Proafile Forums

An asymmetric icebreaker

2014-08-17T05:07:35Z

Asymmetric powered boats aren’t that common. There are a few examples that can be found: the Venetian gondolas for example, and also the lop-sided powered cats produced by Aspen Power Catamarans. Here’s another example:

The “Baltika” is a newly-launched icebreaker. Designed and built by the Arctech Helsinki shipyard in Finland, for a Russian client, this is the first example of an oblique icebreaker - that is, its designed to move through the ice at an angle. Quite different and clever, and also quite obvious but only once the idea is made known.

Sometimes its good to think outside of the box.

Wikipedia - Baltika (icebreaker)

Wired Magazine - March 2013 - Russian ship smashes ice sailing sideways

gCaptain - A Powerful, and Unusual Icebreaker

AAPG - If you Clear It, They Will Come

Why we Cruise…

2014-07-31T13:44:03Z

Hello Everyone,
It always fascinates me to see what motivates people to build a boat and go cruising. What are their reasons? What is it that is calling out to them? Getting away from something? Yearning to reach something? Any personal thoughts from y’all?

Here’s a brief video addressing some of the feelings that keep my fire lit…

https://www.youtube.com/watch?v=YjXlY0uQQg4&list=UUkGtEBaAqfQw2sUYajw5Jbw

Looking forward to hearing about some of your inspirations.

Cheers and Aloha,
claudio

Fibreglass split mould

2014-07-30T19:36:23Z

Hello!

I am working on a different ama configuration for my Kayak. I am aiming for a more tube-like design rather than vee hull. I have made split moulds before but had to join the two halves externally. How do the professionals make invisible joins? All advice gratefully received!

All the best,

Mark

question about lateral rig placement

2014-07-28T15:36:31Z

In a, say 10m Atlantic with cat schooner rig, It seems you could mount the masts along the centerline of the hull, or you could bring them to the windward gunwale, or on top of projections of the crossbeams, in which case the masts might be over the water to windward.

Does anyone have any comments on mounting the masts off-center, either to windward or to leeward?

thanks
Simon

micronesian navigation and crazy french guys

2014-07-25T18:36:44Z

Some of you may be aware that the Micronesian navigation system was as orthogonal to the western system as their naval architecture. The root document on Micornesian navigation is, imho, the chapter by Ed Hutchins, attached here FYI. (Oops. profile won’t let me attach the PDF. here isa link
http://mind.ucsd.edu/syllabi/06-07/Phil285/readings/Hutchins-chap2.pdf )

I found a link - was it here ? to this video of crazy french twins crossing the atlantic in a proa-like ‘outrigger canoe’ (seems like a tacking proa) in 2003 with no instruments of any kind. Probably well known here but If you don’t know it, check it out.
http://www.youtube.com/watch?v=H1xAPJpnWnc
http://www.creartisto.com/sansboussole/expedition_en.html

electric power

2014-07-25T18:10:12Z

has anyone got ideas/experience with electric auxiliary? it seems like a windward ama would be a great place to put batteries (and solar panels). I can see a prop on a long driveshaft connected to a 90 deg gear, projecting from the tramp side of the ama, permitting it to swing to point either direction… maybe that’s a bit ungainly, 😊 Have you eve seen those wild canal boats in Bangkok, with a car engine sitting on a ball joint up in the air, a handle in the front and a huge long prop shaft out the back with a prop on the end? Fast, basic and deadly.
But I digress. I guess a simpler solution is to use an electric trawling motor mounted mishaps on the ama - even in a well, with 180 rotation, or simply reversible (?)

question about rudders

2014-07-25T06:32:34Z

I’ve read several threads about rudders for shunting - vexed topic with no easy solution it seems. My question is slightly different: given Atlantic geometry, what are the pros and cons of putting the rudders on the ama, (at each end), with some sort of lock so the fwd one is inline or allows fine trim tab adjustment?

cross bracing/cross beams, bulkheads and tension rigging

2014-07-22T20:00:06Z

Its clear that the cross beams on a multihull need to be VERY strong. In my case - an ‘Atlantic’ design project, they need to withstand the force of lifting if not ‘flying’ the main hull while burying the ama. My instinct is to keep it simple and light by separating forces, using wires for tension.

I’d appreciate any input from this knowledgeable and experienced community. Pointing out any howling gotchas would be good 😊 ‘Scuse me for giving dimensions in feet and inches, these days I think in that medieval system :(

Also - I’ve read that the Atlantic /Pacific debate has been well worked over in these pages but I can’t find the relevant threads - please point me. I know its a bit boring to rehash old arguments.

My dimensions are at this point notional - (stitch n glue ply build)
Main hull 34’, 6’ max beam, 54” draw, 24” freeboard.
Ama, 20’, 24” max beam, 24” draw, 24” freeboard,
Ama may be canted out slightly, or built asymmetric.
Distance between centerline of mainhull and centerline of ama, 8-10’
Crossbeams extend out to windward at least 4ft to support a long ‘cockpit’ and possible a safety Ama - the idea being to put water tanks out there. (And hang the tender under)

Do any of these proportions look silly?

I will post a drawing or two soon 😊

I’m thinking three main crossbeams. Why? - three low aspect masts (25’?), one stepped on top of each crossbeam along centerline (or maybe toward leeside) of main hull. Each of these units (mast+ cross beam) will be tied together as a triangulated unit, with stays to masthead, and ‘bobstays’ (?) tying ama end of cross beam to mainhull at about waterline. Mainhull has beefy bukheads to take the load of mast and crossbeams.

So essentially, the mast-bulkhead-crossbeam structure is a distorted kite diamond.

I will post a drawing or three soon 😊

At this point, my crossbeams are 18-24” high under the mast step, tapering to 6-9” over the ama.
(Oh yeah, over the main hull, they form the cross section of a more or less conventional ‘cabin-top’, cute eh? The cabin sides (smooth vertical extension of mainhull, no sidedeck) and cabin top will provide more rigidity between mast/crossbeam units.

The crossbeams are 6-9” wide, forming a tapering box with vertical sides. Internally, ply plates form a conventional triangulation with vertical and diagonals (like an old iron bridge). Under mast, three plates, one vertical, two descending toward gunwales. I’m all about spreading stress. 😊
Crossbeams will be sealed (and foam filled?) for floatation.

I will post a drawing or four soon 😊

Assuming 1/2” or 3/8 build with all joins glassed with 4-6” tape, and, probably, one layer of glass on all exterior surfaces, does this general volume/construction sound like its in the right ballpark strength-wise ?

Its all very rigid, at least in this ‘cross section’ sense. What do I need to think of in terms of diagonal and twisting forces? I’m assuming tension wire diagonal cross bracing between cross beams, between mainhull and ama - two crosses.

Ama is bolted on. Three sets of double bulkheads project above ama deck and sandwich the crossbeams, with 4 or 5 1’2” SS through-bolts at each pair of bulkeads. Crossbeam sides/end panels appropriately thickened/braced over ama. That sounds strong enough 😊

Maybe for transport, the main hull can be tilted on its windward side (with appropriate cradles) with crossbeams pointing diagonally up - it would be quite a sight! 😊 There is also the question of windage, I’m considering some kind of simple sloping plane spoiler at each leading edge.

This my design in a nutshell, more details coming on steering, sailplan, interior layout, etc. Looks like I’ll be posting lot of drawings 😊 Masts *may* be rotating teardrop (iceboat like), _not_ wingsails in the interest of reefability. I’d want the total ‘wing’ area to be roughly equal to minimum storm sail area. (Does anyone have experience heaving-to a wing mast schooner?)

Sorry for the long post, and sorry for all the annoying smileys.

thanks!
Simon

practical proa sailplans

2014-07-20T06:17:31Z

For a midsize cruising proa, I want a rig that will shunt with a minimum of fuss, go well to windward, and be amenable to reefing. As nice as the traditional crabclaws are, I just can’t see dragging the rig back and forth. Likewise Bolger and Junkish rigs do not seem to have proven effective - yet. My inclination is to go with the well understood and efficient western mainsail plan, adapted of course for shunting. I’m also keen to maintain low aspect, so a multimast (cat schooner) rig seems smart. The Madness solution seem eminently sensible. Can anyone suggest arguments against this approach - for , say a 32’ boat? thanks!

question about tortured ply deep V hull design/construction

2014-07-20T06:07:37Z

Considering a mid size (~32’ long, 6’ beam) deep V hull, stitch-n-glue, what are the pros and cons of building in a keelson, of say 4x2 or 6"x3” lumber, horizontally. It would provide strength for groundings, a flat for beaching, and a slight increase in internal volume, at some increase in weight, of course. I see it tapered at each end with vertical bows.