daggerboard extension

[popI]

You don't need much keel area when running, but on other points of sail, can you ever have too much? I sometimes find the leeway angle rather extreme on my 26M, and I was pondering ways on increasing it's effectiveness. I thought about a thicker shape, which would be better at the lower speed regime where I see the most problem. A thicker board would not retract into the trunk though.

Then I thought, why not a telescoping extension. It could be form fit to the inside of the existing daggerboard with very little modification to the existing board-just cut the bottom off. The extension could be as long as you like, and as heavy as you like. You would need a secondary retraction rope to retract it, or a two stage system on a single rope whereby the first bit of travel pulls the extension up, and the then once retracted, it pulls the whole board up.

Advantages: higher aspect board generally means greater effectiveness, especially since more area would be added. 20% maybe?
compounding effect of above at large heel angles, which Macs are so prone to.
cheap and easy to construct. can be done in stages with the board still useable interim
increase in righting moment of board due to more weight at base of board.

Disadvantages: added complexity with increased potential for jammed boards, ropes, etc.
increased bending moment on the existing daggerboard trunk, which may be fine, but outside the boat's design specs.
draws more water when extended, and with the increased leverage exerted on the trunk in a grounding, you could do some serious damage.

A final thought regarding the last point: maybe the extension should be engineered as a knock-off assembly in case of grounding, so as not to damage the rest of the boat.

Humbly soliciting opinions, comments. flame away!

[delevi]

Welcome aboard PopI.

Well, the longer the board, the more heel angle for starters. The thicker the board, the more drag. Can there bee too much keel? Honestly, I don't know. My best guess is no if yolu're sailing a high-performance yacht. Yes, if you're sailing a Mac. It actually can work quite nicely in light air but since the boat is so prone to weather helm, in heavier air, the added lfit may actually cripple the boat and force it to round up uncontrallably. The complexity of what you're proposing might make the project somewhat unrealistic, especially if you're modifying the existing daggerboard. The stock board is quite flimsy and will probably fail under load with such a mod. I had a custom made daggerboard with 150 lbs of lead ballast in the bottom 15 inches. I only increased the length by 2 inches, however, which still allows it to fully retract into the hull. The leeway you're experiencing may be partly due to trying to pinch too high in light air. You think you're pointing high but the boat and daggerboard aren't generating enough power, so you're sort of going nowhere fast. Try falling off 10 degrees, build up some speed, then head back up a little. If you do pursue the mod, I'm sure many people on this board, myslef included, will be quite enthusiastic to see the results.

Fair Winds,
Leon

[Terry]

I had a custom made daggerboard with 150 lbs of lead ballast in the bottom 15 inches. I only increased the length by 2 inches, however, which still allows it to fully retract into the hull.
Fair Winds,
Leon

IIRC Leon, in a previous thread you mentioned you obtained that custom daggerboard from Joel at IDA, is that correct? Can anyone with an 'M' get one of those daggerboards or was that a "one-off" item you had made? I have often toyed with the idea of adding leadshot to my daggerboard but as yet have not. It may be easier to just get someone else to make it and then purchase it, any direction you can supply for someone to get a daggerbaord like yours?

[delevi]

Terry,


I'm afraid it was a one time deal. The process was a nightmare for both Joel and myself. He didn't have an M boat to measure and insisted on making the thickness so there would be no play in the trunk. Actually worked out great in the end but took several redos. Joel ended up losing money on this. Suppose no harm in calling him and asking, but don't hold your breath. I was quoted as much as $4K by a local boat yard. My keel, though far from cheap, was a small fraction of that. Wish I could be more helpful.

[egwall1]

I've been reading the posts about weighted dagger boards for the last year or two. I finally decided to give it a try, primarily trying to reduce heel to make my wife more comfortable, thus more inclined to sail more often. I bought six 25 pound sacks of #8 shot (shotgun stuff), plugged the bottom holes in the dagger board, then poured the shot in the top rope holes. Seemed easy, until after increasing the board raising tackle to 6:1 to handle the additional 150 pounds, I still couldn't lift the board all the way up. On inspection, I found the added weight was causing the thin walls of the board to balloon outward, pinching the board in the trunk. Having broken my first board by hitting a submerged rock, I was able to see details of the internal structure in a cross section of the broken piece. The board walls, aft of the widest center portion where there is internal support, thin down to less than 1/8" thick and deflect in and out quite easily. I "drained" out the lead from the bottom holes, and added nine barrel screws (McMaster-Carr) to keep the board at its design thickness. The barrel screws are a two part screw, one side male, the other side female, with a thin, but wide head on each side. I drilled clear through the board thickness every 4" from just above the bottom of the board straight up along a line where the board bulged the most, and installed the screws. After adding back the shot, the board now remains at its proper thickness and lifts and lowers in the trunk normally. I have a few other mods I'm now completing before taking Second Chance out again. I can't wait to see how the weighted board affects performance. If it makes my crew more comfortable, it will have been well worth the hassle. The expense has been nominal - about $200 for lead, screws, and lifting tackle upgrade.

[popI]

Interesting comments, especially the bit about the internal structure of the board. I made a mistaken asssumption that the board was hollow at the bottom.

I posted this thread on the wrong forum. Should have been on the Mac 26 forum. I'll move it now. please join me, if yoiu have a comment. Thanks

[DaveB]

Your original thought of puting the lead shots was ok but you needed to do it in steps and use epoxy or polyester resin every 4-5 inches than harden than do again and again.
Personally I think only fill 12-18 inches down low would satisfy as the higher you go in weight the less you get in stable.If you do this you will need to fill rest with polyester resin to give board strength.
The resin would have sealed the lead and made a solid daggerboard as you go up without distorting the board .
Your daggerboard is much easier to add weight and mod than my centerboard as the effort to raise is much easier.
I resin in my Mac. X centerboard at the low end after I rebuild it.(approx. 1ft. up from bottom is solid polyester resin and approx. 10 inches down from the top of centerboard, this makes the MacX solid for pin and stress points and adds weight at bottom of centerboard but also allows for centerboard to break off in a extreme grounding or underwater log. The balance is close to original lift adding approx. 5-10 lbs to lift. The centerboard now has about 10 lbs more at 5ft depth and the top is still at or lower than water ballest for another 10 lbs.
All I did was strengthen centerboard and give it more stable support and maybe less heel for givein speed. If I had a ballbearing sleave at centerboard 90 deegree turn at deck I would have put your lead shots at bottom of centerboard.
Dave

I've been reading the posts about weighted dagger boards for the last year or two. I finally decided to give it a try, primarily trying to reduce heel to make my wife more comfortable, thus more inclined to sail more often. I bought six 25 pound sacks of #8 shot (shotgun stuff), plugged the bottom holes in the dagger board, then poured the shot in the top rope holes. Seemed easy, until after increasing the board raising tackle to 6:1 to handle the additional 150 pounds, I still couldn't lift the board all the way up. On inspection, I found the added weight was causing the thin walls of the board to balloon outward, pinching the board in the trunk. Having broken my first board by hitting a submerged rock, I was able to see details of the internal structure in a cross section of the broken piece. The board walls, aft of the widest center portion where there is internal support, thin down to less than 1/8" thick and deflect in and out quite easily. I "drained" out the lead from the bottom holes, and added nine barrel screws (McMaster-Carr) to keep the board at its design thickness. The barrel screws are a two part screw, one side male, the other side female, with a thin, but wide head on each side. I drilled clear through the board thickness every 4" from just above the bottom of the board straight up along a line where the board bulged the most, and installed the screws. After adding back the shot, the board now remains at its proper thickness and lifts and lowers in the trunk normally. I have a few other mods I'm now completing before taking Second Chance out again. I can't wait to see how the weighted board affects performance. If it makes my crew more comfortable, it will have been well worth the hassle. The expense has been nominal - about $200 for lead, screws, and lifting tackle upgrade.

[Currie]

IMHO - The interesting thing about adding weight to the daggerboard is that you're probably relieving stress on the board not increasing it.

The real stress on an unweighted board occurs when you're heeling. This stress is pretty substantial and directed upward and to windward - i.e. pushing against the water and heeling the boat. Adding weight uses gravity to relieve some of that stress. It's easy to assume that the weight of the board trying to pull the boat back to upright. If it weren't for the force of the water that would be true.

This would be interesting - there's an easy test to see which way the stress is torquing for those that have weighted boards: While heeling on a beat or reach - raise the weighted board. If the boat heels less (my guess is it will), there was still upward stress even with the weight. If it heels more, the weight of the daggerboard was actually pulling down on the boat while deployed (downward stress). Either way, I'm still betting the most stress you could put on a board is to not weight it.

That being said - another kind of stress is due to possibility of the board "swimming", or oscillating back and forth as it goes through the water. This could happen because the mass is all at one end and the remainder of the board too "springy". So I do agree with Dave, it seems like the whole board should be stronger from top to bottom to control the extra mass. But I do think the stress on the top of board, and on the hull, is probably a lot less than one might think.

just my $.02

~Bob

[Russ]

I too have thought a longer board might help. I was thinking of simply making it longer and dropping it down after launching leaving a foot or so sticking down all the time. The telescoping idea is clever, but it seems the stock board is somewhat flimsy to use.

I had a custom made daggerboard with 150 lbs of lead ballast in the bottom 15 inches.

What performance gains have you noticed with this added weight?




--Russ

[Currie]

I'll let Leon weigh in (pun intended) on his experience. I know he reported good results in other threads. But maybe this is interesting in the meantime.

A while back I was looking at doing a pumpable water ballast (to either the port side or the starboard side). The ballast would be 150 lbs. of water in glassed-in tanks under the rear berth and salon seats. I ran a bunch of numbers to see how much righting action it would add compared to people in the cockpit. Here's one of my pics...



The whole point was to calculate the center of boyancy, and mass of any added weight...people, water ballast, or a weighted daggerboard. Here's some things I came up with.

(BTW - I did the same test for other parts of the cross-section - not just the cockpit - and combined them )...

1.) The water ballast adds about 3 times as much righting (at 30º heel) as a person in the cockpit (150 lbs water same would be the as a 450 lb man in the cockpit).
2.) If caught on the wrong side (unintentional jibe?), water ballast is neutral (at 30º heel) as far as adding or subtracting more heel. Notice how much a person caught on the wrong side contributes to heeling versus the water-ballast.
3.) A weighted daggerboard exceeds that and is more than 3 times as effective as people in the cockpit. Plus it doesn't need pumping when you tack/jibe. One thing though, lead only weighs about 90% of it's "land weight" when it's in the water, so that probably brings us back to an even 3X factor.

At this point I gave up on the complexity of pumpable water ballast and joined the weighted daggerboard fan-club. The mod is a couple of seasons out though. So if any of this is close to right. Leon's 150 lbs of weight in the bottom 15" of the board (that's what I set the pic to), should right the boat about the same as 450lbs of people in the cockpit when the boat is heeling 30º.

(FWIW - I calculated the center-of-boyancy by filling the under-water area of each station in the factory diagrams with a little checkerboard hatch pattern, then picked the spot in each where there was the same number of hatches on the left side as the right - Oy )

Cheers

~Bob

[delevi]

Russ & Bob,

Well Bob hit it on the head. The board weighs a total of 180-200 lbs +/- The real advantage is the 150 lbs all the way at the bottom, which gives approximatel 3 times the righting moment as the actual weight i.e. 450 lbs righting moment. Considering the total ballst of 1450 lbs, this is adds 31% righting moment... in theory. It is difficult to really quantify the changes, especially since it's been around 3 years since I"ve had this keel. Around the same time, I upgraded my sails to high-end racing grade laminates, flatly cut and much more roach on the main and 105 LP on the jib vs. 95 stock. The former makes less heel. The later (added sail area) induces some heel. In my early tests, I estimated an average heel reductin of 5-7 degrees. I would say this still holds true, but honestly, I lost track, factoring the adjustable backstay, performance sais with 3 reefs in the main, 8:1 outhaul, cunningham, furling foam luff for the jib... I have a number of ways to reduce heel, with the keel being just one factor.

I''m not a fan of modifying the stock board. Having had one snap in half (no impact) and two others severly damaged just from sailing, the thin hollow fiberglass, in my opinion, is just asking for failure. This was a big motivator for me when having the custom keel made. In addition to the ballast, the board is extremely strong, doesn't chip like the stock board, and doesn't clank around in the housing. Bob, your concept of less stress with more weight may be accurate, though I would think would apply to stress loads on the DB housing vs the board itself, which still has to cary the weight, which will create much more stress when the boat yaws, impacts waves, especially under power, etc, then the weight in and of itself. I may be wrong but there just isn't much to work with in the stock DB.

As for that water ballast mod.... quite complex; probably not worth it for 150 lbs, considering you get no leverage on that weight. As for anyone looking to add ballast via keel, I would say still plenty of effort and cost for a marginal return. For me, it was worth it, in hindsight, though when I was ironing out the problems, I would probably say differenlty. The performance gains are certainly there, but if you expect a huge difference, you'll be disappointed.

Leon

[Currie]

Good info Leon - thanks.

Yeah, I agree. The trunk does need to suspend and hold the extra weight. I'm guessing that's not too much of a problem since it's "on-end" but who knows for sure . I've always been mighty impressed with how much stress the hull, and especially the standard-issue board take with only 12" remaining inside the trunk when it's deployed.

On the 150lbs of water. At one time I was looking at a system that filled them both at the same time - but I changed the plan. When I saw how benign a filled ballast tank was if it got caught on the wrong side of a tack, I planned it to be filled on one side or the other, not both. This applies about the same righting moment as the weighted daggerboard when the boat is heeling at about 25º. But yeah, it's complex, and the idea was scrapped altogether.

Was a fun excercise though. The big take-home is how useless cockpit bodies are at high-degrees of heel in a boat with such a high freeboard.

Cheers,
~Bob

[Highlander]

I have also been thinking about a couple of canted dagger boards installed into sleeves on both sides of the boat at say the S/B & P/S chain plates not sure if this would be to far aft but would be an easy mods for me using the existing chain plate bolt holes just to try it out no necc drilling unless it becomes a good Mod with a big backing plate on the inside use my original rudders as canted boards when the boat is heeled over I think they would be deep enough in the water and would be pointed straight down when heeled 20-30Deg. small enough not to cause excess stress on the hull with the right amount of backing support if it turns out to be a good Mod then could be permanently mounted with more hardware using the spare rudders would cost me nothing , they would break if they got overstressed without worring about hull damage and are easily avail. if the need comes to replace them ! they could be swing mounted into brkts simular to the SS ruder brkts on the stern or mounted into sleeves and go striaght up & down like the D/B
This would also give you the effect of two draft keels & make the boat more stable for those who are not so nimble inclined & prefer a more stable boat !

J

[popI]

Interesting comments. I would like to make the board thicker, in order to reduce drag at high angles of leeway, and increase lift. Any additional drag at low angles, and higher speeds (typically downwind) could be managed by retracting the board. Unfortunately, I can't figure out a way to do it.

I never seriously considered adding extra weight, and this discussion has reaffirmed that little benefit would result.

I still feel strongly that making the board longer, by way of a retractable extension would enhance performance. The biggest obstacle seems to be the internal bracing in the board. This would have to be removed in the lower foot of the board, where the extension would retract. Perhaps the skin of the board could in this area be stiffened adequately by laminating carbon cloth onto it. I don't know how much additional thickness could be added before the board would bind in its trunk though . I think I will want to get ahold of a broken board before I proceed.

[Nautek]

If you cut a slot in the deckhead above the daggerboard trunk so that when the board is up is protrudes above the deck just under the boom
This way you just need to lengthen the daggerboard with no fancy bits.
There are other boats out there that use this method and it would give you the extra length to the board without major mods
The only hitch I see is if the mast step is in the way you might be able to taper the board at the top

Allan