anti ventilation plate question

[JimS123]

PTT does not impact on the need to have optimal motor height / AV plate position.

 

[boater1234]

I'm realizing that now,I'm going to just leave it as is or upgrade to the power tilt and trim system and electric start because for a few hundred more it's worth it to me even now that I know it won't affect height. The power tilt and trim will at least save my back,lol.

 

[boater1234]

I think my best bet is to get 3 different shims 1/2-3/4-1 inch and see which one gets me right at the keel of the boat,leave that as be,clamp the motor down as much as possible,put my secure cable lock back on,don't think anymore and go fishing and enjoy the boat,that is my plan.

 

[Sea Rider]

Some issues :

-Probably will dial best engine/transom height by just sitting engine on top transom and going for a wot spin with well balanced combo.
-It's important to look out transom to check at which lower leg height is the water splash being produced if any to play with height shims.
-If no water splashes over transom, leave engine sitting there, you're spot on.
-If you vary trim angle in/out 90? will loose best prop grip angle of attack and top HP. (Measurable with GPS and tach)
-If dialing sweet engine/transom height combo will achieve best water performance, top speed and immaculate close tight turns at speed.
-Later can maximize prop if wanting to get all the ponies out of that 25 HP.
-Don't bolt engine to transom prior knowing if will need shims or not.

Happy Boating

 

[boater1234]

This whole thread is mostly about engine height. So why not just do it right and make the av plate dead even with the keel of the boat and be done with it. I think it's established that this motor will run much better with the av plate even with the keel rather than it riding a 1-2 inch below the keel,isn't that correct?

 

[Sea Rider]

Not correct, best engine transom match will depend entirely on engine brand and hull type. A wot test is mandatory to evaluate your set-up first installation, then can go from there optimizing, fine tunning transom height if needed. This post isn't about simple propulsion, were talking about dialing "best propulsioin" for any given engine on any given boat lenght. That's where your boating fun difference starts.

I've seen real stupid boaters modfying transom heights to match per written on engine owner's manual regarding AV plate to be even or around lower keel height without previous testing their combos at open waters. That's the worst stupid out of this world "dry theoretical installation" newbie boaters will tend to go for.

Happy Boating

 

[boater1234]

Well,I'm just going by the hundreds of forums I have searched. I put in google,proper engine height and almost every post and diagram emphasizes to get the av plate as dead even to the keel as possible. It also says if it's a 1/4 inch either way that would be fine. So that is were I'm getting this info from. Lots of guys are riding their engines with the av plate a inch or so under the boat with great results and some over the keel with great results but I won't go over the keel because even know it may never happen I don't want my motor starving for water to over heat or have cavitation on turns. The highest I'm going is dead even or were I am now. All I've heard is if the av plate isn't at least even with the keel it will have unnecessary drag so that would mean less of the lower unit in the water the less drag there will be,isn't this correct?

 

[Sea Rider]

Boater, too much Internet reading, you're drowning already on a small glass of water. Today installed a brand out the box 430 mt boat with a Tohatsu 30 HP engine. Will post this "dry installation" example on a separate thread to show and educate that anticav plate should be even with or around hull bottom is pure BS.

Happy Boating

 

[JimS123]

If I had that much time on my hands I'd be worrying about how the politicians are ruining the country, whether my meager savings will carry me thru retirement, and if the escaped murders in NY are staying in my mountain cabin.

Since I don't, I'll just buy another 30 pack and be satisfied with my 25 Yami mounted "incorrectly" on my tinny, and just go fishin.

As a matter of fact, if it were me I'd trade the jackboat for a deep V. Flat bottoms are not my cup of tee.

 

[boater1234]

Well I hear ya,I care less about politics,I do my best to stay away from that crap,it doesn't matter who runs this country,we're all doomed anyway because they've all retarded in office. That aside I am on disability so I have to much time on my hands to read as you can see. I just never put so much thought into a motor before because I used to just mount them on and go,no looking back. Once you realize you been doing it wrong all these yrs now I kinda think to much. When I get fixated on something I can't just let it go,I have had that issue all my life. I think at this point I'm going to do what I've done the last ten boats,mount it on and go fish and not worry about losing a mph or two because of a little drag,I now know that it won't really hurt anything the way it is and more then likely will fly on my flat bottom jon boat,so I'm mounting it on and going fishing,that is the end of this story,lol.

 

[Sea Rider]

Sit engine on transom and go for a wot spin to your fishing spot, post your results as a refference only. I'll stop being so picky regarding this misunderstood tech matter.

Happy Boating

 

[boater1234]

Sea Rider I was wanting to see how your results came out as well with your new rig,let me know how it runs. Also I understand your trying to help me,I just explained what I have read that's all. There is a cool site called channelblade that explains were the best transom height for an engine. They said standard was 1-2 inches below the keel,for better performance even with the keel,1-4 inches above the keel is for high performance boats. That is what I read. Also says most light flat bottom jon boats usually need the prop a bit deeper so the 1-2 inches under the keel would be sufficient. Right or wrong,who knows. All in all the best way is to lock it down and run it and log wot speed. Also a guy on another forum gave me a great idea if I did need to raise it,make a shim out of a cutting board so it will never rot,I can cut a shim if needed,screw it into the top of the transom and then set the engine on top of it. Plastic cutting boards are hard and strong so it should hold up great if needed.

 

[Sea Rider]

Boater,

If you like to continue about dilaing sweet engine/transom height you're welcomed back. Was ending posting due to saying on your last post that you'll be mounting it on transom and going fishing, that's the end of the story, lol. Post a large side pic of your current middle to lower leg portion to have a look, want to check something.

Happy Boating

 

[Sea Rider]

Dialing best engine/transom height.

Installed this short shaft engine to sit perpendicular to transom, if we look close at picture will see that AV plate is not even with keel (red line) there's a 2 inch gap.



At which lower tail height do you think water flow is passing by at speed, provided that boat is well deck balanced and engine well trimmed as in picture. Which performance would you expect to achieve while testing combo at plane and speed : best, so so, crappy and why ?

Happy Boating

 

[JimS123]

Dialing best engine/transom height.

Installed this short shaft engine to sit perpendicular to transom, if we look close at picture will see that AV plate is not even with keel (red line) there's a 2 inch gap.



At which lower tail height do you think water flow is passing by at speed, provided that boat is well deck balanced and engine well trimmed as in picture. Which performance would you expect to achieve while testing combo at plane and speed : best, so so, crappy and why ?

Happy Boating

Are you anxious to find out the answer, or do you already know and this is a test?

OK, I'll bite.....LOL.

It won't be the best and it won't be crappy, but it will be adequate. It will also be where 99.9% of the boaters (and dealers) will put it because they don't know any better or don't care (except for you and me since we like to experiment)

My guess is with that shallow a V it could be improved by going up , but no more than about 2". I find the deeper the V the higher you can go.

But truly, with that little kicker I don't think the improvement will be dramatic. But then again, since it weighs so little, the time and effort to experiment won't be much either.

 

[Sea Rider]

JimS,

Glad to know that I'm not alone on this misunderstood best engine/transom height crusade. This was a testlike for Boater 123, as the cast on stone reference says that having AV plate even with or slight under keel produces the "best" performance.



Was wondering which type of performance is considered "best" Have already the answer illustrated with pics, will show that what's stated is not a good reference to go for regarding initial dry installations, that's sitting an engine on top transom and thereafter going for a wot spin. If anyone wants to chime in and provide a satisfying answer to this riddle test be my guest. It's just a friendly boating conversation to see how each one addresses things.

Happy Boating

 

[boater1234]

That's about were mine sits,maybe a hair higher then that. Did you happen to test it? If yes how did it peform? I have pics in the beginning of this thread,what did you think by looking at them. I actually took the engine off because I was frustrated. I'm going to move it up a tad with a wood shim for now to around a 1/2-3/4 inch below the keel because I then will run out of room for the clamps. I saw someone on this site who made an awesome transom extender or elevator some would call it. They used two angle pieces with like a inch thick aluminum square tube and bolted it to the transom to raise it to near even with the keel or even a but above. Now once I mount it back on with the shim and if it performs extremely well then I may just leave it as be. My honest answer to that question would of been it ran good because I have never paid any attention to the av plate with all the jon boats and outboards I have ever owned and they all ran as expected,fast and used minor fuel. Every one of my jon boats had the av plate the same 1-2 inches below the keel because I didn't know any better. I still wouldn't know any better now but my curiosity peaked when I said I'm just curious how low the av plate sits under the keel when looking from under the boat in the front,that is when I went on here to question it and now here we are,lol. That about covers how this all started.

 

[boater1234]

I'm going to be mounting the engine back on the boat Thursday with shims. I'm getting a 1/4-1/2-3/4-1 inch thick shims. I'm going to try all 4 to get it the highest possible without losing bite on the clamps. Do you want a picture of my motors whole lower unit up to the water splash guard? I can do that but like I said it's on my stand now and off the boat till Thursday. I just got so frustrated with it. I want to get the height as high as possible because with me,engine and tank in the back that's a load,lol. I plan on having everything else up front,coolers,bait well,all gear to try and shift some of the weight. I'm thinking of putting a heavy wood deck in the front,that will also help with balancing the weight.

 

[Sea Rider]

Water performance results :

-On ideal flat calm no wind water cond : nice overall performance with good prop propulsion at straight water courses at wot or less throttle while maintaining perfect parallel plane to water level.

-On tight close turns on flat calm waters or at straight slight choppy and windy water courses, awfull crappy, "Thumbs Down"

What was found while on its maiden voyage at open sea trail :

That engine sits way high on transom, will need to ideal sit on a 35-36 Cm transom height as opposed to current 40 Cm height which is a tech abberation as you can't possibly fabricate a sib that way when alraeady has huge diam built in tubes that will float hull more out of water, consequently raising engine's lower leg too.

Ideal for that set up to work spot on, would be to dial a transom or engine height for water flow at speed to skim right under upper water deflector plate.




On tight close turns at speed or slight chop prop having less water height to work with, looses best top grip and aerates badly, you can see exposed AV plate at back lower leg which is no bueno. The only possible way to solve this tech flaw would be to chop transom 4-5 Cm down or get an adjustable jackplate and sit engine 2 inches lower and test again. Owner dosen't know about his new sib flaw condition, surely will outcry loudly to heaven...




The water test was conducted on ideal water conditions along sib's max pressure inflated to on all air chambers, engine trimmed perpendicular to water level with state of the art even weight distribution on deck. This engine/transom optimization can be applied to any boat and engine brand, specially tiller driven portable engines to take the max prop grip out of each engine. We've been doing same for the last 7 years with excellent results as we're a boat and engine dealer and dedicated fan boaters as well. Have the knowledge and expertise of both worlds and that's a plus for our customers and anyone out there that would like and want to follow.

Boater, would recommend before doing nada, sit engine on transom and go for a wot spin, will send latter a link you need to follow to the letter if wanting best combo performance.

What I'm trying to school with my posts is that if in pursuit of best combo water performance need to dial a perfect marriage ceremony among engine brand and boat brand with front priest included. Need to DETERMINE firstly if in need going for an engine height optimization, sorry are not issues to assume, think or even ask at boat forums, to each his own water trial test is MANDATORY to solve each own combo's problems.

As I'm always 2 steps ahead, no, trimming engine up or down will not better that situation, as best prop grip will be lost when prop angle of attack is varied from ideal water angle, but that's other theme that works hand in hand with engine height.

Happy Boating

 

[boater1234]

I understood most of that,lol. I also have a totally different boat then what you tested. I'm just going to do what you said Thursday,mount the motor on the transom first. You really don't think I should mount a shim under it yet? Remember I'm a big guy at 300lbs,motor 136lbs and gas say 30lbs so there is close to 500lbs just in the back of the boat so that motor will be sitting deep in the water. I know it will pop on plane with no issues. I do know this motor has unreal torque and will move this boat extremely fast if everything is correct. Like I said before I don't need perfect,I just need were it runs good. Like I posted in my earlier posts I'm realizing it's not a high performance boat,it's just a fishing and pleasure boat. If I can get anywhere near 30+mph out of this set up with me or me and another person I will be I mean extremely happy.


I went with the 25hp for the extra power and to gain a few mph over the 20hp 4stroke suzuki I had which I loved but I also gained 40lbs of weight on the motor going from 97lbs on the 20 compared to 136 on the 25. Big difference in weight. I have no doubt with one or two people the 20 would of moved us really good,in the mid 20s I would guess but It would probably struggle with 3or4 people in the boat. That 20hp was a little powerhouse of an engine. I have given it thought to go back to the 20 due to how light it was and how it performed. My 1436 was a heavy little boat at 200lbs and this boat only weighs in at 290,only 90lbs more but also has a wider bottom for better planning surface on the water so the 20 would be great and use much less fuel,easier to tilt up and down,etc.... so this has also crossed my mind. More then likely there will be no more then two people in the boat,maybe every once in a blue moon three but mostly one or two that's why I've been thinking of going back to the 20hp. I need to give this 25hp a shot first to see how it performs. The back of the boat would also sit a hair bit higher with less weight. I'm also working on me being 125lbs lighter,that would really help to,lol. Ok keep the good info coming,I enjoy reading your information. Ty for the help so far.