Center vs. dagger board

[DJM]

I am still trying to make up my mind about which to use in my marblehead dory skiff.
Things I like about the centerboard:
1) easy deployment
2) everything is attached, no pieces to lose
3) kicks up out of the way when it hits bottom
4) this is what the plans show
5) beach landings easier

Things I like about the daggerboard
1) lighter
2) requires smaller hole in bottom of boat to install ( structural integrity )
3) takes up less room in boat, less chance of siezing a gronicle when tacking
4) easier to build
5) less to go wrong, less to leak
6) less drag when rowing
7) supposed to be more efficient.


So, my question to the group:
Some have stated the daggerboard is more efficient. What exactly does this mean? Will it point higher or sail faster, and why?

Just how much does the centerboard slot slow the boat down when sailing
or rowing?


http://i45.photobucket.com/albums/f67/dpmundy/Beached.jpg

[Thorne]

I've installed a centerboard to convert my Chamberlain dory skiff (similar boat) to sail, and love it. My recomendation is to go with the plans.

As far as taking up more space, have you considered the lost space when the daggerboard is out of the case and on the floorboards while rowing?

Overall, for boats with the room for a centerboard (over 10' in in my judgement), and which won't be raced or primarily rowed, I think a weighted centerboard is vastly superior to a daggerboard. With an un-pinned centerboard and kickup rudder, you can hit underwater obstacles or sail right onto the beach without ruining your day or hurting the boat...

;-0 )

Consider installing a pin to hold the centerboard in three positions: fully up, halfway down, and fully down (or as far down as the plans call for). This allows you to easily pin the board into place for rowing, sailing downwind, and sailing a reach -- plus takes the strain off the pennant during storage and transport.

The pin has one hole in the side of the case, and three holes in an arc in the centerboard. It doesn't have to go all the way through the far side of the case, just into a hole partially drilled into the inside wall of the case.
http://www.luckhardt.com/cb-case5.jpg

[DJM]

Thanks Thorne,

I didn't realize you have been sailing your chamberlain. Have you posted photos that I have missed?

Those were my thoughts about the centerboard also, the only argument about the dagger that holds any weight with me is that is rumored to be more effiicient. ( whatever that means )

If I go with the centerboard, I am going to use an arrangement I saw in one of my books. The board has a lever that sticks out of the top of the box to raise and lower it, and a piece of rubber hose attached to the board to hold the board in position by friction, but still give if it hits something. This is the method shown in "How to Build Glued Lapstrake Wooden Boats" by Brooks and Hill.

[DJM]

Also, I guess I will be rowing about 20% of the time.

[Tom Lathrop]

The ONLY significant thing that is really in favor of a daggerboard is sailing efficiency and I've used plenty of both. If you were interested in a fast sailing boat, you would not have built a dory in the first place. Speed is not all that related to enjoyment of the boat although a slug is no fun either.

One thing you did not mention is that capsizing is much easier with a daggerboard since it can catch on the sail or rigging in a tack when raised.

A centerboard is much easier to live with.

[Thorne]

The reason that I built my case with a top is that all of the boats I've owned have had a capped case -- and I really can't see building one that would be open. I did drill a hole in the top and plug it with a cork to allow access to the centerboard in case it needs to be pushed past any gravel or obstruction in the slot.

Sure seems like the issues of splashing water (either while sailing, rowing or under tow) and snagging lines on the lifting arm would outweigh any advantages. There is also the potential safety issues if the boat is (heaven forfend) swamped -- there is a big open hole in the middle!

;-0 )

But the open top centerboard case certainly has its fans, both here and in the design world, so suit yerself, maytie.

[DJM]

I will have a cap to my centerboard case. The lever arm for the board is 3/8 thick, and only a small slot is needed for it, so I hope I won't get a whole lot of splashing through that. You have a good point about the swamping though. I shall have to give that some more thought. The top of the slot should be about 10" above the waterline.

The nice thing about the lever arm is you don't have to rely on gravity for the board to drop, which could be a problem if some debris gets in the slot. Also, you can tell at a glance where the board is and there is no need to pin the board in place, which defeats the ability of the board to kick up out of the way. The jib sheet might snag on the arm, but I think it will be far enough away from the main sheet to be safe.

Of course, I realize the dory is not a go fast sailing boat, but if the centerboard means I might lose 5-10 degrees of pointing ability, that would be something I would be concerned about. But really I don't know if it would lose any at all, or if it was only a degree or two I wouldn't care. But all I have heard is the the dagger is "more efficient". And really, I am not looking for a acrobatic workout struggling for the last 1/4 knot of speed, I just want a laid back sailing experience, and that also suggests the use of the centerboard.

[Bob Smalser]

"Thunk!"

[DJM]

Bob,
Perhaps this is a newbie question, but is "thunk" the sound a daggerboard makes when it hits a rock?
Dave

[Bob Smalser]

Bob,
Perhaps this is a newbie question, but is "thunk" the sound a daggerboard makes when it hits a rock?
Dave

;) I didn't see "thunk" among the disadvantages of the DB.

For a dory skiff knockabout beach cruiser I think a CB is a wiser choice. Especially when the kids take it for a spin.

[Thorne]

Yes, there certainly is the "Thunk!" factor with daggerboards to keep in mind.

Yet another advantage of centerboards is the ability to use them at varying angles -- partway down for downwind sailing, all the way down for reaching, etc. With the different sailing rigs I'm working on (two different masts, three mainsails, possibly two different jibs), I may need to angle the board (and possibly the rudder) back to deal with weather or lee helm issues.

And not to mislead anyone, I haven't splashed down the dory yet, so I mis-spoke when I said "I love it" regarding my centerboard.

I DO love it, however -- both the centerboard & case and the kickup rudder with yoke head are the most complex things I've ever created from scratch (the dory is restored, not built by me).

I don't exactly go out and fondle them or anything, unless multiple coats of CPES and varnish count as fondling...and then we are ALL in trouble!

;-0 )

http://www.luckhardt.com/rudder-tiller1.jpg

I'd take photos of my lovely new paint job -- Rustoleum Marine white interior & hull with Kirby's 'Blind Green' on the sheerstrake -- but Seattle's weather has come South for a visit and won't leave...(whine whine whinge)

[JimD]

The ONLY significant thing that is really in favor of a daggerboard is sailing efficiency ... A centerboard is much easier to live with.

Yyyyyup.

Note: Apparently with the new forum software short pithy responses are not allowed. I tried to just post the word 'Yup' and got an error message saying posts must be at least eight characters long.

[DJM]

yup!
:) (http://nowhere/)

[JimD]

yup!
:) (http://nowhere/)

Hey! How'd you do that???!!!:mad: :D

[DJM]

The smiley counts as a few characters. Won't work without it.

[sv Lorelei]

Okay, having built and owned both. Build the centerboard. Especially if you're going to be towning this behind anything. Case in point:

We're going to Shelter Island with another couple who had NO sailing experience. It's about a 2 foot chop and we're towing our 8 foot sailing dink with daggerboar. With each wave a little geyser of loverly water introduces itself to the inside of the dink. After about 2 hours Tim needs to pull the dink in to the stern of Lorelei and make a courageous leap of faith in order to bail her out. Stuffed down his shorts was a plastic device (no, not what you're thinking)...an empty ice bag which he then stuffs down the DB trunk to mitigate the hydraulic transfer. All this leaving NOBODY aboard capable of actually sailing the boat if something happened.

Build a centerboard and cap the damned thing.

[John Meachen]

I think your original plan to use a centreboard,together with a length of rubber hose for friction is extremely sound.The main area in which our preferences appear to diverge is that you are intending to use a closed capping and a link with a protruding handle.It will work but I feel happier with the handle of the centreboard coming into the boat via a slot in the capping.This also makes it a lot easier to fit the board to the case as you can reach in and move the board around until the holes are aligned.

[DJM]

Okay, you guys have convinced me. I am going with the centerboard.

[Bob Smalser]

This Gardner-drawn dory CB, case and lifting mechanism is simple, solid, and doesn't let in any water. You'd want to make yours smaller and lighter than this one, of course.....he drew several....use Gardner's dimensions for a boat of your approximate length and sail area.


Traditional Centerboard and Case – Part I, The Board (http://www.woodenboat-ubb.com/vbulletin/upload/showthread.php?t=8948)

Traditional Centerboard and Case – Part II, The Case (http://www.woodenboat-ubb.com/vbulletin/upload/showthread.php?t=4871)

Traditional Centerboard and Case – Part III, Installation with a False Bottom (http://www.woodenboat-ubb.com/vbulletin/upload/showthread.php?t=4743)

[DJM]

feel happier with the handle of the centreboard coming into the boat via a slot in the capping.This also makes it a lot easier to fit the board to the case as you can reach in and move the board around until the holes are aligned.

I guess I wasn't very precise in my description. There will be no linkage, the lever I described will be 3/8 ply mortised into the top forward edge of the centerboard, so it becomes a part of the centerboard, but thinner so I only need a 3/8 slot for it.

[John Meachen]

I hope 3/8 ply will be strong enough.How thick is the board?

[Andrew Craig-Bennett]

Centreboard.

I have a boat with each. Our tender has a daggerboard and the Firefly has a centreboard. Beside the "thunk" factor, as Bob so succinctly puts it, there is also the matter of hauling the plate up when off the wind - do this with a daggerboard and you end up with it so far out of the case that it will foul the boom, turning an accidental gybe into a guaranteed capsize.

[DJM]

Bob Smalser:
This Gardner-drawn dory CB, case and lifting mechanism is simple, solid, and doesn't let in any water. You'd want to make yours smaller and lighter than this one, of course.....he drew several....use Gardner's dimensions for a boat of your approximate length and sail area.
I like that Gardner centerboard, especially the metal rod to raise/lower it. That could be used to free the board if it got jammed, unlike a lifting line. I am not sure if I can adapt this design without moving it too far forward. I think the hump would interfere with my thwart, but I will have to check the dimensions to be sure. The hump also serves to keep the rod inside the case when the board is lowered way down.

My plans call for a rectangular board that fits under the thwart, but they don't show very many other details. I am using Gardners 14 foot sailing whitehall plans to fill in the details, since they seem to be very similar.
What I don't like about the whitehall plan is that it looks like the lifting line would come out throught the bottom of the slot and create drag if the board is lowered very far.

[DJM]

I hope 3/8 ply will be strong enough.How thick is the board?
The board is 7/8 thick. The ply is meranti, and certainly seems to be plenty strong. The lever arm would only be about 8" long, and about 3-4 inches wide.

[John Meachen]

It seems like a sound starting point.Before cutting too much wood it may be useful to add the inside shape of the case to your lofting and draw the lever position with the board half down and fully down.With this information you may be able to minimise the length of the slot in the capping as well as the width.

[Bob Smalser]

I think the hump would interfere with my thwart, but I will have to check the dimensions to be sure. The hump also serves to keep the rod inside the case when the board is lowered way down.


The hump is spose to fit between the thwarts, and you adjust the dimensions accordingly.

http://pic3.picturetrail.com/VOL12/1104763/7711190/101687782.jpg

[Thorne]

Ah yes - I used the same Gardner "sailing whitehall" plan for my kickup rudder, but the centerboard in the Mystic Seaport Museum Chamberlain dory skiff (1890's) plans was the same "humpback" one from Gardner -

http://www.luckhardt.com/cb-design1.jpg

I also didn't like the humpback design -- although Bob's version of it and the lifting bar are **wonderful** -- and modified it as shown above to make it longer and about 10" wide at the front and 9" at the back to fit tightly under the fore and center thwarts (which also hold in in place).
http://www.luckhardt.com/cb-case1.jpg

[DJM]

It seems like a sound starting point.Before cutting too much wood it may be useful to add the inside shape of the case to your lofting and draw the lever position with the board half down and fully down.With this information you may be able to minimise the length of the slot in the capping as well as the width.

I have built I full size cardboard mockup of the board and case to accomplish the same thing. I am still worried about not being able to bail the boat out in case of a capsize. If I can make the lever as arc about the centerboard pivot, it may be possible to build a slot that exactly fits the lever.

[Bob Smalser]

The purpose of the hump is to provide bearing surface for the board against the case opening. The less board-case bearing surface, the more stress on the pin and the quicker it'll wear and leak.

http://pic3.picturetrail.com/VOL12/1104763/7711190/101677477.jpg

It's also important for the case to be well-mortised in both thwarts for solid support running from the bed logs all the way up to the top of the case. That includes running vertical braces from any frames cut by the case opening to the thwarts or at least up the side of the case.

The less stress on the bedlogs and CB pin, the longer the assembly will last without leaking and rebuilding.

[DJM]

Ah yes - I used the same Gardner "sailing whitehall" plan for my kickup rudder, but the centerboard in the Mystic Seaport Museum Chamberlain dory skiff (1890's) plans was the same "humpback" one from Gardner -

It looks like your Chamberlain plans differ from the Marblehead plans quite a bit in centerboard placement. Mine shows the board pretty much centered under the middle thwart. My centerboard pivot is probably 18" behind the mast step.

That is why I may not be able to adapt the humped design. I'll check my plans tonight. Also, when rowing, that cleat might cause some lower back pain;), but it could probably be moved.

[DJM]

The purpose of the hump is to provide bearing surface for the board against the case opening. The less board-case bearing surface, the more stress on the pin and the quicker it'll wear and leak.


Now that makes sense. I have wondered about how the centerboard could withstand side loading, and can see how that hump would help out.

[John Meachen]

While I can totally understand your wish to be able to bail the boat in the event of a capsize,I would imagine that unless you are intending to use buoyancy bags or tanks,water over the gunwhales will be far more of a threat than a trickle through the centreboard case.
As Bob notes,the less stress you impose on the pin,the lower the likelihood of a leak and your plan to use friction rather than lead for holding the board in place will further this aim.It is terrible to contemplate the damage done by trailing if you have several pounds of lead a couple of feet from the pivot and the board hanging in space.As a diversion,it really irks me to see photographs posted on this forum showing lifting rudders left on the transom for trailing.It does the rudder fittings no good at all.

[Hwyl]

The Dyer Dhow centerboard method is good. The top of the case is closed off competely, and the pivot bolt has a handle on it which lowers and raises the centerboard. It's hard to describe, but the pivot bolt is square where it goes throught the board and rotates in the case sides. Joe CSOH has a Dyer, I'm sure he'd send you pictures. I'd stay away from putting weight in the board.

Dick Newick built his daggerboard cases with a triangular space at the back, filled with styrofoam, so on a fast grounding there'd be somewhere for the board to go, yet the case was not as intrusive as a full centerboard case.

My personal preference would be for a daggerboard, it's just so hard to lose all that space in the boat.

The John Meacham discussion. I agree with John, if your going to raise and lower it with a handle, I'd go full thickness, I think both John and I have sailed GP 14's and that's the way they are, I can remember some pretty heavy duty heaving on the handle, I can never remember a problem with water coming up the case. You ought to have flexible plactic (or ox hide if you must) strips to close the opening in the hull anyway, they should stop the splashing.

Cheers Gareth

[DJM]

Bob,
That is a really nice looking craft. It shows you don't have to varnish everything to make a beautiful craft.


edited to remove a question you already answered.