Questions about designing a dinghy mast

[Noah Stone]

Hello, I just have some questions surrounding the design of dinghy masts.

1. Two-Part Masts: I’m curious about the impact of making a mast in two parts on its structural integrity. This question applies to both stayed and unstayed situations. Does dividing the mast into two parts significantly affect its strength or performance? Are there any specific considerations or precautions one should take when dealing with two-part masts?
   
   
2. Mast Shapes: My second question revolves around the shape of the mast. Specifically, I’m wondering if there are any considerable differences between a circular mast and a more airfoil-shaped one. Does the shape significantly influence the performance of the dinghy? If so, in what ways?
   

I’d love to hear your thoughts and experiences on these matters. Any advice or information would be greatly appreciated!

 

[wet feet]

I will leave the first question to the structural engineers.The best way too learn more about the second might well be to read Frank Bethwaite's book,as it has a section on the topic.Hiring a wind tunnel would be much more expensive.

 

[myszek]

Mast Shapes: My second question revolves around the shape of the mast. Specifically, I’m wondering if there are any considerable differences between a circular mast and a more airfoil-shaped one. Does the shape significantly influence the performance of the dinghy? If so, in what ways?

If not rotating, the airfoil-shaped mast can perform worse than the circular one. Currently, the D-shaped mast section is considered to be optimal. Like this one:
View attachment 191429
Of course, you can also consider an airfoil-shaped rotating mast, or a sleeved sail, or some rotating fairing behind the mast etc.

regards

krzys

 

[tlouth7]

A two part mast is always going to be heavier than an equivalent single piece, but structurally you can achieve much the same results. A lot of focus on modern dinghy masts is achieving the desired flexibility, especially the ability for the topmost section to deflect in a gust and so dump power. Compare the nice continuous curve and gust response of a carbon RS Aero mast vs the kink you often see in an aluminium Laser mast.

I have never come across a rotating, foil section, free standing mast but no doubt it could be done.

 

[Noah Stone]

I will leave the first question to the structural engineers. The best way too learn more about the second might well be to read Frank Bethwaite's book,as it has a section on the topic. Hiring a wind tunnel would be much more expensive.

Which of Frank Bethwaite’s books you’re referring to? Are you referencing his 2011 edition or his earlier works? Wind tunnel testing would be interesting although not really a possibility sadly.

 

[Noah Stone]

If not rotating, the airfoil-shaped mast can perform worse than the circular one. Currently, the D-shaped mast section is considered to be optimal. Like this one:
View attachment 191429
Of course, you can also consider an airfoil-shaped rotating mast, or a sleeved sail, or some rotating fairing behind the mast etc.

regards

krzys

An airfoil rotating mast could be interesting has anyone done this on a sailing dinghy?

 

[Noah Stone]

A two part mast is always going to be heavier than an equivalent single piece, but structurally you can achieve much the same results. A lot of focus on modern dinghy masts is achieving the desired flexibility, especially the ability for the topmost section to deflect in a gust and so dump power. Compare the nice continuous curve and gust response of a carbon RS Aero mast vs the kink you often see in an aluminium Laser mast.

I have never come across a rotating, foil section, free standing mast but no doubt it could be done.

I might end up trying to make such a thing, If I do I could make a model on my 3d printer and make a mini wind tunnel and a load cell to record the performance difference, would such a thing give any usable data for a larger version?

 

[messabout]

Way back in the dark ages, Moths used a foil shaped wooden mast. Most of them were rigged so that the shrouds were attached a half inch or so in front of the foil. The gooseneck was a flat piece of stainless wrapped around the mast and extending back for six or eight inches and slightly bent in such a way that it created a stop for the mast auto rotation. That simple layout caused the mast to rotate and the flat bar gooseneck limited rotation in whatever degree the sailor chose.

 

[wet feet]

Way back in the dark ages, Moths used a foil shaped wooden mast. Most of them were rigged so that the shrouds were attached a half inch or so in front of the foil. The gooseneck was a flat piece of stainless wrapped around the mast and extending back for six or eight inches and slightly bent in such a way that it created a stop for the mast auto rotation. That simple layout caused the mast to rotate and the flat bar gooseneck limited rotation in whatever degree the sailor chose.

As far as I know, Moths still use a rotating mast and it tends to be somewhat foil shaped.I'm also pretty sure that iceboats do much the same,so it isn't exactly unknown.

As far as Frank Bethwaite is concerned,I have one of the early editions of his High Performance Sailing and there is a section that covers the development of mast sections.It includes some information about the wind tunnel he developed to aid the process.

 

[Noah Stone]

Way back in the dark ages, Moths used a foil shaped wooden mast. Most of them were rigged so that the shrouds were attached a half inch or so in front of the foil. The gooseneck was a flat piece of stainless wrapped around the mast and extending back for six or eight inches and slightly bent in such a way that it created a stop for the mast auto rotation. That simple layout caused the mast to rotate and the flat bar gooseneck limited rotation in whatever degree the sailor chose.

Interesting how hard would it be able to make this out of cf or gf?

 

[gonzo]

Penguins used to have rotating masts. The setup was a wooden fork protruding to the front of the mast. The crew yanked lines attached to each side to make it rotate when tacking or changing course.

 

[BlueBell]

yanked lines

Is that a technical term?

OP, can you make an enveloped leading edge that surrounds the mast?
A pocket is it called? Like on windsurfers.

 

[wet feet]

Interesting how hard would it be able to make this out of cf or gf?

Not hard at all,for those with experience of those materials.What would be more difficult would be altering the bend characteristics once made.It is much easier to plane off a few shavings or to glue a sliver onto a wooden mast to refine things and that was what the Finns and OK's used to do.The development of the carbon Finn masts was quite a process and had the class not been in the Olympics,it would have taken much longer.As there was an element of national pride involved the defence and aerospace industries were involved and had the resources to move things along.A hobbyist would struggle to compete and a hobbyist without a baseline to work from will probably not have a long enough lifespan to run through all the stages of refinement to reach the perfect outcome.

 

[Noah Stone]

Not hard at all,for those with experience of those materials.What would be more difficult would be altering the bend characteristics once made.It is much easier to plane off a few shavings or to glue a sliver onto a wooden mast to refine things and that was what the Finns and OK's used to do.The development of the carbon Finn masts was quite a process and had the class not been in the Olympics,it would have taken much longer.As there was an element of national pride involved the defence and aerospace industries were involved and had the resources to move things along.A hobbyist would struggle to compete and a hobbyist without a baseline to work from will probably not have a long enough lifespan to run through all the stages of refinement to reach the perfect outcome.

So, if I understand correctly, you’re suggesting that the challenge lies not in the shape of the mast, but in achieving the correct mast bend. So it might be easier to adapt the boat design to use an already tried and true mast?

 

[Noah Stone]

And one more question, what is the performance difference between batons in the sail going vertically or horizontally and the difference between internal batons and an outer structure holing the sail shape like on the WASZP