Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 07-05-2015, 14:46   #76
Registered User

Join Date: Nov 2014
Location: Alameda
Boat: Bluewater 40, Cal 20, Bayliner Avanti
Posts: 275
Re: Multihulls that don't slam

..Sailed a lot in wharram.. no pounding.. Lagoon.. no pounding too.. under 20/25 kn, choppy (very common on bay area) I pound a lot with monohulls.
...maybe I have better feeling in a multihull than in a monohull?/ don't know..
__________________

__________________
En medio de la noche, sigo siendo luz...
garrobito is offline   Reply With Quote
Old 07-05-2015, 16:00   #77
Marine Service Provider

Join Date: Sep 2012
Location: Virgin Islands
Boat: 1999 Leopard 45, 45 foot cat, 1980 Hunter 33, 33 foot monohull
Posts: 405
Re: Multihulls that don't slam

Quote:
Originally Posted by Highland Fling View Post
OMG VMG to the mark is an ABSOLUTE the quickest way to get there it matters not which tack you are on.

Obviously dependent on conditions and where the way point is vis a vis the wind direction and any current running one tack will be/may be favorable (The Paying Tack) doubly so on a round island race IF THE ISLAND will allow that course.

I sailed this boat to maximise VMG to every mark of the course

The courses were very fair I would even say excellent with a lot of windward work into big big seas.

The after race bar talk which we did not partake in, was only topped out by us getting a third place..............to the owner, his wife, myself and the crew that is all that mattered, we were all both amazed and over the moon.

We took the punishment sailed well and were rewarded for some good sailing in very very trying conditions.

Have a go at me for hitting a mark but please don't tell me I am talking rubbish when I give factual info.

I NEVER mentioned boat speed only windspeed and further explained that this was app wind as we did not have a working speed transducer.

What a shame that this has descended into this sort of rubbish.

I was there, no one else here was, just because you have your opinions does not alter my facts as explained here.

I have no dummy to spit out and no axe to grind I gave what I thought was quite amazing factual info on a cat that does not belong to me only to hear opinions that what we achieved was impossible.

I sailed in company with three L420 Hybrids in the BVI's about six years ago Highland Fling took them apart comprehensively.

The one that performed reasonably was advancing the throttles (as recommended by Lagoon) and using the motors to totally minimise the drag of the enormous propsthe L420H had (so he was MOTOR SAILING but denied that this was what he was doing)

So you may appreciate my perception of the L420's sailing performance was not good......pre racing on this diesel powered one in the Heineken.

I was very surprised by how well we could make her go upwind downwind well she was way overloaded and would not surf and catch a wave.

I truly am finished with this thread have fun arguing amongst yourselves.
I think that what we have "is a failure to communicate", due to imprecision, as demonstrated above. When one says "such and such a VMG upwind", that is generally taken to me the objective is directly upwind, not that you are on the layline to the objective. Thus, if the cat is tacking through 120 degrees (true wind direction), which is not unusual when you include leeway, its VMG is half of its SOG. That means that 8 knots VMG means 16 knots through the water, which is impossible, even for the salesmen to claim. IF the boat is tacking through 90 degrees (true wind direction), such as a reasonably close winded monohull, and perhaps a tri and some cats, then the SOG would have been about 11.4 knots, also impossible for the 420.

I originally thought that HF meant that occasionally, or even regularly, they hit 8 knots SOG, which is totally possible. I sail against all sorts of cats in the BVI, some with good skippers and crews, and some with barely any skill aboard, at all, and I have been surprised that the 420 seems to sail a good bit better than I would have supposed. So exceeding 8 knots SOG is definitely possible. But the average would be a good bit less, and VMG? NO way, unless there was a huge current, which is very hard to imagine in St. Maarten.

I suspect that if one asked HF if the Lagoon were doing close to 16 knots, SOG, he would say no. Even 11.4. So, I think it is reasonable to assume that he was hitting the odd 8 knots going upwind, closehauled, but heading straight to his objective. Very different meaning, but a nice turn of speed, anyway.

I would add myself to the list of people who say that all cats slam under certain conditions, without a doubt. You have only to look at what happens when a beam sea peaks between the hulls and is steeper than the bridgedeck clearance will allow. WHAM! And I think these are almost the worst slams. But we are usually talking about upwind slams, and they definitely sound and feel different depending upon whether you are inside or outside, and where.

One other thing is that I do believe that knowing a particular boat and applying some skill goes a long way in reducing slamming. Obviously, loading matters. So does speed. So does reefing at the right time, which doesn't cut down speed but keeps the leeward hull from being driven lower into the water. On some cats, it makes a big difference whether you reef the main or the jib, not in speed, necessarily, but in how the boat drives through waves. Same thing for trim. Depending upon how full my water tanks are, I can trim the bow up several inches, and in some conditions, that helps. Also picking the right angle to the wind and waves. Boats that are always sailed on autopilots are going to hit waves indescriminately, so I think that you will always find that a skipper who hand steers a lot (and steers with regard to the waves) will always report less slamming than the autopilot crowd.

And, finally, I think that because most cats have to sail twice the distance made good, when going dead upwind, due to wide tacking angles, there is much more of a tendency to motor upwind, and straight into the waves, at that. Which causes lots of the slamming complaints. Going at a sailing angle, as the boat was designed to be sailed, reduces slamming tremendously.

But, they all slam, including the Lagoon 420.
__________________

__________________
contrail is offline   Reply With Quote
Old 07-05-2015, 16:08   #78
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 7,454
Images: 69
Re: Multihulls that don't slam

Quote:
Originally Posted by 2Hulls View Post
Calm down, David. If you stick around maybe you'll learn a bit about VMG.

I apologize for being a bit caustic with my first response to you. Instead of saying it was "impossible" for a 420 to sail at 8+kts VMG upwind I should have said something like - "Please explain what you mean by VMG because we may have different understandings of what it means. In my understanding a 420 and very few cruising cats - including my own - have the capability of sailing to a point directly upwind at 8+kts VMG."

I started racing cats in 1978 so I've been around a few courses.

Dave
The best VMG to windward we've done was 7.8 kts. That was in ~20 knots of wind, flat water (Lake Macquarie) boatspeed 11 knots, at 29'-30' apparent. 2 reefs and reduced jib. Apparent wind was around 30 knots.

No offense, but I can't see a Lagoon doing better.

The flat water makes a huge difference. You can sail much faster. At sea, we'd be slowing down due to sea state. Going off waves at 11 knots... not for me.
__________________
44'cruisingcat is offline   Reply With Quote
Old 07-05-2015, 16:28   #79
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,057
Re: Multihulls that don't slam

Would someone point me to what some of these can be found VMG, SOG I can guess at. Love to know, only been on the water for 68 years of 72. Probably like teaching me texting?
__________________
Cadence is online now   Reply With Quote
Old 07-05-2015, 17:16   #80
D&D
Marine Service Provider
 
D&D's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Blue Mountains, Australia
Boat: now working Syd Harbour charters
Posts: 1,459
Re: Multihulls that don't slam

Quote:
Originally Posted by 44'cruisingcat View Post
The best VMG to windward we've done was 7.8 kts. That was in ~20 knots of wind, flat water (Lake Macquarie) boatspeed 11 knots, at 29'-30' apparent. 2 reefs and reduced jib. Apparent wind was around 30 knots.

No offense, but I can't see a Lagoon doing better.

The flat water makes a huge difference. You can sail much faster. At sea, we'd be slowing down due to sea state. Going off waves at 11 knots... not for me.
...+2 nodding here
__________________
D&D is offline   Reply With Quote
Old 07-05-2015, 17:55   #81
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: Multihulls that don't slam

Quote:
Originally Posted by Cadence View Post
Would someone point me to what some of these can be found VMG, SOG I can guess at. Love to know, only been on the water for 68 years of 72. Probably like teaching me texting?

Cadence, VMG stands for velocity made good. Usually meaning the SOG (speed over ground) to an upwind point. Modern instruments can be set to show VMG to a waypoint or directly upwind. This is a useful way to trim and set a course to maximise VMG to a specific point, such as a windward mark. Basically the higher the VMG, the faster you will arrive there. As an example, sailing at 30 degrees to the apparent wind, your boat speed might be 7K. Obviously falling off a bIt will increase boat speed but you will sail more distance, and pointing up higher will decrease boat speed but you will sail less distance. The VMG will constantly calculate and readout and the aim is to maximise it. VMG can also be used downwind to confirm if running or tacking downwind is the better option.
Of course if you've been sailing for 68 years you don't need it, in laymans terms, it's when your 'in the groove'
__________________
monte is offline   Reply With Quote
Old 07-05-2015, 18:30   #82
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 4,332
Re: Multihulls that don't slam

Quote:
Originally Posted by Cadence View Post
Would someone point me to what some of these can be found VMG, SOG I can guess at. Love to know, only been on the water for 68 years of 72. Probably like teaching me texting?
Velocity Made Good (generally the speed component directly to windward--if tacking though 90 degrees over ground, allowing for leeway, it would be only about 70% of the SOG). Thus, to make 8 knots VMG you must be pointing very high and going over 11 knots. Very difficult, and impossible in nearly all boats. My boat will go 11 knots and will point high, but not at the same time! For most multis, anything over 5 knots VMG to windward is very, very good.

Speed Over Ground
__________________
Gear Testing--Engineering--Sailing

Writing full-time since 2014.
Bookstore:http://sail-delmarva.blogspot.com/20...ook-store.html
thinwater is offline   Reply With Quote
Old 07-05-2015, 19:03   #83
Registered User
 
Highland Fling's Avatar

Join Date: Mar 2007
Location: Sunny Scotland but sail in the Caribbean
Boat: Beneteau Oceanis 461
Posts: 374
Re: Multihulls that don't slam

Quote:
Originally Posted by 2Hulls View Post
Calm down, David. If you stick around maybe you'll learn a bit about VMG.

I apologize for being a bit caustic with my first response to you. Instead of saying it was "impossible" for a 420 to sail at 8+kts VMG upwind I should have said something like - "Please explain what you mean by VMG because we may have different understandings of what it means. In my understanding a 420 and very few cruising cats - including my own - have the capability of sailing to a point directly upwind at 8+kts VMG."

I started racing cats in 1978 so I've been around a few courses.

Dave

THIS REALLY IS MY FINAL POST ON THIS THREAD


Wonderful opening you telling me to stick around to learn about VMG then an apoligy for being caustic.....did you read what you actually wrote before your apology???

Please go back and read slowly and carefully what I have written in this thread it was written in a plain unambiguous language.

VMG is an absolute. I would have thought that there can be no question argument or debate about that.

Did you not read as I have already previously explained that I was using the highway screen on the Raymarine plotter to display VMG and had set waypoints all around the course(s) that we had to sail.

The owner, at my instruction, pre programed the plotter with every turning mark that could be used for courses, and we chose the ones that were being used in the race course for the day, as was required and added others as necessary .

We even pre programmed the start line and on at least one occasion we hit the line with one second to go at max boats speed. The owner thought I was over the line and said so at the time, it was that close...BUT we were not over early

I would say from memory that 60% of these waypoints were turning marks of the course, with a few intermediate waypoints to make my helming easier and so I could drive this cat to MAXIMUM VMG not even thinking about laylines until we had to tack to make a mark that was now on our (aft of our) beam and to windward on the other tack.............from memory we were tacking in around 120/130 degrees that being across the ground including leeway as displayed on the plotter mouse trail. BUT DON'T quote me on that OR attack that figure either this is just my perception as the Heineken was a fair number of weeks ago now. I cant even remember now what the app wind angle I was sailing to was.

This was VMG to the (waypoint) mark as DISPLAYED on the Raymarine plotter in HIGHWAY MODE and the plotter also gives a time to the mark .

At a guess 60/80% of these waypoints were direct to windward I can only think of six maybe seven that were not in five races.

For the round island race we beat along the coast of St Martin past Philpsburgh to the St Barth channel then tacked and then beat up to and around Tintamare a mark of the course in 25 gusting 35 knots app then a run down past Marigot then another beat along to the finish line and a turning mark in Simpson Bay that forced you to tack and beat again to the finish line deep in Simpson Bay.

Lots and lots of windward sailing.

As explained previously WE had real problems with riding turns as we were cross winching to the one powered winch.

So we ONLY tacked when we had to, we made long long boards maxing VMG as much as possible as we knew every tack was a killer.

Of course the electric winch packed up on one race running away with the switch stuck in the on position till we tripped the circuit breaker

We did not romp around the course at a constant 8 knots VMG all the time but at times frequently and regularly that was our VMG to a mark that was to windward.

I don't have the time motivation or the energy to go back and work out distance sailed and average boat speed doubly so as it has got nothing to do with a Lagoon 420 NOT Slamming.

And as we had an OOO log speed transducer (you did read that previously?) I would need to look at the tracks on my HH GPS and well this is just getting too silly for words...

Downwind the cat was a dog and I was reaching off as much as possible but killing the VMG as the cat would not catch a wave and surf for any decent length of time.

I have been sailing for over 60 years now, and raced Tornadoes and a Dart Cat. NONE of that is relevant to the facts as laid out here.

I hope that you now understand about my use of VMG. Not my wild guess but as calculated and displayed to me by Raymarine kit

This was how I sailed/raced this cat.......using the plotter to maximise our VMG to the next mark (waypoint) constantly as displayed on the Raymarine Plotter.

What all of this massive thread drift and highjacking has to do with the L420 not slamming is a mystery to me.

FINI
__________________
Now with 600AH of LIFEPO4
kindest regards
David
Highland Fling is offline   Reply With Quote
Old 07-05-2015, 20:28   #84
Registered User

Join Date: Dec 2012
Location: Nelson, New Zealand
Boat: FP Belize 43
Posts: 20
Re: Multihulls that don't slam

Zboss... Sometimes on my cat when I am making crazy VMG's into the wind and I hear a noise like water hitting my boat I rest my margarita glass on the table and turn on my stereo. How good is my life?
__________________
mastequila is offline   Reply With Quote
Old 08-05-2015, 05:30   #85
Registered User

Join Date: Oct 2007
Location: Winters cruising; summers Chesapeake Bay
Boat: Catana 471
Posts: 1,239
Re: Multihulls that don't slam

Quote:
Originally Posted by Highland Fling View Post
Did you not read as I have already previously explained that I was using the highway screen on the Raymarine plotter to display VMG and had set waypoints all around the course(s) that we had to sail.
Yes, I have fully read everything you wrote from the beginning, but I now conclude it is you that have not read or have not understood what I and several others have tried to explain regarding VMG. I believe you have confused VMG upwind with VMG to a waypoint or destination. Only for a moment when the waypoint is directly upwind of you will these two forms of VMG be equivalent. "Classic" VMG upwind is always with reference to an imaginary and moving point directly upwind of your current and constantly changing position. Similarly, "classic" VMG downwind is always with reference to an imaginary and moving point directly downwind of your current and constantly changing position. Knowing VMG to a stationary waypoint or destination rarely has any benefit over knowing SOG or water speed. Indeed, if you are heading directly toward a waypoint, VMG to that waypoint will be exactly the same as SOG or water speed, depending on which one is being used to calculate the V.

Dave
__________________
2Hulls is offline   Reply With Quote
Old 08-05-2015, 10:39   #86
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,057
Re: Multihulls that don't slam

Quote:
Originally Posted by monte View Post
Cadence, VMG stands for velocity made good. Usually meaning the SOG (speed over ground) to an upwind point. Modern instruments can be set to show VMG to a waypoint or directly upwind. This is a useful way to trim and set a course to maximise VMG to a specific point, such as a windward mark. Basically the higher the VMG, the faster you will arrive there. As an example, sailing at 30 degrees to the apparent wind, your boat speed might be 7K. Obviously falling off a bIt will increase boat speed but you will sail more distance, and pointing up higher will decrease boat speed but you will sail less distance. The VMG will constantly calculate and readout and the aim is to maximise it. VMG can also be used downwind to confirm if running or tacking downwind is the better option.
Of course if you've been sailing for 68 years you don't need it, in laymans terms, it's when your 'in the groove'
Thanks for the explanation. Never having had in interest in racing I guess tell tails have done me or plan gut feel. Thanks again for taking the time and making it understandable.
__________________
Cadence is online now   Reply With Quote
Old 08-05-2015, 15:17   #87
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 7,454
Images: 69
Re: Multihulls that don't slam

Quote:
Originally Posted by Highland Fling View Post

THIS REALLY IS MY FINAL POST ON THIS THREAD


VMG is an absolute. I would have thought that there can be no question argument or debate about that.


FINI
Not quite. And this is probably where some of us are at cross purposes.

Unfortunately there are two generally used VMG's. There's the GPS sourced VMG - velocity made good to a waypoint. It would be less confusing if it was called something else, like WCV- waypoint closure velocity, or something similar.

But there also VMG to windward. That's velocity made good to a non -specific point directly upwind of you.

Most wind instruments (when networked with a speed log) and some autopilots can calculate VMG to windward even without there being a target waypoint or a GPS involved.

There's a VMG (to windward) calculator here: VMG to Wind Calculator which also has an explanatory diagram.
__________________
44'cruisingcat is offline   Reply With Quote
Old 08-05-2015, 16:00   #88
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: Multihulls that don't slam

I recently started to explore the VMG function on our Raymarine gear. I found the VMG to windward not very practical due to the large fluctuation in readout. I guess the system needs to use the log and apparent wind first to calculate true windspeed and direction. The figures fluctuated rapidly between 5 and 6 knots so it was pretty useless as a course to steer.
After that I placed a WP 50M upwind and used VMG to the waypoint, which was much more stable and the readout was usable to find the best course to steer, only varying slowly . Conditions were a little choppy, into a 2m swell so the windex was revolving a bit on and off the back of waves, which probably effected the TWD etc.
is this the norm or do others find the VMG to windward works ok?
__________________
monte is offline   Reply With Quote
Old 08-05-2015, 16:39   #89
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 7,454
Images: 69
Re: Multihulls that don't slam

I've had a similar experience with the VMG on the Raymarine ST60 wind. Our Simrad autopilot also displays VMG, (to windward) and is very stable. The Simrad can also steer to optimum VMG, which is nice!
__________________
44'cruisingcat is offline   Reply With Quote
Old 08-05-2015, 17:06   #90
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: Multihulls that don't slam

Wow that is clever!
Yes I'll have to look into the Raymarine setup. I notice the true wind direction shifts 10 degrees every time I tack and port tacks good angle is 30d and starboard is 40d so I assume she needs to be calibrated 5d one way.
__________________

__________________
monte is offline   Reply With Quote
Reply

Tags
hull, multihull

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Request Permission to Come Onboard from Grand Slam Grand Slam Meets & Greets 7 30-03-2012 01:54
For Sale: Slam:Bermuda Hissar Sailing Shorts XL brakauskas Classifieds Archive 0 22-01-2012 19:04
For Sale: Brand New SLAM Ocean Waves Foul Weather Gear Tstullis Classifieds Archive 0 13-10-2011 15:46
Slam Dunk - Brisbane atoll Cruising News & Events 63 01-02-2011 20:26
Heavy Weather and Multihulls Sonosailor Multihull Sailboats 13 07-03-2008 10:03



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 10:11.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.