Thread: Coquina

Here's an example of a slab sided foil, compared to a NACA shape.

It's pretty easy to see which would be easier to make. At the speeds your boat will travel the slab sided foil will work great.

They both are the same thickness and length.

Mickj,
It seems a lot of boards are made of ply in the US as an alternative to metal. I will be doing a glassed wood laminate version and shape as PAR has suggested.

BTW it is interesting that in a letter from NG to LF about Coquina there was a discussion on material for centre boards, the original was I think 1/8" brass or bronze can't remember with wood stiffeners/spacers.

Mike

There are also optimised versions of the slab sided foil.

Slab sided makes a lot of sense sometimes because a "proper" NACA section ends up being very thick as they have to be about 8 to 12% of the effective width of the board in thickness. So even a narrow 300mm (1ft) wide foil has to be 30mm thick (about 1 1/4)

Taking some care to shape the foil does have a lot of performance and handling benefits.

MIK

The NACA shape above is a 8% foil (00 series 12" x 1") and the slab sided is also. A 12% foil would be a better choice which would make a 12" wide board .83" thick. A 9" wide board would be .75" thick with a 12% section.

The parallel sided version is the type I use on all my designs except BETH.

The reason is that it is so much easier to shape than the full NACA which rolls around and takes a careful worker to get it right.

Parallel sided is much easier to shape and can save a bit of timber too.

MIK

One small step for Coquina one giant leap for m2c1Iw.

I took this week off work to make a serious start on the build.

Today I finished assembling the strongback I have spent this week cleaning out the workshop and generally reorganising things still have more to do but I'm pleased with the progress. At least I can get in there now.

Something I have come to realize is there is simply not enough room to build this boat so before any further boat building can occur I will have to dismantle the mitre saw bench to gain 200mm width then make an extendable bench for work on all the long bits.

Anyway here are a few pics as proof I have not been goofing off. The material cost for the strongback is about $55 including screws etc. as I grabbed a chance to buy some boards from a demolition site. That's the good part unfortunately one was about 400mm too short for one of the main planks so a guesstimate was made for an appropriate scarf joint. Turned out OK I think.

My reading on strongbacks recommends securing them the the floor to ensure everything stays square and level. Well I'm going against that advice and making up some caster legs so can move the whole thing around I will however mark the location of the legs so the assembly can be returned to the correct spot. Hopefully this will ensure things don't go haywire. Somebody may wish to convince me this is a bad idea but I can't see any alternative at present.

Cheers
Mike

Dear Mike,

I've used caster-equipped strong-backs on a number of occasions, but in each instance, the casters were used only to move the strongback to a position. From there, the whole thing was raised into a firm location using blocking, heavy angle brackets, and Dynabolts into concrete. You really need to be dealing with half-millemeter tolerances if possible, and I do not think that casters can provide that - no matter how carefully you reposition the assembly. In addition, the casters will inevitably sag slightly as the structure becomes heavier, and when it is subjected to shock-loads during construction - trust me - it will happen!

Ross Lillistone

Hi Ross,
Thanks for your advice I will have to rethink things guess deep down I knew castors are a bad idea but needed someone like you to confirm.

Congratulations on Periwinkle BTW she looks fantastic and you must be extremely happy with the performance, real speed machine.

Thanks again
Mike

Thank-you, Mike.

Yes, Periwinkle sails beautifully, but (as predicted at pre-design time) the balanced lug cat-ketch (Periauger) rig is not the fastest way to get to the up-wind mark! However, as soon as the sheets are cracked, she is off like a rocket.

Periwinkle was designed to be fine and sharp up forrard from the outset, and for a 17 footer, she is a relatively small boat. Weight distribution is critical, and she does not like too many kilos up on the forward thwart. However, that was all anticipated, and with knowledable handling, she goes extremely well.

One particularly gratifying thing is that the third mast-stepping location is very practical. She balances nicely with either the main, or the mizzen, set alone - i.e. sailed as a cat.

Owner John Shrapnel has discovered that in moderate conditions when he is sailing alone, he gets a benefit from reefing the mizzen, and leaving the main full. That way, when he eases the main in a puff (can't do both at once when alone) the reduced area of the mizzen is less likely to take over and induce excessive weatherhelm. So, counter to what one would expect, the proper reefing schedule (when alone) is: -

• deep reef mizzen;
• deep reef main;
• ditch mizzen altogether and move mainmast back to third location;
• ditch main and set mizzen (alone) in its place;
• take to oars;
• go home!

The balanced lug reefs easily and very effectively (read, "very little distortion")
If always sailed with one mast, a sprit-sloop rig would be better, but less convenient that a balanced lug.

So many options - so few lives in which to experiment...

Ross Lillistone

Good on you Mike for getting into it. I'm sure you will sort out the space issues, it will slow you down sometimes, but you aren't racing, so enjoy! It seems that, apart from the actual boat area, long thin space is needed to make and fair or spile the boards and you seem to have some of that.

Just trying to figure out your likely order of work and had a few thoughts. Hope I'm not being intrusive, or jumping the gun on you Mike.
I guess that you can use the strongback as a frame to scarf all the sheets on before setting up the moulds, but then you have to store the big sheets- unless you can make the strakes at that stage too, but that depends on the method and the info in the plans. Do you have to spile them off the moulds or do they provide templates?

Hi Rob and thanks for the suggestions.

Just came in from the shed for a break, I've been madly throwing things out you know if I haven't used it in X years it goes. I'm up to 5 at the moment.

Dismantled the mitre bench and after giving things a bit more thought I 'm going to fix the strongback at a slight angle down the middle of the shop and all the machines as in Bandsaw, TS/router table, Jointer, Drum sander and Thicknesser are going down one wall.

Taking the opportunity to rearrange the ceiling space for more storage, insulate the cyclone and fit a decent manhole cover in the ceiling all things I've been meaning to do for years.

Amazing what a bit of inspiration can do for getting things done, thanks.

Yep the strongback will make an excellent bench for a while plenty of bits to make before the molds (notice merican spelling I'm going all imperial at the moment) go up. Actually I'm building one of Michaels canoes for a bit to practice scarfing ply etc before I take the plunge and will get the transom and stem formed up at the same time.

Ah spilling must admit that aspect of the build had me somewhat concerned but in reading another build it appears alternative methods are available to novices. The the plans are excellent and provide for taking off the strkes in fact the strakes can be rough cut in lots of three so the big sheets can be cut down early in the piece for easier handling.

Well back to it

Cheers
Mike

G'day Mike
For spiling, have a squizz at Ross Lillistone's Periwinkle build - first page of pics, 2/3
of the way down. http://www.baysidewoodenboats.com.au/
I reckon even muggins me could spile strakes accurately that way !!
cheers
AJ

AJ thanks for that Ross surely details his work nicely.

My mentor for this adventure goes by the anonym of Breeze he has put together a fantastic site.

This is the method he arrived at http://web.mac.com/w123.153/Breeze/D...lank_size.html

All this will be new to me, spiling while daunting is something I think
should be attempted, understood and perfected by the budding boat builder..............
then having messed up a perfectly good sheet of ply one should resort to finding an easier way.

Cheers
Mike