise ) …..goes away becomes a none event .I haven’t noticed any excessive roll in my 23 degree deadrise boat .It’s very stiff and turns very flat compared to my previous outdrive “ sports cruiser“


Going larger over 4 M beam circa 40 ft + you also migrate into better balance with the mid engines , less pitching = better sea parting by the level ride enabling more use of the pointy end where the V slices through .As opposed with rear weighted outdrive boat the hull tries to climb up the waves due to pitching causing waves to hit the middle of the hull first .

Its the sum of all of whole package .Each bit brings something to the party .

 

[QBhoy]

Narrow deep v hulls are incredible in the rough and very efficient usually. But down side is that they can be tippy at rest or slow speed. I’ve got a fletcher 19. Narrow thing, but very capable in rough water. Compare this to one of my other boats…a Canadian 18ft thing with a stepped and pad wide hull…that is rock solid and extremely stable at any state…but horrible for violent bone shattering slams, going into a chop. Despite being half a ton heavier than the fletcher. Two very different boats for performance and use…but huge difference in how they behave.

 

[ROSK]

I guess the tricky part is to find out which factor has the biggest impact. I personally prefer heavy boats with a bit slower top speed. Weight will definitely be a factor as well as beam, hull shape, Vertical cog, etc. I guess the hull shape above the waterline will also affect as the volume/buoyancy submerged effects the forces.
Small craft designers need to choose which properties their boats should have and no boats can excel at speed, stability, interior volume/space, low fuel consumption, etc. Daycruisers need to prioritize space for toilet/beds etc. The more requirements they add the "fatter" the hull. If the weight goes up then so must the engine requirements, or they can reduce the V-shape to increase the hydrodynamic lift (I think/guess )
As to comparing Windy and Chris Craft, you must take into account that there is probably a 1 tonn (25%) difference between the two. This will also have an impact on fuel efficiency/ speed.
I have an old Windy 9800 (4,5 tonn ish?), I love the way it handles in rough water with two AD41 VP engines. I must however always make sure I keep the boat level, else it slams into the waves like a flat bottom boat.
I recently worked with a diving company who had a 15 m light diving vessel (Looks like a big fast rescue boat) they can use offshore. To ensure they can use the boat in as much waves as possible while stationary, they had a Gyro installed. Very nice, very expensive

 

[Neil_Y]

Hi guys,

I am wondering why some boats roll at anchor like pigs while others feel a lot more stable and dont even swing?

I was on a Windy Ghibli 28 that is supposed to eat waves but unfortunately did not find anybut the boat was very sensitive at slow speeds and rolled like crazy at anchor.

On the other hand I was on a Chris Craft 28 that felt like a table since I first stepped on it and almost completely unaffected by movements.

Do deeper V boats tend to roll more than shallower boats? Is it a design characteristic that sacrifices seaworthiness somehow or is it something else?

If you're troubled by rolling at anchor it usually means the boat is sitting to the wind rather than facing any swell direction, simple solution is to put out a stern anchor that will hold the bows into any swell there might be. You don't need a big anchor or much chain on a light boat. All boats will pick up a roll of there is any slight beam on wave to speak of.

 

[NBs]

Hi,

the center of gravity of the boat is also affected by the roller and above all the speed and acceleration of the roller. the faster you roll, the more boring it feels.