Thread: Coquina

Hi

I dont have a lot of photos as I seem to get absorbed in building or sailing rather than photographing. Attached is a photo a friend took on launching day. Since then I have tidied a few things up and put the sail numbers W1889 on as I sail from Wangi Wangi NSW. I do have some photos at home that I can send after Christmas showing some of the construction details. I believe Doug Hylan's CD is excellent but I didn't bother buying it although I did visit him in the USA to look at his boats.

As for a Nationals who knows. I am taking the boat to the Hobart Wooden Boat Show in February and I understand there will be one other Coquina there and possibly two. Thats enough to start a competition on the sail past days. The worst I could come is third.

One change I did make is to use heavier sole boards to add weight. Apart from making things stronger it doubles as ballast and if you get swamped the boat will float higher making recovery easier. If I built the boat again I would build some more light timber into the bilge to add the equivalent of Capt Nat's lead shot bags and give postive bouyancy and less space for water. Just my thoughts. I intend to do this when I get around to it along with a few other jobs such as building an Alerion this winter. I also made an aluminium centreboard with a timber trim on top. Capt Nat used various combinations of wood, weighted wood, brass, brass/timber. Mine is 10mm aluminium which is tough, is painted and looks the part, gives some slight extra righting moment (7kgs immersed bouyancy, 11kgs total approx)

"Wizened" W1889 Wangi Wangi RSL Amateur Sailing Club. Wizened is the boat name not mine. Denis GILBERT.

Hi again Denis,
Very cool thanks for posting the pic and I look forward to more.

I hadn't considered a metal plate, not a bad idea did you bother shaping it at all, more to think about and re the sole boards I have been wondering what to use thanks for the tip.

Building an Alerion in a winter! tell us more. and have fun in Hobart wish I was going.

Hi

I used 10mm aluminium cut out with a normal electric cut off saw using metho as a lubricant. Goes through aluminium as easy as chip board. Then the edges were rounded with firstly an electric plane (with metho) and then a belt sander. This time using wax as a lubricant. You touch the belt against the wax then you get 2 minutes of easy sanding. Takes off heaps of material until the belt starts to fill and removal goes to zero. Apply a bit more wax and start again. I have been told that commercial alloy boat makers now use some sort of spray that does the same job and means you dont have to degrease before painting.

The board is painted along with the timber and even with the board up nobody realises it is aluminium. It is also very handy for running aground.

There is no shape in the board just the rounded edges and timber that fills the centerboard slot when the board is down.

I think a lot of people get into raptures about NACA airfoils etc which are not particularly good just that they are available and have a measured set of performance characteristics and people have heard of them. To assist designers they tested a large range of aerofoils with varying thicknesses and location of max width and published figures. Also they are way too fat to use for centreboards like the board on Coquina. For yachts where you can get a proper foil shape, OK use some sort of aerofoil, but there have been a lot of dinghies over the years with either aluminium or steel flat plate keels/centreboards. Boats like the Star and the Finn, both fast boats.

Hmm will definitely need to rethink this centre board thing which may become a centre plate I was intending to do a hard wood strip job, lead weighted and glassed but it is a lot of work.

John Brooks used weighted glassed ply........decisions decisions.

I've cut a 7/8" slot for an expected board thickness of around 20-21mm finished, guess I could pack it to suit a metal one.

The slot is still the normal width. I have just glued and screwed timber to the top edge of the board that is left in the case when the board is down. So the board is still the normal width at the pivot point and along the top edge and still fits nicely in the slot with the timber sealing the slot off as best as can be done at the keel junction.

I also have a piece of plastic conduit about 10 inches that slides over the lifting rope and have added a 6mm slot to the top of the case capping at the rear end of teh opening. So when the board is down the conduit slides down over the rope and sits against the top of the centreboard. Then the rope is slipped back through the slot and down to the cleat on the back of the case as normal. The conduit then also abuts the top of the case on the underside. This locks the board down as required by Cat 7 under the Yachting Australia safety rules for sailing races.

To lift the board just undo the rope pull forward and then lift the board as normal. The conduit can be slipped off if you want to run aground.

Yes, plate style of appendages have been used for many decades, but are not remotely as good as even the most rudimentary of foils, such as the flat or slab sided foil, let alone appropriately sized NACA sections, based on Reynolds number expectations. If you place two identical boats next to each other, one with a plate and the other with a very basic slab sided foil, the foil boat will easily preform better on all points, will have less leeward skidding, will point higher, will be less prone to vibrations and board hum, the appendage will stay "engaged" over a wider range of incidence, etc., etc., etc.

If you match the expected preformance level of the craft with the section that will do most good, the difference between these hypothetical two boats will be pretty dramatic.

Strip planked boards aren't especially difficult, though some have difficulty with the shaping process. I'd recommend a slab sided foil for the Coquina, just because the difference between NACA and this type of foil will not be significant enough to warrant the extra work. This is more a function of how much "presentation" there is on a Coqiuna type centerboard/rig combination. Mik's foils are usually this shape (straight sided) and they are easy to make.

I wouldn't use plywood for a centerboard or rudder. They're prone to fiber failure in all but the lightest boats of which this model wouldn't be confused with.

I'd also reinforce the leading edge of the board with epoxy saturated, single braid, polyester line, set in a shallow groove. I've used this technique for years without a single failure and I blatantly stole this idea from someone equally as convinced of it's preformance. Since using this leading edge protection for 30+ years, I've discovered many others that have as well, all with similar results. Fair in the line with thickened epoxy, then sheath if desired.

Of course a nice aerofoil is better in performance. You will find exactly what PAR says about pointing is right. A Coquina with its gaff rig and flate plate swing board suffers on the beats and unfortunately the shape and rudder drag stop the fun of planning downhill.

While it would be nice to fit a high aspect ratio high effeciency board, the difficulty with the Coquina swing board is that it's chord length is about 800mm while the centreboard slot width is 20mm and all this only sticks about 400mm below the boat shaped like a big triangle or inverted fin with a curved trailing edge. It simply isnt feasible to fit a meaningful aerofoil that would perform better than a flat plate without changing the whole structure and look of the boat. And if you want to go to that effort why not make a foiling moth or a sailboard. A coquina isnt about speed or pointing. Its about the journey of building, the simplicity of sailing and rigging and just doing it easy. If you want to point higher and go faster build a different boat. Gaff rigged clinker in timber is not fast. I find my boat takes me 14 minutes after I have crossed the finish line at the rear of the fleet to derig, put it on the trailer, pack it ready to drive home, get round to the RSL, get a schooner of old, get outside and sit down to discuss the day. Next season I hope to get this part of the days sail quicker.

My reason for the aluminium was simply that it was cheaper, quicker and easier to make than a wood board. Additionaly it doesn't need to have the lead added to keep it from swinging up, doesn't need to be glassed, is tough as hell and offers performance everybit as good as the standard design board. And as a free bonus some righting moment. I also figure it will outlast me by many years.

Thankyou Gentlemen you have both explained most eloquently the advantages attached to alternative methods of centreboard construction so even this wood butcher can comprehend.

The decision making process has been further refined to include the importance of beer, a crucial aspect of sailing well done

I went to Hobart and there were no other Coquina's there apart from mine. I did speak to Ned Trewartha and he has built one. I thought he had built two but only one, for a person in NSW. I hope yours is progressing well.

Originally Posted by wizened

I went to Hobart and there were no other Coquina's there apart from mine. I did speak to Ned Trewartha and he has built one. I thought he had built two but only one, for a person in NSW. I hope yours is progressing well.

G'day Denis,
Progress has been slow since xmas although I did pluck up the courage to commit saw to wood recently and cut out the sheerstrakes. Next step is to rearrange the shop so shaping can commence.

This would be Wizened in Hobart very cool, pinched the pic from the WB thread.

Attachment 162952

Yes, thats my little boat at Hobart. Not presented very well as a nice harbour furl for the sails would look better. Diane and I sailed everyday. We just stepped the masts and rowed out under the bridge not having to worry about opening times. By the way where do I find the WB thread you speak about.

The show at Hobart was fantastic with wooden boats of every size and every type with interesting displays and plenty of boat building information available. Will definately be there in 2013 hopefully with the new Alerion that I am building.

Apologies it's the Wooden Boat Forum and the thread about the Hobart Festival lots of pages and pics. I'm not sure about posting direct links some forums don't like it but here goes and you may need to join to view pics.

Hobart 2011 wbs feb ii to feb 14

Hello again all,
I'm back on the job shaping the sheerstrakes. I had considered calling on the local cabinet maker thinking a shaper would be preferable to all the hand work required for this task but now that I'm into it I'm glad I didn't.
A slow and methodical approach I hope will achieve a reasonable outcome, perhaps not as exacting as a machine but oh well it will have that hand crafted look or hand butchered not sure.

One thing I'm nervous about is a kink in the upper line of the sheer. The pattern started it which came off Dougs drawing and it did line up with the tick marks on the molds but even so it looks kinda strange on the bench, time will tell during the dry fit I might even wheel the hull out of the shop to get a good look at it before the glue up.

So here is the roughing out on the router table note the high tech guide I should have purchased a 19mm bowl bit would have made the job a lot easier. Then we have two mirror image planks triple checked for correct layout.

Attachment 166403Attachment 166402

Next is the hand shaping I cut out a guide then with various tools worked along getting a reasonably consistent shape, not perfect but hey not too bad. The end closest to the camera needs a lot more work yet.

Attachment 166404Attachment 166405Attachment 166406

This pic shows to kink in the top edge it should line up with the turn up to the bow me thinks, weird how a plank looks all wrong on the bench but sits beautifully on the hull, well here's hoping.

Attachment 166407

I hope to get them glued up next week then the hull painted by the end of May ready for turning well that's the plan.

Cheers
Mike

Magnificent, well done! Love the fact that you've made a scraper for finishing. It may be a long haul, but your attention to detail will give a life-time of pleasure.
Cheers
Rob