Thursday, November 18, 2010

18' Tri vs F18 Cat : potentially the full potential

I think an area worth exploring is what the potential is for an 18' tri-as well as how much of that potential is required to whip an F18.
This is an example of what the full potential of an 18' tri is, potentially


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

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.
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. For the tri to work in light air as well as heavy air it is absolutely critical to use two lifting foils on the main hull: in light air they allow the boat to fly the main hull in 5 knots of wind. In every condition they add tremendous pitch control to a very powered up boat.
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)
See Martin Fischer interview about the use of foils in multihull design:


I'll post some specs comparing the "low powered" daysailing version of the 18 tri with an F18. What is very critical to realize is that on either the high powered version or the daysailer the boat will(must) fly the main hull in as little as 5 knots of wind-that is absolutely critical to the success of either version. The boat is simply too wide with too much RM(esp. the daysailer version) to do that without the foils on the main hull. After the mainhull lifts off and speed increases the foils will UNLOAD until ,at some point, the ama takes the full load(either a planing ama or ama+ foil).
The wand is set to control the heeling angle of the boat like it controls altitude on a normal full blown foiler like a Moth. There is a side benefit to using the foils for early liftoff of the main hull and pitch control: because the wand is set for a specific altitude(heeling angle) if the boat begins to exceed that angle even by a little the wand will cause the main foil to pull down. This can be used to sail the fully powered up

daysailer version singlehanded in the same maximum pressure it can be sailed doublehanded. 

No comments: