Thread: Gwen 12 and hull design evolution.

Hi Brian do you see this thread.

Mike

Howdy Brian,

The gwen thread pointed out by Mike has a specific mention from a guy whose family bought Oughtred's own boat. I won't say what it says because it is worth reading direct.

The Gwen was a breakthrough boat in OZ utilising the weight saving of plywood construction which is was designed for, but high performance was really defined by John Spencer who dreamed up the also plywood Cherub plus larger and smaller variations.

The guys that designed the Gwen (Charles and Lindsay Cunningham) went off and designed the whole range of catamarans including the two that took the Little America's Cup off you guys a couple (or maybe three times) - Quest 2 and Quest 3. The Macquarie Innovations speed sailing team has the design side still run by Lindsay.

The Gwen was kinda flat and kinda blunt because of skiff thinking at the time and was a one design with some variations in rigging. Spencer broke into something quite different as his boats were restricted classes so spun off into all sorts of development incluiding the OZ NS14 and the Taser (which was a one design spin off of the NS14).

So the Gwen started to die off as new generations of boats came through. It was a pretty good sailer though, just not improving like the competing classes.

The Cherub, NS14 and its bloodline have been very much more influential to me. Particularly the NS which has very high performance with a very small sail area. The review that the Goat seems to go faster and faster without really seeming to distinctly plane is true NS14 behaviour

I had some pics of how some of the late '90s and 00's Cherubs had swung through and pretty well matched the Goat shape which was Storer '93. No copying or plagiarism, just developments swinging in the same direction.

So the little goat will reflect more of the same ... with some tweaks.

MIK

MIK

Thanks Mike for the link and also MIK for outline of the Gwen. Reading the thread it's clear she provided huge amounts of pleasure to those who sailed Gwens.

Oddly, the long thread about Best 12' dinghy on the US WBF never came up with that kind of enthusiasm and memories. Many lovely designs were posted but as I say, not sailing memories. I guess the WBF is a builders forum more than a sailors forum!

My son Edward bought me Frank Bethwaite's book for Christmas. Huge amount to take in, but my reaction is "wouldn't it be great if they could use all that knowledge to design a moderate boat for us older mature slower... sailors" so we could feel those benefits without getting beaten to death.

Roll on baby Goat.

Brian

Originally Posted by Boatmik

The review that the Goat seems to go faster and faster without really seeming to distinctly plane is true NS14 behaviour

MIK

MIK

Mick

I'm really intrigued by this characteristic of the Goat. I've read it before and it puzzles me. Does it mean that the Goat's hull has a lot more potential, ie. make it go faster and it will eventually plane?

It's been mentioned that a Goat fitted with anything larger than a 4hp (?) motor causes it to stand up with its nose in the air. Discounting hull strengths for a moment, what might happen with a 20hp and two crew sitting on the front seat to hold the nose down? The reason I'm asking is that given enough speed would it plane?

Back in the 70's, a friend of mine earned his Springbok colours and went on to win the world lightweight hydroplane championship. His ultra lightweight hydroplane exhibited the same characteristic of standing on its tail with its nose in the air and he had to lean right over the wheel to apply weight to the nose to get the thing working. It would typically take all of 200m with the engine (Koenig) screaming before it would plane and then he would disappear rapidly from view at insane speeds with a massive rooster tail behind him. Is this what would eventually happen if the Goat hull was subjected to that, ie. it WOULD eventually plane?

Hello Bruce,

What I think that MIK tried to say here is that the GIS does plane but you cannot really define a distinct moment when it starts to do so. In other words, it is difficult to tell when the boat starts to go from waterdisplacing to planing as the transition from one to the other is so very smooth.

Believe me, under the right conditions the Goat definately planes!

Best regards,

Joost

This is what it looks like. Very little fuss, no huge bow wave or anything, just shooting along. As described, simply sets off from the turning mark and speeds up, catching the Scows in front very quickly. Not even set the mizzen properly - concentrating too much to look back!



the wake behind her is all that illustrates her speed. Wind about 15 knots I think.

Brian

G'day Bruce

Speculating out loud here...

I don't think using a motor to make a sailing hull plane is the same as sailing
it on/onto the plane. It seems to me that the thrust vectors work out wrong,
so the hull shape for planing sail boats has to be different from powered ones
to avoid the uglies.

A prop below the boat's centre of forward resistance pushes the bow up.
To keep the boat from back-flipping, you can either weight the bow to keep
it down, raise the prop to reduce the torque lever length, angle the thrust
direction down a bit to lift the stern as well as the bow, or shape the stern to
lift with water pressure (or bits of all 4). The lifting surface is the very aft-
most part of the hull. "Planing" is achieved when the very aft part of the hull
is pushed out of the displacement/speed hole it digs itself in the water.
IF there is power enough.

A sail is thrust happening high above the deck, pushing the bow down. This
is the opposite of a power boat, & needs to be resisted with fuller, lighter bow
sections, have an up-lifted stern profile to pull it down too, opposing the bow
dipping, and crew weight encouraged to move aft. So the lifting surface of a
boat like the Goat is probably the forward & mid sections. Even the extreme
skiff screamers would have to follow this pattern. As the lifting surface is well
forward, it is out of the displacement hole rather earlier & easier than the stern
of the speed-boat. GIS is very light on the water and doesn't dig much of a
hole, it wouldn't take much at all for that big lifting surface to be "planing".

Putting a motor on the sail boat (or a sail on the power boat) turns the design
features of each hull type against itself. So the sail boat bogs down at the
stern, pushing the bow higher. Increased power simply increases the likelihood
of a back-flip. Conversely, a sail on a speed-boat pushes the non-lifting bow
down, & the big rear-end lifts, push the bow still deeper into the water.

Hence the recommendation to only use a little donk on the Goat.

And that could all be drivel, but it seems to fit the observations.
cheers
AJ

Originally Posted by b.o.a.t.

G'day Bruce

Speculating out loud here...

I don't think using a motor to make a sailing hull plane is the same as sailing
it on/onto the plane. It seems to me that the thrust vectors work out wrong,
so the hull shape for planing sail boats has to be different from powered ones
to avoid the uglies.

A prop below the boat's centre of forward resistance pushes the bow up.
To keep the boat from back-flipping, you can either weight the bow to keep
it down, raise the prop to reduce the torque lever length, angle the thrust
direction down a bit to lift the stern as well as the bow, or shape the stern to
lift with water pressure (or bits of all 4). The lifting surface is the very aft-
most part of the hull. "Planing" is achieved when the very aft part of the hull
is pushed out of the displacement/speed hole it digs itself in the water.
IF there is power enough.

A sail is thrust happening high above the deck, pushing the bow down. This
is the opposite of a power boat, & needs to be resisted with fuller, lighter bow
sections, have an up-lifted stern profile to pull it down too, opposing the bow
dipping, and crew weight encouraged to move aft. So the lifting surface of a
boat like the Goat is probably the forward & mid sections. Even the extreme
skiff screamers would have to follow this pattern. As the lifting surface is well
forward, it is out of the displacement hole rather earlier & easier than the stern
of the speed-boat. GIS is very light on the water and doesn't dig much of a
hole, it wouldn't take much at all for that big lifting surface to be "planing".

Putting a motor on the sail boat (or a sail on the power boat) turns the design
features of each hull type against itself. So the sail boat bogs down at the
stern, pushing the bow higher. Increased power simply increases the likelihood
of a back-flip. Conversely, a sail on a speed-boat pushes the non-lifting bow
down, & the big rear-end lifts, push the bow still deeper into the water.

Hence the recommendation to only use a little donk on the Goat.

And that could all be drivel, but it seems to fit the observations.
cheers
AJ

Thanks for the explanations guys. I probably should have just asked at what speed would the hull plane, hey? So it does plane, it's just that the transition is so smooth!

Howdy Guys,

Great discussion!!! You guys are the Dudes! Or you guys are "The Dude" if you are a fan of strange American films! I am.

Planing is kind of a misnomer. There is no such thing as displacement mode unless the boat is dead still and there is no such thing as full planing - ever.

IT is a continuum where at different points some of the weight of the boat is supported by dynamic forces and some by static.

At 2 knots the goat will mostly be displacing, but it would be a brave person who said it was definitely not generating any lift.

And at a very high speed the lift forces are never 100% of the displacement because that would mean the boat would be barely touching the water.

It used to bother me that multihulls exceed "hull speed" or "planing speed" but are quite deep in the water when they do. This does not necessarily mean that they are generating no lift, but because the definitions are so vague it is hard to say they are planing or not.

This is what made me realise that the normal explanations are wrong and start digging deeper. If you look at the tail end of a big powerboat there is a hollow in the water immediately behind the transom. This in some way represents the displacement that is being replaced by lift. I do wonder if you were able to find the end of that hollow behind the boat whether that would define that the boat was doing hullspeed for the boat length plus the hollow length. I haven't seen any literature on this.



Flickr: boatmik's Photostream

If you look at pics of multihulls going fast you can see this hollow (separation) behind their transoms as well ... so it is evidence that they are gaining lift.

Bethwaite was one of the first in dinghy literature to talk clearly about the distance of the stern wave behind the boat being at the right place for the Froude calculation of wave speed vs wavelength. We always estimated the speed to keep our NS14s at upwind using the stern wave to not to go too fast but to turn the extra power into extra pointing and to keep away from the increased drag at "hull speed". I don't think he mentions the hollow though.

So "planing" and "planing mode" and "hull speed" are useful ideas for discussion in the clubhouse after the race but are technically incorrect. However even serious technical designers and writers have not really thought this through so perpetuate the problem.

In the same way that people think the "slot" accelerates air between the main and jib. It was disproven in the late 50s by Smith and others and the original mistake was made by one of the lead aerodynamicists in the world about 100 years ago - nobody bothered to question it.

So ... every boat can exceed hull speed given enough power. Might not be by much in some cases.

AJ is completely right about the vectors of motor compared to sail. I was pretty fascinated by Dave Graybeals comments when he sent me the pics of his goat under power with bow in the air and two kids trying to weigh it down. Perfectly explained by AJ.

So what is planing if it is a continuum of a boat trading displacement for lift?

I think we have to say something quite vague, because the available language is so imprecise.

If a boat can accelerate past the calculated Hullspeed then it is planing is just wrong because it assumes the lift of planing is the prime mechanism for going faster. Multihulls go faster too.

A boat is planing if it leaves a hollow behind the transom might be a better definition, but I think there are some other times when it looks like this is happening at slower speeds.

If you can't define a physical phenomenon clearly then there is an argument that it may not exist.

Bethwaite's book goes into nice detail about how the Australian skiffs moved from boats with a wide, flat run aft to boats with narrow transoms and body but flattened sections right through the boat.

His son Julian was one of the first to really voice the concept with his "PRIME" (boat name/sponsor) balsa strip, two handed 18ft skiffs. They changed everything for the skiffs.

However the moths were there first by a long chalk when they realised that nosediving problems of scow moths could be fixed by not doing something at the bow, but by making the transoms much narrower but only in the last couple of feet of boat length. This fed into the skiff moths (which Julian was spending a bit of time sailing at the time he came up with his PRIME concept) and the NS14 class here. Particularly the work of Michael Nash.

None of this would have happened without the Bethwaites building a strong experimental basis for designing small boats, so I can easily forgive them for saying the concept is their idea.

These shapes also have more displacement through the length of the boat that allows the rocker to be reduced and still keep the ends of the boat out of the water. The 18 footers have gone to the extreme of actually designing the boat to have less displacement than required for the crew and gear. They simply cram forward in light winds to keep the transom out of the water. That principle is also used for "Sinker sailboards".

Less rocker and distributing more planing area through the length of the boat means that the boat doesn't change trim much as it goes faster. The dear old PDR stands on its tail whenever it moves fast because of all that rocker.

Also more planing area through the modern hull shape means the boat doesn't plane with its bow high in the air as it tries to get the back of the boat to the right angle of incidence to develop lift. The older style boats that do this kick out a lot of spray where their flat midbody hits the water for the first time.

Within the International classes the 505 is reasonably close to this concept (which is why it has been such a devastating boat for 50 years and the Flying Dutchman misses by miles getting speed by sheer size and sail area.

Because my favourite sailing boats are the NS14 the goat reflected a lot of those values. And because of the square shaped hull, there is a lot of displacement in the bow (and a lot of planing area) meaning the rocker has to be reduced.

This might sound very logical now ... but the above paragraph really sums up what really happened. I think also because I watched the dinghy trends so carefully for many years I had some instinct about where they were going and could relate that to the flat bottomed approach.

Best wishes
Michael

Mick, that is a terrific history and explanation of progress in this area. It nevertheless surprises me that there is much work yet to be done, but I can also understand why this is the case. It seems that there have been hulls like the 505 where the designers have accidentally "jagged" the flattish and narrow runs aft that closely resemble the modern skiffs, and so have been successful. It's hard to think that this was done on purpose with a great deal of understanding by the designer way back then though, hence my use of that silly "jagged" word, but it is probably apt. However he clearly knew what would likely be a fast hull, so deserves full credit for his achievement at the time.

I'm looking forward to SOG

Fascinating stuff!

The two most important boats developed in the last 50 years are the 505 and the Tornado Cat.

IMHO of course.

Both are quite hard for modern boats to beat so are true breakthrough boats. If the 505 could be built down to 150 lbs and twin wired it would be quite interesting to see how it would go in a modern pack. The Tornado has transformed itself from a speed machine with a degree of delicacy (the early ones were tricky to build so that they wouldn't break) that was able to be improved structurally without increasing the weight.

MIK

There is another discussion in one of the other sections that relates here a little. Graemet is a NS14 dude and saw most of the evolutions.

It is about an NS14 being restored, but some other design stuff is coming out too. We might even see some drawings (maybe) for one of the evolutionary boats from the '70s.
https://www.woodworkforums.com/f32/pa...30/index6.html

This link drops you in the thread where we are discusing more about the designs, but there is also some stuff from Graeme on page 4.

This is a circa 1990's NS14 from Stuart Frezier (from memory).

You can see the vee shaped sections of a ply boat have become full and rounded but still very narrow up in the bow. Section shapes are in black. The old idea of planing on the back of the boat is turned on its head. The front end of the boat is at a much better angle to do that job without upsetting the trim of the boat.

You can see the volume ahead of the centrecase compared to a plywood veed boat. This would be impossible to build in ply.

Since then they have played with the measurement rules in quite an extreme way. There is a required width measurement in the body of the boat a little above the keel that was intended to keep the boats fairly stable.

Now that point resembles a chine in the latest boats rather than hitting it with a fair cross section like Stuart and the others designers in this era.

505 just won the 37th Bloody Mary



Report here "The 37th Bloody Mary Pursuit Race took place in freezing temperatures, snow flurries and gusting northerly 25 knot winds. "

37th Bloody Mary at Queen Mary Sailing Club - Yachts and Yachting Online

Brian