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Shoot, cavitation is the propeller on a boat sucking in air. Like when you pull the plug on the kitchen sink and you get that spiral vortex making noise as air is sucked into the drain. It usually happens when the propeller is lifted to high. The cavitation plate is that flat horizontal fin right above the propeller. If it stays at or just under the surface of the water when on plane, you very close to having the motor adjusted right.

When cavitation occurs the boat is usually above half throttle and thus the transom is being lifted to the top of the water. Two things happen when cavitation occurs. The RPMs jump up fast and the boat loses the pushing effect the propeller should supply.

Usually just takes some adjusting to get it corrected.

No forgiving needed.
Thank you for the info and education,easy enough to understand now,appreciate ya!
 

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Eric from Indianapolis
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Discussion Starter · #22 ·
Ok guys, the saga continues. Thanks to Tom, I got to try out his three blade prop on my boat today. Thanks Tom!!

Here's how the test ride went... I'll start by saying that my boat takes on a little water, but an auto bilge has always kept the water at a manageable level.

My friend and I left from the dock and I slowly applied throttle, until i did get to WOT. And there was zero cavitation, woohoo! The boat topped out at a blistering 8.5mph lol! But wait... After running for 10 minutes or so I noticed my speed dropping on the gps. And then I started to feel just a hint of cavitation. I noticed the boat's bow was pretty high out of the water. So I had Billy take the wheel and I walked up to the bow, the boat immediately sped up to 12.5mph and got on place nicely.

Best guess now is that when the boat took on a bit of water it made the stern get heavy, to the point that the motor was able to suck some air. I did manage to look at the motor while running at speed and I could easily see the top of the cavitation plate.

I'm hoping that when I get my 85lb trolling motor battery and trolling motor mounted back up front that it helps balance the load out and do away with the issues I'm having. Going to try to get that handled over the weekend.

It's going to take some patience getting used to the 9.9. The previous motor was a 35 and it moved right along. I'm just wondering if the boat will be able to get on plane with the weight of two people, trolling motor battery and motor, plus cooler and fishing gear. Only one way to find out!
 

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As long as you are changing the weight of the boat it is going to be hard to get it to preform at optimal efficiency, sitting still the water in your boat is going to seek the lowest level, under acceleration it is still going to seek the lowest level but that level is going to be in the rear 1/3 of the boat, if you are able to get it on plane then the lowest level while still in the rear of your boat is more dispersed, if you loose plane the water will move forward causing the bow to be low and even more water to move in that direction.

I know finding leaks can be a PITA but the best method I have found is to park the boat on a dry concrete shop floor or driveway, fill the bottom with water, go back and check for a wet spot in a few hrs. if you don't find one raise the water level and repeat until there is a wet spot. Keep in mind that the water may not drip directly down running along a ridge line or the bottom for awhile. Good Luck with it.
 

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Eric from Indianapolis
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Discussion Starter · #24 ·
Thanks Jay, that makes sense. Can't expect to the boat to perform well when it's leaking like a sieve. I've looked for leaks before and it looks like water is coming through the keel, and there's a metal rib on the outside making it dang near impossible to seal the leak well. Any suggestions on how to deal with a leaky keel?
 

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Any suggestions on how to deal with a leaky keel?
Sorry. not a DIY suggestion. A professional fix would be to cut the metal rib on both sides of the leak, patch the leak then weld the rib back in, for a guy on a tight budget that would be more expensive than desired I am afraid. If you can find a crack or hole and get to it from the inside you may try JB welding it shut by pushing the JB through with a popsicle stick, etc. then forming a shaped patch to put over it and JB-ing all around the patch. If the leak can not be accessed from either side I am not sure what I would try. Good Luck with it.
 

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Steve from Mississippi
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I did a repair like that to a 12ft boat I gave one of my boys a couple months back. It had an actual hole in a strake about 1/3 back from the bow. I took a piece of aluminum sheet and cut out a square then formed it to the strake on the inside. Then used a map torch and the aluminum braise rod from Harbor Freight to braise the patch all the way around on the inside of the boat. He has been fishing that boat several months now with no leaks. I also braised around a couple of leaky rivets also.
 

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If you can find the leak, an epoxy such as west marine g flex may solve your problem. I believe there are 2 different versions. 650 and 655 with 655 having a thickening “agent” to keep it from being too runny. I applied it to the corner where my transom and floor/bottom meet and it set up hard as a rock( had a crack there that didn’t want to weld up as i had planned). All that being said I have not made it out for a test run to see if it sealed my problem crack( boat does hold water after a good toad strangler)but the epoxy definitely flowed where i needed it to as it cured and set up nicely. Do some research and see if it would work in your situation.
Also the powder/thickening agent is very fine and the slightest breeze will make your work area look like pigpen from peanuts has come to volunteer. So be mindful of the wind
 

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Eric from Indianapolis
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Discussion Starter · #29 ·
Thanks Sam! I've used that G Flex on another boat and it did work very well. It was rock hard, yet seems to flex just enough to not break away from the aluminum in the winter. I may have to give that a shot. Still trying to come up with an official plan.
Aaron, Flex seal seems to work pretty well on the screen door boat lol!
I'm going to head out to Eagle creek tonight for another test run. Fingers crossed!
 
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