Tips on Dagger Board Trunk Construction?

CatBuilder said:

Thanks, Andrew.

I understand what you are saying now. Leave the D until later. How would I join the D section with the already finished product? I am not clear on how to do a taper in that. Do I just grind the D down or make the D with a taper on each end, then use the taper in the foam/glass flat panel and join them up like a patch?
If you followed my suggestion above then you do not have a finished product. The excess trailing edge is cut of square and the D section glued on, there is no need for a taper you dont have a sandwich at the aft end. You have a solid laminate to which you add the extra reinforcement over the D. Until the D section is glued on the case is split at the trailing edge, remember there are two layers of plastic sheet there between the crush foam, thats why the case can be slipped of easily. Also the extra reinforcement layers have to be added to the leading edge. Refer to your diagram.

You did miss something that rberry posted from his designer.

1/2" (12mm) is the size of the trunk gap, but you use bog on the exits of the trunk to make a tight fit after the boards are installed. This provides a nice, neat, easily controlled surface and mating to the existing hull.
OK I did miss that, that being the case then why not just build a plain rectangular case.

The middle of the trunk makes no difference at all, so 1/2" up there is no big deal. Loads on a board are at the keel (hull) and deck level.

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Regarding the discussion of suitability of styrofoam for the spacer, yes the common 22kg/m3 can be used and will not crush.
But I would only use this if making a split case, one side at a time. The reason is that you can not drape it over the leading edge like the spacers I mentioned or the wound rope. You would end up with lots of wrinkles and possibly crimps over the leading edge.

Making the case in halves and joining is not a problem, this is how production cases are made. You use two male moulds to produce each half, but the laminate at the solid leading and trailing edge is kept to a minimum initially. You add the bulk of it after the halves are glued together.

michael pierzga said:

Delrin has it defects. Hard and prone to point loading the foil. Lift keelers are using Thordon.


From Ron Holland yacht design.......

" The pad material was researched and an elastomeric material called Thordon has been chosen. "

"The manufactures provided us with enthusiastic technical support and proof of the materials unusual “memory” properties in returning to its original shape following the application of high local loading, rather like a
very dense sponge. "

" This material will spread out local unevenness of load due to wear, marine growth or
slight shape variations in the keel surface. "

“Bedding in” and bending of the keel foil will also cause slight
unevenness of pressure distribution in the side pad areas."


Inspection hatches on the keel trunk are common for servicing

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I'd like to offer an alternative view seeing as Thordon has been replaced by a more advanced bearing composite in some applications.

I feel manufacturers such as Thordon use the elastomeric properties of their bearing material as a benefit when it may not help at all. If you have a material that gives under pressure whatever mechanical system you have designed will flex more as the bearing pad gives. To transmit forces you don't want rubber, you want a rigid structure. A foil is designed as a precision part which you don't want to twist and bend. There are materials which have as good or better bearing properties with regards to friction, load distortion and thermal change and these are rigid non melting, they also now have surface chemistry and surface properties to resist marine growth.

So if you build a lifting dagger board do you really want it to flex, bend or move in its mount? You spend a fortune getting a super rigid carbon foil so you need the fixings to be as rigid as you can get.

One of the latest materials comes out of Perth it's called Maritex and is used on some high profile applications such as latest (military) submarine dive plane designs as well as yachts like Baltic Yachts panamax in the lifting drive pods. It will exceed the performance of an elastomeric material when under high load in pretty much all cases.

Do some research and see where current technology is.

Phil Locker said:

If there is core involved, then both sides have to be 'glassed.

If your daggerboard(s) have a simple rectangular cross section in the head, this is pretty easy construction. You're just building a box, possibly with a channel for control lines.

If the board(s) are foil-shaped top to bottom, it can be best to use the daggerboard itself as a male mould to laminate the trunk over.

I'm attaching an example of the latter, complete with control line channel.
This one is solid laminate, no core. (actually we didn't use the daggerboard as a mould as it had a curved tip section... we cut a plug of the same foil section but rectangular planform).

Phil

Click to expand...

Phil, what did you use as a spacer between the plug and trunk? Also, could you pm me regarding a build of trunks for my boards? This is wasting too much time for me...