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Old 27 May 2006, 17:57   #1
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Kelp cutter

One problem I have here (common to anybody with an outboard) is a local variety of seaweed called kelp, found along all the shorelines and incredibly strong - get it wrapped round the leg and it will cause the prop to cavitate and won't come off without stopping and giving it a burst in reverse. I have towed a 25m long bit of kelp at over 30 knots before and it wouldn't break! If you have to go through a kelp bed it seems the only way to get through is to hit it flat out and hope the leg cuts through rather than picking it up. It also blocks off cooling inlets which is obviously a bad thing....

So I wondered about something on the leading edge of the leg to cut through it rather than let it tangle around the leg.

Does anybody do anything like this to seaweed-proof their boats elsewhere in the world? Nobody here has tried it as far as I know ... but I can't immediately see any reason why it wouldn't work? It might not be 100% effective but anything that would help has got to be good - there is so much of the stuff close inshore around here.

Thoughts please
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Old 27 May 2006, 18:29   #2
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You can get rope cutters for prop shafts (not totally sure about outboards) which would probably do the job.
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Old 27 May 2006, 21:32   #3
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Some folks have welded the blade of a knife onto the leading edge of the outboard. They do it for this one specific area of coastline where the kelp is thick all year around. I suppose the would work ok. For some reason the thought of it scares me though. These are 50 hp and under outboards. I just learn to go around it as much as possible.
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Old 27 May 2006, 22:13   #4
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Quote:
Originally Posted by boatster_sr4
Some folks have welded the blade of a knife onto the leading edge of the outboard. They do it for this one specific area of coastline where the kelp is thick all year around. I suppose the would work ok. For some reason the thought of it scares me though. These are 50 hp and under outboards. I just learn to go around it as much as possible.
That is kind of what I had in mind, either that or something hanging down from the rear of the transom to cut through anything before it hit the leg. Even a bit of stainless bar just roughly sharpened into a cutting edge would probably do it I think, just not sure how/where to fix it on and wondered if anybody had done anything similar (photos would be great)

Ta
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Old 30 May 2006, 17:55   #5
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I am in the Monterey, CA area (well, actually, that's where I dive; I live a couple of hours north), where waters are known for kelp.

AFAIK, nobody here does anything more special than slight maneuvers to avoid the stuff. It usually isn't a problem unless you hit it going slow (tends to either get cut or get deflected under the skeg if you're moving.) And if you're going slow, I suspect a knife blade on the front is not going to be all that effective.

If I have to go into kelp (which, to be honest, is more often than I like), I simply hit reverse and rev a bit every now and then and clear stuff off. Have only had kelp plug the intake screens once (and that was at speed.)

Of course, there are different types of kelp, so YMMV.

jky
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Old 30 May 2006, 18:56   #6
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Ditto the last post.

I use the same techniques for San Diego kelp, sometimes we trim the engine so that kelp slides off the leading edge. Another important item to watch during kelp patrol is your water intake. Kelp leaflets can block the intake and we all know that water cooled engines don't perform well when the water pump runs dry. As for the knife idea, we tried this many years ago and the first turn of the steering wheel caused the knife bracket to tweak out of alignment. Have fun and enjoy the pleasure of cruising thru the worlds fastest growing plant!

http://life.bio.sunysb.edu/marinebio/kelpforest.html
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Old 31 May 2006, 09:02   #7
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Here's a link for a product called Spurs that uses two blades, one fixed and one rotating with the shaft, to cut entangled lines or other material. http://www.spursmarine.com/index.html.

I haven't read thru the site and can't say for certain if this product works for outboards. If they don't offer a product for that application I'm sure there are others...just can't recall the names at the moment.
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Old 31 May 2006, 12:21   #8
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Cheers for the info

It is not a huge problem here either as you can stay outside it, just that it is along almost ALL the coastlines and there are some places where you have to go quite a long way out to get around it.

My worry is not so much entangling the prop - good blast in reverse fixes that - as the cooling getting cut off and not noticing until it is too late. Also the tell tale on my engine is crap, I have tried to make it spray straight up but it goes out backwards at an angle and you can't quite see it, and at some speeds it gets lost in the wake and you have to slow down to be able to see it.
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Old 31 May 2006, 13:32   #9
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Quote:
Originally Posted by BogMonster
That is kind of what I had in mind, either that or something hanging down from the rear of the transom to cut through anything before it hit the leg. Even a bit of stainless bar just roughly sharpened into a cutting edge would probably do it I think, just not sure how/where to fix it on and wondered if anybody had done anything similar (photos would be great)

Ta
God,I hope i never go mob in front of you!!
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