need help please

[muqdam]

Hay,
I repower my marlin 28 (1992 models) with Suzuki 250 outboard engine and there is 50 kilos different between my old engine 250 Yamaha and Suzuki , now the boat drive become difficult and wasn’t like before because of the extra weight on transom ,please is there any solution to solve this problem ? like putting 50 kilos or more in front of my boat ! thank you :cry: [/b][/b]

 

[Tashmoo]

Difficult how?

The problem could be as simple as the height the engines are set at, the trim skeg not set properly or the props are wrong. I doubt that a total of 50 kg's of additional weigh would have much of an effect.

 

[ElyseM]

as indicated, need more info. did you go single engine to single engine, or twins or what?

50 kg is like having an extra guy with you. on a 28 foot boat would hardly be noticed.

without any more info, i would bet tashmoo has it right with the skeg. ron

 

[muqdam]

the more info that some of you have asked for are ?
my boat is powered with 2*250 suzuki fourstrock, the problem is the nose (bow) up ( not too much ) in crousing speed and squating.
and thenk you ElyseM and Tashmoo for the value answers.

 

[ElyseM]

since you didn't mention steering, i assume they are counter-rotating. if the squatting is on throttle up, that may just be the effect of the extra weight. on my gulfstream with T F200's it will squat coming up to planing speed but then level out nicely.

if the bow up position is very noticeable with the engine trimmed fully down, you might need to check mounting height as tashmoo suggested. ron

 

[Hookup1]

Trim

How did this boat run before you repowered it? As some of the other posts said, I can't believe a 50 kg. difference is your problem.

It sounds to me like your motors are not trimmed all the way down. Check the motor mounts and the engine to see if there is an adjustable stop.

If you look at my boat out of the water with the motors trimmed all the way down the motors are overtrimmed (too far down). This robs some top end speed because its trying to push the bow down but you can always trim them up.

My boat will run pretty level below 8 or 9 knots. Above that speed the boat will squat to the point of coming up on plane at about 17 knots (3800/3900 rpm's). It's nearly impossible to run the boat in between. Once on plane it remains level.

 

[Tashmoo]

Muqdam,

My guess is that the engines are set up such that they trim down too much. Said another way the engines are able to trim too close to the transom. This will keep the bow down and make the boat squat when accelerating. When you are running can you trim the engines up and make the bow come up and run in a level attitude?

The second possibility is as I noted before that the engines are set too low in the water. When you are at speed say 40 kilometers/hr have some one look at the lower units in the water. There are two horizontal surfaces on the lower unit, the lower of the two should be just at the surface of the water. If it is underwater by 3 or 4 cm the engine is set too low.

The other question that was asked that is very important to answer. Do you have counter rotating engines? That is does one propeller spin left and one right? If not this is a big problem.

 

[gradyfish22]

Sounds like bad motor mount height, also, suzuki's typically swing a bigger prop then a Yamaha, did you get the right prop size or go with what the Yamaha had? The added weight on that boat will NOT cause the problem on that size boat at all. Moving weight around will have little effect, and truely will be negative effect, you won;t be solving the issue, but countering it with something just as harmful to your efficiency. The Suzuki's are likely have more torque since they swing a bigger prop on average, but that should help it get on plane easier.

When you get on plane, check how the engine runs in the water and take pictures to see if the plate above the prop is in the water, even with it or above, this should be even with the water, any other position is a sure sign of improper installation height. When you repowered, did you buy engines with the same size shaft? Did you use the same mounting holes or new ones?

If you want the nose up, trim the engines up a little, this should give tyou better efficiency, you should never be fully trimmed down 100%, that is improper operation and will point the nose down, especially with the added torque from the Sukuki's bigger prop.

As mentioned above, are the engines both counter rotating. If you feel the boat wants to go to one side over another and won;t track straight, adjust the zinc skeg above the prop. For twins typically they are slightly towed in to begin, that is usually the best position to start and work from there as needed, but if counter rotating there should not be a need to adjust them.

Also, to note, as you increase speed, it is normal for a boat to decrease its trim angle, this is caused by more boat getting out of the water and the center of lift changing, as the boat speeds up it will become flatter, but about 2.5-4.5 degrees is normal operating angle depending on the conditions and how the boat is loaded.

 

[muqdam]

Thank you for your answer and suggestions , the engines are counter rotating, i bought engines with the same size shaft , and the boat nose little up even when fully trimmed down 100% , The added weight on the boat will NOT cause the problem on that size boat at all , you are correct but 50 kilos on transom are effect even with same size boat .

I well take some pictures to show you the plate shape in the water, if ok or not, I already contact with my Suzuki dealer and they well send some expert to see the engine prop and installation .
Thank you

 

[BobP]

The difference in weight between the big block OX66 250 HP Yamahas Grady installed on that boat for over a decade and the Suzie 4 strokers are not much to speak of.

Did the installation include additional or larger batteries?
Were the oil tanks removed?
Did you remove/relocate anything from the cabin or bow locker ?

Get a professional marine service mechanic to check the installation and boat trim / engine trim setup/adjustments.

 

[gradyfish22]

Even the added weight will have little change on how the boat planes out, the boat will provide lift mostly according to its speed, the location of weight will adjust the boats running angle, but the amount of weight your talking about is not enough to cause the conditions your claimming, they should be very slight, but the boat will get out of the water just as much at comparable speeds with little to no change in that aspect.

I still feel the problem is with the motor height yet, the pictures will help us a lot to determine if that is right or not.

As bob stated, I'm assuming you no longer have an oil well now going from 2 strokes to 4 strokes, and the oil is now located in the engine itself, part of why it is heavier and why the weight of a four stroke is located more aft then in a 2 stroke engine. This will have some change in the boat and how it sits at the dock, but should have little effect on how the boat rides on plane.

We repowered an older carbed engine with a Yamaha HPDI and the newer engine was about 85lbs heavier, the boat sat differently at the dock but rode exactly the same, same angle and all. On a smaller boat you would notice a change in ride from weight a lot more, your change would likely be no more then we saw, and likely less.


I doubt it could be this, but I've seen crazier things so I figured I'd ask anyways.
I'm sure you checked, but just wanted to make sure, are your trim tabs working properly? Is it possible someone maybe reconnect them and switch the wiring backwards so that your running with them down when you want the bow to really be up, I've seen that before and in the water you might not know it but might wonder why the boat is running different, especially if you rarely use the tabs. If they changed the guage's when installing the Suzuki's, did they redo your helm panel? That would be a reason they might disconnect it and how they could maybe be wired backwards, that would surely cause the issues your having. Did you notice if the tabs worked prior to launching?

 

[mronzo]

I bet it's 50 kilos ~100 pounds per engine for 200 plus extra pounds!
I don't think your year Marlin was made to take the extra weight of 4 stroke
engines, an HONEST salesman would have warned you of weight issues
and 4 s. Or he could have just been ignorant , there's no shortage of that!

 

[fishingFINattic]

Not sure if this will help - but a 28' HydraSport was repowered with twin 250 suzuki's at my old marina - the owner kept bringing it back saying it drove funny -
They swapped the lower units (Basically switching which side is countering rotating) and the guy has been happy since!
Tim

 

[gradyfish22]

Never thought of that Tim...great thinking!!! I bet they used the same mounting distance between engines...well if your swinging a bigger prop you might now be harming yourself....your not getting enough flow to the props to produce the power you should be, by switching the lower units, your allowing better water to reach each prop. The best result would have been a wider mounting stance, but that is too late. You are losing a little by having the the thrust outward rather then both inward to work together better, but it will surely be better then a prop that is starved for enough water to bite into properly.

 

[muqdam]

thnak you

Thank you all for yours time and opinions today Suzuki expert game to my boat and from first look he said the engine instillation was wrong and they set them too low, and they have to get them up 3 to 5 centimeters, and he said they well do the work during this week, I rethink you all friends for your honestly and concern and I well tell you after testing about the result. :lol:

 

[SlimJim]

wow GradyFish was right!! Great Call!! I am glad this person will get the problem taken care of.

 

[muqdam]

Hay first I move engines one step up , but that doesn’t look enough then we remove the engines and made new holes and fixed them again that mean four centimeters more and this Friday I well test the boat hope to be ok.

 

[Leebert]

Good luck. I'm interested in how it works out.

LB