anti ventilation plate question

[boater1234]

I have a new 1648 jon boat,flat bottom and a brand new 25hp efi suzuki I just mounted on. I noticed that the anti ventilation plate was like an inch maybe inch and a quarter low from the bottom of the boat. I know most of the jon boats and motors I have had sat like this went fast. My question is with the motor like this and if I get over 30mph with just me and the whole shot being ok when I go test it on ny local lake should I move the motor up or will it be ok as is? I'm only asking because I see some boats,mostly larger boats were it's even with the bottom and most small boats motors I've seen are a little lower. Is this any concern?

 

[Sea Rider]

You need firstly to test combo as it is on flat calm no wind water cond, that's lightly loaded, well trimmed and well deck balanced. Check if having over or aft transom water splashes. Report back findings if you wish.

Happy Boating

 

[boater1234]

Yes,you are correct,I need to see how it planes and handles overall. If I get good performance then I will leave it be.

 

[boater1234]

For peace of mind i took it to my local marina.They told me it will be fine and i would have no issues.He said it's a light boat and a flat bottom so that motor will do just fine.He said the 1.5 inches under the keel won't hurt a thing.He did say if i wanted to push the motor up to make it level with the keel to make me feel better but the performance gained would be so minimal i wouldn't even feel it.He said just go out and fish with it and just adjust the tilt to were you need it and it will be fine he said.I take his word for it as he has never steered me wrong.So that puts my mind at ease a bit.He said most all the small outboards they install on flat bottom jon boats,the anti ventilation plate is usually never level with the keel and is most of the time a inch to an inch and a half under and they never get complaints about boat performance.They said it's perfectly normal.They said if it were inches as in 4 or 5 then you would have issues but one inch is nothing to worry about.

 

[steelespike]

I agree there is no problem. If you were to raise the motor an inch or so it might save you from hitting bottom in the shallows.

 

[boater1234]

So Steelespike you agree with what they said to. They are a great marina here in Florida. He
said the whole effort of un doing what I've done already would be pointless. I clamped the motor down as much as possible,it was difficult to turn the clamps with a wrench and using a towel under it so I didn't mangle the plastic handles and the middle brace in the way,it was a pain to get it extremely tight. I really don't want to raise it an inch or two and have to go through that again,it was a mess. I'm not bolting my motor down that's why I went to the extreme to tighten the clamps down and I put a center safety cable dust in case it did pop off which I doubt it would. It's on so tight the clamps can't be turned anymore. I'm just glad this is no big deal and someone agreed with my marina. Thanks for the reinsurance steelespike.

 

[Sea Rider]

I'll totally disagree on what the techie at the marina said, he's used to sit engines on transoms and voil?. There's an open world out there and the guy just seeing his nose. Depending on engine brand, and HP sitting it correctly will make a night and day boating difference specially running portable engines in which you need to take all those ponies out fast.

How do you think I'm running a 2 stroke portable 18 HP engine on a 450 RIb rated for a 50 HP engine with immpecable hole shot and top performance under any water cond. The answer is best engine/transom height & prop maximization...

Don't give for granted what others theoretically say, must check combo performance under wot trail and adjust engine height if having over or out transom water splashes, which will inevitably slow you down.

Happy Boating

 

[boater1234]

Like I said,I'm going to test for sure first and see were I am with it. If it has tremendous hole shot and awesome wot I'm not messing with it. I know if the motor is performing up to specs,if I need to raise it I most certainly will without hesitation. I will go out soon and gps my speed and how the hole shot is,if like I said it's awesome I will leave it were it is. If I can get near or over 30mph that's plenty fast in a jon boat imo. I'm not going to raise the motor to gain minimal extra mph,like 1 or 2 mph,not worth it to me to tear apart what I did to tighten it down already. It was a pain in the butt.

 

[JimS123]

I'll totally disagree on what the techie at the marina said, he's used to sit engines on transoms and voil?. There's an open world out there and the guy just seeing his nose. Depending on engine brand, and HP sitting it correctly will make a night and day boating difference specially running portable engines in which you need to take all those ponies out fast.

How do you think I'm running a 2 stroke portable 18 HP engine on a 450 RIb rated for a 50 HP engine with immpecable hole shot and top performance under any water cond. The answer is best engine/transom height & prop maximization...

Don't give for granted what others theoretically say, must check combo performance under wot trail and adjust engine height if having over or out transom water splashes, which will inevitably slow you down.

Happy Boating

+1
Dealers are experts to a point, but then again they sell the stuff and don't have the time to experiment or optimize, thus they aren't boaters too. Cav Plate height is a matter of trial end error.

I've mounted quite a few outboards in my time and I can't say I ever had the problems with the clamps like you said you did. Regardless, if the motor has mounting holes you are foolish not to bolt it to the transom. The boat really isn't yours untill you've drilled a few holes in her....

 

[boater1234]

I'm glad I didn't drill holes yet because I may have to raise the motor up if needed. I hand tightened the clamps as much as I could but then I used a wrench to tighten them as much as possible were they wouldn't turn anymore. I will see how it runs,if it runs strong and has great wot,plus great hole shot then there is no reason to mess with it. My manual says to have the anti ventilation plate from even to around a inch below the boat,your a man that prides himself on following the manual as I remember so I'm extremely close to specs. If needed though I will raise a bit. I will test it all out on a flat calm day.

 

[boater1234]

After reading and reading,I've decided to raise the outboard at least an inch by putting a 1x1 piece of wood under the outboard. I'm going to make it as close to even with the keel as possible. Question is will the wood rot out? I'm going to use the clamps for now till I run it and test it out then if it runs good bolt it down.

 

[JimS123]

Don't move it yet. Try it first. Then, repeat with a 3/4" shim. Then, a third time with two shims, and so on. When you hit bad performance, drop down to the next lower position. Chart speed, rpm, time to plane, etc. I also run a performance curve plotting rpm vs. speed. The data will tell you where you need to be. Obviously, you are limited on how high you can go because of clamp position.

I use "One by" oak shims simply because they are a std. 0.75" thickness, and also because OMC's adjustable brackets are in those even increments. Treat them with Flood UV clear and they will last for many years. If you think you might keep the boat for 20+ years and the boat is not garage kept, replace the wood with pvc.

 

[boater1234]

No Title

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.

 

[JimS123]

Being an engineer in an industry that is so competitive that less than the best is not acceptable, I tend to try to get 110% out of my boats. However, in the case of my little outboard tinny fishing boat, I just bolt her on and forget about it.

Just drill a couple of holes, stick in some bolts, go fishing and have fun.

 

[Sea Rider]

Jim,

Touche on Less than the best is not acceptable. In my particular case having just one and only boat and engine love going 101% performance specially running portable engines in which need to take the max HP out of each one for top water performance. Assume Boater 1234 has same one and only boat & engine.

Happy Boating

 

[boater1234]

Well,I went back and looked at the million other jon boats I had to see were the engine was mounted and were the anti ventilation plate was at height wise to the transom. I never really paid attention to were it sat. All of them were at least 1-2 inches if nit a hair more under the keel and all performed extremely great,all had great hole shot and awesome wot speed so maybe this is fine or I'm over thinking it. I will leave it be after rethinking this and test it first. If it performs well I will leave it be,it's not a high performance boat,I need to realize it's a fishing boat to get me hole to hole. If for some reason it performs like crap then I will fix the issue but from everything I gather,fixing the height may only gain me a mph or two which I'm not overly concerned with if it's going over or near 30mph to begin with. Any other info I will take,thanks guys.

 

[MTboatguy]

You are over thinking it, we can all drive ourselves crazy trying to think of things BEFORE we actually test and drive the boat, go plunk into the lake and see how it does, one good thing about it, it is not disposable, so if it does not perform the way you want when you run it on the lake, THEN you can start working on fixes.

 

[Sea Rider]

It's a waste of time asking where's the best engine height. Sit engine flat on transom. Go for a wot spin you alone, with well trimmed combo and weight evenly distributed on deck on flat calm no wind water cond. Once on plane pull your head over transom and check if with over or out water splashes. If none you're at the sweet engine transom height. If with over transom splashes need to shim up the engine till splashes dissapears, if with small out splashes can live with it.

Happy Boating

 

[boater1234]

I'm going to run it and if it performs awesome I'm leaving it alone completely,I'm not going to gripe about being able to gain a mph or two on the performance or if I'm using a hair bit more gas than normal if I moved it up an inch,it would be pointless to do all that to gain so little. Now if it drags and plows and runs slow and terrible hole shot then I fix it. I ran the 20hp efi suzuki and it had unreal balls,serious power for a little motor so I know what to expect from this 25hp suzuki. It should throw me back in my seat if it performs properly.

 

[boater1234]

So I have given this great thought. I'm scratching all these plans to upgrade to the same engine but I'm going to smarten up and get the power tilt and trim and electric start 25hp efi suzuki. It's only $400 more for all that and seems well worth it to me especially when I'm going to keep this boat for many yrs. All the shallow water fishing I do will make me tilt this 136lb outboard up and down all day and eventually kill my back,so I'm going to sell this one and up grade to the full package,makes sense to me,all I need to do is mount this new one on,bolt it down because no need to worry about shims and jack plates as the power tilt and trim will take care of that. I didn't realize how heavy this motor was after pulling it up and down all day,anyone agree with this. I don't have electric start either so that is just a plus.