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Old Sep 06, 2014, 07:44 PM
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The Design Process:

Following the mixed success of the Panic, and the failure of Panic Mk2, vague notions became ideas and then itches that required to be scratched. The Crash disintegrated on the metaphorical drawing board - don't even ask - but the Burn is still giving out a gentle warmth.

My personal motivation is not to design a faster variant of the Britpop - more than enough people, all smarter than me, including BG, are attempting that already - but to find a new line of development. Scarred by the Panic Mk2, the fundamental idea for the Burn derives from the classic Australian surf boat - I mean which basic hull shape is least likely to go down the mine?

After a lot of time spent exploring the possibilities of various CAD programs, I found Freeship suited me best (others tried: Prolines, Hullform 9P, Archimedes, Delftship and Rhino) but be warned. As I discovered to my intense irritation, while Freeship 3.13 will open files saved in Freeship 2.6, the reverse does not apply, and while Delftship may open Freeship 2.6 files, it will definitely not open Freeship 3.13. More on trying to swap files between programs later.

Eventually, however, I arrived at a shape, Burn SW2.7, that not only did I find pleasing - yes, I know, I'm weird - but which when plugged into my friend, Col Thorne's magical spreadsheet showed promise against other known designs.

And then the what ifs began, and many iterations later, I arrived at Burn V1.7 and finally Burn V1.14.

As the Graph from Col's spreadsheet shows (reading SW2.7 as the base line, plus being bad, minus good, and ignoring the dip after 1 knot as an aberration) both V1.7 and V1.14 are slightly inferior up to about 2.5 knots boat speed but after that turn rocket ship, at least on paper.

Then, my friend, Neil Deverell who graciously builds boats for me on account of I have absolutely no aptitude for that sort of thing, pointed out that with the deep forefoot and the LCB being well forward, whichever design I choose would be most unlikely ever to tack when told to. Simultaneously as it turned out, I had been thinking the same thing and playing around with reducing the forefoot and moving the profile of the spring aft.

These subsequent versions V1.15 and V1.17 (we don't talk about V1.16) actually had reduced wetted surface, but because of the other changes... Well look at the second graph.

Contemporaneously, Col and I are trying to find a way to import V1.14 into Hullform 9P, which although being an old, clunky and unstable program from the 90s still offers the most sophisticated hydrostatics package of the programs we know, and which will tell you what happens when a boat is heeled. This, however, is a most aggravating process as none of the other programs will save the design in a file that Hullform will accept. We are reduced to manually measuring the offsets from a printout and importing them as a text file (still working on it). Why bother? Hullform is able to tell me whether the boat will go bow up, which we suspect and not good, or bow down when heeled.

So, bottom line, I have a design which comprehensively violates IOM practical experience but looks irresistibly tempting on paper. What would you do? And if you decided to go ahead, which would you choose to build?

(P.S. For those interested, Col is nearly ready to post his spreadsheet on his own website. Personally, I find it an invaluable tool. I should add that I restrict myself, with one exception, to open-source or trial programs. I know there is allegedly a free VPP on SourceForge but it turns out you have to pay for the vital component and it looks far too difficult for someone like me to come to grips with. If anyone has access to other VPPs, please share the love.)
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Last edited by Emintaka; Sep 06, 2014 at 10:04 PM.
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Old Sep 06, 2014, 08:37 PM
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Radical.. I like it! Are these vpp's representative of an inclined hull form (upwind) or flat (downwind)?

My approach has been 2 parts inclined upwind and 1 part downwind - although I think down wind is about hull resistance and stability and upwind is about inclined hull form AND shift management play a big factor.

You have a lot of volume forward that is going to need a keel forward position up wind. But it definitely should climb in my humble option
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Old Sep 07, 2014, 01:39 AM
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Originally Posted by Whitaker View Post
Radical.. I like it! Are these vpp's representative of an inclined hull form (upwind) or flat (downwind)?

My approach has been 2 parts inclined upwind and 1 part downwind - although I think down wind is about hull resistance and stability and upwind is about inclined hull form AND shift management play a big factor.

You have a lot of volume forward that is going to need a keel forward position up wind. But it definitely should climb in my humble option
Thank you for your encouraging words. VP graphs are for the boats flat. If we can ever get it into Hullform, then we can do heeled. To my knowledge, Maxsurf is the only other VPP available and given the hoops one has to jump through just to get a price, I'm standing on my dignity. Besides, my understanding is that a certain well-known designer relied on Maxsurf yacht VPP figures, only to be cruelly disappointed. Whether Col's equations will prove any more accurate for IOMs, who can say? Guess, we'll have to build the boat to find out.
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Old Sep 07, 2014, 07:55 AM
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I have allways felt that a VPP gives you somebody elses (the program writer) idea of what makes a boat go fast.
I prefer to rely on my own instincts and not be swayed by a VPP.
Anyhow the scaps of paper I design on do'nt come with a VPP.
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Old Sep 08, 2014, 03:00 AM
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Hi Emintaka,

I tried something similar, but maybe not quite as radical ....

It was very fast downwind. I battled to make it climb upwind, but could have worked that out with some rig updates.

I felt it was not quite manoeuvrable enough to be competitive in large fleets.

The max rocker must have been about 40cm from the bow. Upside down, the parallel sides made it look a bit like a sharpened log.
Bow on it looked quite fine and I tried to have a narrow entry, the theory being that it would gain volume quickly as it heeled or stuck its nose in downwind.

In summary, very fast, but not race competetive
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Old Sep 08, 2014, 03:11 AM
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This boat however is showing lots of promise as I fine tune the rigs and ballast.

Dropped all the rigs as low as I can.

Looks quite different in black compared to her sister ships, but I like it
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Old Sep 08, 2014, 10:13 AM
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Quote:
Originally Posted by Craig Richards View Post
Hi Emintaka,

I tried something similar, but maybe not quite as radical ....

It was very fast downwind. I battled to make it climb upwind, but could have worked that out with some rig updates.

I felt it was not quite manoeuvrable enough to be competitive in large fleets.

The max rocker must have been about 40cm from the bow. Upside down, the parallel sides made it look a bit like a sharpened log.
Bow on it looked quite fine and I tried to have a narrow entry, the theory being that it would gain volume quickly as it heeled or stuck its nose in downwind.

In summary, very fast, but not race competetive
Hey, I recognise those pics!
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Old Sep 08, 2014, 05:48 PM
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Quote:
Originally Posted by Craig Richards View Post
This boat however is showing lots of promise as I fine tune the rigs and ballast.

Dropped all the rigs as low as I can.

Looks quite different in black compared to her sister ships, but I like it
Thanks, Craig. How interesting. Trim figures permitting I've decided to get Neil to make 1.14 for me.

Question: Did you find it difficult to tack?

And I like black boats, too. In fact, I alternate between black and white. 1.14 will be black if it goes ahead.
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Old Sep 09, 2014, 05:02 AM
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D design's Avatar
New Zealand, Northland, Totara North
Joined Feb 2012
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Metallic silver all the way
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Old Sep 09, 2014, 12:51 PM
David Cook Victoria, BC Canada
Joined Oct 2012
250 Posts
I did one of my earlier PP boats metallic pink and metallic silver. Any spectator would always cheer for me which pissed off my competitors even more. A good psyche out. My RG65 plug I used cashmere silver a blend of silver and gold. Very sharp. Are we now getting into a paint war or graphics competition? If so, I'm in.
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Last edited by PorkyPig; Sep 09, 2014 at 12:52 PM. Reason: typo
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Old Sep 15, 2014, 04:36 PM
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Bump
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Old Sep 15, 2014, 07:42 PM
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For those open-minded enough to be interested, here, as promised, is the link to Col Thorne's magical spreadsheet

http://radiosailingtechnology.com/in...ht-august-2014

One has to invest time in coming to terms with it but I, for one, found it well worth the effort. People can be as self-righteous as they like about skewed equations in VPPs -- and though it pains me to say it, they may well be right --nevertheless, to be able to make empirical evaluation and comparison of the effect of small changes to the basic design, albeit on a relative basis, is, I submit, extremely valuable.

If you ask me, it beats a scrap of paper any old day, though being a Luddite purist I personally prefer to scratch my designs on the dirt floor of my workshop.
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