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I'm in the process of refitting and repairing some minor damage from skipping over a submerged rock and want to add something better than the multi layers of glass cloth/epoxy that was my current keel protection, especially for beaching. The fiberglass held up fairly well but abraded away in several spots exposing raw wood. Luckily no structural damage to the keel, only to the rudder. My current moorage dries out every day and even though it's a silty bottom in still gradually erodes the epoxy glass as it settles in about 3"

I've considered:
1) extra wood strips and more glass. Cheap, easy to apply, but probably needs constant
repair after contact.
2) UHMW polyethylene. Extremely tough, slippery and anti-fouling, but, not glueable to the
epoxy, and I'm not crazy about exposed screws into the keel.
3) added strips of G-10. Very tough, glueable to epoxy, but, expensive.
4) strips of kevlar or carbon fiber cloth or combination of both.

Any other ideas, pros and cons, opinions, or comments?

Frank (Pahi31 "Mikyla")

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I hope that wasn't white oak you used. White oak has a reputation for being incompatible with epoxy. My Hitia solution was to use a final layer of Dynel, which has held up quite well. It has great abrasion resistance and a degree of flexibility. Additionally, a lot of the issues with crushing under impact can be avoided if one thing is kept in mind when filling voids under glass- the filler must be harder than what is going over it. This means no micro bubbles or other light weight fillers in the epoxy that's under the glass.

Rune M. Christensen said:

I gave keel protection a lot of thought, and read trough this tread several times. So I thought I would contribute back to the forum with my own solution for the Hitia 17.

The keel is very narrow on a hitia 17 and rounded in order to take the glass cloth. This meant that I couldn't really think of a good way to fit a metal strip.

I didn't want to leave i with just glass and epoxy, both because it will be pulled up and beaches with sharp shells and stones, but also because of worry of sailing onto a rock and crush the epoxy.

So the solution is a glued on oak keel for abrasion resistance and impact absorption. Its glued on top of the 3 layers of glasscloth, so if it is damaged a piece can be removed, and a new piece glued in without interfering with the skin of the boat.

It was rounded (with a router) to fit the "keel" and faired in at both ends of the hulls.

Now I hope I can sail without worrying too much about the bottom of the boat :)

I did use white oak, and I have read about the problems some people have reported with oak.

I still used oak a few places on the Hitia in order to test it out myself - I dream of building a bigger wharram in the future.

If some cracks develop, its not a big problem, unless the whole keel falls of. Then I will have to glue in a new one of different wood :)

I think a lot of people are missing a crucial point of having "sacrificial" keel protection. The idea is to sacrifice something in lieu of the keels. That to me means that it must be easily replaceable. If you are glassing in/on your wood or metal strips, then you will be forced to haul out to fix what should have been sacrificial.

When it is permanently attached, it is no longer sacrificial, but an addition to the keel. The method I described on page one of this thread allows one to easily replace a sacrificial strip while the boat is still in the water, because the strip is not glued or glassed to the hull, but simply screwed in place into solid epoxy.

If you pay attention to the details of your installation, and make accurate measurements, the replacement can be constructed on deck and then replaced underwater whenever necessary, which is why I precisely measure the installation holes for the original sacrificial pieces so that can be easily duplicated later.

It's not that it will crack, the glued joint will simply fail. If you're going to experiment, this is probably the place to do it.

I was specifically taught to not use epoxy with white oak. Our lead boat building instructer was a fifth generation wooden boat builder out of New England. He practiced his trade through the period that included the introduction of epoxies into boat building. Too many questions exist to permit me to feel safe about using epoxy with white oak anywhere on a boat where the bond forms part of the structural integrity of the hull.

Rune M. Christensen said:

If some cracks develop, its not a big problem, unless the whole keel falls of. Then I will have to glue in a new one of different wood :)

What I did on a small cat was to build up epoxy to the thickness the screws require to hold the metal strips, but without penetrating into the wood.  This uses a lot of epoxy, but it does ensure no wood gets penetrated.  I based the technique on plaster work where moldings are applied by means of a screed and cross sectional profiles that are dragged through the plaster.  Worked great.  When the epoxy was a green cure I glassed it.  Then I hardware bonded the strips.  Still not sure metal is the answer, but if I was doing it again I would do something similar.  In this case I needed the directional control of keel strips, I just didn't want them to be made of wood, and a maintenance problem.  Wharram scantling call for relatively huge amounts of epoxy in the keel area, so it is really only bad planing if during the process, one ends up with a situation where screws that penetrate the keel run into wood.  Since no strip keel is required, perhaps after turn over one could just rip a slot the length of the external keel and fill that with epoxy then glass in accordance with the normal schedule.  That way when the screws go up, they don't tie into wood, with the possibility of essentially infusing the whole hull skin with water.  Not suggesting metal is the best way to do this, just that if doing it, I would never take the risk of running into wood.  Of course, standard hardware bonding routines already exist to deal with this problem, but in this case it might be better to plan for the contingency early.

As far as UHMW is concerned it is said to be bondable, further research is needed to figure out how effective that would be in service.  Apparently the usual flame process works, and allows epoxy bonding.  There are also a wide range of PSA backed UHMW, which are intriguing, because they are getting something to stick.  Sometimes an existing adhesive will bond with another glue, so epoxy adhesion to the existing glue might be worth asking about.  This strategy works with other plastics like PVC.





Pat Ross said:

"i meet 2 GFK catamarans which hit a log during knight sailing. holes in the hull and bended shafts.. a simple collision shoot in the front helps a lot."

I have already had this experience with a Dead Head in rive in skinny water, that is what has started my interest in understanding how Kevlar may be helpful.

I am not familiar with a "Collision Shoot" or are we using different terms for the same thing "Water tight Collision Bulkheads" maybe even two in each hull and one in each hull on the stern?


Hi Pat: What Hans means by "collision shoot" is the German word for 'bulkhead' (schott).

I am not -yet- a builder, but I am already considering aramide / kevlar as a reinforcment for the bottom of the hull. I am not really entousiastic about putting screws in the wood at this place.
However, I have never used kevlar, and don't relly know if it is suitable in this situation.

Hi; when you get to that point, consider the cheaper - and simpler - solution which Hans used: metal strips (I  used stainless 304, 2cmx3mm) encased in a couple layers of epoxy/cloth). Kevlar doesn't protect against impact...Oh, and yeah, what's keeping you from getting started?

Dennis, I am sourcing the materials now. I'm in Hong Kong, and will built in mainland China. Start hopefully by the end of June.

Oh, I wanted to share this Chinese source with you: Ningbo Seawell Marine, Zhejiang, China, contact: "Lily", tel; 0086-18094544332. They have a large boat assessories catalogue; ex. ABS rectangular portholes, $27(you could do much better incountry). So you're building a Tiki 21; then you only need maybe 20 gal epoxy. Just don't get obssessed with the ply grade...(Malaheursment, il y avait 50 annee, depuis j' apprendu lections en francais, donc je lis bien votre idees...les francaises avant le plus belle histoire en multicoques, n'est pas?!

Hi there

I have used silica flour(finely ground up sand) and epoxy. I am very happy with this using it on the bottom of my keels, skegs and rudders. I also applied it a little way up the keel(around 80 mm) because the keels sink down into the sand and can come in contacts with all sorts of things wanting to damage your keels

The keels were already heavily glassed. This was keyed. I glued on some little spacing blocks to the required thickness I wanted.(approx 12mm) Once set I used a strip of hardboard (the width of the keel) as a former. I put polythene tape on the length of the former and prearranged blocks and wedges to hold onto the keel while it dried. I firstly worked glue into the keel, then mixed up a really thick brew of silica flour and epoxy( it needs to be really thick because it is very heavy and you want to eliminate sag. You can always fill later if you do get sag) I applied this to the hardboard strip and placed it onto the keel. I then held it in place with the blocks and wedges and trowled off the excess once the strip was firmly fixed.

This can be done in manageable sections depending if you are working alone etc. I went to a lot of trouble to do this but now I have complete peace of mind drying out in coral, shells or sand with stones. I coule actually dry out on a boat ramp if needed but I havn't needed to and a bottom with a bit of give is a more sensible approach. I used this on my T 30. I have sold this boat to good friends and know it is in great shape and plan to do the same to my new (used) T 38. Lastly no screwing into the keel!!!!

Good luck Brett

Do any sanding /grinding as soon as poss as this stuff is extremely difficult to sand. I also used a tiling trowel (with the little v's on its edge) to apply to the sides of the keel, skeg and rudder. As soon as this had tacked off I applied more to fill the v's

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