Open source 12-15m high performance/semi-cruising catamaran design

[groper]

Hi all,

So ive basically decided to see where this goes...

ive come up with a rough design idea for a performance cruising catamaran design which is definately biased a little more to the performance end of the spectrum rather than the heavier cruising style of boat.

The idea of making the design open source is to allow many contributers to the idea and see where it can end up. Many minds contributers should result in a far superior design thats well thought out before anyone attempts a build of the design. Im not sure how the file sharing system will work as we all need to use a compatible software model so that we can make changes and share them and over time and continue to build a comprehensive design. Once the design has been hashed out, anyone may download the full design and start building it via CNC plans, 3D printing or by whatever other means you so desire.

First of all, im looking for expressions of interest from those amateur or professional designs who wish to contribute and your ideas on how we can make this work. Please post here if you have an interest in performance cruising sailing cats and have the ability to contribute to the design in any way, large or small. Im sure we we all have our forte`s, let us know who and what so we can get started. Ill post a few images of what i have so far - and we can go from there.

Just need to finish some work and ill be back to get things moving...

 

[groper]

So basically this is where ive taken things so far and gives a feel for where i want to take this.

One thing that is new - well at least i cant find evidnce of people doing it before, is the combined use of vertical dagger boards and curved daggerboards which are offset from one another in a fore/aft manner.

The general idea is that the forward curved foils provide lift in fast reaching and running conditions to reduce WSA and located in the forward biased position will lift the bows more than the sterns to keep the trim flatter rather than bow down and burying when powered up and running downwind. The curved foils are not designed contribute to leeway resistance as they are almost horizontal. This is an arrangement used on the fast trimarans of this era and the curved foils should also be housed in a box which allows for fore/aft rake control to control the Angle of attack. These boards can reduce the lift via retraction and also angle of attack control.

The second pair of dagger boards located aft of the curved foils are strictly for leeway. They are canted inwards so they are more vertical once the boat is heeled. These boards are basically like the centerboard of the same above mentioned trimarans - something the modern tris cant do. There is also the other added benefit of both boards on this cat can be assymetric for increased lift/area compared to symetrical - again the tris only have a single symetrical center board.

Of course there are drawbacks- 4 boards instead of 2 or 3 for a tri. Thats added weight and cost. Thus i doubt this arrangement would benefit smaller catamarans but be better suited to larger cats where the added weight is not a problem to carry in the grand scheme. Also this is not intended to be a fully flying foiler like an around the buoys racer but rather as an ocean going boat. The benfit of the pitch damping of the forward foils is a proven concept and the improvements to safety and comfort are notable in all modern passenger ferrys and other ships using foil stabilization for seakeeping benefits.

In this arrangement, all boards inc rudders are retractable so there is benefits to marine fouling and shoal water navigation ability. There is also the ability to retract the lifting foils and eliminate the drag in light conditions where there is insufficient speed to create a lift advantage by using them.

Ive played with various accomodation layouts already - ive simply left the cabin design off in these renders to create more of a blank page idea in peoples minds

A few drawings to show the concept so far;

foils

• groper
• May 9, 2017

foils front view

• groper
• May 9, 2017

elevation

• groper
• May 9, 2017

 

[Gwion]

Looks like a fun project.

May I preface this with I know nothing.

The forward lifting foil looks interesting. Does it have be be in the hull?
The further forward you move it the greater the lever arm so the smaller (lighter) the foil required.
What about reducing two down to one. Mounting it under the forestay / fore beam with the ability to rotate it aft up under the tramp
when not required.
With no case to worry about you could use a T foil like the moths with a wand controlled trailing edge flap all in the one structure and self contained.
With the ability to cant the structure to the leeward side it would then provide more vertical lift when heeled.

So two curved foils and cases and adjusters all down to one pretty much self contained easier to build unit that won't compromise the hull if hit.

The structure could be designed so that any flex, as it loads up, results in more lift . The opposite happening could be interesting.

Please don't hesitate to tell me to go away if this is silly.

 

[groper]

The thing is - and others have suggested it also -with using 1 foil per hull is you cant optimize the longitudinal position of the vertical component and the horizontal component.

I think we dont want the foil too far forward or it you dont get as much of the hull to lift before it pitches up too far. This positioning is extremely important. With it done right - you get a reduction in WSA as the hull is partially supported by the foil with a slight bias toward lifting the bow as it does so. The calculations involved with getting this part right are over my head at this point - hence starting the thread It must be balanced with the driving force of the sails.
If attempting to use a single foil for vertical and lateral lift the position of the foil is restricted to the center of effort of the sailplan so that the boat is balanced and doesnt laterally load up the rudders.

The big racing trimarans already have this figured out - if you look at them you will see that the ama foils are further forward and the central hull dagger board is raked quite heavily aft to get the correct position for the lateral component. All im doing here is putting both components in a single hull as opposed the trimaran using the central hull and the ama for each purpose.

But theres alot more to the design than just the foils - so please lets not get all hung up on just the foil part of the design. Its just an idea and rather than keep it to myself i thought id share it...

 

[UpOnStands]

you get a reduction in WSA as the hull is partially supported by the foil ...

suggests that you get the negative points of foilers - serious drag etc - without the benefit of true foiling speeds - the hulls are never completely clear of the water.
Of more interest (to me) is how much the COE can be changed by varying the tack point of the jib.
see Saint Barbara https://www.ericwsponberg.com/boat-designs/saint-barbara/
this design was for a mono but catamarans would be easier (?) to design for.

 

[jorgepease]

I also know nothing but since it's performance oriented why not use water ballast to keep trim, that's been done. When I look at it, it seems like the short foil will have problems in waves, seems like you are going to stick, rise, stick rise and end up going slower.

 

[groper]

Why would that be the case when the racing trimarans have already proven the concept?

Think of like this.
Take a mod 70 tri or new multi 50 tri or similar. Remove the center hull and put the dagger board into the port hull. Copy the dagger board and put another 1 into the stb hull.

Remember that the lee hull is heavily pressed into the water in reaching/broad reaching conditions. videos of the tris rarely show it ventilates...

Water ballast...its not as efficient, why carry around extra weight? If ballast was advantageous, theyd be doing already on the racing multihulls. Its more efficient ro lift the front end rather than weight down the stern...

 

[Ad Hoc]

The idea of making the design open source is to allow many contributers to the idea and see where it can end up. Many minds contributers should result in a far superior design thats well thought out before anyone attempts a build of the design. ...

Design by committee rarely yields a good solution. Classic case of too many chefs in the kitchen...nice idea though

 

[jorgepease]

The new Hydroptere website: Home :: L'HYDROPTÈRE - Alain Thébault http://www.hydroptere.com/

---------

Points of note:
--Hydroptere IS the fastest sailboat on the planet-currently holding the record of 51.17 knots over a nautical mile.
--Hydroptere is the largest sailboat ever to go over 50 knots.
--Hydroptere carried at least 10 crew setting her records-more than any other speed record setting craft.
--Hydroptere is the only sailboat to have gone over 50 knots with an onboard head.
--Hydroptere is the only speed record setting sailboat to go over 50 knots
without a wing rig.
--Hydroptere is the only speed record setting sailboat to use a movable water ballast system.
--Hydroptere is the only speed record setting sailboat to have an auxiliary engine(like many other ocean racers).

 

[UpOnStands]

too many chefs in the kitchen..

kitchen just caught fire

What are we shooting for? Clearly not what has already been done.
We need an SOR. 14m LOA 7m BOA. 26k in comfort in up to 30 k wind speed. Will sail in 7 knots, tacks thru 80 degrees.
light ship displacement 4500kg. cruising allowance 1200 kg.
Basically incremental improvements.
Any other goal points?

 

[jorgepease]

True. specs first. I can't contribute in knowledge but I can help if needed in drawing the concept, nice thing about these softwares is it's so easy to collaborate.

 

[UpOnStands]

Is "26 knots in comfort" even possible? I've done 30+ knots in a speed boat but it was not "comfortable". 14m at 20 knots? Maybe active hull control is needed.

 

[jorgepease]

Every speed boat I was in was planing and would require a kidney transplant at high speeds but the big go fast boats don't seem to care, they pass us doing 45-50 while sprawled out on bean bags but it still turns their insides to jelly and they have a hard time walking next day. I know a few of these guys, cracks me up. I suppose a catamaran is supposed to cut through waves so up to a certain point can see it being ok and then after that point it's rodeo time! lol

 

[groper]

Ive watched alot of ocean racing videos over the years and i follow all the major sailing teams and their acheivements. 1 thing that really stands out to me is the impact of the patial foil support systems on the boats ability to maintain speed safely in a seaway. The modern tris are achieving incredible ocean crossing speeds now- like the last trans indian ocean record of circa 5500nm in 4 days by idec sport.

These boats are not full foilers. Noone has yet proven that full foiling is feasable or advantageous in ocean racing - it may happen one day but not yet. But the point ia partial foil supported boats using the curved foils located in a forward position - idec sport curved foil is almost as far forward as the jib tack on the deck!

Its very apparent to me this type of foil provides many advantages and i dont just mean speed.
The pitch and heave damping these foils provide is very significant. I even thought about fitting them on my power cat for this reason alone. The improved seakeeping is well documented not just in sailing but also commercial power boat designs and high speed ferries etc
They also balance the pitch forward when driven hard and that avoids the bows burying like you saw in the video above of the schionning cat. This means a drier and also safer sailing experience.
So back to the requirements...
The requirements are;
simple to build ie all developable surfaces,
Lightweight foam sandwich construction so that smart infusion construction can be used and deliberately designed to reduce the complexity and cost of the build ie keep costs to a minimum,
Enough interior volume to provide a reasonable level of comfort and amenity for 1 couple on extended cruises in tropical climate waters and perhaps room for the odd hitchhiker etc,
An emphasis on sailing performance to provide exhilarating and competitive experiences in regattas but also so the boat always sails rather than motors even in lightwinds and when the wind is hard on the nose,
The ability to cover +300miles per day in favourable conditions,
Shoal draft with retractable appendages for beaching and exploring shallow inlets etc.

 

[Doug Lord]

Farrier Curved foils: