Polar Foil

I have for some months been working on a new idea for our Footy’s which may revolutionise hull appendages

You will no doubt have all at one time or another while doing the washing up had a soapy plate slip from your hands back into the sink and watched as the lip of the plate lifted the edge right back up toward the surface before the momentum died and the reverse happened till the plate settled at the bottom of the sink.

Now imagine that with a sail powering it ~ it would continue to lift till the maximum attitude was achieved and then maintained.

It occurred to me that this effect could be harnessed with our Footy’s and that the dish shape could be added as a hull appendage without affecting the CLR.

This lifting effect could then be harnessed thereby lifting the Footy bow especially on a run when we know that our pride and joys like to think they are submarines!

Having the Polar Foil lifting the bow up would also give additional control in tacking due to the rocker of the foil.

Now you know I come up with some zany ideas sometimes but you also know I like to share them with you ~ well it’s all part of our Footy culture.

My research on the net took me to the Defence Technical Information Centrean ammunition explosives and ballistics site where they were testing different shapes for projectiles.

It occurred to me that if the Army were working on this with different shapes then it must be feasible.

I am going to try some experiments to see if I’m right ~ I decided to call it a Polar Foil because it will be circular and made from white Depron

I would of course welcome your comments and ideas as to how the Polar Foil could attach to the hull or keel
All ideas are welcome no matter how daft it may sound.

I will of course keep you updated and hope that toward the end of the month I might just have a prototype ready for trials

Best wishes

After due consideration it may end up being more of a U shape with the base of the U at the bow end.

Sorry Andy, I have a mechanical dishwasher. :confused: but I will work on your analogy. :graduate:

We’re talking about a little mini ‘hydrofoil’ at the bow, right?

I’m wondering if the induced drag will negate the benefit…

I’m also wonding if it should be somethign that ‘snaps’ into place… (for downwind runs only…) Say, when the jib is fully extended, it hits a leaver to lower the bow foil… and then lifts it as you ‘harden up’…

Of course, a ‘tube’ shaped keel might be an interesting idea… Somethign akin to a [large dia.] toilet paper tube in place of the keel / fin / centerboard…

T-H ~ go try it, fill a sink or the bath with 4 to 5 inches of water take a side plate and with the plate at about 30 degrees down and lip of the plate just under the water, let the plate go.

It will slide in and immediately try to surface, as the momentum slows it reverses the action and trys to do it the other way.

This see-saw motion will continue until the plate reaches the bottom.

I think we could take advantage of these natural hydrodynamics

Interesting ideas you have there would you care to expand them?

Ok, I’m “learning” inventor… so, they’re crude pics, but illustrate what I’m trying to convey. Nothing is to scale or sized right, but you can get the idea / intent… Shape / imagine as needed!

A tube for a fin, either intersecting the hull, or tangent to…
And obviously the tube axis is parallel to the boat’s intended course.

The longer the tube, the more likely you’ll get some ‘fluid compresion’ happening, and that can mean major drag!

A ‘BT -80’ paper tube for model rocketry should do nicely…
(from my other major hobby! And there are some rockets that use ‘tube fins’)


Cut to size & shape, and coat (generously) with Valspar or some other sealant. Probably 1/5" at top, and 1" at bottom…

Ballast can be spread out over an area at the bottom of the tube fin, not the standard ‘torpedo’ shape… But soemthing ‘blended’…




I do see issues that if not aligned properly a loop keel could induce more heel than anticipated…

OK, some more elaboration…

I hope the pics help!

Your ‘bow plane’ is on a pivot, and the pivot obviously has a lever arm.
At the end of the lever arm, is a pin, which rides in a slot. Either a loop in some line, or a slot in a solid something or other (as shown.). there’s a pulley at the bow, and at the stern, forming a loop through-out the length of the boat. (it’s probably in a figure-8 to push & pull as needed…)

As the sail arm is moved, the loop moves. The slot allows for no ‘action’ on the bow plane, unless the extremes are met. So, if the sail arm is moved “out”; the extreme for a run, the loop pushes the lever, rotating the pivot, and lowering the bow plate. Once the mark is rounded, a yank on the stick (opposite direction ) it will pull the loop, and the reverse should happen [the bow plane is raised]. Slacken off, and trim as required for the beat / reach upwind…

The idea is that eh loop allows freedom of ‘play’ while trimming eh sail. It only acts against eh pivot leaver at the extremes…

Obviously a bit of friction on the pivot, to ensure it sticks up or down.

OK, I hope the PDF comes out better!

Yeah, because of water’s dencity, alignment is critical…

But it can be an intersting experiment! And if Andy is wiling to try it, why not! :smiley:

Neat link! I thought there would have been more studies & such, but I guess the dynamics of a tubliar construction & structure requires some radical materials!

is the bow plane going to be in the center of the bow boat (like a centerboard trunk) remember that no part of it can extend beyond/above (assuming you are the extremes) the box at any point in time…

I don’t see how you could get it to release with just a touch (gravity, spring and water pressure) could get it to drop, but then you have to get it back up and stowed. some interesting mechanics. Also by doing this we are adding weight to a boat. In quite possibly the worst place to add weight.
Also when raising and lowering, at least until its set, you’d be adding a fair amount of drag, on a boat that already slows to a crawl when the wind stops… I’m not trying t o stifle any radical ideas. just playing the devils advocate mroe or less…

Hi Marc,

No, conversation is good! I am new to all this… Andy asked for some elaboration on the ideas I originally repsented. This is just that, trying to elaborate on my initial thougths. Yes, the eventual “mechanics” will need thinking through, to ensure they do meet specs.

The riding loop pulls it up & down. It’s not ‘loose’, some stiction / friction / resistance in the pivot point/ pivot tube will hold it up or down. I dunno… An elastic to help hold it up… The sail arm, when ‘out’ keeps it down (against the rubber band tension…)

My concern exactly: adding a bunch-o-stuff up front, adding weight, more ‘movign parts’, holes in the hull, & intrducing a new element that will add some amount of drag… But if he want’s to try it / pursue it…


When you mentioned putting tube under the bow, I had this picture come to mind. It streamlines the hullshape for a more efficient hull and puts more boyancy up front…

interesting concept with a bulbous bow (as it called) but then you be looking at more of a displacement hull and that would increase the whetted surface dramatically…

the bulbous bow help break the bow wave of a ship and increases the efficiency of the hull by lessening the effort to move the boat forward.


As an ex-submariner, i can tell you that bulbous bows are a nightmare.
Submarines rising to periscope depth before surfacing have to be especially alert for other craft that may be approaching them.

Some bulbous bows actually mask the propeller so efficiently that the ship is almost silent in the forward 2 to 3 degree arc

So the last thing you want to do is come to periscope depth right in front of them


RE bulbous bows: My understanding is that the size and volume of the bulb needs to be tuned to the characteristics of the hull and to the intended operating speed. Thus, fine for a supertanker plodding all the way round Africa and up the Atlantic at a steady 12 kt, but not easy (if at all possible) to get right for a sailing craft which will progess at widely varying speeds and, if racing, will be performing frequent quite severe manoeuvres, which will cause fluctuation in through the water speeds. I don’t recall any full size designer of sailing craft who has played with this. Also, like the design of winged keels, it needs lots of computer power.


Elstrom & Kjaerulf played - using quite a lot of Somebody Else’s Money. They gave up.


The big problem with bulbous bows on a Footy stems - sorry about that - from the fact that the most successful versions have been fitted ahead of the normal ship’s bow. This would necessarily compromise a Footy’s waterline length.

The bulb itself is tuned to the normal hull such that its own bow wave creates a hollow in the water at just the same position as the normal bow creates its wave. A certain amount of cancelling-out occurrs reducing the height of the overall wave and hence the mass of water having to be displaced. With less water being displaced less power is needed to move ahead at the same speed.

Russell has mentioned why the concept hasn’t been seen on yachts yet.



Ok I have had to resort to black Depron as an intrim for testing purposes

I first roughly trimmed back the edges till I had the right width and then cut a slice like a segment of orange skin.

For the purposes of the trial I have decided to use GBR221 “PussyFoot”
I decided to use her because she has a massive rig and when running its almost like a spinaker.

Her shallow keel also gives me a chance to fit the Polar Foil to the hull without too many modifications and to change size or style quite quickly if needed.

I figured that if she can still get an element of lift with the mast all the way forward then a rig mounted further aft should have an easier job

If i am feeling any better (trying to get over real Flu ~ not man Flu) this afternoon, I might try a trip to Clevedon to try it out.