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JeffM

Rocker and beam in hull shape

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I find myself staring at microcruisers these days, especially (at this cold season of the year) by enclosed sailors such as the "birdwatcher" type boats of Bolger and Michalak and the fascinating cruisers of Matt Layden, such as his Little Cruiser and Enigma.  [someday I've got to cadge a ride in one of this sort, to find out how I like sailing "indoors."  But there's no denying the appeal when its too cold to sail safely (not to mention comfortably) hereabouts.] 

One thing that makes me curious about Matt Layden's designs is their narrow beam.  He seems to take a boat with marginal room and make it nigh well unbearable (notwithstanding Dave and Mindy Bolduc's 3-month cruises in the Bahamas aboard Little Cruiser).  The only reasons I can think of for a narrow hull in these cases is to make it more easily driven, and reduce the poor handling of a beamy hull when heeled.  On the other hand, these boats have a lot of rocker, which I understand is a trick to increase buoyancy but still keep the ends (especially the transom) out of the water so they don't drag.  But that rocker also increases resistance.  It seems to me a beamier hull would take care of the buoyancy issue and so eliminate the need for so much rocker.  It would also increase stability and allow the boat to carry more sail. 

How far off-base am I here?  And is there something else about these designs that necessitate the particular choices and trade-offs Matt has made?  Does he need a narrow hull to make his chine runners effective, for instance?

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I had the chance to talk to Matt this year at the EC finish in Key Largo and even got to take a sail in "Sand Flea" his 8 foot pram that he sailed in the race. I also enjoy seeing his micro cruisers in action.

I don't claim to know a whole lot about hull design but I think one thing I learned about Paradox, and other ballasted narrow micro cruisers is that in order to make them self righting when knocked down in a heavy sea, they cannot be too wide. There is a maximum width for a ballasted boat before it will have a second stability point...upside down! Paradox for example has a displacement of 1410lbs, (http://home.triad.rr.com/lcruise/paradox1.htm) and is just about as tall as it is wide. It is ballasted and designed to be self righting and very stable so that it could safely make open water crossings. I think Enigma is of similar design.

I also don't see why the chine runners would care what the beam is. They are used because they are an ingenious way of reducing leeway with hardly any trade off in draft which makes them excellent for sailing upwind through Florida bay :)

I agree wider would be more comfortable but to keep it self righting, at some point it would make more sense to use a keel instead of adding more and more ballast to the bottom but then there goes your nice shallow draft and coastal cruising ability which is what Matt designed the his micro cruisers for in the first place, to get into those hard to reach shallow bays and keys. On the other had (as you say, there are always trade offs) you could of course trade width for self righting ability.

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Alan, you DO get around!  Point taken: I just read of a trip by a UK Paradox sailor knocked over by a wave big enough to put his boat over 80 or 90 degrees--a few liters came in through the barely-open roof hatch.  His boat was upright and sailing again even before he'd got his wits about him.  Quite a performance for a 14ft boat.

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I'm thinking that self righting needs be a relationship to how easily is is to knock it down...a narrow deep boat is more easily knocked down (on its side)than a wider shallower and stiffer boat (for the same displacement). It is thusly more easily righted too...but the trade offs must be taken into account...less space, a much easier roll, etc. For every mise there is a compromise...such is the nature of a boat!

Steve

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Hi guys, I just joined the forum because I'm also trying to figure out the chine runner concept. I realise it's an old thread, but while the mystery persists, so should the thread...

Matt Layden explained the chine runner concept to the Small Craft Adviser magazine, you can read the interview here: http://www.freewebs....uild/#398015069. He emphasizes that the chine runners are only a small part - they're just a little fence between the two sides of the hull, so that when heeled, the hull is just one giant hydrofoil creating lift to windward. In addition the large rudder is responsible for at least half the resistance to leeway.

Just in case anyone's wondering what we're talking about, here's his 9' boat Elusion that won class 4 solo in the Everglades Challenge 2010:

Elusion_Matt_Layden.jpg

Perhaps another reason the beam is narrow is precisely so that the boat does heel more. This exposes more of the boat's lee side underwater, sitting the chine deeper down to get the full lifting effect that's so crucial to this design. I'm guessing it's important that the boat heels even in lighter winds.

As mentioned by others, a bonus is that the high height to beam ratio makes it 180 degrees self-righting (hatches closed!) Yes it heels more, but clearly some sailors have accepted compromising their comfort in pursuit of safety, shallow draft and simplicity.

I reckon the rocker is not only pronounced to sit the chine deeper, but also to give lift - just like the top side of an aeroplane's wing. However what I wonder is, why isn't the side of the boat flat just like the bottom of an aeroplane's wing? Of course without curving in the sides, you end up with a scow, or a square punt if taken to the extreme.

For the sake of argument, lets ignore for a moment the fact that a square punt-shape might slap waves and sit higher in the water. My question is, wouldn't square, flat sides, in combination with plenty of rocker on the bottom and enough weight, give even more lift to windward?

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For the sake of argument, lets ignore for a moment the fact that a square punt-shape might slap waves and sit higher in the water. My question is, wouldn't square, flat sides, in combination with plenty of rocker on the bottom and enough weight, give even more lift to windward?

So let me try to understand, you want to ponder the characteristics of a sailing punt with lots of rocker, square flat sides that is fairly heavy and will never see waves?

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I've had a thought - perhaps if the boat's a punt shape, when heeled the bow might act as a kind of forward rudder turning the boat to lee. The sharpie bow might cancel this effect. Perhaps slicing into waves is not the only reason Matt Layden's boats have pointy bows. What do you think?

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