18' Trimaran vs F18 Catamaran

This thread started out to try to see if there were any high performance 18' tris around that could beat an F18-either existing boats or designs whose numbers reflected the probable ability to do the job. To me, it is a very interesting design challenge that could produce an exciting, comfortable and very fast boat. With the numbers for the Magnum 18 tri and Wildcat F18 available to use as a benchmark it is clear that an 18' performance tri with small amas and lifting foils on the main hull(as per my suggestions earlier and below) and either foils or a planing hull to provide dynamic lift on the ama could be in the ball park pricing range of a Wildcat F18. It is further clear that with careful design and engineering the boats would be comparable in weight as well.( Keep in mind that as beachcats go the F18 is on the heavy side). The technical aspects of the boat show a high probability that the tri would be faster than the F18, would be able to sail in the same pressure as an F18 with one or two crew, and would do this while allowing the tri's crew to sit on the side of a center cockpit very comfortably:
--the main hull on such a boat would be physically much smaller than the Magnum 18-with perhaps 20% less weight,
--the rig with 50 sq.ft.(277 all up-1' higher CE) more upwind SA(121 sq.ft. more downwind) than an F 18 would insure the power required to be faster than an F18
-- using carbon tubes for the cross arms would assure the strength and light weight required for a 16' beam vs the Magnums 14'.
--Righting Moment: Max RM for the tri with two 175lb crew sitting on the side of a center cockpit would be 6700ft.lb. which means it could carry the 277 sq.ft. of sail(1' higher CE than an F18) in about the same pressure that an F18 can with two 175 pounders on trapezes (1.5lb./sq.ft. pressure). But while the F18 requires two 175lb crew to sail in this kind of pressure the tri would not. In fact, it could be sailed with a single crew in that pressure with the contribution from the mainfoil of 218.75lb. of downforce. The mainfoil, in concert with the rudder foil,(both on the main hull)act to control pitch and can be used to maintain the sailing angle of the boat with the main hull flying thru a significant variation in crew weight. The mainfoil would not be much larger than a Moth foil( 1.1=Moth; 1.4 sq.ft. tri). The F18 has 4 foils-the tri main hull four, as well, except that two of them are very small-about half an F18 foil-and lift vertically up or down. Learning from the F18 Capricorn(and other race boats) the tri would have a gybing daggerboard assuring excellent windward performance.
-- Ama- the key to the design is that the main hull flys almost all the time. At max RM the ama must support 750lb.(boat weight+ 350lb of crew weight,or approx. 175lb crew +175lb main foil download). The ama could be a single rotating hull that would allow a displacement hull or a stepped planing hull as the case may be. Very experimental.
OR: the ama could be a high L/B design incorporating a retractable (pivoting) foil with 1.4 sq.ft. of area in each ama. This would allow the ama foil to carry 70% of the boats weight(same % as an ORMA tri) using a proven foil system(DSS) that works somewhat differently than a "typical" curved foil: it develops no lateral resistance as a by-product so that 100% of its area is dedicated to vertical lift making it much more efficient than a curved foil. The least expensive of these two options may be the stepped planing hull but that still has to be proven. The DSS foil is proven....
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If you look at the Magnum as a rough guide only and keep in mind that we're just looking to be in the ballpark with pricing it is faily exciting-and accurate- to consider a tri such as this at + or minus, say $2000.
If you look at the technical aspects it is undeniable that the tri would beat the cat-and that's with one hand tied behind its back! The crew of the tri sits on the side of a center cockpit while to sail in the same pressure(1.5lb.sq.ft-max design pressure for the F18) the F18 requires two crew on trapezes. Not only that but the tri can be sailed in the same pressure that an F18 requires two 175lb people on trapezes-singlehanded! More power ,more speed, much more comfort, much easier to sail fast-the tri could be a tremendous addition to "beach sailing" multihulls and the first of its kind(that I know of-even ostlind agrees with that!).
Yes it can!
NOTE: please see the SA/WS ratios for these two boats. They tell the story better than almost anything else showing that the tri has much less drag for its power than does the F18. And remember, this tri is not using all the power that the configuration allows-it is designed to be faster than an F19 AND extremely comfortable and much easier to sail.
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F18
Specifications:
Length: 17' 11" / 5.46 m
Beam: 8' 6" / 2.59
Draft w/Rudder Up: 7.1" / 0.18
Mast Length: 29' 6" / 8.99
Sail Area:
227 sq.ft. upwind SA
454 ft2 / 42 m2 downwind SA
SA/WS:
--two hulls in water- 4.77/1
-- single hull in water- 6.03/1
Bruce Number: 1.66
SA/D: 44.16
W/SA: 3.29
Weight (with spinnaker): 397 lbs / 180 kg
Price as of 6/21/10= $22,500 including everything except trailer
---------------------------------------------------
18 Tri
Specifications:
Length: 18' / 5.49m
Beam: 16' / 4.88m
Draft w/Rudder Up: 6.4"
Mast Length: 31.5' / 9.6m
Sail Area:
277 sq.ft. upwind SA
575 ft2 / 53.4 m2 downwind SA
SA/WS:
-- not flying-5.73/1
-- flying main hull-10.26/1
Bruce Number: 1.83
SA/D: 53.89
W/SA: 2.71
Weight (with spinnaker): 400 lbs / 181.9 kg
Hull Construction: Fiberglass/Foam Sandwich and some carbon/foam sandwich
Price estimate-$22,500-24,500
(Note: Magnum 18=$19,235)
(Note: skin area and volume of tri ama about 1/3rd that of an F18 hull!)
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Ama foil area corrected 6/22/10
SA/WS added 6/23/10

Note: for those that only see numbers and not the picture they paint you should really do something about that. Without analyzing the technical characteristics of a boat you know nothing about it. If you judge a boat by a pretty rendering without at the same time analyzing the technical data for the pretty picture you're not getting the full story. When comparing two boats such as the F18 cat and 18' tri the technical data is critical. You should insist that posters/"designers" who are telling you about a boat and/or comparing one with another provide the applicable ratio's and other details. You should probably make an effort to understand this information.


Below please find the Design Ratio's as compiled by Eric Sponberg to make it easy for people to understand these ratios. I thank Eric for this major effort as it represents a gift to all of us!

 

18' tri-max potential

I think another area worth understanding is what the potential is for an 18' tri.
I've already proposed some ideas that may work and that seem important for doing a state of the art 18' tri. The previous post is a summary of a proposed 18' tri compared with an F18 cat. It does not use all the potential available in the trimaran configuration at 18'-only about 60%.
This is an example of what the full potential of an 18' tri is:

MAX RM:

1) F18-- crew CG at 11' from lee hull CB( 320 X 11= 3520ft.lb.) + boat CG at approx. 3.8' from lee hull CB with windward hull just flying( 396 X 3.8= 1504 ft.lb.)
TOTAL RM = 5024 ft.lb.

2) 18' square tri(18 X 18)-- crew CG at 21' from lee hull CB( 21 X 320=6720 ft. lb.) + boat CG at approx. 8.75' from lee hull CB with main hull just flying(396 X 8.75= 3465 ft. lb.)
TOTAL RM = 10185 ft. lb.
====================

So the max RM from a square tri with the same weight crew as an F 18 is
2.02 times that of an F18(or more). It is probably possible to build a square 18'tri at the same weight as an F18-the Gougeons built a C Class tri(25') with an 18' beam that weighed 300 lb. in 1969. Also, see powerabouts comment in post 16.
My personal opinion is that this MAX RM tri is not necessary to beat an F18. A tri with less max RM would still be more powerfull than an F 18 yet allow the crew to sit in a much more comfortable position. A square tri is not required to meet the target of this thread, nor are trapezes but the power such a boat could develop is food for thought and should suggest that there is a lot of untapped potential here.
But it would sure be cool to see a "Max Square" 18' tri someday!
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Ridiculous comments about foils notwithstanding, the use of foils is becoming
more and more apparent on monohulls and multihulls alike. Foils are tools that can modify characterisics of a boat such that what might be untenable with a foiless design becomes possible with foils. Like an 11' monohull that beats all beach cats under 20'!
A boat does not have to be fully airborn to be using foils successfully-"foil assist" is probably one of the most overlooked applications of foils.
Foils can add stability where only weight worked in the past, they can drastically modify the pitch characteristics of any boat. They can improve handling in rough conditions. They can contol the angle of heel of a trimaran(or catamaran)-and more.
They can't just be tacked onto a design-they have to be carefully implemented.
The absurd sentiment that "because it hasn't been done before it can't be done now" is nonsense.
Carefull, modern, innovative design can make a high performance "beach tri" a reality that will be faster on the water and more comfortable to sail shorthanded or with a crew at a cost comparable to top end cats.
I've put forth some ideas that I think could be part of such a design but by no means are my ideas the last word on the subject.

More Comfort- More Speed- Wide crew range(singlehanded or doublehanded with MAX power)
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See Martin Fischer interview about the use of foils in multihull design: http://catsailingnews.blogspot.com/2010/05/cs-interview-martin-fischer.html

 

18' F18 killer tri

To make a trimaran such as the one I've described work it is essential that the small ama develop substantial dynamic lift.
That may be able to be accomplished using an ROH type hull. That's a hull that operates with a high L/B ratio displacement hull up to X speed where it is rotated and becomes a stepped planing hull. This is a highly experimental solution but would, in my opinion, be worth testing.
Another solution is much less experimental being based on proven results. That is to use a high L/B ratio displacement hull coupled with a retractable lifting foil to generate the needed lift. ORMA 60's and other multihulls have used curved lifting foils to do this but the curved foil was introduced because of beam restrictions on the boats concerned. A better solution might be a horizontal lifting foil extending out to leeward or for that matter pivoted in the center of the ama as low down as possible. There is no requirement that these foils develop any lateral resistance whatsoever so the horizontal foil would be quite efficient in this application if it can be operated at at least 2.5 foil chords below the waters surface. This type of foil,either sliding athwhartship or pivoting like a centerboard is already being used successfully on a number of Hugh Wellbourn's designs.
Since both these solutions are being applied to a small ama it is my opinion that a way to enhance the pitch resistance of the whole boat must be used
alongside either solution. My solution is to use small foils on both the daggerboard and rudder of the main hull which would drastically improve pitch stability-as well as offering side benefits like increased RM if required and the ability to "set" the sailing angle of the boat when flying the main hull.
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Constructive comments and ideas most welcome!--
Below is a picture of Wellborns DSS(horizontal foil), two pictures of a model of the ROH hull that illustrates the geometry of two hulls in one(displacement and stepped planing), and pictures from the aeroSKIFF 14 model of the two foils arranged as I propose them for this trimaran-if a bit larger:

 

This is a very interesting thread.

 

----
Thanks, Hoyt. The whole theme is taking advantage of the phenomenal power of the trimaran coupled with state of the art technology to allow great comfort and ease of sailing singlehanded or doublehanded while at the same time developing the speed to be faster than an F18 cat on all points of sail. This boat offers more than any "beach multihull" that I've yet seen or read about. It's all about the details......
PS- this isn't the only solution possible-but it is the only one I've seen. Constructive comments and ideas welcome!

 

Very interesting thread indeed. The only problem is tha there is no real discussion as ther seams to be 2 camps standing on their position.

Myself I already looked at a 16/18' tri design with good performance, easy to handle (no double trapeze) and affordable. i affraid all the small improvement of a F18 base or magnum 18 base bench mark shoes that you need to put money in the engineering/construction/material to achieve the final goal.

I do not mean that having a wide tri with
- 2 nice low drag WP amas with C foils
- one center hull with rocker and 2 T foils
- a bigger mast and sail area
- a folding system to transport it
would not be faster, i would simply say that it would cost twice the price you propose.

Simplisticly ;
the 2 t foils : that is not cheap see the price of the bladerider ones
a mast 1.2x longer, add 20% on the rigging and 30% to the sail price

I really can't imagine you can compete $$ with a high production hobie.

About the magnum the hull comes from a rowing boat if I am right, to save some production cost...

Any way I would love to sail a fast 18' tri with my kids sitting in the cockpit at the speed of a F18 ;-)

 

Also me when boat can be afforded as a Hobie Wildcat. The messages here and checking about say it can not.

To think one needs only bigger beams, more parts more expense to have same thing and then it is there is wrong direction. Three hulls will cost more. Then foils to decide and pay the cost again.

No good to think of this as real person.

 

=====================
Thanks for the reply! There are only two ways a tri like I propose could be built at the price level I suggest(or less):
1) If a person is very competent in carbon/foam/epoxy/ vacuum technology and build it themselves,or,
2) It is professionally built by a company with enough volume to keep costs down.
It would be important to remember that the amas I propose are less than half the volume and skin area of a Hobie Wild Cat hull-they are not "traditional" amas like one would design for a 40' trimaran. They are not "three hulls" in the normal sense: one hull with two small hulls=less weight than two F18 hulls.
The whole idea here was to show what is possible if the "trimaran" concept was refined and its advantages exploited to a greater degree than seems to be the current approach.
I extended this philosophy further in the on-going design of the MPX-11(12) based on what I learned doing the research on this thread. There is awesome potential for the small trimaran configuration that, so far, seems to have been ignored.
At any rate, its a lot of fun to discover this kind of potential sitting right out in the open just waiting for somebody to tap into.
My personal interest is high speed with a great deal of comfort, but as I point out above(see max 18' RM), the max speed potential of the small trimaran configuration is much higher-at least at 18'- if twin trapezes were brought into the picture.
The smaller boat looks to have speed potential approaching that of a Moth in flat water with very little crew movement and a very wide crew weight range-but it is very, very experimental.
Again, thanks for your post-its pretty cool to contemplate the untapped potential that surely exists for these boats!

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For another take on an "ultimate" 18' trimaran, take a look at the Osprey that Dr. Sam Bradfield is doing. It works on the same princible as does his Rave-but this one is much, much lighter, all-carbon with more SA. The crew doesn't have to move at all since the foils develop all the righting moment. As light as it is supposed to be it should have great light air characteristics and be very, very fast in any condition.
http://www.boatdesign.net/forums/multihulls/18-osprey-multifoiler-dr-sam-bradfield-25343.html

 

one hull with two small hulls=less weight than two F18 hulls This is really a disputable opinion I am affraid. especially if you consider ama that are 18
' long!

Would you propose an innovative concept to buid light cheap hulls why not but you simply rely on subjective high skilled free workers...

technically your design is interesting, commercially you seems far from reality

 

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NO, the ama's would be more like 13' long. And the total "skin area" of one F18 hull is approx. 59sq.ft. while the tri ama is approx.
28 sq.ft.. It is simply a fact that the two amas + one main hull are physically smaller than two F18 hulls. That is a key to the tri's estimated weight and cost-a very important fact based on actual calculation and not speculation.
Don't forget that an F18 has the rep as a heavy cat. For instance , a Marstrom 20 weighs 154lbs LESS than an F18.
http://www.landenberger-sailing.com/spip.php?article102
Commercial success with a concept like this trimaran depends on the company that produces it. If a company like Hobie produced it my target cost in the post above would be quite accurate. A highly skilled individual might be able to build it for slightly less.
The technology used on the tri is dead certain to produce a boat that will beat an F18 but the point is that trimaran tech as pertains to small tris is still in its infancy with great potential for beachcat killing performance available to a designer who is willing to use the most up to date modern technology.

 

Is not only area for making of the cost. Also the many molds as are needed to build whole boat. Hobie cat is 2 molds. this trimaran is four and then is the special expenseive building of the foils and the boxes for them. All the molds are handled several times by many workers. Parts for boat are needed in carbon like Marstrom has to build to have weight this low. What is Marstrom cost now if you compare weight? I tell you. Well over 30,000 Euros ($38,000+)

I come to same place as Josselin. you can think it and not build it. Price is more like Marstrom no matter

 

I disagree-I think you're way off- especially if a company like Hobie did the building. Marstroms cost reflects very low volume. And you're off on the molds as well:four hull molds for the F 18,four for the trimaran. From a design standpoint two ama moldsets are not required-the hulls are identical for the ROH version. From a production standpoint a second ama moldset may be beneficial.
As to foils:
1) F18-two daggerboards, two rudders: FOUR TOTAL
2) 18 tri one daggerboard, one rudder, one main foil, one rudder foil: FOUR TOTAL
Note: if ROH(planing + displ.) hull is used then no more foils; if DSS foils are used in a "traditional" ama then two more foils.
3) Estimated price is up to $2000 higher than F18....

 

Low volume is same. expensive price is same like marstrom. expensive foils also same.

4 molds at hobbie wildcat? no. is same hull both ways

guessed price is $30,000 for trimaran with low volume boat

make funny twisted outrigger hulls make bigger cost as tooling and build together.

 

-------------------------
Are you sure? It seems apparent that the chainplate positioning is asymetric so I would think they'd require two mold sets from a production standpoint.
For some reason I thought the hulls were canted out at the bottom but that doesn't appear to be the case. I find that a bit surprising as well...

What does this mean?


F18 hull:

 

It means you make talk before you discover. mast wire mount is simple thing when part come from mold. Not a problem before join. I think you could know this, yes?

Now you make the reasons as trimaran not being same price as cat. I think this trimaran is low number boat as Marstrom 20. small customer interest. It is big expensive in small number and many many molds with workers to build slowly.

Maybe when stuck with one thinking, then is hard knowing all around you. The free mind lets this in. Not free mind stays shut