4.75m Trimaran Project

Discussion in 'Multihulls' started by kaymaran, Jan 2, 2016.

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  1. kaymaran

    kaymaran Previous Member

    Happy New Year everyone.
    I am sure this will show up a lot of naivety on my part but here is the summary of this year new project I am looking to start fairly shortly. All comments and thoughts will be gratefully received – if anyone actually reads it all - well done...

    A brain dump really so I can hopefully hoover up a lot of thoughts from everyone out there.

    Requirements and Design Notes

    • Ply and epoxy construction as I am confident in being able to do this to a decent level of quality
    o 3 and 4mm mainly​
    o Some use of 6mm for internal bulkheads​
    o 12mm in place for specific reinforcing around mast step and aka/ama brackets​

    • Using an ISO dinghy rig for propulsion

    • 4.75m long main hull and ama’s

    • Approx 4.25m total width

    • It will be mainly sailed in the UK in safe coastal waters around Lymington / Bournemouth / Isle of Wight
    o I would like to do the Round the Island Race at some stage – if it works, is reasonably quick and is even remotely safe...​
    o We sail quite a bit around Mudeford harbour where we can get good winds in a sheltered pretty flat area​

    • Mainly 2 handed sailing with my wife, sometimes single handed either of us, occasionally with other friends
    o I am 75kg​
    o Wife 55kg​
    o Other friends rather more lardy at 95kg and 100kg respectively....​

    • Must be able to be stored in a standard dinghy parking space and be easily trailerable
    o Once built I will be keeping it at Mudeford near Bournemouth​
    o Max width 1.7m when collapsed​
    o Store akas in hull​
    o Use short stubby beams to hold amas flush onto main hull when stored​
    o We will also want to be able to easily trailer it to other locations for holidays etc so all elements to fit safely and securely into / around the main hull on the dolly then road trailer​

    • Quick and easy to assemble / rig ready to sail
    o No special tools required to assemble so simple slot together and locking with cleats​
    o Brackets on amas to be solidly mounted and akas will simply slot in​
    o Aka’s to slot into aluminium mounting tubes bonded into hull which will help to give overall stiffness​
    o All sheets, spinnaker and jib to be left in place in bags​
    o Basic process to get on water​
    o Dolly to waters edge​
    o Take off amas (on stubby storage beams)​
    o Slide in akas​
    o Slide on amas​
    o Tension trampolines which hold amas in place​
    o Tension mast with jib​
    o Whack on main sail and ready to go​

    • Light enough to be easily manoeuvred on land and quick on the water
    o Aiming for 120kg all up which I think is achievable including all rigging and hydrofoils​
    o ISO is 100kg hull weight and is fine to manoeuvre on land​
    o This might take a couple of iterations to get the weight down, the first will be about getting the design working and safe then tweaking where required​

    • Fast and safe
    o I have a need for something fast but as safe as possible as I have serious spinal issues so although I am mobile I can be slow and simply cannot afford a pitchpole event because I will almost certainly end up in a wheelchair for good this time​
    o Speed data for small dinghies / cats / trims seems quite difficult to find with this being one of the few I’ve managed to find:​
    o I regard myself as a fairly conservative sailor and will only gradually up the speed as we test and become more confident and gather data​
    o Hoping initially to be able to hit 15 knots fairly readily which I think should be achievable with the rig size, weight and huge stability. Then really see where we can get as the design progresses​
    o If some of the RS200 speeds in the table above are anything to go by then we have a lot more stability, not a huge amount more weight but quite a lot more sail area​
    o Seeing the docs about the Broomstick trimaran here http://www.foils.org/02_Papers dnloads/071111 Broomstick_4.doc leads me to believe this is surely achievable​
    o Having reached 12 mph (roughly 10 knots) many times in my kayak trimaran with either my 6.5 sqm main or a cut down windsurf sail in 30 odd mph gusting winds I can’t see these speed targets as unreasonable?​
    o Does anyone think my aims are realistic?​
    o Reasonably narrow but planing main hull​
    o Flat raised inner floor on multiple supporting bulkheads​
    o Possibly closed cell foam fill these for “unsinkable” benefit but added weight​
    o Could just partially fill to ensure safety but keep weight gain to minimum​
    o Reverse bow for​
    o wave piercing and to minimise reactive pitching to submersion​
    o reduce spray being thrown out which provides resistance and wet ride​
    o Pretty flat hull bottom with shallow V​
    o Pretty square beam​
    o Thinking 4.25m so 90% of LOA and huge righting moment​
    o Long thin amas for speed​
    o Sharp reverse bow for wave piercing​
    o Shallow V bottoms so not too much slapping on the water but still provide good low down volume for stability and some planing​
    o Tapering to the rear where less volume required and keeps weight down​
    o Powerful rig from ISO dinghy which is very adjustable​
    o 14.3m sq m main/jib​
    o Will convert the jib to be a roller furling system I think once we are past initial testing​
    o 18.8sq m spinnaker​
    o Use the simple ISO system for launching the spinnaker and bowsprit with one line​
    o Control layout will be altered significantly as main hull is a lot narrower than ISO donor​
    o Continuous kicker​
    o Barber haulers will be less adjustable due to width constraints​

    • I am aiming basically for something pretty similar to the Weta design for its capabilities but addressing my concerns with them particularly my other more general concerns
    o Price – I really can’t afford the approx £8k odd for a second hand one here in the UK​
    o All in I’m budgeting £2k including the £900 for the ISO for which I got a spare mast and 3 sets of sails (1 new, 1 almost new) so I will sell the remainder as a fully functional boat to recoup quite a bit of cost to fund the rest of the project​
    o Stability/Safety​
    o We will have quite a lot more sail area for not much more weight​
    o 14.3 sqm main/jib compared to Weta 11.5 sqm​
    o 18.8sqm spinnaker compared to 8 sqm screecher​
    o Pitchpoling​
    o Numerous videos of overpowered accidents on these that seems to result from the low ama displacement (particularly up front) and the amas are also quite short which seems to result in the submarining then turning the boat quite sharply​
    o My amas will be the full length of the boat with more volume up front​
    o The rear aka will be set very far back to give maximum ability to shift weight aft as required​
    o Lateral Stability​
    o I will have a much broader beam to give a much larger righting moment (Weta is 3.5m)​
    o Why buy when you can build?​
    o Prefer to make things where I can and this will be a huge learning experience​

    • Seating/Trapezing
    o Mesh trampolines must be easily attached / stored​
    o Will remain on the akas when stored then simple and quick lashing onto the ama and main hull​
    o Very quick lashing to outer ally beam on ama​
    o We will be mainly be sitting out wide and quite high so hopefully quite dry​
    o Outer edge of trampolines will have an ally spar between the aka/ama brackets on which we can sit right out or stand out on when trapezing​
    o Rear aka set far back for maximum weight distribution​

    • Style
    o I like the reverse bow look and think it will work well with the smallish chop we usually sail in and will help keep it flat​
    o Also reduces windage and will help point higher (I think)​
    o Keeping the sides pretty vertical at the front will reduce the spray going out wide​
    o Reverse bow gives a design challenge for the bowsprit / spinnaker / jib functionality – I want to reduce the chance of the spinnaker getting hung up when lowering which appears to be an occasional issue with the ISO​
    o Open transom for simple draining aft​
    o The amas to be canted so when heeled over they are vertical at approx 2/3 submersion​
    o Where the akas join the amas will be faired in to prevent water hitting square on and so reduce drag. I have seen this a lot with my Sport Tandem trimaran conversion – see video here at around 45 seconds: https://youtu.be/1nI3IfR-_V4. also causes a significant turning moment so whatever can reduce it will be good​
    o Akas to be curved up and away from the water then down to the ama unlike those on the kayak to keep the aka and trampoline higher from the water and reduce any potential drag​
    o Either in aluminium box section or laminated douglas fir like on my kaymaran​
    o Initially will be straight ally tube for ease and then after getting it on the water I can review the final lines required​
    o Regarding the finish I am currently on the lines of a mainly black and silver colour scheme​
    o Once the final iteration has been sorted then I can look at possible sail colours​

    • The mast spaceframe will be similar to the ISO and to be made initially from simple steel for easy fabrication and possibly transition to aluminium once design confirmed
    o The steel can be plastic coated quite easily and cheaply for protection in the meantime​
    o The spaceframe also helps distribute the loads around the hull as well​
    o The stay mounting points will be different but in the same proportion to the ISO​
    o Quite high tension is required in the mast stays so local reinforcement around the hull stay bolts is required and will be integrated into the spaceframe​
    o The mast step will also be integrated into the spaceframe to help spread the large compression load away from a point load on the floor​
    o There will be additional bulkhead reinforcement between the floor and hull around the mast step​
    o The rear of the mast gate will be open to enable really easy mast stepping​
    o Once stepped a simple drop in locking bar will provide strength and safety​
    o The front aka mounting will be integrated into the spaceframe again to spread loads​
    o The spaceframe will extend forward to provide a really strong jib mounting point​
    o Once spaceframe template has been tested in steel I can assess the weight saving by fabricating it in aluminium​

    • Adaptability for future design changes
    o High Priority​
    o I am very interested in foiling - initially around foil assist again as part of the safety at speed trade-off giving us extra stability up front and out wide to reduce accident potential​
    o With this in mind I am looking at and started making some test foils using the www.windknife.com extrusions but won’t have time to finish and test until at least early feb due to huge work commitments in the interim​
    o Seams will be riveted and spot welded then will be sheathed in multiple layers of fibreglass and epoxy​
    o My thought at the front is to use either canted surface piercing hydrofoils like these on the Whites Dragons catamaran http://horsesmouth.typepad.com/hm/2011/01/holy-flyng-cats.html but I will make angled slots within the amas underneath the crossbeams which will be integrated into the aka mounting bracket for strength OR fully submerged inverted T foils using twin vertical spars for simplicity of build and strength and rely on depth from surface to provide altitude control​
    o All of the forces should be transmitted through the bracket and beams not the amass reducing the requirement for excessive strength and weight within the amas​
    o Perpendicular supports can be built in that lock onto the underside of the akas for extra strength (similar seen in the pic above for Whites Dragons above)​
    o This also means that the foils can be pulled up out of the way when launching in shallow water (this will make hull beam even greater using the canted foils) and then once in deeper water can be slid down and locked in place when head to wind before sailing off​
    o If not sailing with the foils then gaskets can be easily attached to reduce turbulence​
    o At the rear use a simple inverted T foil mounted in the main hull with 2 vertical struts for ease of build and strength. The increased in drag not a huge deal for me​
    o I can then look at options of building into a single rudder mounted inverted T system​
    o Initially only use as foil assist but will then be able to extend the foils further to gradually generate more lift as we gain experience and confidence​
    o Initial test foil will be attached to kaymaran to gather data about the amount of lift generated​
    o The initial foil will be a relatively simple flat bottomed profile​
    o The front canting foils will sit inside a simple case which will then sit inside the slot in the amas. This will have a simple screw and shim adjustment system so we can adjust the angle of attack until we are happy and it can then be locked in place​
    o Altitude will be self adjusting using the canted front foil system at the front (or depth if using simple inverted T foil) and purely by depth on the rear T foil​
    o Possible later iteration could have a trailing flap system with a wand perhaps​
    o Low Priority​
    o I have a small electric trolling motor which I will be able to attach and keep the light LIPO batteries in a watertight bag container just for any emergency​
    o Flexible PV panels could be added to help keep the batteries topped up – I know the power generated is not large but for very little weight penalty it might add enough to be worthwhile​
    o I will make a simple lightweight structure that can be stored on the floor of the main hull which can be attached to the aka’s to provide a platform for a small tent if wanting to layup overnight. In a couple of parts made from lightweight ply spaceframe it can act as a false floor when sailing so is out of the way.​

    • Ability to get cheap spares
    o Loads of ISO dinghy kit around for next to nothing​
    o If other suitable donors are found then future iterations could be altered to suit​
    o Dos anyone have other suggestions with decent power / low cost​

    • Storage
    o This is designed for (hopefully) speedy day sailing over to the Isle of Wight and thrashing about locally so not really required but some lockable / waterproof storage useful​
    o The area in front of mast will have simple netted space to store a few dry bags​
    o Spare sheets, cleats etc storable in small storage compartments within hull sides​
    o Small lockable compartments possible in sides​
    o Possible camping platform as explained above​

    I’m happy to make one and test it extensively then I can always remake it after learning the shortcomings as the cost on the hulls/ama’s is pretty trivial in reality, it is more a cost in time than anything else. Obviously anything I can do now to reduce those initial errors all useful.

    I have attached a couple of images from FreeShip but currently don’t know how I can bring the elements together into one coherent design including creating the crossbeams etc. If anyone can help I could happily upload the files or if anyone can explain I would be most grateful. I can see I can export from one file as a part but I’m not clear how I can then position imported parts etc.

    I hope these give some idea of the shape/style. I have also uploaded the hydrostatics files as well if that is of any use / interest for people and might enable more detailed analysis / useful comments on the project. The amas are showing a leak point for some reason that I can't work out at the moment so this will need updating.

    Assuming weight estimates are roughly right the bottom of the transom will be on the waterline loaded up with crew. Is this about right? Once thrashing along and hopefully planing the back will plant down a little so should I sweep this up a bit higher?

    Is it likely that the hull will get up and plane? Can the hull be made any narrower and hence lighter and still plane?

    The first iteration will be made excessively strong and can then be fettled for a lighter faster version once the lessons have been learned from the initial tests.

    I would be very interested in people’s comments about the basic design and elements I can address them now.

    Well done for reading it all!

    Attached Files:

  2. Richard Woods
    Joined: Jun 2006
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    Location: Back full time in the UK

    Richard Woods Woods Designs

    Have you seen my 14ft Zeta and 15ft Strike 15 trimarans? One of those should suit you. One UK. Builder bought an ISO to use for rig and foils

    Richard Woods of Woods Designs

  3. catsketcher
    Joined: Mar 2006
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    Location: Australia

    catsketcher Senior Member

    Not a great start

    Your statement of use is very specific which is good, though there may be some contradictory requirements.

    I think the first one is the lack of mobility and the demand for high performance with low cost. If this is going to foil and have high volume amas then the crossbeams will need to be very well designed and more expensive. As Dick Newick said you can have two of speed, economy and accomodation. In your circumstance the accommodation is the nice helm position and the provision for extra people.

    The hull designs as they are at the moment are, to say it nicely, plain wrong. Firstly the reverse bows. Reverse bows are a function of inward slope of the topsides and not something that gets stuck on (or cut off) Your topsides are vertical so reverse bows are only an affectation. Most important is the unfair nature of the hull design.

    The main hull is a bit of a wedge and has lots of volume aft. The topside curve are unfair. Grab a book on yacht design and get a feel for waterlines, and buttocks. Freeship has a Zebra function that allows you to see unfairness.

    The float has uneven buoyancy distribution and a big flat deck. That is a definite no no in float design. Look at new designs - floats are very tricky to design - more buoyancy up front can INCREASE nosediving potential due to increase in drag when immersed.

    In my humble opinion you are at least a few months off a nice set of plans. My advice is to buy a design from Kurt Highes or even better get the Seaclipper 20 from John Marples. Great boat. You can't get a speedy, collapsible, easy to sail tri easily - it will take a very good designer.
  4. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    Personally I don't really get these super small LoA type trimaran designs unless there is some particular reason you have to have such a short waterline length. Is it to fit in a small shed or carport where does the 4.75m requirement come from?
  5. kaymaran

    kaymaran Previous Member

    Size and shape

    Thanks for the comments. It would have helped I think if I had put up the latest drawings not the earliest. I've attached them - I think they are rather more realistic. Waiting to be shot down....

    I have Richards Strike and Zest plans but neither quite suited me so I thought try and do something that does.

    Quite a lot of the looks with the sweeping up front are purely affectation - I can picture it in my mind how I want it to look on the water. Whether it has a negative impact on the sailing I will find out but based on my skill level and what we will be doing I imagine it will be marginal.

    Kind of like my cars to a degree. I'm not the best driver in the world (can't turn my head and my hands tend to stop working) but I have an old Morgan (always loved the shape) that doesn't really look fast or special but is tuned up hugely with a V8 and weighs practically nothing. Push it too hard and you are in the hedge backwards (found that out on a Round Britain rally one weekend) but 90% of the time I am cruising and only give it some stick when completely safe or some tool in a modern car needs showing up......

    For old car purists it is heresy and for new sports car lovers the handling is lacking (initial understeer that can be corrected with the throttle into amusing but controllable oversteer) but it suits me perfectly.

    Once it is on the water I can review and adjust accordingly.

    Ref the size a couple of things I think. The ISO dinghy I have is 4.75m long but actually most importantly is the space available at the local dinghy park. They are very hard to come by it seems with most places full and with huge waiting lists. There are spaces at Mudeford however and the max they will take is this. Being able to reduce the size down to a normal dinghy width is therefore also critical.

    I also want something that me or my wife can single hand or go out together as the time/mood takes us so something that is safe and easily manageable is key.

    Also the New Forest where we are is massively busy and space for easy manoeuvring let alone parking the car and trailer while sailing is always painful. Being able to just jump in the car to get to it partly set up on the dolly will save a good whack of time.

    I currently take my kaymaran project on the roof of my car as it is really light but there is a bit of set up time walking everything across to the main (very small) beach where we usually launch.

    Lastly this is a nice manageable size to work on in my garage. I will already have to take one of the old cars out to do the work and put it in a temporary shelter for the spring while I get this project sorted.

    Many thanks for your comments so far.

    Attached Files:

  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Perhaps the first question is why a trimaran? It is the most expensive and complicated boat you can design and build. At that short length a monohull has many advantages. I think you decided on a trimaran instead of making a list of what you want the boat to do and then see which design best fits.
  7. Gary Baigent
    Joined: Jul 2005
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    Location: auckland nz

    Gary Baigent Senior Member

    Agree with Gonzo. And you are halfway there with your already wide main hull, chined design. Less than 5 metres length is too short for a trimaran main hull. Some here will disagree but you end up with too wide a hull - so to carry crew weight on a short waterline and your multihull will be probably slower than a planing and conventional mono dinghy of similar length.
    But if you are determined to go the Weta way (which is a monohull with floats, just imo) - then go for it. But a 5.5 metre length would be a better length to start with.
    There are some neat 18 foot trimarans (Sardine Run is one) you should check out in the Joe Farinaccio books.
  8. kaymaran

    kaymaran Previous Member

    Why a trimaran?

    I decided on a trimaran platform due to the stability and safety requirements mentioned above and I simply like them aesthetically.

    I have sailed a few dinghies such as various lasers and catamarans such as Darts and Hobies (Dart seemed a lot better boat than the Hobie - felt quicker and was easier to tack) but most recently Argo and Omega dinghies along with Topaz 14 and 16 catamarans. Stability, safety and easy speed of the cats was obviously good but we would have nowhere to keep one so not an option.

    Moving around on the Laser is quite difficult and painful for me and the possibility of tipping and the problems that would cause me physically are far from ideal.

    The Omega was obviously much easier to get around on but but felt like a big lump on the water and weighs quite a lot to move around on land.

    The Argo was a lot better and felt remarkably stable and we were able to get out through heavy crashing surf from the beach which most other people were struggling with and I was impressed with that. However new they are fr too expensive for me and there appears to be no second hand market for them - the one I saw was about £5k.

    However my wife wouldn't single hand one of these (or similar RS dinghies etc) as she could never move it around and wouldn't be confident enough to even if she could.

    We can't have a little laser just for her and something else for me as not enough space or cash for this.

    So we end up with a trimaran platform that will fit in the available dinghy space and can be moved around easily - and there are not that many options out there that fit the various criteria.

    Sardine run as an example is far too long for the space I have and too heavy to move around.

    I have looked at a Seaclipper 16 for example and like the central cockpit idea to a good degree (my kaymaran is similar) but it is quite heavy I think. They seem to go along at a good clip with a smaller sail area than I am looking at using and a beam of approx 75cm or so - so narrower than mine and I think quite a bit heavier than I hope to make it.

    I think therefore that the 4.75m length and trimaran platform fit my requirements better than a monohull or a larger trimaran so I need to work within those parameters.

    So within these possibly not ideal parameters am I to understand that I am just barking up the wrong tree with my idea?

    The Weta being a dinghy with floats is not a problem for me - is the Weta design not looked on favourably here? It seems to be pretty successful both commercially and practically - moving along quite nicely and pretty straightforward. If not for the cost I would be happy to get one of these but I do really like making things so doing something broadly similar holds a lot of appeal.

    If mine ends up being a dinghy with training wheels then I am certainly fine with that.

    Ref "halfway there" I'm not then entirely clear what you are referring to? Are you saying the main hull is too wide and therefore basically a dinghy? I think it is broadly similar to the Weta but can't find any data to confirm that and is about 14cm wider than the Zest from Richard Woods which is designed to be a single hander and is a foot or so shorter.

    Due to my lack of experience I can't say whether it will plane or not until I build it - if you think not can you give me any pointers or any alterations that might help with this?

    Ref the complication of a trimaran, I don't really see it as that complicated. My last kaymaran project was I know very simple but that went together very quickly and easily and I don't foresee huge problems in the build - trickiest thing will be the mast mounting to distribute the loads effectively across the pretty light hull but again using a simple spaceframe should resolve this quite readily I hope.

    Anyway thanks for any further comments that will help me bottom out the plans or abandon them if it appears they are simply unworkable.
  9. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Small trimarans --Untapped Potential!

    I think the Weta is a tremendous boat and using a planing main hull is a great design choice for small tris. I designed and built two small tri's -one 20' and one 14' back in the 70's-and many other boats since then . The 14, with planing main hull, was great fun-80 sq.ft SA and 80lb all up.
    The trimaran platform offers the designer lots of design latitude-especially when considering foil assist or full flying. Below, is a design with the main hull based on the Cherub called "Banshee Ambulance"(about 12' LOA) plus a concept model of a 12'LOA foiler tri 17' wide with plaining main hull and planing amas(designed to work with foils) . Foils on a tri help it to be able to safely use an oversquare platform to create lots of righting moment/ power to carry sail. To date most small tris have been designed to NOT use the max power available with the trimaran platform and there is tremendous potential for careful, innovative design particularly when incorporating lifting foils. I would suggest that you take a little time and study planing hulls for sailboats. Have you read Frank Bethwaites books on High Performance Sailing? To help you learn about foils there is a book directed at homebuilders called "Hydrofoils: Design Build Fly" by Ray Vellinga and available thru Amazon-a good way to learn the basics of the practical application of foils to small boats. Don't be discouraged but spend some quality time learning more about planing hulls,foils and rigs. I don't know how close you might be to Nigel Irens but he is a really nice guy and an innovative trimaran designer and it would be worth it to try to talk to him if remotely possible.
    I think you're headed in the right direction but I'm not sure you need such large amas. And consider an over square platform. You can build a folding system using hinges with a small sliding tube inside-if the folded height wouldn't be too much for your workplace. Good Luck!

    [​IMG] [​IMG]
  10. kaymaran

    kaymaran Previous Member

    Banshee - v interesting

    Thanks for that Doug.

    I hadn't seen the Banshee previously that is very interesting. I can't find much else about it anywhere.

    I have Ray's book and have been getting some rough calcs sorted out but will need to wait until things are basically together to make sure of my weigh distribution. I could be hopelessly optimistic with the weight I am aiming for.

    I'm also not sure how robust the foils will be so by keeping to simpler inverted twin spar T foils I can be confident of being strong enough but I'm not sure about how other options will work with my current level of fabrication skills.

    Step at a time.

    Main thing is to get a feel if I am vaguely in the right area. Actually building and having practical experience of the results will point me in the best direction.

    The plan is to make the aka's and ama's first and simply lash them onto the ISO and just see how that goes before committing to the main hull. I think that alone will be pretty instructive.

    Any thoughts regarding the current main hull and planing potential?

    Thanks for the comments.
  11. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    A T-foil used as a main foil will require an altitude control system. Relying on surface proximity for altitude control on a full flying sailing foiler will not work.Using it for foil assist can work if designed properly. One advantage of T-foils even with wands is that the center of lift can be further outboard relative to the overall beam of the boat than inward pointing surface piercing foils.
    Surface piercing/planing foils like used on the Quant 23(see last picture below) have real potential on a multihull designed to take advantage of their fairly unique performance.
    For a planing hull that is easy to build and exceptional in performance study the Windmill hull. Keep in mind that if the boat is an efficient foiler design it is likely to be able to foil before it planes. So you need to consider the implications of that fact in your design. In my trimaran designs that are foilers the idea is to rely on the planing hull after the boat foils and makes incidental contact with the water. Then, the drag is much reduced from a displacement hull doing the same thing. The disadvantage is that in "sea hugging" mode in extremely light air the planing hull will have more drag. But that can be rendered harmless by using a foiler design that allows the boat to foil early in say a 5-6 mph wind*.
    * Note that Quant boats has just announced a larger rig for the Quant 23 with the express aim of foiling in a 5 kt breeze with a recognition that foiling in light air is critical for a modern production recreational foiler like the 23. http://www.boatdesign.net/forums/sailboats/quant-23-foiler-scow-53468-3.html#post762136
    An example of this thinking can be found in the amas of Hydroptere. The early versions were short nicely rounded displacement hulls-you can google pictures(see below) of them. They found that when a displacement hulled ama made incidental contact with the water at foiling speeds it caused huge drag. So they changed the ama shape to the stepped planing hull she now uses.
    In a small tri a relatively narrow planing hull can be beneficial not for getting started but for dealing with incidental contact while foiling . A side benefit can be way more forward buoyancy to resist a pitch pole in the unlikely event it should happen.

    Hydroptere's stepped planing ama:


    Hydropteres original displacement amas:


    Quant 23 outward pointing surface piercing/planing foils:

  12. kaymaran

    kaymaran Previous Member

    The hydroptere style is my preferred choice as effectively self leveling and reducing moving parts for mechanical simplicity is always preferred I think.

    I'll see how confident I feel with my fabrication techniques when I get nearer the mark....

    If things look good I can always make much smaller ama's.
  13. redreuben
    Joined: Jan 2009
    Posts: 1,956
    Likes: 203, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Ray Kendrick has a couple of 12' designs that may interest you, he has some older designs which are no longer in his portfolio that were a bit slimmer maybe and had wave piercing type floats. You could stretch them a bit I would think.
  14. Gary Baigent
    Joined: Jul 2005
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    Location: auckland nz

    Gary Baigent Senior Member

    FFSake Doug, can't you turn off your endless neverending repeatable rewind of your usual foiling defecation; this guy wants a simple boat.
    But you're going to have to go longer than 4.75 m to carry two people.

  15. redreuben
    Joined: Jan 2009
    Posts: 1,956
    Likes: 203, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Gary, you just put him on Ignore and everything becomes readable again.
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