SailRocket

Malcolm Barnsley and Paul Larsen have been working on a world speed record machine for some time. Late last year they hit 30 knots and seem to have plenty more potential if they can iron out the bugs.

http://www.whbs.demon.co.uk/sr2/content_fr.htm

I believe that they have essentially taken the Bernard Smith concept from 1962 and made it reality with modern materials. Have a look at the following site and hit the 'Aerohydrofoils' button on the left.

http://www.geocities.com/aerohydro/designframeset.htm

It seems like a very promising concept if they can control the beast as it is not limited by righting moment considerations (like MacQuarie Innovations: http://www.macquarie.com.au/speedsailing.htm) or multiple dragy hydrofoils like longshot: http://www.dcss.org/Savineau/tri_01.htm).

Do we think that they are likely to break the 40 and 50 knot barriers and if not, what are the limitations on their design. Controlability and cavitation of the foils are likely to be two of these factors.

Regards

Dave

 

It could certainly be done. I've heard of those big rigid sail sailboats really huge, flat sail-like panels.

 

I wish th4em luck, but they've got an awful long way to go

> as it is not limited by righting moment considerations.

Maybe not, but that's not the problem. Foil behaviour especially cavitation is the limiting factor.

 

Inclined sails weren't originated by Bernard Smith, but he's the one who made them known (most of the speedsailors I know--bar sailboarders, and even many of them--got turned on to speedsailing reading Smith's books. I know I did (back in 1976). SailRocket shares little with the Aerohydrofoil except for the inclined rig, and the "hook in" foil.

IMO, there are three things they must overcome; you mention two, either of which could be a non-starter (The boat shows a lot of spray = drag. They say it'll get better at higher speeds. I wonder)

The third issue regards inclined rig aerodynamics (of which I know a fair bit; my whole career has been with inclined rigs--in the form of free-flying kites): When you incline the rig, some of the aerodynamic drive is resolved as vertical lift, not horizontal drive. This lift isn't useful as they use a "hook in" foil (which creates yet more lift--downwards--rather than pure horizontal drive). At the same time both the aerodynamic rig and the hook in foil (hydrodynamic lift) suffer their "regular" drag. Since the horizontal lift isn't 100%, but the total drag is, the resultant L/D is reduced. Very high speed sailcraft *must* have high L/D or they can't sail fast (total combined L/D determines the multiple of the wind speed the craft can achieve).

If their L/D is reduced, they need more wind to go a given speed, and so must suffer greater forces (things break) and deal with rougher water. This was the lesson of YPE; use vertical foils, both above and below the water, to get highest L/D = higher multiple of the wind speed. She set her record of 46+ kts in 17 kts of wind. No other boat has equalled this multiple, at anything near this speed.

Dave Culp

 

a few months ago in Yachting World there was mention of a soft wing sail on a standard yacht, apparently it performed really well.

 

Anyone care to comment about Frank Bethwaite's belief that the Smith-type rig (which he spent years working on in front of my childhood home) is inherently flawed?

 

I thought I just did... I agree with Frank on this one (I often don't; his mono-centric approach hampers him, IMO. Yes, I'm including his work with "multihulls").

The "inherent" flaws to inclined rigs aren't irreversible--free-flying kites attack the underlying flaw by increasing effective beam to very large numbers and bringing the sail very nearly vertical; but they bring their own baggage to the party. There's every possibility that an inclined wing Smith-type boat will break the record (vertical foiled examples have their crosses to bear, and can be beat), but frankly I doubt it; the material and engineering advances which might allow it will keep pushing the vertical boats faster, too.

Dave

 

Frank's HSP boats

From what I saw in Franks book, High Performance Sailing, they all had small sails, minimal beam and very inclined rigs. He said that in the gusts they occasionally seemed to work but in the lulls they just sunk. None of this surprises me as all due to the small sails, minimal beam and very inclined rigs. The next time I see Frank down at the club, I will quiz him and put a few lines on the forum.

Dave

 

Dave S, Frank's experiments took place in front of our old house (near the NSC nor'east windward mark). Some had fairly big rigs.

DC, I was referring not to the problems of the "hook foil" (which as you say you'd already explained and thanks for that) and L/D ratios, but the problem of the apparent wind going ahead when a fast boat enters a lull. Frank also comments on p 185 that it's better, given at the wind is not providing a continous force, to use reliable dense water for support rather than a kite rig.

I would just like to emphasise that I can understand that kites may escape both of these problems, so I'm not attacking kites - just wondering about whether these two factors, along with those you mentioned, are also flaws in the inclined rig idea.

I totally agree that Frank is anti-multi (HSP apart and that was a wonderful, wonderful boat to sail) and also doesn't realise how effective a good longboard windsurfer is in ALL conditions. He's approachable about these things, though.

 

No offense taken, I understand what you're saying. The wind going forward and the variable force issues are both control issues, not fundamental ones. Like many of us "old school" designers, Frank likely prefers statically stable systems to statically-unstable-but-dynamically-stable ones (as do I). These problems are emminently solveable, mechanically with wands, wind vanes and the like, and electronically with $1.50 microchips and $2.00 sensors, surplussed from the military. Peter Lynn's two sons are near the leading edge with this, though there are others...

I am REALLY bummed that I wasn't able to find time to run into him while in Sydney. I'd love to spend a couple of afternoons just sitting at his feet, listening to whatever he has to say.

Dave

 

I agree with Dave C that the inclined rig will reduce the effective L/D of the boat and hence require a higher wind speed than an equivalent vertical rigged boat to go the same speed. Macquarie Innovations should theoretically have more than enough righting moment to go 50 knots plus if they can sort out the control (and possibly cavitation) problems that they have.

The cavitation issue seems to be speed limiting factor. Longshot, a hydrofoil with 3 foils; two widely spaced independent incidence controlled foils at the front and one static foil on the rear effectively hit a wall at 43-44 knots. The independent incidence control effectively allows the windward foil to suck down and create more righting moment (and drag) than could be obtained from an equivalent conventional boat. They said that it did not matter whether the wind was 20 knots or 35 knots, they still could not break through the 43-44 knot barrier. They believed that this was due to cavitation of the foils. It seems that cavitation of foils in the 40-50 knot range is probably the reason that windsurfers, Macquarie Innovations and Longshot are all bunched within a 5 knot speed range.

I know very little about partially cavitating and super cavitation foils except that they have a reduced L/D ratio (especially at low speeds). I was wondering whether the inclined rigs could use the brute force of their non-righting moment limited configuration to use partially or super cavitating foils. As Dave C said, the strength of materials (and hence weight) may not allow this to even work even if the cavitating foils do have a workable L/D ratio.

Dave S

 

There's a long-standing thread somewhere here on Boat Design titled "foilers." It may have more information than you want, but there's some very good stuff there on trans-cavitating and super-cavitating foils.

For my money, you have a good point; kites or other inclined rigs may well have the necessary "muscle" to drag super-cavs up onto their feet, and super-cavs are good to something over 200 mph (their top end hasn't been found), and the fastest kites do somthing over 120 mph already (20-year old record). Supercav foils rarely have a L/D greater than 3, but that's enough, given a) lots of wind and b) a strong enough boat to handle a). ;-)

It's also true that at least kiteboats can be built very compact and strong. They have no spread-out rigging loads and no heeling moment to counter--you can design a compact, ultra-strong "loadpath" between kite attachment point and foil; the rest of the boat is just for keeping the water out. It can be very narrow and a wave-piercer if you like (needs no reserve buoyancy).

Dave

 

Maybe Frank Bethwaite is warming to multihulls as he was out sailing a windrider Rave on the weekend ...or maybe he just thought that he wanted something slower in his old age. He is 85 after all.

Dave (Multihull owner)

 

Sailrocket gets a sponsor and has relocated to Namibia, waiting for the right conditions. 50kts by Easter? http://www.yachtsandyachting.com/news/?article=135526

 

Very interseting article by Paul Larsen, the helm.

http://www.yachtsandyachting.com/news/?article=135680

50kts still looks a long way off.