I am interested in the design of daggers and what creates the differences. For example, when racing, or following technically, Tigers on my TheMightyHobie18 it was obvious that the Tigers would lift to weather in a puff and my 18 did not. What about the foils creates the lift? Is there a way to modify an old design, like the TheMightyHobie18, daggers to create the same lift? Is it the length or width that makes the difference? I have thought of creating sleeves for my 18 wells that would accept the newer designs but thinking about it is as far as I got.

Ref: http://www.dreesecode.com/other/aflprimer.pdf

Read this first. Then consider that there is no free lunch <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> It is all compromises and what you want to optimize your boat for. Aspect ratio is the most important property in my opinion, but it can be a double edged sword, especially so in rough weather.

When that has been said, there is a good chanche the world have moved on since your H-18 was built. I would not have modified the existing foils, but got some new ones (or buildt some) and modified the daggerboard wells to accept new boards.

I bet this was more due to the sails and rig on the Tiger and less on the daggerboards.

Except that he's got Tiger sails on an 18 SX mast.

H-18 daggers are low aspect ratio. You could use an old set to make trunk cassettes to hold Tiger style boards.

I bet there are some used Tiger boards out there - a lot of people have gone to the optional carbon boards.

I think creating a gasket that would both fill the well and hold a tiger board would be difficult to do. I most likely do not have the tooling to do it. I guess I could make a mold of the outside of a dagger and trim it to fit. Would be best if the sleeve were removable. Anybody got any ideas on doing this?

All you need is overhead projector sheets of clear plastic and sikaflex.

Wrap the film around the leading edge of the new board (about where it penetrates the bottom of the hull) so that the film matches the surface nicely, put board with film into existing case, fill the gap at the bottom with sika maybe 1" up into the case, wait for sika to cure and remove board, clean up bottom of the new case flush with bottom of hull...

Make sure the new board is pushing against the back of the case, the sika won't take the loads from the trailing edge as well as the back of the case will.

I've seen it done on a competitive 12' skiff. Looked very neat and tidy. It was only about 1cm thick of sika though...

Although there are many things that do promote “lift” to windward (higher aspect dagger boards being just a small one of many), it has been my experience that by far the greatest gain to windward always comes from, firstly the sailers and secondly the sails, or I should say, assuming that they are cut well, the set of the sails. Most of the pointing ability of a boat is controlled by the leech of the main as it is the pressure on the leech that is trying to “push” the transom of the boat to lee ward, off the wind with the resulting effect that the bow wants to point up (particularly in the gusts as the CE of the sail tends to move backwards). One of the biggest failures that I have seen in making a boat point is when, after a tack the crew pulls on and cleats the headsail before the main has been set. This will pull a “bow” in the forestay and luff of the headsail and unless the crew doesn’t “crack” the headsail sheet and reset it after the main is set, it is impossible for that boat to point to its full potential. The criteria usually applies that if a similar boat outpoints you consistently, try a swap with the crew of that boat and see if they have the same problem with pointing on your boat as you have, before deciding that “it is the boat and not the sailers”.

Tiger sails on a totally different mast? No wonder you have issues with keeping up. At a minimum you should have the luff curve of the mainsail re-cut to match your mast bend.
If you have a composite tip, you will never match the efficiency of a Tiger rig in gusts. How well the leech stands is a major factor when going to windward in puffs, and a soft mast-tip will bend in puffs allowing the leech to fall off. I think Bill made a very good point.

The lift of a foil should be carefully balanced against the sailarea (or rig type) you have. If you have increased your sailarea and moved the center of the sails, you might benefit from working on your daggerboards. First check the condition of the boards (scratches, nicks, dents etc.). Playing with mast rake can also be a good thing. But matching the mainsail (and jib luff curve) to your rig is what I think will give the largest increase in performance. To give an example, when the Tornado class needed an performance upgrade to stay in the games, they added a new sail package to the existing platform. It made the boat much faster (not to windward tough, just more powerful), but the foils and hulls was never altered. So the Tornado still sails with really inefficient centerboards with a shape defined back in the 60s. It is still one of the fastest beachcats around due to rig development (mast+sails) and the sailors skills.

Don't forget rig tension either...a sagging forestay is another cause of low pointing.

That's not entirely correct Darryl. The positive effect of weather helm is real but not because you point higher to windward, you can't point higher without luffing/pinching the sails.

The reason a bit of weather helm helps windward performance is because you need to correct it with your rudder, otherwise you'd continue to round up into the wind, which we know is slow.

The force you feel on the tiller while holding your boat on a steady course (preventing it from rounding up) is caused by a force on the rudder blade.

This force on the rudder blade is pushing you to windward, which is good.

If ppl can't picture it, try experimenting on shore with the skipper sitting on the boat in the usual position holding the tiller extension so that the rudder stays straight and have the crew push on the leeward rudder box.

So instead of pointing higher, you aren't slipping sideways to leeward as much, which increases your VMG.

But hangon, having pressure on the rudder is slow because it is drag. The trick is finding the right amount of weather helm so that you provide some lift force to windward to reduce leeway angle but don't increase the drag caused by the rudder being off centre too much.

It's a tricky design problem but can be done fairly easily by trial and error by adjusting the rake and testing.

Really good info, thanks. I am currently working with the mast to attempt to make it conform to the sail. D. Lennard gave me info on how to compare this. I do have a comptip on this mast and was aware of its downfalls. I am very close to the proper bend at this point but can only control the section of mast between the diamonds, the tip is not controllable.
The lift I'm trying to describe is not related to pointing higher. Both boats sailing on the same heading, no change in direction, the Tiger moves toward the wind or lifts to weather. I watched it happen but can't really explain it. It appears I should spend more time on the rig first and then consider a mod to the daggers. I will continue to improve my mast and sail shape, get to more races for comparison, and see where I end up. I'm very satisfied with the boats performance compared to H18s, would like it to be a little more competitive with the newer F boats.

maybe it's not that he's going up... it's that you're slipping down more.

Your daggerboards are just not as efficient as the Tigers. If you are thinking about putting Tiger boards on and just want to check it out without making a commitment to glassing them in then try using some shims. Imagine if you were making a prototype boat and wanted to make sure the placement of the daggerboard trunks. You would make bigger trunks than nessesary so you could move them around some, for and back as well as rake. Use some delrin 1/4 inch sheets. The bottom one will have to be fit unside the 18's daggerboard trunk with a cutout for the new board. The top can be screwed to the top deck so it can be adjusted. This way you will be able to balance the boat without the commitment to perfect placement the first time.

Later,
Dan

It would seem that if you could find a relatively cheap pair of higher aspect daggers, it would be worth a try. I suspect it will only improve the boat's performance to windward.

For making a dagger board trunk adapter, I think either some hardwood (as long as it doesn't swell) or hard plastic, maybe 1" thick. I think I would just make templates out of the existing wells (if you have access to the type of boat your are getting your new dagger boards from, it would be real easy). Hold a piece of paper/wood/cardboard on the underside of each hull and trace out the opening, repeat for the topside. Transfer your tracings to the hardwood, cut out with a jig saw, and epoxy in the boat.

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Expanding foam with this process and then epoxy the leading edge of case. Easy to get rid of if its a disaster and will look like original if you are careful.

Try Spartite, it's an epoxy mix used for replacing wedges at the partners on keel stepped boats. Plenty strong, pourable, and can be popped off later...