Thread: Paradox Micro Cruisers and "Bilge Runners"

Originally Posted by Boatmik

Howdy AJ,
It would be interesting to see how it went on the Teal!!
MIK

Well the original shower leak is fixed (the floor-pan is now cracked, but the duct tape is holding so far..). Another kayak is built & tested (& alterations to design made). 'Eureka' looks like being a spring project due to funding issues caused by the aforementioned cactus shower base. Time to use some of the oregon rafters recovered from the neighbour's renovation & carefully stashed in the backyard under the apricot tree...

Stinker of a day - 39'C according to the thermometer on the back verandah. Moved work-site under the trees in backyard as per photo. Winglets are 1M long & 3" wide for most of their length, widening to almost 4" at rear. (Sorry about the mixed measurement systems - I'm of the changeover generation - fluent in both and neither)

Location is by guestimation, based on a fuzzy memory of how the boat had significant weather helm when last I used the 'big' lug sail. Been using a smaller but much more effective fully-battened Gunter I cooked up for my daughter's micro-catamaran for the last couple of years. But that is up for sale at the moment, so back to the lug-sail it is.

The dowels are to stop them from breaking along the grain. The epoxy securing the dowels & filling some nail holes is curing as I type. Insofar as this is planned, I will finish shaping them, coat them with epoxy, & temporarily screw them in position. Then test sail & amend location/shape, then epoxy/glass them in position. Or discard them. God willing & there still be at least some water in the lower Murray R. that could be as early as late next week. Or not...

Here's hoping...
cheers
AJ

Howdy AJ,

I would be reckoning on altering the shape once it is all glued up so the long edges are radiussed and the leading and trailing edges made more foil-like.

Leading edge shaped in a half ellipse. The trailing edge tapered down to a flat edge about 1/4" wide.

The distance of shaping for the trailing edge - maybe 5 times the timber thickness.

Are you going to just fit it on one side and have the standard leeboard on the other for comparison?

MIK

oops - I mean centreboard (looked more closely at the pics!

Originally Posted by Boatmik

Howdy AJ,

I would be reckoning on altering the shape once it is all glued up so the long edges are radiussed and the leading and trailing edges made more foil-like.
Leading edge shaped in a half ellipse. The trailing edge tapered down to a flat edge about 1/4" wide.
The distance of shaping for the trailing edge - maybe 5 times the timber thickness.

Are you going to just fit it on one side and have the standard leeboard on the other for comparison?

MIK

Something like that MIK. At this stage just rough-shaped & tapered to fit the hull & insert reinforcing dowels. Will do most of the shaping off the hull - rounding & tapering & etc. Hard to compare shape of the two winglets for sameness if they're on opposite sides of the hull. I dare not go seriously thin with the trailing edges because of the vulnerable location of the winglets. The boat tends to get dragged sideways off the trailer & dumped chine-first onto the ground - they are presently tapered to about 16mm from about 25mm max thickness. Most Paradox's appear to be just the 3/4" or 1" thick bottom panel extended past the sides & filleted - seriously robust! The one other photo I've seen (which I cannot now find) showed more like this shape of winglet but still with a pretty solid trailing edge. And that on a boat that goes fore-and-aft on & off the trailer, not sideways & *drop* !

Anyways, there is much yet to do, including figuring out a temporary yet moveable fastening system for testing that is strong enough but doesn't let water into the boat or the winglet. The boat is 6mm gaboon with no framing. Tempting to just glue & glass it & remove bits as required to amend trim...

cheers
AJ

Winglets shaped & epoxy coated. Waited until after midday to apply first coat on a cool day that wasn't warming. 20 minutes after completion and as I left for work, the sun came out & turned the shed into a sauna.

Out-gassing ..... UGH !!! Home at half past midnight, sand it all back & recoat. Bed at 2am. Only did the one. The other can wait until I know whether it is a crock or not.

Fastening is 3 holes drilled oversize near chine & back-filled with epoxy goop. Tape over them & the winglet face & put drywall screws through the tape. Should keep most of the water out, & allow movement fore-and-aft to adjust balance. Big washer and strip of ply on the inside to avoid doing the boat a mischief from concentrated stresses. Might even get to try it this weekend if the weather & other appointments co-operate.

Waved a measuring stick at it last night too for the first time since mark-out. The oregon is actually 35mm thick on the face, so there's a fair bit of taper to the ends & out to the edge (28mm in the middle).

Well, weather & other appointments refused to co-operate. But the port winglet is now temporarily attached & screw holes filled ready to get wet.

Recovered a bundle of meranti slats from a set of louvered kitched cupboard doors a decade or so ago. Still finding uses for them, in this case, aligning & supporting the winglet while I drilled & screwed it.

Duct tape over the hole in the boat and over the hole in the winglet. 50mm perma-pine screws fastened through the tape with cup washers & pads inside to add support. Next weekend will be a 4-day one (shift changeover) so hopefully will get a chance to try it out.

(The micro catamaran in the background is up for sale if anyone wants an experiment that worked surprisingly well. Adelaide sthn suburbs - make me an offer!)

Test sailed it today (Monday) with port winglet only temporarily attached.
The difference was simply stunning !!
For the first time ever, I was able to sail towards a target rather than crab towards it. (I may have mentioned before that the dagger board I made for my Teal is too small. Comparative pic below as to just how small (950mm x 280mm).) Using channel markers as leads I estimate close-hauled leeway was down to maybe 5deg compared with around 20deg on the opposite tack without the winglet.

Observations...
1. Lake Alexandrina is desperately low. Despite drawing only about 700mm, most of Clayton Bay & the Finniss River Junction was unusable. I had to stay in the marked channel. Even 4 months ago it wasn't that bad. Still bottomed out in parts of the channel, especially near Old Clayton point on the northern side. In the Clayton Bay Jetty pics below, the water level -should- be just above Teal's boom.

2. My recollection with this particular sail of the boat having bad weather helm was just plain wrong! The too small daggerboard means it needs heaps of lee helm to keep from blowing off down wind. Can't figure out how I ever managed to sail it down the Finniss from Knott's Landing. (narrow creek, flukey breeze)

3. The winglets on their own are not big enough to beat to windward. That's ok - they were only ever intended to supplement the too-small centreboard. They are big enough to reach, albeit with perhaps 10-20deg of leeway. Ok for skinny water & weeds. Without winglet or dagger board, Teal just slides sideways nearly as fast as she can slide forwards.

4. Despite their widest point being well aft of the CB, they actually induced weather helm, not lee helm. Pulling up the dagger board made the weather helm even more pronounced. I deduce this means that the front bit where the boat is still widening towards maximum beam is doing the lion's share of the work. Very likely, the front 1/3 is producing 80% of the result.

5. Under oars, trimmed reasonably level in a dead calm, the winglet produced neglible drag. Tested by stopping rowing & seeing which way the boat slewed. Always to port, eventually, but only gently.

Anyway, the winglets are about to become permanent fixtures.

cheers
AJ

Great work on this AJ!!!

Originally Posted by b.o.a.t.

Observations...

2. My recollection with this particular sail of the boat having bad weather helm was just plain wrong! The too small daggerboard means it needs heaps of lee helm to keep from blowing off down wind. Can't figure out how I ever managed to sail it down the Finniss from Knott's Landing. (narrow creek, flukey breeze)

Sounds like the centreboard is in the wrong place - as you suggest.

3. The winglets on their own are not big enough to beat to windward. That's ok - they were only ever intended to supplement the too-small centreboard. They are big enough to reach, albeit with perhaps 10-20deg of leeway. Ok for skinny water & weeds. Without winglet or dagger board, Teal just slides sideways nearly as fast as she can slide forwards.

This was the main bit of information I was interested to hear. There had been a lot of hype that they worked well by themselves. Perhaps with Matt's boats the greater depth of hull makes them work better still, but I would be very surprised if they were in the same category as a properly designed centreboard (or leeboard for that matter).

4. Despite their widest point being well aft of the CB, they actually induced weather helm, not lee helm. Pulling up the dagger board made the weather helm even more pronounced. I deduce this means that the front bit where the boat is still widening towards maximum beam is doing the lion's share of the work. Very likely, the front 1/3 is producing 80% of the result.

This is spot on with theory. Basically you get the most lift from where the water has to change direction the most - and most is going to be at the front end. By the way ... that's why deeper foils work better than short ones - they bend more water because they have more "front end"!

But if you don't have more water - then it is a good idea that might make sailing practical.

5. Under oars, trimmed reasonably level in a dead calm, the winglet produced neglible drag. Tested by stopping rowing & seeing which way the boat slewed. Always to port, eventually, but only gently.

That makes sense too. Generally there are two main components of appendage drag. Surface area and frontal area. Both are negligible in relation to the cross section and wetted surface of the boat. There might be more drag as the boat goes faster from wave drag effects - but I won't be betting any money as to the size of the effect.

Anyway, the winglets are about to become permanent fixtures.

cheers
AJ

It is great that this experiment has solved your problem!!!!

One extra suggestion would be the general guidance that if your lateral resistance is too small it starts to make a lot of sense to sail the boat faster upwind. Keep the sail/s eased a few degrees wider and go that little bit faster.

Best wishes
Michael

G'day MIK

Originally Posted by Boatmik

This was the main bit of information I was interested to hear. There had been a lot of hype that they worked well by themselves. Perhaps with Matt's boats the greater depth of hull makes them work better still, but I would be very surprised if they were in the same category as a properly designed centreboard (or leeboard for that matter).

Probably not, but I think they could be made to go close. Certainly enough to make additional gain from a vertical appendage not worth the extra engineering effort for some boats & in some applications. My winglets are very small indeed. I'd imagine if they were doubled or trebled in size (mostly length), one might get by without any leeboard at all.... most of the time.
(Someone else can try that one... too hard to retrofit to an existing boat.)

Originally Posted by Boatmik

But if you don't have more water - then it is a good idea that might make sailing practical.

Perzactly ! Right at the moment, even 700mm draft is too much... from what I've read of the handling characteristics of shallow draft boats such as Chebaccos & Scruffies, horizontal appendages have got to be worth a serious look for us enforced skinny-water sailors.

Originally Posted by Boatmik

That makes sense too. Generally there are two main components of appendage drag. Surface area and frontal area. Both are negligible in relation to the cross section and wetted surface of the boat. There might be more drag as the boat goes faster from wave drag effects - but I won't be betting any money as to the size of the effect.

I'd expect these little wings to be largely unaffected. Teal is pretty slow with my little sail & excess bulk... Wind speed varied from dead calm to about 12-15kts yesterday. I came in to a lee shore with a serious bone in the teeth, and rounded up in 200mm of water with no trouble at all. Try & do -that- in any other sharpie !! For this one trick alone, they are worth the effort.

Originally Posted by Boatmik

It is great that this experiment has solved your problem!!!!

plus one or two that I didn't know about...

Originally Posted by Boatmik

One extra suggestion would be the general guidance that if your lateral resistance is too small it starts to make a lot of sense to sail the boat faster upwind. Keep the sail/s eased a few degrees wider and go that little bit faster.

That's what I've been doing MIK. Bear away, pick up speed, when the board "bites" point up just far enough to maintain speed. Board has been operating just shy of stalling or stalled. Yesterday's trial showed this should no longer be an issue.

Thanks for the comments MIK.
cheers
AJ

Thanks for doing the work and presenting the results here AJ.

Bless your cotton socks!

I think that there are some disadvantages to the chine "wings" as they get bigger. One is that they start to become quite vulnerable to damage.

The other is that as the boat heels their effectiveness becomes greater - so there my be a tendency for bigger ones to trip the boat at speed or in a gust.

But you have an opportunity to test that - look forward for feedback in those areas too.

MIK

Originally Posted by Boatmik

The other is that as the boat heels their effectiveness becomes greater - so there my be a tendency for bigger ones to trip the boat at speed or in a gust.

But you have an opportunity to test that - look forward for feedback in those areas too.

MIK

Won't have opportunity to test these two things MIK. Wings too small, Teal too slow. However.... if The Midge could be prevailed upon to fit something similar to his GIS....

cheers
AJ

Well, the winglets are now permanently attached. Short of an angle grinder anyway. Has added a good 1 or 2 Kg to the total boat weight. Could have gone with less glass cloth but wanted to do some stiffening & reinforcing in a couple of 'soft spots'. Took opportunity to remove paint in areas where it had cracked through to the timber, dry them out, & recoat with epoxy. Evidently just 2-3 coats of epoxy is insufficient in these areas to prevent splitting along the grain. It is tempting to obtain some of this 2oz glass cloth of which Mik speaks to cure the splitting 'properly'.

Will be 6 weeks or so before I get a chance to do any more. MIK has suggested a larger sail & some knees under the mast partner, so those will be next, as per drawing. Plus a larger rudder blade. Should be a vastly more pleasant little boat to sail once all is done.

http://www.freewebs.com/paradoxbuild/buildingblog.htm

just stuck the link in here for my own reference (& so I don't lose it)
good close-ups of Paradox chine runner construction

Originally Posted by b.o.a.t.

Won't have opportunity to test these two things MIK. Wings too small, Teal too slow. However.... if The Midge could be prevailed upon to fit something similar to his GIS....

cheers
AJ

A follow up thought (because I have just written about this concept in another thread) ... I don't think the Paradoxes are particularly fast at that displacement and length - so the Teal is probably a reasonable approximation.

But TEAL is a very light shallow boat - so certainly does not have the hull depth of the Paradoxes.

That it still does not go REALLY well to windward using both the undersized centreboard and quite large (compared to the Paradox) runners together and only does sortof OK on runners alone indicates one of the below is true

1/ The concept of bilge runners works best on deeper heavier boats
or
2/ The deeper hull in combination with the bilge runners is an optimum use of the idea or
3/ The concept has only marginal use and it is the deeper hull providing the lateral resistance. Remember that the Paradox is a similar or similar hull depth to many centreboardless cats which can also go to windward OK without centreboards. They have more speed which helps generate lift, but also they have much, much more sail which will require much more lift anyhow.

Move to slower centreboardless catamarans like James Wharram's and you lose a lot of upwind performance. So much so that his boats are sprouting shoal keels - I remember James saying how such things were "completely unnecessary" ... but back then he also said that bridgedeck cabins were "unsafe" and that feature is appearing now in his designs -the danger of making 100% type statements for things with no theoretical base! The reality is he "likes" particular features - which is valid enough in its own terms of course.

But in a way ... which reason is correct is unimportant because the concept of Matt's Paradox boats is simply extraordinary and it is clear the the package works as a whole - whatever theoretical spin is put on "why".

Best wishes
Michael