Pub talk - how fast CAN a yacht go?

Vern

Vern

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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.
 
Vern said:
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.
Click to expand...

1 > 1.5 x the sq root of the water line length on displacement boats
 
The waterline lenght rule works for going upwind very nicely (and displacement yachts, obviously)

I race a J105, 34ft, It is designed to plane off the wind. We have seen 15kts, off the wind with a spinnaker up. This was in 22kts of wind. The boat had half it's bow in the air and was throwing a lot of water around! :D
 
'Hull speed' is the speed above which resistance increases so much that further increases in speed require impractical amounts of additional power. That is because the boat sits in the trough of its own bow wave. Hull speed is approx 1.4 x sq root waterline length. The constant averages 1.4 but can be higher for fine-lined boats and lower for heavy tubby boats.

There are 3 basic ways of exceeding hull speed:

1. Surfing down the face of a steep wave - any boat can do this for a few seconds at a time.

2. Planing, where the hull form allows the boat to skim along the surface like a speedboat. This is how boats like Open 60s achieve their performance.

3. Narrow hull forms that don't make significant bow waves. Most instances being multihulls.
 
snowleopard said:
There are 3 basic ways of exceeding hull speed:

1. Surfing down the face of a steep wave - any boat can do this for a few seconds at a time.
Click to expand...

I've experienced this on a (roughly) 35 footer. Four of us on board, trying to out do each other at the helm on a broad reach in a fresh (f 5-6) breeze. I think the record stood at just over 11 knots by the time we got to Hurst :cool:
 
Arh! Oi donno 'ow farst they big boys go but Oi remembers beating moi awd mussel drudger through the gull channel some years ago... We wus overtaking this 'ere open 40 sweet as a nut when the Walker log tore right orf the transom!
 
snowleopard said:
'Hull speed' is the speed above which resistance increases so much that further increases in speed require impractical amounts of additional power. That is because the boat sits in the trough of its own bow wave.
Click to expand...

Sitting in the trough of it's own bow-wave

Classboatrace65-L.jpg
 
Vern said:
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.
Click to expand...

6 knots?

You would need God on board to do that. :D
 
Lakesailor said:
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.
Click to expand...

It will certainly be able to hit those speeds briefly, but I would be very surprised if those speeds could be maintained consistently over a period of time.
 
Well, yes, the vagaries of the wind can't be relied on. But the OP didn't ask if he could bend the speedo needle all day long.
I could rely on 4.9 knots in Feckless provided the wind was steady at about 10 knots.
Trouble is here "wind" and "steady" don't sit alongside one another in conversation.
 
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