Ok,I have a question here,need some advice please. I have noticed my anti ventilation plate height is around 1 -1/2 inches below the bottom of my 1648 flat bottom jon boat. Is this correct? I'm fairly certain every jon boat has been the same that I owned but I have read were it should maybe be higher. I have seen like 50/50 jon boats were some were like mine and some were a bit higher as in close to even with the bottom of the boat. Does anyone else's outboard do this. I'm sure I'm just over analyzing the situation and it's probably no biggie unless it was a speed boat or performance boat but any info would be helpful,thanks.
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Anti ventilation plate height
- Thread starter scoobeb
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Through the years I have found the info that is well described in this link to be spot on:
https://www.veradoclub.com/index.php?topic=137.0
The post shows pictures of larger V6 motors, but the info applies to all boats and OBs. It should be a sticky!
FYI - if the post doesn't link automatically ... copy and paste it into your browser to connect.
https://www.veradoclub.com/index.php?topic=137.0
The post shows pictures of larger V6 motors, but the info applies to all boats and OBs. It should be a sticky!
FYI - if the post doesn't link automatically ... copy and paste it into your browser to connect.
Bowhunter1661
Well-known member
I have a Lowe 1440. My current motor is a 1988 Johnson 25. At this time my motor is raised off the transom a 1/2". This puts my anti vent plate dead even with the bottom of the hull. I have not been able to check where the motor rides on the water when cruising due to the fact last time I was out there were 3' waves on Lake Michigan so I couldn't really turn to look. (Though I did turn back to the harbor shortly after spearing a few waves..) . IMO, it is more a matter of on plane cruising and where your anti vent plates sits while on plane. If you have a stern heavy boat you may need to have it higher up due to the stern sagging deeper into the water. My boat sits almost perfectly level with the TM battery under my front deck.
Well I just read my manual and it says around an inch below the keel is fine. I will just have to see how it performs on the water first. If I get near 30mph with one or two people and gear then it's riding right,I will also try to keep an eye on the anti ventilation plate while going wot to see were it rides,I'm betting it will be ok. I just double checked,it's around an inch and a half at the most,like I said,I still need to run it first,it maybe fine. I see tons of flat bottom jon boats like this and they run great.
That is the superior method for setting an OB motor height ...Bowhunter1661 said:
And I'll add, provided that your boat is properly pitched to boot! That link I provided also tells one how to make sure they are wearing the right prop by testing the rig at WOT ...even if you never run it there. It's akin to driving a car with the transmission set into the proper gear.
My biggest boating pet peeves are:
1) Most boat dealers rig the OBs too deep
2) Most OBs are rigged with the wrong (stoo steep) a pitch prop
I went to my local marina and asked the same question there i did here.They said there should be no issue with an inch to even 2 inches below the keel on a light aluminum flat bottom jon boat.It's roughly around 1.5 inches under the keel give or take a mm.He told me most jon boats he has seen that he's come across his marina are that way.He told me i could move it up to make it even on the bottom if i wanted but the performance gained would be so minimal i probably wouldn't even notice.He said i should be near 30mph or better with this new motor with the 12 pitch prop i'm running.I take his word for it.He said just play with the tilt and get the best performance out of it.He said i'm over thinking it and it's no issue at all.Almost all the small outboards he said they install always sit a bit below the keel.He said if were talking inches as in 4 or 5 then we have an issue but a inch will not hurt it a bit.
Yes, the probability is that it won't hurt ... but for those of us who tweak our rigs, we're seeking optimal performance!scoobeb said:
Might not matter on light tin boats, but I know that when I ran a 3-ton rigged tuna boat, I was able to tweak out > 20% fuel economy and performance vs. other comparably equipped, but not optimally tuned rigs.
A 10 to 20% improvement, when you're talking 100+ gallons of fuel per trip, is major $$$ when fuel is at $4+ per gallon on-the-water co$t.
Skiffing
Well-known member
Another consideration for better engine height is fuel consumption.
If you are cruising any distance having the engine height correct will save considerable fuel.
Boat stays on plane at lower RPM w/ similar speed.
If you are cruising any distance having the engine height correct will save considerable fuel.
Boat stays on plane at lower RPM w/ similar speed.
huntinfool
Well-known member
Thank you for this. I've had issues and had just posted a pic of mine. Now I know.DaleH said:
Yes,that makes perfect sense with fuel consumption on a rig using hundreds of gallons of gas. I use a six gallon fuel tank and never go over a mile offshore. I do go like 5-10 miles down the shore line but never out in deeper water. 3-4 foot is my average depth. I will gps it to see what my wot speed is. If I get near or at 30mph that is plenty fast enough in a tiller jon boat. I will see how it runs,if it's dragging bad then I need to raise it up for sure. I have had many jon boats and they all were like this and ran fast. I just never put any thought into it like now. If it's dragging it will be slower than I expect and run like crap. I got this motor for running all over the place and to get on plane with 3-4 people if I ever have that many on board which is rare.
Charger25
Well-known member
scoobeb said:
All mine are like that 1 to 1.5 below the bottom of the boat. Its not that big of a deal. I must say though I have been kicking the idea around of getting a jack plate for the 16' All I need is about 2 more mph to out run a couple of friends boats, we're all running 25's and run the same speed :mrgreen:
What kind of wot speed are you getting Charger25 with the 25hp? I just got the new 25hp efi suzuki and it's a cherry. It's a state of the art outboard,light and from the videos I have seen extremely powerful. I can't wait to get it on the water next week. I'm putting a new removable 1/2 -3/4 inch thick carpeted floor in it. I'm going to wait till fall to mod it out,to hot here in Florida to work,fishing ok but work forget it now.
huntinfool
Well-known member
Adding that much carpet and floor will add a lot of weight. Just saying.scoobeb said:
Every jon boat I've ever owned I put a thick carpeted plywood floor in and it never effected the wot speed ever. It may add around 50lbs for the floor,give or take a little weight,that won't slow a flat bottom boat down imo at all at least in my experience.
Well after reading and reading I'm going to get a 1x1 piece of wood to put under the outboard to lift it at least an inch orso. II'm wondering if the wood will rot out,I never had to do this before so it's all trial and error. Plus it will be sitting off the transom so will the clamps hold it down the same? If the motor runs good like that then I plan on bolting it in but for now I'm using just the clamps. Will the wood work ok and the way I plan on doing this,please any help on this chime in,thanks.
Charger25
Well-known member
scoobeb said:
The 16' is a semi-V . V bow ending in a flat stern with rounded chines. It's a bare bones boat,the bench seats are carpeted with clamp on style jon boat seats. If im running solo the motor is trimmed all the way in, if some one else is in it i'll trim it out a hole or two. Either way it will run a solid 30 mph according to the gps.
One of the guys has a new 25hp 4 stroke electric start Suzuki on a 14' dbl wide mod -v , Thats the fella I wanna out run
Bowhunter1661
Well-known member
I currently have my motor level, using one 1/2" shim. My anti vent plate still digs in the water. Personally, I do not feel comfortable raising the motor more than an inch to a half inch. The clamps start getting too close to the top of the transom for my comfort. Therefore, I made a jack plate to raise it to aprox 1-1/2" off the transom. Also, with the 4.5 inches of setback I may be able to go up to 2-2 1/2" off the transom.
Well Charger25 that is funny I have the same motor. Maybe I'm just over thinking this and should leave it alone if I get near 30mph. My boat is the 1648 flat bottom alumacraft with the 25hp efi suzuki tiller. The boat is light at only 290lbs and I know it doesn't take much to move them. I guess it makes sense to see how it performs first,after all 30 mph is fast in a tiller flat bottom jon boat. The main thing is if I leave it the way it is will it hurt anything? Now if I go out and do like 15-20mph then I know it's just plowing and needs to be raised. If your rig is doing 30mph then I would think mine would also. I called the place were I bought the boat and they told me near even with the bottom of the boat of a bit under is ideal but he said the way I have it won't hurt a thing but it could pull to one side and ride a bit weird,other then that it would be ok. Like I said if it runs like crap I will put a 1x1 shim under it to fix it.
I figured i would just post pictures,that would give everyone the exact height it's at.The issue i have is i'm not working with to much more movement on the clamps.I can probably move it up a half inch or so but there is not much room for allot of movement as you can see.I have the clamps holding it on now as well as 4 zip ties so the clamps won't ever turn to loosen it up.I was going to put a long lock in the holes of the plastic turn handles but i remember how annoying the vibration was so i decided to go with zip ties with no noise.Here are the pictures and please let me know if i'm just to paranoid over this and it will be fine or i do have something to worry about.My manual says from even with the bottom of the boat to a inch is fine,i'm about a half inch off the mark as i measured it.It's around 1 1/2 inches under.This is a light jon boat at around 290lbs so i would think this motor should scoot this boat every bit of 30+mph.Ok, please let me know what you think,thanks.
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Bowhunter1661
Well-known member
Personally I would say you have nothing to loose by raising the motor and only more to gain. Though it likely performs good at that height it very well may perform even better if the height is raised. Possibly a couple mph, maybe only 1 mph? Possibly better fuel consumption? Ods are at that height your anti vent plate is plowing, if that is the case I personally would suggest raising your motor. Many may say leave it. But I am a perfectionist. If my boat isn't in perfect tune i am not happy. That is why I am at this very moment installing my homemade jack plate, to perfectly fine tune the height of both my 15 hp and 25. Without the fear of my motor falling off because it is too high on the transom.
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