General comments

$2000 wood and a day build is hard to belive on that hull
but see your gettin there putting a winnibago on top

 

Yipster,

http://www.paulownia-timber-sales.com.au/Price%20List%20as%20at%20January%202009.xls

and the weight sheet specs it. cheaper than $2000.

they must charge way more in the netherlands. lots of paulownia plantations here in oz.






got the drag down some more Cp is past .8


next goal is to remove some of the fat (white arrow)


here's the new in.mlt for those as interested, and the delftship .fbm

how do you smooth curves and auto fair in delftship? i can't get the option to go black (enable)


suggestions please. . .

 

bob, had a look, bow seems a bit unfair, heck, dont know how to autofair now, manual?

starting with less points 3 for example and putting res high gets you a easy to work with fair hull you can always refine

material can be low priced i know and pricelist is there but there is more involved rite

what i ment early'r above was: why strip plank if you want to keep it cheap and simple like wharam

a flatbottom long dory is stronger and faster build and above hullspeed the chines dont increase resistance

personally i would go nice slooped devellopable plating all the way for deckhouse too

or something like this http://64.251.22.171/articles/design/ngdesign/plaquette_Ekolokat_ENG.pdf dont thrust the daggerboards tho

 

rick,


narrower hulls are sensible. everybody has them.




the clearance is 60cm with a full bridge deck. so hull slamming is going to happen at some angle/speed combination





i don't want to build a larger boat.

i want the huge accommodation a full bridge deck gives.


sailing close to the wind into waves, the faster i go, the more i head in the direction of the waves, the worse hull slam is going to be.


if i had narrow hulls, the slamming would be much worse. i'll slice into waves (which lowers the deck height to the water) and the hulls will go deeper, for longer time, and the faster i go the worse it will be.

the leeward hull will already be pressed down, the windward hull lifted somewhat. (so the deck is lower to the water surface)

so narrow hulls in the worst case of sailing into it, will slice further into a wave (downward loading, so the deck is closer to the water surface), will have least acceleration upwards (so be there for a longer time period), make the deck closer to the main wave peak (forward momentum, exposing the deck for longer to wave superposition), and the deck will already be closer to the water because the leeward hull will already be pushed down when the wave peak hits. the narrow leeward hull will stay down a lot longer traveling into the wave face because it's already depressed 10 cm?



extra fat planing hulls will rise the furthest distance from the wave peak, will rise with the fastest upwards acceleration, will not slice into the wave face due to forward momentum. the leeward hull only depresses a maximum of 7 cm when flying a hull, and so has negligible leeward hull depression normally. the deck then has been exposed to slam for much less time and at a much greater height.



i suggest these hulls have so much more lift than normal, i'll be able to sail faster and closer to head on, with the minimum deck slam for this 60cm deck clearance height.




still might change everything though





"
GODZILLA
and,
Even at 20kts the lift from planing will be less than half the displacement.
"

still crunching numbers/ hull angles / Pa/m2.

still digesting, will reply soonish.

 

yipster

rtfm, there'll be a simple trick to get the option to enable. it'll just take weeks to find is all.


i'll try taking some points out. let you know what happened.


http://64.251.22.171/articles/design...olokat_ENG.pdf

is nice for sure.



"flat. keep it cheap and simple"
nah.
got me little heart set on strip plank. n want lots of round organic shapes just because they please my eye.



cheers,
mal

 

and want wood, wood sucks, even encapsulated in epoxy vinylester etc it gains moist and weight, use foam, ooch what did i say, i'm outta here

 

was reading wharrams yard site http://www.andy-smith-boatworks.com/asite-renewed/index.html
and again very clearly noticed a boat is what you make it outside and in
you also have fixer uppers for a grand, 3k for free labor half builds etc
wharram is also using crab claws that seem to perform well
looked into my alu space frame idea and boards and foams

a boat should be small enough to take home or big enough to live on
phil bolger?

a well, i (we?) miss ya

 

Pa/M2 @ 5ms

further hull ponderings

"at 20kts the lift from planing will be less than half the displacement. "






my reason for having aspect/angle on the entire hull was formed years ago.

basically,
after looking at pictures of many cats sailing, i came to the conclusion that under normal full sail, the nose gets pushed too far down.

a normal sail load pushing the nose down does not appeal to me at all.

this is the reason why i allways intended to have lots of weight near the transom.
so a good full sail load of 300kg makes the hulls sail flat.

(water tanks, fuel tanks, engine and people all in the space between the transom and the chainplate/cabin start will keep the nose out until reefing (ie 400Kg on the sails).









the hulls sail with 0cm at the stem and 15cm deep at the stern

14m2 SA, 1400Kg, so 100Kg/m.


perpendicular 1m2 @ 1ms, Pa = 10000 N

(15cm deep over 14m2 planing surface area

(sin-1 .15/930) x 2hulls SA (15cm over 9.3 meters gives 1 degree angle)

= .02 * 14m2 = .3 * 10000 N
=3000 N



@1ms need 14000N from (angle/area/velocity) to plane

@2ms need 7000N sail force to plane

@4ms need 3500N sail force to plane

@5ms need 3000N sail force to plane





so
"at 20kts the lift from planing will be less than half the displacement." if the hulls travel flat.

if they have 1 degree angle either built in or balanced in, then fully supported at 5ms, 10 knots.

which matches fionas wave drag graph perfectly. ie starts full planing at ten knots

 

Mal
If you take your calculations a step further you would predict a narrower deeper hull of the same displacement would plane easier. That is not the case.

Planing hulls are similar to foils or wings but with only one lifting working surface rather than two. The lift resulting from movement is related to the dynamic pressure not static pressure. The dynamic pressure is a function of the velocity change relative to the far flow up to the point of the flow becoming turbulent rather than streamline. THe highest lift pressure is where the oncoming flow first meets the hull and is slowed down. The aft end actually has negative dynamic pressure because the flow velocity increases as it moves up behind the hull.

Here is another useful little bit of software that you can use:
http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html
If you put your hull values in it you will see that the trim up continues till about 25kts and then levels out - see attached. This is in close agreement with the NACA data I used to work out the lift at 20kts.

You will get more lift at a given speed if you angle the hull upwards but it is nowhere near fully planing at 10kts.

Actually did you see the hull shape of X-IT that Brian Ballard posted:
http://www.boatdesign.net/forums/at...1250153720-my-little-piece-peace-dscn2348.jpg
These hulls are more suited to being easily driven throughout the speed range than your current design.

With the weight you are targetting you can trim it how you like by shifting weight around.

You would find a simple hard chine with narrow flat bottom and some rocker would work well. Have a look at some of the east-to-build beach cat hulls. Most big cat hulls are designed for volume and accommodation. You have gone past this thinking so why not make the most of it?

Rick W

 

quality assurance procedures assures invalid perspective

foam ponderings for you


"
I would be interested to know what foam sandwich boats you have found "soggy". Who built them? I have found that it is easy to get variability in the adhesion so am interested in construction methods and quality assurance procedures used.




all these things are engineered. so there's no sense in considering this aspect at all.

can i suggest looking from two perspectives at the same time? start with the engineering perspective, but also consider MacDonalds killing people.

ie it's capitalism, not engineering.




an organism seeks to survive. there are competitors. they have to make a profit or they won't exist. ergo, the people building right now have made profit. but how do they stay alive?

by cutting costs.
and
increasing marketing


(just like current MacDonalds advertisments on the tele, they market their food as the healthiest food, and back it by science. the reality?, they kill more americans than car crashes. have you seen american bums lately? HUGE!)







so;
survival of the companies that reduce their costs the most, while increasing brain share.

reducing quality while increasing perceptions of quality (increasing rich 3d visual information, shine, lustre, sex appeal triggers)



how do they cut costs?

build time, materials.
and now, you know we're talking foam, and something-esters here.





if you only ever consider from an engineering perspective, you will only ever see MacDonalds as a supplier of scientifically proven good food.

rather than the largest killers of other peoples children on the planet.

(heart attacks
- people are genetically evolutionarily hardwired to POUNCE! on FAT and protein, as in the wild fats and proteins are very hard to come by. food scientists understand these knee jerk circuits and of course tap your knee to trigger the reflex. it's their job)

have a look at american arses next time you can. their butts are HUGE!, and similarly, there is as much fat on the inside, in their arteries.





if you were a surfer and had ever bought a polyester surfboard

(SHINY! NEW! SEXY! LUSTER!

and had the FKING! thing break the VERY first time you used it (leg rope force delaminated the tail) you would be suspicious of survival of the fitest suppliers of goods, engineered or otherwise.





professionals? all yours mate.

 

maths

hi rick.
"
If you take your calculations a step further you would predict a narrower deeper hull of the same displacement would plane easier. That is not the case.
"

no i wouldn't.

do i understand the maths you are talking about?

yes.
i understand exactly what you are saying. and you are correct.

this was just the quickest way of arriving at the required answer

if you ignore the progression, and focus on the relationships, i know you will see.




did pure maths at uni.
used to localised pools of consistency (limited pools of completeness)

engineers are used to universal maths, like the ocean.

but realise that swimming pools DO exist,
and they don't touch the ocean.



(further reading on the philosophy of mathematics;
bertrand russel,
showed how logic breaks down at the first step)




it's a difficult thing to explain to somebody
look at how much drivel i've been forced to write, to defend an OBVIOUSLY wrong mathematics. how can a sane person even consider defending wrong maths?


1 + 1 = 2 is not true, and has never been true

you have two oranges, one is small, green and rotten, the other is fully suculent, ripe and delicious.
you have two small children.

you hand the good one to one child and the crap one to another child.
engineering maths has occurred.
1 + 1 = 2, and everybody is happy.

no.

one child cries and the other is happy.
reality has occurred.
1 + 1 =2 is a con job.





the maths is good, the pool was good, but yes the maths used was not universal, so the relationships are true, the result true, but yes, the steps are of use in this one tiny pool only.

hope you understand.

do you understand the maths that i used now?







i realise the plastics speech uses extreme examples.

but it would just take so much longer to get the point across using normal examples, and then there's counter examples that have to be countered etc etc etc ad nausum.

far easier to ignore an entire invalid methodology than try and reason WITHIN it, on their terms. (and of course, this is your job. to reason within this forest)




can foam/glass/cheap plastic be engineered? to stringent specifications? obviously
is the ISO valid? extra valid
can you defend yourself in a court of law? absatively

well then, engineering wise, i guess foam/glass/cheap plastic is the way forward.


and for normal people it is.
a winnebago is a good product

just not for me. the stiffness loss after ONE year is just too much for me, let alone 30 years.



some of these (i'm drunk by the way) new cats have foam mast bulkhead/beams. see, the engineering says OK, the foam numbers say sure, use it for under the mast because it's 1 meter high, (foam panel) i say get f*cked you *****. it's a trick. twice the depth gives you squared stiffness ? so the numbers say yes! use a foam esky to support 20 tonnes shock load, an i say, i've felt sloppy foam n glass with my feet (as have others on this forum, called the "walking on jellyfish feel". and so, if you argue with engineering, of course its valid to have a mast beam made of 1" thick foam, as long as it's 1 meter deep. see?



i just don't care. it's the entire pool of logic they operate in that is wrong.

and they are bound inside their universe, never to see out.






same as rocker sucking you down.

V's planing pushing you up.


ever held a spoon under a tap? i have. sactly the same as rocker. you can feel the suction.

lowest drag sucks you down. see these photographs?






the bulge in the middle creates a suction, that sucks you down.

for every knot faster, you get sucked further and further down. using more energy, to create more actual displacement.

V's the planing hull, which pushes you up. every knot faster you go, the boat gets lighter (displaces less at the waterline)

 

OK - you wouldn't.

The fastest way to learn is to have a go. Just build it in the way you think will work the best.

Rick W

 

yeh yeh,
but what do you think! about all my advanced theories?

did i convince you that one and one doesn't equal two?????

did i?

)

 

Hey Bob, just to stir the pot, are you sure the hull is being sucked down, or is it falling down because as the bow wave increases due to the energy being applied to it due to the increase in friction because of the increase of hull speed so the water required to create this bow wave is coming from under the hull and thus it looks like the hull is being sucked down but in reality it is falling down.

As far as displacement / planning hulls, i hate to tell you this, but they are the same. We have a saying in the Avitation industry 'With enough horse power even a brick will fly', this also applies to boats aswell (the equation for an aerofoil is the same for a hydrofoil, the only part of the equation that is change is the density of the medium from air to water). I will bet my lefty that a sheet of marine ply on it edge will plane, mind you you will have to be going very fast, and it will not be the most stable thing on the water, but it will plane.

Imagine if they make a propulstion system that is an equivelant to the jet engine in air but for water, the speeds that would capable, the speed of sound in water is much faster than air. Imagine the day they overcome the sound barrier in water and your boat is supersonic in water. The shochwave coming of the hull.

 

No.

The photos of the slender vessel are interesting. I have seen them before but I have not seen the underwater shape. I expect it is deep forward. I have attached a photo of a somewhat better design of slender ship for high speed. It has lifting sections to well aft of the mid section but then the lines lift toward the stern.

It is interesting with planning hulls that the stern is actually pushed down as well as the bow being pushed up. There is a low pressure region where the water accelerates to get from the high pressure under the hull to the atmosphere. It forms a rooster tail as it rises. The attached coloured photo of WHIO might challenge your theories on planing hulls.

The lift to drag from a long slender planning surface is not very good. That is why wide planning hulls take less power for a given weight. As stated before you will not get much lift in your hulls under 20kts because they are slender.

Also the best lift for area will come from flat bottom. Makes for a simple build with a hard chine. Keep the hulls slender so they are easily driven in your normal speed of interest. If you are worried about slamming the bridge floor then flare the sides outwards so buoyancy increases as they bury or load up when heeled.

Rick W