Chine walking? Updated

[Numlaar]

Hey all,

Got a new to me boat...

Its a 15'6" cheetah speed boat... its pretty light as best I can tell, but since I have no manufacturers info on it, I don't know the actual weight on it.

Its running a 1987 Suzuki DT115 (115HP oil injection motor).

Whats happening is, when I take off, I have to have the motor trimmed ALL the way down, I mean all the way... if not, the boat just basically stands straight up in the air, and won't plane off...

Also, when I do take off, and get it on plane, if I trim the motor up where it starts to really pick up speed, there is very, very little of the actual boat in the water, and it starts to shift back and forth pretty bad (its kinda scary actually). I believe this is called "chine walking" (but i'm not 100% sure).

That all being said, I have two questions:

1. Any suggestions on what to do to control this or tame it down some? (short of downsizing the motor).
2. I know smart tabs will help with the planing, but will they also help with the chine walking as well?

 

[TMoNeE]

Re: Chine walking?

Re: Chine walking?

Im not expert but I believe the tabs would help with both, as they will essentially pull the front of the boat down more, so at least more of the boat will be in the water.

 

[642mx]

Re: Chine walking?

Re: Chine walking?

Tabs do help. I don't care for smart tabs, I prefer to drop my own when I need them. Look into Insta-Trims or Lenco's.

 

[Ohioriver]

Re: Chine walking?

Re: Chine walking?

Usually on smaller boats like yours the motor shaft length is a little too long and the motor is trying to lift the hull out of the water, thus chine walking. If your motor has multiple mounting holes where it bolts to the transom move it up a hole at a time until the chine walk goes away. If not a jack plate will correct the problem when the height is set correctly. Trim tabs can help some but usually is a bandade for the real problem which is usually motor height on transom. Manual jack plates are not that expensive compared to hydrolic ones

 

[Capt'n Chris]

Re: Chine walking?

Re: Chine walking?

That's a good bit of heavy horsepower for that boat. I imagine the "stern squat" comes from too much weight and the unwieldy ride comes from too much power. Trim tabs have their occasional place and are used much too frequently to lull one into a false sense of correction. Correct power, correct prop, properly loaded and balanced are the general rules. I'd think a 50-65 2 stroke something on that boat would be just about right. From what I can tell in your photo, your hull has soft chines. Chine walking generally refers to hard chines.

 

[JimS123]

Re: Chine walking?

Re: Chine walking?

What is the max HP specified on the USCG plate on the boat?

 

[Numlaar]

Re: Chine walking?

Re: Chine walking?

Usually on smaller boats like yours the motor shaft length is a little too long and the motor is trying to lift the hull out of the water, thus chine walking. If your motor has multiple mounting holes where it bolts to the transom move it up a hole at a time until the chine walk goes away. If not a jack plate will correct the problem when the height is set correctly. Trim tabs can help some but usually is a bandade for the real problem which is usually motor height on transom. Manual jack plates are not that expensive compared to hydrolic ones

Ok i will look into that... but the motor is already up on the third hole, and sitting pretty high...

The cavitation plate is approximately where it should be... I could only go up one more hole with it.

I'm having the carbs done on it right now, when I get it back, I'll take a pic of the motor height and how its mounted, and post it for you to check out.

 

[Numlaar]

Re: Chine walking?

Re: Chine walking?

That's a good bit of heavy horsepower for that boat. I imagine the "stern squat" comes from too much weight and the unwieldy ride comes from too much power. Trim tabs have their occasional place and are used much too frequently to lull one into a false sense of correction. Correct power, correct prop, properly loaded and balanced are the general rules. I'd think a 50-65 2 stroke something on that boat would be just about right. From what I can tell in your photo, your hull has soft chines. Chine walking generally refers to hard chines.

OK I wasnt sure about the specific term... all I know is, unless I keep it trimmed way, way down, it starts to get super squirrley and shifts a lot, almost to the point of losing control.

 

[Numlaar]

Re: Chine walking?

Re: Chine walking?

What is the max HP specified on the USCG plate on the boat?

No plate anywhere on the boat, and the manufacturer is long Kaput so I cant get a new one...

Its a speed boat and was supposedly set up to take a beefy motor... the motor also matches the year of the boat, so I imagine its what it came with, but yes, I typically only see 115HP on 18ft ish flats boats and the like... The whole setup was only 900 bucks (boat/motor/trailer), and I dont have the cash to go re-powering it... my other boat has a blown motor as well, (its a 75HP), but I may consider rebuilding it at some point.


Thanks for all the replies everyone, I will weigh my options and think on what I want to do with it!

 

[scipper77]

Re: Chine walking?

Re: Chine walking?

I think that is the boat gets squirrely when you trim up too much then the problem is that you are trimming up too much.

My boat is a 185 horse I/O on a 17 footer and I think it does the same thing. I rarely go WOT but the few times I have I can remember trimming up until it got squirrley and then backing off of the trim a little.

 

[Numlaar]

Re: Chine walking? :Updated

Re: Chine walking? :Updated

Well In doing some research on this, and having the boat out a couple more times, I think I have figured out the problem, but overall, don't think there is too much to do about it...

Issue #1: I didnt even notice, the motor has a 5" extender added on to the mid-section to make it a 25" shaft motor, and the boat is set up for a 20" transom... So even with the motor mounted all the way up on the last hole, its still too low in the water...

Issue #2: add to that, the fact that this motor is overweight for the back of the boat by about 100 lbs, it also makes the stern sit way too low (the splash well is only about an inch above the water line, so even with the motor mounted all the way up, the whole thing is sitting way too low.

Issue #3: too much weight on the stern (besides the motor). the boat design puts the fuel tank all the way at the back at the transom, as well as the battery, etc. so again its just a buttload of weight on the back.

All of the above make the motor ride well below the cavitation plate even when on plane.

I was told by my mechanic, this is why the boat is hard to control, and why it gets squirrley when I run it WOT or really anything about 75%... it also wants to try and flip (either left or right) when I take off, even with the motor perfectly straight....

So basically captnchris and ohioriver are both right...

He agress smart tabs would help to a certain extent, but then I would be putting even more weight on the back of the boat... he said the best thing to do would be to power it down to a 3Cyl model of some sorts with a 20" shaft to get it balanced out, and to add some weight to the front of the boat to make the back ride higher...

or take my motor, ditch the boat, and put it on something bigger...

Anyone got a 17-18' V-hull for free? hehehe

Just thought I would let you'll know what the causes where.