McGowan's 23' Tri 'Zip '

------------
Yes-but it wasn't too uncomfortable.
Did you notice the neat molded seat for the skipper on the Exploder? Now thats comfort....

 

Of course i did,
but that`s not comfort, that`s ergonomic.
Comfort u gonna find inside...or not.
And, sailing on the ama, which means more or less running on a blade, is not comfortable.

pogo

 

Zip trimaran

Hi everyone:

Marvin notified me about the discussion on the forum and I thought it might be helpful to reply to a few things. Sorry for the delay.... busy!

Flying hulls - that's where we're going, so why not plan for it? Not too long ago people believed every multihull was unsafe to sail.

Non-folding (but demountable, and trailerable) - the wider the beam overall the lower the angle can be to get the hulls out of the water, and the lighter the weight (and sail area) can be.

Spray (or planing) rails - I see this in my work on inshore fishing boats, and rockweed (seaweed) harvesting outboard boats here in Nova Scotia. A round-bottomed, planing rockweed boat with spray rails will get on a plane quicker than its sistership without spray rails (hulls from same mould, then rails added to one) and carry greater loads at the same time. This works even when the boat is severely overloaded. Check out this picture of l'Hydroptere, the fastest boat on earth. Think they put the spray rails in for looks? Note the rocker on the main hull, but not the rails.

Constant flare to sides of the main hull: an easy choice for a racer/cruiser, especially with the addition of a spray rail. The interior volume increases, weight decreases, and construction is easier than on an S-shaped side, or a side with a berth shelf out each side. Construction on Zip would be all-plywood on the main hull (maybe some foam for racers) except for the bottom, which would be strip planked like a canoe. The amas and cross arms are strip planked in, with light 'glass cloth inside and out, and nodes (think bamboo) or bulkheads at key points. Aluminum plates, bonded to the inside ends of the cross arms, are bolted together and to the hull to lock the amas in place. A bolted-down traveller 'cap' locks as well as the plates lock the aft arms together. Why not have a folding system? Greater beam and lightness are possible with the simple demountable setup than with a folding setup. The trailering width would be 10', but the height would not be excessive. If you only plan on sailing locally, than a borrowed or rented flatbed trailer could be used. The curved Bruce-foils are there for lift, but are curved also because a line near the shroud fitting on the mast could be used to raise the board from the cockpit. Any load on the board would make it pretty much impossible to lift by hand. The strip-planked mast has a 2.5:1 sectional shape, and its planned construction would be stiff enough to not need spreaders.

Rocker - John Shuttleworth had a great article on hull shapes on his website, though it's not there anymore. There is this excellent one that discusses hull shape, construction, and aerodynamics and the effects on seaworthiness, however, which also ties into performance. http://www.john-shuttleworth.com/Articles/NESTalk.html Basically, too fine or too powerful a run influences performance and seaworthiness: too flat and powerful and the bow goes down at speed because the lift aft increases. Rocker is very important and it's good to look at some of the fastest boats on earth to see that they usually do have a fair amount of rocker aft. It's a balancing act of course: one must consider volume, rocker, sectional shape, weight, use of boat, etc... The weight of the whole boat on only one hull in the water plus the bow-downward forces of a lofty rig, plus powerful stern and fine bows can make for some spectacular crashes. There are lots of videos of, especially, cats on the net that show this. I drew up Zip with racer/cruiser in mind, which could be changed to outright racer with a taller rig and slightly different construction. Fully submerged, one of Zip's ama's displaces 135% of the combined-hull/crew resting displacement, and the boat is meant to sail almost level while flying two hulls. There is a fair amount of volume up high and forward on the amas, but the bows are meant to slice through waves, like the Gougeon Brother's Adrenalin. They would take on a bow-down attitude with a too flat and full an ama run. The Gougeon's have fairly flat and powerful runs on the amas of their amazing tri by having them pivot, where the amas are able to stay level regardless of any bow-down attitude of the main hull.

Finally, why go with a designer that designs heavy boats? You can safely ask that of me - a nobody - but you wouldn't ask that of Nigel Irens http://www.nigelirens.com/FRAMEcruising.htm , or fellow-Canadian Steve Killing http://www.stevekilling.com/index.html - designer of Canaan, the Little America's Cup C-Class catamaran defender of a few weeks ago. Killing used to design fairly heavy racers, but also designs electric boats, mahogany runabouts, canoes and kayaks, and racing and cruising sailboats. Check out this video that shows the acceleration of these cats. http://www.youtube.com/watch?v=tpcAeRPTdNQ&feature=related (note the rocker at 6:08) Designing and learning from one type of boat doesn't take away from what you might do with another.

Has a Zip been built? Not yet...


All the best,
Laurie

www.mcgowanmarinedesign.com

 

Yes,
it was helpful to read your wrong conclusions---sorry.

pogo

 

==========
Laurie, thanks for sharing your thoughts on this design-I agree with most of what you've said particularly about flying two hulls and keeping the angle low.
You've done a great design job and I hope to see a powered up version sailing like a bat out of hell with a smiling-obviously comfortable- crew.
Good Luck-and thanks again!

 

Pogo... maybe you can more fully explain the comment just above?


Cards

 

Mmh, i dunna if i wanna...

Short
Sprayrails
The designer has experience with sprayrailsunder motorboats, so do i.
I helped several boats with additional planing rails from humpspeed into semi-deplacement mode and from semi-deplacement-mode into planing mode.
With sprayrails it`s miuch more difficult (yes, there`s a difference between sprayrails and planing rails, and, planing rails can become sprayrails).
Under a trimaran`s mainhull neither sprayrails nor planing rails make for several reason sense: mode , ratio , heeling , nearly constant longitudal trim,....
A motorboat`s fat hull with positive longitudal trim, exploiting dynamic lift with planing rails, controlling longitudal trim with sprayrails*, is another world !

Quote:
"Fully submerged, one of Zip's ama's displaces 135% of the combined-hull/crew resting displacement, and the boat is meant to sail almost level while flying two hulls."

That claim i really don`t wanna comment.
I believe the reason for such a claim can only be lack of experience.
I also think we have other people here that can judge the whole ama design better than i

* sprayrails
Anyone who is interested in how and why might translate this (with a machine?)
(i`m too tired for this job; it`s 21:45h and i wanna drink a beer on my sofa :
http://forum.yacht.de/showthread.php?t=98827&highlight=farr goes retro



pogo

 

Spray rails

Pogo:

The vessel displaces 1,300 lbs (590 kg) at rest. The fully-submerged ama displaces 1,755 lbs (797 kg) or 1.35 x, or 135% of the resting displacement. It's a common way to measure ama volume.

Spray rails on multihulls? The fastest boat on earth, l'Hydroptère, has them. They're quite prominent on the main hull.

Regards,
Laurie

for some reason the picture doesn't seem to attach, so check out these pictures if it doesn't

http://www.hydroptere.com/_en/hydroptere.html#centre

/Users/mcgowandesign/Desktop/hydroptere.jpg

 

---L`hydroptere `s sprayrails are for deflecting spray and not for providing lift like your underwater planing rails want to
---L`Hydroptere`s Sprayrails don`t trimm the boats attitude like Sprayrails on motorboats do
---l`Hydroptere`s sprayrails also exist for static reasons.
--L`Hydroptere`s hull is most of the time out of the water- no hydrodynamic funktion of the rails at all

pogo

 

-------------------------------

Blödsinn !!

 

Pogo:
Of course the spray rails do nothing (aft) when the boat is in the air - it's getting in the air that's the trick. Exactly the point. Spray/planing rails = lift, lift = hull rises. Getting the relatively wide (because of the simple vee-shaped sides and large volume) main hull out of the water is what the rails are for. It's pretty straight forward....
L

 

The amas weirded me out also, low volume, lots of rocker. I thought the whole design looked like some amas from something a bit like Adagion, nailed onto that little mono cruiser at the end of the street, here that never sells. Insert lifting foils into the equasion though, and I am lost. People can draw up all kinds of cool looking things these days without reference to practicality, but this guy comes from a very boaty place. I divide my time between Ontario, and the east coast also, which is where I keep my 23 foot tri.