Are we making any real design improvements??

how do i get a boat desgn for power tech

Hey Guys Can You Help Me With A Project For Power Tech
Thanks Guys
Patrick Lane

 

"First of all hullspeed is typically quoted as 1.34 times the square root of the waterline length "

This "formula" is only for fat (LWL /BWL) 3-1 or 4-1 boats .

Skinny boats 8-1 or better do not observe this rule , as the bow wave IS small enough to power thru. Lightness helps but not that much.

FAST FRED

 

How about some new math...

Hello...

Like most things - the comparing of asthetics and engineering improvements based on ratios and percentages - seems more like one is hiding behind some rather simple math - or burying redundant statistics in useless percentages or comparisons against non similar boats - sort of like Presidential election 'percentages'...

I just design what I want - then go build it - then go sail it - then sell it - then build a boat that is more of what I want based on getting rid of the little things that bugged me about the last boat...

I personally think that some of the most stunning designs and innovations within this industry have been accomplished by people with an intuitive feel for just making things float and go fast...

The math is not the be all and end all - it is more of a means for comparison or projection...

But then I have been called simple...

SH.

 

Trouble is Shaun that if you can put the numbers together you are getting close. Only then should the artist appear !

I have seen so many badly designed one-off boats designed and built by amatuers who thought that their design looked "right". Many of them sit on moorings unused and unsalable ( and unsailable too) waiting for the owner/builder to die so they can quietly sink.

One magnificent yacht I test sailed with a prospective owner had a sheet winch to operate a long tiller ! A quick inspection of the sail plan showed that a 12' bowsprit would need adding to balance the boat and the winch was there to fight the weather helm. Turned out the builder had simply shortened a 40 foot design to 30 feet by simply ommitting the stern an adding a brutal transom. The boat looked good, the nubers said it wouldn't work.. That boat is for sale again, it sells every year.

Remember
If it looks right ...it might be right.
If the number say its right and the system of producing the numbers is proven...it will be right.

Thats an engineering viewpoint ;-)

 

Agree...

Hello..

I agree and I do the math first - basic centers and such - I just hate getting caught up in finite discussions that seem to revolve around beer hall techno me speak more bits...

Anyway - off to work...

 

Cde 850

Erik! I got a CDE 850! Do U want to know more about it? Just send me a mail.

 

new boats and technologies

I do think that we are making some design improvements but there is one problem...they are not showing up because all (or almost all) production boats now underconstuction are not sailing boats for sailors they are meant for the people that hardly go beond sight of a marina and as for the new "racing" boats under production the ones available finacially to real sailors are wimped up w nice interiors, roller furling and all kinds of unracelike trinkets. personnally i have given up on any production boat and have now at the drawings stage a new boat underway. If i were to purchase a boat it would have to be an older boat C&C or F3.

Dylan

958 days till allingy vs challanger americas cup 2007

 

Theories about planing a hull are fine, but don't forget practise .... What I mean is: I have read the theoretical number given by Jeff H (400 sq feet per 1000lbs), but this would all depend on a.o. what windspeed you will be sailing in. In other words what kind of fuel you put in your tank.
As I am in the metric part of the world this would be about 36m² per 450 kg, if I am correct.
Even modern (race) yachts do not have that much canvass up on a broad reach/run, yet they plane. I've been planing my 24', 30', 35' footers for long stretches (sometimes for miles) simply because I keep up all the canvass in 30-40 kts of true wind. We have been planing with yachts even on relatively flat water (lakes) with only 1 or 2 mtr of water under the keel.

This is what all VPP's and ratingsystems have problems with.

If your foils are thin enough to not produce too much resistance, your hull is shallow enough to not produce too much resistance, the hull provides the right lift and you have enough wind (tornado's could even lift the boat right out of the water .....) and a rig that will stay up, planing a modern race yacht is quite possible.
I owned two IOR two tonners and they just went submarine in too much wind on a spinnaker run. But the newer boats just keep accelerating. Handling the boats gets lighter and lighter as they speed off (until .....).

From reshaping a keel on a 30-footer from a 80mm chord to a 120mm chord I know how important low resistance is: with the 80mm chord the 30' planed in 30kts of wind, after the reshaping she needed a 35% bigger spinnaker to plane at about the same windspeed.

Now, whether this is to be seen as an improvement in yachtdesign is up to the individual. Personally, I think it is. I like this kind of sailing (can't wait for the (too) few occassions every year) and it's never been hazardous for my yacht and crew. So, as long as you know when to quit, it's thrilling !

Lucas

Question: do we agree that planing is when the yacht constantly does speeds double her theoretical hull speed or more, her bow and slamming section being lifted from the water to about her keel, on flat water or on waves if she does so also going up waves (not just surfing down) ???

 

Hell yes! Progressing every year,better sails ,better boat construction for both cruising and racing options,better construction techniques,more fun to sail,easier to sail all adds up to improvements to my addiction(sailing).
I really couldnt care less about the equations that go into making my boat go fast and when I think about it I have never actually sailed an equation,could be kinda wet and slow me thinks.
Forget the math and go sail a reasonably new boat.See how much nicer it is to use and there is your improvement.Hopefully the industry can continue in the same vain.
K4s

 

Lucas, what sort of 35'er do you have which will plane for miles on lakes?

Re what we call planing. Naval architects say that it planing occurs when the dynamic lift raises the C of G above the height it is at when the boat is stopped (and supported only by dynamic lift) AFAIK. So it's not really easy to pick from on the boat, is it?

 

249, I think establishing what sailors call planing is important, if we want to be able to talk about we experience on the water. Measuring the shift in centre of gravity is neither very practical nor what gives us a kick. It is the sustained high speeds that do.

That is why I described what I feel planing is. To mention some of the boats we did long stretches of 14-16 kts downwind on (with tops around 20) over the years are:
Sprint 95 (32'), VR30 (30'), Corby 34.7 (35'). The first one with a spinnaker that even was not that big (± 58m²), the other two with 122m² gennakers. If you do not need 'to fall down from a wave' to reach these speeds (surfing) I call it planing. May be incorrect theoretically, but practical for the sailor.

Anyhow, my comment was meant to counter the theory of needing 36m² of sail per every 450kg of boat, which I believe dates from the old days ...
Downwind we now carry 36m² main + 122m² gennaker = 158m² on a 3T yacht incl. gear ex crew. Nowhere near 36m²/450kg. Reaching at around 125-130° in 25kts of wind gets the boat to sustained speeds between 13 and 14,5 kts (GPS readings) .... yes on a lake.

Lucas

 

The Corby planes on flat water? Impressive.

Re "do we agree that planing is when the yacht constantly does speeds double her theoretical hull speed or more, her bow and slamming section being lifted from the water to about her keel, on flat water or on waves if she does so also going up waves (not just surfing down) ???"

Is the degree of bow lift important? Look at some boats that definitely plane - the skiffs. The 12's plane extremely bow-high, yet 49ers and other Bethwaite boats plane with the bow very low; Julian always designs them that way. The bow-high angle can actually be quite innefficient. I've sailed an Open 66 (modified Open 60) that definitely planes, but she doesn't lift out of the water all the way back to about her keel.

I know we can't really measure the C of G rise, but it does seem that strictly defining planing in a way that can be seen from aboard may be so hard as to be practically impossible, AFAIK.

 

Hi 249, (why not become a member, you're here so often .... and it's nice to call someone by his (nick)name ...)

Indeed, bow up is not the way to go. Or better said: the transom down is bad. The 3 boats I mentioned all were/are quite flatbottomed, so out of the water to the keel does not mean bow up (at least not much). We usually keep crew weight at normal positions, unless waves are short and steep (on the Solent for instance). At sea we even sometimes try to get the bow down going off the wave (shifting crew positions) to get her surfing if there is just not enough wind to really get going.
In 1992 I switched from submarining IOR 2-tonners to smaller downwind flyers. That's where I get my kick. And upwind speed has not suffered. It's just a 'little less comfortable'. So to answer this threats topic: yes, to me we gained a lot from material development and research, allowing for design improvements.

Pic attached shows previous 30' one off in typical downwind spinnakerstyle. At 18-20kts of wind doing 11-13 through the water.
Hope we'll get some pics of the Corby on flat water for you next year ...
2nd pic: my 2-tonner had masses of sail, but did not plane !

Lucas

 

Lucas, the 30 looks sweet.

I still like the old IOR busses. That to me looks like maybe like one of the former Hong Kong Dubois 44s from 1979 - La Pantera or Uin Na Mara or something???

Yes, I agree we've gained. My boat (a 2000kg 28 foot/8.5m 1968 NZ lightweight offshore cruiser-racer) was about as quick as any offshore boat of its length in its day, but a new boat of the same dimensions would be faster. Not enormously, though; perhaps 5-7% or less???????????????

 

Hi 249, homerun: Uin-na-mara ! The 1979 Dubois 44.

I also had the 1977 Holland 44 Mandrake. Excellent boats to sail, but not as much fun as the Corby 34.7 .... She would be thundering past them on any course off the wind. Upwind in a breeze the old 2-tonners were a delight, of course.

Lucas