Engine reving up on turns and straight running

[scaley]

I have just bout a new skiff with a 70 hp suzuki on it . the first time I took it out I noticed a kind of stutter after the boat was on plane. then going into a turn the prop looses grip causing the engine to rev up. I think the stutter I first noticed is I think the same thing happening. I have not added anything to the keel and the motor is mounted as low as it can be. What could be the cause?

 

[likalar]

Re: Engine reving up on turns and straight running

Any possibility of posting a picture of the rear of the boat with the motor in normal position? A low side view and low rear view, straight from the back, will help get you some good advice from the experts here. The camera should be low, at "water level" for a telling photo.

Larry

 

[scaley]

Re: Engine reving up on turns and straight running

I have taken A couple of pictures of transom and can't get them to upload on this site. I can email pic's.

 

[steelespike]

Re: Engine reving up on turns and straight running

You need to use a host site to post pics.
Rule of thumb the antiventplate(just above the prop)Should be about even with the bottom of the boat to about an inch above.Use a straight edge along the keel to check.
Is the prop in excellent condition?If necessary there are a number of props that will resist venting.Its possible all you need is a new prop if yours is worn or dinged up.

 

[scaley]

Re: Engine reving up on turns and straight running

The antiventplate is about 1" above the bottom of the boat and the prop is new as is motor and boat. What kind of prop would you suggest ?

 

[steelespike]

Re: Engine reving up on turns and straight running

Do you have a max rpm and speed at wot? Also please the details on the boat?
Also prop size brand and model? Are you sure it is as low as it can go?
To keep it simple and inexpensive a Solas amita 4 blade should solve your problem
and improve hole shot,handling and ability to stay on plane.Prop size would depend on the present prop and your performance.

 

[scaley]

Re: Engine reving up on turns and straight running

I took it out again today and made sure the prop had not spun. This is on a Carolina Skiff JVX 18, The motor is mounted as low as it can be. It cavitates when trying to get on plane to fast and while cornering at 2800 RPMS or more. Would the prop you suggested take care of this or maybe even a hydrofoil stabilizer ? I.m in the break in period on the motor with less than 1 hr. on the motor and I don't want to screw up the engine.

 

[scaley]

Re: Engine reving up on turns and straight running

The prop on it now is three blade alum. 3x14X21.
Thanks For your help

 

[steelespike]

Re: Engine reving up on turns and straight running

I just want to be sure you understand that the mount on your motor may be all the way down on the transom but it may have holes that allow the motor to be raised or lowered further.It just seems unlikely that you would be stuck with a venting issue with the motor all the way down.
Without your max wot rpm and speed we can't suggest an accurate prop change.Looks like we may have to wait till more breakin for those figures.?
If your manual allows occasional bursts take it up there and get us those figures. If you can't run open because of venting your dealer owes you an explanation and or a prop to solve the problem. If he will let you try props start with a 21" 4 blade.Prop so your close to the 6,000 max rated rpm lightly loaded.

 

[scaley]

Re: Engine reving up on turns and straight running

The motor is mounted as low as it can be using the top holes. The engine can't be taken to WOT for a little longer. As soon as I can take it there I will give you the results.
I did email Carolina Skiff and they stated the cavitation plate should be 3/4" to 1" below the bottom of the boat. Mine is 1" above the bottom.
The dealer wants me to contact a certain individual to talk to about the problem I'm having. For three days now he has been away from his desk or on the phone is the message I get and he will not return my call. So don't look like I'm going to get much help from them.
Would a jack plate take care of this and are they hard to install I was looking at a manual one that bass pro has. I'm fairly sure it's a venting problem.
Your help is very much appreciated.
Thanks Ed

 

[steelespike]

Re: Engine reving up on turns and straight running

It sure sounds like venting.
A jack plate will do 2 things it will get the motor in cleaner water and you should be able to fine tune the height in fractions of an inch.Sometimes a jackplate will allow more height because of the cleaner water and the height of the plate related to boat planing angle.I think a jack plate is the best solution as it allows a better setup even on a boat with a good setup in the first place.
If you bought the boat and motor at the same dealer I think he owes you a solution.Has anyone measured the skiff transom.Vertical height not along the angle of the transom.Have you consulted with Suzuki?
Another prop that should help your problem at a reasonable price is the Turning Point Hustler.It resists venting really well and performs close to that of a ss prop.
Unfortunately Hustler results are all over the place to the point of wondering if some are miss labeled.
I found a Suzuki test on a Carolina Skiff.The 70,80 and 90 suzies are esentially the same motor all 20" shaft. a 90 on a 198dlv Skiff was set up in the second hole apples and oranges but same motors physically. Its interesting that the bigger boat with a 20" transom is up one hole.??

 

[River-Runt]

Re: Engine reving up on turns and straight running

I also purchased a new boat this year, a 17ft. Lund with a 90 Merc and experienced some of the issues you had with cavitation but to a lesser extent. I found that at speed the boat was somewhat sensitive to trim angle and would cavitate while going in a straight line at WOT and would also cavitate with minor course changes at speed. I checked the antivent-plate while in the driveway and underway on the river and it looked to possibly be a little low, I couldn?t see the plate itself but a boss with a bolt that is maybe ?? above the plate was out of the water while on plane. I replaced the Mercury prop with a Turning Point Hustler with the same pitch since at a light load we were running just about the 6,000 max rpm at WOT & maybe a little over if I played with the trim. This prop upgrade eliminated the cavitation issue completely, makes the boat handle better and gives a much improved holeshot. It also made the boat plane slightly higher exposing more of the antivent plate. So for me the prop change was the trick. Also I want to mention that when I read my Lund?s owner manual it specifically warned against using a jacking plate saying that it would void the hull warranty, I would recommend double checking your owner?s manual before installing a jack plate on a new boat.

 

[scaley]

Re: Engine reving up on turns and straight running

I was finally put enough time in on the motor and took it to WOT for a short time twice today. I had to gradually take it there to keep it from cavitating. It run ran 34.5 mph at 4500 rpms is all it would go to at WOT. I should mention that I have to keep the motor trimmed down all the way at all times to run it so it wont cavitate. Even slightly trimming it up will cause it to cavitate. This is with the 3 bladed Alum. prop 3x14x21. Still have not been able to contact carolina skiff tech and the place I bought the boat from want them to decide what to do . I,m getting pretty upset with the dealer on this. with the numbers I gave above what would you recommend for a new prop. It's suppose to run between 5000 and 6000 rpms at WOT.
Thanks again

 

[steelespike]

Re: Engine reving up on turns and straight running

If you can't trim up its hard to get a true speed.I would try to get the dealer to let you try a 4 blade 21" pitch prop.With the understanding with him that it may solve the problem but need to be a different pitch.Considering you can't trim up the 34 is a respectable speed.You should check with Suzuki they must have run into this problem.You might mention we are tryng to help you solve the problem and will witness how well he helps, if you get my meaning.There must be a Carolina skiff forum somewhere you could get some help from.Or perhaps a Suzuki forum.

 

[Fed]

Re: Engine reving up on turns and straight running

From what you've said it sounds like the dealer mounted the motor too high. Give them the problem to fix.

 

[steelespike]

Re: Engine reving up on turns and straight running

I went to a Carolina Skiff owners forum and posted the problem.
Second answer from a boater with a 70Yamaha on a JVX18. Vented on hole shot.
A Solas Amita 4 blade solved his problem.Sounds like the JVX 18 may have a transom a touch too high.

 

[scaley]

Re: Engine reving up on turns and straight running

I finally got a call back from Carolina Skiff yesterday. I found out that the transom was not cut down to the proper height at the factory . They have agreed to pay to have it taken care of under warranty. They may give me the option of having a jack plate added or the transom cut down. Not sure which way to go . Any suggestions? I will post results later once the work is completed.

 

[Joshua Nichols]

Re: Engine reving up on turns and straight running

Jackplates are nice

 

[Gary H NC]

Re: Engine reving up on turns and straight running

I think a nice jackplate without cutting the transom would be my option.
Tell them it must be a powered model...

It will also give the motor some setback that can increase performance.

 

[steelespike]

Re: Engine reving up on turns and straight running

I like the jack plate idea it avoids possible damage to the structure of the boat
and provides an excellent device to fine tune motor setup.
Nice that they owned up without any tap dancing,try this,try that,etc.