Flying Sadler

[mick]

My Sadler 26 has a theoretical hull speed of 6.4 knots. Today, in a strong offshore breeze, fairly flat sea, no tide, my GPS several times recorded over 7 knots. The GPS is accurate compared to two other units, one fixed, one handheld. Comments appreciated.

 

[alldownwind]

What would you like us to say? Well done? /forums/images/graemlins/grin.gif
Theoretical hull speeds are just that, theoretical, meaningful only on a flat calm sea when, of course, you wouldn't be moving at all.
All Sadlers are cracking boats and I'm not surprised you did 7 knots!

 

[mick]

[ QUOTE ]
What would you like us to say? Well done? /forums/images/graemlins/grin.gif
Theoretical hull speeds are just that, theoretical, meaningful only on a flat calm sea when, of course, you wouldn't be moving at all.
All Sadlers are cracking boats and I'm not surprised you did 7 knots!

[/ QUOTE ]

No, I'm just confused. If, as you say, hull speeds refer to a completely calm sea, then the speeds recorded are even more surprising as the sea state was choppy. (Around here that means fairly flat.)

 

[john_morris_uk]

'Hull Speed' isn't some invisible or theoretical brick wall which cannot be exceeded. It is the speed at which energy put to attempting to drive the boat through the water faster produces a small increase in speed and a large increase in the bow and stern wave.

You can tell when you are exceeding hull speed by the boat trying to climb its own bow wave and when you look behind you appear to be dragging a wave behind you.

If you plot a graph of 'energy in' versus 'boat speed' the graph is more or less linear to start with but at a certain speed, there is a large change in direction on the graph. The speed at which this elbow occurs is 'hull speed'.

The fact that you have driven your hull at speeds in excess of the 'hull speed' is not unusual. The thing to remember is that if you do it under engine power, you are wasting a lot of diesel.

 

[mick]

Thanks

 

[captainslarty]

Mick, using a gps you are seeing your SPEED OVER THE GROUND, with a little bit of current your boat speed AND the current speed make up the SOG.
In a 9 knot current you could register 15 knots sog no problems.
The theoretical hull speed refers to speed through the water.
Problem solved.

 

[cliff]

Quote from OP "Today, in a strong offshore breeze, fairly flat sea, no tide, my GPS several times recorded over 7 knots" - Note the comment "no tide" If this was actually the case, the GPS will indicate speed through the water.

7 kts TTW out of a Sadler 26 is not bad going IMHO, indeed it is pretty good going. The Sadlers while not "racers" are not exactly slow boats either.
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[Skyva_2]

With enough wind and a light boat with a modern (AWB?) hull shape, the theoretical speed can indeed be exceeded.

A 'classic' long keel hull shape like a Nic 32 would probably not exceed max hull speed.

 

[captainslarty]

Hi
It aint an issue on theoretical hull speed really, you just dont use a gps to assess a boats performance ´through the water´
You can also never really say "no tide" or "no current" in the sea.
Use the paddle wheel or similar sensor if you want to make a valid assessment, not the gps. same for trimming etc, looking at gps speed is of no consequence, but the normal boat speed log is.
Joe

 

[Bajansailor]

Re: Flighty long keel hull forms

Classic hull forms with long keels can quite happily exceed their theoretical hull speed, especially when surfing downwind!
I used to sail a fair bit on Stormy Weather - a lovely classic S & S design from the 30's, 40' waterline length and about 22 tonnes displacement. Her theoretical hull speed is a bit over 8 knots, and we often had 200 mile days when crossing the Atlantic in 1994 - the best speed recorded on the log was 14 knots when surfing down a wave with everything up - while in the 1993 Fastnet we averaged 10 knots the whole way between the Fastnet and the Bishop, with a F 7-8 on the beam.

 

[contessa26]

Re: Flighty long keel hull forms

Hear hear! You can't beat a nice looking boat! Especially one designed by the Great Designer himself. And skippered by his brother Rod in the 1935 Transatlantic and Fastnet races, both which she won. Interesting to hear actual personal experience of the boat's performance though. Thanks

 

[Heckler]

sorry to be a kill joy, the gps records speed over ground, if the tide is doing 10 knts then you could do 10 plus 6.4 theoretical to give you 16.4 knots on the gps
stu

 

[MarkJohnson12345]

As another flying Sadler (32) we recorded down hill speeds of 11.7 knots recently coming up the from Devon towards the Bristol Channel.

The hull speeds are easily exceed as the boat is really falling down the steep waves.

Our average speed over several hours on the GPS was 7.5 knots, but we had 1.5 knots of tide with us, so really the boat speed was only an average of 5.5 knots thru the water.

With strong winds astern, probably F5's, we sailed well, but when a rain cloud engulfed us the winds went onto the beam. With full set of sails up, the boat just flew, doing well over 6.5 knots.

Whilst this season has been windy and prevented us sailing to windward, the down winds sails have been superb. An excellent season as long as the wind direction has been blowing us towards our destination.

MJ