engine depth

[david_r]

i wasnt sure where to post this since my question is a little about depth and a little about my jackplate.

i have already asked a similar question on my other boats so i know where the anti-cavitation plate should ride in relation to the water.

my concern is: how can i properly check the wot depth on a ranger 350v?

the seating is pretty much in the center of the boat so when i have someone crawl to the back im worried the eng will be a little deeper than normal due to the change/distribution in weight.

i tried attaching a mirror to a pole so i could see the water depth on the plate at wot but i couldnt see real good, and the larger the mirror the harder it is to hold it steady while bouncing across the water.

another concern is the jackplate... it is manual so when i raise it up are there any notches or do i have to just try to turn each bolt the equal amount of turns and measure?

sorry if my question is in the wrong forum

thanks for the help

 

[Daviet]

Re: engine depth

Changing the weight distrubition in the boat will not change the relationship of the cavation plate to the bottom of the boat. With the boat on plane, the cavation plate should be skimming just on top of the water or a little bit above the water.

Look at the lower unit of your motor, the water inlets must be under water when the boat is on plane. Look at the distance between the inlets and the cavation plate.

Mine is set so the cavation plate is about 1/4" above the water when on plane.

 

[david_r]

Re: engine depth

so when my 280# buddy crawls to the back of the boat it wont sit deeper in the water because im on plane?

that will amke things much easier............... i was worried it might sit deeper in the rear while on plane with the weight change.

so i guess its off to the lake to see if i can fine tune my lil eng.

i left it in the same position it was in when i took off my dad 150 merc and installed my 115 johnson.

 

[Daviet]

Re: engine depth

The boat might set a little deeper, but the cavation plate depth did not change. The motor is attached to the boat, as if it is one piece.

 

[Chris1956]

Re: engine depth

Having your buddy crawl to the stern will have some effect on the height of the Av plate. The faster you go, the less the effect.

I do not think the effect will be dramatic, and do not have a better way to do it, however.

 

[HybridMX6]

Re: engine depth

To check, let said buddy drive boat and go check it yourself, just don't fall in.
As others have said, the depth ration of the cav plate-to-transom will not change. The back of the boat may ride a little lower in the water, and as such so will the cav plate, but it's not going to change the relation of the two as they are bolted to each other, so one goes lower so does the other one. If you raise the motor anyways when buddy is with you, it will most likely cause it to cavitate, and drop speed/over rev. Just leave it alone, unless it's too far in the water as it is.

 

[Chris1956]

Re: engine depth

Hybrid amd Daviet, You do realize that he is trying to see if the AV plate is on top of the water at planning speeds. if the stern of the boat sits deeper in the water, the AV plate will be deeper in the water, defeating his purpose for looking at it.

David, I do agree that you should look yourself. Most of my frineds would know an AV plate from a zinc anode. The effect of your weight on a bass boat at plaining speed will be minimum, I would think.

 

[Daviet]

Re: engine depth

Chris1956
If the boat is on plane, the water is even with the bottom of the boat. If you move weight to the rear of the boat and it settles 1' deeper and it is still a plane, the cavation plate will have the same relationship to the bottom of the boat. The motor is bolted to the transom and does not change depth as related to the bottom of the boat. If the cavation plate has 1/4" space above the water on plane and I am standing in the bow, and I move to the stern of the boat there will still be 1/4" space between the cavation plate and the water as long as the speed stays the same.

When rigging new boats we used to use a small jack to hold a 2x4 against the keel of the boat, sticking out past the transom, and set the motor depth using the upper side of the 2x4 as the bottom of the boat. Normally we never had to reset a motor when installed that way.

 

[david_r]

Re: engine depth

i decided before we went out i would be the one to crawl back since im lighter.

the engine is around 1.5" too deep so far as i can tell.

i started noticing the extra splah as soon as i got on te rear deck.

we went ahead and went fishing instead of tuning it in

the jack plate on the back is manual.

do i have to use a jack under the eng to help raise it or can i just use the bolts on the sides?....... not the bolts holding it in place but the ones that look like little shocks on the sides.... i cant remember what they are called, lol, but they look like the ones that when you turn the middle both ends grow or shrink like on a tie-rod end on a car.

 

[Chris1956]

Re: engine depth

Daviet, If the Av plate is 1/4" above the surface of the water, while the boat is on plane, and you move to the rear of the boat and the stern sinks a foot under your weight, the AV plate will be underwater.

On all boats, as the water comes off the transom while on plane, it tends to deflect upward. Faster boats has less of this effect. Increasing the weight in the rear causes the stern to sit a bit (an inch or two max) deeper, causing greater water deflection, which throws off the accuracy of the Av measument.

David, You can normally use the adjustment bolts of the jackplate to lift the motor. I would use a ruler to make sure the motor is at the same height on both sides. Also look to see that the motor bisects the transom evenly, and sometimes transoms and jackplates are not always true ot mounted truely.

 

[david_r]

Re: engine depth

Daviet, If the Av plate is 1/4" above the surface of the water, while the boat is on plane, and you move to the rear of the boat and the stern sinks a foot under your weight, the AV plate will be underwater.

On all boats, as the water comes off the transom while on plane, it tends to deflect upward. Faster boats has less of this effect. Increasing the weight in the rear causes the stern to sit a bit (an inch or two max) deeper, causing greater water deflection, which throws off the accuracy of the Av measument.

David, You can normally use the adjustment bolts of the jackplate to lift the motor. I would use a ruler to make sure the motor is at the same height on both sides. Also look to see that the motor bisects the transom evenly, and sometimes transoms and jackplates are not always true ot mounted truely.

thats what has me concerned is the extra weight on the stern when i crawl back to look............ thats why i tried a mirror on a pole.. but that didnt work too well either.

maybe if i can talk my wife (115#) into crawling back to look.......... but you know as well as i do women cant measure... and you know why lol.

i may just try raising it a little at a time ,while watching my water pressure gauge and making sure the eng is still pumping out water fromthe rear, and keep going till i lose water or spin out..... or lose speed however you want to put it.

i would like to get it tuned as good as i can since im underpowered as it is........... plus i dont want to buy the wrong prop just because the eng was a little too deep and dragging.

its a 198? ranger 350v---- 18' --- 7' beem --- and rated for 150 hp............ by my calculations on reccomended hps i shouldnt have put less than a 120hp on it but the 115 is the biggest one i have so im thinking i will just re-prop after i get the eng to correct height and fix my regulator so i can check the max rpms.

i really appreciate all the help and advice i have recieved so far...... i am still open to ideas on how to get her tuned in and i will keep yall updated on my progress/failures.

thanks everyone

 

[david_r]

Re: engine depth

oh and as for the measuring i have loaded up the correct wrenchs of course but i am also bringing my small levels, micrometer (digital) , and tapemeasurer.......... i probably wont need the micrometer but sometimes i am anal so im taking it just in case lol

 

[bob johnson]

Re: engine depth

well with jack plates.... the set back has a lot to do with your set up....

one aspect of the set back is to push the motor higher.....and get less drag...

the best way to do what you want..is to drive along side your boat in another boat and observe what you want .....


I also know that the movement of weight while on plane changes the boats aspect...case in point is my boat on plane and I have my adjustable jack plate up on a higher settingbut I am running nice and not cavitating

my buddy walks to the bow...and it raises the stern enough that I immediately start to cavitate!!!!

and I got to drive the jack back down...or trim down some....

since once up on plane I can trim up to get max speed...

the further your motor is OFF the back of the boat the higher the cav plate can be above the bottom of the hull!!!

I have my hydraulic jack plate set so that wheh it is ALL THE WAY DOWN..it is about even with the bottom of the hull

all movement up takes me above the hull and it runs good with no cavitation about 3" above the hull when on plane...at slower speed i can raise it the full 6 "

bob

 

[Chris1956]

Re: engine depth

David, I want to add to what Bob has said. He is exactly correct that more setback on the jackplate will allow you to raise the motor more. My 6 inch setback manual jackplate allwed me to raise the AV plate 6" above the transom hull, or more. It was a trial and error exercize.

On my speedboat (bassboat-type hull), I had the motor raised up to where the Merc zinc anode was completely out of the water. The boat was very fast, but was finicky on how the trim needed to be set. After some experimentation I lowered it a bit to provide for more driveability and less ventilation, if the trim was not set perfect.