My Little Mule (MLM)

[Inquisitor]

Introduction and Credits

Another A.D.D. moment and diversion from the Z40½. Having never seen, much less sailed, a Proa in person, I thought it prudent to find out about it first-hand before I committed to the 60 foot cruiser. Besides, I want something to sail yesterday... not years down the road.

So... for your consideration and entertainment... My Little Mule

Before I start the design brief, I would like to thank a few people. Many people have influenced and directly contributed to the design of MLM. You would likely be surprised at the amount of analysis behind my ugly test mule. I would like to give credit to those people... Rob Denney, Rick Willoughby, Todd (tsstproa), Doug and a host of other important people from the HarryProa yahoo group.

As the saying goes... the buck stops here. I have made every effort to familiarize myself with the analysis tools that I have been introduced. I have even researched the theory behind these tools to make sure I fundamentally don't violate the assumptions. In some cases we have intentionally violated some assumptions to test some theories of our own. In some cases, I have altered design aspects from the advice of the group to meet design goals of my own. The structural responsibilities are solely mine since my degrees are in composite analysis and design. I am also going out on a limb with some structural theories of my own. I am also attempting to migrate some aerospace techniques to my basement workshop. Unfortunately, I am finding my technician skills are not even a glimmer of the technicians that once built what I designed.

So if MLM breaks up on its first visit to water... it is my fault. If it is slower than expected... it is my fault. If its a glowing success... it'll be an international team effort.

Thank you all.

 

[Inquisitor]

MLM - Design Brief

Here are the design guidelines. They are extremely malleable and will change without notice.

Test bed - The primary goal is to try out a Proa and to then experiment with different aspects. Pieces will be swapped out as the new things are tried.

Dirt Cheap - It is a test bed and is not expected to last a long time. Many things were purchased from local home supply stores, Internet surplus supply or just plainly scrounged up. Many things will be replaced as time goes on. Ply and cheap glass cloth may be replaced with hi-tech foam cores and carbon fiber. Could happen.

Timeframe - I require to have it sailing for next spring in the northern hemisphere. I would like to have it done so I can sail some this fall... although that's looking doubtful. This is a long weekend for me and we'll see how much gets built this weekend.

Speed - Its all about speed. Speed is the only yard stick I will use to determine success or failure. There is a particular sailboat race that I entered for the first time last year. I had a blast! Although I did so-so in my class, my POS monohull took ten hours to do the race that the fast cats were doing in three. Someday... I want line honors. I know, I'll never do it on skill... so I'm going to tech it to death.

Safety - Scratching my head... Safety is not a design consideration... the crew (me) will be wearing life preservers and likely... crash helmets. Sea worthiness is not considered... its for testing on lakes, rivers and bays.

 

[Inquisitor]

MLM - Specifications

• HarryProa style Proa. For those new to Proa's, a HarryProa style Proa is one where the leeward hull is optimized for speed and is as light as structurally possible. It also hosts the sailing rig, rudders and leeway prevention. Think of it as a single-minded hull optimized to sail fast and nothing else. Not even to carry people! The windward hull is likewise single-minded. It does nothing but, carry people and provide the righting moment. Nothing else!
• The initial mast and sails are from a Hobie 16 catamaran. I already had these lying around so it meets the cheap aspect. In the initial "to water" test will be using this rig in a stayed Easy-Rig format. If all works well with the rest of the design, one of the first mutations will be to go to a free-standing wing.
• Mast height 26'
• Sail area 218 sq-ft
• Leeward hull beam 13.9"
• Leeward hull length 30'
• Windward hull beam 24"
• Windward hull length 15.4'
• Beam over all 139"
• Weight (in-flux) ~200 lbs
• Hulls will be allowed to pitch independently.

 

[Inquisitor]

MLM - Current Build Status

Build Time 44.5 hours
Build Cost* $109.44

Leeward hull - all ply cut, bottom and sides assembled with corner stringers.
Windward hull - bottom and sides cut and assembled with corner stringers.
Diagonal beams - started cutting.
Rudders - wood cores cut, one rudder has the beam filament wound.

Tuesday, I hope to post the build pictures.

* There are a lot of things I already have on-hand that I don't consider as my current out-of-pocket expenditures I'm just concerned about how much I spend now. These things were purchased some time ago to experiment with... now they're going into a big experiment. These include:

• 50 lbs spool of fiberglass tow
• 2 gallons of epoxy/hardner
• Many yards of various styles and weights of fiberglass cloth.

If anyone is interested, I'll try to get a quantity and cost of those as I see what is used.

 

[Doug Lord]

Proa

Man, I think that is a cool looking project! Can you explain the design theory a bit-I see what looks like foils on one hull? Looking forward to hear about your progress and design/build iterations as they are devised-good luck!
How do you keep the drag of the little hull low? Will it plane?

 

[zerogara]

I think you should consider a free standing mast as your rigging doesn't make sense to me.

 

[troy2000]

I'm looking forward to seeing pictures of the real thing. Construction pic's as you go would be nice....

 

[ThomD]

I think you draw a pretty boat. I am skeptical about several things, which just makes me want to see your boat succeed all the more.

- I don't buy the hull shape, regardless of what the analysis says about straight keel lines. Flat bottom boats in my experience can be surprisings, but they seem to have more disadvantages than advantages, though in a speed only quest I wouldn't really know.

- 200 pounds sounds way short of the mark. Built lots of plywood boats, they aren't super light in flat bottoms. 3 mm ply tortured might be different. Though not that different once the structure is in.

- Most interested in how that rig will stay up. That rig will create a lot of power, I have the same numbers on my tri, though mine is a Hobie 18 rig, I guess there is inflation in everything. I would love to be able to use it on a proa.

- I put up a thread on HP about independent hull articulation. I didn't realize you were doing one.

- Newbies often jump all over the most radical technology by the bucket load. I think this will be an interesting experiment as to whether a lot of sophisticated analysis can get the job done. A bit like Mythbusters, or academic research where a bunch of experts try to reverse engineer an ancient tech, and then declare it a go or not, when the original took centuries to evolve. I think you are extremely wise to try a test out first. often the first iteration is flawed, but it serves very well to get on the right course.

 

[Inquisitor]

Man, I think that is a cool looking project! Can you explain the design theory a bit-I see what looks like foils on one hull? Looking forward to hear about your progress and design/build iterations as they are devised-good luck!
How do you keep the drag of the little hull low? Will it plane?

Doug, I've followed some of your threads and Hydroptere is an engineering marvel. MLM is a test mule and I'll be trying all kinds of things. Different hulls, a free standing mast, probably a wing... maybe even foils. At first, I'll be so excited for it to just float. It'll be my first sail boat of my own design and construction and I'll be taking small steps. Just messing with and getting the shunting and bi-directional Proa concept as second nature (to me) will be a huge part of my initial experience. Speed will come later!

What you are seeing are the rudders. If you are interested, you might want to join the HarryProa news group and dig up the emails with titles "Leeway Prevention", "My Little Mule", "MLM", "Assymmetric Bi-directional Rudders" for more details. There are over a hundred messages discussing, theorizing and designing their fluid dynamics and structural aspects.

One of the members tsstproa was showing his bi-directional rudders and Rick Willoughby really dug into the fluid dynamics of it. He mentored me in the use of JavaFoil as I followed his lead. The rudders are probably the most analyzed part. Although I can describe the basics, I'm a little fuzzy on why we can have the fore/aft symmetric rudder and ignore the non-optimum trailing edge. I imagine massive separation of flow and thus drag or worse... flutter. But, I trust in his evaluations and look forward to testing his theories in practice.

In theory... they're designed to handle full leeway prevention of the boat. The hull will be running true (AOA = 0). This is one of the major benefits of having the two rudders. Fully loaded up (when flying the windward hull) they will be supporting 600 pounds of lateral load. They will be presenting ONLY 15 pounds of drag. Their basic underwater dimensions are 2'x6"x0.6".

 

[Doug Lord]

Doug, I've followed some of your threads and Hydroptere is an engineering marvel. MLM is a test mule and I'll be trying all kinds of things. Different hulls, a free standing mast, probably a wing... maybe even foils. At first, I'll be so excited for it to just float. It'll be my first sail boat of my own design and construction and I'll be taking small steps. Just messing with and getting the shunting and bi-directional Proa concept as second nature (to me) will be a huge part of my initial experience. Speed will come later!

What you are seeing are the rudders. If you are interested, you might want to join the HarryProa news group and dig up the emails with titles "Leeway Prevention", "My Little Mule", "MLM", "Assymmetric Bi-directional Rudders" for more details. There are over a hundred messages discussing, theorizing and designing their fluid dynamics and structural aspects.

One of the members tsstproa was showing his bi-directional rudders and Rick Willoughby really dug into the fluid dynamics of it. He mentored me in the use of JavaFoil as I followed his lead. The rudders are probably the most analyzed part. Although I can describe the basics, I'm a little fuzzy on why we can have the fore/aft symmetric rudder and ignore the non-optimum trailing edge. I imagine massive separation of flow and thus drag or worse... flutter. But, I trust in his evaluations and look forward to testing his theories in practice.

In theory... they're designed to handle full leeway prevention of the boat. The hull will be running true (AOA = 0). This is one of the major benefits of having the two rudders. Fully loaded up (when flying the windward hull) they will be supporting 600 pounds of lateral load. They will be presenting ONLY 15 pounds of drag. Their basic underwater dimensions are 2'x6"x0.6".

--------------------------
You might check Tom Speers site-at one time he had sections designed for a proa that would be effective either way they moved.. Good Luck!

 

[Inquisitor]

I think you should consider a free standing mast as your rigging doesn't make sense to me.

Actually, a free standing mast is my first expected mod. I'm using this one since... its available and free.

Structurally, the lee hull is designed to handle a free standing mast. Most traditional Proa's (with stays) don't have any support for going aback. Their masts will just fall down! They are meant to always keep the wind on one side... no matter what.

I'll be modifying the Hobie mast. There is a 2' bury and I'll be adding reinforcement to the Hobie mast to help it cope with the bending moment if caught aback. However, for all primary healing and driving forces, there are the three stays to handle those primary loads. The drawings are not quite accurate, as I plan to have the fore/aft stays outside the sweep of the boom.

If you still see an issue, please describe it... either I'll have an oh-s@#$ moment or I'll be able to describe what considerations are in-place.

Thanks

 

[Inquisitor]

I'm looking forward to seeing pictures of the real thing. Construction pic's as you go would be nice....

Thanks for the interest Troy.

After this long weekend, I'll take pictures of the progress and post them here.

 

[Inquisitor]

I think you draw a pretty boat. I am skeptical about several things, which just makes me want to see your boat succeed all the more.

I just wish the pile of sawdust in the basement looked half as good. The sail colors were I guess what it was like when new... now they're all molted, torn and haggard.

I don't buy the hull shape, regardless of what the analysis says about straight keel lines. Flat bottom boats in my experience can be surprisings, but they seem to have more disadvantages than advantages, though in a speed only quest I wouldn't really know.

The leeward hull is probably the second most analyzed aspect. Again, Rick was the mastermind, but it... I follow a little better than the rudders. Here are some things we've (me and the other HarryProa news group) thought about.

Pro's

• The biggest benefit is the obvious simplicity and speed of the building. This alone would probably have made my decision
• Using Godzilla, the analysis says the leeward hull has only 10% more drag than a fully optimized (rounded bottom) hull at displacement speeds.
• That wave theory says as speed builds up, this hull should have a bow up attitude.
• Although we have no tools to predict, we theorize that at speed, between the bow up attitude and the flat bottom, that the leeward hull must start to plane. Any dynamic lift will reduce drag... and the 10% deficit won't take long to eliminate. A rounded bottom won't make enough dynamic lift to plane.

Con's

• I'm no fluid dynamists, but it would appear to me that if you expected a flat bottom hull to also supply leeway prevention, it would be a real mess! The vortex shedding coming away from the sides would probably make a lot of drag and flutter. But remember, the rudders will be run to make the hull run true so hopefully this bad aspect of a flat bottom hull shouldn't exist here.
• Pounding. That'll be a big negative. I'll use pillows.

In summary - I expect it to be slower than normal below ten knots, but above ten knots, I'm hoping for some real excitement (hopefully good). If you are right... I'll only be out about $150 for the whole leeward hull and it'll still be faster than my old Hobie used to be and certainly faster than my current monohull.

- 200 pounds sounds way short of the mark. Built lots of plywood boats, they aren't super light in flat bottoms. 3 mm ply tortured might be different. Though not that different once the structure is in.

Don't know. We will see! The 200 pounds just counts the hulls and beams. Unfortunately, the Hobie mast is quite heavy (I need to weigh it). I've designed the hydrostatics for 700 pounds with the expectations of having a crew of two. If I've really screwed up, I'll have a one man craft.

- Most interested in how that rig will stay up. That rig will create a lot of power, I have the same numbers on my tri, though mine is a Hobie 18 rig, I guess there is inflation in everything. I would love to be able to use it on a proa.

See above message... it should be stay supported except going aback.

- I put up a thread on HP about independent hull articulation. I didn't realize you were doing one.

Would you be able to point me to your thread? I would be interested.

- Newbies often jump all over the most radical technology by the bucket load. I think this will be an interesting experiment as to whether a lot of sophisticated analysis can get the job done. A bit like Mythbusters, or academic research where a bunch of experts try to reverse engineer an ancient tech, and then declare it a go or not, when the original took centuries to evolve. I think you are extremely wise to try a test out first. often the first iteration is flawed, but it serves very well to get on the right course.

At least it'll be cheap if its all chord wood.

 

[Inquisitor]

MLM - Build Update

Cost $109.44
Hours 61

Leeward hull cut out and formed up.
Windward hull cut out and formed up.
Diagonal beams cut out and formed up.
Diagonal beam flanges filament wound.
Rudder blanks formed.
1 rudder filament wound.

 

[garydierking]

Many traditional proas, such as the Fijian camakau, utilize a curved mast prop forming a shock resistant way to prevent the mast from falling down.

Gary

Actually, a free standing mast is my first expected mod. I'm using this one since... its available and free.

Structurally, the lee hull is designed to handle a free standing mast. Most traditional Proa's (with stays) don't have any support for going aback. Their masts will just fall down! They are meant to always keep the wind on one side... no matter what.