keel shoe for long keel grp boat?

[paulsmith]

My bothers boat A GRP Cornish Yawl is suffering damage to its unprotected keel when drying out as Crabbers felt it unnecessary to fit any kind of shoe at manufacture, leaving the gelcoat to the mercy of the sand gravel etc. There are difficulties in Retro fitting a steel shoe in that the base of the keel varies in width along its length and its not flat but rounded in places and flattish in others with varying curves etc. Also a long shoe would have to have lugs on and would need to be drilled and bolted through the keel from one side to another. .The resin is cast with steel shot as part of the ballast so this could be very tricky if not impossible to drill straight likewise drilling from the bottom upwards would have similar drawbacks.I dont think it would be possible to just bond a strip to the bottom as it would be almost imposible to get a contact fit along the length of the boat,and I don't think a strong enough bond would take place.I've suggeted just adding about 1/4 inch of GRP matting as a sort of sacraficial strip to the keel wrapped up the sides an inch or so.I think you can add carbon fibre powder to the resin to make it almost indestructable. Has anyone had any experience of such a mod.or any other ideas?
Paul.

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[moodycruiser]

Would it not be possible to make a mould of the bottom of the keel if the yacht was in slings so that you could then make a former and then a strip from that that would fit ? long winded I know but a possible alternative.


<hr width=100% size=1>Tony

 

[graham]

The steel shot in the resin wont stop you drilling holes if you use good drill bits and a slow revving drill.

Sikaflex would even out any imperfections and also provide a strong bond in addition to any bolts .

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[VicS]

Drilling into the encapsulated ballast sounds a very bad idea to me. You'll not know how well you sealed the bolts in or how long the sealant lasts until its too late.

I'd go for external layers of glass matting which you regard as sacrificial.

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>

 

[jon]

I had the same problem with a Shrimper on a drying swinging mooring.
I have fitted a 6mm 316 stainless keel band to the 27ft Salcombe Trader hull I am now fitting out, screwed up with A4 SS c/s screws and plenty of Sikaflex. I made a pattern from 6mm MDF first. If you wish to see photos email me via address you will find on your private mail.

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[William_H]

Obviously you have to get under the keel to add any sort of shoe. You could make a fibreglass mold of the bottom of the keel put on lots of wax release agent before laying on a few layers of Chop strand mat remove when hard. This would enable you to make a male mold from the female. This could then be used to make a shoe. Some thoughts would be lead if the boat would benefit by more balast down low. Make a plaster or sand mold of the outside size required then fit the female mold into it and pour lead into the gap.The lead shoe should be epoxied on, there should be no need for bolts.
Another option might be to fit a stainless or brass strip along the bottom with tiny self tapping screws. Make sure they don't go deep. If you drill large holes through the strip then you can epoxy and fibreglass over the lot and up the sides. The larger hioles would enable better adhesion to the existing keel. Or you could just add glass and epoxy layers as you have suggested. Being prepared to replace or repair occasionally. Carbon fibre cloth is extremely strong as in stiff but Kevlar is much tougher as in hard to cut so much better for this job. You might be surprised that a little kevlar cloth is not so expensive. (thats the yellow stuff) It is very easy to drape to shape even easier than glass but a devil to cut with scissors. Get the supplier to cut for you. Polyester resin is cheaper but not recommended even though the boat is made of polyester because of it's poor adhesive qualities compared to epoxy. Just a few thoughts which may or may not appeal to you. regards will

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[William_H]

PS don't use Chop Strand mat as the epoxy will not disolve the binder and will not saturate the mat use cloth or wovewn rovings. will

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[oldsaltoz]

G'day Paul,

Had the same problem only double, it was a 40 foot cat.

We solved the problem of keel curve and variation in width by fitting stainless steel angle, a strip down each side of the keel leaving the flat on the bottom.

As for securing it to the hulls, we drilled through both sides and bolted it. If you are concerned about getting the holes straight, consider a line borer, after all they only need to be drilled once.

Just make sure your holes are at least 20 mm oversize, then fill them with epoxy resin and Micro-fibres, then re drill to the required size for the bolts, no sealing required, ever.

When you are ready to offer the angles up to the hull, spread a mix of closed cell balloons and epoxy resin inside the angle and squeeze it out as you fit them.

You can test fit the angles and decide if you want them to overlap for longer life, or trim them for an even finish, if you trim them consider adding a flat bar of stainless the full length, just tack weld it in place, remove it and complete the welding to avoid any heat damage to the hull.

We did this about 8 years ago, still looking good when I checked in January this year.

I hope this helps.

Avagoodweekend........



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