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Old 08-05-2015, 21:53   #91
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Re: Multihulls that don't slam

Yes, most likely a zero error there. They're quite easy to calibrate.
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Old 09-05-2015, 10:45   #92
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Re: Multihulls that don't slam

Bridgedeck slamming? Yep definitely a problem on our Maine 41 with 34" bridgedeck clearance - kayakers LOVE to paddle underneath & bang their paddles along the way!
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Old 09-05-2015, 18:58   #93
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Re: Multihulls that don't slam

I like the noise. It's nicer than a fog horn and keeps the monohulls away from me in the anchorage at night. Sometimes you can get a good Gene Krupa kinda beat going between the wave slap and the halyards...and the vibrations keep the barnacles away and knock off all the slime from the ICW.[/QUOTE]

The above made me smile, Gene krupa!!!! famous for "Golden Wedding". Back to thread, I experience very little slamming in my Lagoon 400.
Regards Peter
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Old 09-05-2015, 21:14   #94
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Re: Multihulls that don't slam

Quote:
Originally Posted by Highland Fling View Post

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
HF, let's make it simple. If your Lagoon is tacking through about 120 degrees as you said, which is quite likely, then if you are making 8 knots VMG upwind, you are sailing at 16 knots over the ground. Do you really think that boat has ever even touched 16 knots upwind? In fact, in all your years of sailing, have YOU ever touched 16 knots SOG upwind in ANY boat? 8 knots upwind SOG is certainly doable, no question. 8 knots VMG? No way. You have confused the definition, as has been explained. By the way, I have never done 8 knots VMG upwind, either, and I eat those 420's alive. And that is MY last word
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Old 10-05-2015, 15:18   #95
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Re: Multihulls that don't slam

Quote:
Originally Posted by monte View Post
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?
I can get VMG U or D (upwind or downwind) from my B&G instruments which use the paddle wheel for speed and VMG U from my Furuno plotter which uses either the paddle wheel or SOG and which I set to use SOG. Because so much of the VMG calc is from the wind inst direction, which varies a lot, I also find both of my VMG sources to not be useful to steer by upwind. They're too skittish and tend to be following indicators because of the lag in boat speed response to changes in wind angle. (The wind angle indication is essentially instantaneous.) But I usually keep one of the VMGs displayed when tacking upwind to glance at occasionally for confirmation that I'm in the ballpark. I find that once I get used to a particular boat that the best VMG indicator is "feeling in the groove". I have used VMG to a waypoint very rarely. I don't see much use for it. VMG downwind is useless unless you can generate enough speed to gybe downwind faster than sailing dead downwind. But VMG D can be confirmation that gybing isn't working for you if the best VMG D you can make is dead downwind....

Dave
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Old 10-05-2015, 16:54   #96
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Re: Multihulls that don't slam

This thread seems to be morphed/drifted into one on VMG. So...

Our Raymarine instruments track VMG (which we always understood to be Vessel Made Good) toward a plotted waypoint or destination. So we tend to use it primarily when we're heading upwind to confirm which is our 'sweet' tack...and then lay courses accordingly. It is also useful where our course involves a number of obstacles/course changes in which event we can set the VMG on the end destination in order to obtain a better estimate of our arrival time.

Accordingly, our VMG tells us progress toward our destination (or waypoint) irrespective of wind angles. If the wind changes but the vessel continues its course and speed, the VMG will stay the same.

For the OP and at the risk of repeating, we experience very little slamming.
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Old 10-05-2015, 17:08   #97
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Re: Multihulls that don't slam

Quote:
Originally Posted by peterp View Post
I like the noise. It's nicer than a fog horn and keeps the monohulls away from me in the anchorage at night. Sometimes you can get a good Gene Krupa kinda beat going between the wave slap and the halyards...and the vibrations keep the barnacles away and knock off all the slime from the ICW.
The above made me smile, Gene krupa!!!! famous for "Golden Wedding". Back to thread, I experience very little slamming in my Lagoon 400.
Regards Peter[/QUOTE]

Gene Krupa, now I know you are talking to old folk.
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Old 10-05-2015, 17:14   #98
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Re: Multihulls that don't slam

Quote:
Originally Posted by D&D View Post
This thread seems to be morphed/drifted into one on VMG. So...

Our Raymarine instruments track VMG (which we always understood to be Vessel Made Good) toward a plotted waypoint or destination.
Your chartplotter will display VMG (VELOCITY Made Good) to a waypoint. However your wind instrument will display velocity made good to windward.
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Old 10-05-2015, 18:36   #99
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Re: Multihulls that don't slam

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Originally Posted by 44'cruisingcat View Post
Your chartplotter will display VMG (VELOCITY Made Good) to a waypoint. However your wind instrument will display velocity made good to windward.
It seems we stand corrected re the meaning of VMG, altho we will shift the blame onto an earlier (and very, very experienced) teacher who clearly operated (and still does) under the same, mistaken understanding...

As for a different VMG on the wind instruments, we'll look forward to checking that out later this week as we embark on our Winter 2015 Exhibition Cruise!

...that, and the absence of slamming...
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Old 10-05-2015, 20:24   #100
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Re: Multihulls that don't slam

Yep. Sailing downwind our ST60 wind displays a negative VMG.


The Simrad chartplotter actually tags VMG to a waypoint as VMGWPT, which helps reduce confusion.
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Old 11-05-2015, 00:41   #101
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Re: Multihulls that don't slam

I would guess this is why there are sparingly few offshore 30-40ft cats than the plethora of 40ft + designs, that the combination of anything near standing headroom in the bridgedeck conflicts with a decent amount of clearance beneath.

So rather than a bouyant centre hull, the underworks or bridgedeck tunnel is more like shaped deflections to resist the effects of slamming yet still allow a modicum of vertical space inside the bridgedeck.

Its a perplexing geometric conundrum that makes the bluewater cat err to the larger and more expensive that folks smarter then I seem challenged to resolve.

So perhaps the question is, is there a 30-40 ft 'with a bridgedeck' design that works well in resisting slamming.
About now I realise I have no idea what Im talking about....
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Old 11-05-2015, 05:33   #102
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Re: Multihulls that don't slam

it occurs to me that cats in marinas don't slam, and monohulls in marinas don't heel. So maybe the best way to avoid those horrible, dreaded, oft repeated drawbacks of the boats is not to sail them.
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Old 11-05-2015, 14:35   #103
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Re: Multihulls that don't slam

How is the Leopard 46 for slamming? Anyone?
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Old 17-05-2015, 12:39   #104
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Re: Multihulls that don't slam

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How is the Leopard 46 for slamming? Anyone?
Our Leopard 46 has a high tunnel and for years I never heard any slamming. Like the guy who claims his Lagoon doesn't slam, I would have made the same claim. Then while sailing in 36+K winds from the west of St.Croix to Tortola in 16 foot seas, I did hear some! So, I agree that all Cats can slam in the right conditions.
The Leopard 46 is an awesome boat, much softer in design than the 47. I need to sail the 48!
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