Launching our Homebuilt Foil stabilised dinghy – this article is to use our experiment as the basis for low cost foiling that anyone can use to build or modify a boat – it sailed nicely in 5 to 10 knots and I didn’t have to do any hiking.
This is not about outright speed (wrong hull type for a start).
It is about stability without hiking out.
On the other hand if it works on this boat … it will work on anything!
No worthwhile video I am afraid – little wind when the photo boat was available on Sunday. We will get some next weekend with luck.
This is part of a four article set
- Part 1 – Sailing Trials in 5 to 10 knots of the hydrofoil stabilised dinghy.
- Part 2 – Building a Hydrofoil Stabilised dinghy – and proposal for comparison using any hull. Up later today
- Part 3 – Video in more wind – Next weekend if there is wind!
- Part 4 – Three Homebuilt hydrofoiling Projects – democratising foiling! Up Next week
Myth busting Foiling Boats – you don’t need a factory and you don’t need carbon fibre.
Everyone knew this once – because the recent history of making foiling work was achieved with homemade foils using timber and fibreglass.
The great Myth about foiling boats is “that it is high tech and everything has to be carbon”. But all the significant development in the Moth Class was with wooden hydrofoils that were fibreglassed with only small amounts of carbon or stainless steel.
The specification itself is to provide a basis for cheap experimentation and comparisons of performance.
The Foiling Moths advanced so quickly because there was a specification and people messed around with the spec and shared information. Wood and glass make fast modifications to homebuilt hydrofoils easier (and cheaper)
Maybe even racing if anyone has a mind to. But also as the basis of comparison with boats in other areas.
What does it feel like – a homemade foil stabilised boat upwind
We had good luck for the first day of testing – 5 to 10 knots and a well sailed Oz Goose as a pace boat. Started to get a feeling of the speed potential.
This section is about that.
Second day when we had a chase boat with cameras – of course the wind died.
Hopefully we will have video next weekend.
The lateral foil to leeward needs to be kept in the water in the lulls. In 5 to 10 knots this meant sitting a little to leeward.
Initially as gusts hit I would follow instinct and make the wrong move. Hiking out brings the foil would to near the surface, would ventilate (suck air from the surface) and then the boat heel and slow.
Well … it is obvious … sit to leeward in the lulls, when the gust comes let the foil do the work – don’t move out to windward.
No Hiking.
But with the same sail they were hiking in the accompanying Oz Goose.
So what to do when a boat with a lateral foil heels?
Don’t move your butt!
Ease the sail and point a fraction lower to get the boatspeed up.
The lateral foil starts to rise because of more lift – fly it up again.
Then I could wind in the sheet again to increase the heeling force. It is a feeling like flying. Boat heels then get speed without increasing the heeling force. Wind drops, move your body a little to leeward. Sheet loads seem higher – greater stability than hiking?
It becomes quite mesmerising watching the foil a foot or two below the water surface.
As the foil produces lift there is a depression in the surface of the water above the foil – which turns into a series of waves that make up the foil wake stretching back. It it like being followed by a small Loch Ness Monster.
It does also show that the homemade hydrofoil is developing lift at low speed.
The photo is at a very low windspeed/boatspeed. These wavelets go quite a way back. On Saturday with more wind and boatspeed I thought the transom was digging in and making a commotion.
But, it was the combination of the hull’s sternwave and the foil’s wake making a noisy quarter wave on the leeward side
So this is the exciting thing – not pure speed but less physical effort
At the moment many foiling systems are more or less being retrofitted to conventional boats.
Many of those boats are very wide – like the IMOCA 60s or some of the supermaxis.
Interestingly it is more moderate beam boats that win most races. They are faster in light winds, faster upwind and can sail deeper angles downwind without losing speed. A bit easier to steer too.
The question is … if we gain stability from a lateral hydrofoil – what is the beam for?
Canoes are light, fast and easy to store and transport. But can be hard to hold upright. PERHAPS this is a good place to start.
Another aspect is that modest length boats for disabled sailors have limited stability (and speed) because the centre of gravity of the crew is so high.
I also think about what will happen when I can’t hike out so hard. That’s why I win Oz Goose races. But I can certainly feel it in my 60 year old bones. The day is not close, but it is coming.
The inspiration of the Quant 28 and 17
Normally a keelboat this size without a canting keel would need 5 to 7 people on the rail.
Same lateral foil but a more beautiful version by Hugh Welbourne for Quant Boats in Switzerland.
The lateral foil is the simplest possible lifting foil.
Video image can take a moment to load.
In terms of stability – see how the crew on the Quant 17 go from full trapezing and hiking to sitting inside the boat when the foils are deployed and to leeward as soon as the boat has any downwind component.
Video image can take a moment to load.
I’m interested in the stability component.
In homebuilt hydrofoil boats Ian Henehan’s modified Oz Goose saw him chuck the hiking wings and start sitting inboard too.
Video image can take a moment to load.
It was like this with a hiking rack before – no longer needed. Simplification and less effort.
Perhaps: an advantage of some rocker for foiling dinghies
We didn’t fit a rudder foil at this stage – even though we built the rudder extension.
The purpose of a rudder foil on all foilers is to hold the main foil at an optimum angle of attack. Usually the rudder foil is adjustable in some way to allow the adjustment of the angle of the main foil.
If the rudder foil is sent lower then the angle of attack of the main foil is increased.
But with the 8ft boat with the extreme rocker it was possible to move back to increase the angle of incidence of the main foil. The base angle is 2 degrees Angle of Attack relative to the static waterline of the boat.
In the gusts of around 10 knots, going upwind, it was possible to move forward or back to reduce or increase lift – speed changes from doing so were instant. So where you sit in/on a rockered boat is a critical tuning factor.
Less rocker might be OK, but some rocker is going to be important. Maybe concentrated in the back end of the boat. I’m not sure if the foil fitted IMOCAs do this with water ballast.
Overview of comparison sailing the hydrofoiled boat against the larger Oz Goose
This is not necessarily a question of speed, though it is nice to get.
Our 8ft boat is absolutely sub optimal as a foil stabilised boat.
- It is short, so potential hull speed is low – 8ft long. This limits foil lift (square of velocity).
- It has a lot of rocker (fore and aft hull curve)
- Crew weight is a very large part compared to the boat volume – it was meant to be a prototype kid’s boat but the curved cockpit was too hard to build. So we repurposed it.
Saturday it was sailing around in company with Job and Jazmine in a Goose who I compete against in that class. They are among the top sailors in the Oz Goose so I know the speeds they hit. And the new boat has an Oz Goose Rig but is only 8ft to the Oz Goose’s 12ft length.
In the lighter patches it was noticeably slower than the Goose, but it was still sailing properly (felt normal/good). It was a faster choice to retract the foil. Pushed out to windward the hydrofoil is above the water to reduce the wetted surface.
With a bit more wind and foil deployed it started to equal the goose upwind. This is not something the shorter boat should be able to do.
The biggest difference – no hiking.
While Job and Jazmine were hiking in the Oz Goose I found it best to move to keep the foil in the water in the lulls – which meant I was sitting centrally or to leeward and not hiking in the gusts.
It is low effort sailing.
Downwind differences – was the 8ft foiled boat able to stick with the 12ft Oz Goose?
Downwind the Goose should have walked away from the smaller boat. I’ve a lot of experience with the 8ft Oz Racer and a GPS and know the boat tops out at around 4.2knots or just about 5. It can go quite a bit faster (up to 8knots) but it takes a lot of wind and it drops back to the 4 to 5kn range as soon as the gust drops slightly.
The Goose, however just loves to accelerate into the 6 7 or 8 knot range and on stronger wind days gets up in the 8 to 12 knot range. And beyond.
So the Goose should get away from the shorter boat.
It did … but not too dramatically. More comparative trials to come.
Now we hope there is more wind next Saturday when we have the photographer and a chase boat.
Our recent articles on homemade foiling and
- Part 1 – Sailing Trials in 5 to 10 knots of the hydrofoil stabilised dinghy.
- Part 2 – Building a Hydrofoil Stabilised dinghy – and proposal for comparison using any hull. Up later today
- Part 3 – Video in more wind – Next weekend if there is wind!
- Part 4 – Three Homebuilt hydrofoiling Projects – democratising foiling! Up Next week
