Prop Ventilating .

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DarrellS

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Hi . I'm pretty much a newbie when it comes to owning a boat and diagnosing problems .
I have a 1992 Lowe "pro fisher" 16 ft . 30hp 2 stroke Evinrude . Manual tilt / trim .
If I run the pin in the second hole the boat will get on a plane but will dig the bow into every little wave .
If I move the pin to the third hole the bow feels like it wants to come up but the prop keeps ventilating .
The cavitation plate lines up with the lowest part of the hull pretty much perfectly .
I have two group 27's under the casting deck on the bow as well as a group 27 at the transom for starting the engine .
The only people I can try to get advice from have heavy fiberglass boats with 100+ hp .
I am getting about 22 mph at a maximum rpm of 4500 rpm .
If I get a blow out the tachometer shows 6500+ rpm , so I'm not too sure if I should worry about a faulty tach .
I can not figure out what prop is on the boat now to use as a reference .
I was convinced I needed more engine to get on a plane until I came to this site .
Now I am considering a Davis instruments hydro foil to discourage the ventilation and get the bow up .
I am also wondering if a 4-6 inch Jack Plate might make more sense so I can get the prop further from the transom to take advantage of the rise of water behind the boat .
I can not move the motor down any further its already as low as possible without modifying the transom .
Curious what you guys have done to correct problems like I'm experiencing .
Please share your experiences and solutions .
 

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A little history would be helpful. I take it that this is a new to you boat. While I have used hydrofoils with great success in the past to help correct planing issues, I would first look at what prop is on it. Use a prop calculator to see if it is the correct size for your application then go from there.


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I'm unsure how to identify this prop , I can not find any numbers on it anywhere . Yes the boat is new to me , I bought it from the original owner who was getting on in his yrs and had stopped fishing . I have looked at the prop calculator and with those batteries up front I am looking at " loaded recommendations " Boat should be in the 750 lb area empty . 18 gallons of fuel back by the transom .
Side console . I guess getting that prop off of there and getting a recommended prop will get me going in the right direction .
I just am trying to figure out how to spend money wisely since money is tight now a days .
Any more than about 8 inch waves makes for a very wet ride with the bow not coming up .
 
Is there anything ahead of the prop near the bottom of the hull? Such as....transducers, livewell drains, dents/dings in the bottom? Those can all help cause ventilation. Is this by chance a tunnel hull?
 
How many times and how many threads will it take before people understand that if the cavitation plate is even and level with the hull on anything but a fine tuned performance boat then it will be too high as soon as you trim up. Drop the motor and trim up higher. Post a pic of the side view showing the cavitation plate and hull bottom trimed in the position that you have “blow out”. Fwiw you do not have blow out. Thats a dangeouse condition on race boats. You have ventalation. Its probably worse when you turn. Drop your engine mounting height and trim up. You will run faster and turn better at speed.
Trim up where you think you want to be and make sure the rear of the cavitation plate is slightly below the hull.
 
Thank you Stumpalump : I'm trying to figure out how to post pictures . And thank you for the clarification that it is probably preferred to run the cavitation plate lower for all around fishing use . Unfortunately I can not lower the engine without cutting the transom because this is how the dealer setup the boat and the mount is resting on the top of the transom .
This is why I have asked for help from you people that have been in this situation and found a way to "Fix" this .
I have read and researched as many posts as I could that are simular to this and I have not seen a solution that actually worked other than cutting the transom , and I will if that is really the only solution to this .
Please let me know if you are able to view the pictures .
https://www.flickr.com/photos/49773465@N03/with/46331753122/
 
Sounds like a jack plate is warranted. Doesn't need to be power trim, just set once & leave it. Notching the top of the transom would lower resale value of boat a bunch, IMO.
 
CedarRiverScooter said:
Sounds like a jack plate is warranted. Doesn't need to be power trim, just set once & leave it. Notching the top of the transom would lower resale value of boat a bunch, IMO.
No dont cut it. A jack plate would solve it but the best thing about it would it puts the prop back in cleaner water that is raised up behind the boat. It also adds steering leverage making them turn really well. If you don’t like spending money then double check to make sure the installer did not shim the motor a tad. You would have to redrill the holes but thats OK. File your prop and skeg clean if they have burrs. Make sure the transition from the bottom to the back of the transom is clean. No big weld boogers or left over hardware that adds tubulance. A fin would help but the thick aftermarket ones add drag and are often way to big. You can cut them down if you buy one but my experiance has been the best by just mounting 3/16” aluminum plate. Basically you are making the cavitation plate bigger. Here is mine. Its probably bigger than you need but its a 48hp on an 18 footer. They work well and stop the bow from pounding down when it raises up over a wake. A jig saw and a drill will wip one up preety fast and you can trim off extra material to tune the size. Any metal place will sell you a small piece.

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With as many references I find when I search on how to "properly" setup a outboard , They all guide a person to put the cavitation plate at the bottom of the boat .
I wish it was made more clear to us unexperienced people that its okay to lower the cavitation plate until " ventilation " stops at the preferred trim setting .
And it certainly does not help when a boat is setup from a dealer improperly .
Us new and unexperienced people think we can trust and believe what a dealer tells us .
So now my next question is , how can I identify a used manual jack plate for my application .
Are jack plates kind of universal ?
I know If I was buying new that I don't need one thats safe for 300 horse power .
When buying used do I just want to make sure its wide enough to accept my engine mount ?
I'm seeing new jack plates on ebay for as little as 175.00 .
 
You can get manual ones cheap. To adjust you have to break out a socket set. Powered ones are nice because you can raise them way up in the shallows when going slow. Personally I can’t believe you cannot get that boat to work like it is. You want as much weight toward the back of the boat as you can stand. All of it if you can. Batteries and gas are the biggest but even anchors and tools add up. Move everthing that you can back and try it again. You want the front very light. What is the hulls rated maximum HP? If its more than what you have that adds to the problem because you have a light engine. Your engine is light anyway. I bet you have trolling motor, anchor, batteries, cooler and gas to far foward. Move it back and try again. You may not need to trim up so high. All boats are very weight sensitive and all boats run their fastest with the weight back. The object is to carry the bow. You are triming up but its not enough umph to carry the bow so you trim more until you ventilate. You will get used to the *** heavy feeling as soon as you see how much better it performs at speed.
 
The boat has not worked right at all since I got it . I just recently installed the trolling motor and had to put the batteries up front under the casting deck .
I tried to put the batteries in the back with the fuel tank and the starter battery but there just isn't enough room for 3 batteries .
I did try the boat on the water with all the batteries just sitting in a mocked up kind of position and when I would stand on the back deck water would come over the transom .
I weigh 175 lbs , so that was when I gave up and moved two of the batteries forwards .
Maybe I'm just asking to much from a 30 horse motor and need to max the power .
The hull is rated for 60 hp but I'm just wanting enough power for the boat to run properly .
I have found a few 50 hp engines from mid 70's but I don't know what years might be very undesirable over another .
I am disabled so I have to make every financial decision very carefully .
I never expected this setup to fail .
I talked to the previous owner over the weekend and he told me it has never worked as good as he has seen other aluminum boats work and told me he thinks it has too small of an engine .
I had a 12 ft jon boat with a 5 hp so I thought I was really getting into a great setup with this boat , low hours , great compression , hull is in great shape .
 
The rpms still raise a flag with me. The boat is obviously on plane. I would definitely ensure the correct prop was on before bolting anything else on. If the tach is correct, 4500 is too low.
Post some pics of your boat.


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Not familiar with the davis foil, so I can't speak for that particular one or design. However, "most" boats that are set up properly, the foil is up out of the water when the boat is on plane. Thus, it really can't do much for reducing ventilation while the boat's on plane.

What about that prop? You don't reckon the hub's spinning do you? The easiest way I know to tell is to remove the prop from the shaft and inspect the front side of it, on the inside where the exhaust goes through, you'll be looking for any little pieces of rubber. If you see any, the hub has likely spun. That is an easy fix for a prop shop, but the "other" issue is that if you're only running 4500 at full speed/full throttle, then you're lugging the motor with too much pitch. That happens a LOT because the school of thought is that more pitch=more speed and that's partially true. The truth is...yes it "can" give more speed "IF" the motor will spin it and a lot of times it won't.

You're correct in that the glass boat guys are a different type than jon boaters. 'Glass hulls are MUCH more efficient when they're on plane-usually. Problem is getting them on plane....takes a lot of power.

I mentioned hull dings, dents, etc. Any of those can let air get under the hull which then passes to the prop and causes ventilation -or blowout. Pretty common out here where the local lake is LOADED with cypress "stumps" that are inches under the water and mostly invisible until you're on top of it. Even sometimes rivets can help cause blowout. 'glass hulls are usually as slick as greasy owl poop and straight as an arrow for a reason. Jon's don't usually have that luxury.

Lowe is one of the few I haven't run much of, so I can't speak much of the hull's design. The one thing about "most" aluminum hulls is that there is a fine line between porpoising and plowing and finding that happy medium can sometimes be really challenging. Seems like a narrower "window" on the cheaper hulls for whatever reason.

It sounds underpowered, but I can't say whether that's the cut-and-dried cause. I've heard of it but never experienced it. There are all sorts of issues that pop up with an underpowered rig. I usually recommend running the rated HP or at least within 10hp of the max rating. If you had to repower it, it may be a better option to look at something newer?
 
FWIW as far foils gone, the SE Sport 200 or 300 are the highest rated, the most efficiency with the lowest loss of WOT, if any loss at all. Just bolt it on, don’t try their snap-on module.
 
I'm pretty sure the hub is good . When I have the trim set for no prop blow out I can hit the throttle as hard as I want and the boat just launches and goes to top speed with out skipping a beat .
Luckily there are no dents or deformities in the hull .
Since this prop has no identifying numbers I am going to trash it .
Today my son and his friends surprised me and installed the Davis Foil , so I guess I'll get to see what it affects before I install a jack plate .
Thankfully with all the input you guys are offering I feel secure that a jack plate will not be a waste of time .
Before I re-power I will sell this boat , This boat has convinced me I am not comfortable in a Bass style boat and want a deep V .
I want a dryer ride and better seating arrangements .
 
I'd get rid of the 2 27 batteries up front and downgrade to 24's ( if you need 24v) or 1 size 27.
I run all day on 1 size 24 with a 55lb Minn kota.

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Thanks GYPSY400 : I will look at trying to put smaller batteries in the back . I let Bass Pro talk me into the 27's and they are just so darned big and heavy its tough to make room for them .
 
I used a lawn tractor battery as a cranking when I had my 16’ with a 60hp. Every ounce helps in these small tins and where those ounces are located is more important. Once you get that sorted out check your RPM again. In the cold air with a light load you should be at or over the max recomended RPM when ringing its neck out. In the summer with a load of fish you will be glad. That “recommended” RPM should read mandatory but get your weight bias sorted out befor you repitch or reprop. I pull tachs out and check the switch setting to make sure its set for a 2 cly and not 3. That will throw off a tach and I’ve had two used boats that were wrong like that. What pitch is your prop? Oh and fwiw we all go thru the same **** when sorting out a new or used boat. Good luck!
 
The good news , Bass Pro gladly let me return the batteries for a full refund . Batteries plus had the group 24 deep cycles in stock , with about 60.00 dollars difference in price .
The group 24's fit back by the transom much nicer than the 27's .
The metal tray that extends from the transom clears the group 24's terminals much nicer , now I wont worry so much about it touching and arcing .
I will have to install the circuit breaker and battery charger in the new location .
Battery tray is installed thanks to my handy son .
Now to run power from the transom to the bow .
Stumpalump : I am surprised of your success with a lawn mower battery . How many cranking amps dis your 60 hp need ? But then I guess my Motorcycle battery has no troubles cranking the 102 inch , Crap !! This is all overkill and heavy !!
 

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A budget way to run power to the bow is repurposed booster cables. I watch for the good long ones to come on sale. I’ve done this on a couple boats both stern to bow and vice versa. Don’t really need a cranking battery with these smaller engines, I just use the deep cycle. Saves an extra battery weighing the boat down.


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