ABC Sib-Rib Installation Guidelines.-

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

Sea Rider, I do not believe he is going to answer you. The pictures he posted in post 20 show that he did exactly as you instructed, so what he is arguing about is beyond me.

The anti plash plate in his original motor installation is nearly at the bottom of the transom and all he did was raise the motor until it was in the position you stated it should be in.

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

Frank. I'll gladly answer a question as to opinion on subject. Term exam implies standing authority on particular topic of which of course OP has no knowledge of AKA hydrodynamics. None the less if asked for opinion how I would do it I would like to see free surface of water emerging from under transom passing below gear case flange aka line #3 in illustration above. I would set motor up for water to pass as close as possible to line #4 as long as it doesn't cause engine water starvation or undue performance problems . Later should not be mistaken with inadequate prop selection as usual OEM prop is too slow for our lightweight RIBs/SIBs with properly seated engines.

Frank if as you say I mounted my motor per OPs suggestion ( I fail to see how furthermore they didn't exist a the time). While I argue I mounted it per owner's manual recommendation (pretty clearly). Which OP says I mustn't follow. Yet then it appears you suggest OP follows it himself. ????? Hence we are arguing same thing. Is that your point?

I'm an engineer and have tremendous respect for books. It's a tall order to not follow one. Extraordinary claims you know require extraordinary evidence.

To further help this study I'm ordering this doohickey Atlas Micro Jacker - T-H Marine Supply AHJM-4-DP - iboats

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

You know, I hung around engineers for quite a few years myself and found some of them knowledgeable and some who only could follow what others told them. You have described just what the gentleman explained in his writeup, yet you want to play a question game. Why, I have no earthly idea. In doing so, you mark yourself as a greenhorn.

I spent many years teaching young engineers the difference between school theory and the real world. They did not know the difference between a positive displacement pump and a centrifugal pump which made for some amusing applications. One of them I called boom boom after he busted the casings on two pumps by misapplication. I also was pleased to work with some of the best in the field who knew how to apply their knowledge and were always keen to learn from others. They excelled at their trade and we pulled off some neat things.

You will find that field experience beats book theory hands down in a pinch. I saved industry a mint of money repairing installations done by people who thought they understood the theory but did not know how to apply it.

That "dohicky" will set back the motor and allow all sorts of discoveries for you. Have fun.

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

You know, I hung around engineers for quite a few years myself and found some of them knowledgeable and some who only could follow what others told them. You have described just what the gentleman explained in his writeup, yet you want to play a question game. Why, I have no earthly idea. In doing so, you mark yourself as a greenhorn.

I spent many years teaching young engineers the difference between school theory and the real world. They did not know the difference between a positive displacement pump and a centrifugal pump which made for some amusing applications. One of them I called boom boom after he busted the casings on two pumps by misapplication. I also was pleased to work with some of the best in the field who knew how to apply their knowledge and were always keen to learn from others. They excelled at their trade and we pulled off some neat things.

You will find that field experience beats book theory hands down in a pinch. I saved industry a mint of money repairing installations done by people who thought they understood the theory but did not know how to apply it.

That "dohicky" will set back the motor and allow all sorts of discoveries for you. Have fun.

Frank you seem to be kin on judging my knowledge and character remotely as well as calling me names when I only expressed my honest disagreement with particular post based on my understanding of this issue and reading subject text. If I misread OP then it was honest mistake. Yet you and OP dismiss everything I present as nonsense instead of simply saying: "that's exactly what I(we) said".

Still when I give acceptable (to you) solution to subject question base on knowledge gained from sources dimmed inadmissible by you and OP you say it matches write up exactly. That does not make sense.

I pretty sure that doohickey will deliver to my expectations I don't expect any surprising discoveries.

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

What you did was exactly what the gentleman said, but for some reason you don't seem to grasp that. I tried to get you to read what was said with an open mind, but for some reason you questioned illustrations without understanding what the implications were.

It is interesting that you used kin for keen and dimmed instead of deemed.

No one said that the text book was wrong, but note that the book does not even take the anti-splash plate into consideration. It certainly does not explain the difference in the lower leg shape above the anti-splash plate, but the OP gave a good explanation of the effect the shape has. He put much thought into helping others with questions regarding mounting their motors.

 

[Sea Rider]

Re: ABC Sib-Rib Installation Guidelines.-

Ribrider,

On first answer you have won + 50 credits, on second answer + flunky 5 credits, definitely need to go for summer boating school. Will respond with proven tech facts both given theoretical answers :

-If water flow passes at speed right through AKA 3, you are right in middle DF and AV plate, this setting will give slight back water splashes due to water climbing through cutting edge and banging against under DF plate and out towards middle wake, can live with it, works fine on flat calm, no windy waters, probably will experiment some prop aeration on extremely choppy waters and at very close turns at speed.-

-If passing through AKA 4 which is definitely your favorite cast on stone, go by the manual brain setting will achieve best prop thrust loss, poor hole shot, excessive aeration on all water conditions and worst scenario at close tight turns, due to prop not having the sufficient amount of surrounding water for blades to bite water efficiently. It's like swimming with your fingers and not your hand fully in.-

To have it clear, it doesn't matter if lower leg sits at 1,2, 3,4 setting as in example as long you do not pass from boring idle or fast displacement speed, as soon you hit the throttle to plane all your problems in less or more degree will automatic start. You really don't know what you're talking about when saying that all OEM factory delivered props must be changed, wrong OEM props with engine well height seated fully delivers max wot factory stated parameters when powering light sibs and ribs. How could have obtained 5800 rpm on a light 380 sib and 5780 rpm on a light 430 rib with just a 18 HP horse. Check posted pics. I'm solo running at 98% of the max 5800 rpm factory stated for that engine. If your current engine does not rev near the peak, it has an issue or probably to poor HP performer for your Milpro size sib.-

You don’t need to be a Harvard PHD Scientist to understand how attack edge cuts water flow as a cheese, it’s just common sense. To clarify, what stated is that in order to have the least lower leg drag and top rpm at wot, water flow must hit AV while it's maintained parallel to sea level and therefore attack edge at 90? as well, there’s your Swiss cheese perfectly cut assuming Oceans are big cheeses. You seem to be mixing and confusing air and water behaviors, to each his own. Bear in mind that water is 10 times denser that air, what works with air will not work as expected on water and vice versa. probably you’re a hell of an Engineer for complicated things but still in nappies doing first steps at boating.-

You’ve Quoted “Extraordinary claims you know require extraordinary evidence” That I know I’m not claiming anything, just stating tech facts well proven under top water conditions and environments which you like to ignore giving pure Mars un proven theory. What's posted won’t be found on any Owner’s Manual, Reputed Engine Dealers, Wilkpedia not even Wikileaks, if wanting to apply them to your set up, be my guest, if not, go on your own experimenting, buy micro jacks a full bag of props, test and re test and have a hell of a engineering time.-

Another OP quote "Yet you and OP dismiss everything I present as nonsense instead of simply saying: "that's exactly what I(we) said". Sorry, we are going in opposite directions, you're heading south I'm heading north. You're the one that is bashing and deeming my proven tech facts with theory.-

Fbpooler, yes, you are darn right, Ribrider is completely ignoring posted proven pics. Hey, we're discussing engines/boat isses, not UFO issues-

Happy Boating

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

Level 4 with power trim would be a disaster. The second you start to trim out, bad things would happen. Likewise, bumpy seas would cause problems.

You also should consider cupping of the prop which also adds to the mix which affects water flow through the prop. There are factors to be concerned about just as important as the amount of lower unit in the water. Trying for maximum speed in flat water is fine, but that ignores water conditions common to boating.

On our 14 ft fiberglass, I tried different mounting heights and trims. For a 1 MPH gain in speed, the motor was set too high for average water conditions. Giving up 1 MPH made for a dependable installation capable of bumpy water boating and sharp turns. Experience works.

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

It is interesting that you used kin for keen and dimmed instead of deemed.

Using grammar as an argument in technical discussion is interesting too. Yes English is my second language just like OP.

No one said that the text book was wrong, but note that the book does not even take the anti-splash plate into consideration. It certainly does not explain the difference in the lower leg shape above the anti-splash plate, but the OP gave a good explanation of the effect the shape has. He put much thought into helping others with questions regarding mounting their motors.

DF plate is secondary device it will act naturally as intended if motor seated correctly for optimum performance. You don't have to worry about its function when motor is at correct height. AV plate is simply frame of reference to determine position of motor relative to boat. Relative position between motor and boat determines water flows around motor leg/gear case. Those in it's order determine drag, prop efficiency, splashes and whatever else is discussed here.

Outboard manufactures place DF plate as such that motor positioned for optimum efficiency will deliver least splashes.

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

We seem to all have trouble reading. Nowhere I've said I must be at level 4. I say it should be as close as possible to level 4 without affecting performance.
Even if you position AV plate level with hull it doesn't mean water will flow at this level. As boat moves forward it displaces water that closes-in raises behind transom. It's not level with free-standing water. Flow around AV plate will depend on relative position of leg to transom. Short shaft motor will be closer if you remember geometry and has to be positioned marginally lower (in relation of keel to AV plate). When I mount jaker plate I should be able to raise motor even higher because surface will be much close to natural level around boat.

With my OEM 10" prop I hit rev limiter going in straight line just past 2/3-3/4 of throttle in my current setup at 5500 rpm (I have a tach too) reaching 21.5-22 mph with motor at neutral trim (AV plate horizontal to water surface). 4.7m, 140-150 kg hull with 220 kg load and 72 kg motor. WOT range is 4500-5500 for Suzuki. That indicates 12% slip which is very reasonable for given conditions. Meaning it runs pretty efficiently without any significant aeration/cavitation. There is no ventilation no problem going over quite substantial chop. Clearly this prop doesn't allow me to use my motor to full potential.

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

Hitting the rev limiter throws calculations regarding horsepower developed out the window. Do you have a power curve for that engine?

The bottom line is that someone spent time trying to explain to new boaters how to best mount an engine, and you immediately began trying to pick apart his conclusions. Due to inexperience, you were in over your head when you started this mess and failed miserably. I would be hard pressed to accept any of your conclusions regarding boats.

 

[Sea Rider]

Re: ABC Sib-Rib Installation Guidelines.-

Ribrider, frankly don't get it, if your sib/engine combo is working at near right for you, what's the point to keep on contaminating this thread that hoped to remain as clean as possible, you should have posted a personal thread and not gracefully hijack mine to start with.

To finish this edless discussion at least on my part and assume Fbpooler too, will say that once you finally install the mini jack you've ordered and start playing with leg heights on flat calm waters, well trimmed engine and sib properly balanced will know what I'm talking about throughout the entire whole post. Gee, If at boxing you throw the towel, at boating will be in need to throw my rib/engine into the blue.....

Happy Boating

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

Motor is rated for 25 hp at 5300. Nothing is thrown anywhere. Gasoline engines are regulated by amount of air they consume by virtue of restricting air flow using throttle plate. If you don't have to open throttle all the way to reach max RPM then there is spare capacity. With 13" pitch prop I max out at 5000 RPM at 25 mph. I need to drop a pitch to 12", possibly to 4 blade to stay on top of RPMS (speed will though be about same). Or find better made prop. My OEM 10" pitch prop looks and feels much more refined than 13" Hustler. With better prop I should be able to get closer to theoretical 28-29 mph.

It's an open forum so it many not stay unpolluted. One of things I'd like to see in guidelines is example (picture) of optimum installation.

Truth to be said I'm not getting jack plate to experiment though it will be much easier but rather would like to make my life easier trolling shallow channels. My favorite launch spot gets very shallow by the end of summer. Raising motor at slow speeds is much more favorable to trimming out in my book. I don't have power trim anyway.

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

SibRider, why don't you open a thread on propellers.

Taking pot shots at another poster is rude, but asking for advice on a problem or discussion you would like to have might be helpful to you.

If you go through the pictures referenced by Sea Rider, you may see just what you are asking for.

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

The only possible picture I see is one I've complained about. There is one showing deflector plate in action. Nice but doesn't tell me how high/low motor is, just nice result. Rest of them show motor positioned on top of transom that doesn't tell me much about relative position of leg and keel. I might be blind of course or maybe my computer doesn't show it.

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

SIBRider, maybe you don't understand, but we have lost patience with your trying to argue mounting height when it was explained quite well. Check out post 25 and you should see the pictures you ask for. Your posts on this thread show an example of a web troll rather than someone looking for understanding.

I am sure the OP would bend over backwards to help someone with a real question as he does quite often, but when it reaches the troll stage, no one has any patience.

 

[Sea Rider]

Re: ABC Sib-Rib Installation Guidelines.-

Sibrider,

Almost flipped my PC rocking chair while laughing out loud on your latest posts, you can drive cracy anyone. Do you have an issue with English being your second language. The overall purpose of the whole thread was to get the max prop thrust, rpm, speed out of a portable size engine without changing original OEM prop and that's at speed or wot cruising where you have the most fun out of your boating combo. Taking Grandma out at idle or displacement speed is other story...

Now you come up with that going for a mini jack is not the way to go, now you like shallow water boating, a mini jack was the way to go for all type of boating, shallow, deep, skiing, pulling tubes. Thread contamination means posting issues that ddoesn't apply when it has previously been throughout the entire post. If you need to discuss my post technically speakig with proven facts as opossed to plain theory of yours, be my guest.-

I'm a boating maniac and perfectionist sharing proven tech facts that's been corroborated after extensive testing under trial and error for quite awhile. I'm real happy with end results as like boating all year long on all types of water conditions burning the least amount of E8 as possible while having extended fun. Tech conclusions are being offered here as a short cut to installing engines on inflatables. This link resumes all about upper DF plate work extensively mentioned which you don't understand :

Tohatsu 20hp w/ 3/4" shim and proper trim - YouTube

The video correesponds to a poster who contacted me having splash issues over transon, before posting end results water flow was hitting aboce DF plate which made the over transom splah along excessive tail drag, gave same posted directions, made height, trim and ballance corrections and now boating happily ever since at nice plane as seen on video which is not an inflatable boat. That speed and perfect plane corresponds to sligh passing middle throttle due to engine was undergoing break in period process. You can't resume perfect engine istallation in just one pic, need many as all are tech related in between them, that?s why is a ABCDE..guideline process.-

Engine height optimization works on most boats with not too complicated hull designs with any brand engine as all of them have DP and AV plates...

Happy Boating

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

Almost flipped my PC rocking chair while laughing out loud on your latest posts, you can drive cracy anyone. Do you have an issue with English being your second language.

Is that rhetorical question?

What's with love affair with OEM prop? Why not maximize boat/motor performance at small expense if motor allows it? Maybe not cheap as dirt but sure replacement props are not particularly expensive. Installation doesn't get any more simple either.
Our friend fbpooler seems to have one for every occasion.

 

[Sea Rider]

Re: ABC Sib-Rib Installation Guidelines.-

If you don't install a induction tach on your engine, have a wot spin to check max achieved rpm with you alone it's a very stupid way of dampening money into the blue buying other prop pitch blindlless. OEM factory delivered prop is a medium pitch prop that works quite well on most light applications. If you need to carry a whole family or move a loaded boat will need to change prop for rpm optimization for engine to work inside safe parameters at ideal near max rpm stated parameters when running wot. It's good to count with a extra prop for different boating aplications, skiing, pulling tubes, you name it.

Fpooler seems to have props well dialed that suits him best for different applications. The issue is not if engine allows as different size/ pitch props will always be allowed to be installed, would say if needed, if already at top rpm with light load, there's nothing to maximize any more, unless it's for a different application as stated above.

Happy Boating

 

[SIBRider]

Re: ABC Sib-Rib Installation Guidelines.-

There is something we agree on. :watermelon:

 

[fbpooler]

Re: ABC Sib-Rib Installation Guidelines.-

I like to maximize performance of my motors and make sure the engine is never overloaded. The effect of the load and sea conditions may make one prop a better selection than another, and there is a big difference when we are talking small boats at times.

Generally speaking, a properly sized standard prop does a good job for a variety of conditions. Changing props without tach readings is just gambling.

In addition to pitch, cupping or other features can make a pretty fair difference at times. Blade thickness and shape are other factors to consider. These factors are generally addressed by the motor manufacturers before they settle on a prop for their motor. The hub must fit the lower unit also, so changing props can lead to problems in this area.

Years ago, 11 in pitch non cupped props were standard on 18 HP Evinrudes, but they changed to a 10 1/2 in pitch prop with a slight cup (single cup) which ran rings around the old standard 11 in pitch on a variety of boats. In speed difference, it was only a few MPH.

The larger the horsepower, the more change you will find with aftermarket props. Don't expect to find an extra 5 MPH with the mid range motors you have on your inflatables. I believe you said something like 13% slip on your hull which is not bad at all for an inflatable hull.

In playing with transom height with a 15 HP motor on a 14 ft fiberglass, raising the motor until it was maxed out, we gained 1 MPH. In rough water, it ventilated like the dickens. Dropping it back down on the transom made for a more user friendly rig, especially when the waves picked up.

As you should know, engineering is not an exact science but depends on theory. Some times you shut off the computer with standards loaded and find answers much different that what the theory would indicate. The only real way to find your limits is with field experience. Switching to SST props with varying degrees of cups or number of blades is an expensive game. When you realize that the gain will probably be only a few MPH, the value received for your money is disappointing.

Tests run by manufacturers enable a cross section of props to be tried which would be very expensive for you and I, so what they come up with is generally a hard project to improve on. Pick a standard prop using a tach to determine proper pitch and you are probably as close to ideal as you need. Don't expect a 1 in difference in transom height to turn a turtle into a hare.

You would probably be best served by installing power trim on your motor.