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What type of speed are we talking about to see real results? Is weight of the object/boat a consideration? I'm just thinking model air plane wing now. lift is restricted by weight and speed...?

The difference increases logarithmically with speed, so you'll see substantial results at 7 to 8 knots--Barely enough to be worth considering on a Mac.

Lift is a function of speed through a fluid. The faster you go, its not just that the force that lift provides increases, its that the efficiency of lift itself also increases, so (for example) a 8 knots the lift isn't just twice as much as 4 knots, its more like 150% as much (depending on the foil).

What limits the sped of a PD racer or any other pram-style dinghy is generally hull speed. However, like a mac they are semi-planing so if they can manage to get up on a plane their speed is unbound. any 8 foot craft's hull speed is 4 knots. You have to overcome a lot of bow wake to go faster.

And add bubbles, err sorry!
Hull speed, notwithstanding, this whole thread verifies several things: an airfoil shape (hydrofoil) through water generates lift, as well as a drag component, based on its shape and size.
Two; optimize the orientation of the lifting body to generate its maximum advantages.
Three; sizing of the force produced, must work properly with the mass, and pointing characteristics of a MacGregor.
Fourpers; You'd better be able to control this Frankenstein (or is that frankenstyne?), when you need to.
Fithpers; Complexity, and cost ultimately determines whether the project is worth the sweat and spit!

So, having said that, I'd still maintain the idea is workable and good. Just that, it's still a somewhat un-mapped distance to actual execution. I think the danger in the drift, is that we get too freaked out about NACA foil numbers, or custom carbon fibre kits, or the like. The existing kit we already have should be quite sufficient to provide the heel reduction we seek.
That's it isn't it? Keeping the sail/mast upright, to generate that extra knot or so? To live a life of lesser heel - to boldly go where no man has gone before (in a MacGregor.)!

What I'd propose to your thread Matt, is to take the existing single dagger-board; which is after all, a symmetrical laminar foil, well suited to the in-elasticity of the medium it's designed to operate in, and just settle for manipulating only that, to achieve the desired goal. I think much less engineering would be involved than two deploy-able foils, and the possibility of an accident replacement, not being a total show stopper.

Pinning, and selectively moving the vertical plane of the foil through say, three degrees, while eliminating any other play, lies the rub. Not impossible - but not easy, either. I'd settle for only halving the hull heel, if this could be pulled off. In addition, I'd like to toss in an idea I've had about integrating a nylon jackscrew, headed at the mast flange, for 12v retraction and extrusion (?). Let me work more on this....(feel free)

Ross

Hey Ross,

All true words. It would be a fool's errand to do any substantial work without verifying that simply angling the existing daggerboard wouldn't work nearly as well.

The issue I've identified with the my test method (jamming an oar down into the trunk to force the trailing edge of the daggerboard to windward) is that it only moves the top (wing root) of the foil, but the hydrodynamic pressure would angle the rest of the board back to center. Maybe--it still needs to be tested.

I've actually been working like a madman on my other "crazy talk" thread about the assymetrical wings, and I'm planning on asymmetrical daggers for that as well.

Nylon Jackscrew? So... There would be a nut at the top of the daggerboard and a nylon screw that went from the mast deck five feet down, such that rotating the screw would cause the daggerboard to raise or lower? The purpose is to support a heavier board?

I'll risk some of the reply here, about that, but I'd rather put it properly into a mod thread once spring arrives, and I can get at the boat to waggle things around a bit. My desire, besides the possible lift gained from manipulating the blade port, or starboard, is to have it behave like a 12v power window on an automobile. Up and down. Not necessarily heavier, though that would be good, but push-button controllable from the cockpit. Given the fact that it's near impossible to easily budge it, in either direction, with way on, and conditions extant that don't allow you the luxury of heaving-to to do so. You'd still have the safety line if something broke.
I'm thinking of a cheap right angle drive working off a 12v drill motor, located inside the cabin space adjacent to, and communicating through the internal daggerboard housing (above the mirror). Attach this to the top of the jack-screw (SS or nylon), which turns through an epoxied a/o bolted follower, on the top face of the daggerboard. As you're not supposed to lower this thing more than a certain distance down through the hull, the hollow board should be able to take the required length of screw while at the same time stiffening some of the wobble inside the channel.
Given the water pressures, at play on the blade, pushing it rearward, I think Brian's (Seahouse) idea about guides or rollers, becomes necessary also. Based on the short conversation we've had at the TO boat show, it looks like a good cooperatively engineered project for this coming season. The only thing that worries me at this point, is some sort of fail leaving you with an extended daggerboard - but I suppose you could always carry a spare drill, and chuck it onto the shaft. Many craft out there rely on 12v accessories: winches, anchors etc, why not a dagger-board?

R.

a jack screw on top of the existing D/B if secured good I am afraid will just rip the top of the D/B right off if u do not turn into the wind to release the side forces of the D/B being held tight against the D/B trunk !! even then i'm not sure the original D/B will last too long as they r really flimsy boards not much meat on them at all & so if u r going to try slightly turning that D/B inside the D/B trunk i also think u r going to shorten its lifespan considerately because it was built & designed to break under excess forces ,so now u r looking @ building a more robust D/B or strengthing the existing one , keep me posted

J

Crikey –

From my armchair, and without being able to refer to my own boat, away in storage, here’s the simplified picture I envision for your idea (I like it, BTW)!

Use a quality 12V cordless drill (tons on Kijiji for cheap- when the batteries die the drill sometimes becomes not worth the price of a new one), chucked to directly drive (so you don’t lose power anywhere, and there's room) an acme-threaded, say 1” dia plastic leadscrew 5- ½ feet long (probably your biggest test-bed material cost). Brass might be doable and available too.

The top meaty fiberglass part of the DB can be drilled and tapped directly for prototyping proof-of-concept purposes, or preferably have a nut loosely fixed to its surface or inset into the top. The leadscrew disappears down into the hollow DB, and might need a hollow tube inside the DB to guide its otherwise unsupported free end and stop it from whipping. This could be attached as part of the top nut as a unit to simplify construction. Some support might be needed above the nut as well to prevent buckling if pushing down under pressure, but this distance is limited to a few inches, if that.

If the top part of the DB is not beefy enough, invert the DB and pour in as much polyester resin as you want to build up the thickness, and at the same time fill in/ move the DB uphaul holes and lines to a more favourable position.

Because you want to ideally mount the leadscrew at the centre of balance of the DB, and that point might be (partly) occupied by the mast (?), you will have to offset it from that point and allow the top end of the leadscrew to float – that is with some flex to it to allow the DB freeplay. I imagine tight quarters in this area.

The DB trunk has a lot of clearance between it and the DB, so you want to allow for all of this movement in rough sea without binding the threads. You could also counterweight inside the trailing edge of the DB to help restore some balance if you need to. Because the leadscrew might flex and bow as a result of not having supported the DB by its centre of gravity, the nut will have to be allowed to also pivot a small amount fore and aft to prevent binding. I think it would be unwise to expect to build in a lot of clearance in the threads to allow for this movement, but you might consider using a split nut at the initial phases to give you some flexibility. The split nut would also provide a method of quick release (if so-built) from the leadscrew to return to the conventional factory DB retraction arrangement if you needed to.

The clutch on the drill will slip when the DB retracts to its upward extent, and when the tension on the DB line peaks all the way down – and you’ll likely be able to hear that, so no limit switches are needed in this simplest scenario. The (adjustable) clutch would also protect the DB structure from being overstressed if you haven’t turned into the wind sufficiently to relieve sidewise friction when retracting or extending it.

Then it’s a simple matter of three wires to a cockpit mounted rocker switch and the battery for up and down, although you might want to add something that indicates the actual position of the DB, such as the original incrementally-marked uphaul line, maybe with a giant bungee attached to the end of it !

You would want to experiment with the pitch of the leadscrew (and single, double, or triple threaded) to find the drill at-load RPM, and low or high speed range of the drill, so you get a reasonable full-travel time without overstressing/ overheating the drill electronics (you can easily install a larger heatsink in these, to prolong life and reliability, they’re usually undersized, if space turns out to be available under the enclosure).

Good luck, and thank you and mastreb for my flight of fancy for tonight – Brian.

seahouse wrote:
Use a quality 12V cordless drill chucked to directly drive (so you don’t lose power anywhere, and there's room) an acme-threaded, say 1” dia plastic leadscrew 5- ½ feet long (probably your biggest test-bed material cost). Brass might be doable and available too.
With the stock dagger-board fully retracted, there's not enough space to install any machinery except for the adjoining area in the flotation pocket above the mirror. I've seen jackscrews of various sizes made out of various plastics, as well as SS and brass. Some have very large flat topped threads (not sure about acme) , and I also seen low pitch spirals which with the right torque, could provide very quick reaction. Considering the power of some of these cheap units I don't think a 90 degree link, or thread or guide roller friction would intervene too much given the short length of time it would be running for.
The top meaty fiberglass part of the DB can be drilled and tapped directly for prototyping proof-of-concept purposes, or preferably have a nut loosely fixed to its surface or inset into the top. The leadscrew disappears down into the hollow DB, and might need a hollow tube inside the DB to guide its otherwise unsupported free end and stop it from whipping. This could be attached as part of the top nut as a unit to simplify construction. Some support might be needed above the nut as well to prevent buckling if pushing down under pressure, but this distance is limited to a few inches, if that. If the top part of the DB is not beefy enough, invert the DB and pour in as much polyester resin as you want to build up the thickness, and at the same time fill in/ move the DB uphaul holes and lines to a more favourable position.
I'd take Highlander (John), and you both into account here and look very thoroughly at that area. Some of the jackscrews I've viewed come with follower nuts attached to plates that could be formed into a 'U' to surround the top of the blade which could be easily bolted into place, perhaps augmented by some set resin or 5200 in that top space. The internal width of the DB would determine the screw width and if nylon could work as a material, no guide tube would be required. Until I (we) can directly shake the whole thing about I don't anticipate enough angling to present a danger of jamming, especially if the screw is somewhat flexible.
Because you want to ideally mount the leadscrew at the centre of balance of the DB.
Because of the water pressure, it's going to cant backwards and sideways, so a centre of balance will be superfluous to a strong attachment position. Only the limit rope needs to find a separate home.
The DB trunk has a lot of clearance between it and the DB, so you want to allow for all of this movement in rough sea without binding the threads.
This would probably be the critical difficulty. Creating a simple roller guide that would eliminate water pressure friction as well as zeroing out most (if not all) of the DB channel play while under way (poetry in motion!). The split nut would also provide a method of quick release (if so-built) from the leadscrew to return to the conventional factory DB retraction arrangement if you needed to. Complicated!
The clutch on the drill will slip when the DB retracts to its upward extent, and when the tension on the DB line peaks all the way down – and you’ll likely be able to hear that, so no limit switches are needed in this simplest scenario. The (adjustable) clutch would also protect the DB structure from being overstressed if you haven’t turned into the wind sufficiently to relieve sidewise friction when retracting or extending it.
Had a big sigh of relief when I read that, as I had not considered it!

Sorry for the liberties with editing your post Brian, but some great considerations there!
Matt, should I get off the party line?

R.

A simple plastic tube like that used for venting gas systems like furnaces is made with a very thick wall , simply drill out the top & bottom plates of the D/B install the pipe inside the D/B & glue on extra end caps this will give ur D/B more strength but still keep its breakaway function as the pipe will break if u happen to break off the D/B thus not damaging the D/B trunk, this will also stiffen up the D/B & the tube will also act as a guide for the jackscrew

J

Likin that! Nothing like a little extra stiffness. Particularly if your Dagger-Board is old!
While we're on the subject, I've never heard anything about the end result of a fail. Does it splinter, or crack clean off?
Also, never having looked at mine (the dagger-board) I came up short trying to find a better than half decent picture of one....

R.

While we're on the subject, I've never heard anything about the end result of a fail.

You'll have to talk to Rob about that - he's had first-hand experience! More than once!

I wanted to ask him the same thing, but the conversation moved on...

Sheesh!

Hey Crikey (response to 4 posts earlier)– no need to say sorry, that’s a great way to format your response, I do it that way in emails too. (It’s not like you spilled red wine all over the table, like somebody did ). Dohhh!

All points taken…

Split nuts are easy to make– saw it in half and contain it – then easy to release. The saw kerf also provides a relief area for the threads to self-clean, somewhat like the flutes in a tap. Or the nut is made from two pieces held together while threading, for zero clearance between them. But really not necessary, I just suggested it as a method of quick releasing that you wrote as a concern.

I was picturing the drill in a housing sitting on top of the deck, but putting it where you suggest certainly has its advantages. Again, I’m going from memory of how this area is laid out, and the space available.

I have a simple method in mind for allowing the nut to float (been there, done that, once or twice) – we need to talk and sketch off-forum, maybe when you have the screw and nut, or I see what you already have? I believe that the success of the plan relies on accommodating wide tolerances with the leadscrew / follower nut alignment, as this can be a point of friction and potentially rapid subsequent thread wear, particularly with plastics.

The DB relies on the large surface area of the DB trunk to bear on to withstand side forces (it’s thin-walled), I think using rollers would require considerable reinforcement (or a large array of rollers) but it’s not insurmountable.

And good suggestion, John.

-B.

Please, continue on! I'd love to see how this works and whether there's significant advantage. The more info I can get without actually doing anything, the better!

I personally would avoid 12v motor and make something manually operated, that can then be secondarily motorized. I'm just into fault tolerance that way.

Yup Mastreb! Almost my thoughts too. Like a cordless drill, geared for maximum torque, with a square drive that fits into the already-present winches, and wind the DB uphaul around that winch. The profile with a 90-degree drill adapter would make this easier to handle.

But that’s not as dashing!

- B. (hopefully not presenting a “lazier than thou” demeaner) .