My AWB achieved Hull Speed - What did I do right?

[johnalison]

When I did my 2 round UK trips the average, inc time spent motoring in & out of port , & through the cally canal & locks etc. was a tiny fraction under 6 Kts. However, only 6 legs each time were over 100 miles, (thus tending to cancel tides) so generally I made sure that I was able to use the tide to my advantage.
As Tranona points out, that makes a huge difference to a passage time. Without using the tides (& waiting for favourable wind, with which I was usually lucky) my average may have been significantly less.

Of course, Brighton/Dover is where this shows. I have done it at a very leisurely pace and still managed the 60 miles in one tide but never managed a proper Charlie Stock over the Estuary. I'm probably too old to enjoy the prospect of foiling cruisers, but four and a half hours to Ostend would be good.

 

[Daydream believer]

Of course, Brighton/Dover is where this shows. I have done it at a very leisurely pace and still managed the 60 miles in one tide but never managed a proper Charlie Stock over the Estuary. I'm probably too old to enjoy the prospect of foiling cruisers, but four and a half hours to Ostend would be good.

Add 10 hours to that & I have done it a few times from Bradwell, pontoon to pontoon. But it has also taken 30 hours, & an awful lot in between. So not all sweetness & light

 

[Tranona]

As a number of posts say, it is all about getting to know your boat's capabilities and how to get the best out of it - then shaping your passage plans to use those capabilities. Having spent most of my sailing life with a slow old style boat based in an area with strong E/W tidal flows and prevailing winds from the east in the spring and west in the summer life is dominated by tides as getting it right adds as much as 25-30% to SOG on springs. Less important going N/S except getting the offset right to avoid ending up down tide of the destination.

Switching to a modern boat for the last few years changed things considerably as the extra speed potential reduced the dependency on tides and Poole Cowes became comfortable in one tide whereas with the old boat would often hit the west going tide change between Yarmouth and Newtown. Really hard work pushing a 2 knot ebb in a boat that on a good day might achieve 5.5 knots! Cross channel becomes 11 hours instead of 13/14 (although did have one memorable 11 1/2 hour crossing with the old boat).

Now I have gone backwards to another old slower boat will have to adjust my approach again, but hopefully not back to sub 5 knots averages!

 

[Concerto]

As a number of posts say, it is all about getting to know your boat's capabilities and how to get the best out of it - then shaping your passage plans to use those capabilities. Having spent most of my sailing life with a slow old style boat based in an area with strong E/W tidal flows and prevailing winds from the east in the spring and west in the summer life is dominated by tides as getting it right adds as much as 25-30% to SOG on springs. Less important going N/S except getting the offset right to avoid ending up down tide of the destination.

Switching to a modern boat for the last few years changed things considerably as the extra speed potential reduced the dependency on tides and Poole Cowes became comfortable in one tide whereas with the old boat would often hit the west going tide change between Yarmouth and Newtown. Really hard work pushing a 2 knot ebb in a boat that on a good day might achieve 5.5 knots! Cross channel becomes 11 hours instead of 13/14 (although did have one memorable 11 1/2 hour crossing with the old boat).

Now I have gone backwards to another old slower boat will have to adjust my approach again, but hopefully not back to sub 5 knots averages!

Sailing to get anywhere in reasonable time is always about boat speed. On very long distances that cover multiple tides, you will always puch some tide. This makes you realise that you must make tidal gates or you will add extra hours to your journey time.

Boat speed is a combination of sail trim, clean hull and minimising drag. Reducing drag can be not towing a dinghy or fitting a folding propeller. A folding propeller will add ½ to ¾ knot of boat speed in most conditions. So on a 10 hour sail you would have covered 5 to 7½ miles more. Better sail trim can add a similar amount. So compared to sailing at an average of 5 knots to do 50 miles, you could cover 65 miles and thereby increasing your cruising range.

Having just completed a full round Britain trip I can only stress how important covering more miles per day can be. Several days I sailed over 80 miles and 60+ miles was quite common. My calculations for boat speed were always based upon the forecast wind direction and speed. Some days it would be 5 knots and others would be 6.5 knots. Generally I exceeded the anticipated average boat speed, however twice the wind did perform to forecast and made close fetches into full beats and caused me to miss 2 tidal gates.

Having seen Tranona's "new" boat, I doubt if many journeys will exceed a 5 knot average. However he is no longer planning many longer day sails, so it should not be a problem for him.

 

[johnalison]

It is strange how one’s expectations can change. Back in the ‘70s I had a 26 Mystere with a petrol engine and we would motor at 4.7 knots and think this was normal, our longest leg being Blackwater-Ijmuiden with only about half under sail. I think it took about 36 hours. With my 34 we regarded Lowestoft -Ijmuiden as a day trip. Even being able to motor at close to 7kn made missing a tidal gate such as that at Den Helder less fearsome.

 

[Tranona]

Having seen Tranona's "new" boat, I doubt if many journeys will exceed a 5 knot average. However he is no longer planning many longer day sails, so it should not be a problem for him.

Yes, the difference between a 5.5 tonne boat with a nominal sail area of 50 sqm and a waterline of 9.5m and a similar displacement with 40 sqm and waterline of 8m. Increases the importance of a good engine and knowing how to use it, particularly to meet those important tidal gates.

 

[Laminar Flow]

To reach hull speed, a relative speed of 1.34, your sails or engine need to generate one HP of thrust for every 500lbs of displacement.

In a F3 one sqrft of sail generates 0.015 HP
In a F4 0.020
In a F5 0.040
In a F6 0.070

Flat water of course.

How soon a boat reaches hull speed depends on the sail area/displacement ratio (SA/D). All things being equal, of two boats with the same SA/D, the heavier one will be faster in light airs. It has simply more SA to overcome the, at lower speeds, predominant frictional resistance.

At higher speeds, folding props have less of an impact, as compared to overall resistance, as the the prop's resistance is proportionately less significant.

Recognized average relative speed for displacement sailing yachts is 0.9. For our 28.25' DWL that works out at 4.8 kts.
Nevertheless, we have averaged 6 kts over 35hrs (210 miles, Ijmuiden - Dieppe) and 6.8 kts over 70 miles Dartmouth - Les Hanois, Guernsey). Under sail, obviously. Our SA/D is 18.

 

[Daydream believer]

To reach hull speed, a relative speed of 1.34, your sails or engine need to generate one HP of thrust for every 500lbs of displacement.
In a F3 one sqrft of sail generates 0.015 HP
In a F4 0.020
In a F5 0.040
In a F6 0.070
Flat water of course.

I am confused
Where do you get the figure of 1.34 from & what is that figure? ie 1.34 of what?
Why does "flat water" make any difference to the drive of the sail. It either gives "X" drive per Ft2 or not.
Surely air density affects sail drive - as proven many times by yachts sailing in the UK then Australia. So where do your HP per ft2 of sail area actually come from & what angle to the wind.
Surely one cannot just quote a figure without further reference?
You said
"Recognized average relative speed for displacement sailing yachts is 0.9"
0.9 of what?.

 

[Tranona]

At higher speeds, folding props have less of an impact, as compared to overall resistance, as the the prop's resistance is proportionately less significant.

That is true and the biggest proportional gains are at low speed, but the gain is still significant at the sort of speeds we are talking about here, that is 5-6 knots. Something in the order of 0.5 knots, and more importantly it is there all the time without any effort from the helm. This is equivalent to an hour reduction in a cross channel passage from Poole to Cherbourg or 132 mpd compared with 120 on a long distance passage such as a transatlantic.

This is the sort of gain I experienced when I fitted a feathering propeller to my old Eventide (a boat not known for its sailing qualities!) and why I have done the same on my Golden Hind. extra important here, because to get the best motoring performance out of the new 30hp engine needs a 17" propeller rather than 15" normally fitted (with the original 20hp). The photo says it all.

 

[johnalison]

My impression is that my 2-blade folding prop gives +/- 1/4-1/2 knot difference but I can believe that three blades might give more. Another significant benefit is the lack of turbulence when folded, making the helm much more sensitive and pleasurable. In any case, I have a rule not to believe anything a yachtsman ever says about speed, presumably due to a genetic similarity to anglers.

 

[Tranona]

I agree. The 2 blade folder on my Bavaria was similar - but drag from the prop on a modern saildrive boat is much smaller than a 3 blade on a full bodied long keeler. One of the reasons for choosing a 17" prop was that the blade area is approx 25% greater than the 16" which is great for motoring and feathering adds no penalty under sail. Not had a chance to try it yet except the initial commissioning of the motor when it did all I expected except the prop is slightly overpitched because of a last minute change in gearbox reduction ratio.

 

[xyachtdave]

I have a rule not to believe anything a yachtsman ever says about speed, presumably due to a genetic similarity to anglers.

Yes I’ve often wondered if it’s faulty equipment or they just lie!

On a club cruise the forecast was a SW5 occasionally a 6. Most of the passage to Ramsgate had late teens to low 20’s, broad reaching. Once clear of North Foreland and hard on the breeze we put a couple of reefs in the main and carried a 100% jib. The most true wind speed we saw was 27-28. The boat wasn’t particularly pressed so no way it was more than that, or we’d been in trouble with our headsail size.

The rest of the fleet were within a few miles of us.

On arrival, let’s call him Bob the Bull Sitter’, reckons he’s had 50 knots over the deck. When I looked surprised he was adamant about the speeds…the boat was doing 10 knots upwind with a big baggy partially furled knackered headsail.

On another occasion he claimed 60 knots. I had to leave the room at that point!

Lots of big numbers being quoted in this thread, my speed and wind logs must under read a mile…

 

[Daydream believer]

Yes I’ve often wondered if it’s faulty equipment or they just lie!
On arrival, let’s call him Bob the Bull Sitter’, reckons he’s had 50 knots over the deck. When I looked surprised he was adamant about the speeds…the boat was doing 10 knots upwind with a big baggy partially furled knackered headsail.
On another occasion he claimed 60 knots. I had to leave the room at that point!
Lots of big numbers being quoted in this thread, my speed and wind logs must under read a mile…

OH! how I miss Seajet in these discussions.
His Anderson 22 would wipe the floor with the lot of us.
Plus, he had an old mate, with whiskers, that were calibrated for wind speed, to the fraction of a knot.. He could tell stories of 50kts on the nose with utmost accuracy.

If one really wants to quote speed, it has to be based on passage times, port to port, against an accurate distance, measured in a series of straight lines, off a chart.
That is what matters in the end.

 

[johnalison]

Not to mention those who managed to sail back from Ostend against a F9 on the nose in a 28-footer. I have to admit that my trips back from Blankenberg were often timed from the offing buoys to somewhere around Stone Banks.

 

[Daydream believer]

Not to mention those who managed to sail back from Ostend against a F9 on the nose in a 28-footer. I have to admit that my trips back from Blankenberg were often timed from the offing buoys to somewhere around Stone Banks.

With 162 crossings to & from Ostend to Bradwell, or Burnham, I have only encountered F9 once. That was in my Stella back in 1976, when one only had the shipping forecast to rely on, which I missed. It was only for a short period & I just hove too for 4.5 hours. To catch one the whole way, & "on the nose" would either be plain poor weather watching, or some other death wish . I have encountered winds approaching F8, with a few gusts into F9 when well on the way, so continued. An F9 is not a few gusts; no more than an F8 is.
But several times I have had the sense to turn back after an hour when I realised I had bitten off more than I cared to chew.
An F9 in the southern N sea is not to be sniffed at & I would suggest that it would be a rare small boat that could make decent headway to windward. I recall the first time a huge wave broke in front of me. Foam tumbled down the face & I screamed in fear. The wave washed right over the deck & cabin & into the non self draining cockpit. I had to pump frantically. Lots more did the same thing but I learned that a broken wave has less force than one just about to break. Those were the ones that really hit the boat hard.
For me it was a close reach to the Toungue light vessel ( I needed a target for my DF set & a light to aim at at night)& up through the Edinburgh channel the following day. I hove too over the Falls bank, where I hoped I would not be run over by any shipping whilst I slept. Waves still washed over the boat from time to time.
So those who talk glibly about F9 on the nose (or F8 for that matter) in small boats do make me wonder.
I have only encountered a true F9, out at sea, rather than along the coast, twice in 52 years.
But to each his own & well done to those that can manage it.

 

[johnalison]

With 162 crossings to & from Ostend to Bradwell, or Burnham, I have only encountered F9 once. That was in my Stella back in 1976, when one only had the shipping forecast to rely on, which I missed. It was only for a short period & I just hove too for 4.5 hours. To catch one the whole way, & "on the nose" would either be plain poor weather watching, or some other death wish . I have encountered winds approaching F8, with a few gusts into F9 when well on the way, so continued. An F9 is not a few gusts; no more than an F8 is.
But several times I have had the sense to turn back after an hour when I realised I had bitten off more than I cared to chew.
An F9 in the southern N sea is not to be sniffed at & I would suggest that it would be a rare small boat that could make decent headway to windward. I recall the first time a huge wave broke in front of me. Foam tumbled down the face & I screamed in fear. The wave washed right over the deck & cabin & into the non self draining cockpit. I had to pump frantically. Lots more did the same thing but I learned that a broken wave has less force than one just about to break. Those were the ones that really hit the boat hard.
For me it was a close reach to the Toungue light vessel ( I needed a target for my DF set & a light to aim at at night)& up through the Edinburgh channel the following day. I hove too over the Falls bank, where I hoped I would not be run over by any shipping whilst I slept. Waves still washed over the boat from time to time.
So those who talk glibly about F9 on the nose (or F8 for that matter) in small boats do make me wonder.
I have only encountered a true F9, out at sea, rather than along the coast, twice in 52 years.
But to each his own & well done to those that can manage it.
[/QUOTE
I have never encountered anything more than F7 in open water, but my F9 gibe was in relation to an account I once heard. As well as doubting the F9, I also assume that ‘on the nose’ for many people means ahead of the beam. Now that I have a wind meter I can’t lie about it, but I think that many of us refer to gusts as if it were the true wind. I have recorded 57 knots of wind on two occasions, but both times it was no more than very windy and the peak figure recorded just a freak flip of the whirly things. Similarly, I have recorded 11.5 knots through the water while under way, but for no more than a few seconds and with a meter adjusted for 6.5 kn and probably over-reading by around 5% at the higher speed. I think the worst seas we met were not in the open but when coming out of the Roompot with 3.5 kn tide and against 25+ kn wind that was forecast to be 15, when we did our submarine imitation.

 

[Chiara’s slave]

I am confused
Where do you get the figure of 1.34 from & what is that figure? ie 1.34 of what?
Why does "flat water" make any difference to the drive of the sail. It either gives "X" drive per Ft2 or not.
Surely air density affects sail drive - as proven many times by yachts sailing in the UK then Australia. So where do your HP per ft2 of sail area actually come from & what angle to the wind.
Surely one cannot just quote a figure without further reference?
You said
"Recognized average relative speed for displacement sailing yachts is 0.9"
0.9 of what?.

Those numbers add up for us almost perfectly If we said our boat, ready to sail, with some water and fuel on board, and 2 crew with a set of dry clothes each, we might weigh in around 2300kg. That’s pretty much 10 x 500lb. We have 600 sq ft of white sail, and plane at the bottom of F4, the speed jumps from about 6.5 to 8 kn upwind, and the sternwave detatches from both main hull and the immersed ama. According to his table, we should be getting about 10hp from the rig. The rest of it, I have no idea.

 

[xyachtdave]

So those who talk glibly about F9 on the nose (or F8 for that matter) in small boats do make me wonder.
I have only encountered a true F9, out at sea, rather than along the coast, twice in 52 years.
But to each his own & well done to those that can manage it.

Bob (mentioned above) gets that sort of weather once a month according to his Raymarine gear.

You must have been very lucky!

?

 

[Daydream believer]

Those numbers add up for us almost perfectly If we said our boat, ready to sail, with some water and fuel on board, and 2 crew with a set of dry clothes each, we might weigh in around 2300kg. That’s pretty much 10 x 500lb. We have 600 sq ft of white sail, and plane at the bottom of F4, the speed jumps from about 6.5 to 8 kn upwind, and the sternwave detatches from both main hull and the immersed ama. According to his table, we should be getting about 10hp from the rig. The rest of it, I have no idea.

Upwind?In a trimaran? ? ? ? ? ?

 

[Chiara’s slave]

Upwind?In a trimaran? ? ? ? ? ?

Ye of little faith. You’ve not come across a Dragonfly in your travels, obviously.
If you have a minute, heres the ‘how to’