Looking for an old 26M Centreboard

[brianhar]

I'm thinking of trying an experiment with placing a bit of weight into a centreboard. Main issue is that my grand design will essentially trash a centreboard to carry it out, So to save a lot of money, I thought I would ask if anyone has an old centreboard that has been damaged and would be willing to part with it for a small fee (donate would be even better ).

My idea runs something like this:
- cut the centreboard in half lengthways (for / aft),
- have a Stainless Steel internal frame manufactured to take the additional weight and fibreglass that in,
- Fibreglass the two halves back together again,
- fill all internal voids with a mixture of resin and lead shot,
- adhere a roll or two of lead sheet to the outside of the centreboard (comes in a roll from Bunnings),
- glass over the top of the lead sheet & Gelcoat to finish.
- another item to design in, will be to try and get the thickness of the centreboard to fit the case a bit better and not get so much slop.
- I'll also be reinforcing the centreboard case.
- haven't worked out the raising / lowering bit yet.

So, if someone can help me out, please let me know.

Thanks

Brian

[Cato]

first question is why?

the current centre board is hollow and when all the way down adds about 80kgs of weight below the water line?

cool thinking by Macgregor - the centreboard initally is hard to get up from the fully down position.. but once it has begun travelling up.. the water clears the C/board and thus getting lighter.

not sure why you would want to bugger around with a very clever design and make dagger board that is redundant.

Paul

[brianhar]

Paul,
my thinking here is reasonably simple. When sailing the boat to windward, the boat immediately heels to 20 degrees and when pushed to 30 degrees. In comparison to other trailables, I'm reefing far earlier than them and am on my 2nd reef in 20 knots. Not a good place to be in, when I'm one of the few nuts who trys to race the boat. The boat performs very well on a beam, or downwind with the kite going. I've now got the boat pointing at the angle I want, but cannot exert the amount of sail pressure to make the boat go forward at a reasonable speed.

The water in the ballast tank and centreboard is of the same specific gravity as the surrounding water (duh!). So my thoughts are that the water ballast does not transfer to righting moment until some of the ballast water is raised higher than the surrounding water by heeling (20 degrees). This would transfer to a maximum amount of ballast water to be raised higher than the surrounding water to be half of the 550ltrs (that would be a 90 degree heel, with the admiral protesting).

So I want to have a muck around with making a weighted centreboard (like I've had in so many other trailables). The experiment might fail, but it's worth a crack.

Regards

Brian

[Mac26Mpaul]

I'm sure I read a thread of someone doing this on this site somewhere. You may be better off seeing if you can find a board on the US part of the site. I think they sting ya about 500 bucks or something here for a new one and there is unlikely many second hand ones about here. Its probably cheaper to find a US second hand one and pay shipping...

[Cato]

Hi Brian
yep correcting thinking regarding the Righting Lever "G Z" and an increace in weight in the lower aspects of the C/Board

As the boat heels around G ( Centre of Gravity) Be aware as you increase the weight G moves up and the KG lenghtens increasing the force on GZ.

I like your theory - however consider the following.

IF your able to stiffen the boat by increasing the weight in the keel, and she is able to sit more upright in stronger weather, the control surface of the keel has not increased, and you will probably find yourself increasing leeway quite substantially. So you have improved your pointing ability, however your CMG has you sailing further away from the Mark.

I wonder if there is another solution.

Rig tuning and sail twist.

in heavier weather depowering the upper section of the Mainsail is the key
in the big boats we pump on more backstay ( i mean hydralic ram pump) the objective here is to bow the mast and thus opening up the leech.
As the Mac's dont have back stays, runner or checkstays - that kinda rules that out.

In the smaller boats they ease off the Vang to get the sail leech to curl.


Does your main have leech telltales? - especially the top batten telltale.

WHen close hauled - set the main so that all leech telltales are flying horizontally. combination of Mainsheet tension and vang tension. I used to be the Mainsheet hand on the GPrix boats in Syd. All the work was done by constant traveller positioning. The macs have a small traveller and this dosent help. a full athwartship Traveller would really help.

Optimum sailing angle is 15 - 25 des as you know which is what your trying to achieve by stffening her so you can carry at least the first reef longer. are you still holding the Genoa in this wind of have you changed down to the Jib?
Are you racing with enough moveable human ballast? and crew who can do a quck headsail change?
regards
Paul

[bartmac]

There's been centreboards for sale on Ebay......dealer in/near Newcastle NSW........also the last forum entry mentioned no back stay......my 26X has one but no tightening device

[Cato]

Ahh .. right
Im not familiar with all Macs.. the M's dont have a Backstay.

an effective and reasonably priced backstay adjuster is:

Teminate the backstay about 2m shorter than it is now, and swage and hard eye(thimble) for a an FWR (flexible wire rope) Block to be shackled on.
Fix a pad eye to either side of the transom (near the base of the pushpit posts)
make a "saddle" from the same size FWR of the backstay with swaged hard eyes(thimbles) on each end.
Lenght of saddle - from starboard transom pad eye (standing end) up to FWR block and approx 200mm past the block.
make up a 3:1 purchase(luff tackle) - using a fiddle block and cam cleat (shackled to the port pad eye) and a block and becket (shackled to the running end of the "saddle" - roved to advantage)

hope that helps
Paul

[brianhar]

Cato,
for racing, I have a purpose built fully battened Mainsail , with extensive telltales fitted. I tend to use the Main (and associated rig similar to a skiff. I'm thinking that this sail may be a bit flat and does not like to drive through the rough stuff. More play in this area required.

My headsail is a self tacking jib that I rarely change over to the genoa. The winds in Melbourne are more often towards heavy than light, and the boat sails a lot more balanced with the jib (IMHO). The other great aspect of the self tacker, is the reduction in risk for tacking stuff ups. Once set to the tension I like, it is left alone until the top mark when I furl it and release the kite.

I like the idea of seaching eBay. I'll give it a try.

Brian

[Cato]

HI Brian
Sail Plan seems spot on.
the Centre of effort for the working jib is low and forward, and a flat main seems like the right shape for higher wind speed.

I'm interested in how your new keel performs

Paul

[brianhar]

Well, the search for a centreboard is over.

The wonderful Cameron from Blue Reef yachts has done me a great deal on a new centreboard.

I suppose a 'plug' for Australian Mac owners to use Blue Reef Yachts is appropriate at this point.

Thanks Cameron, much appreciated.

Now I just have to find some time to start the mod!

I'll post some information as it comes to hand (don't hold your breath)

Brian