Why don't yachts have wave cancellation

[Dave_S]

If hull speed is a major hurdle for monohulls why don't even cruising boats have a form of wave cancellation to coincide with hull speed ?

[fxykty]

Originally Posted by Dave_S

If hull speed is a major hurdle for monohulls why don't even cruising boats have a form of wave cancellation to coincide with hull speed ?

Not sure what you mean by wave cancellation, but the more modern hull forms with little rocker help to minimise the hull speed boundary through less displacement wave making.

Cruising boats by their very nature have (generally) relatively high displacement and greater volume underwater, hence the transverse wave with the midship trough does become an obstacle in flatter water and upwind. Reaching and running there’s probably less of a speed hump, unless the boat has more rocker and a lower prismatic coefficient (i.e. skinnier and shallower ends, deeper and wider midships). Other than for wetted surface, shallow boats with fat ends don’t care as much for hull speed.

[wholybee]

Read this:
https://en.wikipedia.org/wiki/Bulbous_bow

[cal40john]

Marchaj's book relates a 6 meter that had a bulb bow. It generally didn't help. As the link in the previous post states, a bulb bow only works well at one speed, since sailboats don't travel at one speed the bulb slows the boat at other speeds.

[chrisr]

i think it also has something to do with heeled waterlines. monos sail on an angle of heel which may upset the way the bulb offsets the wave form ?

it has been tried on catamarans (one of our earlier cats had small bulbs) and i recall roger simpson was quite keen on the idea

however don't see any these days - maybe they don't look 'cool'

cheers,

[valhalla360]

You do see some of the modern racing hulls being wide and flat so as to be semi-planing and some cruising boats have adapted this to some degree.

[leboyd]

Isn’t that what a foiling monohull does?

[MicHughV]

The limitations of a standard sailboat hull are well known and documented, basically limited by the bow and stern wave created as the boat moves thru' the water.

To overcome this hurdle, yacht designers have realized that to go quicker, the hull must be raised out of the water, hence the proliferation of foiled craft in events like the Vendee, etc.

Foils are not for everybody though, so many modern sailboats now have the French style plumb bow and flat-ish bottom to induce some kind of " planing hull" effect, but like most cases with sailboats it's a compromise, whereby you can have some, but not all the features.

[Dave_S]

Thanks all.

I hadn't imagined an extended bulb like on cargo ships, but a secondary widening (or narrowing) of the hull, enough to create an out of sync wave pattern, enough to minimise the hull speed effects.

I hadn't considered the degree of difficulty in designing for various angles of heel. Thanks chrisr.

[Yellowtulip]

The latest generation of Mini-Transat and IMOCAs have “Scow bows”. Their main function seems to be to add buoyancy at the bow to mitigate against the boat slowing when it is foiling in big waves. The extra buoyancy allows the bow to “skim” the wave tops rather than bury in them. The foils, of course, allow these boats to overcome the “hull speed” limitations.

https://neeva.com/search?q=scow+bows+images&src=nvobar

[Dave_S]

Originally Posted by Yellowtulip

The latest generation of Mini-Transat and IMOCAs have “Scow bows”. Their main function seems to be to add buoyancy at the bow to mitigate against the boat slowing when it is foiling in big waves. The extra buoyancy allows the bow to “skim” the wave tops rather than bury in them. The foils, of course, allow these boats to overcome the “hull speed” limitations.

https://neeva.com/search?q=scow+bows+images&src=nvobar

Interesting reading, thanks.

[Bowdrie]

The Beam/Length ratio has to be taken into account for displacement hulls, and even then, massive HP is needed whether by sail or machinery.
Example, a WWII era destroyer with, say, a WL of ~375' has a "supposed" hull speed of ~25>26kts, but yet could hit 35>36kts.
However, the beam was only ~40', a beam/length ratio of well over 9:1 but with huge HP numbers.
That would be similar to us having a 45' boat with a beam of 5'.
Even the old square riggers were running B/L ratios of ~ 7:1 and given enough canvass could exceed their theoretical hull speed.
Of course, other factors involved also.

[Ike]

Originally Posted by Dave_S

If hull speed is a major hurdle for monohulls why don't even cruising boats have a form of wave cancellation to coincide with hull speed ?

You will get more detailed and thorough answers to this kind of a question on https://www.boatdesign.net/ where most of the regulars are in the design business. Be more specific about the type of boat. A general question like this is too broad. Narrow it down. Are you talking about Cruising sailboats? Monohulls? Multihulls? What size? etc. Even in the Category of cruising sail boats there is a wide range of hull types, keel types, length/beam ratios, and I won't even broach the subject of hydrostatics and coefficients.

[mqholt]

In terms of wave interference in catamaran design, there are a number of good threads on the boatdesign.net site:

https://www.boatdesign.net/threads/w...amarans.64814/

https://www.boatdesign.net/threads/e...amarans.65613/

And asymmetrical hulls help in reducing hull wave interference. Our boat, Excess 14, uses asymmetrical hulls in a production cat:
https://no-frills-sailing.com/vplp-a...lls-excess-14/

[Djarraluda]

the 12m class in America's Cup developments did a lot of studies and experimentation with these but also concluded that the set speed nature of the benefit was outweighed by the drag caused at other speeds.