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Quk&DrtyPete
07-04-2002, 04:24 PM
This question is about a *****glass rudder from a 30 ft Watkins sailboat. Friend ran aground and hit a rock. Rudder post is 2 1/2 ss tubing with about a 1/4 wall thickness. The rudder is now out of alignment with the rear edge touching the hull. This is what we think the problem is. The rudder is a spade type not attached to the keel. We believe it is a foam core fiberglass covered. Internally we think there is a spade shaped ss piece attached to the rudder post. To repair are plan is to slice the rudder open the way you would slice a hard boiled egg the long way. Saws of various types to be used. We think the internal ss plate has moved in the foam core or the post is bent. Whatever repair that is necessary we will do then epoxy the whole thing back together. I know that this is way off topic but I am trying to help a friend. Is this plan workable? I have never worked with a foam core before. Thanks

mmd
07-04-2002, 06:19 PM
Sounds like a reasonable approach to "forensic boat repair". You may find that the metal "spade" inside the foamcore is bonded to the core, meaning you will have to shave away the foam (destroying it) to see if it is broken. If I understand your description of the assembly - and that you are correct in this - I expect that the weld between the "spade" and the rudderstock has broken, allowing the rudder to rotate about the stock. Be prepared for the eventuality that the investigation may destroy what is left of the rudder. Before you begin surgery, carefully measure the rudder (not only it's profile shape, but it's sectional shape, too; it is most likely a NACA foil shape) so that if it becomes a total loss, you can re-create it accurately. It's not a big deal, really. Just be sure that you use the proper materials & procedures. The toughest thing to do well (aside from perfect symmetry of shape & form) is to get adequate laminate-to-core adhesion - delamination on cores is a common problem. There are several core-bonding compounds available at reasonable cost - use them. Don't believe the yard "know-it-all" who tells ya that slathering resin on the core prior to applying the first laminate will work, 'cause it ain't gonna. As you do your repair/rebuild in that stuff we here speak so boldly against, keep in mind an analogy that the woodheads here can appreciate: any fool in a hurry can make a board longer by nailing a couple of boards together, but it takes patience, understanding of the materials, and attention to detail to do it properly with a carefully prepared scarph joint. Fibreglass demands the same care; it ain't just "lay on some kind of itchy cloth and slather googe on it". If you'd like to talk a bit more about the technical tidbits without making the die-hard woodheads here go apoplectic, e-mail me at my profile address.

[ 07-04-2002, 07:22 PM: Message edited by: mmd ]

Quk&DrtyPete
07-04-2002, 07:05 PM
Thanks for your reply and answers to my questions. I do not think that the weld is broken as the rudder and post turn as one unit and the rudder stock does not appear to be loose within the rudder. I have not worked with the core laminate Resin? material which you mentioned.

mmd
07-04-2002, 08:56 PM
Sorry about the misinterpretation - I assumed that "the rear edge touching the hull" meant that it had rotated until it jammed. I think I follow now. As you suggested, it is probably either a bent rudderstock or the foam/glass rudder has shifted on its mount. The latter is more likely, 'cause if the stock was bent it would most likely be where the stock enters the hull and you would be able to see stress damage in the 'glass in the area of the fulcrum of the bend. The deal with the core-to-laminate bonding material is that the unprepared core foam will wick away the resin from the first layer of 'glass causing resin starvation and a "dry" bond that is prone to failure. The bonding material, such as ATC CoreBond, is a two-part resin with fillers about the consistancy of body putty, that is compatible with FRP resins. You trowel on the corebond and screed in to the cells of the core material and then lay the initial 'glass layer on while still wet. The corebond fills the open core cells and provides a medium - sort of like primer on an auto paint job - for the subsequent layer of 'glass to bond to. A chat with a local rep from a 'glass materials supplier will be very benefitial. My same advice about preparing for the loss of the rudder is still sound, I think.

Hugh Paterson
07-06-2002, 06:41 AM
A quick add on to mmd's good advice, if you find the rudder stock bent, think long and hard about trying to straighten it to achieve a quick repair, if it gets another whack it may fail leaving you with no steering! Where the rudder tube is laminated onto the hull have a close look around the bonded area to check for delamination and or stress cracks. I have seen similar damage in the past that results in a constant weeping leak around the bottom of the rudder tube. How was it damaged in the first place?

Shug