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Thread: Rock guard for 3.3 HP Merc/Nissan

  1. #1
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    Default Rock guard for 3.3 HP Merc/Nissan

    I did a search, but didn't find much. Does anyone have a picture of a rock guard that will work on a small horse power motor? I've heard this motor is hard on shear pins and I would like to protect the little prop as best I can in shallow water. I'm thinking some small rods off the cav plate, but would rather not reinvent the wheel when I'm sure someone else has already come up with a good design.,

    Thanks,

    Joe

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    Supporting Member Amigo Will's Avatar
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    Looked for one for my 3 1/2 merc and was told they don't make them because it would use up to much H/P
    Now left only to be a turd in the forrest and the circle will be complete.Use me as I have used you

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    One idea would be to cut a steel/aluminum plate to bolt to the cav plate and overlapping an inch or so past the front (forward if running) side of the motor. Drill it at the forward end and run a threaded rod through the hold and bent to follow the angles of the built-on skeg (assuming it has the same general design as most other small outboards. Make the rod long enough to extend level back beyond where the prop extends to. Essentially, it is just running a rod along the forward edge of the lower unit that continues out the back, so it will touch the bottom before the prop does. Make sure it is sturdy enough of a rod (1/2" or so) so it won't bend up into the prop if/when you do find a rock. A good modification to this is to wrap it with some rubber tubing where it is up against the lower unit which will cushion the impact of rocks instead of running the rod right into the lower unit.

    I don't have any pictures right on hand, but if I run across something I will try to post it. Let me know if you have any questions.

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    skeg1.jpgHere is a picture of what I was describing. Hopefully it will work. It is on a 15hp outboard, but the same basic design should work on smaller outboards I would think.

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    Default Mac's River Runner

    Quote Originally Posted by Lowrider View Post
    I did a search, but didn't find much. Joe
    I use Mac's and am happy with it. I've abused it enough to bend it a little, but no failures. They make one for your little outboard:
    http://www.propsavers.com/River%20Runner%20Prices.html

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    Thanks guys!!

    Prop saver, the circular kind, looks like what I was thinking of making, although either would certainly protect from bottom strikes. I had in mind small fingers that would bolt on to the cav plate but the round one that goes around the prop looks like it would give better protection.

    Thanks again for the response and info!!!

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    Quote Originally Posted by Lowrider View Post
    Thanks guys!!

    Prop saver, the circular kind, looks like what I was thinking of making, although either would certainly protect from bottom strikes. I had in mind small fingers that would bolt on to the cav plate but the round one that goes around the prop looks like it would give better protection.

    Thanks again for the response and info!!!
    I have had troubles with the round guard that goes around the prop with 9.9 and 15hp outboards. They had a problem with getting rocks pinned between the prop blade and the guard, stopping the prop dead. I think the guard worked well with larger rocks, and probably would be better than the other guards we mentioned because it protects all around the prop, but was a liability (in my experience) in areas with small diameter sand/gravel. It cost us a couple drive shafts due to the load imparted on them when the prop went from full speed to zero in no time flat. I don't know for sure if this would happen with your smaller outboard, but I would definitely consider it.

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    Quote Originally Posted by anchskier View Post
    I have had troubles with the round guard that goes around the prop with 9.9 and 15hp outboards. They had a problem with getting rocks pinned between the prop blade and the guard, stopping the prop dead. I think the guard worked well with larger rocks, and probably would be better than the other guards we mentioned because it protects all around the prop, but was a liability (in my experience) in areas with small diameter sand/gravel. It cost us a couple drive shafts due to the load imparted on them when the prop went from full speed to zero in no time flat. I don't know for sure if this would happen with your smaller outboard, but I would definitely consider it.
    I've heard that too, but since I run the river-runner, I haven't seen it myself.

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    Hmmmm.....definitely not interested in breaking drive shafts!

    Maybe I will go back to my original idea of using 3/8" rod or tubing coming down from the cav plate in front of the prop. I have some scrap CM tubing I was going to use and weld it on to a piece of 1/4" flat stock that I would bolt to the cav plate. The river runner does not seem like it would protect from anything that the prop could hit on the sides, but then most things you would hit I suppose would come from the bottom.

    Back to the tree stand after my toes warm a bit....opening day of deer gun season today. #2 son got a nice 9 pt (5x4) very early....all I've seen are doe.

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    you are correct on what you say about what it will potect, have lots of sheer pins or a different type of eng [one with a slip clutch in the prop]

    SID

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    I've had a few rocks wedged in between my prop protecter and the prop over the years. When the motor is lifted nice and high, it occurs less. At the height I run my motors, I've never hit the lower unit, the only thing that happens is the prop and skeg protector deflects the motor upward when I hit bottom. The best thing you can do when that happens is to back off the throttle (if possible) and take it a little slower over the shallow river bed that is covered with small flat rocks (the worst). The prop produces enough force to pull small rocks up off the river bed and right through the prop when the going gets shallow. They don't do much damage to the prop though. Once every three days of running like that though, and you have to file the rough edges of the prop when it starts cavitating. Hondas like to blow up lower units during punishing abuse like this, some may disagree but most other outboards can take this kind of abuse year after year. Look at the lower unit of a Tohatsu or Suzuki and compare it to the lower unit of a Honda of equal horsepower.........you'll see a real big difference.

  12. #12

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    Quote Originally Posted by FamilyMan View Post
    I use Mac's and am happy with it. I've abused it enough to bend it a little, but no failures. They make one for your little outboard:
    http://www.propsavers.com/River%20Runner%20Prices.html

    That's the one I use as well.
    "If your not the lead dog.... the view never changes"

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    I think I am going to make something that morphs the bottom protection with a couple fingers on the sides to guard against side impacts.

    We have mostly mud and sticks/logs here on the Eastern Shore but you don't need to go too far into the hills to run into flat and round river rocks. While the River Runner seems to provide skeg protection it leaves the sides wide open to hitting stuff which is what I was trying to prevent. My 6 hp Johnson has taken some pretty hard impacts and that is the main reason why I wanted to protect the little Merc.

    I will try to put something together and see how it works. I'll try to post a picture when I'm done in case anyone is interested.

    Thanks again for the info and comments!!

    Joe

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    Quote Originally Posted by Lowrider View Post
    I think I am going to make something that morphs the bottom protection with a couple fingers on the sides to guard against side impacts.

    We have mostly mud and sticks/logs here on the Eastern Shore but you don't need to go too far into the hills to run into flat and round river rocks. While the River Runner seems to provide skeg protection it leaves the sides wide open to hitting stuff which is what I was trying to prevent. My 6 hp Johnson has taken some pretty hard impacts and that is the main reason why I wanted to protect the little Merc.

    I will try to put something together and see how it works. I'll try to post a picture when I'm done in case anyone is interested.

    Thanks again for the info and comments!!

    Joe
    keep in mind that anything that runs out to the sides of the prop are going to disrupt the water flow to the prop, taking away some of the efficiency. With a 3.3, you don't have a lot to start with. The good part about the ones like what I showed and the others talked about here so far was that they just extend from the existing skeg, having very little, if any added disruption to the water flow.

    Good luck with whatever you end up with. I'd be interested in hearing how it all works.

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    Good point!

    Interestingly, the 3.3 pushes my 17' almost as well as the 6 hp and on about 1/4th the fuel on flat water. That would not be the case going up stream where the power makes a big difference.

    I bent some 3/8" CM tubing that I think will protect the sides and I'm playing with a couple ideas on how to attach it to the skeg and cav plate. I was going to bend some flat stock to come off the skeg and I ran out of oxygen for the torch so I beat it into shape with a 3lb hammer...not happy with the result.

    Stay tuned...something will take shape...I hope!

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    your rock hopper for the small eng , you do have the idea on how to build it, the way you a fix it is to drill, bolt ,an locktight it, to the plate an a u shape flat bar on the skeg an bolt it in place hole through the sked with a drill good luck

    sid

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    If you can, try to inspect the prop on that motor, if it uses brass shear pins, get rid of them and substitute pins made from nails, or find some steel sheer pins that might fit. The 3.3 is a great little motor. They weigh 22lbs and are a heck of a back up for any a square stern.

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