Another computer aided drawing of a boat shaped object

[Lewisboater]

I would like some informed opinions and CONSTRUCTIVE criticism on the following set of drawings. No it is not a "design" in the sense that I am going to go out and build it tomorrow but it IS an excercise. I have not had much experience with multi-hulls (except my noodled canu) so I would like some feedback on the various performance aspects between the two hull shapes, sponson/ama positions (too deep/not deep enough, too far back/forward etc), cockpit location, choice of rig etc. I would also like an explanation of WHY you think what you think about it and WHY your proposed solution should be used and to what benefit. Frankly I don't care if someone thinks it is ugly...that has nothing to do with the performance so is irrelevant. I would like to thank one and all who reply for thier input.




I was looking at the Triak design ( http://www.triaksports.com/paddling/ ) and thinking that that design going to the EC would be rather uncomfortable to use over an extended period and perhaps I might give a try at one that I might be more willing to use. I oriented it more towards the sailing aspect and a bit less the paddling side. There are two iterations for consideration here...a shallow Vee version and a Flat bottomed version. For all practical purposes the two hulls are near identical but I actually think the Vee'd version would be as easy to build and with the filleted vee running the lenght of the middle...actually stiffer. First the Vee version which I originally drew. The hull would be a composit of build methods...the bottom would be of 4mm ply, the chine strake would be of 2-3mm and the sides and most of the deck would be SOF to reduce weight. The sponsons would be of 2 or 3 mm ply bottoms and SOF for the rest. Framing would be of cut out plywood joined by Cedar Stringers...typical SOF style. The boat would be built top down so the bottom would be stitched and filleted to the lowest stringer after the skin was attached. This should provide a light stiff structure that has a bit more resistance to sub surface nasties like coral.

The cockpit is significantly larger and deeper than the Triak and in wet weather could use a skirt to keep water out. The boat is wider and would be correspondingly a bit more difficult to paddle but...with a removable seat and a good bed roll to pad the bottom there would be sufficient room to sleep comfortably nestled in the hull under a small boom cover or simply a tarp. In order to keep the boat innards open, a single high aspect pivoting leeboard would be used for lateral resistance (heel would not be much of a factor so a single board should suffice). Steering could be foot operated, push/pull operated or hand operated via a handle bar affair mounted at the forward edge of the cockpit and cabled to the rudder quadrant. For sail power and ability to handle spars easily I propose either a form of Gunter rig or perhaps a high peaked Sprit or Lug sail and a fractional Jib. The mast should not exceed 12 ft in length and would be stepped on the deck, mounted on a ball and socket with a forstay and shrouds. The forstay should be led back to a small winch near the cockpit so the rig can be lowered without having to try and get forward (not really practical). The sponsons would either unbolt or fold up...depending on how stiff the support arms needed to be to stave off twisting in a seaway although the actual CB of each is near the middle of the arm/sponson joint area. The drawing is crude and the actual connection would span from the edge of the sponson to the centerline. Also...there is no top to the sponsons in the drawing...obviously there would be in reality.







Design length : 16.878 [ft]
Length over all : 17.375 [ft]
Design beam : 3.020 [ft]
Beam over all : 8.750 [ft]
Design draft : 0.375 [ft]
Midship location : 8.439 [ft]
Water density : 63.989 [lbs/ft3]
Appendage coefficient : 1.0000
Volume properties:
Displaced volume : 7.917 [ft3]
Displacement : 0.226 [tons] 505 lbs in salt
Total length of submerged body : 16.125 [ft]
Total beam of submerged body : 8.713 [ft]
Block coefficient : 0.1503
Prismatic coefficient : 0.7419
Vert. prismatic coefficient : 0.5968
Wetted surface area : 42.697 [ft2]
Longitudinal center of buoyancy : 6.380 [ft]
Longitudinal center of buoyancy : -12.767 [%]
Vertical center of buoyancy : 0.249 [ft]
Midship properties:
Midship section area : 0.662 [ft2]
Midship coefficient : 0.2026
Waterplane properties:
Length on waterline : 16.125 [ft]
Beam on waterline : 8.713 [ft]
Waterplane area : 35.376 [ft2]
Waterplane coefficient : 0.2518
Waterplane center of floatation : 6.451 [ft]
Entrance angle : 11.861 [degr.]
Transverse moment of inertia : 56.680 [ft4]
Longitudinal moment of inertia : -1429.1 [ft4]
Initial stability:
Transverse metacentric height : 7.408 [ft]
Longitudinal metacentric height : -180.26 [ft]
Lateral plane:
Lateral area : 4.118 [ft2]
Longitudinal center of effort : 7.745 [ft]
Vertical center of effort : 0.224 [ft]






And here is the Flat bottomed version...another 95 lbs displacement for the same draft but I really don't know if it is needed. Unless you are carrying a lot of dense stuff, there isn't really a whole lot of volume for the extra weight.




Design length : 16.878 [ft]
Length over all : 17.375 [ft]
Design beam : 3.020 [ft]
Beam over all : 8.750 [ft]
Design draft : 0.375 [ft]
Midship location : 8.439 [ft]
Water density : 63.989 [lbs/ft3]
Appendage coefficient : 1.0000
Volume properties:
Displaced volume : 9.345 [ft3]
Displacement : 0.267 [tons] 600 lbs in salt
Total length of submerged body : 16.127 [ft]
Total beam of submerged body : 8.713 [ft]
Block coefficient : 0.1773
Prismatic coefficient : 0.7218
Vert. prismatic coefficient : 0.7001
Wetted surface area : 44.177 [ft2]
Longitudinal center of buoyancy : 6.492 [ft]
Longitudinal center of buoyancy : -12.072 [%]
Vertical center of buoyancy : 0.226 [ft]
Midship properties:
Midship section area : 0.803 [ft2]
Midship coefficient : 0.2457
Waterplane properties:
Length on waterline : 16.127 [ft]
Beam on waterline : 8.713 [ft]
Waterplane area : 35.594 [ft2]
Waterplane coefficient : 0.2533
Waterplane center of floatation : 6.419 [ft]
Entrance angle : 11.864 [degr.]
Transverse moment of inertia : 56.721 [ft4]
Longitudinal moment of inertia : -1423.5 [ft4]
Initial stability:
Transverse metacentric height : 6.296 [ft]
Longitudinal metacentric height : -152.10 [ft]
Lateral plane:
Lateral area : 4.095 [ft2]
Longitudinal center of effort : 7.782 [ft]
Vertical center of effort : 0.224 [ft]

[Sailor]

Where do you keep your light sabre? That thing looks, from above, like something Luke Skywalker would have.

[paladin]

Is this a powerboat or intended to be a sailboat......

The "Outriggers will have to be longer to get more volume. The outrigger hull will have to support 100% of the weight of the multihull under hard sail....
they need to be longer and forwayrd to at least 15-25 % aft of the bow otherwise you risk tripping in waves...pitchpoling ain't fun...I did it in an Aussie boat....
As the boat heels the floats are buried at an angle, you can either make them assymetrical or cant them outward about 8 degrees.
I don't see a centerboard...undersail it will be very difficult to control...no longitudinal stability.

I are just an amachoor at this so whadda I know.

[B_B]

I thought the idea of ama's/outrigger's was to keep them out of the water until needed - reducing wetted surface at low speed or angle of heel?

?

[Y Bar Ranch]

some random thoughts from a budding designer/analyst...

A rolling moment would also result in a nose down pitching moment since burying an outrigger would move the center of buoyancy of the craft aft.

The outriggers would be interacting with the waves coming off the bow in ways I don't understand. I'd guess in a good way at some speeds and not so much at others?

What if you had the outriggers in the front instead of the back? Not as sexy, but all three hulls would be hitting clean water.

Last, it kind of looks like an LCS.

[JimD]

I think Chuck said most of it. It still looks like its geared towards paddling or possibly motoring. For an emphasis towards sailing the amas need to be bigger and farther forward. The sail is going to drive the hull down precisely where there is little to keep it up. Also the main hull looks like a kayak with a transom. It needs to be narrower at the waterline for better performance, assuming you'd like decent performance. These are the reasons sailing tri's look the way they do. That triak looks nice in the pics on very flat water but I'd be curious to see some video of it sailing in a blustery chop. So it looks like what you've done is redrawn the boat that inspired it, and unfortunately, little else. Sorry to sound harsh. Frankly, I think I'm on the right track with my own kayak to sailing tri conversion. Its a narrow beam hull so it will end up about 20" waterline beam, which is still a couple or three inches over optimum. The amas are 12 feet long, the crossbeams 8 feet apart, meaning there is still room for a proper paddle stroke. Of course its all going to end up a little brawny and heavy for paddling since its main purpose is sailing:

[mommicked]

I don't know much about outriggers and sailing kayaks, but that basic hull looks like the kind of kayak my wife wants me to build her. Most kayaks are too narrow for her non sea-faring self, and she wants something with more beam and less speed. I also like how you did the broad transom (looks nice) but she's practically double ended at the water line. Nice touch.

How wide is the main hull at the waterline? How much will she displace, and how many sheets would it take to build her, if you don't mind my asking?

[huisjen]

My understanding is that if the main hull is going at hull speed, the amas should be sized for a matching hull speed, i.e. the same length, or at least close. I don't know if anyone can talk about modeling the wave interactions of the hulls at different speeds and distances apart.

Dan

[Dan St Gean]

It does look like a triak with a twist of having a cockpit with the ability to sleep in. Good ideas to keep it light. You'd really be in the same performance range as the BSD sailing rig stuff, without the advantage of being able to stow it as easily. I think you might be better off either moving the amas forward like some other posters mentioned, or going with longer amas like Chief over at watertribe is putting together. If the point is to be a paddlable sailboat, what percentage of loss are you willing to deal with under paddle? Is it more like the Warren kayaks with big rigs or is it more like the Triak? If the latter, it's going to need a pretty small rig like the BSD 32 or possibly 38. This is less than an Opti although the hull form should be a bit more slippery. It's tough to design a really good paddling hull that is a competitive trimaran and vice versa. I suppose it's best to design for the paddling side of things since we humans produce so little power compared to sail. Its a facinating conundrum!

Dan

[B_B]

is it just me or does this picture look completely photoshopped - no bow wave or spray, sea looks positively still (no blur)...