Author Topic: Ed's boat in Perth  (Read 52894 times)

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Murray in N.Z.

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Re: Ed's boat in Perth
« Reply #15 on: March 28, 2012, 03:38:31 AM »
But Bryan y'all forgot the most important part.... it just looks shippier, may be because of the aditional height and extra feet.

Anyway mate whats the story on the fancy formular for HP/Speed. Is it applicable to the GA, am I way off track, is it anuther innernet (praise be to Al Gore) spoof, does that only apply to the Northern Hemisphere with its floating on top of the world lighter water or what. Ed seems to be rethinking fitting a huge 300hp firebreathing supertanker engine as a result and I dont want to be the one responsible for putting him crook. Roughly (educated guess) what HP do you reccomend to get his 20Knots.... of course there are variables like gearbox and prop bite but could it be done with say ..... 100hp?
Thanks
Muzza.


Brian.Dixon

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Re: Ed's boat in Perth
« Reply #16 on: March 28, 2012, 12:13:30 PM »
But Bryan y'all forgot the most important part.... it just looks shippier, may be because of the aditional height and extra feet.

Anyway mate whats the story on the fancy formular for HP/Speed. Is it applicable to the GA, am I way off track, is it anuther innernet (praise be to Al Gore) spoof, does that only apply to the Northern Hemisphere with its floating on top of the world lighter water or what. Ed seems to be rethinking fitting a huge 300hp firebreathing supertanker engine as a result and I dont want to be the one responsible for putting him crook. Roughly (educated guess) what HP do you reccomend to get his 20Knots.... of course there are variables like gearbox and prop bite but could it be done with say ..... 100hp?
Thanks
Muzza.

Shippier, eh?  OK ...I like that.  It definitely looks "shippier" when you're standing under the bow and looking up at it...

As far as speed predictions go, there are many methods available and several calculators online.  Most will not be accurate, but all will be within a reasonable doubt of reality.  That said, I would suggest taking it a step further if you want more accurate speed predictions.  The attached spreadsheet contains Savitsky's methods along with later refinements (Blount, Lee, etc) and is pretty good ...but keep in mind that it does not take into consideration things like the parasitic drag from outboard skegs, strakes on the bottom of the boat, imperfections in the surface, humps and hollows, propeller efficiencies or the lack thereof (slip) etcetera and it DOES assume that the boat has a traditional drive shaft and rudder.  These models tend to be more accurate on heavier, beamier, boats than on lighter and relatively narrower boats such as the Great Alaskan.

What I did for speed prediction (and I'll need to dig up my hydrodynamics results for you after I get home from work), was to use the Savitsky+ analysis in RhinoMarine, an add-on for my Rhino 3D CAD program that I used for modeling the Great Alaskan.  Again, all the little things that take away from speed (parasitic drag and imperfections) are not considered, so even those results need to be modified.  I originally modeled a 22' Tolman Jumbo and came up with a scaling factor to make the results match up with reality, then I modeled a 26' Great Alaskan (modest load) and multiplied the results by the same scaling factor.  To take a guess at how Ed's boat will perform, I would predict the same 26' Great Alaskan with the attached spreadsheet, then modify the numbers to model Ed's boat, and then derive a scaling factor between the two.  Once there, you can use that scaling factor to adjust the speed and power predictions from the 26' boat to Ed's football-field-length (haha) boat and you'd be in the right ballpark.

If you want to keep it simple, figure 40# per horsepower as the minimum and 25# per horsepower maximum and go pick your motor and prop.  This would result in about a 150 hp minimum sized outboard and a 250 hp maximum if you assume 6150# (that's the number you used, right).  I think in reality that you will be surprised at how this boat moves easily and I'd probably limit Ed's boat's horsepower to something more like 200 or 225 hp.  With this horsepower, I would expect the boat to move along in the mid-thirty knot range or possibly faster.  Anything above 40 knots or so starts to become an inaccurate prediction in my book because minor hull variations (humps, hollows, etc) start coming into play more as the boat goes faster.

Brian

Murray in N.Z.

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Re: Ed's boat in Perth
« Reply #17 on: March 29, 2012, 01:59:39 PM »
Bryan... Shoot me... 35 knots, thats hellish fast for a 26' boat. well at least it is around this part of the world. Maybe the seas are a bit different on top of the world but down here in the bottom half most hulls would get a real pounding doing that speed for long and if the hull didnt suffer the poor old captains body sure would. Heck we would be over the fishing spots before the proverbial cup of tea has been made and consumed. Of course y'all dont have to drive it like ya stole it all the time.

Seeing as our fuel is 2 to 3 times dearer down here we tend to travel a bit slower and save quite a few bucks.

Well there ya go Ed, choose the desired speed, tell Brian and he will give more accurate guidelines for engine HP.

Brian.Dixon

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Re: Ed's boat in Perth
« Reply #18 on: March 29, 2012, 04:48:18 PM »
Let's see ...we all live in the same world and the world's oil is sold on the open international market, and shipping oil (or fuels) to Alaska has got to be just as expensive as anywhere else.  Hmmm... We all pay a similar price for oil, so why the 2 or 3 times higher prices down under?  Hmmm...  Lemme guess, it's your loving government taking a chip out of your wallet in taxes, no?

Brian


Murray in N.Z.

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Re: Ed's boat in Perth
« Reply #19 on: March 30, 2012, 01:41:37 AM »
Brian.... How dare you suggest such things !!! Our government assures us that they know whats best for us and are only acting in our best interests.... and its all the fault of global warming caused by cows farting and smokey deezil 4x4s.
Thats why about 1/3rd of of all N.Z. bred folks head overseas to Ozzy to make a better life for themselves... Ed included and me most probably early next year once I get qualified.
Soon the only ones left here will be the politicians and the unemployed, oh and a couple of million immigrants from hot parts of the world all ripping each other off.

Seriously tho would 100HP produce around 20 Knots?

Brian.Dixon

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Re: Ed's boat in Perth
« Reply #20 on: March 30, 2012, 11:55:05 AM »
I forgot to go looking for the hydrodynamics info last night, but I doubt 100 hp will move you at 20 knots.  I forget what the minimum horsepower for planing was, but it's higher than that... I'll check into it tonight...

Brian

PS:  Remember, if you ever hear a knock on the door and there's a guy there that says "Hi, we're from the government and we're here to help" ...just walk him down to the other side of the road and then shoot him ...don't want that muck in YOUR yard!

Ed Snyder

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Re: Ed's boat in Perth
« Reply #21 on: April 10, 2012, 09:58:48 AM »
hahahahahahaha, couppla clowns here for real....

See Muzza, 300 Hp is good! aye Brian, push a rugby field along quite nicely!

Muzza you git da drift on that * Planing.xlsm file at all? Me either.....

Brian you kinda know what your taking about, so, if I want to drift along at max 20 Knots, with an oiler, what HP, prop and/if what gearbox ratio say with a Vee drive? Feel free to use that * Planing.xlsm file Brian :-)
 Actually if it wasnt 12 a.m.. might have a play with it myself

Ed
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Ed Snyder

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Re: Ed's boat in Perth
« Reply #22 on: April 10, 2012, 10:02:21 AM »
 8) :P :-X
Oh yea, flipped the hull last sunday, 6 of us did in - rolled her ova on tyres, real light too....
Not waving....... Drowning!

Brian.Dixon

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Re: Ed's boat in Perth
« Reply #23 on: April 10, 2012, 11:50:53 AM »
Yeah ...that spreadsheet's not too bad.  It, like all such models, leaves out things like parasitic drag, variation due to choppy seas or wind or swells etc... but it gets you in the right ball park.  I'll see if I can get time to play with if in the next couple of weeks.

Lightweight?  That's one of the beauties in this build method.  Other methods have you turning over a MUCH heavier assembly when it's time to turn the hull over.  With this method (Renn Tolman's method), the hull is as light as it can possibly be when it's turned over and that allows people to build a much larger boat without special equipment (cranes, slings, giant gimbals and tripods etc).

Brian


Murray in N.Z.

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Re: Ed's boat in Perth
« Reply #24 on: April 13, 2012, 05:38:09 AM »
C'mon Ed. y'all know the innernet (praise be to Al Gore) rules.... if theres no foters it never happened!  ;)

Ed Snyder

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Re: Ed's boat in Perth
« Reply #25 on: April 17, 2012, 10:52:39 AM »
Some pix of the turn over
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Ed Snyder

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Re: Ed's boat in Perth
« Reply #26 on: April 17, 2012, 11:00:56 AM »
more pix
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Brian.Dixon

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Re: Ed's boat in Perth
« Reply #27 on: April 17, 2012, 11:36:12 AM »
She's lookin' sweet, Ed!  You might find your waterline is a bit canted towards 'stern low' ...the boat will float more horizontal than that, but then again, you might be aiming more for the on-plane attitude?  She planes 4 degrees bow-high at 21 knots... just as a point of reference.  The planing angle drops to 2.8 degrees at 40 knots, and the boat should float with about 1-1/2" bow-high trim at rest (assuming exactly the same layout that I designed into it...).  Somewhere I read that a waterline with a slightly belly to it (lower in the middle) is best looking overall since it accommodates a variety of trim angles.  Just ideas...

Brian

PS: More pix coming?  Your 'turned over' hull still looks upside down ...well, right side up to us but that's because you're on the wrong side of the planet hahaaaa

Murray in N.Z.

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Re: Ed's boat in Perth
« Reply #28 on: April 17, 2012, 11:31:44 PM »
Ed.... Hull looks great, waterline may be a bit optimistic in view of the 3000HP supertanker engine, Vdrive reduction unit and Kort Nozzle going in it!

Hate to have to tell you this.... but according to the foters they didnt turn it over yet. I reckon y'all just got on the waipiro with a bit of free BBQ thrown in and after a few hours it looked like it was turned over from your head down point of view!!!!!

That your Moko on the ground? looks like he is trying to copy the unable to walk properly  growdups.

Next time y'all are going to turn it over dont start drinking till its well done!!! ;D

Muzza.

Ed Snyder

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Re: Ed's boat in Perth
« Reply #29 on: April 18, 2012, 09:02:53 AM »
Oh heck, file too bg too small, lol, eyes glazing ova 11 pm, here goes more
Not waving....... Drowning!