How to make a daggerboard - quick, cheap and easy?

[Neil C.]

The daggerboard on my old woodie 2631 is completely cream crackered. It's split from top to bottom in 2 places, and never fitted the case properly anyway as it was not the original board for the boat. I'm contemplating making a new one, but it doesn't need to be super- light / mega stiff / the last word in high aspect ratio foil technology. Rather, I just want to shape a bit of wood into something spitfire-wing shaped and go sailing. I can get a reasonable impression of the necessary section shape by tracing the shape of the bottom of the case where the foil exits the hull. I have 2 questions:

1. Old wooden foils are often stripy, made from alternating pale and darker strips of wood bonded together before shaping. What kinds of wood are best for this?

2. Would it be feasible to use a couple of sheets of 10-12mm ply bogged together as a starting blank, assuming this foil would be sheathed in glass and /or carbon cloth once shaped?

[flatbackcaper]

1, often balsa and cedar
2, how about cutting longditudinal strips and glue those together will be more rigid core laterally

[gav_sims]

I thought alternating red and white cedar was the popular choice?

A ply board that is foil shaped will have nearly all of the outer ply skins removed and is unlikely to be suitable (unless it is similar in section to a mirror centreboard..... sheathing in glass/carbon will of course help.

[ade white]

Here is a suggestion: If you use ply, use marine ply. If you 'bog' 2 together; I suggest you laminate a carbon weave or glass cloth between when you 'Bog.' That will really increase the strength and stiffness. then shape and sheath.
if you use 2 woods make sure they are the same density. this will help to make the shaping uniform, if not it will look like corrugated roofing and be crap.  sorted, next.

[Torchy]

I like Ade's suggestion of plywood with central carbon laminate.

Loco's prototype lifting foil is carbon laminated onto core of glued softwood strips...Roland and Crootie conception (can I say that on a family site?)

[ade white]

...following on from my previous reply; the easiest solution, would be to bond 2 structural foams together sandwiching 200/500 gm glass weave, shape and sheath. Forget the wood, as the cost different is minimal, probably cheaper, and time + effort making would be  reduced drastically. Roland did have the very same stuff, (12 mm) ideal for this type of project, knocking around..............

[JimC]

I never heard of balsa core in Cherub boards back in the day: it sounds like a major pain in the neck to try and shape.
I think the striped cores were just for visual effect to be honest, I can't think of any great advantage to them bearing in mind all cedar was good enough anyway.

A ply board will break unless you have so much carbon and glass on the outside it was hardly worth bothering with anyway and will weigh a ton. I think the only virtue in ply cores is that if you are doing a lash up board for a low stress boat the stripes are quite handy for making the shape roughly even.

A classic Cherub core would be strips of the same cedar, but end for ended/generally shuffled round so all the grain is in different directions. If you don't do that it may warp. You wouldn't think that it could warp inside a nice solid skin, but you'd be wrong. Halo's first daggerboard ended up with lengthwise sawcuts two thirds way down in order to force it back into some kind of shape.

I don't see any virtue in having a carbon skin down the middle between two core halves. Surely by the time it does anything the outer skin and core will have failed anyway and it'll be toast.

I honestly don't know whether a foam core will be easier than a wood one, never having tried it, but if you can get someone to cnc a core for you that will certainly be easier!

[Neil C.]

Thanks for all the suggestions everybody. I think I'll avoid the plywood board idea. Now that I think about it I tried making a plywood daggerboard for my Unicorn catamaran many moons ago. It lasted about 3 minutes. Looking at local suppliers it seems the yellow cedar is more difficult to get, but the red cedar is freely available and apparently about 20% lighter anyway. So the plan is to use that, alternating the orientation of each strip as Jim suggests. Should have the main bulkhead repair finished this weekend, then on to making the board.

[Phil Alderson]

If you have access to a router then marking out contours, and then running a groove along at the right depth is a real time saver. You just attack with a belt sander till the grooves dissapear and you have a shaped foil.

I drew the contours in CAD, printed out and stuck it to the core. With a foam core it was easy to follow the line by hand. A wooden core may be more sensitive to having a sharp blade.

I don't see the benefit of having a carbon layer in the middle of the foil. The board is mostly loaded in bending, and the centre of a bent beam will not see any stress.

[ade white]

This is a good argument, I see the comp center layer having effect for adding a bit of strength but mostly adding stiffness to the core material. If the side profile was flat I agree with it being a waste of time. However the outer sheath and areofoil profile shape is if bonded well to the center layer and core, could give the added strength required.
I agree not to be used on a new project and not something for a production system.
If you also created a box section, or 3 layers for the core this would be better.
The post is for a quick, cheap and easy fix for a old boat it should be fine, light and strong enough.
Shoot me down...

[Clive Everest]

The laminate on the centreline does not add to the strength of the foil but can help to make the back edge a lot more damage resistant.

I have made foils quickly and cheaply in the past using hot wire cut Styrofoam blanks from http://www.foamwings.co.uk/Pages/Site/Default.asp
These are not expensive for the time it saves shaping, and the profile is very accurate.
The Styrofoam is not structural. You need a substantial wooden stringer down the centre and thick laminates. The section can be cut to allow for the laminate thickness.

They can also be used to make female moulds.

Clive

[Neil C.]

I have made foils quickly and cheaply in the past using hot wire cut Styrofoam blanks from http://www.foamwings.co.uk/Pages/Site/Default.asp
These are not expensive for the time it saves shaping, and the profile is very accurate.

Very interesting. I can see that would produce a much more accurate shape than I could hope to achieve with my Grandad's old plane and a belt sander. The question is whether my laminating skills would be good enough though. I'll give it some serious consideration.

[JimC]

I see from the website foamwings do "inset spars" in spruce or carbon. I should have thought an inset spar/stringer of spruce down the middle would be an enormous timesaver. 
To save money in the past I've just put a strip of uni carbon down a board on maximum thickness, even stopping short of the bottom, and done the rest in glass. Do you think there's any virtue in that Clive? There does need to be enough to take all the loads, so what, double up on what you'd use for a complete board, but only 25% of the chord? That would save 50% and reduce wastage.