Minimal proa
I love where you are going with this!!!
A perfect proa for a roadtrip. You could probably carry this one in a (large) backpack for sailing and fishing in remote waters.
Which program do you use to create these pictures?
Cheers,
Johannes
Which program do you use to create these pictures
Solidedge by Seimens
Only started using a few weeks ago, it is ok but has some very frustrating bits. I am a teacher so have a free copy.
TINK
Inflatable proa, work in progress, pretty accurate cad model plus contingency, weight as drawn 32kg/28kg heavy/medium fabric. Still requires rig and board. This is after going through a weight reduction exercise.
Tending to favour the ply minimal proa which looks about the same weight, has better hydrodynamics, a much more ‘known’ entity and overall a much safer concept.
TINK
Kept trying to remember where I’d seen a hull like that…....
Kept trying to remember where I’d seen a hull like that…....
Yes not the best for hydrodynamics, part of the reason I an rapidly favouring good old plywood plus the weight, the vaka ‘skin’ ( sides, top and bottom) only weighs 6.2kg. If I can get all the glueing, coating and reinforcements for 6kg it will be the same weight as the medium weight fabric inflatable.
The image below illustrates the concern. It is a bow on view of the ply and inflatable proas
Red is inflatable midships section
Purple is ply displacement
Green is ply freeboard
To get the buoyancy of the inflatable it has to be wide and 0.9m longer than ply. It is then a less than impressive 13:1 L/B (ply 16:1). However the width does not result in a lot of usable freeboard so additional structure is required.
Have had the idea of replacing the structure (two parallel tubes etc) with a deep ply I beam which could simplify everything but quick calculation shows little weight savings to be made.
Tink
Tink,
I think you’re thinking clearly here. I have mostly the same feelings about inflatables. Inflatable=unproven and unknown in homebuilts, not much lighter, less hydrodynamic in almost every way.
After I arrived at the same conclusions though, I saw:
1) Catapult catamaran. The rigid bow seems to fix most hydrodynamic problems with inflatables. https://www.youtube.com/watch?v=m8B6g2K_q9c
2) inflatable material is potentially cheaper and easier to build with (I have yet to make anything that floats so that is a big ??)
3) my 5 M proa, as designed, would fit inside of my mid-size sedan; vaka, wood frame, mast, yard and all. No need for car topping or trailer.
I then decided to push on with my inflatable proa because I would not forgive myself if I didn’t at least try to make it work. If it fails in some way, I’ll reuse the sails and rigging and transfer it to a more “conventional” DIY boat.
Your current conception of an inflatable sure looks workable though; quite logical and similar to commercial construction it seems minus the wood bits which seem like they would ease construction.
Tink,
I then decided to push on with my inflatable proa because I would not forgive myself if I didn’t at least try to make it work. If it fails in some way, I’ll reuse the sails and rigging and transfer it to a more “conventional” DIY boat.
I am at least a year way from building, have to launch and test my TP03 first, I will let you be the path finder and watch your developments with interest, good luck
TINK
I have been working on the ply CAD model of the minimal proa and improving the accuracy of the inflatable proa estimate. The calculations should be very accurate as calculated from CAD for part weight and coatings using surface area and figures from Gougeon boat construction. The only estimate is for gluing and reinforcement (small high density fillet and 40mm 175g glass tape). All weights include a 10 % contingency.
VAKA only
Inflatable heavy duty material 18.2kg (40.0lbs)
Ply 15.7kg (34.6Ibs)
Inflatable medium duty material 14.9kg (32.8lbs)
Comparing with the Ducky 13 inflatable CAT at 35kg sailing weight (77lbs) and unstayed 5sq m sail my inflatable proa is clearly a little over engineered.
I think with a bit of thought I could get an inflatable vaka with medium duty material for 12 kg which is quite appealing, I feel more CAD modelling is required.
Anyway below is ply minimal proa with deck removed
Red hull 3mm Okoume, 5 off 9mm ring bulkheads
Yellow foam
Blue aka, mast and board support 9mm Okoume
Just a reminder of the scale LOA 3.7m 12’ 2” beam 320mm 9”
TINK
One of the major reasons to go to a solid foam surfboard style construction on the Bionic Broomstick was the difficulty in filleting the inside joins on a 8” (max) hull 20” deep. Any scheme to work in the ends took it out of the easy simple build category.
Minimal proa has a lot of appeal, BB was conceived primarily as a testbed for features on the proa I really want to build but it is looking better on it’s own merits.
But… there’s always the comparison to a little double blade solo canoe which is the gold standard in bang for the buck. I’m off for a week on the Buffalo National River in Arkansas to explore same.
cheers,
Skip
One of the major reasons to go to a solid foam surfboard style construction on the Bionic Broomstick was the difficulty in filleting the inside joins on a 8” (max) hull 20” deep. Any scheme to work in the ends took it out of the easy simple build
But… there’s always the comparison to a little double blade solo canoe which is the gold standard in bang for the buck. I’m off for a week on the Buffalo National River in Arkansas to explore same.
Thanks for the very valid points,
TP02 similar construction, had small chine logs which eliminated the need for internal fillets and reinforcement. I my pursuit for weight reduction I had eliminated them, I think your right it is an error. The chine logs where glued to side panels before assembly so it all went well. Because of the chine log I could sand a good fillet on the outside and then tape TPo2 strong and is dry.
The inside of the bow was a total pain and needs a rethink.
You are not wrong about a canoe, there is a great quote by Herresoff about their virtues, have great trip
TINK
I have started thinking of what my ideal boat would actually be, that led me to thinking about the type of sailing I enjoy. Other than sailing my two previous proas I have a vivid memory of an afternoon skimming above Ullswater, (lake in English lake district) at the end of the sliding seat of my IC in a stiff breeze. That was over ten years ago and I sailed my IC every weekend from dawn until dusk. Now other commitments, family etc limit the time I get to sail and my active boat is a RS Vision for the family. The IC is moth balled for the day when I get time to commit to it. The IC is tremendous fun but that fun comes with a price, you need to sail it regularly, for me anyway and be very fit if you are not very good at it.
It is not necessarily the speed that makes the IC fun but that you are out on the seat away from the boat skimming above the water and the fact that due to hull shape it is very quiet and peaceful.
I think similar exhilaration will be experienced with the layout of the minimal proa.
The RS Vision may seam like an unusual choice after an IC but there is a logic. It is very versatile, apart from being able to take family and friends it can be sailed single handed in most weather conditions. The weather where I sail is very variable and frequently different from the forecast, after a long drive I want to be able to sail. I even have small storm sail for going up wind and the use the asymmetric down wind in a blow. The other thing is it is maintenance free and very quick to rig. It might seam strange for someone who builds boats not to like tinkering with them. I value my time at the sailing club and like to maximise my time actually sailing. Building boats and tinkering is a winter activity and in many ways separate from actual sailing.
Now where to sail, though I dream of sailing in different and wonderful places the reality is I sail at a sailing club. Both the clubs I have been involved in recently are firm dinghy clubs, multihulls are actually not allowed. My current club sees me as a bit of a novelty and has given me a temporary disposition, this may not last. Because of the size of TP03 I take up two berths, not ideal. The smaller size of the minimal proa helps solve this, plus I will reduce the beam to the same as a typical wide dinghy. Easy transport and car top ability will be useful if the club changes its mind about me sailing it.
Finally where to build, I have an garage 16ft square, but with family demands on space usable space in reality is 14ft by 8ft.
So in summary,
IC type exhilaration, skimming over the water like a seagull
Versatile to sail in force 1 to 5
Very quick to rig and maximise time on the water
Reliable, no need to tinker at the club, I can do that over winter
Small size, single berth, no wider than typical wide dinghy (helps with building space also)
All this rationalising has lead to some changes
Nice simple, reliable, reef able standard balanced lug rig.
Keep it simple, add a steering oar, leeboard will move fore and aft somewhat to balance.
Keep it simple, and reliable, ply construction rather than the inflatable.
Picture an IC on Ullswater (not me) and a better view of Ullswater.
Tink
Progress, now folds to the same width a a laser,
May not be everyone’s ideal boat but I like it
Its a neat folding mechanism, but is it really that useful on such a small boat? Are you going to throw it on top of your car? Easier to do that in pieces.
I thought that the lashing method of Gary Dierking’s boats would be tedious in practice. But its actually a very civilized system. One end of the lashing line is tied to the vaka, and it terminates in a cleat. I find it much nicer than the tedious bolts that hold the two halves together, that need tools, are intolerant of sand, etc.
Just a thought.
Now, a big one that you carried around on a trailer, and broke down frequently, maybe the folder would make sense. But that’s just my 2c.
chris
folding mechanism, but is it really that useful on such a small boat?
You are of course 100% right, I put my ideas out here for feedback good or bad, it is great not to work in a vacuume. It also is quite simply visually wrong.
The reason for the folding is not for transport it is for storing at the sailing club, the berths are very narrow as you can see and the boats crammed in. It is about conforming as much as posible to the sailing clubs norms.
On TPo3 I am experimenting with some lovely stainless ratchet straps, if I like these I would only need 1 to fix both Akas to the Vaka, the Akas are only 300mm apart. For the Ama I was going to use the system below, nice and simple. I also like the how the p5 from Germany does it.
I can’t imagine it will take more than five minutes to break it all down if storage becomes an issue. It is also only 1.8m wide fully assembled same as RS400 a popular dinghy at the club
TINK
On TPo3 I am experimenting with some lovely stainless ratchet straps, if I like these I would only need 1 to fix both Akas to the Vaka, the Akas are only 300mm apart. TINK
That’s what I use to attach my ama to my vakas. Not even stainless steel. In that case, WD40 to the rescue…
I used to have the clamp and bolts thing (with wing nuts so no tools per say).
I prefer the ratchet…
Cheers,
Laurent
PS: I’ll get a picture if you want, when re-assemble the boat after repair…. Soon!