Optimizing a Tri for Light air

[Samnz]

Originally Posted by catsketcher

Monos are good boats for a reason. Why do multis beat them usually? Because monos have higher FORM drag (high speeds) and lower stability (higher winds). In light winds the highest drag is from induced drag (making your boards work too hard) and wetted surface area. WSA is the real killer for multis.

Have a look at the little dinghies they race in lakes and ponds in the UK. Light weather and not long distances and they end up looking like little round tubs. A sphere is the perfect light weather boat (as long as the wind doesn't blow much over half a knot or so) A half sphere is the ideal shape for getting max volume in minimum surface area. Your Farrier is not at all like this and so you get killed by the WSA. I am sure the Melges crew get forward to get the broad bum out of the water and get the boat floating on the round forward sections to reduce WSA- this is light wind mono 101.

Monos kill multis even more when they can heel over to leeward to get the sails to draw earlier. As they heel the reduce wetted surface even more. Then on top of that a mono is so much more responsive to sail in light winds. You can feel the boat groan when the crew walks heavily on deck. Tacking is much easier (you may even roll a sport boat) and so you lose far less speed every tack. You also can tack on windshifts that a tri (but especially a cruising cat) would lose heaps of momentum in. Tactically a mono will love light winds in shifty breezes and a course straight upwind and then straight down.

Depending on the mono you will be in power up gear (I call it first gear) until the boat starts sighing. Then you start going for speed (2nd gear). Its not really until the mono reaches max stability that the multi will really make huge strides - monos are pointing now. When you start to fly a hull (just reaching max stability) the monos are depowering all they are worth.

So unless you make a tri like a mono - fat, you are going to find yourself getting beaten in the very light stuff by a similar high tech mono. Try and be nice about it. I am sure you get your own back most of the time.

cheers

Phil

Phil your so wrong on this one sorry. If we compare our Orma 60 Vodafone with Limit a full on 60 ft racing mono the orma 60 wins everytime any breeze any angle!

Vincent the answer is so simple, your boat is too heavy and has not enough sail area. fix one or the other or even better, both...

Of course a tri with same weight and sail area will be slower than a mono in light breeze! more drag! the whole point of a multihull is its light and can carry more sail

[Samnz]

http://racetrack.org.nz/boat_ranking.php?s=1

see Vodafone is 1.9 vs the keelboat at 1.4!!!! and vodafone is a much much older design!

[Vincent DePilli]

"Vincent the answer is so simple, your boat is too heavy and has not enough sail area. fix one or the other or even better, both..."

This seems right. Weight is the key.

But I am not interested in a tri that designed to fly the main hull, like an Orma 60 or (closer to home) the Seacart. Too scary, not right for cruising. And no lifting foils—expensive and complicated and heavier. I want a 2 foil boat that does what that the F31 does (excluding fold), but that weighs much less, and can be built with New zealand style backyard med tech.

I suspect that this conservative dream boat would want to have water ballast for when I get scared, which is often.

This is probably a dream unless the economy improves significantly. Purely entertainment’s sake, I am putting together a spreadsheet that compares what I could get from selling my boat ($80,000 -??), with the cost of building a new hull/beam package, and using the rig and all the bits from the existing boat.

[Gary Baigent]

Vincent, it is easy to improve on stock multihull designs ... but you have to accept tradeoffs/sacrifices - meaning a determined, not half assed, attack on weight, which means gutted accommodation, no junk and clutter aboard, no motor, fuel tanks and so on. If you want to sail cheaply, you have to be somewhat Spartan in your approach. Remember what Dick Newick said regarding speed and luxury, you can't have them both. Also by dumping junk, your boat immediately gains power plus becoming lighter in weight - which allows you the luxury of speed to run away from dangerous situations, more buoyancy, more righting moment ... and most importantly, less sail area horsepower to gain this speed. Lightweight means safety.
Anyway, all this is obvious stuff ... but surprisingly few people will adhere to it. Conformity and class conscious nonsense takes over - "no way are we going to squat on our boat like a Polynesian on an outrigger." Misses the point; the greatest luxury is effortless speed.
Anyway, I'll post soon the latest images of Seditious Sid - a crazy boat that has the above philosophy. You could downsize the rig and still have a very fast boat .... but the accommodation is not salubrious.

[oldsailor7]

Phil hit it on the head.
Light weight, low wetted surface, for light winds.
Thats what makes the Buccaneer 24 so good. It is light. Has a moderate L/B ratio & near semi-circular bottom---(low wetted surface), dihedral on the crossarms for fast tacking and keeping the floats out of the water in light airs.
Coupled with a high Bruce number it leaves other boats for dead in light wind flat water conditions.

[luckystrike]

Dear Phil,

I find it difficult to discuss such a theme without any visualization. In general we have all the same opinion: "A light boat with a good sized sailarea and a mainhull that has a shape that is designed for that wheight (not a fat hull with a light wheight) shall be faster allround than the F31 (even a light one) and be able to beat the melges 32, without sacrifising seaworthyness and small drawbacks in the question in the interior space.

Have a look at this:

http://www.multihulldesigns.com/desi...ck/d30tri.html

and this

http://www.multihulldesigns.com/desi...dingarmtri.htm

Fine mainhulls with a 10.5 to 1 ratio, light wheight, reasonable interior, good stability, built from wood or sandwich. Swinging-, folding-, sliding- or fixed demontable beams, just as you like it to have.

Its all there, no need to reinvent the wheel.

Grreeetings from the North Sea Coast, Michel