I've been to the Paris boatshow yesterday and made some pictures of the new planing hullshape that is used by new Mattia F18 and the new 16 footers by Mattia and Ventilo.

go to http://www.catsailor.com/forums/sho...ge=0&view=expanded&sb=5&o=14

to see the pictures.

This is a link to a thread of posts on the F16 forum so if you are not interested or even offended by F16 talk than just skip those parts or don't follow that link.

Wouter

Wouter, nice pics.

Interesting hull design, if that won't plane, nothing will.

Are you sure they didn't put the hull on upside down?

http://www.geocities.com/f16hpclass/F16HP_boat_show_ventilo_zipo.html

There are a few others that I didn't post on this forum

wouter

Thanks for the pics Wout.

The turbulator is intended to help keep attached flow around the boards and or stern would presume ,-does this theory work from tank test to reality on these boats .-

Funny ,I built a similar flat bottomed hull shaped cat in 87 with similar rocker profile and pinched bow sections .I missed it by not having enough hull cant ,-had 3 degrees only , of course nothing like this had been attempted .
Also used 2 smaller attached foils-boards on each hull set at the outer edges paralell to each other so the planning effect would not be disturbed by the boards in the hull center where hydrodynamic lift forces would be at work .again the reasons for the turbulator .

It worked really well downwind ,but just not enough time or $ to proceed at that time .Sure was fun though.

Been describing these types of hull shapes the last couple years on the forums in design discussion ,-it is nice to actualy see some being developed .

Have some old 35 mm slides ,-I,ll have to transfer to a web site and post em sometime .

The sport has always been about better faster safer boat developement which the direct competition of Formula type class racing brings .

thanks for the pics
Happy Holidays
Carl

Do the foils in the rudder make it pitchpole-prone? It looks like it would benefit from inclining the asymetric boards a bit to get some vertical lift (and bounce less)...

Is it faster then the Taipan, in practice?

Thanks,

I would butt.u.me. that the ventilators work under the same idea as the do on powerboats.... they "suck" air under the boat and then the boat is riding on bubbles and not just water...less friction. At these speeds, will be interisting to see how it works.

The foils on the rudders should control the attitude based on how they are angled... they could help or hurt you depending on their angle. They use something similar on the 14 and 18' skiffs.

Will R

thanks Will ,hi Luiz

Hard to imagine this tabulator working on a cat hull as it would on a power boat in flat water where it could draw air in .
cat hulls --2 -- sailing at speed ,--one is partially submerged well below the surface where air could be drawn in ,-given the amount of rocker in profile it will not lift the tab location close to the surface ,and the other hull should be already skimming or just clear of the water surface ,-the turbulator as applied does little ,-particularly in larger waves . Also the tubulance from air bubbles would reduce rudder efficiency ,-the cause of rudder cavitation and loss of steering at higher speeds .
Tank tests to reality , it will be interesting .Happy to see development ideas ,-hope this works and a great amount is learned from it.

Always pictured this type of planning cat hull more of a flat lined hull side profile .
The ideal cat hull shape we will see soon will be more canted hulls with full forward section flat planning shapes -with small molded in forward lifting foils projecting at a close angle parelell to the bottom flat hull,--an extention of it in effect .
Luiz touch on this idea with his folding forward foil concept .
This will help balance the cat under spin with the C E being more in line with C L R , lifting the back boards varying degrees to achieve this balance .
The other benifit of these forward lifting foils is allowing a longer spin pole and luff angle to the spin ,-which creates more lift from the spin ,-more similar to 18 skiff spin luff angles and forward settings on longer spin poles .

On the bump aspect , the ideal will be a boat that partially lifts up at speed ,but still sails through the waves to some extent ,-a balance between a pure planning type hull and displ.type hull for better low range speeds .
The planning flat canted hull with forward small foil combined with straighter fuller aft sections more in line with planning powerboat hull shape design may be the ideal .
In lighter wind these types of planning hull shapes would need to be sailed in more of a bow down attitude lifting the sterns more ,-which we do anyway ,-just moreso .

What I experienced on the flat planning hull sailing it briefly was a suttle different quicker more independant hull motion through waves , not large differences .

Proper design-light weight ,-maybe larger beam or wings for more power sooner ,--sooner planning ,would be part of the design features required for this type of planning cat design along with others mentioned .-
Maybe this type will be the very hi speed planning HT FORMULA 20 CLASS in the not too distant future.
L-20 W-220 Sail ar 300 sq ft ,-spin 400 - beam 20 ft max with racks or wings . -
Put your helmet on strap in on with 3 on the wire and let er fly .-This would be worth watching on T V !!!
FALLING ASLEEP TRYING TO WATCH THE am cup .

fun stuff
Happy holidays
Carl

Carl,

I remember not too long ago you were talking about once sailing a flat bottom planing catamaran and remember you said it appeared to be very unstable and difficult to steer (correct me if I mis-interpreted).

I remember a while back looking into designing a set of floats for an R/C airplane I once had. You will notice that most, if not all, airplane floats have that same type of 'turbulator' and if I remember correctly, my research at the time indicated that that step (similar to the step in the old 'step hydrofoil' racing powerboats) was important for steerage and stability of the hull at slower speeds. Perhaps this is the intention of this step. I've got to report to jury duty here shortly but perhaps someone will have some time to research this a bit.

well, I had a few more moments and found the following text from this website http://www.stenulson.net/rcflight/watrfly2.htm. I gather that the step does introduce air into the water which makes the rudders more effective and it also increases the incidence, while in displacement mode, of the forward 'planing' portion of the hull so that it will climb out of the water and plane sooner (i.e. sitting still, the forward section is angled upwards and out of the water).




Task 1: Staying afloat (hopefully upright!) Requires about 130% of "Neutral Buoyancy" Displacement, and adequate setup dimensions as far as float length and float tracking width to remain stable in all, including crosswind handling conditions.

Task 2: Maneuvering, Low speed; requires effective Water Rudder Design; This task requires the ability to steer effectively at speeds below where the air rudder is effective, and in windy conditions, without inhibiting the Drag Reduction Task later... see the water rudder design section for more insight on this subject.

Task 3: Maneuvering, moderate speed, in what is referred to as "Displacement mode", where the floatation provided by the float's displacement carries the weight of the floatplane. (Wing does not generate noticeable lift at this speed, except for the upwind half of the wing magically jumping into the air when turning crosswind... (grin)) In this mode, the tails of the floats sit deep in the water, possibly completely submerged; if float tails are narrowed to a very narrow wedge, they will allow water to be drawn in along the sides of a water rudder installed behind the tail, providing very effective steering. Squared off "boxy" float tails begin to develop "Cavitation" in this speed range, and water rudders located behind the tails on this type loose steering authority before the air rudder is really more than marginally effective. (This has led many to design water rudders which extend well below the bottom surface of the float tail... fine for this specific task, but a serious liability in later phases when drag reduction becomes the critical task....)

Task 4: TRANSITION from displacement mode to Planing Mode As full power is applied, the propeller exerts all of the thrust it can at low airspeeds. The water seems to be clinging to the floats, not wanting to let them plane out and free. The wing does very little to help in this phase; it's not generating any noticeable lift for quite a while yet! To get this task done well, the float bottom forward surface design becomes the most critical operating area; step height and shape are also at their most critical in this task, as is step location relative to the balance of the entire plane. Here's what has to happen: the bottom of the forward float hull, working with the thrust generated by the propeller, and working against the drag of the water, has to "climb up" onto the surface of the water, getting the water to shear away from the sides of the floats, and then out from under the afterbody of the floats, leaving only air underneath, behind the step. We're fighting our main battle with the capillary action of water here; this capillary action helps a well designed water rudder stay effective at increased speeds, as it loves to follow rounded surfaces and edges, clinging rather than letting go too easily. Sharp edges are best for float bottoms, and sharply defined edges well under 90 degrees are better, while rounded edges are bad news in this effort to break free of the water's hold. Sidecut is also very helpfull; that's where the top of the float is narrower than the planing surface, and as little as 5 degrees has proven to be very effective.. Triangle rails along the very outer edges provide a sharply defined edge, either "tunneling" water under the float hull bottom surface, or cleanly shearing it away from the sidewalls, enhancing the effectiveness of the float planing surface, and are arguably the most effective edge treatment we've seen.

Step design and location also comes heavily into play in this task, and the next. If the step is located too far forward, porpoising can be the result- pitch instability and a failure to plane stabily; you will have to be on the elevator stick all of the time. If the step is too tall, this can also result in less stability in many aspects of operation, especially in the transitions. If the step does not have a clean, sharp rear edge at the rear edge of the float hull's planing surface, it will be more difficult to get the afterbody of the floats well clear of the water, which is essential for the next task. Too low of a step could also result in difficulties in getting the float afterbody clear of the water, but we're talking about an average step height on 40 size floats at 1/2" working well on a good design; an average step height of 9/16" works well on my 60 size floats. NOTE: if the planing surface is too narrow, it can't be fixed with a taller step; adding the triangle rails will help marginal floats. Raw brute power may make it work when an adequate engine can't get the job done, but the real answer is to have adequate planing surface width to do the job right in the first place. Remember, you want to have good handling characteristics on the landings, too.

-Really enjoyed the pics from the Paris boat show Wout thoughtfully provided ,-and really enjoy design related discussion of new ideas. The new boats are fasinating ,-and look well designed .2 sent e mail on this topic ,-both know more than I do ,but will try to define the ideas drawn out for this type of planning cat design that I have just for fun..hey they asked for it .
The intricacies of design and how they relate to one another is difficult and in rating boats even using a sophisticated cad design comp 3 d modeling and performance prediction type programs now available ,-it is still the big unknown quantity,-
How well do design aspects interrelate ,--mast to sails to variation in shapes -to volume calc -C E to CLR -handling characteristics ,-tuning and boat handling by skippers of different ability. all unknown and subject to endless refinement.-Any cat design is subject to this type of needed refinement and improvement as part of the process.

Basic current thoughts on planning cat design are
1-basic hull -The need for more canted hulls that place the flat lifting bottom hull at optimum angle just beyond designed heel angle that result from sail forces at work and resulting heel angle are key , This varies dependant on beam and hull volume, and planning ability .
If a typical cat w 8.5 beam is drawn out at a sailing heel angle with the windward hull skimming the surface its is approx 12 degrees , more in waves ,--More hull cant is required than this min. due to side forces and keeping the hulls on plan once there. You do not want a hull type that falls off plane.--This is one main problem with the pure foilers .
2-allignment of hulls in relation to one another , -
Canted hulls do not allign . Bow down tendancies of cats as they accellerate with wind-sail forces are the problem . A canted design with deeper bows will become more mis alligned causing form drag, once one hull lifts ,no problem ,but at lower speeds a large problem . We have seen some C Class designs with a destinctive toe in look for this reason .-The other direction for canted hull design is more volume and less depth at the bows as we see in some newer design with canted hulls .The Inter line is an example .This lends itself to developing the planning hull.
Balance and lift --
Sufficient flat bottom hull area at correct sailing heel angle being designed in may be assisted by a small forward foil or board ,-it may be retractable or molded in , pictured as an extention of the bottom angled hull back from the bow ,-It would require a swept back leading edge to avoid damage and enable beach landing . Standard boards further aft would provide tracking ability as in most design though further aft to balance CLR with forward foils.The leeward working foil would provide added lift and the windward would provide some resistance with its reverse angle . This more forward CLR with back boards partially raised when under chute should allow a more forward position of it in sailplan and still balance the helm well. Key for the skiffs is a higher luff angle set on longer spin poles that help provide more lift from the chute .
Multiple benifits from the extended forward foils.

This type of cat should track in a straight line well and have sufficient side resistance from foil boards rudders and L and v shaped straighter hull lines.
More mast rake in the design is important and hull volume aft to carry crew weight with more straight line profile more consistant with planning powerboats is needed ,-though am unsure to be honest. More beam -wings or rakes with more power in the sailplan are the huge advantage multihulls have over monohulls that just tip over without this stationary initial stability.
A larger dagger type retractable rudder may also be a needed part of this planning type cat design for added control and balance options , I like the through hull type with a wide flat planning stern would look good and be very strong and simple ,-2 moving parts-- the rudder and circular hull section fitting it slides into .Think the Olsen 30 uses this currently.
Again this fits into the intricacies of this type of hull design .
This type of larger balanced rudder may be able to take the place of aft boards in some design applications .It would reduce weight and -area further.
Light weight is crucial along with all other elements of proper design ,--just a hobby of interest for me but always fasinating to talk design ideas.

Please add your ideas to it .

Have fun
Carl

Carl-
I was actually thinking the "ideal" planing cat might be rather narrow beam between the hulls with wide racks for righting moment and the intent of the design to have flat surfaces when the boat is level utilizing BOTH hull sterns (and a possibly retractable flat "panel" that would drop down or extend down from the rear beam between the hulls??) to plane when conditions are good for planing but the ability to "fly" one of the hulls when planing conditions are poor (due to narrow inter hull beam, tall powerful rig, and ability to bring crew weight where needed- even to leeward!) and so when the hulls are canted (at that 12 degrees or whatever) the in water hull shape would more nearly approximate the current designs (long, narrow and circular)-
What do you think??

Kirt

Kirt, your making it sound like a skiff. *chuckles*

Hi Stewart -Kirt

or a tri --there are great foiler tri designs with the design intended to lift the leeward working ama -
A center planning type tri hull could be added .

Weight complexity etc would be the drawbacks of the planning hull Kirt descibed .
Both hulls would help but when is a cat sailed level at speed ,

Think there is suffecient area in a hull as descibed along with a small forward angled lifting foil set at correct cant to plane .

Some in certain flat water high wind broad reach conditions have felt this on I-20s ,-the boat hitting over 25 on the GPS and feeling really skittish at those speeds ,-trying to plane.

The combinations of proven ideas and design concepts have to be refined ,sometimes in a trial and error process but the intricate combinations of solutions to the planning cat hull are progressing .
Fun stuff ,-hope we see some planning types soon .
Carl

If I recall correctly.. I believe it was Beasho or fat boy (murray)(maybe monkey (bethwaite)) that designed (never built) a skiff..
That had foils on the sides of the wings.. a windward cantered mast with a genacker.. In theory the boat planed till it lifted on the foils..
In reality it would have been a tri.. with a planing centre hull.. Much like the foiled moths we have here..
Being 30 od feet out on a wing and on foils.. thanks but no thanks..

Carl,
==see inside:

CARL-or a tri --there are great foiler tri designs with the design intended to lift the leeward working ama - A center planning type tri hull could be added .

LUIZ - Exactly. And unlike a cat, you can force a tri to plan in its aft sections by means of slightly inclining the amas forward. When it heels the main hull authomatically raises the bow. This design feature is also good to prevent pitchpoling and maintain a good angle of attack for the foils.

CARL-Weight complexity etc would be the drawbacks of the planning hull Kirt descibed. Both hulls would help but when is a cat sailed level at speed. Think there is suffecient area in a hull as descibed along with a small forward angled lifting foil set at correct cant to plane .

CARL-Some in certain flat water high wind broad reach conditions have felt this on I-20s ,-the boat hitting over 25 on the GPS and feeling really skittish at those speeds ,-trying to plane.

LUIZ - ...but finding an insuficient planing surface. Add the foils and it will fly. The Catri 27 was reported sailing at (sustained) 27 knots in flat waters - planing on foils and main hull. The designer expects speeds approaching or equal to Open 60s in equal wind/wave conditions (but the tougher ones, naturally). Planing cats should be able to sail even faster because they don't carry a cabin, head, etc.

CARL-The combinations of proven ideas and design concepts have to be refined ,sometimes in a trial and error process but the intricate combinations of solutions to the planning cat hull are progressing .

LUIZ - I hope to see planing multis become dominant eventualy. It is only a matter of time.

CARL-Fun stuff ,-hope we see some planning types soon .
Carl

LUIZ-Yes!

Hi Luiz

Great post ,-design discusion -ideas are always fun .
Like to throw out ideas for designs and hope it inspires others to be inventive and creative . I really enjoy beautifull design in 14 ft cats or 120 ftrs ,-tris , sailing craft of any type .

Happy Holidays
Carl
p s
you may have left out an att pic ,--not sure

Stew-
I believe there is such a boat pictured in Bethwaite's book- Had small ama's as I remember rather than foils on the end of the racks and was a single hander-

Kirt

Just noted on Scuttlebutt Europe that Yves Parlier has designed and is building a BIG planing cat!!
Go to http://www.parlier.org and check it out!

Kirt

Kirt,
I know Frank Bethwaites tri (surf ski with wings and almas)but that is a completely separate beast to what was proposed..

The "ultimate 18"
Working back into vague memory banks.. (it was in the early 80s)..
Hull was nomex carbon back then this was radical..
cantered 20-30 degree to windward wing mast (to get lift al la wind surfers new back in the 80s).. Jib and genacker (thinking this means it was "beasho" who wrote the article Australian sailing, as beasho was the guy who reinvented the genacker)..
Mast was held by the wings (sorry cant recall the wing widths but guess it could have been 30 foot..)
On each wing was a surface piercing "plate" .. Imagine a smaller version of foiled open 60 "Hydroptiere" (sp?).. Then you have the idea..

Fortunately for the 18teen guys life insurance companies under the old 18teen rules this would have been classified as a tri.. Thus never built..