i550class.org

So after 6 or so years, I've come back to my i550 plans with fresh eyes.

I've been planning for the last few weeks a prototype honeycomb/carbon sandwich i550 build. I've also been looking around at some other boats, Thompson 650, Shaw 650, Leech 650 etc. I really do like the concept of a length that lets the vessel compete in ABSA events (see http://www.asba.org.au/), which require a minimum length of 6 meters.

So, having figured that a honeycomb/carbon build won't be class legal, I thought - why not scale it up to 6 or 6.5? We would scale to 6 meters by increasing dimensions by 10%, scaling to 6.5 meters would be 20% (give or take - it's actually slightly less in both cases). With a thicker honeycomb core and the carbon skin, the boat should still be quite stiff.

I'd really like to know the thoughts of the i550 crowd on a larger, scaled up prototype.

I would talk to Andrew who built hull 1 (Tokyo Trash Baby) He has sold TTB and is now building a Leech 6.5 in Brisbane,
http://forums.sailinganarchy.com/index. ... 719&page=1
http://tokyotrashbaby.blogspot.com

Carbon Fiber was built with an removable tail section to meet a 20 foot requirement rule where she raced (also added more lead). I think Chad had done a rendering of the boat for Ben. Look in Ben’s blog http://bensboogers.blogspot.com for pics. micah202 now owns the boat and has removed the added length to race other i550s in the NW.

Jon

hi there,,,I got the removable piece when I got Carbon-offset,,but haven't messed with it yet...almost would'a this winter in local PHRF,,but ended up joining an all-carbon 40'er--how could I resist!?

....my thoughts on your plan......if you're going to the extent of a honey-carbon custom,,,I'd suggest you might want to round-out the hull across the bottom somewhat,,,or at least reduce the hard-chine effect with a ~10''-1' panel at midships which goes ~3-4'' up the hull-side....methinks curved panels would enhance the qualities of the materials used.....build a male plug,,add some shape,,I believe flat panels require more framing,,,and you'd have a lot more elegant boat,no?

I spoke to Andrew about both the i550 and the Leech, and he was very helpful, even offering to let me come around and take a look at the Leech.

Regarding the rounded hull, I agree entirely. To get rid of the boxy look does however change the hull from looking anything like an i550 (which may be good). I don't mind the look of it at all. I have attached a couple of renderings, but it really is a different boat. Is this the extent of "round" you were thinking Micah?

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...that's HOT!....though if I was going to the extent you'd be ,I'd have a plain curve across the bottom,,
,,,,if there's some reason you're working with flat panels for simplicity,,I'd probably just add a single ~1' panel on each side,,at ~20degree angle to the bottom--whatever the heel angle is.

...I think it's the shaw's that have round bottom's for home-builders.
....the i550 promoters emphasize the i550's -simplicity- for first time carpenter-builders,,but a male-plug would save more time than it takes to fabricate,,,and with some stringers would go a -long- way with the flexibility of your coring

With honeycomb it should be reasonably simple to get great sweeping curves like the rendering. I guess my questions is, whether full round bilge or an additional panel (moving/changing the chines), what impact does it have on performance? Is the chine critical to the i550 upwind, or is it more of a hinderance? Will the boat plane as well without the wide flat aft section?
All very interesting questions!

danielrose wrote:With honeycomb it should be reasonably simple to get great sweeping curves like the rendering. I guess my questions is, whether full round bilge or an additional panel (moving/changing the chines), what impact does it have on performance? Is the chine critical to the i550 upwind, or is it more of a hinderance? Will the boat plane as well without the wide flat aft section?
All very interesting questions!

....upwind,,, there might be some lateral resistance from the hard-chine that's losted,,but I'm pretty sure the turbulence is pretty bad there,,
,,and that's seen clearly at the stern in light-medium winds,,where a bit of heal has the lee corner dragging,,,call it the 'knuckle-dragger effect'
.......... if you flatten the boat,you reduce that turbulence but gain a bunch more wetted surface---all part of the game in one-design,,,but something you might want to address if you go 'free-willy'

....downwind--nothing matters,,you're GONE!...
.....though I have noticed that the hard-chine in the bow will tend to cause a bit of 'tracking' in some conditions,situations.

...I should note that my boat is at or beyond as flat as the design,offsets,rules perscribe,,,so these symptoms are likely at a maximum on my boat

The hull material restrictions for this Class are about to be eliminated, but I think it's a moot point for Aus since you have only ever had non-OD, handicap/rating racing so far as I understand it.

Taking the i550 design and just rounding the chine a bunch probably won't work- the boat will sink by the amount you remove, and you'll have a more deeply immersed transom, etc. Unless you're pretty good at this, I think you'll be money ahead to buy a design that suits your needs.

Compare the shape you've drawn with these...

The homebuild version of the Shaw 6.5 is an all strip-planked hull:

(This is the one in CA)

The Leech 6.5 uses flat panel topsides, then is strip-built below the chine.


Jim Donovan's D20 (about 21' I think) has a similar setup, with a curved bottom and flat panel topsides. His design is a little more M24-ish, less S Hem ballasted dinghy. I'd put it on the short list if I was thinking of building something bigger…
This is pretty inspiring reading: http://forums.sailinganarchy.com/index. ... opic=95302


…and, if flat panels appeal to you, here's the GT6:

The leech process will be the way I will build the first VELOCITY 7.1

Chad wrote:
Taking the i550 design and just rounding the chine a bunch probably won't work- the boat will sink by the amount you remove, and you'll have a more deeply immersed transom, etc. Unless you're pretty good at this, I think you'll be money ahead to buy a design that suits your needs.

.....yeh,,,I suppose you'd be best to add some 'v' at the centre,,to compensate for area lost at the chines ,if you decided to play with the 550's plans,,,but you're probably best to go with an established design ,no?

micah202 wrote:

Chad wrote:
Taking the i550 design and just rounding the chine a bunch probably won't work- the boat will sink by the amount you remove, and you'll have a more deeply immersed transom, etc. Unless you're pretty good at this, I think you'll be money ahead to buy a design that suits your needs.

.....yeh,,,I suppose you'd be best to add some 'v' at the centre,,to compensate for area lost at the chines ,if you decided to play with the 550's plans,,,but you're probably best to go with an established design ,no?

Yeah, that was my point...
...and I think you'd widen the beam at the chine/make the sides more vertical (hey, that's what the round-bottom guys have ready done!), probably add some rocker but keep the run aft pretty straight, and maybe bulk up the chest area/forward quarter and shift the ballast/cg a ways forward. But doing all that starting from the i550 design is like starting with an A to get to an AC.

Thanks for all the replies guys - greatly appreciated. I'd already been taking a look at the Shaw, Thompson, Leech and so forth. I think they are definitely great looking machines.

I think the benefit in the i550 is the comparative simplicity of construction. I think at the moment I'm looking at a moderate scale up of the i550, around 10% in length and 7% in width. This makes it around 6 meters LOA whilst retaining trailable beam. It should still be relatively simple to construct, and with the honeycomb/carbon construction I can simply have the sheets of honeycomb 10% larger from the factory. Nesting diagrams should then still apply (in a rough sort of way).

Cheers