Raise it or leave it alone?

[litespeed]

Hey guys, quick question about engine height. I have a little 15' flats/bay boat. The boat has a manual jack plate with 4 inches of setback. As it is now and how it was in the video below, the anti-ventilation plate is about 1/2 inch below the water surface when partially trimmed down and cruising like in the video. When I go a little faster or go to WOT, I trim the engine up just a tad and the AV plate is 1/2 inch above the surface of the water.

As it is now I have pretty good control over trim in all conditions and holeshot and drive-ability is decent. Is it safe to raise it another 1/4 inch or so without having to worry about the engine being starved of water? I don't have a water pressure gauge and don't want to install one. How far under the water should those pick up holes be on the LU?

In the video, I was cruising at 29MPH at 3500RPM. Today I raised the jack plate another 1/4 inch but have not water tested it yet. Also, in the pics below, I included some pics of where I started. The top hash mark on the jack plate was the initial height and the little dot is where it was in the video. The last mark is the adjustment I made today. With a level on the keel, the AV plate is a little over 2 inches above the bottom. The LU water pick up is about 1/4 inch below the top of that level.

VIDEO LINK: https://youtu.be/NYwpSQQdiZU

[XstreamVking]

You should be ok. Water rises as it leaves the transom to cover the intakes. BUT!!!!! with out a pressure ga or a temp ga you will not know until the overheat sensor goes off and by that time it will be too late and the water pump will be cooked. On a lo power and lo speed boat going higher is not what you want sometimes. It might be better, or not, performance wise. It may start to cavitate in turns or lose some of it's ability to be trimmed up to adjust the attitude of the boat as well.

[litespeed]

Thank you for the quick reply! I will proceed with caution.

Good points!... I definitely don't want to lose the ability to trim the bow up and have blow outs in turns.

I would like to have it as high as possible without drive-ability issues like you mentioned. The boat drives better at slow speeds with the engine trimmed all the way down. The only reason for getting it as high as possible is not for speed but for navigating shallow waters on grass flats and around mangroves with the engine all the way down.

I read somewhere about people plugging the top 2 holes on the intakes, but would like to avoid that as well. Does not have to be perfect, it's just a little fishing boat.

I'll be sure to use a selfie stick next time to see how high the AV plate is at faster cruising speeds as well as WOT and trimmed up for top speed. I think that speeds close to WOT with the engine trimmed up high is the only time I need to worry about those holes being out of the water.

Edit: I like your location! LMAO! Just about everywhere these days...

[Glasstream15]

PLEASE invest in a water pressure gauge. It is the MOST IMPORTANT gauge on an outboard. It can save you bunch of green in many situations. And learn to glance at it frequently.

You can pick up trash around the water pickups, the pump could be failing, you could (probably not, but could) over trim and suck air. It's just a "Linus security blanket" and makes you feel good.

[phillnjack]

if you dont want holes in the dash then simply add a small home made binnacle to hold the gauges.at the very least get some long tube and have the tell tale up near where your sitting so you can see the water coming from the tell tale hose ???from your pics of the motor and the jack plate, you can raise that all the way up and will still be getting plenty of water to the motor.you wont need to trim out so much so will be getting the motor more levelled out = more speed etc and should not do too bad in the turns.what I would do is add a bit more setback by simply putting a 1 inch ply board between jack plate and transom, if you want more setback then do the same between motor and jack plate, that would give you 2 inches more setback. By doing that the motor can go up more and easy get more water to it.the motor would be in cleaner water that has risen up.you can also then raise the motor to its highest hole setting in the bracket to give another couple of inches.on my boat I raise the motor up 7 inches and back 5 inches and get no problems at all with water pressure. its mostly those with 15 inch mid sections on 20 inch transoms that need the low water pick ups. they take their motors all the way up on jack platesif you look at those with the short mid sections they are 5 inches shorter to begin with, so even at your highest possible point they are up another 5 inches.!!get the boat hull bottom level to the floor and then trim engine dead level, you can then raise the motor until the centre line of the propshaft is level with the bottom of the transom. thats roughly up 7 inches.. you should still get enough water, BUT this is where the pressure gauge comes into play.it would let you know for sure if you have enough water getting to the motor... cheap insurance, easy to install and dont even need to be in the dash.just my take on it all..

[litespeed]

Thank you all for the input! It looks like it will be next week before I am able to water test it again.

If I do install a water pressure gauge, where do I tap into the block? I remember seeing a couple of small brass plugs on the back of the head. One at the bottom and one at the top.

The reason I'm hesitant to install the gauge is the tubing. I restored this boat at the end of 2016. New gelcoat and quite a bit of fiberglass work on the inside, every screw, nut, bolt, wire, cable, accessory and fitting is brand new. It's basically a new boat. I also had Chris Carson rebuild the power head for me a few months ago. The boat is so smooth and quiet it's almost ridiculous. The engine is quieter and smoother "at speed" than the 4 stroke it replaced. The video above proves it. It's almost "electric quiet".

Anyway, the cable tunnel where all the wires can cables go to the console is crammed to the max. and getting that tiny tube in there would be damn near impossible. I'm not kidding! It would take the better part of a day to remove some of those cables and cram them all back in there just trying to get that little tube through there. The risk of damaging some of the wiring or cabling just to install that tube is not worth it. Maybe I could mount the gauge to the engine? I don't know.... I need to think about that one.

[XstreamVking]

An old controll cable core wire makes a good stiff skinny snake. Push the snake thru. Duct tape the tube to the snake and pull it thru. A little soapy water does wonders too.

[phillnjack]

just go straight to the fitting for the tell tale for pressure gauge. it is just a hose that goes from the tell tale fitting to the gauge, no wires just small hose.

more accurate than using the t- fitting that will come with the kit.

[litespeed]

I have not been out since I last posted this. I raised the jack plate another 1/2" and went out with the wife yesterday to try it out. At that position, the anti-ventillation plate is around 1/4" out of the water and looks good with the trim all the way down. Runs pretty good, no problems blowing out in turns, gets on plane nice, etc... However, I have lost the ability to trim the bow up and pretty much any trim upwards off of full down and it starts to ventilate. Bummer.... On the way back we had to out run a small thunderstorm and I was unable to hit full throttle because I could not get the bow high enough even with a 20kt head wind from the gust front! So, I'm going to put it back down to where is was and call it good. Not that big of a deal. Thanks again for the input on this!