why do people cut down their 20" motors?

[pcrussell50]

i've been hanging around the allison scene, [in the cyber sense, as afaict, there are none here in socal]. every so often, i read about someone who cuts his motor down from a 20" to a 15". this seems odd to me for a full sized boat like an allison. only thing i can think of is, maybe less wind resistance off the cowl when you are full-tilt with the jack plate way up?

did i guess right?

-peter

[Riverratt]

Lower center of gravity for better handling

[JWTjr.]

it looks cooler.

Lower CG is good theory, but it really doesn't do a whole lot in practice.

John

[roostertailn826]

relieves stress on transom, and what john said way cooler looking

[paul folks]

all of the above plus it looks cool as s**t

[paul folks]

but you know what looks better then a 15"???






a 12"

[pcrussell50]

lol. i'm glad i'm new to all this and don't yet know what looks cool and what doesn't. cutting down a center section and getting new drive and shift shafts and water tubes and all sounds kind of expensive to do mainly for looks. watch in a few years, i'll be doing the same thing... and telling/lying to my wife about how much better the boat will handle for the cost. :)

-peter

[PropWash]

Cut down mid sections are often used in racing because it does make a difference to handling (some would argue the difference is small, others will disagree).

A cut mid is the sort of modification you do after you already spent a years salary on propellors looking for that extra 0.5mph.

It looks cool because it says "I'm serious about going fast - I'm looking for every advantage I can get".

[paul folks]

i know when i 1st put my mirage river racer together w/ a 20" motor then did sum mods to the motor got a prop worked 4 the boat i switched 2 a 15" motor and gained 3mph on gps and made boat handle 10 better due to the fact i could get the mot 1 1/4" above the pad rather then 1/4"

[PORT]

I am in the process of doing it now. I run real high on my 21 Skater and need to relieve the stress on the top of transom before it rips. Time will tell

[afr]

there ya go three reasons
cg / prop height and stress

[pyro]

...and reducing aerodynamic drag from the motor itself...

[99fxst99]

How is the driveshaft shortened, or can you buy the shortened shaft?

[afr]

...and reducing aerodynamic drag from the motor itself...
yea and this one so four reasons
unless you have one of my cowls :D

[propmanjay]

The factory 15" is much stronger than the fishing mid. The 15" weighs more than the fishing 20." I have "Bat Turned" my Ally in the high 90s and was glad for the low CG.

[rock]

If you are switching to a 15" factory mid as opposed to cutting one down you also gain 2" setback. I run all 15" stuff and I like the way the boats handle much better.
Rock

[clamponracing]

Don't get me wrong a 15in mid looks sweet but i kinda like the old school look a
20in merc jacked sky high it scares the crap out of the car motor guy's :D

[Matt Gent]

Length of midsection has no effect whatsoever on the stress the transom sees. The extra 2" setback of the factory 15" would actually make it worse.

[P man]

Length of midsection has no effect whatsoever on the stress the transom sees. The extra 2" setback of the factory 15" would actually make it worse.

x2 on that

How much does a 15" mid weight as compared to a 20" single ram bass mid?
I guess a cut 20 would save a few lbs from a stock 15"

[paul folks]

i know my factory 15" can on a cut down 20" bracket is lighter then the factory 20" seen it on the scales not much but was lighter.... motor tucks up nice on the rear race cowl instead of sticking 10' above it was able 2 get motor 1" higher and also bolt 2 hole lower on the jack plate instead of the bottom hole on the bracket so less stress there also and as i said i did see a gain in speeds on top end hole shot was better able to turn a bigger (30p instead of 28p) and it stoped hoping @ 70-75 mph again this was on a 01' mirage river racer w/ a 2.4 200...

[hydroholic]

Handles better on the Vector with a 15" mid ,gained a little speed on top, probably due to the better handling. Has a much narrower range that it porposes in and is a little better out of the hole. And YES , looks cool as hell!:thumbsup:

[Frank Molé]

Don't get me wrong a 15in mid looks sweet but i kinda like the old school look a
20in merc jacked sky high it scares the crap out of the car motor guy's :D

me too :thumbsup: :eek: :cheers:

http://i200.photobucket.com/albums/aa158/frankmole/newmidshots001.jpg

http://i200.photobucket.com/albums/aa158/frankmole/boatshots006-1.jpg

[85allison]

I know when I went fro a 20" mid to a 15" cut down mid on my old Allison XST it gave me a huge increase in speed and handling. And on my XB2002 I cant see why I would ever try a 20" motor on it. 15" is the only way to go!!

[Riverratt]

Length of midsection has no effect whatsoever on the stress the transom sees. The extra 2" setback of the factory 15" would actually make it worse.

I don't see how it would not put more stress on the transom with a 20" over a 15". Look at the pictures that Frank posted and look at how much leverage the motor has when the jackplate is raised all the way up compared to if you had a 15" you could lower the jackplate keeping the stress centered.

[baja200merk]

My speed increase was minimal but i did notice it handled a little better. It looks way, way better then a 20in!

[tunnels]

Length of midsection has no effect whatsoever on the stress the transom sees. The extra 2" setback of the factory 15" would actually make it worse.


"Length of midsection has no effect whatsoever on the stress the transom sees"

wow you've never heard of the effects of short and long levers ??
So your saying a 15 " and and 25 " put the same amount of stress on the transom !!! :confused:
Depends how you interpiting the word stress i surpose !.
They are both pushing the boat through the water the same but the 25 " is wanting to twist the transom a lot more than the 15" is , 10inchs makes a huge differance ! :eek:

[Rigaud]

"Length of midsection has no effect whatsoever on the stress the transom sees"

wow you've never heard of the effects of short and long levers ??
So your saying a 15 " and and 25 " put the same amount of stress on the transom !!! :confused:
Depends how you interpiting the word stress i surpose !.
They are both pushing the boat through the water the same but the 25 " is wanting to twist the transom a lot more than the 15" is , 10inchs makes a huge differance ! :eek:

I agree 100%, same as using a pipe on a rachet for easier leverage. But they are mentioning cutting from 20" to 15" by the way

[DavidW]

If you run both of the prop shafts at the same height and one is just jacked up more with a jack plate to put the prop shaft in the same place as the shorter motor, and the jack plate bolts into the same spot on the transom your lever is no longer. You are not stressing the transom more with the longer mid. The clamp bracket and jack plate are being stressed more with the longer mid but not the transom.

I am not bashing short mids, their advantages are many . I have a 16" mid on my OMC that powers my action so I know. Just think about it . Your bolts are still the same distance from the prop shaft in both cases

Now, a longer mid mounted on a taller transom that is designed for a long mid does have more stress on it because in this case the lever is longer

[havingfun2]

you've never heard of the effects of short and long levers ??

On a hydrostream V I have been wondering the same idea, but from a side to side versus forward and back motion.
<O:p
To keep them on the pad, one needs to corrective steer..correct?
What is the effect of a lets say a 200 pound power head and the side to side momentum it has when one shortens this stroke by 4 to 5 inches?
<O:p
Basically the linear centre of balance on the whole outboard itself.
<O:p
I’ve not tested or weighed. it would be a good experiment, but I’m sure the final answer would depend on spefics like power head and lowers..even prop weight.
<O:p
<O:p

[PORT]

The powerhead is lowered while the prop shaft will be at the same height as before, which = less stress.

[DavidW]

On a hydrostream V I have been wondering the same idea, but from a side to side versus forward and back motion.
<O:p
To keep them on the pad, one needs to corrective steer..correct?
What is the effect of a lets say a 200 pound power head and the side to side momentum it has when one shortens this stroke by 4 to 5 inches?
<O:p
Basically the linear centre of balance on the whole outboard itself.
<O:p
I’ve not tested or weighed. it would be a good experiment, but I’m sure the final answer would depend on spefics like power head and lowers..even prop weight.
<O:p
<O:p
This is one reason the shorter mid is better

[DavidW]

Years ago I had a checkmate v-mate copy that had a 6 inch wide pad. I ran a 200 with both a 15 and 20 mid. Everything else the same the 15 handled much better and the boat was faster because it was easier to control.

[StratosVT]

i've been hanging around the allison scene, [in the cyber sense, as afaict, there are none here in socal]. every so often, i read about someone who cuts his motor down from a 20" to a 15".

People cut them because they don't want to spend the money to buy a 15 incher!

Reasons people would want a 15" mid:
1. Pimp factor
2. Better handling
3. Cable steering wings line up correctly and steering works correctly

That being said, cutting one down is not going to make it equal to a factory 15"er. The factory deal has heavy duty clamp bracket and you don't have to worry about welds breaking.

[AnthonySS]

IMHO - I am still a BIG fan of 20" motors. I have never been a fan of how the water can look like it's swamping the powerhead coming-off plane and find it difficult to remove the cowl when you are on the water with the SS and a chopped transom (maybe I am too old to bend down that far :) ). I also find it easier to read what the engine is doing when you do a shoulder glance at it (its more visible) Plus i think it sounds way rauchy-r with the plenum sucking air at ear level :)

I think a well set-up boat with a 20" also handles very well and goes very fast.

? - Is the replacement rate of the water pump higher on SS motors or is the tuner shorter and exhaust diffused differently on a SS?

[Frank Molé]

IMHO - I am still a BIG fan of 20" motors. I have never been a fan of how the water can look like it's swamping the powerhead coming-off plane and find it difficult to remove the cowl when you are on the water with the SS and a chopped transom. I also find it easier to read what the engine is doing when you do a shoulder glance at it (its more visible) Plus i think it sounds way rauchy-r with the plenum sucking air at ear level :)

I think a well set-up boat with a 20" also handles very well and goes very fast.

i also think they wont trim up as far....................:cheers:

[AnthonySS]

yes good point Frank...BTW - your transom photo is the look that I think is VERY cool :) ...

[AnthonySS]

A few more for you Frank (Old School) :)

[clamponracing]

A few more for you Frank (Old School) :)
Totaly cool :thumbsup:

[Frank Molé]

A few more for you Frank (Old School) :)

THE MONSTER :thumbsup:...and THANKS..................

[clamponracing]

Now for the all out drag boat i would say the 15 is the ticket definetly if you got pulley steering
and wing plates. But think about it this way Glenn Reynolds set the v bottom speed
record 129mph :eek: with a 20in mid. I would say that alli had to handle fairly good to reach those kinda speeds .

[Frank Molé]

i get mine over 100 ok :thumbsup:

http://i200.photobucket.com/albums/aa158/frankmole/shaunsfastshot.jpg

[clamponracing]

Thats a sweet lookin stream :thumbsup: :cheers:

[Frank Molé]

Thats a sweet lookin stream :thumbsup: :cheers:

thanks :thumbsup:

[Matt Gent]

I agree on the side-to-side loads, but this is negligible compared to the fore/aft and up/down loads. Maybe my statement was a little strong but nobody has ever failed a transom from side loads.

Six pack of your favorite beer to the first person who can draw me a free body diagram showing that a short mid lowers the load on the transom.

[Matt Gent]

wow you've never heard of the effects of short and long levers ??
So your saying a 15 " and and 25 " put the same amount of stress on the transom !!! :confused:
Depends how you interpiting the word stress i surpose !.
They are both pushing the boat through the water the same but the 25 " is wanting to twist the transom a lot more than the 15" is , 10inchs makes a huge differance ! :eek:

Nope. Two major loads on the transom, moment from the weight of the engine * the setback to the engine Cg, and moment of the prop thrust * propshaft height relative to transom. Neither is a function of shaft length.

Again, draw me a free body diagram and I'll send you your favorite beer.

[Matt Gent]

BTW given that I still want a 15" mid for the Vandal. First, they look cool. Second, I think I can get the propshaft height I need without a jackplate, and I want to minimize setback. Need to measure someone's 15" motor to be sure.

[Jon50]

ronnie did a beautiful 15 on my vking nd it handles much better

[roostertailn826]

A 15" mid does reduce stress on a transom when a 20" leg motor is jacked up it puts more stress on the upper part of the transom due to the mounting brackets not distributing the forces of the motor equally as designed. It also puts stress on the mounting brackets as well because there is less surface contact. On a 15" inch mid one only has to raise the motor a little to get the same engine height. This allows for very even weight and force distribution on the transom and clamp brackets. Just my $.02

[AnthonySS]

Don't forget that some performance hulls had thier transoms designed around 20" motors thus distributing all loads well and setting the motor at the optimum hieght for optimum performance without the use of a jack plate. Typically the factory transom height was in the 24-27" range as opposed to the 21-22" range.

[Ted Stryker]

The physics of a 20" vs. 15" lever is correct, but the theory application in this particular subject is incorrect... The leverage is applied according to how far Your prop shaft is from Your jackplate's true height center, period... The physics of a using a longer wrench is correct when talking about wrenches, because the force on the lever is moving farther away from the pivot... When talking about outboards, the distance from the force(propshaft) to the pivot(height center of jackplate) remains the same... If 20" mid applied torque the way that many have miscalculated, then a 20" mid set at the same shaft height as a 15" mid would give more bow lift -- it doesn't... Also if this were true then a 15" would also be noticeably faster everytime, because it would transfer more pressure parallel to the water, instead of wasting torque in a twisting motion, also false...

A previous post that got it right --


If you run both of the prop shafts at the same height and one is just jacked up more with a jack plate to put the prop shaft in the same place as the shorter motor, and the jack plate bolts into the same spot on the transom your lever is no longer. You are not stressing the transom more with the longer mid. The clamp bracket and jack plate are being stressed more with the longer mid but not the transom.

I am not bashing short mids, their advantages are many . I have a 16" mid on my OMC that powers my action so I know. Just think about it . Your bolts are still the same distance from the prop shaft in both cases

Now, a longer mid mounted on a taller transom that is designed for a long mid does have more stress on it because in this case the lever is longer

[havingfun2]

The leverage is applied according to how far Your prop shaft is from Your jackplate's true height center, period
<O:p
I’m not an expert on this, just personally thinking about it.<O:p
My thoughts are true center is the center of the bolt holes in the transom as this is where the contact or transfer of energy is applied to the hull.<O:p
<O:p
Agreed, when one lifts a jack to replicate a prop shaft height I believe the forces between the prop and the centre of the transom holes would be the same.<O:p
From a center of balance point of view, the next variable is the center of the transom holes to the top of power head/ cowling.<O:p
<O:p
Above this center line, the balance would change based on how high the power head needed to be.

[tunnels]

When talking about outboards, the distance from the force(propshaft) to the pivot(height center of jackplate) remains the same.
What i cant gather from all this is the centre of the prop should still stay the same height from the bottom of the boat YES OR NO ?:(
and because you have cut 5 inches out of the mid section the bolt holes stay the same ?? the pivot point cant be the same !!:eek: because you have cut 5 inches out of the mid section and lowered the overall height of the outboard by 5 inchs !! and in doing so you have bought the bracket on the outboard 5 inchs closer to the propshaft , so your theory of levers being the same goes out the window !!:p

(propshaft) to the pivot(height center of jackplate) remains the same. This is very missleading because in fact you have lowered the upper section of the ouboard down ! Right ? :cool:
so if you dont have a jacking plate this theory is all a waste of time ?? :confused:
But what about the 5 inchs of scrap metal i have laying on the floor with all the shavings and expense , how do i account for that ?? :nonod:

[Matt Gent]

A 15" mid does reduce stress on a transom when a 20" leg motor is jacked up it puts more stress on the upper part of the transom due to the mounting brackets not distributing the forces of the motor equally as designed.

The BIA pattern remains the same, and the clamp is much more stiff than the transom. I'd argue they are equivalent.

Either way this is a moot point since you can't raise or lower the engine 5" on the mounting bolts to get to the same ideal prop shaft height. You can only have this discussion apples-apples if the engine is mounted on a jackplate.

[Matt Gent]

What i cant gather from all this is the centre of the prop should still stay the same height from the bottom of the boat YES OR NO

The ideal/target propshaft height is the same regardless of engine shaft lengh. In other words, YES.

So the powerhead is lower, and the tilt pin is lower. None of this has an effect on the loads seen by the transom.

Engine weight, engine setback, thrust, and propshaft height (to the bottom of the boat) are the significant factors in transom loading.

[Ted Stryker]

Don't forget the fact that the bottom mounts do the pushing and there distance from the jackplate height center remains the same in this discussion... It's their distance in height from the jackplate center that effects the twisting motion... Maybe I can try it this way -- You say that the torque applied to the upper mounts increases when their distance from the propshaft increases, hey Your right... To go further remember that this given increased torque has to also TRAVEL THAT SAME 5" EXTRA DISTANCE DOWNWARD to apply itself to the jackplate... This same extra 5" downward that it must travel negates the increase that happen on the way up... Another example, abstract but the same priciple... Get Yourself in a push up position with Your hands (jackplate) on a bathroom scale... Take note of the weight in Kilo's when Your arms are extended straight... Now begin to lower Yourself, this will move You elbows (upper mounts) further from you pectorals (propshaft) to replicate a 20" mid... The weight on the scale will not change because the relation between the Your palms and body didn't change... At the end of the day the pivot piont is where the force is applied to the hull (bathroom scale)...

[tunnels]

The ideal/target propshaft height is the same regardless of engine shaft lengh. In other words, YES.

So the powerhead is lower, and the tilt pin is lower. None of this has an effect on the loads seen by the transom.

Engine weight, engine setback, thrust, and propshaft height (to the bottom of the boat) are the significant factors in transom loading.

Answer being that if you chop 5 inchs out of your mid section you have to lower the motor that amount by using a jacking plate ! Right ? so only advantages are , it looks cool ,even sitting on the trailer and lowered the centre of gravity plus has destressed your tramson a little plus lightened you wallet in the process !:thumbsup:

[tunnels]

Something that never ceases to amaze me is in all the fast boats or any boats i have seen , Theres never any form of Fairing between the aft end of the cowling between the boat and the motor cover ! Like just a big gap !! Even the boats cowling never leads into the engine cover properly .
Guys are so obsessed with trying to gain that little extra advantage from anything but this is never given any thought to . Yes i now you have to work on the motor and get in that area .:rolleyes:

What about aerodynamicly designed engine covers ?? :confused:
less wind resistance less drag ????

[tunnels]

Don't forget the fact that the bottom mounts do the pushing and there distance from the jackplate height center remains the same in this discussion... It's their distance in height from the jackplate center that effects the twisting motion... Maybe I can try it this way -- You say that the torque applied to the upper mounts increases when their distance from the propshaft increases, hey Your right... To go further remember that this given increased torque has to also TRAVEL THAT SAME 5" EXTRA DISTANCE DOWNWARD to apply itself to the jackplate... This same extra 5" downward that it must travel negates the increase that happen on the way up... Another example, abstract but the same priciple... Get Yourself in a push up position with Your hands (jackplate) on a bathroom scale... Take note of the weight in Kilo's when Your arms are extended straight... Now begin to lower Yourself, this will move You elbows (upper mounts) further from you pectorals (propshaft) to replicate a 20" mid... The weight on the scale will not change because the relation between the Your palms and body didn't change... At the end of the day the pivot piont is where the force is applied to the hull (bathroom scale)...

You are completely missing the point of all of this ! while doing your push ups You need to move your toes 5 inchs closer to your hands and the scales and then try the same thing again !!!:confused:

[Ted Stryker]

Something that never ceases to amaze me is in all the fast boats or any boats i have seen , Theres never any form of Fairing between the aft end of the cowling between the boat and the motor cover ! Like just a big gap !! Even the boats cowling never leads into the engine cover properly .
Guys are so obsessed with trying to gain that little extra advantage from anything but this is never given any thought to . Yes i now you have to work on the motor and get in that area .:rolleyes:

What about aerodynamicly designed engine covers ?? :confused:
less wind resistance less drag ????

STV, Mirage's, Allison, Quartershot, F1, Triads, etc, all offer boats will these fairing... Whatever distance is left between the fairing and cowling is to aid in the engines breathing to the front of the manifold... BTW, re-read Matt Gents post..

[Ted Stryker]

You are completely missing the point of all of this ! while doing your push ups You need to move your toes 5 inchs closer to your hands and the scales and then try the same thing again !!!:confused:

Oh man, where to go from here... The toes have zero to do with this... Try standing on the scale and squating down

-body weight = propshaft
-knees = tilt pin
-femur and tibia/fibia = midsection
-feet = jackplate

[tunnels]

Oh man, where to go from here... The toes have zero to do with this... Try standing on the scale and squating down

-body weight = propshaft
-knees = tilt pin
-femur and tibia/fibia = midsection
-feet = jackplate

Ok be a little more scientific then move your feet closer to your knees by 5 inchs and what will happen ?? so your feet have no weight on them at all ??

Try standing on the scale and squating down yeah right !

[Ted Stryker]

Uhmm, nevermind...

[P man]

which dot has a greater twisting force acting upon it?

[tunnels]

which dot has a greater twisting force acting upin it?

same !

[lowlifeAE21]

my question is who cuts down 20"mids to 15", whats it look like, how strong is it and how much does it cost??

[P man]

same !

So if the black dot doesn't no the difference why would a transom?

I agree that the upper mounts as well as the jackplate itself would be stressed more but not the transom

[P man]

this is a cut 20

[Riverman]

Given an equal propshaft height, a shorter mid should make the boat more stable about the longitudinal (roll) axis.

[paul folks]

only way i would think the stress is less is when your towing on a trailer i know w/ my 20" i had 2 trim motor way up in the air to keep it from hitting the ground but w/ my 15" i could keep it trimed down... and i would think w/ it trimed up it would be harder on the transom rather then trimed down

[tunnels]

I know w/ my 20" i had 2 trim motor way up in the air to keep it from hitting the ground but w/ my 15" i could keep it trimed down...

Now think about whats written here .
Means the 20" leg was 5" further down in the water (below the bottom of the boat ) than what the 15 is now .:eek:
Confussing ?? :confused:

[Frank Molé]

I know w/ my 20" i had 2 trim motor way up in the air to keep it from hitting the ground but w/ my 15" i could keep it trimed down...

Now think about whats written here .
Means the 20" leg was 5" further down in the water (below the bottom of the boat ) than what the 15 is now .:eek:
Confussing ?? :confused:
This is my last post for this to much conflicting info for me !:leaving:

:iagree: i see your point :thumbsup:

[paul folks]

sorry i didnt read your post just put down my 2 cents on that just like my other post where just my opion..

[tunnels]

:iagree: i see your point :thumbsup:

PLease forgive me for pursisting with this subject ( which is of great interest ) but the words we use and the way we go about trying to discribe things can be totally confusing to someone that dosent understand the subject you are trying to discribe !.
A little like reading a Asian road map for a country you have never to been to before and writing you cant understand and means nothing .
We see and know all about these things but how do we convey this information of what we know to someone that hasnt got a clue .
Theres some pretty interesting answers been posted on this site !!
Have a nice day all !! :D

[glastron dan]

dont know much about this but if your looking for a real reason, i would ask the record holder 129 mph , if he would cut his shaft just to look cool,wind factor, and everthing else im not ready to cut my breaker bar down when i get more power through a long bar. that being said he didnt have a shortie am i wrong?

[espen]

I am dreaming of a 17" cut down midsection on a 250XS...the engine is already in top bolt holes and that doesnt look good and I need it higher for top speed... can I just cut the mid or is the trim/swivel bracket to long for 17" ??? Who can do this work ?
Espen

[Jason Johnson]

It ain't just for them Mercury boys either :D

[Air It Out]

Has anyone tried a 15'' mid on a 22 Progression?

[pcrussell50]

Given an equal propshaft height, a shorter mid should make the boat more stable about the longitudinal (roll) axis.

i haven't driven a fast boat, and i haven't driven a boat fast, [does that make sense?] so take this with a grain of salt...

BUT

i still remember a thing or two about physics since the early 90's in college.
the way i'm visualizing it, the shorter height might make it easier to displace, [iow, less stable, BUT ALSO easier to recover]. to use something i DO understand, airplanes: a plane with a short wingspan relative to it's size, like a fighter jet, rolls about it's longitudinal axis very easily, [iow, it's less stable in roll], but it also recovers very quickly, with the right input. a plane with a long wingspan relative to it's size, like a passenger jet, is very stable and resistant to roll, AND if it has rolled, it's much more difficult to recover.

could this in fact be in play with a tall outboard versus a shorter one?

-peter

[Matt Gent]

That's the reduced polar moment of inertia about the longitudinal axis mentioned a few posts earlier.

And no, trimming up doesn't hurt the transom more either. It REDUCES the load seen by the transom. I've posted this before in another of these threads. Track where the Cg of the motor goes as you trim up.

[tunnels]

It ain't just for them Mercury boys either :D

Looks neat as !! Hard to work out where it was cut ?:confused:

[Trimmed Out15]

Ronnie cut mine, looks and runs great

[tunnels]

Ronnie cut mine, looks and runs great

I would say it is smoother running as well ??:thumbsup:
Looks good !!

[Ted Stryker]

Thank You P-Man for a simple illiustration that is superior to a thousand words that I have typed regarding this subject in the years past.. This topic will arise again, but I'll have a better illustration to put some clarity behind words that seem to be confusing... ;)

[Ted Stryker]

i haven't driven a fast boat, and i haven't driven a boat fast, [does that make sense?] so take this with a grain of salt...

BUT

i still remember a thing or two about physics since the early 90's in college.
the way i'm visualizing it, the shorter height might make it easier to displace, [iow, less stable, BUT ALSO easier to recover]. to use something i DO understand, airplanes: a plane with a short wingspan relative to it's size, like a fighter jet, rolls about it's longitudinal axis very easily, [iow, it's less stable in roll], but it also recovers very quickly, with the right input. a plane with a long wingspan relative to it's size, like a passenger jet, is very stable and resistant to roll, AND if it has rolled, it's much more difficult to recover.

could this in fact be in play with a tall outboard versus a shorter one?

-peter


Although I can't put hard calculations to this, I have read where the 20" motor can actually make a vee bottom boat handle more stable through chine walk... The theory was that the flywheel being further away from the boat's roll axis uses it's gyroscopical resistance to motion change to help the boat from irregular movement.. Did I explain that worth a poo..?

[tunnels]

Although I can't put hard calculations to this, I have read where the 20" motor can actually make a vee bottom boat handle more stable through chine walk... The theory was that the flywheel being further away from the boat's roll axis uses it's gyroscopical resistance to motion change to help the boat from irregular movement.. Did I explain that worth a poo..?

Wow!!! now thats getting technical !!! :D

[fishn4cash]

A 15 is sweet no doubt but that 12 is insane

[Ted Stryker]

Wow!!! now thats getting technical !!! :D

If You think that's impressive, You should have seen how many times I couldn't seem to crank My boat motor because the kill lanyard was coiled up under My arse... :o:o

[RONNIE]

I do them for 2.4 2,4 offshores and 300 pm and 300x motors
Pm me if you are interested

thanks John and Kieth for the kind words buy the way I'm in the middle of another 300 pm for a local skater right now

[Jason Johnson]

Mine wasn't "CUT" it is a mixture of parts, the mid is from a 1984 60hp 2 cylinder Mariner. I did it for the looks, I am sure that it must help the driving, but I learned with the long one.