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Old 19-09-2009, 18:22   #1
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Broke My Center Board in Half

I have an Irwin 27' with a swing keel and have broke it in half. The half I have broke is goan and never to be seen again. Therefore I dont know how much it waighs or what it was made of. I am trying to determin how much balist was in the old swing keel. Or perhaps the ballist is in the shoal part of the keel. Also thinking of perhaps changing the entire design into a modified full keel. Any input in the matter would be appreachated.
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Old 20-09-2009, 13:32   #2
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Originally Posted by macktub28 View Post
I have an Irwin 27' with a swing keel and have broke it in half. The half I have broke is goan and never to be seen again. Therefore I dont know how much it waighs or what it was made of. I am trying to determin how much balist was in the old swing keel. Or perhaps the ballist is in the shoal part of the keel. Also thinking of perhaps changing the entire design into a modified full keel. Any input in the matter would be appreachated.
There are a few options as I see it:

1. Recreate the lost section using same metal (a metallurgist can tell you the metal – and why it failed for that matter) and weld the two sections together. At this point you can either continue as before (if the weld is fair) or you can pull it up or glass the whole thing in while in the up position. I met a fellow a while back who glassed in his swing keel and didn’t really notice a difference. You mileage may vary.

2. See a Naval Architect about engineering a new keel. I would personally recommend you start with someone like Eric Sponberg a he has some experience in this sort of stuff.
3. Sell the boat.
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Old 20-09-2009, 13:38   #3
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How do you know you have only lost half of it? I wonder if the pin has gone and you have lost the lot?

I don't know the boat, but willing to bet it is a piece of sheet steel. You need to find another owner who you could take the measurements off and have one made up.

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Old 20-09-2009, 15:16   #4
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There is a sketch of how your center board should look at this web page: IRWIN 27 Sailboat details on sailboatdata.com (units English)
I doubt that there is any ballast in a small board like that. If it is like the center board on my Tartan 27' it weighs just over 100 pounds and it's main function is to help when sailing close to the wind or upwind.
The center board on my boat was designed to break away in the event of a hard grounding so as not to damage the center board trunk and sink the boat. Quite possibly your center board was designed to do the same. Did you break it while running aground?
You can probably get exact specs as to how your center board was made from somewhere. A good place to start looking might be at an Irwin owners group (sailboatowners.com claims to have an Irwin section) or perhaps the mfr. themselves.
Good luck.
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Old 21-09-2009, 20:10   #5
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So i know i havent lost it because i dove under and looked. and i know i never ran aground. It broke just under the trunk. Was hard to tell but looks like it was made of glass. The tide was running hard in the harbor when i went under so the water was mudded up.

The drawing calebD sent was deffently a help in seeing just how the hull was shaped. I have spoke with my friend whom is a fiberglass expert. ( I say this with the upmost respect to the fiberglass guys out there. As i am in the marine buisness and know there are alot of clamers out there that they too are experts. However he really is an expert.) He has explained alot to me in the matter and is going to help me redesign the keel. I will be going with a fixed keel around a foot depper.

If any body has oppinions on the matter i would be greatfull to listen. And thank you all for your help.
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Old 24-01-2011, 17:39   #6
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I too have lost my swing keel in my irwin 34 citation,any ideas anybody on weight and shape of the original?
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Old 24-01-2011, 18:51   #7
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A lot of 60's 70's boats were made with Cast Iron C/Bs. It shouldnt be too hard for a local foundery to make a new mould off the remnants of the existing board. As long as they get the Chord (thickest part) in about the same position the rest should be pretty easy. (assuming that yours was cast iron of course)

Even the local shiprights should be able to make up a glass over lead/iron board for you.

Converting to fixed keel will mean you will lose the ability to beach the boat or anchor in very shallow water. One of the little bonuses of small centerboarders.

Speaking of fixed keels. The CLR is brought forward with that fin in its fully down position. By attempting to make a fixed keel that follows the line of the boats hull you would end up taking the CLR aft somewhat. Unless there was some clever design work, to keep the natural lines of the boat as well as holding the CLR in position, I really dont see the benefit in putting a fixed keel on a boat like that.

Do this exercise. Print the Image here
IRWIN 27 Sailboat details on sailboatdata.com

then draw some pencil lines following the shape of your new fixed keel. Compare that to the shape of the CB and the before and after CLR.

Cheers
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Old 24-01-2011, 19:06   #8
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thanks alot Oz,,we run a marina on coast of ga.I run the service portion and am a highly skilled fiberglass man for a start ,so i will facilitate the building of it myself,,just need to find out if it was ,wood,iron ,bronze or what?and what its crucial weight is.Length should be easy to calculate as the well minus clearance is still there of course to measure,got to figure out the pin and pin replacement as well,just bought the boat yesterday,a steal,a sweetie as well,upon hoisting today discovered the swing keel is gone ..so i have nadda to reference for the rebuild,i have the capabilities and know how to build a wide variety of configurations and materials,but i need to know if its weight is included in the total needed ballast,,thanks again for you r contact and insight
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Old 24-01-2011, 19:15   #9
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Looking at the irwin website You'll find dimensions and instructions for replacing the centerboard on a 25/26... I suspect it's not much different on a 27. You do want accurate dimensions, but the construction is typical glass over foam, not metal... Verify that with other irwin owners.. search the web for irwin owners groups, irwin specific websites, and whatever else you can find... look for dimensions, the building part of it is simple.... If you have to, find one for sale and go take the measurements yourself

actually finding one for sale, then talking to the owner could be very a very useful approach. I don't think irwin was using lead or bronze centerboards, they were more than likely, using the same glass and glass over foam centerboards found in similar boats (like the 25 on that website). Very simple to build, you just need the dimensions.
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Old 24-01-2011, 19:29   #10
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thats helpful,it is a 34 Irwin citation though,not a 27,,,guess if its foam/frp it will need some sort of bottom weight to make it stay down huh?got to figure the hinge pin replacement situation out though ,,search alot on irwin ,trying to find this info,honestly hope it
IS foam/frp instead of cast or metal,was quite the shock seeing it gone all together,,got to find those dimensions,thanks again for the help
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Old 24-01-2011, 19:35   #11
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Quote:
Originally Posted by macktub28 View Post
I have an Irwin 27' with a swing keel and have broke it in half. The half I have broke is goan and never to be seen again. Therefore I dont know how much it waighs or what it was made of. I am trying to determin how much balist was in the old swing keel. Or perhaps the ballist is in the shoal part of the keel. Also thinking of perhaps changing the entire design into a modified full keel. Any input in the matter would be appreachated.
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thats helpful,it is a 34 Irwin citation though,not a 27,,,guess if its foam/frp it will need some sort of bottom weight to make it stay down huh?got to figure the hinge pin replacement situation out though ,,search alot on irwin ,trying to find this info,honestly hope it
IS foam/frp instead of cast or metal,was quite the shock seeing it gone all together,,got to find those dimensions,thanks again for the help
Sorry Maellene I was refering to the OP... I don't know the specifics of either, but I suspect the same... its an educated guess, and I advise looking for owners of the same boat for specifics... However, you should not need any additional weight as a glass over foam centerboard is very common and the 100 or so pounds it weighs is plenty to keep it under water. But, and I must emphasize, you need to confirm with owners of the same boat, what their centerboard is made from or weighs, and the dimensions of it... there are certainly centerboards that are made of heavy metals to provide ballast, but From my quick and dirty research, that is not how irwin did things...
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Old 24-01-2011, 19:43   #12
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groovy doovy thanks again
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Old 24-01-2011, 19:53   #13
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just scored heavy with LOTS of info on the Irwin yachts website,,they had drawings with all the dimensions,specs& .core materials list as well as more ,like pivot pin replacement ect/...danks again
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Old 24-01-2011, 19:58   #14
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Old 05-11-2013, 23:28   #15
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Re: Broke My Center Board in Half

Quote:
Originally Posted by ozskipper View Post
A lot of 60's 70's boats were made with Cast Iron C/Bs. It shouldnt be too hard for a local foundery to make a new mould off the remnants of the existing board. As long as they get the Chord (thickest part) in about the same position the rest should be pretty easy. (assuming that yours was cast iron of course)

Even the local shiprights should be able to make up a glass over lead/iron board for you.

Converting to fixed keel will mean you will lose the ability to beach the boat or anchor in very shallow water. One of the little bonuses of small centerboarders.

Speaking of fixed keels. The CLR is brought forward with that fin in its fully down position. By attempting to make a fixed keel that follows the line of the boats hull you would end up taking the CLR aft somewhat. Unless there was some clever design work, to keep the natural lines of the boat as well as holding the CLR in position, I really dont see the benefit in putting a fixed keel on a boat like that.

Do this exercise. Print the Image here
IRWIN 27 Sailboat details on sailboatdata.com

then draw some pencil lines following the shape of your new fixed keel. Compare that to the shape of the CB and the before and after CLR.

Cheers
Oz
in case anyone is going to convert a centerboard or deep, skinny fin to a long keel of shallow, long fin:

the CLR of a shallow long fin is farther towards the stern than on a center board or deep skinny fin boat. the difference between the CE of the sail plan and the CLR of the boat is called lead. the CE should be forward of the CLR. in a center board, deep fin the lead can be as little as 6% of the LWL of the vessel. as the keel gets longer and shallower, the lead needs to be greater, as much as 25% of the LWL. if you do not do this, you will end up with excessive weather helm. if the lead is greater than 25% of the LWL, in a long keel, you will get lee helm.

skinny deep fins and center boards are more sensitive to balance than long keels.

it's going to take a bit of trial and error, as well as deign on paper, to get the right keel shape and location, for your purpose. I did it to a dagger board dinghy with great results. but I took my time and got the shape and location just right. trial and error was the final crucible of each design I tried. you can only accomplish so much on paper, without real world input.
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