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Old 05-02-2019, 04:08   #1
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Hull speed Lagoon 400

Does someone here knows the hull speed of the Lagoon 400 / 400S2?

Thank you very much!
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Old 05-02-2019, 11:49   #2
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Re: Hull speed Lagoon 400

If the effective wateline length is 39', then 1.34*sqr of 39 is 8.37 knots, and at 1.78 its 11.12. This means that wave resistance will start to rise sharply at 8.4 knots, and will flatten out at 11 knots. If you sail with full sails in 30 knots of wind with AWA at 90 dgr. you should get over 16 knots of boatspeed - if you sheet the genoa to the spring clamp and the boat is not too overloaded
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Old 05-02-2019, 12:25   #3
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Re: Hull speed Lagoon 400

Thanx, that makes sense. I was wondering why I could run much faster at 15.8kn on beam reach / broad reach.
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Old 05-02-2019, 13:35   #4
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Hull speed Lagoon 400

Hull speed is more of a limit on wide body hulls, if a hull is thin enough, hull speed isnít so much of a limit.
I donít know if itís true or not, but I have been told that is why destroyers are so narrow beam
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Old 05-02-2019, 13:52   #5
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Re: Hull speed Lagoon 400

the resistance is more to do with weight in my opinion. Thin hulled overloaded is slower than wider hulled and not overloaded. Seen enough evidence of that.

There is another factor to consider and this are sea waves. If they happen to have speed that is similar to boat speed and you going with the waves, they will not let you go faster. Hulls immersed deeper, although waves were small. Tryed to push in this situation, actually brought some instability and unnecessary forces to the rig.
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Old 06-02-2019, 01:32   #6
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Re: Hull speed Lagoon 400

I was just wondering what the best speed would be downwind / broadreach on passages and when to slow down / de-power the sails. Sometime you are running smoothly and feeling not much wind, and when looking at the GPS plotter, you are over 12kn.

Of course sea state is a very important factor, especially when surfing the waves vs. beating to them.

On some storm tactics they recommend to depower the sails and even use ropes or a drogue to slow down, so I am curious what speed is considered safe or desirable when running in strong winds, would it be something near the hull speed to use the water resistance as a brake or would it be a higher speed to reduce the wind pressure on the rig?

I guess I will find out soon.
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Old 06-02-2019, 03:04   #7
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Re: Hull speed Lagoon 400

this is my experience, worst seas so far.

--------------------
Day 4 - that is when fun started !


Beautiful morning, glassy water and clear skies until cloud line from south starting to get closer. And one could see very thick clouds and beautiful massive cloud formations. I was thinking - this looks like more than what weather forecast said - up to 25 kn.


We packed up everything and moment arrived when clouds came over us. And we were greeted by up to 60 kn gusts and near freezing temperatures and rain.


In 1/2 hour seas raised quite a bit and I started thinking plan B. Then luckily settled down to around 20 kn. We raised second reef and enjoyed beautiful sail around 7 kn thinking that was it. Then in 1 hour 8 kn, then in next hour 9 kn, then in next 10 kn ! This was too much for our leisurely comfort. Decided to take down mainsail. This turned out to be an error. We have used new downhaul line to take sail down downwind from cockpit- worth the gold. Force of wind was actually too much to pull it by hand as battens glue to spreaders and just dont budge. Used winch to downhaul. For the moment thought to leave third reef as then could still take it all down but, skipped that step. And used only triple reefed jib to move.


Weather continue to deteriorate, seas building. And unfortunately wind moved forward so jib could not handle situation and had to turn engine on If third reef could continue to sail and enjoy more comfort ad sail gives stability. Once sail down, cant take it back as seas too large.


We were forced to motorsail next 48 hours. Seas were building and kind of stopped at 5m. There were some scary much larger waves. We had waves on beam. I was very nervous looking how our boat gone over these monsters. And big one come in pairs or in triplets. First looks big and then after it crossed second bigger behind, and sometimes third even bigger... Was not worried about boat flipping but about violent impact of these waves on boat and us. Could not sleep and for some time hand steered. It is not easy, especially if one has to do it for several days. And when no moon, one just guesses when that sound of large wave coming closer. It is interesting that large waves come from very different directions, like 90 deg from where majority travels.

In these waves our boat has not failed once - no flying glasses or water in cockpit although beam reaching in near storm conditions (largest seas ever for us). Observing action, contribute this behaviour to 3 things - 1 autopilot has to be on high sensitivity setting. When big ones come in a group there is no time to lose direction, not even for part of a second. It has to maintain perfect direction else dangerous next one can get you on a side. At high speeds this is in my opinion most important. My sensitivity had to push to 7, normally 3. What if AP fails in these conditions , we both got scared of this thought.


2. Boat shape - wide hulls and third small middle hull allow boat to swing thru the top of large steep wave without any effort. This was most hairy to look unfolding. And after intense continuous 48h watch of this action, I was able to sleep for an hour in the end so i guess trust boat bit more.


3. And last, one has to keep speed up. Fast enough, one escapes full force of group of waves. So, I am not convinced any more drogue is a good idea.


I have also tested drive downwind and it appears one can nicely pass/neutralize large wave by turning 60 degrees from direction of wave travel.


Simpy, to get away without damage, one needs luck as well. Preparation can do only that much.


Finally on day 5 in the morning seas abated so we could pull up sails. We had very nice beam reach sail from 8 to 10 kn in 3-4 m waves. This enabled us to arrive in Bundaberg in the evening and now safely anchored in the river.


Wow, what a passage !!! Gained lots of experience and insight.


We tired a bit and we had no seasickness. And we still like traveling world with the boat.
-------------------
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Old 06-02-2019, 03:17   #8
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Re: Hull speed Lagoon 400

You were going on beam reach in that conditions with wind and waves from the side?

I probably would go either to the wind, hove to, or running broad reach, but not waves and wind on the beam with 90į broadside.
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Old 06-02-2019, 03:29   #9
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Re: Hull speed Lagoon 400

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Originally Posted by arsenelupiga View Post
the resistance is more to do with weight in my opinion. Thin hulled overloaded is slower than wider hulled and not overloaded. Seen enough evidence of that.
Schionnings tested this and found the exact opposite to be true. They built a hull at 13.5:1, then tested it with increasing loads and found little degredation in performance.
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Old 06-02-2019, 03:33   #10
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Re: Hull speed Lagoon 400

this was direction we needed to go. If crests got bigger would have to turn broad reach away from course.

Surfing down the waves - did not like it at all. If DDW, there are random unusually large waves coming from 90 deg ie on the beam in our case.

Not all storms are same, i guess. Need to see what boat likes. Also need to decide what you will do in pitch dark - need some sort of set and pray setup.
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Old 06-02-2019, 04:09   #11
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Re: Hull speed Lagoon 400

My best bet in dark would be motor either to the wind or with the wind, maybe on some angle to reduce slapping and get some advantage on more time / room between two waves to get is as comfortable as possible. Maybe change course to get out of it quicker if possible.

Heave-to would also be an option if there is no schedule and no lee shore nearby, would likely do it with the reefed genoa standing back, handling the main in 3rd reef requires to go to the mast in standard setup. Maybe a modification to get the 3rd reef remotely by a separate line may change my mind on this, but manually attaching the main to the mast scares me somehow.

Heave-to with the jib allows handling the mainsail depowered / shaded by the jib, so one can set it or get it down more safely.
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Old 07-02-2019, 03:05   #12
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Re: Hull speed Lagoon 400

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Originally Posted by arsenelupiga View Post
the resistance is more to do with weight in my opinion. Thin hulled overloaded is slower than wider hulled and not overloaded. Seen enough evidence of that.
Correct Arsene, for a given displacement, the waterlinebeam should be 2.5 times the hulldepth. Many OZ designs would be faster with more hullbeam at the waterline (but the same weight). But most multihulldesigners dont like to hear this.
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Old 08-02-2019, 21:00   #13
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Re: Hull speed Lagoon 400

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Thanx, that makes sense. I was wondering why I could run much faster at 15.8kn on beam reach / broad reach.
You have managed 15.8kn reaching ?

This must have caused couple of heart attacks among "Lagoon is the fastest when motors" crowd.
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Old 08-02-2019, 21:38   #14
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Re: Hull speed Lagoon 400

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Correct Arsene, for a given displacement, the waterlinebeam should be 2.5 times the hulldepth. Many OZ designs would be faster with more hullbeam at the waterline (but the same weight). But most multihulldesigners dont like to hear this.
Which OZ designs would these be?

Do you have a website of boats you've designed?
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Old 08-02-2019, 23:05   #15
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Re: Hull speed Lagoon 400

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Originally Posted by django37 View Post
Correct Arsene, for a given displacement, the waterlinebeam should be 2.5 times the hulldepth. Many OZ designs would be faster with more hullbeam at the waterline (but the same weight). But most multihulldesigners dont like to hear this.
I have contact details for Jeff Schionning and Tony Grainger. No doubt they would welcome your advice as to how they are getting it so wrong.
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