Tomahawk: Peoples Foiler?

"If you can sail, you can foil!"

Gee, here is a quote from that foiler maniac on SA on March 5th:

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Jon Howes says the weak point is mid range and the foil should excell in heavy ,rough conditions and will have an early takeoff. Many times ,in discussing a Peoples Foiler, I have said that the priority must be EASE OF SAILING-over and above anything else.Second Priority: light air take off.
Who cares if the Moth is faster when anyone that can sail can foil a well designed boat using the Tomahawk foils.
From the experienced foilers that have sailed these foils they are much easier to learn to sail than any current bi-foiler and that means a MAJOR breakthru.....

 

Come on, Doug, get a grip, will ya? Before you pronounce the second coming of the Foil Jesus, would you simply stop blabbering about things that you assume will happen in the future? If you have that kind of a sense of stuff about to happen, then why in the world aren't you already as rich as Warren Buffet? It's this simple... you can't and you're not. Let it go.

Take a moment and digest all of your wonderful futuristic predictions from the past five years and tell us which ones have actually come to pass. I can list them for you if you find it necessary to dodge the question. Hint.... it's not something on which one should stake their reputation.

Give it a rest, let the thing play-out in its own time and space and quit shilling for Howes. The guy can speak for himself.

 

I don't want to get in the way of a good fight, but often point out, when enthusiasms start to get in the way, that the art of engineering is being wrong with grace, learning from it and moving on. The Tomahawk foil is an application of a foil section I developed for another, rather extreme application that may (note "may", not "will") remove much of the difficulty of foiling for the average bloke/blokess with the potential for high speeds in the right conditions/points of sailing.

When fully sorted, it may even be quick upwind, however, if too slow to surface run then it will always be slower than a conventional foil. Surface running can occur upwind but obviuously the power needs to be present to get it into surface running mode in the first place. What it has already proved (on the sailboard) is that when fully established at the surface it is very quick. How this compares to a conventional foil, or even a well sailed conventional board, only comparative testing will show although I am fairly confident in the board application that it is faster than the conventional approach.

As for the amount of vertical surface below the foil, yes, this is small but it only needs to work without assistance from the bit above when the boat is sailing fast and it seems to be sufficient for in these conditions. We are currently performing some final optimisations (losing the tee foil on the rudder and using a surface runner here as well, for example, which gets rid of the twist grip. Weight shift can then be used to squash the rudder foil down at low speeds, at higher speeds both foils then surface run).

I think the boat is likely to be slower around a course than a current Moth but much easier to sail/simpler. The board, from Linton's comments, can be pretty terrifying. Since I am not (yet) a board sailor I have to take his word on this. In case it got missed when posted elsewhere, here is the email I got from him after first flights on the board:

"Sam and I both sailed

Oh my word!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

That was the scariest bit of fun I have ever had.

Damn it felt as though it was quick or as quick as I want to go!

Apart from some side slippage issues and fin stall (which can happen on normal windsurfing) the board was really close to being very good.

Jon I reckon I will soon have all the information you will need to properly design this.

Buzzing

Linton

We will talk"


My sailing experience: self taught at age four in a modified Royal Air Force dinghy that used to be carried in a Lancaster (apparently), moved on to an Oppy, sail number 285 which makes me feel ancient, thence to Moths, both the British kind and the foreign version of inferior manufacture (Empire moment there, sorry), various charter experiences getting all the while heavier and more traditional, current boat, five tons of decaying rainforest built in 1936 and anything else I can scrounge a ride on.

Jon.

 

I can understand traditional surface foil technology this was what Rohan Veal used on his first but not class legal International Moth it used a V shaped foil supported from each wing and just as per a powered hydrofoil it self levelled. As we have the designer here how does the tomahawk cope with waves if the foil are working close to the surface which is implied by the name?

 

I think you may be thinking of Brett Burvil who used two surface piercing foils forward and one t-foil aft. He won the first race by a foiler in the Moth class with this configuration. Veals first flying Moth was a bi-foiler designed and built by John Ilett.
Burvils foiler was ruled illegal in the Moth class as a "catamaran configuration."
Burvill sailing his boat and a boat with his foil system:

 

Tomahawk Foils

Excellent post by Jon Howes from Yachts and Yachting's Tomahawk thread ( http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=5271&PN=2 )

"As the foil was my concept I may be able to lay to rest some of the speculation regarding how it works.

The facets towards the aft side of the upper surface are designed to ventilate progessively from rear to front as speed builds. When fully non-ventilated the section is highly cambered and generates a lift coefficient of around 0.77 and this gives a very low lift off speed.

When fully ventilated (from the mid-chord aft facing step on the upper surface) the lift coefficient is 0.2. Between these two extremes there is a need for an intermediate condition so that, as the foil approaches the surface, sufficient speed has already been achieved to fully ventilate and no loss of lift occurs as the foil surfaces.

I have missed out a lot of developmental steps here, but briefly, the pressure coefficient at the leading edge of the last facet is the lowest on the upper surface when completely unventilated and so giving an air path to this location (by an aft facing step or channel on the vertical strut) leads to early ventilation. The aft facing step on the facet tapers from root to tip and the step is swept (as is the foil). In combination these two features lead to a progressive ventilation growth across the span. By the time the ventilation is approaching the tip the next facet forwards is generating a healthy low pressure coefficient and the ventilation can either jump forwards from the aft facet or be fed to the step at the leading edge of the forward facet and a similar ventilation growth, and steady reduction in lift coefficient then occurs as speed continues to increase. By now the foil is approaching the surface and when it finally breaks out into surface running no sudden lift change occurs. The ventilation cavity follows the foil when submerged and, in design, is treated as an integral part of the foil section.

As for drag, just like an aircraft, this is in two parts, lift induced drag and skin/profile drag. The profile drag of this family of sections is always higher than that of a conventional section if below cavitation speed, however the lift induced drag follows the same rules as any other lifting surface, ie, three things matter: wingspan, wingspan and wingspan. A comparison would be a lift to drag ratio (L/D) for a conventional section of around 100, for this section it is 22. When used on a 3D foil, the lift induced part becomes important and a conventional foil may then give around 12 to 15 whereas the ventilated section as we use it here gives about 10.

In conclusion, upwind we will not beat a moth in moth conditions. With the wind free, after all the conventional foils have cavitated this thing will keep going and speed will be limited by nerve and structural failure. Note that this section was originally developed for my Monofoil project and is designed to behave beyond 100kts (getting there is another problem but if you don't design for it......). The foil on the dinghy will give simple sailing, low lift out speed, relatively shallow draft and, if the conditions and nerves allow, high speeds on the freer points of sailing.

I notice the comments on combiantions of surface running foils with submerged foils below. We are experimenting with this on the dinghy rudder to give some tactile feed back to allow the correct incidence to be maintained. It could also be used to give crude ride height control to a submerged lifting foil but will obviously have problems if the speed increases sufficently for the submerged foil to lift the SR foil away from the surface. We put this in the patent application because you need to (?) but I do not have much faith in it as a design approach.

On a sailboard it gets very interesting since cavitation will not occur, the board is kept away from wave impacts (and hence much of the source of drag on a planing board) and the span loading is reduced by at least a factor of two giving a much lower lift induced drag. If you want easy foiling go for the dinghy, if you want to scare yourself go for the board.

Jon."

 

You are describing a surface piercing set up here. The Tomahawk foil is surface running. When fully ventilated and at design incidence all the lift comes from the lower (pressure) face, the suction face is unloaded. It can therefore operate below the surface or actually on the surface in which mode it forms a cambered planing surface but does not suffer from the drag caused by wave slap on a planing hull.

Jon.

 

Jon Howes, for this foil to function properly as a planing surface, what is the maximum heel angle ?

I imagine it must be fairly horizontal to function as a planing surface?

 

Can it be in the same league of efficiency if you make it fore aft symmetrical?

Tc; I'd still call it planing even if you'd have to tilt it 45' (or even uspside down) due to the required lift vector - if, at that speed and depth it was ventilated.
Just to be obnoxious I'd say it was then more a half V than an inverted T.
I think I've observed that the boats that can, tilt their T foil until the normally vertical surfaces are more or less unloaded - this usually decreases sail drive if exaggerated though.

Look at kiteboards in high winds for examples of extremely deep half V planing hull shapes

 

Tcubed and Sigurd,

This is possibly the aspect of this foil that I have most trouble getting across. Sigurd has it about right however.

Because it is ventilated with all the lift, in the design condition, from the pressure face it does not care particularly whether it is running at the surface or not and so if rolled it works exactly as designed although submerged. Sigurd had it about right by describing it as half a vee in this mode.

Jon.

 

Ok but there is then a spanwise gradient of operating depth/conditions.

How does the foil react to being at varying depths at the same time?

<<<<<<<<Look at kiteboards in high winds for examples of extremely deep half V planing hull shapes >>>>>>>>>>

Yes but is a very low aspect shape. This foil has the opposite aspect ratio and i wonder how the ventilation transitions to nought at the most immersed end.

 

It doesn't mind at all. The ventilation only has to overcome hydrostatic pressure which means that it remains nice and progressive as it moves out to the underwater tip. The heeling moment must reduce as this occurs since the underwater tip will progressively lose lift as the ventilation progresses.

Jon.

 

Try Alinghi to install your foil under their new trimaran

Hi,

I am just a enthousiastic sailing spectator but to my humble opinion:

Why don't you try to have your foils installed in the next sparring partner for the BMWO tri. http://www.bymnews.com/photos/displayimage.php?album=240&pid=87864

Rumours are that Ernesto is somewhat willing to pay a bundle to help innovation. Until now I have somewhat heard that the Dogzilla project has been canceled by the recession. But if Alinghi gets the chance to bluff Larry Ellison of again he might be interested.

On the other hand, Hydroptere crashed a month ago and they have not the same foils but to handle a maxi tri in waves at 50 + knots boatspeed is a dangerous expedition. I have a proposal to install a ejectorseat with parachute as it happens. Just as in jet fighters.

What do you think of it?

 

Tomahawk Foiler

Unfortunately, I got an e-mail from Ovington boats this morning saying they will not be going ahead with the Tomahawk in the forseeable future. Damn shame! But it will only be a temoporary setback for what will prove to be a major development in foiler design.....

 

I was wondering how much it will cost. That's the second question for a people's foiler I would guess -the first being "can I fly it?"