Pub talk - how fast CAN a yacht go?

[Bobc]

The first bit of this video is somply the dog's dangly's.

TP52 (see big dinghy for definition).

Hw fast???

http://www.youtube.com/watch?v=Z9DVKm7a254

 

[Sybarite]

As I'm sure is quite obvious, my experience is very poor with boating generally.
So apologies if this is a daft question.

My Kestrel 22 grp, is likely to sail at 6 knots apparently, once the weed is extracted and someone capable is on board.
How about the 30 and 40 footers?

A chum in the pub a couple of nights ago, thought the big boys sail at 30 knots.

This is the fastest. They touched 61 knots before breaking up!

http://www.youtube.com/watch?v=rRuLpZoTIoQ

They are broad reaching (you can see by the waves) but the sails are hard in because of the apparent wind.

 

[Bobc]

Foiling's cheating though.

 

[AngusMcDoon]

A chum in the pub a couple of nights ago, thought the big boys sail at 30 knots.

Bog standard cruising Dragonfly trimarans will peak at 22 knots and on a good day average 15 knots over a few hours. Racing versions and more lively models like Seaons (still only a production 9.4m boat though) add 3 knots to that. These figures are for boats of 8-12m loa who never fly the main hull. Hull speed formulae don't apply to these boats.

EMcC averaged 18 knots round the world.

Big boys sailing at 30 knots? Multihulls only.

 

[sailorman]

Cor, wish my Leisure 17 went as fast as that one.

 

[Twister_Ken]

Bog standard cruising Dragonfly trimarans will peak at 22 knots and on a good day average 15 knots over a few hours. Racing versions and more lively models like Seaons (still only a production 9.4m boat though) add 3 knots to that. These figures are for boats of 8-12m loa who never fly the main hull. Hull speed formulae don't apply to these boats.

EMcC averaged 18 knots round the world.

Big boys sailing at 30 knots? Multihulls only.

I've been aboard a 1720 doing 25kts. Scary.

 

[Cheburator]

35ft JOD35
Did the RTI Double Handed. Between the Needles and St Catherine's we were averaging 10.8knots with a No2 and full main. Max speed was 13.4knts. Between St Catherine's and Bembridge we hit 14.8knts max and averaged 11.1knts. Wind was WSW 23knts, highest gust was 27knts. Upwind we were hitting 6knts at 30deg true wind. Hull speed for us is 7.93knts, but the hull shape has a lot to answer for

 

[haydude]

Why's that then. My dumply little Seahawk 17 (14 ft lwl) would do 5.3 knots (gps) so I can't see why a 22ft (19.5lwl) boat wouldn't achieve it's hull speed (5.92 knots) and maybe that bit more.

Yeah right! GPS, so that is going with 2kts tide.

 

[capnsensible]

Yeah right! GPS, so that is going with 2kts tide.

I have heard those lake district tides can be tricky.......

 

[FistralG]

Bog standard cruising Dragonfly trimarans will peak at 22 knots and on a good day average 15 knots over a few hours. Racing versions and more lively models like Seaons (still only a production 9.4m boat though) add 3 knots to that. These figures are for boats of 8-12m loa who never fly the main hull. Hull speed formulae don't apply to these boats.

EMcC averaged 18 knots round the world.

Big boys sailing at 30 knots? Multihulls only.

Current record for an Open 70 is 24.8kts over a 24 hour period so 30kts is entirely feasible for short bursts.

 

[Lakesailor]

Yeah right! GPS, so that is going with 2kts tide.

You're lack of insight embarrasses you.
No tides
No current

 

[snowleopard]

You're lack of insight embarrasses you.
No tides
No current

Can't see the need for snide remarks. Hull speed for 14 ft LWL is 5.24 knots. If the boat has overhangs the LWL will increase as the bow/stern waves build up so 5.3 is perfectly feasible.

 

[VO5]

And has anyone considered that the preofile of the leading edge of the rudder may have something to do with it as well ?

 

[duncan]

And has anyone considered that the preofile of the leading edge of the rudder may have something to do with it as well ?

how?

the formula is basically one that, as said, applies to all craft that are unable to escape from their own bow wave - it is a theoretical maximum.

whether sufficient force can be bought to bear to enable such a maximum to be approached is another matter entirely - although here the drag or drive (from an airfoil) will be a factor (as will many other elements).

LWL can also change considerably with angle of heel on some craft, and often increases as speeds approach the theoretical maximum as well (through the created wave form)

 

[fireball]

Can't see the need for snide remarks.

It was only in response to Haydudes ill-advised remark ... and quite tempered really ...

 

[VO5]

how?

the formula is basically one that, as said, applies to all craft that are unable to escape from their own bow wave - it is a theoretical maximum.

whether sufficient force can be bought to bear to enable such a maximum to be approached is another matter entirely - although here the drag or drive (from an airfoil) will be a factor (as will many other elements).

LWL can also change considerably with angle of heel on some craft, and often increases as speeds approach the theoretical maximum as well (through the created wave form)

I'm not quoting. I am only tossing in an idea.
It occurred to me that boats cleave through the water using their keels to be followed by the rudder. Invariably the rudder encapsulates a rudder stock, which has to stand up to considerable force as the rudder, via its leading edge is dragged through the water.
If the leading edge is clumsy, one would imagine it would reduce hull speed. Yes or no ?

 

[snowleopard]

If the leading edge is clumsy, one would imagine it would reduce hull speed. Yes or no ?

There is a relatively small component of drag from underwater appendages but the greater part of the resistance at 'hull speed' is wave resistance. It is the wave component that increases exponentially when LWL = length of bow wave. Other components increase in a much more linear fashion.

If you eliminate wave making by having a very narrow hull, you can go on increasing speed by piling on more power so there is no sudden increase in drag from keels, rudders and other underwater bits.

 

[Woodlouse]

The speeds attainable by monohulls these days are approaching those possible by multihulls. The VO70's can beat 40 knots on a good day, but average speeds are of course are a lot lower.

 

[duncan]

I'm not quoting. I am only tossing in an idea.
It occurred to me that boats cleave through the water using their keels to be followed by the rudder. Invariably the rudder encapsulates a rudder stock, which has to stand up to considerable force as the rudder, via its leading edge is dragged through the water.
If the leading edge is clumsy, one would imagine it would reduce hull speed. Yes or no ?

hull speed is a maximum figure, only achievable when the driving force and drag permit.

boat speed is a function of driving force and drag until you get to hull speed - at which point it doesn't matter how much more driving force you add, or drag you reduce; you won't go faster.

so in the context of this thread it's irrelevant.

I hope this helps

 

[Twister_Ken]

boat speed is a function of driving force and drag until you get to hull speed - at which point it doesn't matter how much more driving force you add, or drag you reduce; you won't go faster.

You would - it just depends on the nature and power of the driving force. Imagine you're being towed by a frigate, for example