A Photo & Discussion Forum for Wharram Design Enthusiasts
I was speaking to a fishing cat builder a while ago,the boats he builds are called Kevlar Cats on the sunshine coast.I ran my original idea of kevlar strips down the keels etc.His answer was quite interesting in that he said to me people think this material is indestructible and the amount of repairs he has had to carry out because of this mindset was not insignificant.Undoubtedly the stuff is strong but just cutting it is a major pain in the ass.I told him of my sacrificial keel with a stainless steel strip for keel protection and he advised me as an amateur builder to rather go down this route.One only has to look at the failures of those mega spendy racing yachts to get the idea.I would love to be able to use this stuff but the extra work invovled may not justify the end result.
Thank you for passing along what was told to you.
I am very interested in hearing from Dave The Boastsmith and Frank Olsen who have direct personal experience with Kevlar and have commented in this thread. Of course it was some time ago. If they are still around they would have real experience of how the product performed for them by this time.
Well I'm not Dave or Frank but I was building whitewater kayaks in the 80's before the rotomoulding took over.
I built boats with and without kevlar [and other exotics]. The fail point for both is the same ie. the point at which THE RESIN fails. The nature of the fail is very different.
With glass only the strands tear leaving a gash whish leads to a waterlogged boat which may now suffer further damage even total loss.
With kevlar the strands do not break but span the line of pulverised resin holding the hull together and reducing water flow. With a self-draining flap [or duct-tape!! ] this boat will finish the race.
With sheathing the fail is when water can reach the ply. This will happen when an impact is severe enough to crush THE RESIN. I do not think that kevlar will add greatly to the ability of the resin to survive such an impact. This does not have to be a large tear - in time a lot of water will find it's way through even a small area. The value of kevlar to me would be to lessen the chance of a collision leading to a stove-in panel and flooding.
The other way to achieve this is to fit good rubbing strips buy fat fenders and watch where you are going!!!
The degree of hardship on the keel of a boat varies greatly from owner to owner. I accept that many are happy with a couple of layers of glass. I leave mine on a drying mooring . This is 700 groundings a year. Even the softest mud contains stones etc. Somewhere there is a spot where a fisherman chucked his ballast overboard. One day I will dry out in top of my own mooring block. Murphy's law clearly states that it will be the same day that there is a small chop running so that my boat will be repeatedly lifted and dropped 4""onto it. This is not abrasion. This is banging,smashing ,crashing,etc. The resin will be pulverised and even if the various cloths stay intact the water will come in.I should say more correctly that it was and it did because I have been there and had to do the repair. I now have a hardwood strip and the fixings are as per Gougeon Bros. in oversize holes filled with resin. Good enough for them good enough for me.
Stand back from the theory for a moment. If you left your boat tied to a quay without fenders or a rubbing strip for a season even with exotic cloths what condition would you expect it to be in?? The keel of a boat takes this abuse x 100. Out of sight out of mind??
A word on taking care and only going aground carefully etc. You will have no control over the re-floating. I dried out on one of the Isles Of Scilly. I intended to stay a few days. When the tide filled that night it brought with it a full onshore gale. Short lived unseasonal and not forecast but I nearly lost the boat. Be careful out there!!
Well according to Johnny Cash as long as you are not a boy named Sue ....
Hey thank you for taking the time to share your personal experience. My desire is to improve my chances in an open water crossing where sometimes containers are awash below the water line. I have no belief that shoring up a hull with Kevlar will mean that the boat will survive unscathed but I am interested in improving my chances. The absolute safest collision boats I think would be steel but those multihulls just don't seem to abide that construction method, not to mention the cost.
If I offended anyone by my request for comments from those who have personal actual experience I apologize. There is much hearsay on the net and I would like to get the info directly from the horse myself as well as avoiding the marketing folks.
You certainly did not offend me and no apology is called for. I now fear that perhaps it is I who have offended you and I assure you I had no intention of this.
I am aware that my opinions are just that - my own.
I also perhaps should add that I am very firmly in the "just do it" or GO SAILING camp which you should consider when weighing any advice I gave.
I am grateful to you for bringing up the subject of keel protection again as I had intended to reply to an earlier discussion but did not get around to it. Yeah you guessed - I went off sailing...
BEST OF LUCK WITH YOUR BUILD
I am not adding the kevlar strip anymore. The hassle and cost don't pencil for me. I use several layers of 1708. I frequently pull the boat up on the beach. There are sometimes rocks in the sand. The bottom paint does not care for the beaching. I have hit several rocks at speed and have suffered some scratched paint and minor gouges. I to worry about bouncing off the bottom when the boat settles. I don't bottom out daily on my mooring but with extreme tides I do. The Tiki 8ms we built for the Marriott go up on the beach several times a day and after two years the wear is really minimal. I will apply one more 3" strip when the boats are hauled this fall. These boats go our 3 times a day with a full load and provide me with excellent feedback about what works well and where I can improve.
....The absolute safest collision boats I think would be steel.....
i think that there is no 100 % material against impact. a looting container hit with 5 knots spend on a corner will break a steel hull too. watertight bulkheads and or floaters like empty plastic bottles will keep you up. the deck on our tiki is made out of ply and Airex fome. regarding the designer plans, the boats deck should float 4 inch above the water surface. you get wet feet but maybe can still sail to a safe place and safe the boat.
this is all very theoretic. you will probably never hit a log or container on a clam day. it is maybe windy, bad visibility and high wave. we are here in malaysia in the moment. 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.
sailing is not so dangerous... if you are a potential lotto winner. you maybe will hit a container on the way...;)
"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?
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 :)
And a closeup...