Planing Trimarans

[CT 249]

Originally Posted by ActionPotential

For me it has to be hydrodynamics only but I am happy with just skimming, I just can't accept the inbetween because I can't see the justification of where you draw the line.

What boat can be supported by hydrodynamic lift only? There's a thread here by skiff designer Alan Smith that says (I think) even an 18 Foot Skiff going flat-stick has something like 30% of its displacement supported by buoyancy. Ergo, no dinghy or skiff planes according to your definition. That seems a bit harsh.

Thinking of the waterflow over my speed and slalom boards makes me think they have an element - very small, but still present; of buoyancy lift. So it seems that neither speed boards or even water skis at slow speeds plane under the proposed definition that all lift must be dynamic.

Isn't there a fairly commonly expressed definition that planing is when dynamic lift lifts the boat's centre of gravity above its static level? While it's not really practical to work out, it is a distinct line between planing nad non planing.

[mike leneman]

Well, I think that is what Chris and I have been saying all along. The hydrodynamic lift is always just a percentage of the overall lift. On a planning sailboard or skiff, etc. the percentage of hydrodynamic lift compared to static lift is pretty high......and look at the shape and area for planning. It's flat and a pretty big (as a percentage of boat) area as well.
This is not the case for the center hull of a Farrier tri. There is a pretty small area, it's not flat, there is a lot of rocker and the percentage of lift is pretty small.......I'd say less than 10%, if that much.
Cheers,
Mike

[peerliane]

Thank you Mike
You are probably right about the time schedule but we give is goals like this to go forward. It's intersting to know that someone as already used ply and styrene sandwich. What kind of glue did you use?

About the design, I have to say that it is not because few people did follow this way that it is a wrong one. Designers and racers often do things wich are "already working". Look at these maxi multihulls (like 60 foot open before) ; they are all cats but tris are coming and I bet in few years there will only be tris... And it's not a matter of available material at the time. So let's carry on and we will see...

[mike leneman]

Peerlaine,
We used epoxy with fillers to bond the styrene foam to the plywood, then we glass the plywood with light cloth and epoxy.
Keep on building ! and keep us updated on the progress..........
Unfortunately these projects always take longer than we think.
Cheers,
Mike Leneman

[sailsocal]

Originally Posted by peerliane

We are currently building a 50 foot trimaran that (we hope) will fly. ...
We'll get an answer soon; our boat will be in the water end of february...
Thanks for anyone comment.

Did you do any computer simulations or build scale models of this design before starting construction?

[peerliane]

We did some calculations before starting anything and we also built dinghyes .On the computer the shape of the mains and of the floats start to give significant lift at 5 knotsof speed. What we are trying to imagine is the behavior of such triangle shape hull when it hits a wave; and we couldn't find any computer program able to predict this. Nothing is better than a full scale experiment. Given the price and the ease of building, we thing that it won't be a big problem to re-buid the amas afterwards for a more classical shape...
To Chris, I want to say that we are using polyurethane glue (the one that foams a littke bit) that goes inside the polystyrene foam ( 2 to 3 millimeters) , the bonding is very good. This glue is easy to use (no mix, sprayable) and cheap.
Sorry not to answer very quickly to the post; we are working hard ( and hot right now!)in the shed wich is computer equiped but no link to the web.

[Dan S]

Originally Posted by RHough

Cliff's Notes version:
Dave Culp who has forgotten more about the nature of sails and kites than most of us will ever learn is wrong. My Model boats look to me that the bows lift, so it must be the spinnaker. To support my claim I'll post some advertising and a link to a Swedish site that has nothing to do with boats.
Anyone convinced?

Can you say lame name recognition!!!

[Pericles]

There are a number of videos that show giant trimarans racing along with one ama and the hull completely clear of the water. In all cases, it would appear that the ama that is supporting all the boat weight is not planing, but is slicing through the water.

http://messingaboutinboats.typepad.c...ve_to_see.html

http://www.cammas-groupama.com/en/index.jsp

http://www.trimaran-idec.com/

Pericles

[lorenzo98]

hi
here some movies:
http://www.youtube.com/watch?v=ZL2_pGuksTA
http://www.youtube.com/watch?v=CxbaC5gOonY
finely after a lot of work my tri is sailing!!!
LL

[grumpy old man]

Originally Posted by Crag Cay

My comment (in posts 212 and 215) related to the aero dynamic lift generated by a windsurfer with the rig canted to windward and a monohull running deep and trimmed upright. That's why I posted the picture of a windsurfer.

And my question was, does the lift generated in these instances disqualify them (windsurfers and monohulls) from ever planing, as it would appear to contravene the stated definition that planing must be by 'lift from hydrodynamic forces on the hull only' ?

there is no lift created by a canted windsurfer rig all the pressure is downwards through the mast base or the sailors feet otherwise the windsurfer would be impossible to control... try ít and see.... the lad in the picture is bunny hopping over a wave and has been captured in a moment of time ... his next action is to put pressure down with his feet because if he loads up the rig he'll just nose dive ... wind surfers are the ideal medium to discover what happens at the point of planing because the board and rig are an extention of your body and you feel every nuance of what the forces and resistances are ....no maths theories needed .....ur either planing or ur not thers nothing in between

[grumpy old man]

if a planing tri is the way of the future then get a volvo 60 dump the lead attatch some outriggers and break a few world sailing records ... it would save a fortune in R&D ... i think not ..... mr farriers use of a center hull design that uses hydrodynamic lift to reduce W.S.Area and form drag by taking advantage of the transfer of displacement to the outrigger is not original.. but the fact that he has used this concept successfully in a comercially produced trimaran is .. he has been able to get the best compromise between hull volume and speed by producing a shape that will plane when the distibution of righting moment , displacement and boat speed are in balance (any body who has sailed a sinker sailboard will know exactly what i mean) ... His boats no doubt perform very well and the sensation of acceleration as the main hull drops the drag and the lee float loads up would give the impression that the whole boat is 'planing' . but a cat doing the 'wild thing 'experiences that same surge of acceleration from similar forces and they dont plane... planing trimarans dead down wind in a gale maybe .. in real life nah

Originally Posted by grumpy old man

. planing trimarans dead down wind in a gale maybe .. in real life nah

===================================
Besides the fact that a couple of the worlds best trimaran designers claim that their hulls plane(Farrier-main ; Antrim-ama) the same old same old just goes on and on and on.
From a Weta ad: " Sails like a fast planing dinghy, but without the fear of capsizing." And there is even a new design that calls itself a "trimaran/skiff". Now no one in their right mind would name a boat a "trimaran/skiff" if the main hull didn't plane,would they?
http://windcraft.net/index.php?optio...=144&Itemid=56
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Boating New Zealand claims the Weta main hull planes: http://www.tcdesign.co.nz/Weta_A4x2.pdf

[tobybirch007]

I'm not sure this is the ideal thread to make my first post, but I'm going to risk it anyway. I also didn't read this entire thread, it's just too long. But, I can't resist commenting on this subject.

My view of a planing hull would be one the rises out of moving water on it's own, with no power needed. I think a good way to test whether or not a hull is planing would be to attach an un-masted hull in a fixed location in a moving stream.

I believe the planing effect is caused by the vertical component of force when the fluid encounters a plane (hull). It's exactly like what happens when you stick your hand out of a car speeding down the highway. In a nonmoving boat, there is no planing force, therefore the weight of the boat is countered by the weight of the water displaced, causing it to float (steady state).

When a moving boat has a surface below the waterline, the force exerted on the hull is directed upward or downward (depending on the surface orientation) as well as in the direction of the original force. This is true unless the plane is exactly parallel or perpendicular to the fluid flow. The weight of a boat is lessened by this force, causing it to rise in the water in order to displace less water, seeking a steady state.

So, any hull I've ever seen will plane, it's just a question of whether or not the boat is loaded correctly and going fast enough. Also, on some level, all boats do plane.

I think the question should be "Does this boat plane significantly at realistic speeds to be considered a planing hull?"

And just to weigh in, I believe the farrier boats do not plane. I think the rising main hull is do to heeling about the ama. But, it is possible that the main hull is planing, causing the ama to bear large side-wind forces that make it appear to be bearing the weight of the hull...

[Chris Ostlind]

Originally Posted by Doug Lord

...And there is even a new design that calls itself a "trimaran/skiff". Now no one in their right mind would name a boat a "trimaran/skiff" if the main hull didn't plane, would they?

Other than the above conclusion as a representation of pretzel logic, some would say that the original nomenclature is pure genius.

[grumpy old man]

Originally Posted by Chris Ostlind

Other than the above conclusion as a representation of pretzel logic, some would say that the original nomenclature is pure genius.