Keel Bands – Width and Thickness

[Martin Ward]

I am hoping that someone could shed some light on the following for me. I will be fitting new keelband to the bottom of my boat soon. Having checked the class rules I can seen that a keelband can be as narrow as 9mm and as wide as 22mm. My question is would it be within the class rules and within the spirt of the class rules to flare out the width of the keelband from 9mm to 22mm just before the centreboard slot to help water flow around the centreboard.

I assume that there is no reason why a keelband must be of a parallel width or depth.

In other words the keelband would be increased in cross section and perform the function of a sometimes described as a Fairing Plate.

I would be interested in hearing from anyone who has tried this or seen a OK with keelband which has been flared out in width. I assume that the same could be done with the depth of the keelband by increasing the thickness of the keelband from 3mm (the minium under the rules) to the maxium permitted by the rules ie 10mm.

Regards

Martin Ward

[bob193]

whatever you do to the keel band is added weight to the hull. most modern boats do not have them fitted , on glass boats it is part of the moulding. this along with other extraneous bits such as spray deflectors and floorboards are a thing of the dim distant past. if its in the rules you can do it if it gives a min and max dimension it must be within those. simples

[Martin Ward]

I’m surprised as my understanding was that you have to have a Keel Band fitted and that the boat was out of class if it did not have a Keel Band fitted. The part of the rules which leads me to believe this is copied and pasted below.

A keel band, minimum section 9mm wide by 3mm deep, maximum section 22mm wide by 10mm deep, of any material shall extend for a distance not less than 3500mm, measured along the keel band, from the aft face of the transom. The radius of the bow forward of a point 3500mm from the lowest point of the aft face of the transom, measured along the base line, shall not exceed 11mm.

I am assuming that it can be flared out to 22mm as the centreboard slot is 22mm wide in order to except a 20mm wide centreboard. Therefore I am assuming that the practice of flaring out the keelband to the width of the centreboard slot is provided for in the rules.

There was a proposal to change the rules and make the Keel Band optional at the same time the rudder blade changed from a 31 degree angle to a 15 degree angle but I though the proposal to drop the keelband was unsuccessful?

Regards

Martin Ward

[Tony Woods]

Martin, I’m not sure about your tapering idea but yes you’ve got to have a keel band. Bob, do you need to borrow a scredriver to put yours back on?!

[bob193]

strange didnt have one when i bought it from robert cj and no sign of screw holes, he bought it from simon shaw so some very naughty people in the class

[Martin Ward]

What I am trying to describe, in my round about way, is increasing the width (and or depth) of the Keel Band just before the centreboard case to promote water flow around the centreboard board.

I can remember Rodney Pattisson writing about a simular thing in the Flying Dutchman class where he use to use to create a small mound out of filler on top of the Keel Band just before the centreboard to easy the water around the centreboard. I would not like to copy this pratice but as the rules allow for the keelband to be as wide as 22mm the same width as the centreboard slot I assume that the rules have been drawn up with this practice in mind otherwise why have 22mm as the maxium width of the keelband?

I will be making my Keel Band out of wood/glass epoxy to keep the weight down and reduce the number of screw holes required. It would be very easy to flare out the width of the Keel Band using this method.

I would be very interested to hear from anyone who has built OK’s whether professional or amatuer and has come across this issue.

Regards

Martin Ward

[Bill B]

I don’t know of an OK with a maximum keelband. I can not see a problem with what you want to do though I am not sure if it will make an advantage. The rules were drawn from original wood boats where a protective keelband was used. Some people would have wanted to try boats with no band and a smoother underwater shape so the rules require some “band” as a raised bit on the bottom of the boat in the centre.
When they made glass boats the obvious thing was to mould the required shape into the hull, which is what they do.

Usually the glass boats have the centre shape at the front of the c/b case faired into the ones that are each side of the case, this might be what you want to do. When I had a wooden boat I didn’t do that but chamfered off the blunt ends to reduce resistance.

You don’t have to be able to unscrew them and take them off. You can use plastic bands glued on.

Bill

[Martin Ward]

Bill

This center shape located just before the centerboard slot (on plastic boats) sounds very like the idea which I am describing. I am thinking of using wood/glass epoxy as I want a light weight keelband which I can fit using as few screw holes as possible.

If anyone has a photo of a plastic boat using the sort of centre shape Bill is describing then I would find this very useful. May be we should have a gallery of construction details on the Website. Unless there is one already and I have missed it.

Regards

Martin Ward

[davecooper]

Here’s Chris Perry’s new keelband (Idol Composites icebreaker). The tight line isn’t part of the boat – it’s the measurement baseline!
[attachment=0:1pjm497g] keelband.jpg [/attachment:1pjm497g]

I think your idea of a construction details gallery is completely brilliant, Martin. How soon can you start?

Dave

[Martin Ward]

Dave

This photo is just what I hoped someone would post. It shows exactly the sort of Keel Band flared out around the centreboard case which I thought would be fitted after I had read the rules. The only difference I had in mind was using a shallower angle when narrowing the Keel Band down from maxium to minium width.

The other issue is the total width shown at the point where all three parts of the Keel Band meet is wider than 22mm. By all three parts of the Keel Band I mean the Keel Band either side of the centerboard case and the strip in the middle, measure at either end of the centreboard slot. I assume that this combined measurement doesn’t matter as each part of the Keel Band has a separate width measurement and therefore the band could be as width as 66mm across the end or beginning of the centerbaord case.

It will take me a long time to complete replacement the bottom on GBR1251. I would have no problems photographing constructional details (for example of the wood/glass epoxy Keel Band) as I go along. This details should help other OK Sailors with their queries when they have to work on their boats.

Regards

Martin Ward

[Chris Perry]

I need to be more careful, letting people put pictures of my bottom on internet forums is the kind of thing you would expect from Paris Hilton, and not an OK sailor…..

I can only hope it measures, but it does look smooth and shapely……….

Chris

[GBR1501]

you find the strangest thing on this internet… Chris’ white bottom….. :?

obviously dave measured it befor you’ve put the slot gasket on …..LOL….

Hope Alex has fitted mine…

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