Centreboard.

[heymacaulay]

I need to make a new rudder and centreboard.

I note some people are using balsa rudders. Can anyone tell me the method of construction? I’m assuming they are sheathed in fibreglass mat and epoxy.

Has anyone tried using balsa laminate for centre boards or are they not strong enough?

Thanks

[Meryl Todd]

It is possible to build high performance foils which are light and stiff using fibreglass or exotic cloth.

There are two design approachs.

First, deriving the strength from the exterior using the core fundamently as a packing device. The core material can be foam, balsa or other light wood. Foils can be built by lay-up in a female mould or by shaping the core and male moulding. The latter is better for a one off production.

Second, deriving the strength primarily from the core and sheathing it with fibreglass. The core can be wood, laminated wood, or lightweight ply shaped to the final dimensions of the foil minus the thickness of the sheathing, say 1mm.

The choice of approaches depends on the thickness of the foil as the lightcore method derives its strength from the distance apart of the exterior materials.

The Sabre foils are very thin. The original concept was they were basically flat foils constructed from ply. The rudder is relatively moderately thick and not subject to excess sideways loading. It is therefore possible to build a balsa cored rudder. The centreboard is relatively thin, and subject to significant sideways force, and thus relies on the strength of the core. A balsa cored board would not be stiff enough without several layers of fibreglass making the total weight excessive. The optimal construction in terms of weight/stiffness ratio is therefore to build a wood laminate board and sheath. The result will be the lightest board for the required stiffness, it will be both lighter and stiffer than the traditional ply centreboard.

There has been substantial research on foil design but little work on the Sabre style parallel sided sections. However, research on Mirror foils some twenty years ago found NACA 4 digit shapes gave the best performance.

[heymacaulay]

Is there anything in the rules about using carbon fibre over a light weight timber on the centre board or rudder blade.

Ryan

[heymacaulay]

Is there anything in the rules about using carbon fibre over a light weight timber on the centre board or rudder blade.

Ryan 😈 😈

[heymacaulay]

Carbon Fibre is NOT PERMITTED in the construction in the construction of Sabre Class Yachts.This includes hulls, foils and fittings. The only reinforcement for GRP construction is E Glass.

Phillip Johnson
National Measurer

[Meryl Todd]

Perhaps there may be merit in having a copy of all the Sabre rules on the website, as at the moment the Rules and Measurement Section only details measurements.

I have found the measurement details are very useful since they went on the web site last July, with only a couple of minor interpretations needed since then to ensure the Sabre I am slowly rebuilding is totally legal.

[heymacaulay]

The measurement rules were put on the web site to help people who own boats but may not have a copy of the building notes. Generally people who need more detailed information are building a boat and have or should have a set of building notes. The measurement rules were published on the web site in their current form as it was the quickest way i.e. no editing required of a large publication. It should be noted that no offers to run the web site have been made to date. The other reason that only a limited amount of information was published is because the Sabre Building Notes are a copyrighted document and the Association does not want boats being built where no building notes have been purchased.

Phillip Johnson
National Measurer

[heymacaulay]

Quote:

Well as brief as your comment is it explains alot.

[Meryl Todd]

The problem is the great majority of people rebuilding an old boat do not have a ccopy of the construction notes. An example is a simple replacement of a boom, I built one in accordance with the published measurement rules but now have been told it is illegal because the mainsheet block hangers are incorrect and not in the appropriate place. I find the whole processs rather frustrating when I am trying to comply with a secret set of rules which can not be published for fear of breaking copyright. Do I have to buy a set of consruction notes just to replace components?

[heymacaulay]

fitzwarryne,

I am not sure what the Association’s Official Stand is on copies of the book. My own personal view on that topic is that if you own a boat, Timber/GRP or Composite, you should be entitle to have a copy of the handbook.

If you built your own, you should have bought a copy from the Association. You cannot get a Sail Number any other way. The Sail Number is what you are actually paying for here, not the cost of the Book.

If you purchased a boat new from a builder, or second hand, you should have received the original copy of the book issued for your boats Sail Number and construction from the person you bought it from.

If you have lost/damaged your book or bought second hand and did not receive your original book, there should be no reason why you cannot go to the Association and request a replacement copy, which should be heaps cheaper (Printing and Postage costs only possibly) than a new issue, as you are not asking for a new sail number, just a replacement book. This would be safer than borrowing a mates and copying it yourself, as a new Association produced copy will have all the latest ammendments.

Regards . . .

Willy . . .

[Author]

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