clivee1
Member
After 3 years of sailing UK Cherubs we have decided to fit foils to our boat.
The UK Cherub class split from our Australian cousins in the early 90s when in response to dwindling fleet numbers and perceived threat from new UK SMOD asymmetric classes the class adopted asymmetric kites before the fleet down under were ready to do so.
In 1997 the asymmetric got bigger and since 2005 we have had twin wires 15.5m^2 of up wind sail, 23m^2 kites on 12' boats that weigh 70kg fully rigged. We have a small but vibrant fleet with recent nationals being won by boats designed by Kev Ellway, Paul Beiker and a derivation of the Nuplex 12' skiff from David Lee. T foil rudders are universal.
Crew weights are typically 130 - 150kg. Within the fleet there is a mix of young light adults / couples and ageing skiff sailors sailing with their offspring.
It is one of the few active open development classes remaining in the UK.
Foils are fully legal.
Many will ask why they are not already standard. the boats are very similar to Kiwi R Class where they have been shown to work.
I think that the broad range of conditions we see in the UK and a the daunting prospect of trying to stay on the side of a short trapeze dingy during crashes have put most off.
Last year Graham and Eddie Bridle converted their boat having won every thing possible with Eddie rapidly outgrowing the restricted space at the front of the cockpit. They showed that the boats can fly but have not managed to reliably get around the race track.
Compared to the Moth our sail area to all up weight is similar upwind and potentially much better downwind.
(15.5m^2 / 210kg Vs 8.25m^2 / 110kg upwind).
With twin wires and 1.8m beam our sail carrying ability is better.
However our hulls are only one foot longer, nearly 3x the water line width and carrying twice the weight so getting to take off speed is going to be a challenge. We do not have the aero dynamic efficiency of the Moths high aspect una rig and minimal hull. I have no expectations of getting close to their performance.
As an un athletic 50 year old sailing with my 13 year old son I have no desire to do 30kts on the wire. Others can try that.
We typically sail at 8-10 kts upwind. It would be nice to see this increase. Downwind we routinely do 15-18 and occasionally hit 20.
The biggest challenges are going to be take off at low wind speeds and having good enough control to avoid the crashes that would eject us off the front.
Our solution is a twin centreboard Pi foil configuration with a large main foil.
I was going to make the foil with a 1.6m span but have reduced it to 1.45m so that it still loads onto the trailer and so that we can roll it for rigging with the foil retracted against the hull. The foil area is 0.22m^2, giving 30% more area to weight than the more recent moth foils. This gives a 10:1 AR similar to the Blade Rider or first Mk2 foil but lower than the more recent ones.
The Pi foil configuration allows the wand to control the pitch of the entire foil which should give better height control than just the flap.
It also allows a centreline wand to be used.
It is was much easier to build as there are no structural T joints or complex flap assemblies.
We have used a DAE41 foil section that was developed for low Reynolds human powered flight.
It has low Cd for Cl near zero to Cl ~1.5 which is higher than we would ever want to use because at that level the induced drag would be higher than the hull drag if we were low riding. The section has quite a high pitch moment. To counter this we have added a tail plane to the foil.
This can be adjusted to tune the load on the push rod.
We sailed for the first time 2 weeks ago. The boat would take off readily but height control was very poor, and we had some bruising crashes.
We had our second sail last weekend after tweaking the tail plane. Control was much better but we were both nervous after the previous crashes. Youtube link below - how do you embed a youtube vid?.
We have no commercial aspirations for the project. No expectations of breaking records but do hope to have some anarchic fun.
Come and see us at http://www.uk-cherub.org/forum/index.php/topic,1946.0.html
or http://www.uk-cherub.org/doku.php
or better still come and join us on the water or in the air.
The UK Cherub class split from our Australian cousins in the early 90s when in response to dwindling fleet numbers and perceived threat from new UK SMOD asymmetric classes the class adopted asymmetric kites before the fleet down under were ready to do so.
In 1997 the asymmetric got bigger and since 2005 we have had twin wires 15.5m^2 of up wind sail, 23m^2 kites on 12' boats that weigh 70kg fully rigged. We have a small but vibrant fleet with recent nationals being won by boats designed by Kev Ellway, Paul Beiker and a derivation of the Nuplex 12' skiff from David Lee. T foil rudders are universal.
Crew weights are typically 130 - 150kg. Within the fleet there is a mix of young light adults / couples and ageing skiff sailors sailing with their offspring.
It is one of the few active open development classes remaining in the UK.

Foils are fully legal.
Many will ask why they are not already standard. the boats are very similar to Kiwi R Class where they have been shown to work.
I think that the broad range of conditions we see in the UK and a the daunting prospect of trying to stay on the side of a short trapeze dingy during crashes have put most off.
Last year Graham and Eddie Bridle converted their boat having won every thing possible with Eddie rapidly outgrowing the restricted space at the front of the cockpit. They showed that the boats can fly but have not managed to reliably get around the race track.

Compared to the Moth our sail area to all up weight is similar upwind and potentially much better downwind.
(15.5m^2 / 210kg Vs 8.25m^2 / 110kg upwind).
With twin wires and 1.8m beam our sail carrying ability is better.
However our hulls are only one foot longer, nearly 3x the water line width and carrying twice the weight so getting to take off speed is going to be a challenge. We do not have the aero dynamic efficiency of the Moths high aspect una rig and minimal hull. I have no expectations of getting close to their performance.
As an un athletic 50 year old sailing with my 13 year old son I have no desire to do 30kts on the wire. Others can try that.
We typically sail at 8-10 kts upwind. It would be nice to see this increase. Downwind we routinely do 15-18 and occasionally hit 20.
The biggest challenges are going to be take off at low wind speeds and having good enough control to avoid the crashes that would eject us off the front.
Our solution is a twin centreboard Pi foil configuration with a large main foil.
I was going to make the foil with a 1.6m span but have reduced it to 1.45m so that it still loads onto the trailer and so that we can roll it for rigging with the foil retracted against the hull. The foil area is 0.22m^2, giving 30% more area to weight than the more recent moth foils. This gives a 10:1 AR similar to the Blade Rider or first Mk2 foil but lower than the more recent ones.
The Pi foil configuration allows the wand to control the pitch of the entire foil which should give better height control than just the flap.
It also allows a centreline wand to be used.
It is was much easier to build as there are no structural T joints or complex flap assemblies.
We have used a DAE41 foil section that was developed for low Reynolds human powered flight.
It has low Cd for Cl near zero to Cl ~1.5 which is higher than we would ever want to use because at that level the induced drag would be higher than the hull drag if we were low riding. The section has quite a high pitch moment. To counter this we have added a tail plane to the foil.

This can be adjusted to tune the load on the push rod.

We sailed for the first time 2 weeks ago. The boat would take off readily but height control was very poor, and we had some bruising crashes.

We had our second sail last weekend after tweaking the tail plane. Control was much better but we were both nervous after the previous crashes. Youtube link below - how do you embed a youtube vid?.
We have no commercial aspirations for the project. No expectations of breaking records but do hope to have some anarchic fun.
Come and see us at http://www.uk-cherub.org/forum/index.php/topic,1946.0.html
or http://www.uk-cherub.org/doku.php
or better still come and join us on the water or in the air.