12' jon boat 6hp motor slow

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  #1  
Old 05-14-14, 10:44 PM
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12' jon boat 6hp motor slow

Hello,

I have a little 12 foot flat bottom aluminum jon boat and a 6hp johnson from the 1970s. The motor runs great, I just performed a tune up, but the outfit is pretty slow. My fishing buddy is heavy, at 300lbs. I am not, at 160 lbs, but that's a good load on that boat, along with some gear and a gas tank. The little 6hp only pushes it a few miles per hour, maybe 5. Is that to be expected? The thing is singing along at high rpm, but not going anywhere. The front of the boat is pushing water away... would a v-hull help? Would a different prop help? I can live with it, but I always find myself wishing for a little more speed, especially when I'm in the gulf and a storm starts brewing. I like the setup because I can slide it in the back of the truck and go down to the remote little shallow access in the marsh close to my favorite fishing spot. Anything much bigger and it would require a trailer and more hassle.

Thanks for your input.
 
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Old 05-15-14, 12:46 AM
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A very lightly loaded Jon boat will skim by pretty much on the surface of the water although not quite as well as a true planing hull IF it has enough power. A moderately or heavily loaded Jon boat will wallow through the water and the blunt bow wastes a tremendous amount of power pushing the water ahead of the hull.

So yes, a vee hull IS faster, provided that you do not overload it AND you have enough power to "get it up on the step" where a majority of the hull is actually out of the water and the vee "cuts" through the water easily with the prow easily slicing the headwater and the flare causes the bow wave to roll off to the sides.

Something else to consider is that the greater the ratio of length to beam (essentially the narrower the vessel related to the length) the faster the natural hull speed with minimal power. That's one reason a canoe is both fast and easy to paddle.

Amazing I still remember that from college, more than forty years ago, when I took my degree in marine engineering. I never worked under that degree so it is even more amazing considering the more recent things I have forgotten.
 
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Old 05-15-14, 03:35 AM
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You won't get much more speed out of that motor on any small boat. I'd say you have a nice little setup there -- inexpensive to maintain and easy to launch.
 
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Old 05-15-14, 05:35 AM
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The maximum weight capacity of your boat is probably about 450 pounds. 300lb buddy + 160lb moderator + 70lb motor + 50lb fuel & gear = overloaded boat.

I assume that you alone in the boat probably can get up on a plane. I had a 10ft pointed bow, flat at the stern aluminum boat and it would get up on a plane with just me in the boat and move pretty fast, maybe 20 mph. A second person was just too much. It would get close but just could not climb over the bow wave and it would wallow along at about 10 mph. Unfortunately I don't know of a boat small enough to put in the bed of a pickup that will go very fast carrying that much weight.
 
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Old 05-15-14, 04:59 PM
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Thanks. I picked up a 12 foot v-hull sea king aluminum boat today. I'm going to try it out instead. I think it will part the water rather than push it out in front and go faster. I have a couple of props for the motor. One has 2 blades, the other has 3. I don't know the pitches of them. Is one preferred to the other assuming they are the same pitch?
 
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Old 05-15-14, 09:19 PM
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A two-bladed propeller is more efficient than a three-bladed propeller. Adding blades will allow more blade surface within a set diameter so the three bladed propeller might seem more efficient but the flow of the water (more accurately the "working fluid") is impeded by the lesser clearances between the blades. Propellers are by nature (physics) low-speed devices and when used in high speed operations there is a greater amount of "slip" which translates into lesser linear travel than the pitch would ordinarily suggest.

This post just about exhausts my memory of of hull design and propellers. If you have any questions concerning small steam plants for marine propulsion, ask away.
 
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Old 05-16-14, 12:08 AM
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I called it a V-hull, but it's more of a semi-V. It starts off with a v and levels off to a fairly flat bottom.

Thanks for the prop info!

If I decide to steam power it, I'll holler atcha!
 
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Old 05-16-14, 05:17 AM
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I would try a three blade if the motor can handle it's pitch. If you had a top speed I would worry more about efficiency but I think you want as much prop biting the water as the motor can handle.

---
I remember an aeronautical article about propellers. A single blade is theoretically the most efficient. Awfully difficult to balance though. Then a two blade was best for high speed cruise and efficiency while three blades favored climb.
 
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Old 05-16-14, 01:09 PM
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I really should elaborate on my statement that a 3 (or more) bladed propeller is less efficient than a 2 bladed model.

Ignoring the diameter and the speed (rpm) of the propeller the pitch of the propeller is what determines the amount of linear motion. The problem is that as the pitch in any given diameter is increased the "slip" also increases. To get around this the propeller is made with a larger diameter. This works okay until the "tip speed", the rate at which the outer edge of the blade is moving through the working fluid, gets too high. High tip speeds in water lead to cavitation and erosion of the blades and in air high tip speeds translate into excessive noise as well as cavitation and erosion.

To overcome these deficiencies it is necessary to keep the diameter or the speed below certain parameters. Another factor is that often physical clearances will limit the diameter of the propeller. In order to move enough of the working fluid it is then necessary to add additional blades and even though this will lessen the efficiency of each individual blade, the overall increase in performance is a net gain.

Okay, now my memory IS running on empty!
 
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Old 05-16-14, 06:15 PM
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Whew... okay, I went to the OMC guy in town who has one of everything from the 1950's to date in his huge buildings, but he had no knowledge of any prop for this motor with less than a 7 pitch. He says I need more horsepower, and he may be right, but I think I can do better with what I have. I haven't tried the modified v-hull yet. It may be all the difference in the world, since it won't be shoving the water in front of me and the bottom is wider. With that combination, I might be able to pull it up on a plane...maybe...might be wishful thinking. If I can get 10 mph or so I'll be content I think. I think I'll just try both props. It's not hard to swap them.

Thanks for the info! I won't get to try it until Sunday afternoon.
 
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Old 05-18-14, 11:10 AM
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There is no substitute for horsepower as you're already aware of. Being in the small engine industry. But that may not be the case maybe.

I picked up a 12 foot v-hull sea king aluminum boat today
I suspect the out board engine remains on the 12 foot boat during transportation???

Or is newer boat Towed on a trailer? Or do you remove engine each time??? To carry in bed of truck??

My thinking is the engine is low horse powered so the engines weight is easy to carry, lift then mount on the transom. A one person job. If you due remove it each time???

Try using different trim positions on the outboard. Prop correctly angled into water raises the bow more during higher running speeds. Might help. Boat should then come up on Plane sooner.

Just offering suggestions, if I have the facts correct and the newer boat details correct. Advise.

 
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Old 05-18-14, 08:44 PM
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I just toss the boat in the back of my truck and put the motor in the boat, then mount it on site. I took it out today and we tore up the fish... 2 of us got our limit of sea trout, plus we got 3 reds and 3 flounder! The new boat only goes 6 mph though. I think I am going to look for a 9.9hp to put on it. Think that will do the trick?
 
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Old 05-19-14, 07:32 AM
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I think I am going to look for a 9.9hp to put on it. Think that will do the trick?
To some degree a larger engine will make an improvement. The considering factor, as I am understanding it to be, engine weight is going to be the primary factor. Since the engine gets removed each time boat gets transported. Has to be a one person job imo. Since one can not always have another person along to help lift engine on and off transom each time. You might have to go alone some days....

Should be a sticker indicating maximum engine weight the transom can handle. Might want to refer to that before buying another larger engine....???? Good Luck. Keep us updated. Hopefully this thread is not coming to it's conclusion....

Glad you had a good day fishing too!... Any day fishing is better then a day working...

 
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Old 05-19-14, 10:07 AM
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I'm pretty strong and fit, so handling a bigger motor shouldn't be a problem. I have a guy who is interested in trading a nice 9.9 for the 6. I think I'll do it if he will. If so, I'll post an update. Something else I need to figure out is how to keep from chewing up the prop on the oyster beds. There are so many in the shallow areas where I'm fishing that you can't really keep from hitting them.
 
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Old 05-19-14, 11:24 AM
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Try titling engine toward bow. Raised slightly rearward. Less prop in the water when over shallow areas. However, go slowly and be sure water intakes still remain in water and the exit water remains the same flow as when prop is at full vertical depth.

Maybe I should use the term prop shaft? Angled slightly forward toward the bow instead of fully vertical. Anyway, the tilt angle can be set easily. Several positions located on the engine base. Some engines if not all require be in neutral or reverse to allow engine to tilt. It's a safety to prevent engine from popping up should prop or prop shaft coming into contact with anything unseen below waters surface.

Measure length of prop shaft that's below the bottom of the boat. Then you'll know more about where not to tread... Proceed carefully over the oyster beds and rocks, etc. Measure as you go and be careful. Tread slowly. BTW. Tides change.

Chipping a prop very slight may not seem to cause to much damage. However, anymore then very minor impact can cause prop to become out of balance, crack and later may burst apart at higher speeds, etc.

IMO, Always best to replace the prop if in doubt. Boat repair shop can better advise, despite what some may say. You have to trust some body at times. Just like your customers trust you.... Be right over with all my outdoor power equipment...
 
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Old 05-23-14, 09:25 PM
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The deal on the bigger motor fell through. I have been looking at youtube videos os 6hp johnsons on 12 foot boats and they are moving pretty good, even getting on a plane. Mine won't with noting but me (160 lbs) and a 3 gallon tank in the boat. I'm beginning to think something might be wrong with the motor. It runs well though.
 
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Old 05-24-14, 09:39 AM
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You never mentioned trying the tilting of the prop down or up slightly... Push engine Down away from you (prop needs to be further under bottom more) should raise the bow up under power. Try and advise results. Might just need more horse power. Larger engine with more power.

Maybe should take entire boat with engine attached to a local boat repair shop. Ask a pro. Might have the wrong prop presently installed....????

All else fails, trade engine in and buy newer one with more horse power!!! No substitute for cubic inches... Fishing season about to begin. No time to fiddle around with petty issues...

Around here there is no fresh water fishing... DRAUGHT!!!!...
 
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Old 05-24-14, 06:11 PM
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Yeah, I tried the motor tilted different ways and actually got the best results with it down all the way, but no joy. I also tried both OEM props that are available. I picked up an old 9.5 evinrude today for cheap and tried it. It's not running 100% perfectly, but it only got the boat up to 11 mph according to the gps and still wouldn't plane. At the boat ramp, another guy came in with a boat bigger than mine, probably twice as heavy, and he and his wife probably equaled what my buddy and I weigh, and he had a 9.9 on the boat. I asked him if the motor moves his boat pretty well and he said it gets up and goes really well. I just don't get it.
 
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Old 05-25-14, 05:28 AM
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Are the old motors you're using making their full horsepower? I would assume that your old 9.9 is not actually producing full power and it might be a good bit less than full power.
 
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Old 05-25-14, 06:02 PM
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Could be. I am working with this old stuff because I don't know what I want yet, or what fits my needs yet, and I don't want to put a lot of money into a setup that I think I want and then figure out doesn't really fit the bill. The old 6hp is one I've had forever, always works when I want it. Good motor.

I'm cleaning the carb on the 9.5, and tuning it up. It has 2 new coils, new points, new condenser, and new pump impeller and housing on it. The points were set a bit too close, and the throttle/advance timing was way off from what I could tell, so I adjusted those. A rain storm came up, so I packed it up and went inside. I'll see how it does tomorrow I guess. The motor overall looks to have very little use for its age, and although I haven't put a gauge on it, the compression feels pretty sharp, so I think the motor is able if I get everything in order.
 
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Old 05-26-14, 09:48 AM
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I am not familiar with flat bottom boats. Not popular out my way. I could then be wrong in my thinking it is as easy to get up on plane as a v hull??? Maybe flat bottom boats never really obtain the same bow lift like a v hull or semi v hull??? Advise.

Or can they obtain a plane of the bow like a v hull but just require more horse power???? Those in the know kindly Advise...

Attempting to type less here. So I'll refrain now from asking. Yeah Right...LOL!!! Flat bottom seems to be or may be more stable (less side to side rocking) while standing up and moving around maybe???? Benefit over a v hull???
 
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Old 05-26-14, 10:28 AM
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I'm no expert, but flat bottoms are less tippy and seem to draft a little less water. They get up on plane quite easily, but they beat and smack a lot harder on waves with no ability to part the water.

I think that if one requires more hp than the other, I would say the modified v-hull might take a little more provided all else is the same. It may just be that what I'm trying to do is not reasonable to expect.
 
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Old 05-26-14, 01:10 PM
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I would say the modified v-hull might take a little more provided all else is the same.

Are you sure about that? Seems to me, thinking logically anyway, a flat bottom has more surface area causing more drag. More side to side stability in a flat bottom at the expense of drag and reduced speeds. Might have to ask a pro. Could be the reason an air boat has a flat bottom. Stability over speed maybe. Ask an alligator hunter why some use an air-boat or a Jon boat instead of v hull?

Just might be what you're expecting isn't possible? Could be but hoping not. I am a boat owner myself. As the saying goes. All boaters have two Happy days. The day they buy a boat... The day they sell their boat. Ha Ha....
 
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Old 05-26-14, 09:51 PM
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Haha, I know all about the day you buy and the day you sell. I have a 20 foot deck boat I am putting up for sale right now. The thing has a 115 johnson on it that keeps blowing head gaskets. Then I have a 14 foot general purpose boat with a 75 johnson on it. I could use it where I'm trying to use the little jon boats, but it's a little big for what I'm doing.

I'm fishing in some really shallow flats in the Gulf of Mexico. The flats start off with grass marsh and there are sloughs that run through them. I put the jon boat in these shallow sloughs that are dry or nearly dry when the tide is out. There are oyster bars that are up above the water when the tide is out. This requires a pretty small boat to put out here and follow the sloughs out to the flats, where the water gets a little deeper (2 to 5 feet) for several miles out. The water is shallow but the fishing is awesome and there are few people, no commercial or residential development, it is beautiful and natural. I just need a boat that can run shallow, not have to be trailered, and be able to handle 2 foot seas and be fast enough to not get tossed around in the waves. Here are some pics so you can see why I'm so intent on fishing here. The big creature that came to visit us is a manatee (sea cow).











 
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Old 05-27-14, 12:03 AM
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Awesome!! I'm following your thread as I work to get my 14 footer back in the water after several years. Just got my 20 hp back from a tune up (replacing my old 18) and hope it will plane as my very old 18 would not. The 20 is a 1967 and only had 2 tanks of gas through it before it went into storage, virtually brand new. Although my area is all fresh water, yours reminds me of why I want to get out there.

Let me guess, sea trout and fluke.
Bud
 
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Old 05-27-14, 07:27 AM
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Where you're fishing looks like where I spent my high school summers living on a boat and playing in the salt marshes. Almost everyone used flat bottom boats. The big boats were Carolina Skiffs which have a very distinctive sound you can hear from far away as they slap the water. Then there are air boats and finally the flat bottomed jon boats. The v bows do handle chop and ride better but they draw more water at the bow and take a little more power to get on a plane. Mine with a pointy bow had rounded/soft chines that were good if you had to drag the boat sideways across the flats but make is more tippy if you stood off center. In the marshes where you are I'd probably stick with a flat bottom but you already know how well it can handle 2' waves.

---
Oh, and always go out with some emergency sun cover and a lot of water. I got stuck once wayyyy back in the marsh and had to wait, roasting in the sun for the next high tide.
 
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Old 05-27-14, 04:57 PM
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Yep, it's a cool place to fish but the tide can get you stranded if you aren't careful. In the pic of fish, there are 10 sea trout, 2 redfish, and 3 flounder.

I'm back to the drawing board again. I'm thinking of scrapping all my plans and starting over because what I have going isn't working like I planned. I may go with a larger flat bottom console steer with a 40 horse and just trailer it there.
 
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Old 05-28-14, 10:51 PM
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I got tired of messing around with the little boats bobbing around in the water, old motors, and all the crap that goes with it. I picked this up today... 16 foot flat bottom console steer, 40 hp mariner
(the one made by Yamaha). I drove by it yesterday and knew it would be exactly what I need for what I'm trying to do and do it a lot more comfortably, so the price was right and I got it. We'll see how it does this weekend.
 
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Old 05-29-14, 07:16 AM
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Sweet! I know trailering is a pain but it will be a lot easier on your back and the bigger boat will be safer in the open areas with bigger waves not to mention a whole lot faster.
 
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Old 05-30-14, 02:44 AM
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Nice! You are now officially a member of the I Need a Bigger Boat Club. The boat you have now will grow. In ten years it will be too big to trailer and you'll be dealing with dock space at the marina.
 
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Old 05-30-14, 05:06 AM
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Rick, I'm laughing. Last fishing trip with a good friend was in a 16' fg in Little Eggs Harbor NJ. Then he moved to Florida. When I asked what he picked up for a boat he replied "a 29' Cuddy" docked at the marina. LOL

cheese, I know it is too late, but my son took my newish 5hp Evinrude into camp this weekend and used it on a 14' aluminum v hull. What caught my attention was when he mentioned the motor ran great and easily planed the 14 footer with him and his young son, maybe 250 lbs total. I would not have expected the 5 to be able to do that.

Your new toy looks awesome. I hope we see more pictures as I obviously need more practice identifying salt water fish.

Bud
 
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Old 05-30-14, 10:19 PM
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Lol... well, I'm probably not in the "need a bigger boat" club, 'cause the whole reason I went to the little jon boats was because I had (still have) such a big boat that I hated it. I have a 20 foot deck boat with a 115 johnson on it and we would put it out at a big landing 7 miles from my fishing spot and work my way over to it from the deeper side. It cost us a fortune in gas, always needed something, had trailer problems from such a heavy boat beating on it, required my big truck to haul it anywhere we went, and was just a cumbersome thing altogether. It would get up on a plane and go 24 mph though.

I am downsizing to make things easier and more affordable. I am putting the deck boat up for sale and probably the 12 foot semi-v hull boat. The 12 foot flat bottom I will probably keep because when we go camping, I can throw it in the back of the truck and still have the trailer hitch free to haul the camper. I might keep the 9.5 johnson to run it with.

I'm going out this weekend to give the new boat a run, and I hear the fish are biting...so... hopefully I'll be back with some more fish to identify .
 
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Old 06-01-14, 04:18 PM
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We went, but the weather was a bit rough. We caught a couple more trout, another flounder, and a Jack Crevalle. This little boat will flat out run. It got me and 2 other people way up out of the water on a nice plane and skipped across the swells like it was nothing. I wish it had a little more freeboard while sitting there fishing though because once in a while a wave would hit the side or back and come over a little. Not enough to turn the bilge pump on, but I don't like water coming in the boat. It calmed down a bit just before this huge mother-ship looking thunderstorm loomed over us, and we got back to the landing just in time. All-in-all, I am pretty happy with this setup so far. The trolling motor helped get us through the shallow spots. I hit some mud and oysters with the prop but didn't ruin it... just took some paint off and roughed up the edges a little. I may just use the trolling motor up close and not even run the outboard until we get out a bit further when the tide is low like that.
 
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