8 Responses to “J-24 Sailboat Converted to a Trimaran”

1. ian Says:
   October 21st, 2012 at 6:49 pm

   Can this please be the final nail in the coffin for the idea that all successful trimaran main hulls *must* be long and skinny for the boat to perform and/or track?

   Nobody seems to be manhandling the controls and the boat is obviously moving quite nicely in not a ton of wind…and the J 24 hull is 24′ LOA with a whopping 8.9 feet of beam. That’s tubby even by mono standards, but fast because it’s light and has very minimal draft (low wetted surface) and very flat aft sections like a motorboat so it can surf/plane even as a monohull hauling an extra 950 lbs or so of ballast and 3-5 crew.

   This thing doesn’t even have purpose designed amas and in the middle video you can see it accelerating and beginning to surf/plane and there’s hardly any whitecaps and no big swell, just wind waves…I guarantee you that boat is faster there than my Cross 24 would have been, and that boat was no slouch for its size and designed from scratch by a true master and design innovator.

   Throw off those “long and skinny is best” shackles and full displacement thinking and there’s a world of monohulls out there that would make excellent tri main hulls, that are already exceedingly fast in their own right whether on plane or not…and were designed by a true master and design innovator as well-

   http://www.flying15.org.uk/flying15/about.asp

   http://www.sail-world.com/USA/index.cfm?SEID=0&Nid=40824&SRCID=0&ntid=0&tickeruid=0&tickerCID=0

   “It is anticipated the hull and deck will weigh around 1000 lbs. ”

   a 33 foot FRP over foam boat that sans rig weighs barely more than what a stock J-24 carries as dead ballast weight, with an even more “correct” length to beam ratio than the J boat ( it’s still narrower than the J)…all in a boat that planes already as a ballasted monohull- food for thought.

   speaking of Uffa Fox and tri hulls- this one looks like a tri already, just missing its amas…and could use the same sized donor amas as the J 24-

   http://1001boats.blogspot.com/2012/06/fairey-atlanta.html

2. Stefano Says:
   October 21st, 2012 at 9:56 pm

   Ian wrote: Can this please be the final nail in the coffin for the idea that all successful trimaran main hulls *must* be long and skinny for the boat to perform and/or track?

   Well, probably yes…although from some other sites it may appear that this idea risks to be buried alive (check on w17 site for example). Other previous nails may well be magnum 21 trimaran (I personally measured a 1:6.3 bwl/lwl ratio, and perhaps what Farrier writes of his own tris: from TT 720 through F 27 to recent F 22: flatter run and wider (and a higher sail/dspl ratio).

   My own experience tells me that with little power (kayaks, lesser canvassed proa or tris) having a sleek long hull ( 1:10 ratio) with some angle to get on a plane on a small wave set may be beneficial, but it really needs to be narrow and long.

   A fatter hull needs more power. So if you do not intend to deal with tall masts and plenty canvas ( like more or much more than 30 sqm per metric tonne) , you’d probably be better off with a sleek hull with a flat run aft perhaps.

   I’m drawing my own tri a 22 ft. It is a design that needs to strike a balance between ease of construction, ease of conduction and performances, including carrying 450 kgs payload ( 1000 lbs on 22 ft). It will have some dihedral forward, to help get some lift to get on a plane, it will have a 1:9 bwl/lwl ratio roughly, not too much rocker – about 1 ft over 22 – and it will have a flat and wider aft run, carrying the mid ship section all the way back.
   It will carry 26 sqm of sail upwind, over 2000 lbs ( 0,9 metric tonnes fully loaded) roughly a 30: 1 sail/dspl ratio, but then it will have a gennaker and a 52: 1 ratio downwind or on a broad reach in lighter winds. In brief, I’m trying to get inspired by semi planing one step hulls of the beginning of XXth century with ( I hope) a target cruising speed capable of reaching the low teens with the mentioned modest power in a beaufort 3-4 (Mediterranean summer breeze). The amas will hopefully be two dart 18 hulls (we need to get them from the seller yet) thus capable of a more powerful rig should need be.

   ANYONE THERE WITH A SPEED PREDICTION PROGRAMME WILLING TO CHECK ON THE ABOVE MENTIONED FIGURES ? I’d love to receive some feedback before cutting the plywood.
   Bye to all, Stefano

3. ian Says:
   October 22nd, 2012 at 12:37 am

   Hi Stefano-

   The hull you describe sounds very much like the type of boat I’m talking about with the beam carried far aft…assuming that it has very little hull draft and the runs are kept very flat it should be very easily driven even at fairly wide dimensions whether it is truly on plane or not.

   I totally agree with you about kayaks and canoes being optimized for low power but I think the length/beam ratio is maybe getting more credit than it deserves as far as why these boats can make good small tri center hulls- they also are built very light as a rule and that makes for good tri building in general, and maybe even more importantly they are both hulls designed to remain upright in use, rather than working best when heeled over like many long, skinny sailboat designs of the past.

   That’s a huge part of what might or might not make a good monohull conversion and a lot of skinny mono hull width is about self righting from knockdowns and seahandling when heeled as much as it is about speed potential.

   Now of course when you say “canoe” most people in the US think of Indians paddling on rivers…but even with double ended canoe designs Uffa Fox managed to get them to plane very early on and knew exactly what he was doing-

   “…Flying Fish has the longest length and smallest beam permissible under the rules, and as can be seen from the lines, these dimensions produce a very easy and sweet-lined canoe. But when we look at the lines of these light and very fast sailing hulls we must always bear in mind that they plane two-thirds of the way around a triangular course, and even close reaching will get up and scoot along the top of the water, and for this reason their lines must be studied from a different viewpoint than that taken when studying an ordinary sailing craft.

   The sections are V’d forward, and are gradually flattened as they go aft where they are almost flat. The buttock lines also carry this out for they come down steeply forward, and then run aft almost parallel with the keel line, this giving the long flat run, necessary for planing.”

   http://www.intcanoe.org/iclife/hist/uffa_flying_fish.html

   note that the hull draft on this boat is 5 inches…there’s hardly any boat there at all, and that’s sitting still.

   here’s more-

   “Canoes sailing to windward or in light weather are travelling at a speed equal to the square root of their waterline length, or slower with the chine aft out of water. At such a low speed, the minimum wetted surface is important, so she has a round bilge for three quarters of her length.

   Off the wind in a fresh breeze, or a wind of greater force, she travels at up to four times the square root of her waterline; then it is that the chine aft tells its tale, for where the water clings to a round, it cuts clean away from a sharp corner. The chine also extends the planing bottom outwards and gives greater planing power.”

   http://www.intcanoe.org/iclife/hist/uffa_sailing_boats.html

   I don’t know that the above qualifies as a speed predicting program, but if Uffa Fox says you can do 4X theoretical hull speed in semi planing mode, then I’d be inclined to believe him…regardless you seem to be on the same path that he was and modern materials and a tri platform shouldn’t do anything but help.

4. ian Says:
   October 22nd, 2012 at 3:49 am

   here’s a neat video of some international canoes in action-

   http://www.youtube.com/watch?v=Exb6i3E3r-4

   very speedy in pretty light air and the hiking plank makes it exactly like a tri if the amas fell off and the guy is trying to get back to the dock before it capsizes…why not just put some amas back on and relax?

   Most interesting to me is the planing ability despite the relatively narrow double ended designs, which is a function of the boats having a very different bow and stern sections that look like a maxi ocean racer bow grafted onto a wide pin tailed surfboard with very hard rails (a chine). The difference between the super fine exits of traditional paddle canoes and kayaks and this flatter wider exit is the difference between hitting hull speed easily with man sized power input and then hitting a wall no matter how much more power you apply, or exceeding theoretical hull speed easily and regularly even with relatively small amounts of sail area.

   In the video, also note the almost complete absence of rooster tails or any visible stern wave or wake, and very little bouncing compared to similar sized racing skiffs going really fast…there’s obviously a lot more going on here than meets the eye when it comes to what will/won’t plane or go fast, and how to do it…these boats obviously use the power they harness very efficiently and would seem to be an ideal candidate for grafting some appropriate small beach cat hulls onto for a smoking performance tri conversion…

   I can see this-

   http://www.sailnut.com/international-10-meter-canoe

   with one of these as ama donor-

   http://nswptca.papertigercatamaran.org/gallery.html

   -making a very exciting under 250 lb 17 ft performance tri that would be a million times easier and more comfortable to sail than the canoe (or the cat) alone and would still be ultra fast for its size, for not a ton of money compared to anything else that would give you that kind of performance potential.

   It could satisfy the go fast planing hull types as well as the people who like the traditional pointy boats with fine exits.

   You could also build from scratch in ply-

   http://www.internationalcanoe.yachting.org.au/?Page=24752&MenuID=How_to%2F13919%2F0%2F%2CBuild_an_IC%2F13920%2F0%2F

5. Stefano Says:
   October 22nd, 2012 at 9:58 am

   I wish to thank Ian for his fast and informed ( as always) comment. After posting my comment, I did some research on semi-planing hulls and yes, the graphs show that the figures range in between 3 and 4 times the square root of lwl expressed in ft.
   (A small digression here: I am amazed at how many graphs and formulas do not express the measurement units nor the axis meanings. I would not have got past junior high school if I did such a thing, which explains much of our scientists success when they migrate to find better jobs).

   So… square root of a 22 footer lwl is 4,69 and the predicted speed thus would fall in between 14 and 18.8 knots.

   Personally, I will take anything close to 10 knots in 3-4 beaufort as a big success, especiually it the huls will not pound too much ( other reason for putinng a V section forward) since I ignore in figures what a ” flat run aft” is ( mine will be 10-12 inches rocker), the dihedral angle that would be best for “lift” ( I will ask the sail maker to draw a gennaker with some lift power though) and what “reduced wetted surface” would mean. In fact, with my old PC programme ” plyboats 2″ I am trying to get the best figure of wetted surface/displacement at a maximum heel of 8 degrees.
   I also ignore what the step should be like, but I’ll check this stuff on a closeby museum that has many planes and hydroplanes hulls with steps on show.
   I also read that steps in the hull create an intended turbulence mixing water and air so to reduce friction drag from hull/water ( high) to hull/water+air ( lower).

   I’ll strive to make the whole tri at least pleasing to the eye since thing I really loved in Uffa Fox boats is their looks, especially Atalanta. So again Ian, thanks for sharing :-)
   I hope here my Italian eye trained to beauty will help in the effort.

   Yours friendly, Stefano

6. Stefano Says:
   October 22nd, 2012 at 10:08 am

   For Ian again…

   Reading and quoting Uffa Fox from the same article on flying 15 lines:

   (…) So while I think these lines we are now looking at are very fast indeed, I do not think they are fast round a course, and the moral of all this is that designers must put into the hands of helmsmen instruments, which, while being fast, are well within their capabilities, so that plenty of spare energy, both mental and physical, is kept in reserve, for the planning of their race and the sailing of it, enabling them to conduct operations in a seamarlike manner rather than in a state of feverish excitement throughout ” (Uffa Fox)

   I wish I knew this man !! The bottom line of good handling and “manners” at sea are totally within my design goals and priorities, and stand higher than maximum speed overall.

   Again thanks for sharing… Stefano

7. ian Says:
   October 22nd, 2012 at 4:01 pm

   Stephano-

   I truly envy your being able to go visit a museum full of Italian seaplanes, which are without a doubt some of the most beautiful machines of any kind ever created…and in the case of this one, still the fastest propeller driven seaplane in the world since 1933-

   http://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Macchi_M.C.72.jpg/800px-Macchi_M.C.72.jpg

   http://img577.imageshack.us/img577/4917/italianafmuseum132.jpg

   I think you are correct about the air induction aspect of stepped hulls being a major reason for using them on fast planing powerboats…on a float plane float that’s some of it, but not so much for speed potential as for helping to quickly break free from the water surface entirely, the same way steps on three point hydroplanes do.

   But on a float plane float some of the step design there and especially the aft sections with the extreme fine exit and very upwardly angled straight rocker aft of the step are all about nose high trim attitudes on takeoff and especially landings…a really flared nose high landing means that the aft section of the float becomes the entry point and a wide flat planing hull shape here could potentially trip the entire machine and slap it down on the water hard enough to destroy it…when you look at it this way you see that the aft section of a float is really more like a bow pointing backwards.

   So there’s some stuff that is directly applicable, and other stuff that isn’t unless your ama is regularly breaking free of the water and re-entering it (like in big seas), which it very well might and a plane float style ama and step might make perfect sense.

   Another thing to consider is that step placement fore/aft can affect overall pitch trim when underway because the air/water mix behind it is less buoyant. On a powerboat with a step and wide transom, this has the benefit of causing the stern to sink slightly into this foamy mixture and assume a better trim for planing when underway, but still have a full depth transom. On a float plane it means that as you apply power the step makes the plane assume a more nose high trim needed to take off and the grip of the water on the float lessens.

   When angled other than 90º to the hull, steps can also induce a turning moment…some deep vees do this on outer chines, to help fatter boats turn better as they roll onto that section of hull that is designed to always turn.

   On a heavily canvassed tri I can see this kind of asymetrical step being used on an ama to counteract negative helm tendencies as the hull is pressed harder and engages the step, which might allow larger less balanced rigs without strenuous helm input to control them going to weather…but what really intrigues me is the idea of using a directional step on the main hull to not just affect that hull but to also direct and modify the flow of its wake so as to optimize the flow that the ama works in/on…

   a step in the main hull will bring the stern wave more forward, which puts the amas in a position to surf naturally on that wave if they are shaped and positioned properly…it’s not that you are making more power, just re-harnessing some of what was used to make that wave in the first place.

   This “ama surfing the main hull wake” idea has been used on some of the big power tris like Earthrace/Ady Gil that have the amas very far aft and tucked into the main hull wake…if you look at this pic-

   http://www.barking-moonbat.com/images/uploads/earthrace2.jpg

   you can see a bit of this positioning- imagine wanting to catch that stern wave on a surfboard and you would want to be paddling hard right about where that ama is sitting, which is that magic point where the wave takes over and you are riding it.

   at speed it’s even more dramatic-

   http://www.sail-world.com/photos/Alt_Earthrace%20finishes.jpg

   the amas are just buried in that stern wave, again very similar to the attitude a surfboard takes right before it uses that stored energy of being sunk to pop forward and plane right along as long as there’s a wave.

   hard to do that with a sailing boat that needs the width for stability and more ama buoyancy forward…but a step in the main hull might bring that wave forward enough to get some of that effect on a more traditional sailing tri hull layout.

8. Small Tri Guy Says:
   November 29th, 2012 at 2:54 pm

   The Tricote trimaran is another beautiful “monohull to trimaran” conversion – http://www.tricote.fr/construction.php

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