Small trimarans under 20'

Frolic

I found this that shows three Piver designs including the Frolic:
click-

 

Sorry OS7, I misread - since the topic was under 20 feet.
Piver designs are under rated - actually not understood correctly ... because many people overbuilt them with large cabins etc and destroyed their performance.
Piver was way ahead of his time.
My only experience is on a modified Nugget (daggerboard added, rotating mast) - the more than 40 year old design is still an excellent sailer.

 

To be clear, this thing, wish I could remember the name, was a foil stabilized monohull, not in any way foil born so while the foils were fat they were nowhere near as fat as an ama, they were only big enough so the boat would sit upright at rest then the outside face shape provided the hydrodynamic lift to stabilize it under sail. It was I believe a production boat in the UK but probably no a successful one. I liked the concept because you sat in a comfortable hole in the hull facing forward like the much later Windrider tris. It was not neccesarily as fast as the beach cats but still plenty fast I would guess without the acrobatics.

Steve.

 

Thanks Doug, yes I remember that now, same general concept for sure. Now if the crossbeam on the 20ft version were to share a common pivot as the rotating mast sits on and was rotated using dyneema lines and tackle you would be able to swing it around so the stabilizing foils were in front of and behind the hull it would make for an easy trailering package. In 20ft you could easily have a cockpit for maybe 4 people and the beam could be wide enough for people to sit out on, with a legal road width of 8'6" the possibilities are endless whereas beach cats are hobbled by the trailering width restrictions somewhat although 10ft on a tilting trailer is really enough on a 20ft cat.

Steve.

Steve.

 

Mmmm it's a nice computer concept but the engineering practicality would make the concept doomed to failure. Think of the stresses on the one central pivot and the strength of the beam that would be needed to support the entire weight of the vessel and its passengers + rig loading+ Wave impact + longitudinal loadings and then you lose all the benefit of the crew bring able to move their ballast about meaning smaller sails.

Not sure on this one

 

Pivoting crossarm

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I think Gary may have already done the pivot thing on one of his boats or is planing on it-it's good idea if properly engineered.

 

Yeah, I think it would work best with a monofoiler rather than a tri though as an ama is bound to be longer than legal trailering width so you would be faced with added complexity. It seems to me that anything that extends ramp time turns people off, which is why Farriers system swung the mediumsized trailable multihull market in the tris favor.

Steve.

 

Unique small Tri by Steve Curtiss

Check this out:
http://smalltrimarans.com/blog/?p=10004

Here are the criteria Steve chose for his newest boat: (from Part three of Steves article in Small Trimarans)

Since I wasn’t getting any younger, I decided to take a last best shot at a small, easily transported, really high performance trimaran and I wanted to use the things that were learned from the last ten years and two previous boats, the M3 and the Twinsail. Here’s a list of the major items to be include in the design:

1. Trimaran hull layout for best stability with least wetted area

2. The main hull should be approx 12 ft long and should be fully planing (flat or slightly concave), hopefully beginning in 6-7 kts and staying steady in 10kt+ of wind. I wouldn’t expect it to plane tight upwind, but that would of course be wonderful.

3. Amas should be light but rugged and provide more flotation than on the M3

4. Total sail area should be a little more than the M3, in the neighborhood of 7 M (74 sq ft)

5. Center of effort for the sail area should be lower than the M3, so the double sail concept should be used, but this time I want to try it with the masts side by side (biplane) forward of the sailor. To my knowledge this has not been done very successfully in a really small trimaran. The Hobie Trifoiler was very fast, but was large, heavy, and wide as well as dependent on hydrofoils. Other successful biplane rigs I’ve seen were large scale ocean racers/cruisers. The smaller biplane experiments, like putting a rig on a Puddle Duck Racer or a small catamaran, didn’t look like they were very exciting performers, and could get into situations where the sails were blocking each other. The trick seems to be to have a design that will sail fast, since the rig performs best upwind, and fast boats are going to windward most of the time if you look at the relative wind vector.

6. The prototype should be made from (relatively) easily available parts where possible so it’s less expensive to build, changeable, and adaptable. Murphy’s Law says that whatever you’re absolutely sure is the greatest design will turn out to need some tweaks, or even major overhauls.

7. The prototype frame portion should be made out of materials that I can easily work with, which for a mostly metalworking guy means more parts in aluminum and stock plastics and fewer in fiberglass/carbon or wood.

8. The sheet control forces should be significantly lower than on the M3. The M3 had forces in the 35-40 lb range in stiff wind, and it would be better to keep sheet forces below 20-25 lb. That probably means I would need to go to a line with some pulley reduction instead of a boom rod, and perhaps use a ratchet or cleat arrangement.

9. The seating should allow the sailor to move from side to side, but not a huge amount. It should be a mostly face-forward cockpit, sailed like a wide kayak rather than like a dinghy, thereby allowing a somewhat lazy grey-haired guy to relax a little and not have to dash across the cockpit, hike out, crawl around on webbing, or trapeze.

10. The steering should be by a wheel rim segment connected to the rudder in such a way that it provides steering wheel directional control (turn right to turn the boat right) rather than tiller control (turn right to go left). I’ve sailed all kinds of tillers and rod controls and it’s just a personal preference. The design could be switched easily.

11. The sails, masts, and booms should be kids’ windsurfer type for low cost and high efficiency, hopefully with transparent sail material, fiberglass masts, and curved luff socks.

12. The boat should be easily transported in sections by a guy trying to minimize chiropractor costs, so no piece should weigh more than about 45 lb, and all should fit easily in/on my small pickup. Various small wheels or dollies might be helpful.

So what does all this mean? I wasn’t completely sure, but the very first thing I did was to build a small crude model of a possible layout in wood, paper, and brass tube. To make the model complete, I had to include my intrepid test pilot, Cardboard Man.

click for much larger view:

 

Latest render on plans for the 16' tri.
Weight target: 130 lbs
Mast height: 24 ft
Beam: 12-14 ft
Mast cant: 15 degrees
Foil assist on both amas
Ama length: 12 ft
Crew: 1
Sails shown: Main, Jib, and code 0 spinnaker(Probably on roller furling)

 

Nice looking artistic plan, harder to built !
To my knowledge an tri experience (I buit and sailed 3 from 32' to 15' lwl) , seems the dagger board location corresponds to the sail area with genaker, should give a huge weatherhelm going to windward with main and jib ! Farrier uses front of the mast pit location on his designs, but with a big aft rake on the daggerboard. Most of well trimmed tri designs have the daggerboard aft the mast. Also unbalanced rudder will result in big steering loads !
It will be outstanding if you achieve 130 lbs, unless you use A cat Epoxy foam/carbon technology !
Cheers
Patrick

 

Rcnsneg :
Last thing, just leave the top of the sail squared, an angled batten is Ok to hold the leech, together with horizontal tension on the top of the sail. I you angle the top upward, you need a rigid extension of the mast to hold it !
Cheers

Patrick

 

Weight is bit optimistic to say the least, having built a 16ft cat with not unsimilar specs and sail rig, out of carbon in a mould, at 103kgs then if you start adding in foils, canting rig and two sets of beams ?

The top line A Class boats with single Uni rig and built of prepreg are 75 kgs

 

It's skin on frame, and it weighs about 90 lbs right now, so I think it can't be that heavy.

About the weather helm, does the canting mast impact that much? 30 degrees of mast range is quite a lot.

I currently have a centerboard there, but I want to seal over and cut away most of the centerboard box and replace it with a daggerboard. I will probably put a Hobie 16 rudder assembly on it so I'm not worried about that.

About the sail top, why can't it be angled? I've seen a few A cats that do that, and the batten is sufficient to hold out the corner, it would just be more floppy.

 

Canting the mast to windward gives leeward moment, just like heeling monohulls gives windward. moment eqals the aerodynamic thrust times the windward or leeward motion of the center of pressure. What does you 90 lbs weight include ? Hobie cat rudders are balanced but very heavy ! A cat sails are just square top. Leech is hold by the tension on the top of the sail and the compression on the batten, yes if you increase the angle above square it will be more floppy, it is a matter of geometry. But I doubt it is very useful !

 

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A "peaked up" square top theoretically gives a slight aerodynamic advantage.
Lots of Aussie 18's use it and I used it on the aeroSKIFF rig. A diagonal batten works fine.