Bre keel

[Peter Belgium]

Hi,
My motherlanguage is not english ,so sorry for mistakes written.
I am very interested in a Bre,but have a question.

Is the keel,when down, going up  touching the ground,or even stones(at slow speed)will something be damaged,can it be done without problem?
Thanks for your comments

Peter

[Jonathan Stuart]

Peter,

The keel on a BRe is a centreboard that swings backwards, thus generally when you hit something the centreboard will move back (assuming the boat is moving forwards) and not be damaged. Of course, it still depends on what you hit and at what speed but the centreboard touching something is far less of an issue than with, say, a lifting keel.

[Peter Belgium]

Tnx Jonathan,

how does the  system works for  lowering the keel ,is this with a line?

[Jonathan Stuart]

Yes, there is a single line that controls the lowering and raising of the keel. The centreboard is weighted so no downhaul line is needed. To lower the centreboard you just release the line from a cam, lower it as much as required and then trap the line in the cam again. To raise the centreboard just pull on this line - there are blocks in a 4:1 arrangement in the centreboard case that make it easy to lift the centreboard despite its weight.

[Barry C]

Peter,

There have been several forum discussions about centerboard and rudder damage and how to prevent and repair them, for example:

http://www.swallowyachtsassociation.org/?page_id=17&URL=http://www.swallowyachtsassociation.org/smf/index.php?topic=676

Swallow will install stainless strips on the forward edges of both the CB and rudder as a reasonably priced option. If you sail in stony places (and who doesn't?) these seem like a good idea!

[Graham W]

Here's a BayRaider from underneath, showing centreboard and rudder.  The centreboard will kick up on deeper rocks than the rudder.

[Matthew P]

Fitting stainless steel strips might make centre boards and rudders more robust but they may increase drag by changing the cross-sectional profile of the foils in the critical area near the leading edge.  I don't have any quantitative evidence for this opinion but various text books support this view.  Of course you might argue a neatly fitted stainless strip is more streamlined than some ugly dents.

Gladys now has a carefully profiled rubber tip on her rudder which seems to have absorbed a few knocks.  In the event of a really hearty knock I expect the rubber tip will fall off, which is fine.  Something has to give somewhere.

Matthew
BR20 Gladys

[Llafurio]

Matthew,
why should anybody fit a protective strip which alters the cross section profile?
-There are half-round protective strips available which can be set into the leading edge of board and rudderblade fully flush with the profile.
Claus

[Matthew P]

How many people have experienced humming foils?  I used to think foil humming on my beloved Drascombe Coaster was its way of telling me that that the boat was enjoying itself. Now I think it is a cry of distress. I believe one of the reasons Swallow Boats (Yachts!) perform well into wind is the well-designed profile and accuracy of the keel and rudders.  I agree with you Claus, most people would not consciously change the profile of the foils to the detriment of performance.  The problem is how sensitive profiles are to variations from their design and the degree to which performance is effected.

If the protective strip is fitted fully flush with the profile it may not be too detrimental, although I still have doubts about a simple half round section replacing a carefully designed nose profile. From what I have seen of the half-round stainless steel protective strips, there tends to be an indentation between the back of edge of strips where they join the glass fibre profile.  My concern, based on reading various books and articles, is that it takes a remarkably small defect or variance from precisely designed profiles close to the leading edge to prematurely separate water flow away from foil and hence cause significant drag – even if the flow is not strictly laminar.

Articles and bits of books I have read (or at least the bits without hard sums) include: 

https://www.ericwsponberg.com/wp-content/uploads/keel-and-rudder-design.pdf

https://books.google.ie/books?id=Cr-pCAAAQBAJ&lpg=PA228&dq=yacht%20fin%20leading%20edge%20critical&pg=PA228#v=onepage&q=yacht%20fin%20leading%20edge%20critical&f=false

Principles of Yacht Design (3rd edition – there is now a 4th) Lars Larsson

and High Performance Sailing by Frank Bethwaite

While some of it is concerned with exotic high performance boats, I believe there is quite a lot of material here relevant to rugged gnarly, practical folks like us.  Most of this is out of date by the way but still relevant.

If there are any well qualified fluid dynamicists amongst our gnarly, practical ranks who can contribute some theoretically sound but practical and simply explained opinions I'd be very pleased to hear them.

Finally I acknowledge that boat performance is a consequence of compromises across many factors including foil, hull, sail and ancillary equipment design and construction but the ultimate determining performance factor remains the nut on the helm.
 
Matthew
BR20 Gladys

[Graham W]

After I had stainless steel protection strips fitted to the front of my foils, my nut on the helm pointed out numerous failings on my boat that would prevent it ever going as fast as Gladys, despite him doing the important stuff at the tiller end.  Foremost of the failings was a vibrating centreboard at anything over four knots, which impressed him not at all.  Rather than remove the protection, I faired in the sharp edges of the stainless strips with sealant so that they presented a smooth profile with the foils once more.  The vibrations ceased and the matter wasn't mentioned again.

I think I read somewhere that the slightly rough leading edge of the unprotected foils is deliberate and designed to improve laminar flows.  I can't remember where this was and certainly not in the books that Matthew mentions.  If so, the smooth surfaces of the stainless strips, despite being faired in, may still be a disadvantage. Anyway, I haven't installed slot strips across the bottom of my centreboard slot, so am reconciled to ever being slower than Gladys.

[Llafurio]

A flush protective strip in the leading edge, this is how it's done:

Classic Marine does not give all dimensions of the keelband material strips, so maybe ask Moray McPhail for exact full dimensions or look up at Toplicht:
www.toplicht.de/en/shop/bootsbaumaterial/profilschiene for the available dimensions of the strip material .

Decide tentatively upon which profile will come closest to the strip of leading edge GRP you are going to cut off. 10 to 16 mm width will work very well. 

Set and block your calliper jaw the width of the keelband material you have chosen, and scrape the calliper jaw hard at right angle down the leading edge. Length approx 12 " on the board, and 1 1/2" on the rudderblade, measured up from lowest tip. Mark the tiny scrape to make it stand out better for the jigsawing.

Use an electric jigsaw to cut off the marked GRP strip on the leading edge. Take the cutoff strip and measure it again for width and thickness and go buy the keelband strip material which matches or comes closest in its dimensions. 

Cut the right length of strip, give some extra length for the horizontal heel part (1- 2 "), drill and sink holes into it, bend it to match your cutout best, set it in Sika, use a bit of sanding on the cutout if neessary, drill little holes as seats for the screws, screw it on and wipe the Sikaflex flush with the surfaces. Done. No more damage to the board and blade from accidental hits.

It`s simple enough for you to DIY, but I would much prefer the yard doing it as standard for all new boats. These GRP boards and blades all are gonna hit something under water sooner than later, and the unprotected GRP edge splinters like glass. Been there, too often.

P.S. Dec. 1: "It`s simple enough for you to DIY". Well, it's not, considering all the preparations and worksteps required. To remove and to re-insert the board while the boat sits on the trailer is a major effort in itself, as is removing the wooden centreboard top which often is fast glued to the plastic, especially on the BRes, and which has to be levered and broken off.
But then, when on the other hand you see the damage inflicted on the board by impacts, a fundamental repair is required anyway because the water will seep in to the board along the laid bare glass fibres inside. And also, a word of caution, the board may split open, vertically, in it's entirety like butterfly wings. Seen that happening to a french BR in the Morbihan. Gruelling.

[Peter Taylor]

Having just looked at this thread, by coincidence on Sunday I saw a BRe with protective stainless steel strip attached to the leading edge of the rudder. The stainless steel looked like the sort sold as rubbing strake and it stuck out to either side of the rudder profile with black sealant filling the gap behind. 

I'm no fluid hydrodynamicist but I do know that to get any foil to work effectively you have to fight to keep the flow laminar and attached to the foil as far back as possible - ideally all the way. I would think that the stainless steel strips would cause flow separation at the very front of the rudder - in other words you may as well just use a flat plate, as many rudders are.

Even fairing the strips smoothly towards the rudder profile will still result in a huge change to the cross section compared to the design profile. Whether this matters I don't know, I suspect most of the time the rudder is working in a highly turbulent flow regime anyway and often it is at a significant angle to the flow. I would imagine the effect might be more noticeable for the centreboard which probably has a more critical profile and operates in a more controlled flow regime.

Humming or similar vibration from the foils suggests eddy shedding in a sub-critical Reynolds number flow regime - something you almost certainly want to avoid! (see attached photo of eddies in marine stratocumulus behind an island - this is what's happening). Foil roughness may actually help in promoting super-critical Reynolds flow (in the same way that golf balls have dimples to make them fly truer) and suppress large eddy formation. At one time slightly rough "carbon" paint coatings were in fashion for racing dinghies based on a similar reasoning. However the fashion didn't last long. Smooth is better if you can keep the flow attached!

My conclusion: if I decide to protect my foils I'll look for something better than stainless steel rubbing strake!

Peter

[Llafurio]

Having just looked at this thread, by coincidence on Sunday I saw a BRe with protective stainless steel strip attached to the leading edge of the rudder. The stainless steel looked like the sort sold as rubbing strake and it stuck out to either side of the rudder profile with black sealant filling the gap behind.  ...

ARRGH! -That is how NOT to do it, of course.

[Graham W]

Foil roughness may actually help in promoting super-critical Reynolds flow (in the same way that golf balls have dimples to make them fly truer) and suppress large eddy formation. At one time slightly rough "carbon" paint coatings were in fashion for racing dinghies based on a similar reasoning. However the fashion didn't last long.

So the roughness at the front of both BR foils was deliberate on the part of the yard?  Everything else about them is mirror smooth.

My conclusion: if I decide to protect my foils I'll look for something better than stainless steel rubbing strake!

A forward-looking fishfinder?  With fast progress in electronics, it's surely only a matter of time before such machines are cheaply available, even for those of us who don't own superyachts.

To be fair to armoured BayRaiders, SeaRaider Craic also hums to itself. I don't know what causes this, as I'm fairly sure that its foils are as naked as the day they were born.  It seems to come from the front somewhere and only above six knots. Which is most of the time

[Llafurio]

..-
To be fair to armoured BayRaiders, SeaRaider Craic also hums to itself. I don't know what causes this, as I'm fairly sure that its foils are as naked as the day they were born.  It seems to come from the front somewhere and only above six knots. Which is most of the time

Craics foils are plywood, not GRP, and delivered with no protection fitted. After the tips of board and rudder were beaten to mush after a single week in Scotland, I had to sand them back down to the hard core and resined them over together with a single layer of glass mat, quite invisible. That was in 2005, and held very well to this day.