How to brace MK1 Firefly centreboard case

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slimtim
Posts: 53
Joined: Thu Nov 20, 2014 8:23 pm

How to brace MK1 Firefly centreboard case

Post by slimtim » Thu Mar 29, 2018 9:53 pm

Hello, thanks to STEVEB highlighting it, I have become the owners of F2103 Scallywag - I can't think of a better name!

She is in very sound condition having been in the same ownership for 50 years and in a garage for the last 20+ - with a little sanding and varnishing will be up and ready for our Firefly Open at Tamesis on the weekend of 21/22 April - please come along if you can.

Can anyone tell me how I should attach a brace between the centreboard case and somewhere solid? I'd like to do this as part of the refurb.

I'm asking as the buoyancy tanks don't look structural enough and so I'm assuming that I will need to glue hardwood blocks to the floor and use them as attachment points?

Thank you in advance for any help/suggestions/pictures.

Michael Brigg
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Re: How to brace MK1 Firefly centreboard case

Post by Michael Brigg » Thu Mar 29, 2018 11:13 pm

This was how my Mark 2 was done...
2006__04_06 096a.jpg
(29.58 KiB) Not downloaded yet
Basically the "forward thwart" needs to be extended out to the hull and glued / bolted by some ingenious method to the hull.

On Mark 1 this is often cheived by putting the CB brace onto the top of the buoyancy tank and then bolting it down to the stringer that holds the Tank to the hull. (You can see where this is on a varnished hull as it is marked by a line of screw heads.

Heres a link to the NFa Register showing my boat...

https://fireflyclass.co.uk/?s=F3184

You need to read a relevant part of the Firefly rule book as there are some restrictions on where you must put the brace. Join the NFA forum and speak to the technical Secretary.
Last edited by Michael Brigg on Fri Mar 30, 2018 4:47 pm, edited 1 time in total.
Michael Brigg

slimtim
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Joined: Thu Nov 20, 2014 8:23 pm

Re: How to brace MK1 Firefly centreboard case

Post by slimtim » Fri Mar 30, 2018 7:18 am

Hi Michael

Many thanks for your reply - I have been reading your many posts about all things Firefly with great interest.

The pictures are helpful, although I had expected the bracing to be at the front of CB case (as it is on older Merlins) so I will clearly need to read the Firefly rules to get it right.

I'll also check whether I can put epoxy a mounting block to the floor rather than relying on the tank structure.

Thanks again, will you be coming to the Tamesis open on 21/22 April by any chance?

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PeterV
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Re: How to brace MK1 Firefly centreboard case

Post by PeterV » Fri Mar 30, 2018 9:35 am

I braced my Fairey Finn centreboard case to the floor just by the side tanks. I epoxied the strut to the angle between the floor and the tank. I did it to be sure the boat was strong enough for rough sea sailing and its lasted 6 years so far, so, if your rules allow it it's certainly a viable option.
PeterV
Finn K197 & GBR564
Warsash

Michael Brigg
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Re: How to brace MK1 Firefly centreboard case

Post by Michael Brigg » Fri Mar 30, 2018 10:46 am

slimtim wrote: Thanks again, will you be coming to the Tamesis open on 21/22 April by any chance? although I had expected the bracing to be at the front of CB case (as it is on older Merlins) so I will clearly need to read the Firefly rules to get it right.

I'll also check whether I can put epoxy a mounting block to the floor rather than relying on the tank structure.
I've pasted these comments in from stuff I wrote on the Firefly forum...

The positioning of a Strut or “Forward Thwart” is not in question.
As long as it is more than 2070mm in front of the transom its legal.

In practice that means anything forward from the centreplate pivot which is given as 2098mm from the aft side of the transom.
The form and construction is currently entirely (so far as I am aware) determined by personal preference.

Provided it is forward of 2070mm there is in fact nothing in the rules to prevent you from using it as an attachement for toestraps.

This is an example of design creep in the Firefly. First of all one must ask why the presence of a “strut” in these areas might be seen as a problem. Bearing in mind the obvious fact that additional struts or thwarts might get in the way of crew movement what possible advantage was envisaged to be prevented in the original wording of this rule?

My personal theory is that this was to prevent the incorporation or use of “hiking Bars,” or “joy sticks” that had become the norm in the International 14 durind the early post war years, at which time if I recall Trapeze wires had been outlawed. Presumably it was felt that a specific aspect of the way fireflies should be sailed was almost to emphasize the need for a crew with strong thighs as a way of promoting a degree of athleticism.

Perhaps it would also have been part of a rule within the National Twelve restrictions that was ncessary to make the firefly legal in this class as well.

However we are now stuck with it as a rule and if it is to be changed, then the reasoning behind the change must be sound.

The use of “Foreward thwarts” (I prefer Plate stiffener” as the plausible name of a fortifying Winter Cocktail to be taken by crew members before racing between November and April)was originally developed to improve the berformance of the centre plate box. In older boats these are more often than not used by the crew as a solid toe hold and the stress of this use weakend the join at the hog. A floppy plate case is a slow boat! The logical placing of a stiffener from the Shroud Knee to the forward vertical support of the plate has been subsequently developed into a thwart on which the crew sits facing Backwards, and with this has developed the need to produce a Mark1A and Mark 3A foredeck, to make room for the crew.

The other important change (and consequence is the Forward bulkhead for a bow tank.

The original fittings for attatchment of Centreplate pulleys for the plate hoist and also for the toe straps lie on the hog well forward of this bulkhead and so alternative points of attachment are now required. The Plate stffener becomes the only logical point available and we suddenly find ourselves in the midst of a conundrum where the laudable process of rescuing an old wooden hull to make it competitive becomes impossible without a rule change.

I do not think anyone will be using a “joystick” these days and as such I cannot see any harm in making a small change to this rule so as to prevent confusion or misinterpretation. It is an important one perhaps for the technical committee to put their minds to in order to legitimise what has become common practice.
Michael Brigg

Michael Brigg
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Re: How to brace MK1 Firefly centreboard case

Post by Michael Brigg » Fri Mar 30, 2018 11:51 am

PeterV wrote:I braced my Fairey Finn centreboard case to the floor just by the side tanks. I epoxied the strut to the angle between the floor and the tank. I did it to be sure the boat was strong enough for rough sea sailing and its lasted 6 years so far, so, if your rules allow it it's certainly a viable option.
An important consideration for the "forward thwart" in the firefly is that it should not restrict crew movement, which is already quite limited (even with the new ruled extra height on the gooseneck/boom) and especially so if you have a Mark 1 deck layout. This is the layout with a small V breakwater in front of the mast. You will certainly have had this originally as you say the boat has Buoyancy tanks, although it may in its past life have undergone a Mark 2 or 3 conversion.

My personal preference was to place the forward thwart at a level with the top of the plate case supported by the wood frame that contains the plate bolt / pin. This provides a useful height for attachment of control lines easily reached by the crew, and also provides a useful bit of boat to hook your foot around if you need to make a sudden move when hiking out.

This position is also convenient to sit on for the crew, and can be extended out from the Centreplate frame, resting on top of, but not placing a strain on the Tank, and brace against the hull on or adjacent to the wood block supporting the shroud attachment. Along the inner surfce of the hull the ply structure of the tank is Scewed and glued down to a 3/4in stringer that will take screws, though it is better to strip down to bare wood and glue this to the top of the tank. The collective area of attachement will be more than adequate to avoid point loading the tank, unless you use the structere to attach ropes to suspend the boat in your garage roof (or theme pub) :roll:

:idea: Off topic, but a word of warning. DO NOT trust the shroud plate if it is held by Screws. In an old boat these are waiting to pull out and almost certainly, if brass, will have nail sickness! Failure of the shroud attachment will lose your mast and potentially damage your decks. Replace these screws with bolts from outside the hull (you can countersink and cap the heads for a neat job.)

For team racing, (these days one of the more important racing activities of a Firefly) a plate brace at sitting height provides a reasonably comfy support for the crew to sit on (facing backwards) while watching for other boats. Firefly racing is often quite close, so the same advice applies to positioning the crew where they can keep you informed of traffic.

Another important consideration is how the strut may obstruct storage of your jib stick. These are very important downwind in a firefly. The mark4 convertion presents a real issue to the storage question, and this is one of its main weaknesses (especially as the class decided not to adopt fly-away poles) and with a Bulkhead across the bow, the stick has to float around in the bottom of the boat.

A low down strut will get in the way of retrieving the pole especially if you are sailing at your limit or in steep waves. If the pole goes under the thwart, you struggle to retrieve it, and if on top of the thwart, it might be easily trodden on and broken. :cry:

At the end of the day almost every racing woodie has these struts and there are as many designs as there are sailors. Visit an open meeting, (or any week end at Thamesis you will see a selection and make your own choice.

I will not be at Thamesis as I have a Rowing regatta and dinner in Cambridge that week end, and my boat has a hole in it that needs repair, (A bit like my attic. See "Oops" in Banter :evil: )
Michael Brigg

slimtim
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Joined: Thu Nov 20, 2014 8:23 pm

Re: How to brace MK1 Firefly centreboard case

Post by slimtim » Fri Mar 30, 2018 9:27 pm

Michael, very many thanks for the extremely informative posts. I have plenty to work with and can visualise how my approach to plate case reinforcement will go - as you say, a floppy case is no good.

I will try to report back in due course.

Thank you again.

Rupert
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Re: How to brace MK1 Firefly centreboard case

Post by Rupert » Sat Mar 31, 2018 9:37 am

Saskia has a very simple strut from the top of each side of the case to the top of the side tank. This is much stronger than anything diagonal leading to the floor. It should be as far forward as possible, and also acts to keep the buckets in place. I also have the centreplate cleats mounted there, as it keeps the boat uncluttered.
The struts are just made from the square hardwood you get from the moulding rack at B&Q, I guess 3/4 inch, maybe 20mm. Each end is cut to fit the differing heights of case and tank, then they are fixed each end with epoxy and a screw. Must have been there nigh on 25 years, now.
Rupert

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