Peter Venn has been using hovercraft for more than 40 years. From weed control, mining support to extensive fun rides, he’s done most things.
His current workhorse was custom built for him. Essentially a widened, lengthened Viper, it has a separate lift engine at the front and a Subaru EA81 driving a large thrust fan.
Although based on a extended segment hull, the craft has no ducting to feed air to each segment. The intention was to fit a loop segment skirt, but that didn’t happen. Instead Peter fitted standard extended segments. While the craft would cruise and perform well, it was very difficult to take off from a floating start. Since there was no pressure distribution, Peter developed a wild rocking technique to get the hull to initially lift from the water.
He was never really happy with the string of changes and developments he tried to improve the skirt performance.
So he was very interested when I told him about the trials I had been doing with bag skirts on that hull profile.
Needless to say, we decided to do it.
The Design
We decided to go head first and do a skirt based on my 2017 trials – a dual bag.
The craft is a one off so we spent a lot of time getting the measurements for the hull. Then the skirt was 3D CAD modeled.
Click image to view a 3D version in a new window
The obvious issue with fitting a bag skirt to a segment skirt hull is that the fixing points are the same profile all around the craft. The practical wisdom is that bag skirts need to be constrained differently at the front to minimise the pitch down motions. Sometimes this is done by tailoring – adding in panels and joins to make the skirt fit in a particular way.
Since this was quite experimental, we decided to stick with the same profile all around and just sew the panels together. If the shape of the front of the skirt was poor or behaved badly, then the skirt could be picked apart and a new front made.
The sections of the little wear bag at the ground contact point were not going to be joined to one another. At the intersection of two panels there was to be no join between the wear panels. The idea was that this was where the inflation air and any water would escape.
Build and test
Peter made the main bag from PVC material and sewed the joins. He decided to not add the lower bag before actually running the skirt.
Without the wear panel skirt, the ground contact point was much further outboard than intended – in fact getting very close to the stability limits for a bag skirt. However the craft hovered and ran.
The first issue that appeared was the lack of hoverheight compared with the segment skirt. Peter has a steep ramp to leave the river at the bottom of his property and the front of the hull was impacting the ramp.
Second was the spray over the front. After many years of very little spray and staying dry, it was annoying but manageable
The kicker was that it was difficult to load on to his trailer. The bag skirt extends out much further than the extended segments and that extra width is much lower. The trailer had simply not been designed for that width.
The skirt is bounces a lot which is consistent with the ground contact being so far out. Although Peter didn’t do a lot of operation with this skirt, he didn’t have a plough-in as you might expect. It looks like the propensity of the skirt to deflect upwards meant that it didn’t tend to get dragged under the craft, leading to a plough-in. Then again, it was probably Peter’s decades of driving experience.
The drawbacks of the skirt, especially the trailer, meant that we didn’t persist any further.
The TP6
Peter Venn has been using hovercraft for more than 40 years. From weed control, mining support to extensive fun rides, he’s done most things.
His current workhorse was custom built for him. Essentially a widened, lengthened Viper, it has a separate lift engine at the front and a Subaru EA81 driving a large thrust fan.
Although based on a extended segment hull, the craft has no ducting to feed air to each segment. The intention was to fit a loop segment skirt, but that didn’t happen. Instead Peter fitted standard extended segments. While the craft would cruise and perform well, it was very difficult to take off from a floating start. Since there was no pressure distribution, Peter developed a wild rocking technique to get the hull to initially lift from the water.
He was never really happy with the string of changes and developments he tried to improve the skirt performance.
So he was very interested when I told him about the trials I had been doing with bag skirts on that hull profile.
Needless to say, we decided to do it.
The Design
We decided to go head first and do a skirt based on my 2017 trials – a dual bag.
The craft is a one off so we spent a lot of time getting the measurements for the hull. Then the skirt was 3D CAD modeled.
The obvious issue with fitting a bag skirt to a segment skirt hull is that the fixing points are the same profile all around the craft. The practical wisdom is that bag skirts need to be constrained differently at the front to minimise the pitch down motions. Sometimes this is done by tailoring – adding in panels and joins to make the skirt fit in a particular way.
Since this was quite experimental, we decided to stick with the same profile all around and just sew the panels together. If the shape of the front of the skirt was poor or behaved badly, then the skirt could be picked apart and a new front made.
The sections of the little wear bag at the ground contact point were not going to be joined to one another. At the intersection of two panels there was to be no join between the wear panels. The idea was that this was where the inflation air and any water would escape.
Build and test
Peter made the main bag from PVC material and sewed the joins. He decided to not add the lower bag before actually running the skirt.
Without the wear panel skirt, the ground contact point was much further outboard than intended – in fact getting very close to the stability limits for a bag skirt. However the craft hovered and ran.
The first issue that appeared was the lack of hoverheight compared with the segment skirt. Peter has a steep ramp to leave the river at the bottom of his property and the front of the hull was impacting the ramp.
Second was the spray over the front. After many years of very little spray and staying dry, it was annoying but manageable
The kicker was that it was difficult to load on to his trailer. The bag skirt extends out much further than the extended segments and that extra width is much lower. The trailer had simply not been designed for that width.
The skirt is bounces a lot which is consistent with the ground contact being so far out. Although Peter didn’t do a lot of operation with this skirt, he didn’t have a plough-in as you might expect. It looks like the propensity of the skirt to deflect upwards meant that it didn’t tend to get dragged under the craft, leading to a plough-in. Then again, it was probably Peter’s decades of driving experience.
The drawbacks of the skirt, especially the trailer, meant that we didn’t persist any further.
Back to the drawing board.
Share this:
Like this:
Paul Moody