angled bilge boards/ dagger boards

[wayne nicol]

hi, i have been scouring all the old threads,
didnt want to breath life into some of the older threads, and my question is a little different.
i have a day sailer, with a rounded hull design, ie not hard chines, and flat bottom.
it currently has a daggerboard.
it heels quite significantly when going to windward, i cant help but think that the daggerboard is angled so far over to the windward side, that it cant be working very effectively to prevent side slip.
i am considering changing the daggerboard to two retractable bilge boards, with the trunk opening just above the boot stripe. with the board angled outboard when deployed, similar to bilge keels.

this would put the new trunks exit up in the coaming, - boat has lots of freeboard, so there is lots of space for a decent trunk length, for strength.
the angle would be a lot more efficient , wouldnt it?
and when working off the wind, both boards could be lifted, and the trunk slots would be above the waterline, improving efficiency.
many thanks
wayne

[Toxophilite]

Pictures, make and dimensions of you day sailor would help a lot. It would give those who can help you insight into your idea.

Is it that your weight isn't enough to balance the boat to windward in normal conditions?

[The Q]

You mean like this?
232215_fe96d8b6ef3929049529364fd6b2b495.jpg
The above is a Red Fox 200
It's been done several times with both commercial boats like above and home builds.
Also it's been done with boards which swing up.
The oldest version being..
figure9-8.jpg
I seriously looked at twin boards on my boat, but I mostly sail on shallow rivers of 100ft to 200ft width. Using twin boards , would mean tacking off the bank early, and require rapid swaps of board sometimes every 30seconds to a minute when tacking.

One thing to remember is with twin board you don't want them to be symmetrical, you want true aircraft wing shape asymmetric. Having the "flat side" of each board facing out.
Fig1-1.jpeg

[timo4352]

Interesting idea Wayne.....possible things to ponder....
...sure you already know that fixed bilge keels need not be raised or lowered, and help the boat stand upright when on the hard...



http://forum.woodenboat.com/showthre...board-question



https://www.finnsailer.dk/buying-the-boat
https://www.finnsailer.dk/the-bilge-keels



https://bills-log.blogspot.com/2010/...uising_09.html
A neat dinghy cruising boat - does anybody know this guy from the UK? (woodenboat.com)

[Ben Fuller]

Where you want to be researching is in scow land. E-Scows, C-Scows the current Melges scows. They've beem doing this for decades.

[John hartmann]

French NA Gilles Montaubin has also drawn several boats with dual, canted daggerboards which might be worth some study.

[johngsandusky]

You might test leeboards before doing surgery on your hull.

[Dryfeet]

While--Technically-- you might gain efficiency with your proposed solution, and to other's points, this has been done via a number of acceptable solutions, I'd suggest that the difference in a small boat is so small that you will never really notice it in practice. Probably not worth the considerable effort... unless you just want to tinker or have a serious engineering mindset/fascination.

[wayne nicol]

While--Technically-- you might gain efficiency with your proposed solution, and to other's points, this has been done via a number of acceptable solutions, I'd suggest that the difference in a small boat is so small that you will never really notice it in practice. Probably not worth the considerable effort... unless you just want to tinker or have a serious engineering mindset/fascination.

yes you are absolutely correct, i am afraid it may be the latter point that you made
even a small gain would be advantageous and justify the time spent.

[wayne nicol]

French NA Gilles Montaubin has also drawn several boats with dual, canted daggerboards which might be worth some study.

many thanks, any links to a website or anything, i am struggling to find anything on a search
thanks

[wayne nicol]

Many Thanks Timo, yes the bilge keels will helop with the boat on the beach, but due to the rocky nature of our beaches, i never put it on the beach, anchor and skiff!
its the angled bilge keels, that did get my brain working in this direction though, and the progression to retracting daggerboards seemed logical!

[wayne nicol]

You mean like this?
232215_fe96d8b6ef3929049529364fd6b2b495.jpg
The above is a Red Fox 200
It's been done several times with both commercial boats like above and home builds.
Also it's been done with boards which swing up.
The oldest version being..
figure9-8.jpg
I seriously looked at twin boards on my boat, but I mostly sail on shallow rivers of 100ft to 200ft width. Using twin boards , would mean tacking off the bank early, and require rapid swaps of board sometimes every 30seconds to a minute when tacking.

One thing to remember is with twin board you don't want them to be symmetrical, you want true aircraft wing shape asymmetric. Having the "flat side" of each board facing out.
Fig1-1.jpeg

thanks Q, great images thanks
i had intended to use foiled boards, but some of the reading i did, said that the foiled boards were more prone to stalling when coming about.
but i thought i would try them anyway, seems pointless to make all this effort without going to the max anyway.
if they do in fact stall the boat significantly, i will build flatter boards!
many thanks
wayne

[SHClark]

It is unlikely that you will net an improvement in performance by converting a normally proportioned day sailer to bilge boards. It is, however, certain that you will improve performance by making a properly shaped dagger board. I don't know the size of your boat, but excessive heel is often a matter of helming technique, crew placement and sail trim.
SHC

[Woxbox]

What SHC says. If speed is the goal, first be sure that you have good sails set and trimmed effectively. That's where significant gains can be made. The daggerboard, not so much.

[wayne nicol]

It is unlikely that you will net an improvement in performance by converting a normally proportioned day sailer to bilge boards. It is, however, certain that you will improve performance by making a properly shaped dagger board. I don't know the size of your boat, but excessive heel is often a matter of helming technique, crew placement and sail trim.
SHC

Many thanks, i do hear you, trim is of the utmost importance, i do agree.
this boat has a fair bit of windage, is 25'LOA, i do think the daggerboard is too small, it also heels over significantly.
there is not much i can do about changing the heel, unless i slack right off on the sails, or put a ton of lead in a deep keel. it is a trailerable boat. one or two people on the high side is not enough to reduce the heel significantly.
of course we do everything to trim and tame the heel as much as we can, but if she is heeling over 25 degrees from vertical, i can just see that the current daggerboard is side slipping significantly due to its angle. the primary objective with this exercise, for me, is to improve the angle of the dagger board in relation to the boats angle.
hence the need for twin daggerboards.

as with the high windage, we need all the help we can muster for improving our upwind sailing.

what are your suggestions with regards to a proper daggerboard design, i assume its more than just an asymmetrical foil.
the current board protrudes a wee bit over 5' below the hull, and if i recall correctly its about 14" wide- but i would need to measure that to be 100% sure.
many thanks

[wayne nicol]

What SHC says. If speed is the goal, first be sure that you have good sails set and trimmed effectively. That's where significant gains can be made. The daggerboard, not so much.

not speed per se' Dave. but rather to improve the upwind performance and get closer to the wind, right now she is quite far off the wind, and tacking is a laborious affair.
i just want to improve it as much as i can. i know it will never be what a keel boat can do, but i should be able to improve upwind performance somewhat!
make our outings a bit more enjoyable.
i dont race, so speed is not an issue.
many thanks

[SHClark]

I need to know more about the boat to make anything but general platitudes. Is it a known design that is published somewhere or can you give more particulars.
i wholeheartedly believe that weatherliness is paramount to enjoyment. This is the beauty part of sailing.
Steve Clark

[Michael_Owen]

I like your idea of the canted boards taking a bigger "bite" out of the water. I had never thought about the heel angle being so much that the board loses its grip.

But, it does seem like dealing with the bits above the water would be easier. Does your boat have reef points on the sail? Or maybe just a better/longer DB?

Good luck with what ever you choose to do!

MIke

[Dryfeet]

Sheeting angle affects windward performance notably. So too, does age/cut/shape of sails. If old, you're potentially getting drag and heeling moment instead of drive. These two things alone will probably make a bigger improvement/dollar and time invested in re-doing the whole underwater geometry. (And SHC's comment regarding simply having a well shaped foil with the existing depth, etc is not to be underestimated)

But all this takes away your desire to tinker so I offer my apologies. BTW, do not put any toe-in on your bilge boards as that will seriously destroy your windward ability-- I've never really seen too many successful attempts with that.

[Toxophilite]

I really want to see a picture of this 25' boat, that has a daggerboard.

Do you mean centreboard?

Too much sail area?

Is this a homebuilt design?

I asked for pictures and information earlier. Is there a reason you can't share that information?

not speed per se' Dave. but rather to improve the upwind performance and get closer to the wind, right now she is quite far off the wind, and tacking is a laborious affair.
i just want to improve it as much as i can. i know it will never be what a keel boat can do, but i should be able to improve upwind performance somewhat!
make our outings a bit more enjoyable.
i dont race, so speed is not an issue.
many thanks

[Woxbox]

not speed per se' Dave. but rather to improve the upwind performance and get closer to the wind, right now she is quite far off the wind, and tacking is a laborious affair.
i just want to improve it as much as i can. i know it will never be what a keel boat can do, but i should be able to improve upwind performance somewhat!
make our outings a bit more enjoyable.
i dont race, so speed is not an issue.
many thanks

Wayne, OK, so it's pointing ability that the boat lacks. But my experience is that this aspect of sailboat performance has more to do with the sails than with the fins, whatever they may be, below the boat.

For example, my boat has a pair of bilgeboards. They are flat sheets of plywood that present a triangular shape below the hull when dropped. The shape doesn't meet any test of efficiency used for high performance sailboats. But the boat will nevertheless reliably tack through 90 degrees as shown on the GPS in moderate conditions. In higher winds and waves, the tackling angle is greater, as is the case with any boat, but still not at all bad. What I've also found interesting is that it doesn't make a big difference if I have both boards down, or just one, or even if just the windward board is deployed. What this boat does have are new sails made by a very competent sailmaker, and I've taken care to adjust them so that they set well and the boat is balanced properly.

You said this in the first post:

and when working off the wind, both boards could be lifted, and the trunk slots would be above the waterline, improving efficiency.

You haven't said just what design boat you have, but most any round bilged 25' sailboat wouldn't sail properly at all if the daggerboard or centerboard were completely raised while sailing off the wind. This is again a question of balance and a need for something under the hull to make the boat track and respond to the rudder.

So yes, you can add a pair of daggerboard trunks that angle outward in an attempt to improve windward performance. It is standard practice in some very high-tech boats. Such boats often have two rudders as well -- also angled outboard. But from what you've explained so far, I'd be surprised if the change would fix the problem.

Some photos of your boat under way would be very helpful, especially showing the sail shape. Also, a description of exactly how the helm feels when working to windward. Is it neutral, so that if you let go the boat continues straight? Or does the boat exhibit heavy weather or lee helm? Besides excessive heel, what else is the boat telling you?

Most any sailboat can be tuned to perform satisfactorily -- certainly good enough for a comfortable day sail. But the real source of the bad behavior needs to be identified first.

Here's a Mini Transat design with a pair of canted daggerboards and matched rudders. These boats also carry a deep bulb keel, which in some cases can be swung to weather.