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kid
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Joined: 11 Jan 2010 Posts: Location: Bells Beach
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Posted: Tue Sep 28, 2010 3:22 am Post subject: Lordy!!!! |
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I was digging through the catalogue of an online used-book store when I stumbled upon a copy of Lindsay Lord's "Naval Architecture of Planing Hulls". I can't make top or tail of most of it, as it really is about boat building. There is one little bit about width/length aspect ratios which made a bit of sense. I promptly went outside and hacked out a little paulownia paipo, observing the 0.4 aspect ratio found by Lord to be optimal for planing in his experiments. I'm guessing that it'll ride like any other 37 inch piece of wood, but I'm quite proud of myself for maybe figuring out a page or two of engineering speak!
![](http://i1023.photobucket.com/albums/af357/bjkid/IMG_7347.jpg) _________________ "It's not a beer-belly, it's a displacement hull"
www.deluxepaipo.com |
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puurri
Joined: 26 Oct 2009 Posts: Location: sydney, OZ
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Posted: Tue Sep 28, 2010 5:06 am Post subject: |
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Yeah, I posted this as a part reference on Realsurf a few years back. In short; belly boards are planing devices in their own right but once a rider is installed the formula changes as legs and part of torso reduce it to a semi displacement hull unless the rider moves forward and uses longer swim fins to decrease drag and increase planing surfaces. This of course varies when the board length and wave height/ power increases to compensate for drag. Tailoring hull length and other dims to compensate for rider height and weight optimise the board's performance but wave power is a major determinant of speed.
Fins (board) of course increase control but at the expense of drag but the advantages are proven as the rider has no need to use his legs as a drag/stall quasi control device and slow hull speed. Fin surface and length vs hull length is still a dark area and the usual ones on offer (FCS etc) are for standups and a better shape is seen in Barry Hutchins personal board (though in need of development). Might I suggest here that folk consider experiment with base to height ratios on a "suck it and see" principle". BTW DO NOT OFFSET FINS as they impede speed and a rider's body is more than sufficient to encourage changes in direction.
A critical portion is in the leading 20-30% of the hull where a preferred elliptical hull form (outline and rail shape) engages the wave face. (and also the departure surfaces where in best design minimises drag)
Girouard? has something to say in the interviews portion of this site. |
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kid
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Joined: 11 Jan 2010 Posts: Location: Bells Beach
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Posted: Tue Sep 28, 2010 5:22 am Post subject: |
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Hey Puurri,
I get what you're saying. This board isn't big enough to ride in the forward position (superman-style) so my legs and torso would be dragging. This would cause the board to displace more than plane I guess.
Thanks for the tip on the hull bottom. I'll check out the interviews. I did use that type of design on the spoon/hull thing I posted about yesterday. I'm still to test it in clean conditions, but it does sit much higher and tighter in the face than the flat HPD style boards I've been making. _________________ "It's not a beer-belly, it's a displacement hull"
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puurri
Joined: 26 Oct 2009 Posts: Location: sydney, OZ
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Posted: Tue Sep 28, 2010 5:33 am Post subject: |
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Aya, look at Barry Hutchins photos on his board and follow suit. (BTW I took the one at Garie showing it in closer format) |
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kid
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Joined: 11 Jan 2010 Posts: Location: Bells Beach
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Posted: Tue Sep 28, 2010 6:01 am Post subject: |
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Nice pic!
The Hutchins interview is one of my regular reads. There's so much there I want to try! Who was the other one you mentioned in reference to the hull bottom? I searched the interviews for Girouard, but I couldn't find it.
Oh yeah, and I'm sorry if I took your earlier criticism badly. I realise the old English bellyboards are a design dead end, but they are good fun.
Now I'm really enjoying the ideas and designs from some of the more progressive surfers in the resources on this site! I reckon I could go a lifetime and only ever get a handle on a small percentage of them! _________________ "It's not a beer-belly, it's a displacement hull"
www.deluxepaipo.com |
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