What is "Hull Speed" Anyway

[TJ D]

Originally Posted by B00B00

Wow TJ, I just checked your boat details on your blog, that is a seriously impressive bit of kit!
I have met the designer Paul many times over the years, hes a great guy.

Hey, thanks. We feel really privileged to own her, that's for sure. I was honestly totally sick of sailing, previously having owned a few very heavy 'blue-water cruisers'. Jenny and I were considering buying a house, in fact.

Then, RS came into our lives at just that moment. Funny how life works. I'm grinning like an idiot most of the time we're out on this thing. It's really awesome to be able to sail very conservatively and still have daily runs that are really good.

We just had lunch with Paul in Seattle a few weeks ago. I also really like him. I think he really likes what he does, and he's just as happy to talk boats with ordinary sailors like us as he is someone like Russel Coutts. That's pretty rare in the racing business.

Have a good one.
TJ

[Dockhead]

Originally Posted by B00B00

Wow TJ, I just checked your boat details on your blog, that is a seriously impressive bit of kit!
I have met the designer Paul many times over the years, hes a great guy.

I've had the privilege of seeing Rocket Science in person, when TJ and Jenny visited us in Cowes this year. Photos don't really do her justice -- she is nothing like a converted race boat as you might imagine -- she is full of ingenious details and beautiful craftsmanship. Yep, TJ is a luck guy . . . . And it totally makes sense to cruise on such a vessel, for anyone who actually likes to move and change scenery . . .

[Polux]

Originally Posted by estarzinger

Actually Polux, the volvo guys do in fact quite often wear drysuits - but breathable ones usually - like this here:

HPX GORE-TEX OCEAN DRYSUIT

I had one of those on board and one of these: https://www.kayakacademy.com/collect...nt=15911323206

multi-race Volvo guys in fact recommended both options to me.

They were both brilliant - much much better than a typical sailing foul wear gear in several regards - you NEVER get wet at all inside, and they provide excellent flotation and warmth in the water, and they are fast and easy (with the front zip) to get in and put of. They have integrated socks - so you can wear anything you want on your feet. The second one you can get with a custom fitting which is quite nice.

Yes, maybe they have them too, even if weight is at premium on those boats but what they normally use are top performance offshore suits, not very different than the one that I have for more 10 years (Musto). Even so it is too hot for most sailing on hot climates.

Regarding Mapfre, the boat that I posted as an example you can see on this video on m 0.40 the equipment on a rack and a guy using part of the suite:

https://www.youtube.com/watch?v=BK540ox6c0g

You can see on the video below (min 3.51) that Brunel crew uses a similar equipment...and this is on the 3rd leg, the colder one and with worst seas.

Taking the opportunity to wish you and all a great new year!

https://www.youtube.com/watch?v=K4G83dDH_KE&t=280s

[Yellowtulip]

I've been following this thread with interest. Many years ago I read one of Marchaj's books, getting the distinct impression that "hull speed" was a decidedly woolly concept.
On 12th September 2016 I sailed (two up) from Cherbourg to Cowes. My boat is a Westerly Storm.
LWL 27 feet
SA/D 16.67
D/L 256.62
Displ. 5130 kgs plus enough gear for three months' cruising
"Hull Speed" 6.8 knots or so.
We left Cherbourg at 0700. There was no wind so we motor sailed until about 1300 when a good breeze sprang up. We turned off the motor and soon had to put a reef in the mainsail (we use a 100% blade jib). From 13.40 to 16.30 we covered 22.2 nautical miles by GPS. That's an average of 8.8 knots or thereabouts.
Here is the recorded track from iSailor (chartplotter software)



The part of the voyage I refer to is between the two waypoints marked A and B. The tide was running west during this time. The overall average speed for the entire 76.6 miles was 6.6 knots.
Here is the page from my log.



I hadn't considered that there was anything unusual about that part of the trip. It was just a cracking sail! Considering the figures, I suspect my estimate of the wind speed is very conservative. We didn't have working wind instruments at the time.

[Yellowtulip]

Sorry about the duplication of the pics. Don't know why it did that.

[DotDun]

Originally Posted by Yellowtulip

I've been following this thread with interest. Many years ago I read one of Marchaj's books, getting the distinct impression that "hull speed" was a decidedly woolly concept.
On 12th September 2016 I sailed (two up) from Cherbourg to Cowes. My boat is a Westerly Storm.
LWL 27 feet
SA/D 16.67
D/L 256.62
Displ. 5130 kgs plus enough gear for three months' cruising
"Hull Speed" 6.8 knots or so.
We left Cherbourg at 0700. There was no wind so we motor sailed until about 1300 when a good breeze sprang up. We turned off the motor and soon had to put a reef in the mainsail (we use a 100% blade jib). From 13.40 to 16.30 we covered 22.2 nautical miles by GPS. That's an average of 8.8 knots or thereabouts.
Here is the recorded track from iSailor (chartplotter software)
......

The part of the voyage I refer to is between the two waypoints marked A and B. The tide was running west during this time. The overall average speed for the entire 76.6 miles was 6.6 knots.
Here is the page from my log.
......

I hadn't considered that there was anything unusual about that part of the trip. It was just a cracking sail! Considering the figures, I suspect my estimate of the wind speed is very conservative. We didn't have working wind instruments at the time.

22.2nm in 170 minutes is an average speed of 7.8kts

[Yellowtulip]

Originally Posted by DotDun

22.2nm in 170 minutes is an average speed of 7.8kts

I stand corrected, but still greater than "hull speed".

[valhalla360]

Originally Posted by Yellowtulip

I stand corrected, but still greater than "hull speed".

Hull speed is not an exact number so when you start talking about 1/10ths of a kt accuracy, it's not consistent with the definition.

If you keep throwing HP at the problem, you will go faster than "hull speed" but each kt faster requires drastically more power than the last extra kt.

In the right conditions, sails can easily put out more power than the engines on a typical displacement cruising boat, so if you have say a 25hp engine spec'd to make hull speed with a small reserve, the sails might be able to generate 50-100hp and squeak out an extra kt or two.

[Dockhead]

Originally Posted by Yellowtulip

I stand corrected, but still greater than "hull speed".

Yes, and it's very, very fast. While my boat can get up to 0.7 knots above nominal hull speed fairly easily, holding it there and averaging such speeds is another matter. Under perfect perfect conditions I can just about average nominal hull speed but have never been able to do it for as long as 24 hours (that would be a 223 mile day).

[Yellowtulip]

Originally Posted by Dockhead

Yes, and it's very, very fast. While my boat can get up to 0.7 knots above nominal hull speed fairly easily, holding it there and averaging such speeds is another matter. Under perfect perfect conditions I can just about average nominal hull speed but have never been able to do it for as long as 24 hours (that would be a 223 mile day).

After reading this thread, I was curious to see what speeds we have attained, but I had to wait until I could fetch my log book to verify my subjective impressions. This was the only instance I could find at this speed. There was one other trip from Roscoff to Treguier, but that was tide assisted. We usually average around 6.5 knots in favourable reaching conditions, (as we did for this entire trip) setting sail area for comfort rather than speed, but on that particular occasion I was more gung-ho than usual.
I wonder what a racing crew with a small spinnaker might have achieved?

[Yellowtulip]

I've just been looking at my data again to consider the possibility that I wrote down an incorrect time. I take the time from the GPS cross-checked against the ship's clock and my watch, but round to the nearest minute, so it's possible that the time taken was three minutes longer.
Here's the log book pic again:


The average speeds between 13:40 and 14:22, and again between 14:22 and 16:30 are consistent with the longer period, so I don't think I got the times wrong. Unfortunately I erased the plot on the paper chart I used which would have been another verification.

[Paul Elliott]

Hull speed is a squishy number. My boat has a LWL of 33' 7", which gives us a nominal hull speed of 7.77 kts. That LWL does stretch out a bit at speed.

As I've mentioned previously, when pushing hard we often exceed 10 kts for a while, and have touched 12 kts on a couple of occasions (in zero appreciable current). But our average speed is certainly less than that. We have had a few 200nm days, which is an average speed of 8.33 kts. This requires lots of wind and as much sail as we can carry. We have had *many* 180 and 190 mile days. Our 7.77 kt hull speed should give us 186 nm/day, so on a very good day we will average that. The typical sailing day is probably closer to 160 nm.

Just another datapoint, FWIW.

[SV DestinyAscen]

Originally Posted by Paul Elliott

Hull speed is a squishy number. My boat has a LWL of 33' 7", which gives us a nominal hull speed of 7.77 kts. That LWL does stretch out a bit at speed.

As I've mentioned previously, when pushing hard we often exceed 10 kts for a while, and have touched 12 kts on a couple of occasions (in zero appreciable current). But our average speed is certainly less than that. We have had a few 200nm days, which is an average speed of 8.33 kts. This requires lots of wind and as much sail as we can carry. We have had *many* 180 and 190 mile days. Our 7.77 kt hull speed should give us 186 nm/day, so on a very good day we will average that. The typical sailing day is probably closer to 160 nm.

Just another datapoint, FWIW.

If I may piggy back on this. Arleigh Burke destroyers have a hull speed around 30 knots. Endurance cruise is about 20-25. Flank speed is officially classified but in excess of 35.

Hull speed is just a rough and useful guide re hydrodynamic performance and point where diminishing returns really escalate. Not sure why some are so focused on putting others down.