anyone that knows alot bout jack plates

[champlain-champ]

i have a rather large problem.... last year i purchased a new motor it was a 2004 115 merc with a 20 inch shaft... i put it on my 1987 stratos 179v. when i purchased the motor i wasnt sure what shaft length i needed. the guy at the local marina said all bass boats have a 20 inch shaft.. well after putting it on my boat and taking it out a bunch i realized that the shaft is too short i lowered the jack plate as low as i could and it planes out really fast ive tried different props etc.. and the boat never seems to run on plane right... im always pushing water and the nose is always close to the water so when its a little windy and i got 2 foot waves i spear them and lets just say it makes for a wet ride.. even when the waves arent that big...the nose sprays so much water that it blows on me and soaks me... i should have got a 25 inch shaft but i didnt know any better and i dont really have the 6 grand to buy another motor. i got a steal on this one... i tried putting hydrafoils on it to keep the nose up but all that did was slow my boat down even more... i get about 36mph with a 17 pitch.. i had a 19 and got about 38 but i chipped that and got a 17 from a friend dirt cheap. next year i plan on running a 21 for the extra speed. but my question is this... "is it possible to take the jack plate off of my boat and bolt it back on upside down so that instead of jacking the motor it lowers it?   i only need to go about 3 inches... i was wondering if anybody on this forum has any input on this and knew if it would be bad on the transom or the jack plate or anything i really think this could work and it could save me alot of money. i have no other option but to try this... or get wet on every tournament day there is... its def worth a try as long as im not looking at ruining the structural integrity of the boat or having the motor fall off i dont see exactly what it could hurt it would almost be the same as if it was upright. you dont know how many times i get beat by boats with 75 horses on them... its embarassing... lol i really miss my evinrude xp150 it was bored etc... and it did 67mph.. probably the fastest 150hp ive ever seen however it was the most unreliable. it got to the point where it took 10 minutes to get the thing started wether it was warmed up or cold. and the prop shaft had a serious wobble. i didnt feel like spending 3 grand to rebuild the power head and then another 2 grand on a new lower unit. anyway if anyone has any input on this crazy idea please feel free to share. even if you dont have any idea about it.. let me know what you think COULD happen

[Sam]

Need to post this in the boating section.

All I know is that you better follow the manufacturer's instructions when attaching the jack plate to the boat and make sure your boat can support a jackplate via your manufacturer's specs.

I know of a Yamaha that flew off the boat on the Potomac as the bolts were the wrong kind and not long enough to hold the motor onto the boat. 

[champlain-champ]

well i know i have the right hardware. and i know the boat specs support a jack plate. its been on there for 8 11 years. i was more worried about lowering the motor if it would cause stress to the transom. im not really worried about it falling off. im more worried about hitting a rough wave and cracking the transom or something along those lines. obviously the weight will still be the same but im wondering if lowering the motor those 3 inches would put the angle of pressure a little different and possibly mess it up. i also have to take a look if it will even work or if the motor would hit the top of the transom when i trim it all the way up. i think i looked at it last year and it wasnt a problem.

[champlain-champ]

i was really hoping there would be some kind of redneck out here that has a camaro on cinder blocks in their front yard that has tried this and had success lol

[cart7t]

A 25" shaft isn't going to help you.

It's quite clear you're failing to get sufficient lift in the bow. Whether that's due to a hooked hull, waterlogged stringers or a really bad engine height setup/prop selection is impossible to tell with the info you've given us. BTW, the max HP on that boat is at least 150hp so you're already under horsepowered to begin with. What kind of RPM numbers are you running with that boat a WOT?  What are these props you're running?  You'll need numbers along with current settings on the engine height before anybody can start telling you what to do. 

[cart7t]

BTW, you are trimming the motor up after the boat has started to plane out after the holeshot right? 

[simplejoe]

Cart, what if he got a larger jackplate like a 12" lift and if he put it down the whole way do you think it would change the height or would it be the same?

Just a thought.

[R520dvx]

I would think if you were still 3 inches too high, that you would be overheating

[cart7t]

Cart, what if he got a larger jackplate like a 12" lift and if he put it down the whole way do you think it would change the height or would it be the same?

Just a thought.

You don't increase the speed by sticking the motor deeper into the water.

He first needs some numbers, like engine height and tach readings at WOT before any kind of suggestions are made.  He's gone from a stroked 150hp down to a 115.  He's clearly not getting bow lift and the whole hull is draggin in the water causing the low speed.  He needs to determine why there's no lift first.  A 115, while not max hp for that hull should at least be able to lift the nose of that boat better than what he's getting. 

[champlain-champ]

im thinking it has something to do with the prop. i have a 17 pitch and im only getting about 5/8's throttle and then it starts to over rev. the prop just cant give me all that my engine has to give. i was thinking that the motor is too high because shouldnt the fins above the prop be in line with the bottom of the hull?

[CFFF 1.5]

From what I have read and seen if you have a jack plate your anti-cavitation plate can be a few inches above the bottom of the hull because of the set back. I think your main issue is prop size and not trimming the motor up was the boat is on plane. Like other said you would have over heating problems if the motor was too high. You first need a prop that will give you the correct RPM's when at wide open throttle. Once you have that you will be better able to diagnose the problems. Also a water pressure gauge would be helpful to show you that your motor isn't too high, and will help you know when you may have trimmed the motor up to high.

[champlain-champ]

FIRST. i know how to trim my ******* motor once the boat is on plane. and i know when i over trim it and it chops water. this isnt my first rodeo. the motor does not over heat. and the prop is the one that the motor calls for except the pitch size is smaller than i think it needs be. however. i believe that wether its a 17 pitch or a 21 the only variance would be top end speed the bow still does not have sufficient lift. its not horrible but its deffinately not where i want it. the spray from the hull should start from where I disagree sits in the boat and from there back should be the only part of the boat in the water when running. mine starts from 4 feet back on the bow. i know thats not right. can someone please tell me if those fins above the prop (the ones that you can attach hydrofoils too) if those are supposed to line up with the bottom of the hull. thats what i was told and i was told thats why my boat doesnt lift properly

it seems that when i trim my motor up i should be able to trim it a tad bit more before it chops water. and i believe the reason for that is because the hull is forcing the water down and the prop cant "grab" enough of it. i really honestly thing that my motor is between 2-3 inches too high.

im not an expert and nor do i need a d**n pressure guage etc.. ive had boats and been in boats my whole life so i know how to run one and its not user error. im pretty sure its height.

and other than the pitch being off thats basically the only solution. and i have a feeling that the pitch would not affect the bow that drastically.

[DawsonH]

What is the max horsepower rating for your boat? Is it possible that it is absorbing water anywhere? Is the motor already bolted in the top hole?

[cart7t]

Quote

FIRST. i know how to trim my * motor once the boat is on plane. and i know when i over trim it and it chops water. this isnt my first rodeo. the motor does not over heat. and the prop is the one that the motor calls for except the pitch size is smaller than i think it needs be. however. i believe that wether its a 17 pitch or a 21 the only variance would be top end speed the bow still does not have sufficient lift. its not horrible but its deffinately not where i want it. the spray from the hull should start from where I disagree sits in the boat and from there back should be the only part of the boat in the water when running. mine starts from 4 feet back on the bow. i know thats not right. can someone please tell me if those fins above the prop (the ones that you can attach hydrofoils too) if those are supposed to line up with the bottom of the hull. thats what i was told and i was told thats why my boat doesnt lift properly

it seems that when i trim my motor up i should be able to trim it a tad bit more before it chops water. and i believe the reason for that is because the hull is forcing the water down and the prop cant "grab" enough of it. i really honestly thing that my motor is between 2-3 inches too high.

im not an expert and nor do i need a d**n pressure guage etc.. ive had boats and been in boats my whole life so i know how to run one and its not user error. im pretty sure its height.

and other than the pitch being off thats basically the only solution. and i have a feeling that the pitch would not affect the bow that drastically.

If you were an experienced boater you'd know you're just wizzing in the wind here without some numbers. We don't know about your prop other than it's a cheap 17". We don't know your motor height in relation to the bottom of the pad. You're not translating any tach readings to let us know what RPM's you're spinning.

Any advice you'll get at this point is **** slung at the wall.

[champlain-champ]

the RPMS at *** are usually right around 5,200 but its actually not *** because i cant even get 3/4 throttle before it over revs because the pitch is so small.

[DawsonH]

Are you sure its the pitch and not something wrong with the hub?

[R520dvx]

The cavitation plate will be above the pad ..... usually, the center of the prop shaft is gonna end up around 3 inches below the pad or less. A decent prop can create a bunch of lift .... also, you may want to take some of the weight out of the front of your boat ..... especially if you went from 150 hp to 115 .... you lost some weight on the back end and changed the balance.

[cart7t]

http://sites.mercurymarine.com/portal/page?_pageid=126,53050,126_53052&_dad=portal&_schema=PORTAL

That's a link to Merc's prop selection guide.  It's a pretty basic guide that doesn't take into account engine height nor current performance of the boat other than top speed.

Just using the sketchy info you've provided, the guide says you should be running a 21-22p prop. That doesn't take into account that your boat is under HP'd, we don't know the true RPM at WOT since you're way over-revving before you even get to WOT and you have a jack plate on it which you apparently don't know the exact distance from the bottom of the pad to the prop shaft.

BTW, that 115 Opti can be run all the way up to 5750 RPM's per Merc.  5200 is on the low end of that max rev scale.

[GLADES]

Quote

the RPMS at *** are usually right around 5,200 but its actually not *** because i cant even get 3/4 throttle before it over revs because the pitch is so small.

You need to get the correct pitch prop on your boat before you can intelligently evaluate the jack plate.

If your motor prop shaft (bullet) is 3.5" below the pad, you will be in the ballpark. Your jack plate should be centered at this height to allow some adjustment higher and lower.

Most bass boats use a 20" motor. I don't think your motor is the problem.

Some hulls do not ride high in the bow. It could be anything from weight distribution, hull design, and excess weight ( IE soggy flotation) or a lack of horsepower which you have with the 115HP vs 150 HP.

Running the jack-plate upside down sounds a bit crazy and is not necessary.