Engine height - does this look about right?

[sprocker]

Hi All,

I bought a new boat complete with a 2014 Suzuki DF115. With clean bottom, and average load of fuel, I'm getting around 25knots at 5200RPM at WOT.

I'm thinking this should rev a bit higher at WOT, and maybe get me the 28-30knots that a friend is getting with the same boat/engine setup.

Before i start messing with prop changes etc, I took some photos of the boat on the plane at 19knots, and trimmed out nicely.

I would very much appreciate your help/advice on whether I should try lifting the engine one hole according to the position of the aero plate in the pics below?

[Moonlighter]

The anti-vent plate looks to be well under the water surface in those photos. It should be just skimming the surface or getting some water splashing over it, so yes, i would say lift it. Tip: put some red or orange sticky dots on the top trailing edge of the plate, makes it easier to see!

Secondly, you need to get that engine revving to at least 6000rpm at WOT. My DF 115 will hit 6200, you are well short of where you need to be for optimum performance, economy and speed. And engine life. You are over-propped currently and the engine will be lugging.

So, lift the engine until the anti-vent plate is as described above. This should help you pick up a few rpm, then change props. Every inch less pitch will get you 150-200rpm extra revs.

You dont say what size prop you are currently running. It is well worth getting a Suzuki stainless steel prop, they are soooooo much better that the alloy ones!

I run a 3 blade 14 x 20" Suzuki stainless on my boat. Its a very frequently used prop on this engine when the engine is well matched to the boat it is on. But i dont know your boat and its size and weight, so we dont know what prop to suggest.

Let us know how you go.

[Auburn02]

Agree with everything Moonlighter said.

For a quicker verification measure though, you say you have a friend with the SAME boat and engine combo? If so, where is his motor height on the transom compared to yours?

Unrelated - what's the tube with the red cap in the motor well?

[sprocker]

Firstly thankyou for your help so far gents, it is very much appreciated, and a useful tip on the red dots to make things more visible Moonlighter.

A little more info in answer to your questions Moonlighter:-

Boat: 2014 Jeanneau Merry Fisher 645
Engine: 2014 Suzuki DF115

L.O.A 6.90 m
Hull length 6.45 m
Overall width 2.54 m
Beam 2.50 m
Waterline beam 2.29 m
Draught 0.53 m
Light displacement 1,543 kg
Displacement with maximum load 2,410 kg

Propellor is Suzuki Aluminium 3 blade 14 x 19

So my next steps will be to find a window in the weather so I can get her out and make a few runs at WOT, to check the WOT revs and height of anti-vent plate. I will then update my findings.

Auburn2 - My pal with the same boat is working overseas at the moment, and is not likely to be anywhere near his boat for the next six months (He lives approx 300 miles away from me, so I cant pop in and take a look very easily). The red cap is just a cover for the locking engine mount.

Once again many thanks for your help so far.

[Moonlighter]

Ok, well, you certainly seem to be making that DF115 work pushing a boat that big, wide and heavy. Unless it is a very shallow V, which it must be, because i just checked the factory website and they do not mention the hull V at the transom, and state that the standard engine is a 115hp. Surely it cant have much V at the transom??

Anyway you will need to find a prop with something like 3 or 4" less pitch.....

Just to give you a comparison, my DF115 is pushing my Surtees 5.5 plate alloy cuddy cab, 18 degree V hull, and boat, motor and trailer combined weighs in at a touch under 1200kg. The trailer tare weight is about 450kg from memory, making the boat and motor loaded with gear and a full tank of fuel about 750kgs plus crew. 35 knots at 6200rpm. Not a "fast" or slippery hull, though.

You are pushing double that weight, but I have just found reports of people running motors as small as 90hp on those boats, so they must be very easy to push through the water and slippery, efficient hulls.

Just surprising (and catches me a bit off guard!) when i am used to my friends with boats that size and they run 200-250's - admittedly their boats are 20-23 degree deep V offshore boats that take some pushing.

Anyway, the same rules apply regardless - you still need to select a prop that allows the motor to spin up to 6000rpm or very close to that at WOT. The 4 strokes love to rev and performance and acceleration out of the hole will be much better if you get it into that upper end of the recommended rpm range.

I know the stainless props are expensive but they do perform very well compared to the alloy. Better grip, less cavitation, more efficient and more durable.

By the way, many manufacturers set the motors too low from the factory, because they fear owners complaining about props cavitating or blowing out as they take corners. Especially if alloy props are being used. They can almost always come up a hole or two and still perform very well, especially with a decent stainless prop. The more of that leg that is out of the water flow, the less drag, and thus the more efficiently the boat will run.

If you've got access to a block and tackle its an easy job. I lifted mine that way, have also done it with just a couple of mates and used the trailer jockey wheel method. if you want to try the "trailer method" let me know and i will spell it out for you!

Good luck, keep us posted, and find out what prop your friend is using.

[sprocker]

Managed to find some decent flat water at the weekend so had another couple of runs at WOT.

Over a few sustained runs with engine trimmed I was getting 28knots (GPS) and reaching 5700revs, so I guess I should be aiming for an extra 400RPM with engine lift and new prop?

MY wife took a couple of vids of the AV plate which I will upload tonight.

Meanwhile here is a pic of the rear of the boat to answer one of Moonlighters previous questions about the depth of the V at stern.

[Moonlighter]

Its a pity you cant get a look at your friend's boat o see where his motor is mounted. Any chance you could get someone where he lives to take a photo and email it to you?

Thanks for the photo - as I suspected, your hull has quite a shallow V at the transom, which means it is a lot easier to push than a deep V boat. Hence the 115 being acceptable horsepower for the boat. Explains a lot.

Also, its good that you could get in a couple of decent WOT runs with the engine trimmed out to the max. 5700 is not too far off the desired range. And its far better than the 5200 you thought it was getting!

I would still aim for a absolute min of 6000 with a light load, however.

Anyway, its always best to sort out engine height first, and then check what revs you get again before you play with props.

You might pick up 100-150rpm possibly with just the engine height change. Or maybe it wont change much at all. Unfortunately it really is a "adjust, test and see what happens" situation.

It then depends on whether you typically load the boat up with people and gear more than when you tested. If so, I would be tempted to suggest you drop to the next size down in prop pitch. A rough rule of thumb is 150-200 extra rpm for every inch less in pitch.

So 2" less pitch should give you up to 400rpm, and that would put you smack in the pergect range, especially with the engine lift.

So, one step at a time. Engine height set correctly first, then props if still required.

A last comment: I know they can be expensive, but the Suzuki stainless steel props are MUCH MUCH nicer than the aluminium ones. They grip the water better in turns, hang on better when accelerating, and go faster and use less fuel. If you can get one of them ........
You could possibly find that lifting the engine might make your alloy prop lose grip on the water, in that situaion, the stainless prop would likely still hang on perfectly.

[sprocker]

Here is a short (Not very good) video of one of the WOT runs from the weekend. Can you see anything from this?

http://vid1249.photobucket.com/album...psdvb13dlw.mp4

[Harper]

Still looks too deep to me.

Here's some pictures of my adventures in mounting my DF150. Originally, the manufacturer mounted the motor at the lowest possible level. The first three pictures are with it moved up two holes. Up two holes was still not high enough. The next two pictures are with the motor up one more hole (three holes total). Still not high enough ... the anti-ventalation plate was still at least two inches underwater on plane. And you can see in the pictures, that up three holes has the anti-ventilation plate well above the extended line of the keel. The pictures with the solution are in the next posting (only 5 pics allowed per post).

[Harper]

So I ended up installing a hydraulic jack plate. The pictures show it in the highest position (up 6 inches). On plane it runs just about perfect at up 3½-4 inches. Yes, I have to be careful on turns, and have to lower it occasionally for the harder turns, but that type of turn is not one that I usually make anyway. Just normal course adjustments require no height adjustments at all. Both cruise speed and top speed have increased 5-6 MPH, and mileage improved by over ½ MPG. I mounted the motor on the jack plate up two holes, knowing that it needed to start out higher anyway. In this ideal position, the plate rides right on top of the water, with water splashing on the top. One thing I've noticed .. it causes a little bit of a rooster tail mounted that high.

Had to do some searching, but just found the two pictures of the motor in action with the jack plate. This is my first run with it, so it's only up about 2½ inches. It's difficault to see, but the plate is just below the water surface ... last two pictures....

[Moonlighter]

That last photo is a good one Mike - you can see the end of the anti-vent plate quite well, getting splashed but out of the solid flow of water. Spot on.

[sprocker]

Thankyou for posting that Mike, it does show how low mine is in the video.

Looks like I need to get a lift out booked!

[ChrigelKarrer]

To find the right hight for a Suzuki outboard is a unfortunately a awkward story.
It seems to me that the right, working height depend on the transom shape as i had only problems with mounting them and on boths of my boats the AV plate need to run burried to avoid ventilation.
The Venture 34 i recently repowered with twin DF300AP ventilates with the AV plate on the right heigh (slightly above the water surface) and the ventilation is between completely unusable (Powertech OWS 17'' with vent holes) to barely usable (Mercury Mirage Plus 18'') to almost fine (Suzuki 3x16x18.5).
The engines where mounted second hole (should be the same as the F250 engines before) from the top and ventilated with the same Mirage Plus props i had on the previous F250.
As every haul with the forklift is 300$ i did not changed the engine height, i just tried the 3 propellers above with unsatifactory results.
The same story was in 2012 with my dive panga where i switched from a F150 to a DF200 and same engine height was giving bad results so we had to drop the engine all down and still i can not trim up more than 10% as the propeller will suck air.
Also the same story was on my dive RIB in Italy going from twin a50hp optimax to single DF300AP, several tries to lower the engine till we had to cut a notch to drop the engine even more.
The Venture 34 has a Eurotransom with the step below the transom, the dive panga has a half tunnel before the lower unit and the dive RIB has some kind of a Keel.

Meanwhile i belive that Suzuki Lower Units are more sensible to mounting height and this depends on the hull/transom shape. I believe that eurotransom transoms with a step need that the engine is mounted lower than usual than on a straight transom as Harper's boat.
This problem may become worst with stern heavy boats as the inclination of the transom is steeper than on lighter transom boats.
The steeper angle of the transom edge probably create a turbulence or hit the diagonally upgoing "bracket/eurotransom" and introduce air in the water flowing to the propeller(s).

The only way is to run the boat with the engine high and lower it accordingly till the engine don't ventilate anymore, not in tight turns and especially not in following seas.

I am thinking about to mount mine on hydraulic jackplates to solve me two problems:
1° ventilation at various sea conditions and loads and sometimes i can run them higher with lower fuel consumption
I use my boat for dive and fishing charter and can have 14 people or less people and dive gear or only a few anglers aboard.
2° lower unit is half in the water when the engines are on the locks.
Jackplates should be able to lift the engines completely out of the water while tited up

Chris